Experimental validation for impacts of temporal-spatial variant ionosphere on GEO SAR using GNSS satellite signals

Geosynchronous SAR (GEO SAR) is susceptible to ionosphere due to the ultra-long integration time and ultrawide coverage, resulting in image defocusing and image drift. This paper demonstrates a validation experiment of analysing ionospheric impacts on GEO SAR focusing. The validation experiment consists of data acquisition of the global navigation satellites system (GNSS) satellites signals (including GPS and Beidou IGSO satellites), equivalent pre-processing, GEO SAR signal modelling, image focusing and evaluating. The recorded data are equivalently transformed into the space and time frame of GEO SAR. Then the phase errors induced by ionosphere in GEO SAR can be generated from the equivalently preprocessed data and then incorporated into the GEO SAR signals. The following image focusing and the impacts analysis are accomplished. In cases of the current GEO SAR system configuration, the existence of ionosphere will induce image drifts but can be corrected through image registration techniques. In other aspects, the image can be well focused in range direction. But for the azimuthal focusing, the second and higher derivatives of TEC will result in defocusing and the thresholds of wellfocusing are dependent on the specific GEO SAR system configuration.