Assessment of regional satellite navigation systems in GNSS reflection experiments

Recently, the potentials of GNSS signals as sources for remote sensing have been investigated and verified through some ground-based and airborne experiments. In particular, the GNSS reflection can potentially be used in altimetry, sea-wind retrieval, seawater salinity detection, tsunami warning, ice-layer density measurement, humidity measurement of land, and detection of moving targets. In Asia-Pacific region, the deployment of Japanese QZSS and Chinese Beidou has created some impacts on the enhancement on the positioning, navigation, and timing service. The paper assesses the use of these regional satellite navigation systems (RNSSs) together with global navigation satellite systems (GNSSs) for space mission. In the past, the joint Taiwan-US FORMOSAT-3/COSMIC mission for meteorological, climatological, ionospheric, and geodetic studies has successfully provided a significant amount of GPS radio occultation (RO) data for better modeling of climate model, forecasting of weather, and monitoring of ionosphere. Owing to the success of the FORMOSAT-3 program, the FORMOSAT-7/COSMIC-2 mission attempts to explore signals from multiple GNSSs as well as several RNSSs and space-based augmentation systems (SBASs) to facilitate the operational capability for weather forecast and space weather monitoring. In the FORMOSAT-7 mission, a concept that is under investigation is the use of these navigation signals for spaceborne reflection experiments. In the paper, a mission analysis is performed to assess the reflection events with respect to the RNSSs/SBASs and GNSSs. It is shown that signals from RNSSs/SBASs are more reliable sources from the perspective of reflection experiments in terms of viewing geometry, repeatability, and duration of each profile.