ABSTRACT
The LT4A satellite is the world's first IGSO satellite capable of receiving GPS and BDS signals. It is also the world's first SAR satellite in high orbit. Based on the received GNSS data, the data availability and measurement quality were first analyzed, and then the accuracy of the 30-h and 72-h arc length orbit determination results were verified using the orbit overlap method and the laser ranging verification method. According to the data analysis, the onboard receiver of the LT4A satellite can receive an average of 3.9 GPS satellites and 4.0 BDS satellites in a single epoch. The PDOPs of GPS observations, BDS observations, and combined GPS + BDS observations are 21.66, 25.96, and 15.81, and the number of epochs with more than four satellites is 32.6%, 37.6%, and 98.5% of the total epochs. The cycle slip ratios of the GPS and BDS observations are 6.3% and 28.9%, the pseudo-range noise is 1.75 m and 0.95 m, the carrier phase noise is 0.46 mm and 0.35 mm, and the average CNR are 44.6 dB-Hz and 46.9 dB-Hz, respectively. When only GPS observations, only BDS observations, and combined GPS + BDS observations are used, the average RMS of the overlapping results for the 30-h arcs is 4.091 m, 4.319 m, and 2.274 m, and the laser range verification results are 0.994 m, 0.978 m, and 0.277 m. The average RMS of the overlapping results for the 72-h arcs is 3.242 m, 3.199 m, and 1.807 m, and the laser ranging verification results are 0.527 m, 0.687 m, and 0.356 m. The onboard real-time orbit was used for observations to determine the orbit, resulting in a 95.4% improvement in the RMS of the original real-time orbit.