OPTICAL AND DIGITAL SEASAT SAR PROCESSING TECHNIQUES: A COMPARISON 
OF ACCURACY RESULTS 
Dr. Abdalla Elsadig Ali 
University of Khartoum 
Sudan 
ABSTRACT 
The paper reports on the results of an investigation into the metric 
accuracy of four Seasat SAR images that cover the same area but have been 
differently processed. Two images have been optically processed using the 
Environmental Research Institute of Michigan (ERIM) optical processing 
facility; the other two images have been digitally processed, one by the 
Royal Aircraft Establishment (RAE) at Farnborough and the other by Deutsche 
Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR, FRG). 
Ground control points have been selected on each image, measured and 
transformed to the terrain system using suitable mathematical transform- 
ations. The discrepancies between the known and the transformed coordi- 
nates were used to compute the root-mean-square errors for each polynomial 
solution. The results show that the optically processed images contain 
substantial scale errors, as compared to the digitally processed images, 
and that the effect of using higher order polynomials is more noticeable 
on the optically processed imageries than on the digitally processed ones. 
Comparison of the results of the two digitally processed imageries shows 
that,as far as the present experiment is concerned, the DFVLR image 
demonstrated superior geometric accuracy. 
INTRODUCTION 
Seasat-A, launched by NASA in 1978, was the first civilian satellite to 
carry an imaging radar system onboard. Because of the special character- 
istics of the satellite, e.g. those relating to the special parameters 
of the orbit, processing of the Seasat SAR data posed considerable problems 
to the remote sensing community. 
Because of the fact that it is the first spaceborne radar system to which 
civilian users and researchers have had access, there has been much interest 
in developing new methods for processing the SAR data. A number of 
processing systems had been proposed and/or developed in order to carry 
out Seasat's SAR data processing. Some of these systems are optical in 
nature; others are digital processors (Table 1). 
GENERAL LINES OF SEASAT SAR IMAGE PROCESSING OF THE TEST AREA 
The purpose of this paper is to report on results obtained after testing 
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