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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
Author(s) -
Tian Liqiao,
Li Sen,
Li Yong,
Sun Zhaohua,
Song Qingjun,
Zhao Jun
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016322
Subject(s) - buoy , radiance , remote sensing , seawifs , environmental science , ocean color , skylight , spectroradiometer , water quality , moderate resolution imaging spectroradiometer , colored dissolved organic matter , reflectivity , marine engineering , optics , geology , engineering , physics , mechanical engineering , ecology , chemistry , satellite , phytoplankton , organic chemistry , nutrient , biology , aerospace engineering
Water‐leaving radiance ( L w ), or remote sensing reflectance ( R rs ), is a fundamental parameter of water color remote sensing. However, obtaining accurate and precise measurements of L w is quite challenging. This study is intended to illustrate the design and implementation of a novel floating optical buoy (FOBY) to measure L w 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 R rs 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 R rs 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.