Calibration of the first space-borne SAR instruments, with only one swath and based on passive antenna technologies (e.g. ERS-1) required the in-flight characterisation of that single-swath instrument over well-known scatterers (reflectors, transponders, and rain forest sensing data). Modern systems evolved to more access flexibility, and therefore to multiple beams and multiple polarisation, that led to the use of complex active phased antennas. In-orbit calibration of such complex SAR systems can be a very time-consuming and expensive exercise that takes time off the spacecraft lifetime. The full characterisation on ground presents the additional risk of a limited validity if during the early phases of the in-flight operations a number of sub-arrays suffer degradation (i.e. failure of T/R module functions or irrevocable phase and gain drifts). If this type of degradation occurs, an in-flight re-characterisation of the instrument throughout the different beams (i.e. using repeating passes over the rain forest etc.) is the only way to maintain the requuired accuracy. After lessons learnt during the ENVISAT ASAR commissioning, this paper presents a new concept for SAR calibration built around a mathematical antenna model based on accurate on-ground measurement of the instrument, a set of post-launch external measurements to be performed during the initial commissioning period, periodic in-flight internal characterisation, and the internal calibration data to be taken during and together with the sensing data. Such an accurate antenna model is a very powerful tool both for the pre-flight characterisation of all antenna beams, and for in-flight estimation of the actual patterns.
Efficient calibration of active-phased-array SARs
2006
4 Seiten, 2 Bilder
(nicht paginiert)
Conference paper
English
Efficient Calibration of Active Phased Array SARs
German Aerospace Center (DLR) | 2006
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