2.1. 
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INTRODUCTION 
The Earthnet Programme Office, at Frascati, Italy, is 
responsible within the European Space Agency for the acquisition, 
processing and distribution of remote-sensing data. The problem 
of controlling, monitoring, and validating data has been 
anticipated, and methods to implement quality monitoring have 
been developed for some sensors. Synthetic aperture radar (SAR) 
data presents special problems. For the ERS-1 satellite, an 
efficient and effective quality control of the SAR data is being 
developed. 
Two large data sources are available at ESRIN. The first 
set has been acquired from the SEASAT satellite, having been 
recorded at the Oakhanger ground station. The second set has 
resulted from the airborne multifrequency, multipolarization 
radar belonging to the Canadian Centre for Remote Sensing. The 
radar is carried by a Convair-580, and is referred to in this 
paper as SAR-580, These data sources have been utilized to 
develop some of the techniques described below. 
The need to handle image data from many sources has 
determined that objective properties of the image should be 
measured when assessing quality. It is preferred that these 
measurements should use natural features and not specially 
constructed reflectors, for example, since only then can 
operational quality control procedures be set up. 
This paper describes some of the activities that have been 
carried out by Ethernet in the field. The paper includes 
reference to Earthnet associated work on calibration and 
simulation, 
ACQUISITION 
The Requirements: 
  
The general requirements for acquisition, recording and 
archiving of data from a spaceborne SAR, are not different from 
those imposed by any high data rate sensor, e.g. Landsat thematic 
mapper. In particular, the requirements are dictated by the 
attempt to solve the following problems: 
a. The high data rate on the downlink from the spacecraft 
imposes: 
- use of high speed recorders 
- use of high density media.