The performance of the radar 
The primary goal of the RADARS AT mission is to generate economic 
benefits from the use of the radar data. For this reason when the mission 
requirements for RADARSAT were being defined careful consideration was 
given to the selection of the radar frequency. Experimental data was gathered 
from a wide variety of sources, including an ongoing multi-frequency airborne 
SAR experimental program. It was quickly discovered that on the one hand 
the range of possible applications of SAR data was far wider than had 
previously been expected but on the other it would require a very versatile 
SAR to provide data suitable to meet all these needs. 
This requirement has led to a design for a single frequency SAR which can 
function in a number of different modes under the control of an on-board 
computer. C-band was selected as the optimum frequency because it enables 
the greatest number of application needs to be satisfied. Each day ground 
control will transmit to the satellite a schedule of the day’s activities listing 
times at which the SAR is to be turned on and off corresponding to the 
geographic locations where the data are to be acquired. Associated with each 
SAR turn-on is a file of radar parameters specifying the required SAR mode. 
The SAR antenna consists of an array of emitting elements each fed with a 
constant amplitude signal thus defining the shape of the radar beam. The 
phase of these signals is programmable, however, and this permits the width 
and pointing direction of the beam to be selected at will in the range 
direction. As the satellite moves along its track the data from which the radar 
image is created are collected continuously. In this way, controlling the beam 
width, in effect, controls the swath width of the resulting picture. Associated 
with these variable swath widths are corresponding variations in the size of 
the resolution elements on the ground. 
Control of the beam direction enables the incidence angle to be varied. This 
allows a given site on the ground to be imaged from different directions thus 
permitting additional information to be obtained for features in the scene 
which are sensitive to the incidence angle. It also allows stereo pairs of 
images to be collected which can be used jointly with radar shadow 
information for geomorphological studies or alone to produce topographic 
maps. Where the scene parameters of interest are not sensitive to incidence 
angle the variable incidence angle can be used to increase the frequency of 
opportunities for obtaining images of a given site.