Design of validation experiment for analysing impacts of background ionosphere on geosynchronous SAR using GPS signals

Geosynchronous synthetic aperture radar (GEO SAR) is susceptible to the ionosphere due to its ultra-long integration time and ultra-wide coverage, resulting in image defocusing and drift. A design of a validation experiment for analysing ionospheric impacts on GEO SAR focusing using global position system (GPS) signals is presented. The experiment consists of data acquisition and equivalent pre-processing of the GPS signals, along with the following contaminated GEO SAR signal modelling, imaging and evaluation. The key step is the pre-processing part for the equivalent transformation of the recorded data into the space-time frame of GEO SAR. Thereafter, the phase errors induced by the ionosphere in GEO SAR can be generated from the pre-processed GPS data and then incorporated into the simulated GEO SAR signals. Finally, the image focusing and impacts analysis are accomplished. In cases of the current inclined L-band GEO SAR system configuration, the existence of the ionosphere will induce image drifts but these can be corrected through image registration techniques. Another aspect is that the image can be well focused in range direction; however, the azimuth focusing is dependent on the second and higher derivatives of TEC, the thresholds would be determined based on the specific GEO SAR system configuration.