资源环境科技发展态势分析平台

Knowledge of the variation and regulation of the diffuse attenuation coefficient is important for management of lake water quality and ecological environments. Data were collected seven times (378 samples) from 2006 to 2011 in Lake Taihu to improve the existing semianalytical model of diffuse attenuation coefficient at 490 nm (K-d(490)) by measuring in situ K-d(490) and remote sensing reflectance (Rrs). This semianalytical model was applied to determine the long-term variation of K-d(490) and its driving factors from Moderate Resolution Imaging Spectroradiometer (MODIS) images. Our semianalytical model of K-d(490) improves the retrieval accuracy of K-d(490) from 29.60% to 22.58% (root-mean-square percentage error) and 24.28 +/- 18.54% (mean value +/- standard deviation) to 19.29 +/- 14.34% (mean absolute relative error). The K-d (490) from maps produced from MODIS images clearly present the temporal and spatial variations of K-d(490). This indicates the suitability of using the improved semianalytical model and MODIS to observe K-d(490) in turbid shallow inland waters. Long-term MODIS observation of K-d(490) shows distinct seasonal and spatial variations. Temporally, the highest and the lowest K-d(490) were found in winter and in summer, respectively. Spatially, high K-d(490) values were primarily distributed in the southwestern and northwestern Lake Taihu, and relatively low K-d(490) values were distributed in Meiliang Bay and Gonghu Bay (the eastern part of the lake and East Bay were excluded in this study due to invalid retrieval results of K-d(490)). Many covarying points were found between K-d(490) and maximum wind speed from long-term observations, suggesting that wind-induced sediment resuspension is the principal driver of high K-d(490). Correlation was also observed between K-d(490) and heavy rainfall events, suggesting the regulating effect of heavy rainfall.