Overbounding observation errors considering elevation-related distribution characteristics for maritime RT-PPP integrity monitoring

Abstract Integrity monitoring ensures the reliability of Real-Time Precise Point Positioning (RT-PPP) by calculating the Protection Level (PL) in maritime applications. Overbounding the non-ideal observation errors for the PL plays a vital role in suppressing Misleading Information (MI) and improving system availability, including significant non-Gaussian errors such as multipath. The traditional two-step overbounding algorithm always uses a global overbounding coefficient with the largest value to envelop all non-ideal distribution of observation errors. The non-Gaussian errors, like multipath, can cause severe the non-ideal distortion of low-elevation-angle satellite observation errors, leading to the generation of larger overbounding coefficients. Furthermore, the PL can be constructed based on the traditional two-step overbounding algorithm in the position-domain to envelope Positioning Error (PE), and the MI can also be avoided. However, the constructed PL suffers from excessive conservation, and may reduce system availability. Therefore, a non-ideal observation error overbounding method considering elevation-related distribution characteristics is developed for maritime RT-PPP integrity monitoring. The method integrates the two-step overbounding algorithm to determine the differentiated overbounding coefficients related to different elevation intervals. Meanwhile, it is validated using two sets of real maritime experimental data in offshore and ocean areas. The results demonstrate that the developed method generates PL that more closely matches the PE The availability of the integrity monitoring system is improved by 16.18% and 11.88% for the two scenarios, respectively. The developed method can enhance the availability level of integrity monitoring. It can be applied to the dynamic positioning system of offshore vessels, thereby reducing the risks in precise operations.