A Floating Optical Buoy (FOBY) for Direct Measurement of Water‐Leaving Radiance Based on the Skylight‐Blocked Approach (SBA): An Experiment in Honghu Lake, China

Abstract

AbstractWater‐leaving radiance (Lw), or remote sensing reflectance (Rrs), is a fundamental parameter of water color remote sensing. However, obtaining accurate and precise measurements of Lw is quite challenging. This study is intended to illustrate the design and implementation of a novel floating optical buoy (FOBY) to measure Lw directly in the field based on the skylight‐blocked approach (SBA). To assess the performance of FOBY, an experiment was conducted in Honghu Lake, China, a typical shallow turbid lake. FOBY‐derived Rrs can characterize the spectral features of different water types including water with kelp as substrate, relatively high chlorophyll‐a contents, and high amounts of suspended sediment (SS). FOBY‐derived Rrs is superior to that from a portable spectroradiometer (PSR 3500+, Spectral Evolution Inc.) based on the conventional above‐surface approach (ASA) in terms of data quality and stability. FOBY measurements had a quality assurance score (QAS) of 0.98 and a mean coefficient of variation (CV) of 3.6–7.0%, while the mean CV for PSR measurements is more than 2 times larger than that of FOBY in the visible domain. The measurement uncertainties may result from self‐shading, sensor tilt, and the immersed depth of the cone (IDC), which deserve further investigations. In the future, long‐term continuous floating observations of different aquatic environments can be conducted using the instrument with well‐refined data quality control.