A comparison between above-water surface and subsurface spectral reflectances collected over inland waters

Abstract

The objective of the research was to undertake a quantitative comparison of spectral-reflectance measurements made slightly above the surface of water bodies with the measurements made slightly below the surface. The study is focused on three rivers; two in Georgia, USA and one in Japan. As expected, the differences in reflectance are not constant and vary with the wavelength. The contribution of surface-reflection effects to the surface reflectance measured slightly above the water is both pronounced and highly variable, but although they do alter the magnitude of the upwelling signal, they do not change the general shape of the spectral profiles. The correction of surface-reflection effects by assuming a proportionality factor (ρ) is not considered to be efficient for inland fresh water bodies. For in situ spectroscopy, the recommended approach is to measure upwelling radiance slightly below the water's surface as a means of minimizing extraneous noise. Researchers should be aware of the potential for diminishing the validity of findings because of measurement errors.

Keywords:

• above-water reflectance
• subsurface reflectance
• sun glint

Acknowledgements

The authors acknowledge the financial assistance provided by Kochi University of Technology (KUT), Japan and logistical support provided by the Center for Advanced Land Management Information Technologies (CALMIT), University of Nebraska-Lincoln.