Research on Enhancement Scheme of GPS Occultation Open-Loop Tracking Strategy

GPS radio occultation detection technology is a new application technology, mainly using GPS for edge detection of the atmosphere and ionosphere. In the low troposphere, it is difficult to track the low tropospheric part (about below 10 km) of the rising occultation using the closed-loop mode. The open-loop mode can effectively overcome the limitations of the closed-loop mode, improving the quality and quantity of low tropospheric occultation observations. The traditional open loop tracking is L1C guided L1P capture, and then L2P capture. The overall design is a serial design, and L2P tracking takes too long. In order to improve the available duration of dual-frequency, this paper optimizes the L2 capture strategy. Through the open-loop prediction, the model pseudo-range placement channel is obtained to get code phase, which directly guides L2P code capture and tracking. At the same time, L1P and L1CA are made into a synchronous code loop, and the L1P code acquisition and tracking process is eliminated to shorten the L2P code acquisition and tracking time, thereby solving the problem of long time to track L2. This article compares the availability of in-orbit data and inversion results of the two tracking schemes, and concludes that the new tracking strategy has increased the available time of dual-frequency data by about 20 s, while increasing the atmospheric dry temperature and dry pressure index profiles below 10 km, which provides effective data support for the low tropospheric atmosphere detection, and at the same time provides verification of tracking algorithms for the development of GNSS occultation receivers.