5 Remote Sensing in Hydrological Modeling
87
5.2 Remote Sensing in Operational Hydrologic Modeling
Runoff. Runoff cannot be directly measured by remote sensing techniques. However, there are two general areas where remote sensing can be used in hydrologic
and runoff modeling: (1) determining watershed geometry, drainage network, and
other map-type information for distributed hydrologic models and for empirical
flood peak, annual runoff or low flow equations; and (2) providing input data such
as snow cover, soil moisture or delineated land use classes that are used to defme
runoff coefficients.
Watershed Geometry. Remote sensing data can be used to obtain almost any
information that is typically obtained from maps or aerial photography. In many
regions of the world, remotely-sensed data, and particularly Landsat TM or SPOT
data, are the only source of good cartographic information. Drainage basin areas
and stream networks are easily obtained from good imagery, even in remote regions. There have also been a number of studies to extract quantitative geomorphic
information from Landsat imagery (Haralick, et al., 1985).
Topography is a basic need for any hydrologic analysis and modeling. Remote
sensing can provide quantitative topographic information of suitable spatial resolution to be extremely valuable for model inputs. For example, stereo SPOT imagery can be used to develop a DEM with 10 m horizontal resolution and vertical
resolution approaching 5m in ideal cases (Case, 1989). A new technology using
interferometric Synthetic Aperture Radar (SAR) has been used to demonstrate
similar horizontal resolutions with approximately 2m vertical resolution (Zebker et
al., 1992).
Empirical relationships. Empirical flood formulae are useful for making estimates of peak flow when there is a lack of historical streamflow data. Generally
these equations are restricted in application to the size range of the basin and the
climaticlhydrologic region of the world in which they were developed.
Most of the empirical flood formulae relate peak discharge to the drainage area
of the basin; see for example United Nations Flood Control Series No.7 (United
Nations, 1955). Landsat data are used to improve empirical regression equations of
various runoff characteristics. For example, Allord and Scarpace (1979) have
shown how the addition of Landsat-derived land cover data can improve regression equations based on topographic maps alone.
Runoff Models. One of the fIrst applications of remote sensing data in hydrologic
models used Landsat data to determine both urban and rural land use for estimating runoff coefficients (Jackson et al., 1976). Land use is an important characteristic of the runoff process that affects infIltration, erosion, and evapotranspiration.
Distributed models, in particular, need specifIc data on land use and its location
within the basin. Most of the work on adapting remote sensing to hydrologic modeling has involved the Soil Conservation Service (SCS) runoff curve number
model (U.S. Department of Agriculture, 1972) for which remote sensing data are
used as a substitute for land cover maps obtained by conventional means (Jackson
et al., 1977, Bondelid et al., 1982).
87
5.2 Remote Sensing in Operational Hydrologic Modeling
Runoff. Runoff cannot be directly measured by remote sensing techniques. However, there are two general areas where remote sensing can be used in hydrologic
and runoff modeling: (1) determining watershed geometry, drainage network, and
other map-type information for distributed hydrologic models and for empirical
flood peak, annual runoff or low flow equations; and (2) providing input data such
as snow cover, soil moisture or delineated land use classes that are used to defme
runoff coefficients.
Watershed Geometry. Remote sensing data can be used to obtain almost any
information that is typically obtained from maps or aerial photography. In many
regions of the world, remotely-sensed data, and particularly Landsat TM or SPOT
data, are the only source of good cartographic information. Drainage basin areas
and stream networks are easily obtained from good imagery, even in remote regions. There have also been a number of studies to extract quantitative geomorphic
information from Landsat imagery (Haralick, et al., 1985).
Topography is a basic need for any hydrologic analysis and modeling. Remote
sensing can provide quantitative topographic information of suitable spatial resolution to be extremely valuable for model inputs. For example, stereo SPOT imagery can be used to develop a DEM with 10 m horizontal resolution and vertical
resolution approaching 5m in ideal cases (Case, 1989). A new technology using
interferometric Synthetic Aperture Radar (SAR) has been used to demonstrate
similar horizontal resolutions with approximately 2m vertical resolution (Zebker et
al., 1992).
Empirical relationships. Empirical flood formulae are useful for making estimates of peak flow when there is a lack of historical streamflow data. Generally
these equations are restricted in application to the size range of the basin and the
climaticlhydrologic region of the world in which they were developed.
Most of the empirical flood formulae relate peak discharge to the drainage area
of the basin; see for example United Nations Flood Control Series No.7 (United
Nations, 1955). Landsat data are used to improve empirical regression equations of
various runoff characteristics. For example, Allord and Scarpace (1979) have
shown how the addition of Landsat-derived land cover data can improve regression equations based on topographic maps alone.
Runoff Models. One of the fIrst applications of remote sensing data in hydrologic
models used Landsat data to determine both urban and rural land use for estimating runoff coefficients (Jackson et al., 1976). Land use is an important characteristic of the runoff process that affects infIltration, erosion, and evapotranspiration.
Distributed models, in particular, need specifIc data on land use and its location
within the basin. Most of the work on adapting remote sensing to hydrologic modeling has involved the Soil Conservation Service (SCS) runoff curve number
model (U.S. Department of Agriculture, 1972) for which remote sensing data are
used as a substitute for land cover maps obtained by conventional means (Jackson
et al., 1977, Bondelid et al., 1982).