Analysis of space-borne GNSS radio occultation events prediction
Aiming at the problem that the durations of space-borne global navigation satellite system(GNSS)radio occultation events are usually only a few tens of seconds,especially for rising occultation events,where the negative elevation angle satellite signal are required to be captured and tracked as soon as the occultation event started,to obtain timely and effective occultation observation duration,based on the tracking of open-loop occultation signals assisted by priori orbital information,the paper proposed a fast prediction method,which reconstruct the basis of tangent height to assist occultation receiver in capturing and tracking GNSS occultation signals in order to ensure the high quality and effective duration of the occultation observations:the local curvature center of the Earth was corrected to obtain more accurate tangent height;and the judgement conditions for occultations were set and the extreme values were used to quickly predict the events that meet the threshold;finally the global center and radius of curvature were analyzed.Experimental result showed that the center of curvature could be corrected up to a maximum distance of 45 km and the radius of curvature fluctuates within a range of 65 km,which could be sufficient to affect the accuracy of occultation prediction.Simulational results based on the measured data of the constellation observing system for meteorology ionosphere and climate(COSMIC-2)revealed that the false negatives rate of global positioning system(GPS)and global navigation satellite system(GLONASS)occultations would be below 3%and about 14.5%,respectively,and the start time of predicting occultations would be mostly about 5～10 s earlier,which indicated that the tangent height-based occultation predicting method proposed in this paper could be effectively used for predicting satellite-based occultation events,for assisting the receiver in the capturing and tracking of GNSS occultation signals,and improving the data volume and effective observation duration of occultation observations.
global navigation satellite system(GNSS)radio occultationoccultation predictionEarth oblateness correctionopen-loop signal trackingconstellation observing system for meteorology ionosphere and climate(COSMIC-2)
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