Directional and angular effects on the spectral reflectance of waters with variable amounts of total suspended solids

Fábio M. Breunig; Waterloo Pereira Filho; Lênio S. Galvão; Edison Alberti; Joceli Gross

doi:10.1117/1.JRS.13.024524

10 June 2019 Directional and angular effects on the spectral reflectance of waters with variable amounts of total suspended solids

Fábio M. Breunig, Waterloo Pereira Filho, Lênio S. Galvão, Edison Alberti, Joceli Gross

Author Affiliations +

Journal of Applied Remote Sensing, Vol. 13, Issue 2, 024524 (June 2019). https://doi.org/10.1117/1.JRS.13.024524

Abstract

Viewing geometry is one of the most important factors to consider when water bodies are observed from satellite sensors with large field of view. We examine the directional and angular effects on the reflectance of waters with different concentrations of total suspended solids (TSSs). In the laboratory, we measure the reflectance in five view zenith angles (VZAs) and eight view azimuth angles (VAAs) for optically shallow waters having four concentrations of TSSs. Seven empirical models to estimate TSSs based only on the reflectance of the red band (∼660 nm) are evaluated. In addition, we analyze Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra reflectance measured in 13 consecutive satellite overpasses. The results show that the reflectance of the inland-like water is affected by data acquisition geometry. The best wavelength to estimate TSS is 625 nm for most VZAs and VAAs. The lowest correlations between reflectance and TSS are observed at extreme viewing with the anisotropy decreasing with increasing concentrations of TSSs. Directional and angular effects are also observed for MODIS (acquired and simulated data) with TSS underestimates observed close to the orthogonal plane for all VZAs, and TSS overestimates observed in the principal scattering plane in the forward scattering direction. More anisotropic waters are observed for VZA greater than ±30 deg. Results highlight the need for correcting MODIS data for bidirectional effects in inland water studies.

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Fábio M. Breunig, Waterloo Pereira Filho, Lênio S. Galvão, Edison Alberti, and Joceli Gross "Directional and angular effects on the spectral reflectance of waters with variable amounts of total suspended solids," Journal of Applied Remote Sensing 13(2), 024524 (10 June 2019). https://doi.org/10.1117/1.JRS.13.024524

Received: 21 December 2018; Accepted: 20 May 2019; Published: 10 June 2019

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KEYWORDS

Reflectivity

MODIS

Data acquisition

Data modeling

Scattering

Anisotropy

Solids

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