Several factors play a part in determining the geographical coverage of ERS products, including instrument, orbital configuration, ground station coverage and operational constraints.
The ESA ground stations directly acquire SAR data over the European area, while the global dataset for the LBR instruments is obtained using the on-board recorders. Other stations around the world also receive ERS data thus extending the coverage of the SAR Image Mode.
ERS-1
ERS-1 and 2 - Geometric & Radiometric Characteristics
ERS data are subject to speckle, SAR antenna pattern loss and range-spreading loss, and are acquired in slant range. Further, there may be terrain-induced radiometric effects and terrain distortion (foreshortening and layover). Various levels of processing are available to correct these effects:
• Speckle reduction is achieved by multi-look processing
• SAR antenna pattern loss and range-spreading loss can be corrected by calibrating the image
• Slant range can be corrected to ground range
• Terrain-induced effects can be corrected by the application of a Digital Elevation Model
• Data can be georeferenced to a map projection
