Complex phase error and motion estimation in synthetic aperture radar imaging

Synthetic aperture radar imaging is based upon coherent signal processing methods that mold various radiation patterns of a synthesized array to extract Doppler information. The success of such coherent processing algorithms greatly depends upon correct phase synchronization of the collected SAR data. Complex phase errors, i.e., fading as well as loss of coherence, in SAR imaging result in presence of speckle and/or severe degradations in the reconstructed image. Moreover, unknown movements of a dynamic object in the SAR's target scene could also result in erroneous Doppler information and, consequently, degraded reconstructions. In this presentation, we invoke a SAR wave equation-based system model, that accurately represents the interaction of the impinging radar signal with the target to be imaged, to estimate complex phase errors and motion in the target scene. We first use the SAR system model to estimate the complex phase error across the synthesized aperture from the measured corrupted SAR data via combining the two wave equation models governing the collected SAR data at two temporal frequencies of the radar signal. We then use the SAR system model to show that the motion of an object in a static scene results in coupled Doppler shifts in both the temporal frequency domain and spatial frequency domain of the synthetic aperture. These two Doppler shifts are used to estimate the velocity of the moving object.