2.3. 
3.1. 
82 
Other more advanced technologies are not envisaged: rotary 
head recorders (Ampex) do not appear to be ready for operational 
use. Digital optical discs (Thomson-CSF) in the versions 
available at present do not have the capacity beyond 1-2 minutes 
of data, and in the foreseeable future do not seem likely to 
achieve the required transfer rates (4.1 Mbit/sec at present). 
Playback for Processing 
  
The playback of the data, after initial recording, has to 
be performed in order to input data to a processing system, 
either for reformatting or for preprocessing. Current input data 
rates to processing systems vary between l and 10 Mbytes/sec, 
including the cases where high speed parallel access disc 
subsystems (CDC, FUJITSU) are used for data input. This means 
that the recording media used for acquisition has to be played 
back at reduced speed, or that some demultiplexing of the data, 
according to some logical scheme (e.g. spectral channel, I/Q) has 
to be performed in order to input lower data rates on reduced 
capacity channels. 
In the first case, playback Speed not lower than a factor 
16 of the recording speed is recommended if bit rate is to be 
kept to the specifications. The Presence of an error detection 
and correction system may allow the limit to be exceeded. 
VALIDATION 
System validation can have two purposes: 
i) monitoring of intermediate and final data quality to ensure 
that the system performs to a Specification, and 
ii) validating the system capability to derive geophysical data 
which agrees with measurable ground truth. 
Techniques of performance monitoring are reviewed with 
specific reference to the work on SAR data Sets being carried out 
at the Marconi Research Centre, and at Earthnet, ESRIN. An 
example of the validation of geophysical data extraction is 
presented where the technqiue involves correction for the sensor 
transfer function. 
Techniques for Performance Monitoring 
The products from seven processors were assessed using 
SEASAT data [1]. The assessment was based on: 
- point target related measurements 
- distributed target related measurements.