Space-borne Ka-Band Across-Track SAR Interferometer

Abstract

The results of an ESA study concerning a future Ka-band SAR mission and instrument concept are reported. One aim of the study has been to explore the feasibility of a future single-platform, across-track interferometric SAR instrument with HRTI-3 performance of its Digital Elevation Model data product. The possibility of accommodating an interferometric instrument with electrically large across-track baseline on a single platform is a unique opportunity to avoid the temporal decorrelation of repeat pass concepts at lower carrier frequency. On the other hand, sensitivity requirements of space-borne instruments demand the use of electrical large antennas; these inevitably require Digital Beam Forming capabilities. Hence these become a fundamental part of the present design issue. An instrument architecture is presented which minimizes antenna masses attached to the ends of its long boom, and which constrains the installation of electrically active units or components to the satellite body. These features support a very stable instrument while keeping implementation complexity moderate. To achieve this, Digital Beam Forming techniques are applied both in elevation and azimuth direction. The SAR and InSAR performances of the instrument concept are reported. The assessment of the expected In-SAR performance requires a full account of all mechanical, thermal, and electrical errors which persist after the proposed calibration measures. These include an innovative multi-squint procedure which allows to calibrate mechanical oscillations of the boom from the SAR data itself, in the on-ground processing stage. The procedure is related to motion-compensation correction methods used in airborne SAR. While the presented instrument concept is geared towards high-resolution data products with only moderate scene sizes, optional instrument architectures can also be considered which offer wide swaths at reduced resolution. It is concluded that Ka-band offers a number of promising instrument alternatives for future interferometric SAR missions with rewarding performances.