## Southern Great Plains 1997 (SGP97) Hydrology Experiment Plan Section 11 - Science Investigations

Goto Section in Document:
1. Overview
2. Soil Moisture and Temperature
3. Vegetation and Land Cover
4. Soil Physical and Hydraulic Properties
5. Planetary Boundary Layer Studies
6. Satellite Data Acquisition
7. DOE ARM CART Program
8. Oklahoma Mesonet Program
9. Operations
10. Data Management and Availability
11. Science Investigations
12. Sampling Protocols
13. Local Information
14. References
15. List of Participants

11. SCIENTIFIC INVESTIGATIONS

Investigators actively participating were asked to submit an abstract describing their planned activities. These are included here as provided.

1. Meyers, Baldrocchi

2. Kustas, Schmugge, Jackson, Prueger, Hatfield, Sauer, Starks, Norman, Diak, Anderson, Doraiswamy

3. Starks

4. Miller, Mohanty, Tsegaye, Rawls

5. Daughtry, Doraiswamy, Hollinger

6. Entekhabi, McLaughlin

7. Entekhabi, Rodriguez­Iturbe

8. Barros, Bindlish, Yanming

9. Peters­Lidard

10. Kumar

11. Chauhan

12. Diak, Norman, Kustas

13. Finch, Burke, Simmonds

14. Browell, Ismail, Lenschow, Davis

15. Salvucci

16. Njoku

17. Houser, Shuttleworth

18. Laymon, Crosson, Fahsi, Tsegaye, Manu

19. van Oevelen, Menenti

20. Mahrt, Sun

21. Valdes, North

22. Mohanty, Shouse, van Genuchten

23. Famiglietti

24. Elliott, Senay

25. Islam

26. Doraiswamy, Daughtry, Jackson, Kustas, Hatfield

27. Wood, Jackson

28. Wetzel

29. Duffy

30. Humes

31. England, Judge, Hornbuckle, Kim, Boprie

32. MacPherson, Mailhot, Strapp, Belair

Investigator(s): Tilden P. Meyers and Dennis D. Baldocchi

Institutions(s): NOAA/Air Resources Laboratory Atm Turbulence and Diffusion Div:

Title:Continuous Long­term Energy Flux Measurements within the GCIP Domain

Numerical regional and global scale models will continue to be used for future climate and hydrological assessments. However, predicted climate scenarios are sensitive to the surface layer processes such as evapotranspiration and soil moisture. Preliminary results have shown significant variations in predicted evapotranspiration from the land­surface submodels that are currently used. Observational data sets that allow for detailed testing for an annual cycle are few. The credibility of climate simulations depends on the predictive capabilities of the submodels used in the parameterizations of the physical and biological processes. Long­term continuous measurements of water and heat fluxes are needed to assess and reduce uncertainties in the land­surface models. The results from the proposed work plan will provide a data base that can be used directly to meet the first two objectives of the GCIP scientific plan which are (1) to determine the temporal variability of the hydrological and energy budgets over a continental scale, and (2) to develop and validate coupled atmosphere­surface hydrological models.

Continuous measurements of the surface energy balance components (net radiation, sensible heat flux latent heat flux , ground heat flux , and heat storage ) will continue at the Little Washita Watershed Latent energy fluxes from the soil and canopy systems will be determined to provide a complete data set for (1) the evaluation of the surface layer submodels currently used in synoptic scale and general circulation models, and (2) the determination of seasonal probability distributions and statistics for evaluating predictive capabilities of models. Measurements of additional hydrological components include precipitation and soil moisture. Other measurements that will continue to be measured include solar and net radiation, air temperature and humidity, wind speed and direction, and soil temperatures. Biophysical data will include determinations of leaf area indices, stomatal conductance, and surface albedo. Data from these sites will be used to: 1) evaluate the temporal variability of surface fluxes as a function of season; 2) determine daily and weekly probability distributions of energy fluxes; 3) evaluate and test current surface­biosphere submodels that are currently used for both short and long term numerical weather prediction; 4) determine the relative latent energy contributions from the soil and vegetative components as functions of season; and 5) test a hierarchy of models for estimating the surface energy fluxes from standard meteorological data.

Tilden P. Meyers

423­576­1245

FAX: 423­576­1245

FED EX: NOAA/ATDD 456 S. Illinois Avenue Oak Ridge, TN

Use of Optical and Microwave Remote Sensing for Mapping Surface Fluxes During the SGP Experiment

Investigators/Institutions:

Bill Kustas, Tom Schmugge & Tom Jackson/USDA­ARS Hydro Lab Beltsville, MD

John Prueger & Jerry Hatfield/USDA­ARS Soil Tilth Lab, Ames, IA

Tom Sauer/USDA­ARS SPA Fayetteville, AR

Pat Starks/USDA­ARS Grazing Lands Res. El Reno, OK

John Norman, George Diak & Martha Anderson/Univ. of Wisconsin, Madison WI

Paul Doraiswamy/USDA­ARS RS & Modeling Lab, Beltsville, MD

Radiometric temperature and passive microwave observations provide unique spatially distributed surface boundary conditions for surface energy balance modeling. Several relatively simple remote sensing models have recently been developed and tested with ground­truth measurements for computing the surface energy balance (Norman et al., 1995; Kustas and Humes, 1996; Anderson et al., 1997; Zhan et al., 1997). There has also been recent applications of remote sensing data from weather satellites in a simple hydrologic model for monitoring vegetation growth and predicting crop yields (Doraiswamy and Cook, 1995). These modeling algorithms will be applied to remote sensing data collected over the whole SGP study area, but with primary focus on the El Reno site where there will be ground truth hydrometeorological data collected by J. Prueger, B. Kustas, T. Sauer and P. Starks. These data will include standard weather data (wind speed, wind direction, air temperature, relative humidity, solar radiation and precipitation), the surface energy balance, and profiles of soil moisture, temperature and soil heat flux. There will be several aircraft flights with the TIMS instrument coordinated by Tom Schmugge for collecting high resolution thermal­IR data in the early and later morning in order to evaluate the Two­Source­Time­Integrated­Model (TSTIM; Anderson et al., 1997) and the Dual­Source­Energy flux­Model (DSEM; Norman et al., 1995) with local flux observations. In particular, the high spatial resolution TIMS data can be used to evaluate how well the TSTIM model performs on small pixels and whether simple methods exist for interpolating 5 km flux estimates from GOES down to the small scale of 10's of meters. The daily surface moisture maps from the ESTAR passive microwave observations on the P­3 aircraft coordinated by Tom Jackson will be used to test a version of DSEM that uses surface moisture for surface energy flux predictions (Zhan et al., 1997). Landsat TM and NOAA AVHRR data for the study sites and surrounding area will be acquired, processed and mapped by Paul Doraiswamy. In addition, the ground­based measurements of evapotranspiration and soil moisture profile changes will be used for testing the hydrologic model predictions (Kalluri and Doraiswmay, 1995; Doraiswamy, et al., 1997). Once model validation/calibration is performed at the El Reno site, the models will be used with satellite data (i.e., LANDSAT, NOAA­AVHRR and GOES) for mapping fluxes over the entire SGP domain. These estimates will be compared to regional fluxes derived from aircraft eddy correlation and LASE measurements.

References:

Anderson, M.A., J.M. Norman, G.R. Diak, W.P. Kustas and J.R. Mecikalski. 1997. A two­source time­integrated model for estimating surface fluxes using thermal infrared remote sensing. Remote Sensing of Environment [In Press]

Doraiswamy, P.C. and P.W. Cook. 1995. Spring Wheat Yield assessment using NOAA AVHRR data. Canadian J Remote Sens. 21:43­51.

Doraiswamy, P.C., P. Zara S. Moulin and P.W. Cook 1997. Spring wheat yield assessment using Landsat TM imagery and a crop simulation model. (Submitted to Remote Sensing of the Environ.)

Kalluri, S. and P.C. Doraiswamy. 1995. Modelling transpiration and water stress in vegetation from satellite and ground measurements. Presentation at the 1995 International Geoscience and Remote Sensing Symposium. Firenze, Italy , p1483­1487.

Kustas, W.P., and K.S. Humes. 1996. Sensible heat flux from remotely­sensed data at different resolutions. Chapter 8. In: Scaling up in Hydrology Using Remote Sensing (J.B. Stewart, E.T. Engman, R.A. Feddes and Y. Kerr editors) John Wiley and Sons London pp. 127­145.

Norman, J. M., W. P. Kustas and K. S. Humes. 1995. A two­source approach for estimating soil and vegetation energy fluxes from observations of directional radiometric surface temperature. Agricultural and Forest Meteorology 77:263­293.

Zhan, X., W.P. Kustas, T.J. Schmugge and T.J. Jackson. 1997. Mapping surface energy fluxes in a semiarid watershed with remotely sensed surface information. Preprint of the 13th Conference on Hydrology, American Meteorological Society, pp. 194­197.

Bill Kustas

bkustas@hydrolab.arsusda.gov

USDA­ARS­Hydrology Lab

Beltsville, MD 20705 USA

Voice: (301) 504­8498

Fax: (301) 504­8931

Title: Investigation of spatial distribution of soil water and heat flux.

Abstract: A series of Soil Heat and Water Measurement Stations (SHAWMS) have been installed on the Little Washita River Watershed (LWRS) which make profile measurements of soil temperature, soil heat flux, the three parameters of soil heat, and soil moisture. Data from the SHAWMS will be used to investigate the temporal and spatial variability of soil water and heat flux under rangeland condtions and to provide another source of ground truth data for the ESTAR instrument. A limited number of SHAWMS will be installed on the Ft. Reno site under both natural rangeland and winter wheat fields to investigate differences in these fluxes for representative ground cover conditions in central Oklahoma.

