Abstract
The accurate remote estimation of the Secchi disk depth (ZSD) in turbid waters is essential in the monitoring the ecological environment of lakes. Using the field measured ZSD and the remote sensing reflectance (Rrs(λ)) data, a new semi-analytical algorithm (denoted as ZSDZ) for retrieving ZSD was developed from Rrs(λ), and it was applied to Geostationary Ocean Color Imager (GOCI) images in extremely turbid waters. Our results are as follows: (1) the ZSDZ performs well in estimating ZSD in turbid water bodies (0.15 m < ZSD < 2.5 m). By validating with the field measured data that were collected in four turbid inland lakes, the determination coefficient (R2) is determined to be 0.89, with a mean absolute square percentage error (MAPE) of 22.39%, and root mean square error (RMSE) of 0.24 m. (2) The ZSDZ improved the retrieval accuracy of ZSD in turbid waters and outperformed the existing semi-analytical schemes. (3) The developed algorithm and GOCI data are in order to map the hourly variation of ZSD in turbid inland waters, the GOCI-derived results reveal a significant spatiotemporal variation in our study region, which are significantly driven by wind forcing. This study can provide a new approach for estimating water transparency in turbid waters, offering important support for the management of inland waters.
Highlights
Water transparency, which has been widely and regularly measured with Secchi disk in both limnology and oceanography, is key information for assessing the water quality and trophic state
(3) The developed algorithm and Geostationary Ocean Color Imager (GOCI) data are in order to map the hourly variation of ZSD in turbid inland waters, the GOCI-derived results reveal a significant spatiotemporal variation in our study region, which are significantly driven by wind forcing
The parameters from these lakes showed a coefficient of variation (CV) between 17.36% and 142.64%, which indicated high dynamic ranges and substantial variability amongst the samples in the study areas
Summary
Water transparency, which has been widely and regularly measured with Secchi disk in both limnology and oceanography, is key information for assessing the water quality and trophic state. Secchi disk depth (ZSD, m) is the depth at which the disk, lowered from the surface, is no longer visible to the observer, and is a measure of transparency or vertical visibility in the water body. Traditional methods of estimating ZSD 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 ZSD [2]. Substantial efforts, which are based on remote sensing methods, have been made to obtain ZSD for describing the spatiotemporal variability of water properties in marine, coastal, and inland waters [3,4,5,6,7]
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