4,1, 
86 
Current work involves the comparison and validation of 
direct sea truth with data extracted from SAR images using the 
package above, A recent paper [5] provides further examples of 
the technique, 
This example provides an excellent illustration of the 
need for total validation, where before deriving the geophysical 
data, full compensation is made for the sensor, The example 
emphasises the need for users to be fully aware of the sensor 
imaging process before geophysical measurement from the image, 
SIMULATION 
Introduction 
Simulation is an important aspect of any remote sensing 
mission, from the early development phase, where simple computer 
programs can be used to establish basic system parameters, 
through to post-launch validation exercises, where simulated and 
real images of terrain can be compared. The simulation can take 
many forms, from analytic approaches using computer based 
techniques of varying degrees of complexity, to empirical methods 
utilizing antennas mounted on towers or aircraft. 
In the particular instance of spaceborne synthetic aperture 
radar systems, there is a need to make potential users aware of 
the quality of the expected products in order to create a wider 
market for these products as and when they become available. The 
SEASAT experiment was a good advertisement for such systems 
(despite its brief operational life), but differences in altitude 
and particularly radar frequency precludes use of SEASAT images 
to demonstrate the products from, say, a C-band satellite system. 
Aircraft overflights such as the SAR-580 compaign are of 
importance, but the large discrepancy between the platform 
heights for aircraft and satellite systems leads to substantial 
differences in the nature of the two sets of images, primarily 
due to the range of incidence angles covered by the different 
systems. 
The use of computer based tools therefore appears most 
attractive, although the approach taken depends on which aspects 
of the system are of prime interest. Two types of simulation 
tool can be readily identified: those seeking to model the SAR 
process, including pulse transmission and reception, the radar 
subsystem and data processing, and those which simulate typical 
SAR products directly. A brief discussion concerning each type 
of simulator is expanded below.