References:

Patrick J. Starks

pstarks@grl1.ars.usda.gov

(405) 262­5291

fax (405) 262­0133

USDA­ARS­GRL

7207 W. Cheyenne St.

El Reno, Oklahoma 73036

Investigator: Doug Miller

Collaborators: Binayak Mohanty, Teferi Tsegaye, Walter Rawls

Title: Combining Soil Survey Information and Point Observations of Soil Physical and Hydraulic Properties to Improve the Extension of Pedo­Transfer Functions to Regional Areas.

Abstract:

Soil moisture is a much sought after parameter for a wide range of modeling and management applications. Direct measurement of soil water status, however, is an expensive, time-consuming exercise which is largely prohibitive beyond a few select areas. Previous work has shown the utility of "pedo-transfer" functions to predict the water retention curve or unsaturated hydraulic conductivity of the soil. These functions are based on commonly measured soil physical properties such as particle-size distribution, organic matter content, and bulk density. Pedo-transfer functions in combination with routine spatial information from soil survey and spatial information on topographic and land surface characteristics could potentially be used to improve regional estimates of soil moisture.

We will focus on combining spatial information from soil survey, topographic and land surface characteristics with point observations of soil physical properties and soil moisture content to improve soil moisture predictions. The Little Washita River Basin in the southwestern portion of the SGP97 operations area will be the location of detailed study and correlation of field observations of soil physical and hydraulic properties. Ground sampling for this work will be performed in conjunction with soil moisture sampling in support of the main remote sensing objectives of SGP97. Manpower for sampling and access to sampling sites may, necessarily, restrict our opportunities to obtain a full range of representative soil map units. However, it is our hope that we can obtain enough samples to be able to characterize several key combinations of soil, topographic, and land surface conditions which in turn may be used to test our ability to "scale up" to larger areas.

Sponsor: NASA through the Penn State EOS IDS Investigation of the Global Water Cycle

Spatial variability of biomass and fraction of absorbed PAR within the SGP97 site.

Craig Daughtry and Paul Doraiswamy, USDA/ARS Remote Sensing and Modeling Lab, Beltsville, MD

Steven Hollinger, Illinois State Water Survey, 2204 Griffith Dr., Champaign, IL 61820.

Abstract:

Relationships between phytomass production and absorbed photosynthetically active radiation (PAR) have been reported for numerous plant species (Daughtry, et al., 1992). The fraction of absorbed PAR (fA) may be estimated from multispectral remotely sensed data (Prince, 1991). Together these two concepts provide a basis for monitoring vegetation production using remotely sensed data. Our primary objective is to characterize the spatial variability of vegetation within the SGP97 site. We will sample fresh and dry phytomass, leaf area index (LAI), and fA in approximately 60 fields and will extract the multispectral data for each field from Landsat TM scenes. Most of the fields for vegetation sampling will also be used for the gravimetric and profile soil moisture sampling. Global positioning system (GPS) data will be used to register the images and locate the sample sites within the images. Various models will be used to relate the multispectral and vegetation data (Moran et al., 1995) and to estimate phytomass in other fields of the SGP97 site. In addition, for selected fields of winter wheat, we will measure crop residue cover using line­transect methods (Morrison et al., 1993) and will estimate residue cover for other fields using multispectral data from Landsat and other sources (Daughtry et al., 1996). Anticipated products include land use/cover maps, maps of vegetation density, and crop residue cover maps for the SGP97 site. These data should be useful for developing and extending various surface energy balance models and vegetation assessment models from local to regional scales.

References:

Daughtry, C.S.T., K.P. Gallo, S.N. Goward, S.D. Prince, and W.P. Kustas. 1992. Spectral estimates of absorbed radiation and phytomass production in corn and soybean canopies. Remote Sensing Environment 39:141­152.

Daughtry, C.S.T., J.E. McMurtrey III, E.W. Chappelle, W.J. Hunter, and J.L. Steiner. 1996. Measuring crop residue cover using remote sensing techniques. Theor. Appl. Climatol. 54:17­26.

Morrison Jr, J.E., C Huang, D.T. Lightle, C.S.T. Daughtry. 1993. Residue cover measurement techniques. J. Soil Water Conserv. 48:479­483.

Moran. M.S., S.J. Maas, and P.J. Pinter Jr. 1995. Combining remote sensing and modeling for estimating surface evaporation and biomass production. Remote Sensing Reviews 12:335­353.

Prince, S.N. 1991. A model of regional primary production for use with coarse­resolution satellite data. Int. J. Remote Sensing 12:1313­1330.

Craig Daughtry voice 301­504­5015

USDA­ARS Remote Sensing and Modeling lab fax 301­504­5031

10300 Baltimore Ave email

Beltsville, MD 20705 cdaughtry@asrr.arsusda.gov

Investigators/Institutions:

Dara Entekhabi, 48­331, MIT, Cambridge, MA 02139

Tel: (617) 253­9698

Fax: (617) 258­8850

Email: darae@mit.edu

Dennis McLaughlin, 48­209, MIT, Cambridge, MA 02139

Tel: (617) 253­7176

Fax: (617) 253­7462

Email: dennism@mit.edu

Title: Using Data Assimilation to Infer Soil Moisture from Remotely Sensed Observations: A Feasibility Study

Abstract:

A state­space formulation of the data assimilation problem is developed including the following components: near­surface soil moisture and subsurface profile dynamics, surface energy balance, multispectral radiobrightness, soil type and pedotransfer functions. The data assimilation model will be tested using data from numerical experiments whose statistics are derived from the SPG97 and Washita92 experiments.

References:

McLaughlin, D. B. , 1996: Recent advances in hydrologic data assimilation, Reviews of Geophysics, 977­984.

Investigators/Institutions:

Dara Entekhabi, 48­331, MIT, Cambridge, MA 02139

Tel: (617) 253­9698

Fax: (617) 258­8850

Email: darae@mit.edu

Ignacio Rodriguez­Iturbe, Dept. Civil Engineering, Texas A&M University, College Station, TX 77843

Tel: (409) 845­7435

Fax: (409) 845­6156

Email: iri9280@vms2.tamu.edu

Title: On Space­Time Organization of Soil Moisture Fields: Dynamics and Interaction with the Atmosphere

Abstract:

The decrease in second­order statistics of soil moisture random fields under aggregation may be estimated using scaling functions whose parameters vary in time (during dry­downs) in a predictable manner and whose parameters have known dependencies on soil and climate properties. We plan to use the multiple scale observations of soil moisture fields using a variety of platforms and sensors to characterize the required scaling functions. Next using simple models of dry­down and percolation, we intend to relate the parameters of these functions to soil and climate properties.

References:

Rodriguez­Iturbe, I., G. K. Vogel, R. Rigon, D. Entekhabi, F. Castelli and A. Rinaldo, 1995: On the spatial organization of soil moisture fields, Geophysical Research Letters, 22(20), 2757­2760.

Scaling Issues in the Retrieval and Modeling of Soil Moisture ­­ A Geomorphology Perspective

Ana P. Barros, Rajat Bindlish, and Li Yanming

The Pennsylvania State University

ABSTRACT

Remote sensing and the prospect of long­term monitoring of soil moisture over large areas offer unique opportunities in hydrologic science both for climate studies and for operational applications. Pertinent research issues include: 1) the formulation and accuracy of the algorithms used to transform the remotely­sensed signal (i.e. surface radiometric temperature) into estimates of soil moisture; 2) scaling and the relationship between the scale of measurement and data resolution; 3) data assimilation into operational mesoscale models. In this context, the objectives of our research are to:

1) investigate and quantify the functional dependencies between observed soil moisture dynamics at different scales and the forming and development factors that determine the properties of soils in their natural setting­­climate, vegetation, topography and geology;

2) investigate and quantify the functional dependencies between remotely sensed brightness temperatures at different scales and soil forming and development factors;

3) elucidate the scaling mechanisms implicit in remotely sensed brightness temperatures at different resolutions, and determine the effective scale of measurement at each resolution;

4) use the results of 1), 2) and 3) to constrain a transformation model to retrieve soil moisture. Sensitivity analysis to will be conducted to evaluate model's accuracy and transportability;

5) evaluate the skill of a mesoscale model, specifically MM5, when remote­sensing estimates of soil moisture are used as surface boundary conditions in operational mode. The focus is on short to medium­range forecasts of surface temperature, humidity, and precipitation.

Multidimensional spectral analysis, system identification techniques such as cluster analysis and self­organizing neural networks, geostatistics and deconvolution methods will be used to identify soil­topography, soil­vegetation, soil­climate and soil­geology relationships. Data from SGP97 will be analyzed along with data from previous field experiments (e.g. Washita­92 and 94).

Vertical Profiles of the Atmospheric Boundary Layer and Upper Air for the Southern Great Plains 1997 Field Experiment

Principal Investigator: C. D. Peters­Lidard

Environmental Hydraulics and Water Resources

School of Civil and Environmental Engineering

Georgia Institute of Technology, Atlanta, GA 30332­0355

tel: 404­894­5190; fax: 404­894­2677

e­mail: cpeters@ce.gatech.edu

Abstract

In support of the eventual goal to integrate remotely sensed observations with coupled

land­atmosphere models, Georgia Institute of Technology and the National Severe Storms Laboratory propose to provide vertical profiles of atmospheric pressure, temperature, humidity, wind speed and wind direction during the Southern Great Plains 1997 field experiment (June 17­July 11). Our sounding design is based on three science needs directly related to the existing objectives of the experiment:

(1) Provide boundary and initial conditions for coupled atmospheric­hydrologic modeling;

(2) Provide data necessary for atmospheric correction of thermal remote sensing; and

(3) Support water vapor and heat budget computations over the SGP97 domain.

