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

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.

Surface Water Monitoring Systems—The Importance of Integrating Information Sources for Sustainable Watershed Management

“…Floating buoy stations have been used to measure horizontal movement, moreover, the direction of flow can easily be measured anywhere in an inland water body and is easy to install [49]. Besides, the advantages of floating buoys are their fixed design [50], ability to continuously monitor data rapidly for in-situ measurements, the acquisition of long-term monitoring data, reduced costs [51] and fast measurements [52]. However, the unsteady nature of floating stations as a result of waves reduces the accuracy of their data [49].…”

“…However, the unsteady nature of floating stations as a result of waves reduces the accuracy of their data [49]. Other reasons include the overestimation of the amount of cyanobacterial biomass [50], reduction in the accuracy of data measurements [51] and the minimization of data transmission [52].…”