The 2-Look TOPS Mode: Design and Demonstration With TerraSAR-X

Burst-mode acquisition schemes achieve wide coverage at the expense of a degraded azimuth resolution, reducing, therefore, the performance on the retrieval of ground displacements in the azimuth direction, when interferometric acquisitions are combined. Moreover, the azimuth varying line of sight can induce discontinuities in the interferometric phase when local azimuth displacements are present, e.g., due to ground deformation. In this contribution, we propose the interferometric 2-look terrain observation by progressive scans (TOPS) mode, a sustaining innovation, which records bursts of radar echoes of two separated slices of the Doppler spectrum. The spectral separation allows to exploit spectral diversity techniques, achieving sensitivities to azimuth displacements better than with StripMap and eliminating discontinuities in the interferometric phase. Moreover, some limitations of the TOPS mode to compensate ionospheric perturbations, in terms of data gaps or restricted sensitivity to azimuth shifts, are overcome. The design of 2-look TOPS acquisitions will be provided, taking the TerraSAR-X system as reference to derive achievable performances. The methodology for the retrieval of the azimuth displacement is exposed for the case of using pairs of images, as well as for the calculation of mean azimuth velocities when working with stacks. We include results with experimental TerraSAR-X acquisitions demonstrating its applicability for both scenarios.