An improved algorithm for estimating the Secchi disk depth from remote sensing data based on the new underwater visibility theory

Abstract

The Secchi disk depth (ZSD) is a widely used parameter for evaluating water clarity. Here we propose an improved algorithm, which is based on a new underwater visibility theory, for retrieving more accurate ZSD from remote sensing reflectance (Rrs) in various waters. Two improvements were carried out in the new algorithm. First, we used a hybrid quasi-analytical algorithm (QAA_hybrid) instead of the sixth version of QAA (QAA_v6) for retrieving more accurate total absorption coefficient ( (λ)) and total backscattering coefficient ( (λ)) even in turbid inland waters. Second, we used a dynamic / ratio (i.e., ratio of diffuse attenuation coefficient of upwelling radiance and diffuse attenuation coefficient of downwelling irradiance) instead of using the fixed ratio (i.e., 1.5). The results obtained from in situ Rrs show that the improved ZSD estimation algorithm gave more accurate ZSD estimations, with the root mean square error (RMSE) reduced from 0.2 to 0.1 in log10 unit, mean absolute percentage error (MAPE) reduced from 39 % to 20 % (N=178 with in situ ZSD values between 0.3 -20.8 m). We then applied the improved ZSD estimation algorithm to the 2003-2012 MERIS images for Lake Kasumigaura to further confirm the performance of the improved ZSD estimation algorithm. The 2 results obtained from 19 matchups demonstrate that the estimated ZSD matched well with the in situ ZSD, with the RMSE of 0.11 m and the MAPE of 15%. The improved ZSD estimation algorithm shows a potential to estimate more accurate ZSD values from remote sensing data in various waters.

Optimización del monitoreo de la transparencia del agua, por medio de MOD09GA

“…El procedimiento se repitió excluyendo, a su vez, todos los N pares disponibles. Adicionalmente, para verificar la validez del modelo, se utilizaron los estimadores estadísticos R 2 y rmse (detalles del procedimiento en [35], [48]- [51]).…”

“…La banda centrada en los 858,5 nm (banda 2) tiene una aplicación más práctica en la estimación del total de los sólidos en suspensión en aguas interiores [32]- [34]. Sin embargo, esta misma longitud de onda puede ser utilizada en la derivación de valores de la pds, teniendo en cuenta que la turbidez del agua está directamente relacionada con las medidas que pueden obtenerse con el disco de Secchi [33], [35]- [37].…”

Retrieval of Secchi Disk Depth in Turbid Lakes from GOCI Based on a New Semi-Analytical Algorithm

“…Four turbid waters-Lake Dongting (28 • 31 E)-are observed in our study. As the second, third, and fourth largest freshwater lakes in China, Lake Dongting, Lake Taihu, and Lake Hongze have water areas of~2794 km 2 ,~2338 km 2 , and~1577 km 2 , respectively ( Figure 1). Lake Erhai is the second largest freshwater lake in Yunnan Province.…”

“…Traditional methods of estimating Z SD largely depend on cruise surveys, which are laborious and time-consuming. The large coverage characteristics of satellite data makes it a perfect tool for describing the spatial and temporal variability of Z SD [2].…”

“…The Z SD of Lake Taihu and Lake Hongze were estimated based on in-situ data and GOCI images to improve the algorithm of retrieving Z SD in inland turbid water. The main objectives of this study were: (1) to develop a new semi-analytical algorithm of Z SD for inland turbid waters, (2) compare the performance of the new scheme with the existing semi-analytical algorithm, and (3) to obtain the spatiotemporal dynamic characteristics of Z SD from GOCI observations.…”