SPOT-5 DORIS oscillator instability due to South Atlantic Anomaly: Mapping the effect and application of data corrective model Original Research Article

South Atlantic Anomaly (SAA) affects the astronomical satellites and other spacecraft that orbit the Earth at several hundred kilometers altitude; these orbits take satellites through the anomaly periodically, exposing them to several minutes of strong radiation. The SAA-related frequency shift of Jason-1 DORIS oscillator is well known and the corresponding studies were published in the past. Recent analyses indicate that SPOT-5 DORIS oscillator is probably also affected, even if with lower influence. The first goal of this study is to obtain some evidence of the SAA effect on the SPOT-5 DORIS oscillator; this was carried out by analyzing frequency estimates and post-fit residuals. Furthermore, geographical grid maps are presented, displaying the estimated oscillator frequency drift and its time derivative.The second goal of the paper is to present an empirical DORIS observation corrective model, based on the application of the frequency drift derived from the previously created grid map. Analyses of the post-fit residuals, zenithal tropospheric delay and station height bias confirm that the application of the data corrective model strongly reduces the SAA bias. Despite the fact that the data corrective model significantly improves the solution and compensates most of the data corruption, the total elimination of SAA-related bias was not achieved. The last part of the paper is analyzing the long term changes of the SAA effect on the SPOT-5 DORIS observations. The results confirm that the SAA effect was significantly rising during the period 2008.0–2012.0 and that during these 4 years it has doubled in size.