On the measurement of remote sensing reflectance by a traditional above-water approach in small water bodies

Small water bodies are an important part of the Earth’s freshwater system, protecting biodiversity and providing ecosystem services. Because of various surrounding features, it is unknown to what extent we can obtain accurate remote-sensing reflectance ( R rs ) of such an environment by the conventional above-water approach (AWA). In this study, we used both AWA and the skylight-blocked approach (SBA) side-by-side to measure R rs in a typical small water body. It was found that the variation of R rs in the UV-blue domain from AWA is around 50% and is inconsistent with the variation of the total absorption coefficient ( a t ) obtained from water samples; on the contrary, the variation of R rs obtained from SBA is highly consistent, with a coefficient of variation under ∼ 5 % . These results highlight the large uncertainties in the measured R rs from AWA due to the complexity of such an environment and further echo the robustness of SBA to measure R rs in the field, even in such challenge environments.