Chlorophyll-a Retrieval in Turbid Inland Waters Using BC-1A Multispectral Observations: A Case Study of Taihu Lake

Turbid Class II inland waters such as Taihu Lake exhibit a "spectral uplift" effect driven by suspended particulate matter (SPM) scattering and colored dissolved organic matter (CDOM) absorption, which can obscure chlorophyll-a (Chl-a) signals in the visible-red-edge region and challenge retrieval under small-sample, collinear feature settings. Using multispectral observations from the BC-1A satellite (carrying the Lightweight Hyperspectral Remote Sensing Imager, LHRSI) and synchronous satellite-ground in situ measurements acquired over Taihu Lake in late autumn, this study proposes Chl-a-oriented PCA-RF (COP-RF), a leakage-safe inversion framework integrating correlation screening, principal component analysis (PCA), and random forest (RF) regression. Candidate band-combination features are generated, and PCA is applied for orthogonal compression to mitigate collinearity before RF learning. A stratified five-fold cross-validation based on Chl-a quantile bins is adopted, with screening, standardization, and PCA fitted only on training folds. COP-RF achieves stable performance under the current dataset (R2=0.671, RMSE =1.80μg/L, MAE =1.25μg/L). Spatial inversion shows higher Chl-a near shores and bays and lower values in the lake center, consistent with Sentinel-2 hotspot ranks.