Reliably Calibrated SAR Systems - the Precondition for ARD

Abstract

The main objective of providing analysis-ready data derived from spaceborne instruments is enabling the application and usage of data without the necessity for explicit expert knowledge about producing this data. Furthermore, data from different acquisitions and sensors should be comparable. And finally, there must be a certain quality, consistency and reliability of the data. The key to achieving this goal is through calibration. For a spaceborne SAR system, calibration is understood to include all procedures required to eliminate systematic errors, like instabilities through thermal drift or geometric offsets through the internal delay of the instrument. However, efficient calibration of any complex spaceborne SAR systems requires sophisticated concepts, precise algorithms and tools, as well as adequate and well maintained facilities. For more than 25 years, DLR has been playing a key role in the calibration of modern spaceborne SAR systems. It has established the DLR SAR Calibration Center, which is constantly developing novel analysis tools based on precise algorithms and operates a SAR calibration facility composed of a large number of reference targets deployed and maintained within an area of 120 km x 40 km in South Germany. An example of comprehensive activities is DLR’s independent system calibration of ESA’s Sentinel-1A and Sentinel-1B satellites in the framework of the European Copernicus program. In this respect, the complete in-house development of a new generation of remotely controlled C-band calibration transponders was an important milestone. These transponders together with remote controlled corner reflectors became the primary calibration reference for the Sentinel-1 mission. In order to be well prepared for future SAR mission with bandwidths up to 1.2 GHz in X-band or full polarimetric applications at lower frequencies, the development of innovative transponders will continue. After a short introduction of the need for SAR system calibration, the DLR’s facility will be presented with its possibilities to calibrate future and innovative spaceborne SAR systems efficiently.