**2. Materials and Methods**

This study consists of (1) the introduction of the "precision index" for use in the quality control assessment of GNSS-R data; (2) a daily rasterization demonstration over the Mekong Delta based on the precision index obtained from the Lv. 2 product; (3) a demonstration of the temporal Kalman smoother over the Mekong Delta using the precision index as the reciprocal number of observation errors (Lv. 3 product); and (4) cross-validation with PALSAR-2 quadruple polarimetric data that have been preprocessed with a polarimetric decomposition method and ground observation data. A flowchart presenting the methodology of this study is illustrated in Figure 1.
