Recovering time and space varying phase screens through SAR multi-squint differential interferometry

In this paper we discuss the estimation of time and space varying phase screens through multi-squint SAR differential interferometry. Spatial variations of the phase screens along the synthetic aperture and far from the scatterers result in defocused images, whereas temporal variations from an acquisition to another within a sub-look of the resolution cell result in unwanted decorrelation. Time changes of the phase screen may also occur close to the scatterers and those will be the hardest to recover as they mimic target decorrelation during acquisition. Given the availability of a reference passage unaffected by phase screens, multi-squint interferometry provides way to estimate, and eventually compensate for, both the temporal and spatial variation of phase screens, allowing the recovery of the information content within a SAR image stack. This topic is relevant to new potential spaceborne SAR systems operating at longer wavelengths, affected by ionospheric disturbances, or in geosynchronous orbit, affected by the evolution of the water vapors within the integration time. In this work we cast the problem in terms of estimating the 2D (time and space) spectrum of the phase screens, and show that there exist an optimal integration time that minimizes their impact.