GLOBAL VS LOCAL RANDOM FOREST MODEL FOR WATER QUALITY MONITORING: ASSESSMENT IN FINGER LAKES USING SENTINEL-2 IMAGERY AND GLORIA DATASET

Machine learning (ML) methods such as Random Forest (RF) have shown promises to estimate Secchi Disk Depth (Zsd). However, lack of a comprehensive dataset has been a long-lasting issue for training ML models in remote sensing of water quality. To aid the training process, the GLORIA dataset has recently provided access to hyperspectral in-situ measurements of remote sensing reflectance (Rrs) along with associated water quality parameters for globally representative inland and coastal waters. We use simulated Sentinel-2 Rrs to train a global model using GLORIA and then validate it on independent data from Finger Lakes, USA. When compared to RF model trained on Finger Lakes data, the validation results indicate better performance (Mean Absolute Error (MAE) 37%) as compared to the global model trained on GLORIA ( MAE 94%). However, when the global model was validated on independent dataset from GLORIA (i.e. Lake Erie), the results were promising (MAE 34%). Therefore, the models can be used to estimate Zsd globally, provided the uncertainties in deriving satellite based Rrs are accounted for.