In addition to these science needs, surface and boundary layer profiles will provide data to support the estimation of roughness lengths and stability correction functions and to study boundary layer top entrainment processes and vertical structure. We plan to deploy two sounding systems: one boundary layer and upper air sounding system and one tethersonde system collocated within the Little Washita River Watershed in the southern portion of the SGP97 domain. The launch times will coincide with the launch times of the ARM/CART IOP Sounding program, and will therefore provide complete coverage around the boundary of the SGP97 domain to support vapor budget computations.

Sponsor: NASA (Program Manager: Ming­Ying Wei)

References

Betts, A. K. and A. C. M. Beljaars, Estimation of effective roughness length for heat and momentum from FIFE data, Atmos. Res., 30, 251­261, 1993.

Peters­Lidard, C. D. and E. F. Wood, Spatial variability and scale in land­atmosphere interactions: 2. Model validation and results, submitted to Water Resour. Res., 1996b.

Ziegler, C. L and L. C. Showell, Chapter XII: Atmospheric Soundings in Hydrology Data Report Washita 1994, eds. P. J. Starks and K. S. Humes, NAWQL 96­1, USDA ARS, Durant OK, June 1996.

Investigator(s)/Institutions(s): Dr. Praveen Kumar, Hydrosystems Lab. # 2527B, 205 North Matthews Avenue, Department of Civil Engineering, University of Illinois, Urbana, Illinois 61801

(217)­333­4688

Fax (217)­333­0687

email: kumar1@uiuc.edu

Students:

Patricia Saco (saco@uiuc.edu)

Ji Chen (jichen@uiuc.edu)

Title: Estimation, Modeling and Simulation of Soil Moisture Variability and Surface Energy Balance Using Multisensor Measurements at Large Scales

Abstract:

In order to understand the feedback interaction between land and atmosphere we need a method to characterize the near surface soil­moisture variability and surface energy balance at a vast range of scales. Due to the formidable cost of making such measurements the strategy adopted is to make fine scale measurements of limited coverage embedded within coarse scale measurements of larger coverage using instruments on different platforms. The PI has recently developed a multiple scale conditional simulation (MSCS) technique [Kumar, 1996] to obtain soil moisture fields by combining the multisensor measurements (obtained at multiple scales). The technique uses multiple scale Kalman filtering algorithms for the estimation and a conditional simulation technique for obtaining realistic soil­moisture fields. It relies on a fractal model of soil moisture [Iturbe et al., 1995]. The method can be easily extended to multiple variable fields such as the energy balance components at the land surface. The objectives of our participation in the Southern Great Plains Experiment are to:

(a) Extensively validate the multiple scale conditional simulation technique for a wide range of scales and soil­moisture conditions;

(b) Apply it to multiple variable surface energy fields and assess its performance;

© Assess the impact of the conditionally simulated fields on the atmosphere.

References:

1. Kumar, P., Application of Multiple Scale Estimation and Conditional Simulation for Characterizing Soil Moisture Variability, submitted to {\em Water Resources Res.}, 1996.

2 Rodriguez­Iturbe, I., G. K. Vogel, R. Rigon, D. Entekhabi, F. Castelli, A. Rinaldo, On the Spatial Organization of Soil Moisture Fields, {\em Geophysical Res. Letters}, 22(20), 2757­2760, 1995.

VEGETATION EFFECTS ON SOIL MOISTURE ESTIMATION

Narinder Chauhan

Code 923

NASA/Goddard Space Flight Center

Greenbelt MD 20771

301 286 4840

FAX: 301 286 1757

E­mail: nsc@fire.gsfc.nasa.gov

The estimation of soil moisture depends strongly on the vegetation and its quantization. I will be working with Paul Doraiswamy of USDA and David LeVine of GSFC/NASA for the characterization of vegetation. The plan is to participate in the collection of gross vegetation parameters such as plant density, LAI, vegetation water content, etc. for most of the vegetation in the area. In addition, specific vegetation types will be targeted for collection of detailed canopy geometry data. This can involve measuring canopy architecture, leaf and stem angle distributions. In the past, the measurement of soil moisture under certain crops, like grass and alfalfa has been a problem. The plan is to characterize such crops with a higher degree of accuracy and to use theory (Discrete Scatter Models) to compare predictions with passive microwave measurements. The goal is to learn how to characterize these vegetation canopies to accurately estimate soil moisture.

Investigators: George R. Diak and John M. Norman, University of Wisconsin­Madison

William P. Kustas ,USDA­ARS

Title of Investigation: Estimation and Validation of Evapotranspiration at 10 km Scales During The SGP­97 Experiment

Abstract:

We will investigate the performance of a two­source time­integrated model (TSTIM) for evaluating the surface energy balance over the domain of the SGP­97 experiment. This model is comprised of a surface component (describing the relationship between radiometric temperatures, sensible heat flux and the temperatures of the air, canopy and soil surface), coupled with a time­integrated component (connecting the time­integrated surface sensible heat flux with planetary boundary layer development). The required data inputs are radiometric surface temperatures at two times (from GOES), analyzed surface and upper air synoptic data, and vegetation cover estimates from satellite sources. Surface energy balance components will be estimated at approximately a 10­km resolution over the SGP­97 domain. These estimates will be compared with available surface and aircraft­based flux estimates. The TSTIM has the ability to utilize information on soil­surface evapotranpiration from any source. Using the SGP­97 data, we will also investigate how microwave­based near­surface soil moisture estimates from passive microwave sensors can be incorporated into this model.

References:

Anderson, M. C., J. M. Norman, G. R. Diak and W. P. Kustas, 1996: A two­source time integrated model for estimating surface fluxes for thermal infrared satellite observations. Accepted for publication, Rem. Sens. Environ.

Diak, G. R. and M. S. Whipple, 1995: A note on estimating surface sensible heat fluxes using surface temperatures measured from a geostationary satellite during FIFE­1989. J. Geophys. Res. 100, 25,453­25,461.

Norman, J. M., W. P, Kustas and K. S. Humes, 1995: A two­source approach for estimating soil and vegetation energy fluxes from observations of directional radiometric surface temperatures, Agric. For. Meteor., 77, 263­293.

Contact:

Dr. George R. Diak

1225 W. Dayton St., #205

Phone: 608­263­5862 Fax: 608­262­5974 email: georged.@ssec.wisc.edu

Title: Estimating Soil Hydraulic Properties from Airborne Passive Microwave Data ­ The Effects of Subpixel Heterogeneity

Investigators/Institutions: J. Finch and E. Burke, Institute of Hydrology

Abstract:

A physically based model that couples a soil water/energy model to a microwave emission model (MICRO­SWEAT) has recently been developed. MICRO­SWEAT predicts the time series of microwave emission from input parameters of the soil properties, soil water status, vegetation parameters and a time series of meteorological data.

One application of MICRO­SWEAT has been to successfully estimate soil hydraulic properties from ground­based microwave data, i.e. essentially point measurements, by fitting the model to detailed time series of data. The next step in this line of research is to estimate soil hydraulic properties at the spatial scale of a pixel of remotely sensed data. The proposed research will investigate the effect of sub­pixel heterogeneity in soil hydraulic properties, soil roughness, vegetation water content and soil moisture on microwave data.

The objectives of the project will be achieved by using the microwave values predicted from MICRO­SWEAT. The ground and ESTAR data acquired during SGP'97 will provide a data set that contains both the input parameters for MICRO­SWEAT and microwave data that can be used to test the values predicted by the model. The proposed research will make additional measurements on the ground of the soil and vegetation parameters required by MICRO­SWEAT at a series of sites in order to quantify the spatial heterogeneity within a pixel of the ESTAR data. Between 50 and 100 sites will be selected to represent the variations in soil and vegetation and measurements of soil moisture taken daily except during periods of rapid change when a reduced number of sites will be monitored more frequently. Other parameters will be estimated at different periods reflecting their rate of change. The key input and validation parameters which will be measured are: rainfall, plant height, leaf area index and leaf angle, vegetation water content, surface soil moisture, TDR soil water down to 120 cm, surface roughness, soil bulk density. In addition, gravimetric soil moisture samples for calibration will be collected and soil samples will be taken for laboratory analysis. The field data will be analyzed to assess the temporal and spatial variability of the input parameters required by MICRO­SWEAT.

The first step of the modelling will be to test the values predicted by MICRO­SWEAT against the values recorded by the ground­based microwave radiometer in order to verify that the model is predicting the values to an acceptable accuracy. The next stage will be to use MICRO­SWEAT to predict the microwave emission from the range of soils and land cover types that occur within a pixel of the airborne remotely sensed data. These values will then be aggregated to produce a time­series of 'averaged' values that will be tested against the values of the airborne remotely sensed data. A sensitivity analysis will be carried out to assess the contribution from the different land surface parameter combinations to the time series of 'averaged' remotely sensed data. Finally, the simulated times series of remotely sensed data will be inverted to estimate the soil hydraulic properties of the pixel and a comparison made between these values and the variability of the values actually occurring within the pixel.

