Quality Control of Cygnss GNSS-Reflectivity for Robust Spatio-Temporal Detection of Tropical Wetlands.

The aim of this study is to develop a robust methodology evaluating spatio-temporal dynamics of inundation status in tropical wetlands with currently available Global Navigation Satellite System Reflectometry (GNSS-R) data by proposing a new quality control technique "precision index". The study is applied over the Mekong delta, one of the most important rice production system, while consisting of aquaculture and natural wetlands (e.g., mangrove forest, peatlands). CyGNSS constellation [1] data (2018 August-2021 December) were used to evaluate spatio-temporal dynamics of the coherent reflectivity G over the delta. Firstly, reflectivity G, shape and size of each specular foot-print, and precision index were calibrated in each specular point and reprojected on 500m resolution grid with daily temporal resolution (Lv.2 product), which considers various bias causing factors (i.e., velocity/effective scattering area/incidence angle). The Lv. 2 product was temporally integrated at every 15-days with Kalman smoother (+/- 14 days temporal localization with gaussian kernel: 1s=5 days). By applying the smoother considering the difference of incidence angle, regional-annually dynamics over the delta was clearly visualized A discussion of the GNSS-R results consistency with the spatio-temporal pattern observed by SAR data is reported.