IV SYSTEM CALIBRATION 
Calibration is a very important issue in modern remote sensing radars, especially when data 
from different radars or multitemporal data from one sensor are to be compared or if 
measurements have to be compared to models. Several precautions are taken in the KRAS 
radar design to enable fairly accurate system calibration. The main ingredients in the 
calibration of the KRAS radar are : 
1) Design for maximum stability of the analog radar front end 
2) Internal calibration loops 
3) Accurate antenna calibration 
4) Comparison with a 5.3 GHz noise scatterometer. 
First of all the stability of the system is ensured by applying design techniques usually 
applied in radiometer systems. One of the important factors is that all RF components 
including the TWT+EPC will be temperature stabilized to an accuracy better than 1°C. 
Another important feature of radiometers is that of frequent automated calibration. This is 
implemented in the KRAS radar design by using a number of internal calibration loops. Both 
a sample of the TWT drive signal and the TWT high power output ( sampled via a -60 dB 
cross coupler) is injected in the calibration switch. The calibration switch includes a 
programmable precision attenuator and an average power monitor, and the sample of the 
drive signal or the attenuated high power signal can be injected in the receiver either before or 
after the LNA. There is still some doubt whether the RF leakage can be kept sufficiently low 
to enable simultaneous calibration of the TWT and the LNA. All these measurement options 
are supported by the digital signal generator, that allow the transmission of extra calibration 
pulses concurrent with normal SAR operation. 
The slotted waveguide antenna which is presently being developed will be calibrated in the 
Electromagnetics Institutes Radio Anechoich Chamber using spherical near field antenna 
measurement techniques. It will be attempted to include the antenna pod/radome in the 
measurements. 
Finally the collected SAR data will be compared with data gathered with a C-band noise 
scatterometer that was recently developed at the Electromagnetics Institute , [Skou,1987]. 
V PROJECT STATUS 
The project is presently in the construction and test phase. The RF generator/calibration 
switch and the receiver have been finished and have passed initial tests. The TWT+EPC 
system will be integrated and tested mid 1988. The antenna system is presently being 
developed at the institute and measurements on test samples show good results, so the 
antenna construction and test is expected before the end of 1989. The control computer is 
presently in the software development phase. Major parts of the high speed digital electronics 
have been finished already. Integration and test will take place in the first half of 1989, and 
the first flight test will be carried out in the summer 1989. 
The subsequent phase of the project, which includes real-time processing is planned to be 
finished late 1990. 
It is finally noted that the funding for the project including the real-time processing has 
already been granted. 
Extensions of the project might include polarometric measurement. 
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