Sponsor: UK Natural Environment Research Council

Staff:

Dr. Jon Finch

Institute of Hydrology

Wallingford

Oxon OX10 8BB

UK

tel. + 44 (0)1491 838800

fax. + 44 (0)1491 692424

email: J.Finch@ioh.ac.uk

Dr. Lester Simmonds

Soil Science Department

UK

tel. +44 (0)1189 316557

fax. +44(0)1189 316660

Miss Eleanor Burke

Institute of Hydrology

Wallingford

Oxon OX10 8BB

UK

tel. + 44 (0)1491 838800

fax. + 44 (0)1491 692424

email: E.Burke@ioh.ac.uk

Investigator(s)/Institutions(s):

Edward V. Browell, PI, NASA Langley Research Center,

Syed Ismail, co­I, NASA Langley Research Center,

Donald H. Lenschow, co­I, National Center for Atmospheric Research

Kenneth J. Davis, co­I, University of Minnesota

Title: INVESTIGATION OF MESOSCALE VARIABILITY IN CONVECTIVE BOUNDARY LAYER DEVELOPMENT USING LASE

Abstract:

One of the four objective of the Southern Great Plains 1997 (SGP97) Experiment is the examination of 'the effect of soil moisture on the evolution of the atmospheric boundary layer and clouds over the southern great plains". This study seeks to advance our understanding of this coupled land­atmosphere system, a fundamental component of the hydrologic, weather and climatic systems. We will study the spatial variability in the development of the convective boundary layer (CBL) over a fairly uniform land surface with spatially varying soil moisture content. Soil moisture will be measured with ESTAR on­board the NASA P­3 aircraft. NASA's Lidar Atmospheric Sensing Experiment (LASE) will also be flow on­board the P­3 aircraft. The LASE instrument, reconfigured to fly on the P­3, will be capable of resolving the vertical and horizontal structure of the developing CBL, including information on the two dimensional moisture structure of the atmospheric boundary layer. LASE and ESTAR together will provide a unique and comprehensive mesoscale remote sensing data set for studying the evolution of the CBL and its relation to the land surface. This study will benefit from complementary data from the Canadian Twin Otter aircraft (real­time images of boundary layer structure obtained by LASE can be used, when appropriate, to guide the Twin Otter). Other in situ surface and tower measurements, and satellite remote sensing data will also be used in this study. The primary goals of this research are: evaluation of the influence of soil moisture on the local surface energy budget (SEB) over the SGP97 region; 2) evaluation of the influence of mesoscale spatial variability in the SEB on CBL development, including CBL depth and cloud cover; 3) quantification of the CBL water vapor budget (advection, entrainment, evapotranspiration) using remotely sensed and in situ data; and investigation of microscale mechanisms responsible for the entrainment of tropospheric air into the CBL.

References:

Kenneth J. Davis, Assistant Professor phone: 612­625­2774

Department of Soil, Water, and Climate fax: 612­625­2208

University of Minnesota email: kdavis@soils.umn.edu

1991 Upper Buford Circle St. Paul, MN 55108­6028

Investigator: Guido D. Salvucci, Boston University, Dept. of Geography

675 Commonwealth Ave., Boston, MA 02215

617­353­8344

Fax 617­353­8399

gdsalvuc@bu.edu

Title: Detection and modeling of transitions between atmosphere and soil limited

evapotranspiration in the southern great plains summer 1997 experiment

Abstract:

Salvucci [WRR 33(1), 111­122, 1997] presented a simple diagnostic model of bare soil evaporation which expresses the daily rate of evaporation during soil limited periods as a function of the duration (td) and average rate (ep) of stage­one (potential) evaporation. The model does not require in situ estimates of soil hydraulic properties or initial water content, as these are implicitly related to td and ep. Surface and remote observations of detectable changes in near surface moisture content, temperature, and albedo may be used to estimate the transition time (td). With extensions to estimate stressed transpiration from grasses, the model thus has the potential to yield ET estimates over large areas using satellite data. The microwave estimates of soil moisture collected over the month long SGP experiment will be used in conjunction with concurrent surface flux measurements taken at the ARM sites to further test and develop this methodology, with special emphasis on the detection of transition time via microwave­estimated surface soil moisture dynamics.

References: Salvucci, G.D., 1997. Soil and moisture independent estimation of stage­two evaporation from potential evaporation and albedo or surface temperature, Water Resources Research, 33(1), 111­122

Sponsor: NASA Grant NAGW­5255 "Thermal and Hydrologic Signatures of Soil Controls on Evaporation"

Investigator: Eni G. Njoku

Institution:Jet Propulsion Laboratory

Title: Multichannel land parameter retrieval at different spatial scales

Abstract:

Soil moisture is the dominant effect on microwave emission from soils at L­to C­band for soils with low to moderate vegetation. Surface roughness, temperature, and low­opacity vegetation cover affect soil microwave emission, but to lesser extents than soil moisture. As the opacity of vegetation cover increases it becomes the dominant effect on the microwave emission, and can mask the soil moisture signal. Multifrequency retrieval algorithms are a means for utilizing the varying sensitivity of brightness temperature to the surface parameters at different frequencies to correct for vegetation, roughness, and temperature in retrieving soil moisture. Theoretical simulations using models based on recent empirical data show that multichannel algorithms should work well in practice. However, there have been few opportunities to demonstrate this in actual field experiments. SGP'97 provides an opportunity for such a demonstration. Truck­based L­, S­, and C­band measurements are planned, providing data at a local scale, and L­band aircraft data and AVHRR satellite data will be available at the 1­km resolution scale. SSM/I data will be available at a 50­km resolution scale, providing a historical database of 19.3 and 37 GHz brightness temperatures over the SGP'97 site at that scale. We will provide the AVHRR and SSM/I data to the SGP'97 experiment database as a contribution of this investigation. Soil moisture retrievals will be performed at three scales, using different algorithms and available data sets: (1) local ­ truck­based; (2) regional ­ aircraft microwave/satellite AVHRR; (3) time­series ­ satellite SSM/I. Soil moisture retrievals for these cases will be compared with in­situ observations and output from numerical models over the SGP'97 site, and results of the analyses will be published. Research using the truck­based, aircraft, in­situ, and model data will be performed in collaboration with the data providers.

References:

Njoku, E.G. and D. Entekhabi (1996): Passive microwave remote sensing of soil moisture. J. Hydrology, 184, 101­129.

Njoku, E. G., S. J. Hook, and A. Chehbouni (1996): Effects of surface heterogeneity on thermal remote sensing of land parameters. In: Scaling Up In Hydrology Using Remote Sensing (J. B. Stewart, E. T. Engman, R. A. Feddes, and Y. Kerr, Eds.), Wiley, New York.

Investigator(s)/Institutions(s):

Paul R. Houser (NASA­GSFC), and Jim Shuttleworth (U. of Arizona)

Title: Regional In­Situ Profile Soil Moisture and Surface Energy Flux Observations in support of the 1997 Southern Great Plains Experiment.

Abstract:

Our contribution to the Southern Great Plains 1997 experiment will be in four areas: (1) general mission support through surface gravimetric sampling and processing, (2) profile soil moisture observations using TDR and gravimetric techniques, (3) Soil characterization at selected sites, and (4) operation of a surface energy and water flux station at the ARM central facility.

Observations of Profile Soil Moisture and Characteristics:

The primary objective of the Southern Great Plains 1997 (SGP97) Experiment is to map soil moisture using an airborne passive microwave radiometer (ESTAR, LeVine et al., 1992) over a 60 km by 250 km area in central Oklahoma for a one month period during the summer of 1997 (Jackson, 1996). Passive microwave instruments are only sensitive to moisture in the top few centimeters of soil, but knowledge of moisture in the entire soil profile is essential for hydrologic, ecologic, and climatic studies (Wei, 1995; Ragab, 1995; Jackson, 1980). Therefore, profile soil moisture observations will be essential for understanding the relationship between the remotely­sensed measurements and deeper moisture stores. Profile measurements will enable further development and validation of methodologies that extend remotely sensed surface soil moisture estimates to the entire root zone (Jackson, 1980), will enable the definition of vertical soil moisture error correlation structures which are essential in soil moisture data assimilation studies, and will help to calibrate existing profile sensors. Profile soil moisture observations using Campbell heat dissipation probes are currently in place in the SGP97 area at 14 Little Washita Micronet, 5 Oklahoma Mesonet, 2 ARM Central Facility, and 5 El Reno sites. Observations made with these sensors are known to vary with soil characteristics and temperature, therefore each of these sites will be instrumented with an ESI MoisturePoint profile TDR that will be monitored daily during SGP97 (installation done prior to the experiment by Pat Starks, USDA­ARS El Reno), and profile gravimetric observations at selected sites (mostly at El Reno) will be collected as frequently as possible (selected soil cores will be sent to the USSL for water retention, and soil characterization analysis). The TDR probes and MoisturePoint equipment for this plan are currently available (Pat Starks, USDA­ARS, and Ron Elliot, OK Mesonet), and both truck­mounted and hand operated gravimetric sampling equipment is available (USSL­Binayak Mohanty), but truck sampling may be limited to the EL Reno facility. The existing profile soil moisture sensors are located next to weather observation stations that are typically on the edges of fields in non­characteristic soil and vegetation. To assess the representiveness of these observations, additional in­field TDR profile observations will be made at a subset of sites (2 at the ARM Central Facility, 2 at El Reno, and 1 at the Little Washita). It is thought that a minimum of 3 in­field TDR observations will be necessary at each of these sites to assess the field average profile soil moisture. At one site (El Reno) a larger number of in­field TDR observations (9 samples) will be made to determine if 3 samples is adequate for determination of in­field average profile soil moisture. Approximately 4 of these 21 additional probes are currently available (Pat Starks, USDA­ARS), leaving only ~17 to purchase ($350ea * 17probes =$5950)!

