Evaluation of the potential cartographic accuracy of Radarsat and JERS-1 data

Synthetic aperture radar images reveal geometric distortions, which are caused by different sources. The aim of this study is to quantify the geometric quality of some of these images-SGF product type (path image), standard beam mode, beam positions S2 and S3 Radarsat and JERS-1 level 2.1 images, acquired in the region of Ariquemes - RO. A set of control points were acquired by using a GPS receiver in the area of study and differentially corrected. The planimetric and altimetric errors of these points are about 1,11 and 2,19 meters, respectively. These points were used as ground truth and compared with geometric properties (linear distances and angles) measured over the images. The uncorrected images presented relative scale and rotation errors of about 2 pixels. The images were geometrically corrected (geocoded and ortho-rectified) and had their geometric characteristics analyzed. The reduction of the relative scale and rotation errors obtained with the processes of geometric correction of the images were of 1/3 of pixel (4,17 meters). Visual inspection of an overlay of the SAR images and a GPS collected road network indicated a reasonable degree of coincidence. Results obtained with the calculation of the absolute accuracy of the geocoded and ortho-rectified images showed errors of absolute localization smaller than a pixel, varying from 5,42 meters to 12,24 meters to geocoded images and from 5,62 meters to 11,72 meters to the ortho-rectified ones. The images with viewing angles ranging from 24° in the near range to 31° in the far range (Radarsat S2), 30° in the near range to 37° in the far range (Radarsat S3) and 32° in the near range to 38° in the far range (JERS-1), acquired in regions with moderate altimetric variation (the area of study presents altimetric variations from 100 to 376 meters), presented geometric errors acceptable for mapping at 1:40000, 1:25000 or 1:20000 scales depending on the class of the mapping product to be obtained