Télédétection et ressources en eau/Remote sensing and water resources
327
CONCLUSION
It can be argued that the simplicity of this approach combined with the availability of remotely
data, makes this approach very attractive for operational monitoring of surface fluxes in arid and
semi-arid areas. The major problem with this approach is that the relationship between remotely
sensed variables and those needed for process formulation are empirical. In this regard, such
relationships are site specific. This represents a major handicap for generalizing such approach.
Furthermore, if one always needs to redo calibration for each individual site, one can legitimately
challenge the effectiveness of this approach. One alternative approach of using remotely sensed
data for quantitative purposes could be to combine SVAT type model with radiative transfer
model. The principle of this method is to use the SVAT output such as surface temperature and
soil moisture as input to radiative transfer models. The radiative transfer models will simulate in
a given waveband the spectral signature of the surface as it can be observed by a remote sensor.
By minimizing the differences between measured and simulated remote sensing variable, on can
assume that the resulting surface fluxes are correct. This approach is certainly more robust, but it
needs accurate SVAT and radiative transfer models, which are not readily available at this time.
ACKNOWLEDGEMENTS
Thanks to Dr. D. Stannard and Dr. D. Nichols for providing us with the data. Thanks to T. Valero for
his comments. Funding for this study was provided by French PNTS and ORSTOM. The Data used here
were taken during the Monsoon '90 Experiment: NASA Interdisciplinary Research Program in the Earth
Sciences (IDP 88-086). The first author was supported during the experiment by the NASA Earth
Observing Program (NAGW2425). The authors are particularly grateful to USDA-ARS personnel in
Tombstone for their support during the experiment.
BIBLIOGRAPHY
Asrar, G., Fuchs, M., Kanemasu, E.T. and Hatfield, J.L. 1984. Estimating absorbed photosynthetic
radiation and leaf area index from spectral reflectance in wheat. Agro. J. 76, 300-306.
Brutseart, W. 1975. On a derivable formula for long-wave radiation from clear skies. Water Resour.
Res. 11, 742-744.
Chehbouni, A., Kerr, Y.H., Qi, J., Huete, A.R. and Sorooshian, S. 1994. Toward the Development
of a Multidirectional Vegetaion Index. Water Resour. Res., 30, 1339-1349.
Chehbouni, A., Lo Seen, D. , Njoku, E.G. and Monteny, B. 1996a. A Coupled Hydrological and
Ecological modeling Approach to examine the Relationship between Radiative and Aerodynamic
Surface Temperature over Sparsely Vegetated Surfaces. Remote Sensing Environment. In press.
Chehbouni, A., Lo Seen, D., Njoku, E.G., Lhomme, J.P., Monteny, B. and Kerr, Y.H. 1996b.
Estimation of sensible heat flux over sparsely vegetated. J of Hydrology, Hapex Sahel special issue,
in press.
Chehbouni, A., Nichols, D., Njoku, E.G., Qi, J. and Kerr, Y.H. 1996c. On the use of radiative surface
temperature to estimate sensible heat flux in Nevada. Remote Sensing Review, In press.
Goutorbe, J.P., Lebel T, Tinga, A. et al.. 1993. HAPEX-Sahel: A large scale study of land-atmosphere
interactions in the semi-arid tropics. Ann. Geophysicae, 12, 53-64.
Kalma, J.D. and Jupp, D.L.B. 1990. Estimating evaporation from pasture using infrared thermometry:
evaluation of a one-layer resistance model. Agric. For. Meteorol. 51, 223-246.
Kustas, W. P. and Goodrich, D.C. 1994. Water Resour. Res. 30, 1211-1226.
327
CONCLUSION
It can be argued that the simplicity of this approach combined with the availability of remotely
data, makes this approach very attractive for operational monitoring of surface fluxes in arid and
semi-arid areas. The major problem with this approach is that the relationship between remotely
sensed variables and those needed for process formulation are empirical. In this regard, such
relationships are site specific. This represents a major handicap for generalizing such approach.
Furthermore, if one always needs to redo calibration for each individual site, one can legitimately
challenge the effectiveness of this approach. One alternative approach of using remotely sensed
data for quantitative purposes could be to combine SVAT type model with radiative transfer
model. The principle of this method is to use the SVAT output such as surface temperature and
soil moisture as input to radiative transfer models. The radiative transfer models will simulate in
a given waveband the spectral signature of the surface as it can be observed by a remote sensor.
By minimizing the differences between measured and simulated remote sensing variable, on can
assume that the resulting surface fluxes are correct. This approach is certainly more robust, but it
needs accurate SVAT and radiative transfer models, which are not readily available at this time.
ACKNOWLEDGEMENTS
Thanks to Dr. D. Stannard and Dr. D. Nichols for providing us with the data. Thanks to T. Valero for
his comments. Funding for this study was provided by French PNTS and ORSTOM. The Data used here
were taken during the Monsoon '90 Experiment: NASA Interdisciplinary Research Program in the Earth
Sciences (IDP 88-086). The first author was supported during the experiment by the NASA Earth
Observing Program (NAGW2425). The authors are particularly grateful to USDA-ARS personnel in
Tombstone for their support during the experiment.
BIBLIOGRAPHY
Asrar, G., Fuchs, M., Kanemasu, E.T. and Hatfield, J.L. 1984. Estimating absorbed photosynthetic
radiation and leaf area index from spectral reflectance in wheat. Agro. J. 76, 300-306.
Brutseart, W. 1975. On a derivable formula for long-wave radiation from clear skies. Water Resour.
Res. 11, 742-744.
Chehbouni, A., Kerr, Y.H., Qi, J., Huete, A.R. and Sorooshian, S. 1994. Toward the Development
of a Multidirectional Vegetaion Index. Water Resour. Res., 30, 1339-1349.
Chehbouni, A., Lo Seen, D. , Njoku, E.G. and Monteny, B. 1996a. A Coupled Hydrological and
Ecological modeling Approach to examine the Relationship between Radiative and Aerodynamic
Surface Temperature over Sparsely Vegetated Surfaces. Remote Sensing Environment. In press.
Chehbouni, A., Lo Seen, D., Njoku, E.G., Lhomme, J.P., Monteny, B. and Kerr, Y.H. 1996b.
Estimation of sensible heat flux over sparsely vegetated. J of Hydrology, Hapex Sahel special issue,
in press.
Chehbouni, A., Nichols, D., Njoku, E.G., Qi, J. and Kerr, Y.H. 1996c. On the use of radiative surface
temperature to estimate sensible heat flux in Nevada. Remote Sensing Review, In press.
Goutorbe, J.P., Lebel T, Tinga, A. et al.. 1993. HAPEX-Sahel: A large scale study of land-atmosphere
interactions in the semi-arid tropics. Ann. Geophysicae, 12, 53-64.
Kalma, J.D. and Jupp, D.L.B. 1990. Estimating evaporation from pasture using infrared thermometry:
evaluation of a one-layer resistance model. Agric. For. Meteorol. 51, 223-246.
Kustas, W. P. and Goodrich, D.C. 1994. Water Resour. Res. 30, 1211-1226.