Observations of Surface Water and Energy Fluxes:

The DOE­ARM program has embarked on an extensive environmental observation program in the Oklahoma and Kansas area. As part of this program, observations of surface water and energy fluxes are being performed with eddy correlation and Bowen ratio techniques. To characterize the quality of these observations for use in applications such as validation and calibration of regional land surface and atmospheric modeling projects, a well established eddy correlation system will be co­located with the ARM surface flux measurement sites at the ARM Central Facility.

The University of Arizona's CO2/H2O eddy correlation system (Shuttleworth) will initially be co­located with other mobile surface flux measurement systems at the EL Reno Facility for a period of a few days just prior to the SGP97 experiment for intercomparison. During this time, two other Campbell LiCor Bowen Ratio systems may be deployed and maintained at El Reno as part of this project. The UA eddy correlation system will be re­deployed to the ARM Central Facility at the start of the SGP97 experiment. It will be located near the ARM Bowen ratio system in rangeland vegetation for two weeks, and near the ARM eddy correlation system in a winter wheat field for two weeks. The exact location and height of the UA system may vary from the ARM sensors to minimize fetch problems.

Personnel: Paul Houser (available for experiment duration)

Chawn Harlow (available for experiment duration)

Jim Shuttleworth (questionable availability)

NASA­GSFC: Houser's salary, computer support, GPS

NASA­HQ: Houser's Travel, and hopefully some equipment

U of Arizona: NASA Contract NAS­5­3492 will provide salary and travel for 1 student, computer support, 1 flux station

Cooperator(s):

USDA­ARS (Pat Starks at El Reno): cooperating on MoisturePoint TDR sampling

USDA-ARS-SL (Binayak Mohanty): Use of soil sampling equipment, possibly including a hydraulic press for use at El Reno

Oklahoma Mesonet (Ron Elliot): Use of 2­3 MoisturePoint "Boxes"

References:

Jackson, T. J., 1996. Southern Great Plains 1997 (SGP97) Experiment Plan, http://hydrolab.arsusda.gov/~tjackson/.

Jackson, T. J., 1980. Profile Soil Moisture from Surface Measurements. Journal of the Irrigation and Drainage Division, June 1980.

Le Vine, D. M., A. Griffis, C. T. Swift, ant T. J. Jackson, 1992. ESTAR: A Synthetic Aperture Microwave Radiometer for Measuring Soil Moisture. International Geoscience and Remote Sensing Symposium 1992, Vol 1.

Ragab, R., 1995. Towards a continuous operational system to estimate the root­zone soil moisture from intermittent remotely sensed surface moisture. Journal of Hydrology, 173:1­25.

Wei, Ming­Ying, editor, 1995. Soil Moisture: Report of a Workshop Held in Tiburon, California, 25­27 January 1994. NASA Conference Publication 3319.

Primary Contact:

Paul R. Houser

houser@hydro4.gsfc.nasa.gov

(301)­286­7702

fax (301) 286­1758

NASA's Goddard Space Flight Center

Hydrological Sciences Branch / Data Assimilation Office

Code 974 (Bldg. 22, Room C277)

Greenbelt, MD 20771

Participation in SGP97 from the

Center for Hydrology, Soil Climatology and Remote Sensing

The Center for Hydrology, Soil Climatology, and Remote Sensing (HSCaRS) under NASA sponsorship has as one of its objectives to develop a Local­scale Hydrology Model (LHM) and a Regional­scale Hydrology Model (RHM) that can utilize periodic input of remotely­sensed soil moisture data to "adjust" the surface soil moisture field used to calculate root zone moisture. In addition, we recognize the need to address the issue of disaggregating large pixel soil moisture data from satellites to the process­scale represented in the hydrologic models. The Southern Great Plains 1997 (SGP97) Experiment will provide data necessary for HSCaRS to pursue its hydrologic modeling research objectives. HSCaRS will provide support to the SGP97 Experiment and acquire additional characterization information needed for hydrologic modeling by conducting research in the following five areas:

1.) Relate surface soil moisture measurements to the soil moisture profile:

We will install and operate a soil profile station (see description below) on each of the two plots in the vicinity of the calibration plots to relate the observed surface soil moisture to the underlying soil moisture profile. One energy balance Bowen ratio (EBBR) station is available for deployment at the SLMR calibration site to relate soil moisture changes to surface energy fluxes. Depending on which site is selected for the calibration site, instead we may choose to deploy the EBBR in the Little Washita River basin. Additional meteorological measurements, including rainfall, air temperature, relative humidity, shortwave and infrared radiation wind direction and speed will be made at the SLMR site. Chip Laymon (GHCC) will service these stations and will also assist Peggy O'Neill in SLMR operation and data acquisition.

Up to four additional soil profile stations will be deployed in the Little Washita River watershed to a.) provide additional points for relating remotely­sensed surface soil moisture to the underlying soil moisture profile, b.) to relate SHAWMS soil profile measurements at field borders to measurements within the field, and c.) provide time continuity to periodic manual soil moisture profile measurements to be made at approximately 20­30 sites in the SGP97 study area (coordinated by Paul Houser). Bill Crosson (GHCC) will be the lead on this activity.

Description of Soil Profile Stations:

Soil moisture and temperature measurements will be made at several depths down to about 75 cm in each pit. Soil moisture will be measured using Water Content Reflectometers (Campbell Scientific, Inc.), a device based on time domain reflectometry, and using Soil Moisture Probes (Radiation and Energy Balance Systems), a device based on electrical resistance. Soil temperature will be measured in each pit using soil thermistors. Ground heat flux will be determined using a heat flux plate installed at 5 cm depth plus the heat storage in the upper 5 cm layer calculated from the time rate of change of temperature, which is measured using 4­sensor averaging thermocouple probes installed at 1, 2, 3 and 4 cm depths. We are currently examining techniques to derive the soil dielectric constant from Water Content Reflectometers or similar sensors. At this point this appears feasible; if so, we will provide dielectric constant profiles at one or more of the profile stations. This information should be valuable in understanding both SLMR and ESTAR measurements vis­a­vis soil moisture measurements in the upper 5 cm as well as in the profile.

2.) Soil hydraulic property characterization:

Accurate knowledge of the spatial distribution of soil hydraulic properties is necessary for SGP97 soil moisture retrieval as well as for hydrologic modeling activities. Soil profiles will be described and sampled for texture, hydraulic conductivity, bulk density and porosity at the sites where the HSCaRS soil profile stations are installed. A representative grass and winter wheat field in the Little Washita River watershed will be sampled (up top 100 samples each) for surface hydraulic properties. All soil samples will be analyzed at Alabama A&M University. Teferi Tsegaye (Alabama A&M University) will be lead on this activity.

3.) Classify vegetation:

An accurate land cover classification is necessary for the SGP97 soil moisture retrieval algorithm and subsequent hydrologic modeling. Landsat TM data will serve as the basis of the classification. HSCaRS will provide personnel to support this effort being coordinated by other SGP97 team scientists. Ahmed Fahsi (Alabama A&M University) will assist in this activity and coordinate additional student support provided by Alabama A&M University.

4.) Surface soil moisture variability:

Some understanding of the spatial variability of surface soil moisture is required to a.) assess the accuracy of using a limited number of gravimetric samples for remote sensing verification, b.) assess the accuracy of the remote sensing technique to represent the mean surface moisture of the field, c.) assess the linearity of integrating moisture variability by the ESTAR instrument within a single pixel, d.) test mixed­pixel algorithms, and e.) evaluate field­ and sub­watershed­scale hydrologic processes. While this activity will be conducted with a large cooperative group from many institutions, HSCaRS scientists from GHCC and Alabama A&M University have contributed significantly to developing the science and implementation plans for this activity. Teferi Tsegaye has particular interest in studying field­scale variability and Chip Laymon and Bill Crosson have interests in the application of these data to remote sensing interpretation and verification of hydrologic models.

In addition to field sampling, Chip Laymon is developing a GIS application for rapid mapping and evaluation of the field measurements. Site information and field measurements will be downloaded nightly from portable data recorders to a PC. These data can then be uploaded into a GIS application and for mapping and production of soft and hard copy output and thereby used by the field team leaders in redirecting labor resources the next day. In addition, near "real­time" visualization of the field measurements will contribute greatly to morale by making the science more tangible and understandable to those participating.

5.) Develop and test surface TDR measurement capability:

The surface soil moisture variability study (#4 above) is dependent on a portable, rapid measurement technique. Recent advances in time domain reflectometry techniques have resulted in sensors with "on­board" signal processing. We are currently investigating the ability to modify several off­the­shelf products for use in surface (0­5 cm) soil moisture determination. Preliminary results indicate that we will be successful in providing an instrument for use during SGP97. Current research is focusing on sensor intercomparison and calibration. Recommendations on equipment are forthcoming.

HSCaRS Participants:

Global Hydrology and Climate Center

Chip Laymon week 1, 2, 4

chip.laymon@msfc.nasa.gov

Bill Crosson week 1, 3, 4

bill.crosson@msfc.nasa.gov

Vishwas Soman

vishwas.soman@msfc.nasa.gov

Alabama A&M University

Ahmed Fahsi afahsi@asnaam.aamu.edu

Teferi Tsegaye tsegaye@asnaam.aamu.edu

Andrew Manu amanu@ asnaam.aamu.edu

Rajbhandari Narayan rajbhandari@asnaam.aamu.edu

~ 5­8 grad. students 2 week each ?

