Applicability evaluation of Landsat-8 for estimating low concentration colored dissolved organic matter in inland water

Inland waters, characterized by small scale but a large number, play an important role in the carbon budget and global carbon cycle. Colored dissolved organic matter (CDOM) is a significant indicator used for tracing dissolved organic carbon (DOC) in inland waters. Accurate remote-sensing estimation of CDOM concentration is still a challenge due to complex optical properties of inland waters. Many efforts have been made to estimate high concentration CDOM, leading to a knowledge gap in using remote sensing to estimate low concentration CDOM, which results in difficulty and uncertainty for estimating total carbon storage in global inland waters. Currently, few studies are devoted to estimating low concentration CDOM, while Landsat-8's applicability for estimating low concentration CDOM is still unknown. In this study, two datasets, NRL_SFE and Lake_Erie, were collected to represent extremely low CDOM conditions that a(CDOM) (440) (the absorptions of CDOM at 440 nm) ranges 0.215-1.165 m(-1), and 0.066-1.242 m(-1), respectively. The best CDOM retrieval model (validation results: R-2 = 0.78; RMSE = 0.161 m(-1); MRE = 26.02%), a(CDOM)(440) = 0.483x(-1.776), x = R-rs(B2)/R-rs(B4), was developed for monitoring CDOM in the two regions. Results show that Landsat-8 and the best model work well for estimating low concentration CDOM in inland waters. In addition, we have proved that Landsat-8 surface reflectance products, which are freely provided by USGS, are convenient and useful for developing remote sensing algorithm of CDOM estimation after correcting water surface reflectance. The image-derived CDOM's spatial patterns in Lake Erie demonstrate the Landsat-8's applicability to observe spatiotemporal variations of low concentration CDOM.