Characterization Of The South Atlantic Anomaly-induced Frequency Variation Of The Sentinel-3a Ultra-stable Oscillator

A DORIS positioning system was on board the Sentinel-3a satellite launched on 16 February 2016.The ultra-stable oscillator of the system is affected by high energy charged particles trapped by the Van Allen belt when the satellite flies over the South Atlantic region,specifically over the South America.This so-called South Atlantic anomaly phenomena causes a frequency variation and eventually results in a clock error of the oscillator.Satellites such as Jason-1 and SPOT 5 also have encountered this problem.Even though a new improved version of the oscillator has comes up,the problem is much moderated but still exist.In this thesis,the Sentinel-3a Satellites,which also carries a DORIS system,is verified to have a similar problem by comparing its clock offset and frequency offset distribution with a trapped particle radiation model generated from the SPENVIS tool.The geodetic distribution of the Sentinel-3a frequency offset and frequency changing rate is consistent to the distribution of the trapped proton flux of the SPENVIS model.The changes of the two variables along time are also consistent but with a lag,proving that the radiation anomaly have an obvious impact on the frequency variation of the USO.