Determination of the Downwelling Diffuse Attenuation Coefficient of Lake Water with the Sentinel-3A OLCI

Abstract

Abstract:The Ocean and Land Color Imager (OLCI) on the Sentinel-3A satellite, which was launched by the European Space Agency in 2016, is a new-generation water color sensor with a spatial resolution of 300 m and 21 bands in the range of 400-1020 nm. The OLCI is important to the expansion of remote sensing monitoring of inland waters using water color satellite data. In this study, we developed a dual band ratio algorithm for the downwelling diffuse attenuation coefficient at 490 nm (K d (490)) for the waters of Lake Taihu, a large shallow lake in China, based on data measured during seven surveys conducted between 2008 and 2017 in combination with Sentinel-3A-OLCI data. The results show that: (1) Compared to the available K d (490) estimation algorithms, the dual band ratio (681 nm/560 nm and 754 nm/560 nm) algorithm developed in this study had a higher estimation accuracy (N = 26, coefficient of determination (R 2 ) = 0.81, root-mean-square error (RMSE) = 0.99 m −1 and mean absolute percentage error (MAPE) = 19.55%) and validation accuracy (N = 14, R 2 = 0.83, RMSE = 1.06 m −1 and MAPE = 27.30%), making it more suitable for turbid inland waters; (2) A comparison of the OLCI K d (490) product and a similar Moderate Resolution Imaging Spectroradiometer (MODIS) product reveals a high consistency between the OLCI and MODIS products in terms of the spatial distribution of K d (490). However, the OLCI product has a smoother spatial distribution and finer textural characteristics than the MODIS product and contains notably higher-quality data; (3) The K d (490) values for Lake Taihu exhibit notable spatial and temporal variations. K d (490) is higher in seasons with relatively high wind speeds and in open waters that are prone to wind-and wave-induced sediment resuspension. Finally, the Sentinel-3A-OLCI has a higher spatial resolution and is equipped with a relatively wide dynamic range of spectral bands suitable for inland waters. The Sentinel-3B satellite will be launched soon and, together with the Sentinel-3A satellite, will form a two-satellite network with the ability to make observations twice every three days. This satellite network will have a wider range of application and play an important role in the monitoring of inland waters with complex optical properties.

Remote Sensing Estimation of Lake Total Phosphorus Concentration Based on MODIS: A Case Study of Lake Hongze

“…Therefore, the key water quality parameters that affect the TP concentration is the SPIM in Lake Hongze. The average concentration of the Chla in Lake Hongze was 14 ug/L, which is much lower than that in other lakes in East China, such as Lake Taihu [17,45] and Lake Chaohu [63], which are basically above 20 ug/L. There was no significant correlation between the Chla and TP, and the low Chla concentration in Lake Hongze indicates that P mainly comes from the sediment, not microorganisms.…”

“…Due to the low reflectance of the water body, around 10% of the effective information received by the satellite is from the atmosphere, hence the atmospheric correction is an important part of the water color remote sensing [12,66]. It is difficult to obtain highly accurate R rs values from satellite images of extremely turbid inland waters due to the complex optical conditions, from elevated concentrations of optically active substances to algal blooms [17,67,68]. Since the existing atmospheric correction methods are mainly aimed at relatively clean ocean waters, their applicability is not very appropriate to the study of the inland water quality parameters [5,66,69].…”

“…The concentration and composition of the Chla and SPM will not only affect the optical properties of the lake, but it will also affect the TP concentration [16,17,45]. In order to analyze the influence on the accuracy of the algorithm, the substance concentration and ratio was ranked in an ascending order, each 20 samples were divided into a group, with five samples at the intervals.…”

“…When the proportion of the SPIM in the SPM increases, the microbial concentration decreases. Algae particles, which have a strong influence on the inherent optical properties of a water body, are often important factors affecting the estimation of the water color parameters by remote sensing [17], thus the accuracy of the algorithm will increase rapidly. However, when the proportion of the SPIM in the SPM exceeds 78%, the accuracy of the algorithm shows a downward trend (Figure 6d).…”

“…The TP could affect the growth and reproduction of plankton in the water [13], in addition, TP is associated with optical active constituents (OACs) in the water, including the SPM, Chla and chromogenic dissolved organic matter (CDOM) [12,14,15]. These three substances are the main substances that determine the optical characteristics of the water bodies [16][17][18]. Many studies have found the relationship between the spectral reflectance and TP by statistical methods, but there is no unified conclusion [19][20][21].…”