Resolving Diurnal Variability in Water Constituents from Above-Water Radiometry

Abstract

Diurnal change in biogeochemical variables such as phytoplankton populations and turbidity has important implications in marine ecosystem. The diurnal variation in surface water constituents can be inferred by radiometric measurement made from above the water. Retrieval of water constituent concentration from above-water radiometry involves (1) pre-processing of radiometric measurements (e.g. sun/sky-glint removal, angular correction with bidirectional reflectance distribution function (BRDF)), and (2) application of inversion algorithms that enables the estimation of water constituents from remote sensing reflectance (Rrs). To retrieve reliable time series of diurnal variation in biogeochemical variables, it is critical to verify that the process/algorithm are robust for sun angle changes and other changes in ambient conditions.

In this study, we use in-situ measurements of both water constituents and radiometric measurements for diurnal cycles, and analyze the diurnal stability of the Rrs estimation and the water constituent retrieval processes. In the field campaign conducted during May. 20-June 6, 2016 around oceans around Korea Peninsula, biogeochemial variables such as chlorophyll-a and suspended particulate matters (SPM) concentrations, and absorption by chlorophyll-a, gelbstoff, and non-algal particles were measured. Radiometric observation for both in-water and above-water radiometry were acquired by Prof