AN EVALUATION OF AIRSAR AND SIR-C X-SAR IMAGES FOR MAPPING NORTHERN FOREST ATTRIBUTES IN MAINE, USA/

In previous work by the authors, multifrequency, polarimetric airborne synthetic aperture radar (AIRSAR) data were used to characterize fore st categories and biomass density of a forest area in Maine, USA. This study area was included as a test site for ecological studies during the Spaceborne Imaging Radar C/X-band Synthetic Aperture Radar (SIR-C/ X-SAR) missions in 1994. The SIR-C/X-SAR missions provided the first o pportunity for Earth scientists to receive multifrequency and multipol arization SAR data from space from a single platform. During the Space Radar Laboratory missions in April and October 1994, images from AIRS AR and SIR-C/X-SAR were acquired for the same areas within a few days of each other. In this paper, the capabilities of AIRSAR and SIR-C/X-S AR images for characterizing a northern hardwood-boreal transitional f orest were evaluated and compared. The use of multiple frequency, pola rimetric information to produce forest-cover classification, biomass e stimates, and forest spatial pattern analysis were investigated. The r esults from SIR-C/X-SAR compared with those from AIRSAR were generally similar despite different available frequency (C-band, L-band, X-band vs. C-band, L-band P-band) and resolution (25.0 m vs. 8.3 m). AIRSAR data better enabled the mapping of stands of hardwood and mixed: fores ts than did SIR-C/X-SAR data. However, SIR-C/X-SAR produced better cla ssification results for conifer forest stands. There was no great bene fit from using higher resolution for classification except for forest stands in which there were mixtures of species (i.e., hardwood and sof twood). A comparison of the image data also showed that both instrumen ts could provide reasonable estimates of biomass density up to about 1 5 kg/m(2). At higher biomass levels, both AIRSAR and SIR-C showed the well-known biomass saturation effect. The average biomass densities de termined from the AIRSAR and SIR-C images were reasonably close at 9.7 kg/m(2) and 9.0 kg/m(2), respectively. Finally, spatial character of the image data was examined by using perimeter and area relations and lacunarity analysis. The results were consistent between. the two inst ruments and showed that the forest opening patterns were self-similar for openings greater than about 3 ha. (C)Elsevier Science Inc. 1997.