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Encoding of SAR imagery data (mono- or multi "spectral" data) is an 
operation aimed at removing redundant SAR imagery data end speckle 
distortion. Data reduction is achieved by entropy coding and image 
enhancement by adaptive speckle filtering. Because the processing is 
information preserving, it is as such transparent to the user. 
Data extraction from imagery data is aimed at providing the user with 
specific types of information which is oriented towards a specific 
application, e.g. the extraction of sea-wave spectral data for 
oceanographic research purposes. Data extraction processing may result in 
a large reduction of data volume. 
The image generation processing puts the most stringent requirements on 
the performance of the processing system and is therefore analysed further 
in this paper. 
2. SAR IMAGE GENERATION PROCESSING 
Table 1 gives the specification of a typical C-band radar sensor and in 
Table 2 the associated image specification for which the processing task 
will be analysed. The processing functions to be executed for image 
formation are (in segmential order): range compression, range migration 
correction, azimuth processing (specified later). 
In addition to the main processing operations, data analysis is performed 
in order to feed the processor with updated mean Doppler and Doppler rate 
information, which varies with the satellite's orbital position. 
Figure 1 depicts the block diagram of the overall processing system. 
The selection of processing device technology is mainly governed by power 
and weight constraints. For range compression analog (Surface Acoustic 
Wave) devices outperforms digital device technology with this respect and 
is therefore applied prior to baseband convertion and ADC. Sample 
interpolation, associated with linear range migration correction is 
conveniently implemented by controlling the ADC sample instants. Al] 
remaining processing functions. i.e. those relevant to time stretching of 
the range samples arriving in bursts and azimuth processing are performed 
by a digital processing system. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
IF Range 
radar Compression | ; C > Azimuth SAR imagery 
signal , (SAW) » Processing » 
IF to a 
baseband Mean 
conversion |Doppler ) Doppler rate 
info... . information 
Range migration 
control 
Main 
Aux. data Control Telecommand 
  
  
  
Fig. 1 - On-board SAR processing system diagram