Future Spaceborne SAR Systems based on SCORE: Intrinsic Limitations and Possible Solutions

Abstract

Scan-on-receive (SCORE) is a promising digital beamforming technique for future high-resolution wide-swath synthetic (HRWS) aperture radar (SAR) systems. By pointing the receive pattern in real time towards the expected direction of arrival, and combing the antenna receive channels, SCORE achieves a sharp and high gain receive beam in elevation. SCORE allows for improved SAR imaging performance compared to the conventional approach. However, it is also sensitive to new errors, associated with angular mismatch in the SCORE steering. Future HRWS systems should deliver images with radiometric accuracy lower than 0.5 dB. Because of the demanding requirements, it is important to investigate how the error sources affect the final output image. This thesis focuses on the radiometric quality degradation induced by the pulse duration and topographic variation. Individual and mutual effects are analyzed both from a theoretical and numerical point of view. The current knowledge on SCORE losses is extended, new expressions for the image quality degradation of distributed targets and point targets are derived. Numerical simulations are performed using a simple end-to-end simulator based on assumed reflectivity models and real SAR images. The simulations confirm the theoretical derivations, and evidence scenarios where the SCORE losses could be problematic. The obtained results show that the losses due to the pulse duration and unmodelled topography cannot be accounted for separately. For a given pulse duration and terrain height, the SCORE loss depends on the properties of the reflectivity scene, the slant range position, the SCORE pattern shape and steering velocity, as well as the choice of SAR receive window function. The relevance of the analysis is validated by considering realistic scenarios.