THE USE OF IMAGING RADARS FOR ECOLOGICAL APPLICATIONS - A REVIEW

At the behest of NASA's Mission to Planet Earth, the National Research Council recently conducted a review on the current status and future directions for earth science information provided by spaceborne synthe tic aperture radars. As part of this process, a panel of 16 scientists met to review the utility of SAR for monitoring ecosystem processes. The consensus of this ecology panel was that the demonstrated capabili ties of imaging radars for investigating terrestrial ecosystems could best be organized into four broad categories: 1) classification and de tection of change in land cover; 2) estimation of woody plant biomass 3) monitoring the extent and timing of inundation; and 4) monitoring o ther temporally-dynamic processes. The major conclusions from this pan el were: 1) Multichannel radar data provide a means to classify land-c over patterns because of its sensitivity to variations in vegetation s tructure and vegetation and ground-layer moisture. The relative utilit y of data from imaging radars versus multispectral scanner data has ye t to be determined in a rigorous fashion over a wide range of biomes f or this application. 2) Imaging radars having the capability to monito r variations in biomass in forested ecosystems. This capability is not consistent among different forest types. The upper levels of sensitiv ity for L-band and C-band systems such as SIR-C range between <100 t h a(-1) for complex tropical forest canopies to similar to 250 t ha(-1) for simpler forests dominated by a single tree species. Best performan ce for biomass estimation is achieved using lower frequency (P- and L- band) radar systems with a cross-polarized (HV or VH) channel. 3) Like -polarized imaging radars (HH or VV) are well suited for detection of flooding under vegetation canopies. Lower frequency radars (P- and L-b and) are most optimal for detecting flooding under forests, whereas hi gher frequency radars (C-band) work best for wetlands dominated by her baceous vegetation. 4) It has been shown that spaceborne radars that h ave been in continuous operation for several years [such as the C-band (VV) ERS-1 SAR] provide information on temporally dynamic processes, such as monitoring a) variations in flooding in nonwooded wetlands, b) changes in the frozen/thawed status of vegetation, and c) relative va riations in soil moisture in areas with low amounts of vegetation cove r. These observations have been shown to be particularly important in studying ecosystems in high northern latitudes. (C) Elsevier Science I nc., 1997.