Precise SAR Antenna Pointing Determination using Phase Coherent Difference Images

Abstract:
Most modern spaceborne SAR systems are equipped with a phased array antenna to adjust the antenna beam to the acquisition geometry to gain best performance and to increase the access area. An antenna model can be used to predict the radiation pattern of the SAR antenna based on the selected antenna excitation coefficients which reduces the effort and time compared to verifying each single antenna pattern individually. The predicted patterns only need to be verified for certain samples after the model is initially aligned with the real SAR antenna. One challenge for future SAR missions employing large deployable reflector antennas, like ESA’s BIOMASS or DLR’s Tandem-L is that due to the large antenna structure the antenna alignment is no longer fixed but may change within a short period of time. This makes traditional antenna pointing determination using homogenous distributed targets like the Amazon Rainforest inapplicable, as pointing variations along the orbit are untraceable due to a lack of suitable targets which are not evenly spread over the Earth. A novel technique is proposed which allows precise pointing determination also over inhomogeneous areas using phase coherent difference images to extract the elevation antenna pointing. First results using TerraSAR-X acquisitions will be shown to verify the technique.