4 Integration of Remotely Sensed Data into Geographical Infonnation Systems
73
Multi-spectral satellite image data are processed to generate thematic maps (see
Chap. 3). SPOT stereoscopic data are suitable for digital topographic, thematic
map production at scales of 1:50,000 and better (Gugan and Dowman, 1988;
Swann et aI. 1988). Data derived from various sensors can be integrated to derive
improved map products with higher detail of cartographic information (about 1520%) than from an individual image (Welch and Ehlers, 1988).
Two or more data layers can be employed in an overlay operation to merge spatial information. Figure 4.6 illustrates the overlay concept for both raster and vector data layers. Schultz (1993) applied this overlay technique to derive maximum
soil water storage information by merging plant root depth data (derived from
land-use classification of Landsat image) and soil porosity data (derived from
digitized soil maps) for the Ennepe reservoir basin (see also Color Plate 5.A).
During the overlay operation arithmetic and! or Boolean operations can be performed on input layers (Mattikalli, 1995). Overlay operation is invariably utilized
in most of the GIS applications including the examples presented below.
4.3.2
Integrated Use of Elevation Data
Digital Elevation Model (DEM) data are useful to derive a variety of information
including slope, aspect, curvature etc. Fett et aI. (1990) utilized 50 m x 50 m DEM
data resampled to correspond to 30 m resolution of Landsat and generated land
slope (relevant to flow velocity) and exposure to the Sun (relevant to evapotranspiration) in the Volme River basin, Germany. Slope angle (~) and upslope drainage area (a) derived from DEM are employed to calculate soil moisture deficit
using the TOPMODEL topographic index, In(a / T tan ~), where T is the local
saturated transmissivity (Romanowicz et aI., 1993).
Weights
2
3
Composite Layer
Vector Layers
Fig. 4.6. Illustration of an overlay operation on data layers in a GIS. Mathematical operations can
be perfonned on input thematic layers to derive new infonnation as well as to conduct complex
spatial analysis
73
Multi-spectral satellite image data are processed to generate thematic maps (see
Chap. 3). SPOT stereoscopic data are suitable for digital topographic, thematic
map production at scales of 1:50,000 and better (Gugan and Dowman, 1988;
Swann et aI. 1988). Data derived from various sensors can be integrated to derive
improved map products with higher detail of cartographic information (about 1520%) than from an individual image (Welch and Ehlers, 1988).
Two or more data layers can be employed in an overlay operation to merge spatial information. Figure 4.6 illustrates the overlay concept for both raster and vector data layers. Schultz (1993) applied this overlay technique to derive maximum
soil water storage information by merging plant root depth data (derived from
land-use classification of Landsat image) and soil porosity data (derived from
digitized soil maps) for the Ennepe reservoir basin (see also Color Plate 5.A).
During the overlay operation arithmetic and! or Boolean operations can be performed on input layers (Mattikalli, 1995). Overlay operation is invariably utilized
in most of the GIS applications including the examples presented below.
4.3.2
Integrated Use of Elevation Data
Digital Elevation Model (DEM) data are useful to derive a variety of information
including slope, aspect, curvature etc. Fett et aI. (1990) utilized 50 m x 50 m DEM
data resampled to correspond to 30 m resolution of Landsat and generated land
slope (relevant to flow velocity) and exposure to the Sun (relevant to evapotranspiration) in the Volme River basin, Germany. Slope angle (~) and upslope drainage area (a) derived from DEM are employed to calculate soil moisture deficit
using the TOPMODEL topographic index, In(a / T tan ~), where T is the local
saturated transmissivity (Romanowicz et aI., 1993).
Weights
2
3
Composite Layer
Vector Layers
Fig. 4.6. Illustration of an overlay operation on data layers in a GIS. Mathematical operations can
be perfonned on input thematic layers to derive new infonnation as well as to conduct complex
spatial analysis