Ionosphere and Ground Motion Estimation from Azimuth Subbands

Abstract

SAR based estimation of glacial motion is a key tool to globally monitor the effects of climate change on the cryosphere. Glacial movement between two observations is measured via cross-correlation, but azimuth offsets are biased by shifts of the SAR impulse response due to linear variations of the ionosphere along the azimuth direction. Due to increased sensitivity of higher-wavelength systems to the ionosphere, the next generation of L-band earth observation missions requires the precise estimation of the differential ionospheric state and subsequent compensation of ionospheric azimuth shifts. In particular, we require turbulent ionospheric components to be recovered and compensated, due to their large contribution to azimuth offset biases. However, current estimation methods are not able to reconstruct high-frequency ionospheric perturbations as a result of smoothing or are sensitive to both azimuth ground motion and ionosphere and thus can not separate the two effects. The second derivative of the azimuth phase history allows to separate azimuth ground motion from ionospheric effects, providing additional information on the ionospheric state. In this thesis, we investigate the improved estimation of the differential ionospheric phase screen from three azimuth subbands in combination with split-spectrum measurements. Using simulated data, we show that three azimuth subbands enable the recovery of high-frequency ionosphere even in the presence of strong azimuth ground motion.