Liu, Y; Xiao, CC; Li, JS; Zhang, FF; Wang, SL (2020). Secchi Disk Depth Estimation from China's New Generation of GF-5 Hyperspectral Observations Using a Semi-Analytical Scheme. REMOTE SENSING, 12(11), 1849.

Water clarity, commonly measured as the Secchi disk depth (Z(sd)), is an important parameter that depicts water quality in aquatic ecosystems. China's new generation Advanced HyperSpectral Imager (AHSI) on board the GF-5 satellite has significant potential for applications of more accurate water clarity estimation compared with existing multispectral satellite imagery, considering its high spectral resolution with a 30-m spatial resolution. In this study, we validate the semi-analytical model with various Quasi-Analytical Algorithms (QAA), including QAAV5, QAAV6, QAAL09 and QAAM14, for the AHSI images with concurrent in situ measurements in four inland water bodies with a Z(sd) range of 0.3-4.5 m. The semi-analytical method with QAAV5 can yield the most accurate Z(sd) predictions with approximated atmospheric-corrected remote sensing reflectance. For 84 concurrent sampling sites, the estimated Z(sd) had a mean absolute error (MAE) of 0.35 m, while the mean relative error (MRE) was 25.3%. Specifically, the MAEs of estimated Z(sd) were 0.22, 0.46, and 0.24 m for Z(sd) of 0.3-1, 1-3, and 3-4.5 m, respectively. The corresponding MREs were 33.1%, 29.1% and 6.3%, respectively. Although further validation is still required, especially in terms of highly turbid waters, this study indicates that AHSI is effective for water clarity monitoring.