RADAR REMOTE-SENSING OF FOREST AND WETLAND ECOSYSTEMS IN THE CENTRAL-AMERICAN TROPICS

We analyzed airborne synthetic aperture radar (AIRSAR) imagery of fore st, wetland, and agricultural ecosystems in northern Belize, Central A merica. Our analyses are based upon four biophysical indices derived f rom the fully polarimetric SAR data: the volume scattering index (VSI) , canopy structure index (CSI), biomass index (BMI), calculated from t he backscatter magnitude data, and the interaction type index (ITI), c alculated from the backscatter phase data. We developed a four-level l andscape hierarchy based upon clustering analyses of the 12 index para meters (four indices each for P, L, and C band) from two test site ima ges. Statistical analyses were used to examine the relative importance of the 12 parameters for discriminating ecosystem characteristics at various landscape scales. We found that ITI was the most important ind ex (primarily C band = CITI) for level, vegetated terrain at all level s of the hierarchy. BMI was most important for differentiating between vegetated and nonvegetated areas and between sloping and level terrai n. These findings indicate that upper canopy spatial characteristics a nd flooding in marshlands (reflected in the CITI) are more important t han biomass in differentiating many tropical ecosystems with radar dat a. The relative importance of the indices varied with vegetation type; for example, PVSI was the most important for distinguishing between u pland forests and regrowth, and PCSI was the most important for differ entiating swamp forest types. Finally, we evaluated the potential of p resent and future spaceborne SARs for tropical ecosystem studies based on our results. Most of these SARs are single channel systems and wil l provide limited capability for characterizing biomass and structure of tropical vegetation. This is especially true for C band systems, wh ich produce data similar to our CBMI parameter, which was one of the l east important in our analyses. The SIR-C/X-SAR and proposed EOS SAR a re future spaceborne multifrequency fully polarimetric SAR systems, an d they will provide a significant contribution to tropical ecosystem s tudies.