Investigator(s)/Institution: P.J. van Oevelen, Dept. Water Resources, WAU,

Wageningen, The Netherlands

M. Menenti, Winand Staring Centre, Wageningen, The Netherlands

Title of Investigation: Estimation of spatial soil moisture fields estimation using sensor fusion: SSM-I, ERS, Radarsat and ESTAR

Abstract:

Microwave radiometry has been widely accepted as the most practical tool to estimate spatial soil moisture fields, especially at L-band the results have been encouraging. However, currently there are no spaceborne microwave radiometers available with an acceptable resolution to be used in watershed studies. Therefore, the usefulness of SAR, in particular Radarsat and ERS, to estimate the same type of soil moisture fields as is possible with the airborne ESTAR (at a resolution of 1 km) will be investigated. The combination of data originating from various sensors to estimate the same property is referred to as sensor fusion. Within the EOS framework this study will also investigate the usefulness of low resolution SAR systems such as ASAR and the application of these fields in Numerical Weather Prediction models. To facilitate this study an extensive soil moisture measurement campaign will be set-up using portable TDR's (Time Domain Reflectometry), an FD (frequency domain) sensor along transects/grids and the EM38 instrument to give a more spatially average measurement over the same transect/grid. The grid size and spatial sampling scheme should be set up such that the measurements are representative enough to cover the spatial resolutions of the various sensors (25 m up to 1 km). All these measurements should occur as closely as possible to the overpass times of the various instruments.

References:

Investigator(s)/Institutions(s): Larry Mahrt (Oregon State University) and Jielun Sun (University of Colorado/NCAR)

Title: Aircraft measured surface fluxes and relationship to soil moisture.

Abstract: The Canadian Twin Otter and the NOAA LongEZ will be deployed during SGP to measure the spatial variability of fluxes of heat, moisture and carbon dioxide. The LongEZ will fly primarily low level flights below 50 m (subject to final FAA approval) to concentrate on surface flux measurements while the Twin Otter will fly multiple levels to include vertical structure of the boundary layer and assessment of entrainment of dry air. Two principal modes of operation will be "chasing" spatial gradients of surface moisture and coordinated flights with the P3. Additional flights will feature tower-aircraft flux comparisons.

The aircraft data, and eventually the tower flux, Mesonet and sounding data will be archived at Oregon State. The aircraft data will be quality controlled and evaluated in terms of flux sampling errors. The analyzed fluxes will be provided to the community along with a suite of other processed parameters such as surface roughness and surface radiation temperature. The analyzed fluxes from the two aircraft will be combined with the sounding data, the Mesonet data, LASE water vapor measurements, ESTAR brightness temperature and the soil moisture estimates to examine the response of the boundary layer to spatial variations of the soil moisture and the feedback of boundary layer evolution on the surface moisture fluxes. For example surface dryer conditions lead to greater heat flux, boundary layer growth and entrainment drying which reduces the surface relative humidity. For a given soil moisture, this enhances the soil moisture loss. Its effect on transpiration depends on stomatal control.

Methods are being developed to estimate area averaged moisture fluxes by modelling the evaporative fraction in terms of remotely sensed variables including the surface radiation temperature, red and near infrared channels and microwave band.

Larry Mahrt

COAS OSU

Corvallis, OR 97331

mahrt@ats.orst.edu 541 737 5691 fax 2540

Jielun Sun

MMM NCAR

P.O. Box 3000

Boulder, CO 80307

jsun@elder.mmm.ucar.edu 303 497 8994 fax 8171

Space-Time Characterization of Soil Moisture Variability for Assessment of

Sampling Errors by Space-Borne Sensors and Related Ground Truth Issues

Investigators:

Juan B. Valdes, Department of Civil Engineering and Climate System Research Program

Gerald R. North, Department of Meteorology and Climate System Research Program

Abstract

There is a great need of a set of observations of soil moisture that cover large areas and time intervals. The available records of Washita'92 have been extensively analyzed and used in our research but the data set have some limitations both in temporal and in areal extent. The planned experiment would greatly improve the data availability of soil moisture. In our research we are planning to use those measurements to characterize the space-time spectrum of soil moisture to be used in the estimation of sampling errors by sensors that are intermittent in time and/or space. The measurements will also be used to estimate nominal parameters for one-layer/two-layer models of the upper soil zone to carry out controlled experiments of proposed missions. The statistics of the observed point values on the ground and the observed surrogates on the overflights will be used to determine the possible bias in a procedure similar to the one carried out for precipitation.

Juan B. Valdes

Department of Civil Engineering

Texas A&M University

College Station TX 77843-3136

(409) 845-1340

(409) 862-1542 FAX

e-mail: jvaldes@tamu.edu

SGP-97: An Integrated Validation Framework

Investigators: B.P. Mohanty, P. Shouse, M. Th. van Genuchten (U.S. Salinity Lab)

Rationale:

The spatio-temporal dynamics of water and energy transport across the soil-atmosphere boundary layer in relation to climate change, hydrology, near-surface thermodynamics, and land use is still poorly understood. The problem of accurately estimating regional-scale soil water contents of the near-surface, variably-saturated (vadose) zone is complicated by the overwhelming heterogeneity of both the soil surface and the subsurface, the highly nonlinear nature of local-scale water and heat transport processes, and the difficulty of measuring or estimating the subsurface unsaturated soil-hydraulic functions (the constitutive functions relating soil water content, soil-water pressure head and the unsaturated hydraulic conductivity) and soil thermal properties (heat capacity and soil thermal conductivity). As remote sensing techniques make it increasingly possible to obtain large-scale soil water content and heat flux measurements, validation of these measurements using ground-based data and/or indirect estimates from relevant soil, landscape, and vegetation parameters is essential.

Objective:

The overall objective of our project is to develop and evaluate an "integrated validation framework" for remote sensing data of soil moisture content in the shallow subsurface. Specific scopes of our investigation for SGP-97 experiment will include:

1. Coupling of digital soil maps (e.g., SSURGO, STATSGO) with soil hydraulic and thermal property databases (e.g., UNSODA) using ARC/INFO geographical information systems (GIS) and neural network (NN) based pedotransfer functions (PTFs) (in collaboration with Doug Miller, and others).

2. Identification of important soil (e.g., soil type, texture, porosity, bulk density), landscape (e.g., slope, aspect, elevation, depth to water table), and land use/cover (vegetation type, vegetation density, management practice, etc.) parameters for establishing pedotransfer functions to describe soil hydrologic and thermal properties of relatively large land areas (in collaboration with Jay Famiglietti, Charles Laymon, Doug Miller, Paul Houser, and others).

3. Measurement of soil water retention and hydraulic conductivity functions across the space and time domains of SGP-97 experiment (in collaboration with Paul Houser and others).

4. Investigation of the suitability of different exploratory data analyses, Bayesian statistics, spatial statistics, numerical or other up-scaling techniques for estimating effective soil hydraulic and thermal parameters of the larger land areas (pixels) from point measurements in the vadose zone (in collaboration with Dennis McLaughlin, and Dara Entekhabi).

The ultimate purpose of this research is to obtain pixel-scale estimates of the soil hydraulic and soil thermal properties for possible use in land-soil-atmospheric interaction simulation models to test space-borne measurements of transient soil moisture and soil temperature data, thereby yielding alternative (provide supplementary data) to ground-truth measurements.

Investigator/Institution: Jay Famiglietti, University of Texas at Austin

Title: Ground-Based Investigation of Spatial-Temporal Soil Moisture variability in Support of SGP '97

Abstract: Surface (0-5 cm) soil moisture exhibits a high degree of variability in both space and time. However, larger-scale remote sensing integrates over this variability, masking the underlying detail observed at the land surface. Since many earth system processes are nonlinearly dependent upon surface moisture content, this variability must be better understood to enable full utilization of the larger-scale remotely-sensed averages by the earth science community. The overall goals of this investigation are to (a) characterize soil moisture variability at high spatial and temporal frequencies; (b) understand the processes controlling this variability (e.g. precipitation, topography, soils, vegetation); and © determine how well this variability is represented in a time series of 1-km (approximately) remotely-sensed soil moisture maps. Specific tasks are to (a) quantify the spatial-temporal variability of surface moisture content (mean, variance, distributional form, spatial pattern) in selected, representative quarter sections by means of supplementary sampling; (b) assess the accuracy of the remotely-sensed soil moisture maps by comparing ESTAR-derived mean moisture contents to those observed in the field; © assess the representativeness of remotely-sensed maps of mean moisture content with respect to the underlying variance within quarter sections; (d) determine how well larger-scale (full section to small watershed scale) observed patterns of soil moisture are preserved by the remotely-sensed maps; and (e) characterize the processes controlling soil moisture variability from the quarter-section to the small watershed scale, with implications for the environmental factors which influence spatial-temporal variations in the accuracy and representativeness of the remotely-sensed soil moisture maps.

A team of seven researchers (listed below) will conduct this investigation and will be on site for the full duration of the experiment. Site selection and the spatial-temporal frequency of intensive sampling are currently under investigation in collaboration with other SGP investigators. A portable sampling methodology, critical to the feasibility of this effort, is also under study at MSFC with promising results to date.

Beyond the implications outlined above, the proposed research will also have significance with respect to: sensor sensitivity and the design of future instruments; the potential utility and success of larger-scale remote sensing (i.e. in the presence of greater heterogeneity); improved understanding of soil moisture variability across spatial-temporal scales and its role in land-atmosphere interactions; and the parameterization of soil moisture and related processes in models of land surface hydrology.

