InSAR Phase Errors Due to Range Misregistrations

High quality InSAR measurements require precise and accurate range coregistration both between the reference and the secondary SAR images, and between the reference SAR image and the Digital Elevation Model (DEM) used for computing topographic phase. However, this requirement is not invariably satisfied due to the occurrence of range misregistrations. The range misregistration can occur between the reference image and the DEM, between the reference and secondary images, or due to the inhomogeneity within the range resolution cell. Our analysis reveals that, apart from the decorrelation effects, the effects of all three misregistration types ultimately reduce to that of an equivalent misregistration between the reference image and the DEM, which manifests as a phase error. Moreover, a closure phase error can be induced by the InSAR phase errors from the range misregistration between the reference and secondary images, as well as the inhomogeneity of the range resolution cell. We derive the InSAR and closure phase errors from both geometric and signal theory perspectives, assuming a homogeneously distributed target. We further extend the derivation to different types of targets. The derived InSAR and closure phase errors are confirmed by simulation and real-data experiments.