Sunglint Detection for Unmanned and Automated Platforms

Abstract

We present an empirical quality control protocol for above-water radiometric sampling focussing on identifying sunglint situations. Using hyperspectral radiometers, measurements were taken on an automated and unmanned seaborne platform in northwest European shelf seas. In parallel, a camera system was used to capture sea surface and sky images of the investigated points. The quality control consists of meteorological flags, to mask dusk, dawn, precipitation and low light conditions, utilizing incoming solar irradiance (ES) spectra. Using 629 from a total of 3,121 spectral measurements that passed the test conditions of the meteorological flagging, a new sunglint flag was developed. To predict sunglint conspicuous in the simultaneously available sea surface images a sunglint image detection algorithm was developed and implemented. Applying this algorithm, two sets of data, one with (having too much or detectable white pixels or sunglint) and one without sunglint (having least visible/detectable white pixel or sunglint), were derived. To identify the most effective sunglint flagging criteria we evaluated the spectral characteristics of these two data sets using water leaving radiance (LW) and remote sensing reflectance (RRS). Spectral conditions satisfying ‘mean LW (700–950 nm) < 2 mW·m−2·nm−1·Sr−1’ or alternatively ‘minimum RRS (700–950 nm) < 0.010 Sr−1’, mask most measurements affected by sunglint, providing an efficient empirical flagging of sunglint in automated quality control.

Physical, Bio-Optical State and Correlations in North–Western European Shelf Seas

“…It is presumed that perceived color of seawater in the NWES is strongly driven by CDOM and SPM although chl-a plays a seasonal and local role for example in the Central North Sea [32][33][34][35]. In situ station (blue dots) sampling was done in the German Bight (1)(2)(3)(4)(5)(6)(7)(8), North Sea (9-26), Inner Seas (27)(28)(29)(30)(31)(32)(33)(34), Irish Sea (35)(36)(37)(38)(39)(40)(41)(42)(43), and Celtic Sea (44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60). Region naming is based on maps from The Germany Federal Maritime and Hydrographic Agency [34] and International Hydrographic Organization [35].…”

“…A detailed description of the instrumental setup and quality control of measurements is presented in a previous study [36]. The quality control involved eliminating contaminated measurements, i.e., those taken at dusk and dawn before significant incoming solar radiation could be detected, under rainfall, or with excessive glint as detected by an image algorithm [36].…”

“…A detailed description of the instrumental setup and quality control of measurements is presented in a previous study [36]. The quality control involved eliminating contaminated measurements, i.e., those taken at dusk and dawn before significant incoming solar radiation could be detected, under rainfall, or with excessive glint as detected by an image algorithm [36]. To compute water leaving radiance L W (θ sfc , Φ, λ) and remote sensing reflectance R RS (θ, Φ, λ), surface reflected glint correction was implemented according to a recent protocol [37] with the basic Equation (1):…”

Automatic Assessment of Acquisition and Transmission Losses in Indian Remote Sensing Satellite Data

“…Sunglint is a transient anomaly that occurs when sunlight is reflected from the seawater surface directly into the down looking optical sensor (Garaba et al, 2012). In order to eliminate this uncertainty in detecting impulse noise, sun glint was also detected using SWIR band (1.55 -1.75 microns) data of AWiFS sensor.…”

A research port test bed based on distributed optical sensors and sensor fusion framework for ad hoc situational awareness

“…This has to be considered especially in mobile applications, where the covered scenes can change rapidly. In the case of interference, the video image information of sea surface conditions, like the presence of reflected sunlight, could even be useful for supplementary quality information and flagging criteria for above-water optical measurement systems (Garaba et al, 2012(Garaba et al, , 2013.…”