Sponsors: NASA, NSF, University of Texas Geology Foundation

Participants:

Stewart Franks
Marcia Branstetter Tel: 512-471-8547 marcia@maestro.geo.utexas.edu
Johanna Devereaux Tel: 512-471-8547 jdev@mail.utexas.edu
Karen Mohr Tel: 512-471-8547 kmohr@maestro.geo.utexas.edu
Jay Famiglietti Tel: 512-471-3824 jfamiglt@maestro.geo.utexas.edu
Steve Graham Tel: 512-471-5023 steveg@mail.utexas.edu
Matt Rodell Tel: 512-471-5762 mattro@mail.utexas.edu

All at: Department of Geological Sciences, University of Texas at Austin

Austin, TX 78712, Fax: 512-471-9425

INVESTIGATORS: Ronald L. Elliott, Professor and Gabriel B. Senay, Post-Doctoral Fellow

INSTITUTION: Biosystems & Agricultural Engineering Dept. Oklahoma State University

Stillwater, OK

TITLE: In-Situ Soil Moisture Intercomparisons and Scale-Based Validation of an T/Soil Moisture Model

ABSTRACT:

Our investigations will be focused on two topics: (1) intercomparisons of soil moisture measurements; and (2) validation of evapotranspiration/soil moisture modeling at various spatial scales. These investigations will depend on ground and remote sensing data that are collected during the SGP97 experiment, as well as measurements that are made on an ongoing basis in Oklahoma. Analyses related to topic (1) will be conducted in the relatively near term, whereas studies of topic (2) will be longer term in nature.

(1) The senior investigator has been directly involved in the addition of soil moisture sensors to 60 of the 114 Mesonet sites across Oklahoma. These sensors include a single TDR (time domain reflectometry) probe that provides layered data from five soil depths down to 90 cm, and four heat dissipation devices which are installed at depths of 5, 25, 60, and 75 cm. The TDR measurements are made periodically and provide data on volumetric water content, whereas the heat dissipation sensors are logged continuously and provide data on soil water potential. We not only seek to check the consistency between these two sources of data, but also to develop a soil- and sensor-specific calibration of the heat dissipation sensors to volumetric water content. The more intensive TDR sampling that will be done as part of SGP97 will enable us to expand these calibration data sets for the Mesonet sites in the study area. Furthermore, the surface (and perhaps profile) gravimetric sampling that will be done as part of SGP97 will provide a third, independent set of soil moisture data. With soil bulk density information from the sampling sites, the gravimetric data will be converted to volumetric water content and compared to the in-situ measurements. The OSU investigators will help to support the gravimetric sampling in the northern part of the SGP97 study area.

(2) The investigators and their colleagues are developing a GIS-based simulation model for estimating daily latent heat flux (evapotranspiration) and soil moisture at various scales across a heterogeneous landscape. The model is physically based, tracks the soil water balance, and makes use of three data "layers" -- soil, vegetation, and weather. The highest resolution data layers consist of 4-hectare cells, each of which is considered homogeneous. Mesonet sites are well suited for validating the model at "points", but it becomes much more problematic to validate at larger scales. Soil moisture and surface flux measurements from SGP97 will provide a valuable data set for checking the model at various space (and time) scales.

This work will be funded through the combined support of the Oklahoma Agricultural Experiment Station and the Oklahoma NSF and NASA EPSCoR programs.

Investigator(s)/Institutions(s): Shafiqul Islam, University of Cincinnati

Title: Scaling Properties of Soil Moisture Images

Abstract: An outstanding research question critical to the integration of remotely sensed soil moisture into global models is how adequately the inherent spatial heterogeneity is represented at scales commensurate with current generation mesoscale and global climate models. To address this question, a framework is needed that can bridge the scale gap between the scale of remote sensors and large scale model resolution which can take into account the role of spatial heterogeneity. Recent research on spatial rainfall and streamflow has shown that they may exhibit scaling-multi scaling characteristics (Gupta and Waymire 1990). Our analysis of remotely sensed soil moisture images from Washita '92 experiment has shown that soil moisture also exhibits multi scaling properties (Hu et al.,1997). We hypothesize that the soil moisture images can be decomposed into large scale feature parts and small scale fluctuation parts. This decomposition will not make any apriori assumption regarding the structure of the soil moisture fields. Our preliminary results suggest the presence of simple scaling for the small-scale fluctuation parts. The limitations imposed by the data have allowed only three levels of decomposition and it is not clear over what range of scales such simple scaling exists. Using SGP97 data, we will explore and hopefully establish a relationship among the multi scaling properties observed in rainfall, soil moisture, and other land surface variables.

References:

Gupta, V.K. and E. Waymire (1990): "Multiscaling properties of spatial rainfall and river flow distributions", J. Geophys. Res. 95 (D3), 1999-2009.

Hu, Z., S. Islam, and Y. Cheng (1997): "Statistical characterization of remotely sensed soil moisture images", in press, Remote Sensing of Environment.

Investigator(s)/Institution(s): Shafiqul Islam, University of Cincinnati, Elfatih Eltahir, Massachusetts Institute of Technology

Title: Relative Merits of Microwave Measurements of Soil Wetness and Radar Measurements of Rainfall for the Purpose of Estimating Soil Moisture Profile

Abstract: Recent studies in land-atmosphere interactions have shown that large scale soil moisture information as well as estimate of the soil water within the soil column is essential for accurate partitioning of surface fluxes. Current microwave measurements of soil moisture provides an excellent estimate of the soil water content within the top few centimeters. For the first time entire United States will be covered by the NEXRAD systems that would provide very detailed spatial information of rainfall. We plan to explore a fusion approach that combines microwave measurements of soil moisture and radar measurements of rainfall within a coupled land-atmosphere model to infer the soil moisture profile. In this experiment, we would also compare and contrast the relative merits of microwave (for soil moisture) and radar (for rainfall) to infer soil moisture profile within a single- and multi-sensor mode. The planned SGP97 data set would be an ideal test bed to examine the validity of this proposed approach of multi-sensor fusion for soil moisture profile estimation.

Sponsors: University of Cincinnati and Massachusetts Institute of Technology

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Shafiqul Islam

Cincinnati Earth System Science Program

Department of Civil and Environmental Engineering

University of Cincinnati Phone: (513) 556-1026

P.O. Box 210071 Fax: (513) 556-2599

Cincinnati, Ohio 45221-0071 email: sislam@fractals.cee.uc.edu

Investigators/Institutions:

Paul Doraiswamy and Craig Daughtry, USDA/ARS, Remote Sensing and Modeling Laboratory, Beltsville, MD

Tom Jackson and Bill Kustas USDA/ARS, Hydrology Laboratory, Beltsville, MD

Jerry Hatfield, USDA/ARS, Soil Tilth Laboratory, Ames, IA

Title of Investigation:

Study the techniques for retrieval of biophysical parameters from remote sensing and evaluate models for Leaf Area Index, Biomass and Energy balance of different canopies in the SGP experiment site.

Abstract

The seasonal vegetation dynamics will be monitored, using Landsat TM and NOAA AVHRR imagery acquired between May through July 1997. Ground measurements of LAW and green biomass will be monitored during the June-July period by Craig Daughtry. Several canopy models estimating surface reflectance (Verhoef, W., 1984), LAI (Clevers, J.G.P.W. et al., 1989 & Rahman H. et al., 1993) and biomass (Moran, M.S. et al., 1995) will be tested for their applicability in three major types of vegetative cover in the SGP study area. Biophysical parameters retrieved from remote sensing using several models will be evaluated. The extrapolation of parameters from field to region scales using models will be investigated for monitoring the vegetation dynamics throughout the summer period. Landsat TM and AVHRR data will be processed to provide good registration accuracy for correlation with ground samples collected through the study period.

Soil moisture and surface energy balance modeling to extrapolate measurements from aircraft and flux stations to the surrounding areas will be investigated in collaboration with T. Jackson and W. Kustas. Geospatial statistical analysis of soil, vegetation, and atmospheric parameters measured on the ground will be used in developing models to study techniques for extrapolating parameters from small to large areas.

References

Clevers, J. G. P. W., (1989), "The application of a weighted infrared-red vegetation index for estimating leaf area index by correcting for soil moisture", Rem. Sens. Environ., 29:25-37.

Moran, M.S., Maas, S.J., and Pinter, P.J., Jr. (1995). Combining Remote sensing and modeling for estimating surface evaporation and biomass production. Remote Sensing Reviews. 12:335-353.

Verhoef, W., (1984), "Light scattering by leaf layers with application to canopy reflectance modeling: the SAIL model", Rem. Sens. Environ., 16:125-141.

Utilizing Data from the Southern Great Plains Experiment with RADARSAT Data

Eric F. Wood, Princeton University, Princeton, NJ 08544

T. J. Jackson, USDA ARS Hydrology Lab

The goal of our participation in the Southern Great Plains Experiment is to develop improved remote sensing techniques for areal estimation of soil moisture, and to demonstrate that RADARSAT, either alone or in conjunction with other satellite and hydrologic observations, can provide soil moisture fields at regional scales. To date, the application of microwave radar remote sensing to soil moisture estimation has been hampered by several difficulties, including its sensitivity to vegetation and surface roughness, and understanding the relationship between observations from remote sensing instruments and point measurement values.

The planned research activities are the following:

1. Field data collection. In discussion with Tom Jackson, we plan to participate and focus our collection at the USDA El Reno site. We are assuming that this site will have a surface flux station so point water and energy balance modeling can be carried out, post experiment. We are also planning on utilizing field scale data collected in the Little Washita and point measurements from the CART-ARM sites. These data will help us extend the research to scales more consistent with regional estimation.

2. Soil moisture retrievals. Test and develop calibration strategies for soil moisture retrieval algorithms for the RADARSAT satellite data using the above field data., and estimate spatial maps of soil moisture. This work will build on research developed under our SIR-C funding.

