Abstract
The quality control of remote sensing reflectance (Rrs) is a challenging task in remote sensing applications, mainly in the retrieval of accurate in situ measurements carried out in optically complex aquatic systems. One of the main challenges is related to glint effect into the in situ measurements. Our study evaluates four different methods to reduce the glint effect from the Rrs spectra collected in cascade reservoirs with widely differing optical properties. The first (i) method adopts a constant coefficient for skylight correction (ρ) for any geometry viewing of in situ measurements and wind speed lower than 5 m·s−1; (ii) the second uses a look-up-table with variable ρ values accordingly to viewing geometry acquisition and wind speed; (iii) the third method is based on hyperspectral optimization to produce a spectral glint correction, and (iv) computes ρ as a function of wind speed. The glint effect corrected Rrs spectra were assessed using HydroLight simulations. The results showed that using the glint correction with spectral ρ achieved the lowest errors, however, in a Colored Dissolved Organic Matter (CDOM) dominated environment with no remarkable chlorophyll-a concentrations, the best method was the second. Besides, the results with spectral glint correction reduced almost 30% of errors.
Highlights
The quality assessment of remote sensing reflectances (Rrs ) is an essential task due to the crucial role of Rrs products for water quality monitoring [1,2,3]
The Chl-a concentration ranged from 1.37 mg·m−3 to 797.8 mg·m−3, SPM ranged from 0.10 mg·L−1 to 44 mg·L−1 (Table 4), and most of the samples presented a high composition of particulate organic matter
The Chl-a concentration ranged from 1.37 mg·m−3 to 797.8 mg·m−3, SPM ranged from 0.10 mg·L−1 to 44 mg·L−1 (Table 4), and most of the samples presented a high composition of particulate organic matter (POM), excluding the Nova Avanhandava (NAV)’s samples
Summary
The quality assessment of remote sensing reflectances (Rrs ) is an essential task due to the crucial role of Rrs products for water quality monitoring [1,2,3]. Of the radiometric quantities are registered by remote sensors [4]. Rrs should be carefully measured and post processing must be used to retrieve the most reliable optical information [5]. The Rrs is defined as the ratio of water leaving radiance (Lw , W·m−2 ·sr−1 ·nm−1 ) and the downwelling irradiance (Ed , W·m−2 ·nm−1 ) that reaches the water surface (z = 0+) for a specific viewing geometry (θ, φ that represents zenithal and azimuthal angles, respectively). The Rrs can be defined as the ratio of backscattering (bb ) to the bb plus absorption (a), which are inherent optical properties (IOPs) [6]. Rrs is mathematically described as Equation (1) [7]
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