USING ERS 1 AND ASAR IMAGERY FOR MAPPING FOREST IN FRENCH GUIANA

ERS 1 and ASAR imagery were used for mapping the forest area of French Guiana for 1992/1993 and 2003/2004, respectively. For the 1993 map 61 ERS 1 precision images were received. The ASAR data for the 2004 map were 107 VV polarization images of swath IS4 (incidence angle 33 degrees). The ERS data sets included multi-temporal acquisitions of two to five dates from the same location whereas the minimum number of overlapping images in the ASAR set was four and maximum six. The imagery was ortho-rectified using the digital elevation model of the Shuttle Radar Topography Mission. Three features were computed using the SAR data: average texture, average amplitude of the overlapping images, and temporal variability of the backscattering. A classification to forest and non-forest was done using a combination of unsupervised and supervised techniques. Reference data to estimate forest area and its confidence intervals and to validate the SAR based maps were collected by making a point sample from two Landsat image mosaics, from 1990 and 2000.