Determining switching threshold for NIR-SWIR combined atmospheric correction algorithm of ocean color remote sensing

Accurate atmospheric correction is decisive for ocean color remote sensing applications. Near infrared (NIR)-based algorithm performs well for clear waters; while shortwave infrared (SWIR)-based algorithm can obtain good results for turbid waters, however, it tends to produce noisy patterns for clear waters. A practical strategy is to apply NIR- and SWIR-based algorithm for clear and turbid waters, respectively, which is called NIR-SWIR combined atmospheric correction algorithm. However, the currently applied switching scheme for the NIR-SWIR algorithm undermines the atmospheric correction performance. This study aimed to find an applicable switching scheme for NIR-SWIR algorithm. Four MODIS land bands were used to switch the NIR- and SWIR-based algorithms. A simulated dataset was used to evaluate atmospheric performance of NIR- and SWIR-based algorithm. The switching threshold for each MODIS land band was determined as an R_rs value at which SWIR-based algorithm performed better than NIR-based algorithm. The switching scheme was evaluated using matchups of simultaneous MODIS Aqua images and AERONET-OC data, and then tested with a MODIS Aqua image over the western Pacific Ocean. Results showed that the switching threshold for R_rs(469), R_rs(555), R_rs(645)and R_rs(859)were 0.009, 0.016, 0.009 and 0.0006 sr⁻¹, respectively; R_rs(645)with a threshold of 0.009 sr⁻¹ and R_rs(555)with a threshold of 0.016 sr⁻¹ worked well for NIR-SWIR algorithm, while R_rs(469)and R_rs(859)produced worse performance. Therefore, R_rs(555)> 0.016 sr⁻¹ or R_rs(645)> 0.009 sr⁻¹ was recommended as the switching scheme for NIR-SWIR algorithm. Considering contrasted estuarine, coastal and some inland waters, combining NIR- and SWIR-based atmospheric correction algorithm with the proposed switching scheme should be useful for remote sensing monitoring over these waters.