Performance of 3-D Surface Deformation Estimation for Simultaneous Squinted SAR Acquisitions

This paper addresses the performance in the retrieval of 3-D mean deformation maps by exploiting simultaneous or quasi-simultaneous squinted synthetic aperture radar (SAR) interferometric acquisitions in a repeat-pass scenario. In multi-satellite or multi-beam low Earth observation (LEO) missions the availability of two (or more) lines of sight allows the simultaneous acquisition of SAR images with different squint angles, hence improving the sensitivity to the north-south component of the deformation. Due to the simultaneity of the acquisitions, the troposphere will be highly correlated and, therefore, will tend to cancel out when performing the differential measurement between the interferograms obtained with the different lines of sight, hence resulting in a practically troposphere-free estimation of the along-track deformation measurement. In practice, though, the atmospheric noise in the differential measurement will increase for increasing angular separations. The present contribution expounds the mathematical framework to derive the performance by properly considering the correlation of the atmospheric delays between the simultaneous acquisitions. To that aim, the hybrid Cramér-Rao bound is exploited making use of the autocorrelation function of the troposphere. Some performance examples are presented in the frame of future spaceborne SAR missions at C- and L-band