86
R.O. Dubayah, E.F. Wood, E.T. Engman et al.
ing practitioners. In the fITst portion of this chapter, the traditional application of
remote sensing in operational hydrology will be briefly reviewed. More comprehensive treatments of this area can be found in texts such as Engman and Gurney
(1991). More recently, sensitivity studies with Atmospheric General Circulation
Models (AGCMs) have shown that land surface processes affect climate at regional to global scales. These studies include the effects of albedo, soil moisture
anomalies, surface roughness (which affects evaporation), and land cover change.
Further understanding the role of the terrestrial hydrosphere-biosphere in Earth's
climate system, and understanding the nature and effects of possible changes to the
terrestrial water balance as a result of changing climate and land surface characteristics, is of central importance to the World Climate Research Program (WCRP)
of the World Meteorological Organization. It is expected that these questions will
be answered using process-based, terrestrial water and energy balance models.
But, it is recognized that questions regarding terrestrial hydrology within the climate system cannot be answered through ground-based observations alone, due to
the scarcity of land surface observations and difficulties in representing hydrological processes at large scales.
Remote sensing potentially may provide the required inputs for hydrological
modeling at regional to global scales. As a result, remote sensing initiatives have
included field experiments (e.g. the First International Satellite Land Surface Climatology Field Experiment, FIFE) that have linked ground measurements with
remote sensing algorithm development. In addition, there are now consistent, longterm remote sensing data archives from satellites such as A VHRR (Agbu, 1993),
GOES (Young, 1995) and SSMII (Hollinger et aI., 1992).
By the late 1990's new and enhanced meteorological satellites and higher spectral resolution land surface sensors being launched under NASA's Earth Observing
System mission, combined with faster computer networking and data handling
capabilities, will give operational hydrologists access to new types of land surface
and hydrologic data. In the second part of this chapter, we discuss the potential for
utilizing these data for hydrological modeling.
To fully understand both the historical and potential use of remote sensing for
hydrological modeling, it is important to recognize that Eq. (5.1) is not directly
useable as a hydrologic model. Each of the terms is often parameterized in terms
of the catchment characteristics or conditions. For example, a change in soil
moisture is the result of either evaporation or infiltration depending upon whether a
dry or rain period is being considered. These processes (models) require information on land surface/cover, soil texture, initial soil moisture, and perhaps topography. Historically then, operational hydrology has used conceptual models for
which there is the possibility that remote sensing can provide some of the model
parameters. For modeling land-atmospheric hydrologic interactions, there is the
desire that remote sensing provide both model parameters (even those which may
change with time) and meteorological data, like surface air temperature, humidity,
precipitation and radiation, which would permit model simulations based solely on
remote sensing data.
R.O. Dubayah, E.F. Wood, E.T. Engman et al.
ing practitioners. In the fITst portion of this chapter, the traditional application of
remote sensing in operational hydrology will be briefly reviewed. More comprehensive treatments of this area can be found in texts such as Engman and Gurney
(1991). More recently, sensitivity studies with Atmospheric General Circulation
Models (AGCMs) have shown that land surface processes affect climate at regional to global scales. These studies include the effects of albedo, soil moisture
anomalies, surface roughness (which affects evaporation), and land cover change.
Further understanding the role of the terrestrial hydrosphere-biosphere in Earth's
climate system, and understanding the nature and effects of possible changes to the
terrestrial water balance as a result of changing climate and land surface characteristics, is of central importance to the World Climate Research Program (WCRP)
of the World Meteorological Organization. It is expected that these questions will
be answered using process-based, terrestrial water and energy balance models.
But, it is recognized that questions regarding terrestrial hydrology within the climate system cannot be answered through ground-based observations alone, due to
the scarcity of land surface observations and difficulties in representing hydrological processes at large scales.
Remote sensing potentially may provide the required inputs for hydrological
modeling at regional to global scales. As a result, remote sensing initiatives have
included field experiments (e.g. the First International Satellite Land Surface Climatology Field Experiment, FIFE) that have linked ground measurements with
remote sensing algorithm development. In addition, there are now consistent, longterm remote sensing data archives from satellites such as A VHRR (Agbu, 1993),
GOES (Young, 1995) and SSMII (Hollinger et aI., 1992).
By the late 1990's new and enhanced meteorological satellites and higher spectral resolution land surface sensors being launched under NASA's Earth Observing
System mission, combined with faster computer networking and data handling
capabilities, will give operational hydrologists access to new types of land surface
and hydrologic data. In the second part of this chapter, we discuss the potential for
utilizing these data for hydrological modeling.
To fully understand both the historical and potential use of remote sensing for
hydrological modeling, it is important to recognize that Eq. (5.1) is not directly
useable as a hydrologic model. Each of the terms is often parameterized in terms
of the catchment characteristics or conditions. For example, a change in soil
moisture is the result of either evaporation or infiltration depending upon whether a
dry or rain period is being considered. These processes (models) require information on land surface/cover, soil texture, initial soil moisture, and perhaps topography. Historically then, operational hydrology has used conceptual models for
which there is the possibility that remote sensing can provide some of the model
parameters. For modeling land-atmospheric hydrologic interactions, there is the
desire that remote sensing provide both model parameters (even those which may
change with time) and meteorological data, like surface air temperature, humidity,
precipitation and radiation, which would permit model simulations based solely on
remote sensing data.