8s than The particular subsystems are the Knowledge Engineering Workstation (KEW), the Image Quality Analysis 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
he main Workstation (IQW), the Software Engineering Workstation (SEW), the Front/End Hostcomputer (FEH), the 
on orbit ST-100 Arrayprocessor (ST-100), the Corner Turn Memory (CTM) and the Real Time Input Facility (RTI). 
The Local Area Network connects all systems with interactive tasks like software development, process con- 
| related figuration, image quality analysis etc. with the high throughput computers FEM, ST-100 or RTI. As a special 
sone device the CTM will be used as a data buffer between HDDT, the regular input medium to the processing 
m be system, and the ST-100 Arrayprocessor. It will be loaded directly from HDDT with a full reproduce speed 
y t of 105 Mbit/sec. From this point the SAR data are accessible randomly in range and azimuth with a DMA 
ery fas speed of 40 MByte/sec. 
1a gain. The data flow (see Figure 3) is organized as follows: First of all the Data Management System sends a pro- 
oreover cessing request to the KEW. There the order will be worked out to a full scene configuration. After the HDDT 
has been mounted and automatically positioned the data transfer will take place for a full ERS-1 scene in about 
roducts 15 seconds. Now the ST-100 can start the required correlation task up to the final processing level. At the 
d-range end the data are stored on a disk of the Front/End Computer ready for being transferred to the Image Quality 
Workstation or to the Data Management Computer. 
ent has 
1apters, 
IQW KEW 
rdware 
icts per 
roduct. image or À | commands 
R. raw data data 
LAN 
Nirpose commands A | commands 
rdware data data 
i | 
DATA NRTI raw FEH commands | RTI 
MANAGEM. * AOD "data input”, : HDDT 
FACILITY * CCT status * ANTENNA 
(mace raw gata raw data 
image ata inpu input 
oa data output 
SHARED ST100 2H date 7 CIM 
DISK | 
  
  
  
  
  
  
  
  
  
Figure 3. ISAR data flow 
Basically SAR imaging and processing is a twodimensional operation whose coordinate axes are designated 
across track and along track respectively. The Range-Doppler-Algorithm uses a separate matched filter oper- 
ation implemented in the Fourier frequency domain and turns out very advantegously in terms of quality and 
speed. It is a very well known and documented procedure and has therefore been chosen as the standard 
processing algorithm for ISAR. 
375