Tianmu-1 Constellation GNSS-R In-Orbit Performance: Spatiotemporal Characteristics, Product Applications, and Polarimetric Features
Feixiong Huang, Cong Yin, Yan Liu, Yueqiang Sun, Junming Xia, Weihua Bai, Qi Tang, Xianyi Wang, Qifei Du, Yuerong Cai, Zhuoyan Wang, Cheng Liu, Hao Zhang, Peng Hu, Ruhan Wu, Guangyuan Tan, Hao Qiao, Fu Li, Congliang Liu, Xiangguang Meng, Xiuqing Hu
Abstract
This paper introduces the Chinese Tianmu-1 GNSS-R constellation of 22 small satellites launched in 2023–2024 and comprehensively evaluates the latest version of the in-orbit data. First, the mission design and instrument technology are described, which largely builds on the Fengyun-3/GNOS-II missions. Notable innovations include full-GNSS compatibility and dual-polarization antenna. Then, the spatiotemporal characteristics of the constellation are analyzed—specifically, coverage percentage and mean revisit time at different latitudes. Next, the accuracy of its science products including ocean surface winds and land soil moisture has been assessed, with two application cases demonstrating the mission’s utility for monitoring tropical cyclones and flooding. Finally, this paper for the first time evaluates Tianmu’s polarized observations including Horizontal (H), Vertical (V), Left-Hand Circularly-Polarized (LHCP) and Right-Hand Circularly-Polarized (RHCP). Analysis of the signal-to-noise ratio and reflectivity shows that the dual-polarimetric observations follow the trend of theoretical models and hold promise for advancing land remote sensing.