High-Coherence Oriented Image Formation Algorithm Based on Adaptive Elevation Ramp Fitting for GNSS-Based InBSAR Systems

The uncertainty of the elevation of target area in bistatic synthetic aperture radar (BiSAR) introduces image defocus. This uncertainty becomes much worse in global navigation satellite system-based BiSAR interferometry (GNSS-based InBSAR) applications, where the primary problem is a decrease in the coherence of the image pairs. In this paper, a high-coherence oriented imaging algorithm based on adaptive elevation ramp fitting is proposed for GNSS-based InBSAR systems. First, GNSS-based InBSAR signal model is established considering elevation error. From this model, the expressions for position offset and interferometric phase error caused by the elevation error are derived. Then, to improve the elevation fitting accuracy, full-scene fitting is replaced by subarea fitting, and adaptive subarea segmentation is achieved based on the points with complete resolution cells and image valleys. Finally, elevation fitting is performed in the subareas. The algorithm can obtain high-coherence image pairs with low image resolution introduced by GNSS-based InBSAR systems. Simulation and raw data are used to prove the effectiveness of the proposed algorithm in GNSS-based InBSAR.