using primarily laser tracking data which have an accuracy of less than 1 meter in the position and less than 
10 cm/s in the velocity and it will be available few weeks after acquisition. Therefore it is one of the main 
differences between the Fast Delivery Processor and the Off-line Processing Facility that high precision orbit 
data are used which are not available shortly after data acquisition. 
The refinement of the satellite attitude measurements in its three axis, roll, pitch and yaw as well as the related 
acceleration figures will be done by a cross-correlation of a replica of the theoretical antenna pattern positioned 
according to the attitude data with several ensembles of the real azimuth spectral data. This operation can be 
done randomly and repeatedly of across the swath and along the whole 100 km in azimuth supported by the 
fact that the data are accessible in both image directions without ‚delay and that the host will be a very fast 
machine with a floating point performance of 2 Megaflops. 
Another topic of accuracy will be the calibration of the range chirp and the compensation of the antenna gain. 
High precision will also be applied to the calculation of all parameters relevant to the latter items. Moreover 
each complex sample will be represented with 32 bit throughout the processing. 
In order to give the user a full flexibility for his choice of product, a whole family of intermediate products 
(level 1.5) will be available which comprise the Fast Delivery Product, Bulk Products in slant- or ground-range 
and even products with complex pixel representation preserving phase information. 
The system is designed to achieve a throughput in the order of 6000 products per year. This requirement has 
several consequences in terms of hardware and software design which will be described in the next chapters, 
The software related aspects will be given comprehensively in a separate paper [Noack, 1986] 
The requirements high precision and high throughput have been the main driving factors for the hardware 
selection. It has already been mentioned that the processor shall be capable of processing 6000 products per 
year. Assuming standard operation times this results in a processing time of 1/2 hour per level-1.5-product. 
Moreover the system shall be flexible to be adapted to other spaceborne sensors like the German XSAR. 
There has been chosen a distributed, parallel architecture arranged as a lattice whose nodes are single purpose 
CPUs and the branches represent computer-computer links. Figure 2 gives an overview of the ISAR hardware 
configuration. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Figure 2. 
KEW IQW SEW 
1 1 4 
LAN 
FRONTEND AT 
MIPS 5 SELECTABLE 
MFLOPS 2 HDDT, ANTENNA 
DMA 2 MB/S 
  
  
  
  
  
  
  
  
  
  
  
  
  
ST100 CTM 
MEM 1 MWORD MEM 2 
MFLOPS 100 DMA 40 MB/S 
DMA 100 MB/S DUAL PORT 
COMMANDS 
  
  
ISAR hardware configuration 
COMMANDS AND DATA 
  
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