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with a Floating Point Systems (FPS) AP-120B array processor. A plan is being 
made now to augment the VAX with an APTEC peripheral control unit to be able 
to efficiently utilize multiple array processors for a higher throughput rate. 
A real-time digital processor for survey processing of aircraft SAR data is 
also desirable for the purpose of on-board verification of data quality and 
experiment site. Simulation has indicated that a 10 m resolution single-look 
image would be adequate for the survey purpose. A development project for the 
design and implementation of such an aircraft SAR on-board survey processor 
was initialized in the fall of 1983. Preliminary specifications include real- 
time production of single-look 10 m resolution image over 10 to 15 km swath 
width. For this on-board processing application, we propose to use a special- 
purpose hardware processor. At L-Band radar frequency, with a 16 point azimuth 
presum filter, the azimuth compression ratio for 10 m resolution is in the order 
of 20. Including the oversampling effect, the number of samples for azimuth 
correlation reference function is approximately 40. The range compression ratio 
is close to 100 which is obtained from the product of the length and bandwidth 
of the radar transmitted pulses. The processor throughput rate is approximately 
50K pixels per second, i.e., 1K pixels per line and 50 lines per second. Assuming 
the time-domain correlation as the baseline, the computational rate required 
is approximately 7 million complex multiples and accumulations per second. This 
is not a demanding requirement compared to the capability of commercially 
available integrated circuits for signal processing. Provisions are also made 
that the processor can be reprogrammed for C-Band radar operation, which is 
expected to occur in 1985. 
The SIR-B data will be processed both optically and digitally. The basic SIR-B 
SAR parameters and summary of the performance specifications of the optical and 
digital SAR processors are listed in Table 2. The SIR-B mission is designed to 
acquire a total of approximately 80 hours of raw data. The plan is to complete 
the optical survey type of processing in about 12 months after the completion of 
SIR-B data acquisition, and about one-tenth of the digital raw data -- 7.5 hours 
worth -- processed digitally over a two-year period. For optical processing, 
minor modifications were made to the existing JPL optical SAR processor to improve 
image geometric performance and to provide better film annotation. The software 
and hardware system for SIR-B digital processing is based on the SEASAT Interim 
Digital SAR Processor (IDP). The system equipment includes a Gould SEL 32/77 
computer, four FPS AP-120B array processors and a number of data storage disk 
drive units. The digital data are input via a Thorn-EMI high-density-digital- 
recorder. The digital correlation algorithm for SIR-B resembles that for the 
SEASAT SAR data. Software modifications were made to: 1) provide greater amount 
of flexibility to handle different input quantization bits, different radar look 
angle and the associated swath width, etc.; and 2) improve the geometric and 
radiometric performance of SIR-B SAR imagery relative to that of SEASAT. The 
7.5 hr. (approximately 2000 images) processing requirement of SIR-B necessitates 
a dedicated SAR processing facility fully utilizing the IDP thus requiring a 
shift of the aircraft processing to the VAX computer.