3. Analyses. Intercompare remotely sensed soil moisture maps derived from RADARSAT with those developed from airborne ESTAR passive microwave sensors,

and with field data collected at El Reno, Little Washita and CART-Arm sites

4. Scaling. Study the scaling behavior of both airborne and satellite radar and derived soil moisture fields so as to develop strategies for regional soil estimation with lower resolution data than that collected in the SGP Experiment.

The anticipated results of the research include an improved understanding of and estimation abilities for soil moisture at catchment to regional scales, and to understand the relationship between remotely sensed soil moisture and ground observations.

Eric F. Wood

Department of Civil Engineering

Princeton University

Princeton, NJ 08544

Tel: 609-258-4675

Fax: 609-258-2799

(efwood@ceor.princeton.edu)

Investigator/Institution: Peter J. Wetzel/NASA GSFC

Title of investigation: Validation of PLACE land surface model using SGP97 observations

Abstract: The SGP97 experiment provides a unique opportunity to validate land surface models on scales ranging from point to regional. As part of the ongoing validation of the PLACE (Wetzel and Boone, 1995) model, data from SGP97 will be applied to provide initial conditions for the model and to validate the model's predictions of soil moisture (Wetzel et al 1996; Boone and Wetzel 1996) and of evaporative fluxes. Eventually it is hoped that a data set can be developed which will be used for validation of other land surface models participating in the Project for Intercomparison of Land surface Parameterization Schemes (PILPS).

References:

Wetzel, P. J., and A. Boone, 1995: A parameterization for land-atmosphere-cloud exchange (PLACE): Documentation and testing of a detailed process model of the partly cloudy boundary layer over heterogeneous land, J. Climate, 8, 1810-1837.

Wetzel, P. J., X. Liang, P. Irannejad, A. Boone, J. Noilhan, Y., Shao, C. Skelly, Y. Xue and Z.-L. Yang, 1996: Modeling vadose zone liquid water fluxes: Infiltration, runoff,

drainage, interflow, Global and Planetary Change, 13, 57-71.

Boone, A., and P. J. Wetzel, 1996: Issues related to low resolution modeling of soil moisture: Experience with the PLACEmodel, Global and Planetary Change, 13, 161-181.

Investigator(s)/Institution(s): Christopher J. Duffy

Civil and Environmental Engineering Dept., 212 Sackett Bldg Penn State University University Park, PA 16802

(814) 863-4384 (814) 863-7304 fax cjd@ecl.psu.edu

Title of investigation: Hydrogeologic Reconnaissance SG97

Abstract:

This investigation will involve field, library and agency (state, federal) research in order to compile available hydrogeologic data for the SG97 study sites. The compiled data will include geologic maps (digital and paper), groundwater level maps, and hopefully a reasonable number of historical well records. Field work will involve 1 week of site reconnaissance during June 97 (to be determined) including photographing all stream gaging stations, soil moisture sites, important landforms, geologic outcrops or other features of hydrologic interest. The hydrogeologic data base along with the site photos will be put on a CD-Rom and made available to all investigators. Christopher Duffy will initially work with Doug Miller who has the soils data compiled. The overall objective is to get at least a baseline of information on groundwater response during the experiment and to get some notion of the historical spatial and temporal variability in groundwater levels.

References: A Two-State integral-balance model for soil moisture and groundwater dynamics in complex terrain, WRR, 32(8), 2421-2434, 1996.

Ground-Based Visible and Near Infrared Radiometry

Karen Humes

University of Oklahoma

Collaborating with: Bill Kustas and John Preuger (Flux measurements)

Craig Daughtry (vegetation sampling and ground radiometry)

Ground-based remote sensing measurements will be acquired in conjunction with flux measurements at the El Reno site and vegetation sampling at various sites. These measurements will be used to help develop and validate algorithms for several purposes: a) the estimation of surface fluxes with remotely sensed data; b) atmospheric corrections to satellite and aircraft data; c) the estimation of land cover and biomass from remotely sensed measurements. The radiometers to be used will include the 4-band Exotech radiometers (with bandpasses matching the TM and SPOT sensors) and occasional measurements with the ASD hyperspectral radiometer.

Relating 19, 37, and 85 GHz field brightness measurements to SSM/I data during the SGP'97 Hydrology Experiment

A.W. England, Jasmeet Judge, Brian Hornbuckle, Ed Kim and David Boprie

The University of Michigan, Ann Arbor

ABSTRACT

We propose to monitor 19, 37, and 85 GHz sky- and ground-brightness and thermal infrared ground-brightness at the ARM SGP'97 site and to relate these observations to contemporaneous SSM/I data. The dominant landcover will be senescent winter wheat or, after the wheat is harvested, wheat stubble. The relatively low canopy column density in either case will allow some sensitivity to surface soil moisture at 19 GHz. Our radiometer system will be on a 10 m tower and will view the winter wheat/stubble at the SSM/I incidence angle of 53o. Data will be collected at half hour intervals for the duration of the experiment. Diurnal vegetation and soil samples will be collected periodically throughout the experiment. SSM/I data will be obtained from NSIDC and will be resampled to the Equal Area SSM/I Earth - grid (EASE - grid) for comparison with the field measurements.

We will use our Land Surface Process/Radiobrightness (LSP/R) model to relate brightness at L-, C-, and S-band frequencies, and at the SSM/I frequencies to surface soil moisture and to local stored water. The LSP/R model has been validated in a series of Radiobrightness Energy Balance Experiments (REBEX) for prairie grassland in fall and winter (REBEX-1) and prairie grassland and bare soil in summer (REBEX-4). Our SGP'97 data will be combined with available meteorological and radiant flux data to validate the LSP/R model for winter wheat/stubble. Once validated, the model will be forced by observed weather and downwelling short- and long-wavelength radiance to predict 19, 37, and 85 GHz brightness for each of the dominate terrains within the SGP'97 region. These brightness will be aggregated for each local pixel of EASE-grid according to landcover fractions to yield a pixel brightness that can be compared with the resampled SSM/I data. We are particularly interested in a running comparison during a significant dry down period.

-Investigators/Institutions: J. Ian MacPherson, PI, NRC Canada, Jocelyn Mailhot, co-I, AES/MRB, J. Walter Strapp, co-I, AES/MRB, Stephane Belair, co-I, AES/MRB NRC = National Research Council of Canada MRB = Meteorological Research Branch, AES = Atmospheric Environment Service

Title: Mesoscale modelling of the convective boundary layer during SGP97

Abstract:

The study addresses one of the main objectives of SGP97 "to examine the effect of soil moisture on the evolution of the atmospheric boundary layer and clouds over the southern great plains during the warm season". The investigation will focus on comparisons of detailed observations during SGP97 with mesoscale simulations using the MC2 (Mesoscale Compressible Community) model (Benoit et al. 1997) coupled with advanced land surface schemes, such as ISBA and CLASS (Noilhan and Planton 1989, Verseghy 1991), two models participating in PILPS. The high-resolution (order of a few km) models will be complemented with detailed spatial analyses of soil moisture measured with the ESTAR and SLFMR radiometers. The simulations will be compared with various measurements such as LASE, the Twin Otter aircraft turbulent flux observations, surface and tower measurements, and satellite remote sensing data. This will provide a unique opportunity to investigate various aspects of the structure an devolution of the convective boundary layer (CBL) during SGP97, on a variety of regional and local scales.

The study also has some connection with another field study, MERMOZ, having objectives similar to SGP97. MERMOZ took place in Canada during June 1996 and will continue in August 1997, to examine several aspects of the CBL, in particular the influence of soil moisture on CBL evolution and entrainment processes near the CBL top (Mailhot et al. 1997a,b).

References:

Benoit, R., M. Desgagne, P. Pellerin, S. Pellerin, Y. Chartier, and S. Desjardins, 1997: The Canadian MC2: A semi-Lagrangian, semi-implicit wide-band atmospheric model suited for fine-scale process studies and simulation. Mon. Wea. Rev., (in press)

Mailhot, J., and the MERMOZ Scientific Team, 1997a: MERMOZ Project Report. Recherche en prevision numerique, Atmospheric Environment Service, Dorval, Canada, 156 pp.

Mailhot, J., R. Benoit, S. Belair, J.W. Strapp, J.I. MacPherson, N.R. Donaldson, J. Goldstein, F. Froude, M. Benjamin, I. Zawadski and R.R. Rogers, 1997b: The Montreal-96 Experiment on Regional Mixing and Ozone (MERMOZ): An overview and some preliminary results. Bull. Amer. Met. Soc. (submitted).

Noilhan, J., and S. Planton, 1989: A simple parameterization of land surface processes for meteorological model. Mon. Wea. Rev., 117, 536-549.

Verseghy, D.L., 1991: CLASS - A Canadian land surface scheme for GCMs. Soil model. Int. J. Climatol., 11, 111-133.

Jocelyn Mailhot, Recherche en Prevision Numerique, Environnement Canada, 2121 Trans-Canada N., Suite 500, Dorval, Quebec, CANADA H9P-1J3.

Phone:(514) 421-4760 Fax:(514) 421-2106

e-mail (Internet): Jocelyn.Mailhot@ec.gc.ca

Stephane Belair Recherche en Prevision Numerique Environnement Canada, 2121 Trans-Canada N., Suite 500, Dorval, Quebec, CANADA H9P-1J3.

Ian MacPherson, Flight Research Laboratory, NRC, Ottawa, ON, K1A 0R6

Walter Strapp, Cloud Physics Research Division, AES, Downsview, ON, M3H5T4