Algorithms for path radiance and attenuation to provide color corrections for underwater imagery, characterize optical properties, and determine bottom albedo

Patty D. Pratt; Kendall L. Carder; David K. Costello; Zhongping Lee

doi:10.1117/12.266396

6 February 1997 Algorithms for path radiance and attenuation to provide color corrections for underwater imagery, characterize optical properties, and determine bottom albedo

Patty D. Pratt, Kendall L. Carder, David K. Costello, Zhongping Lee

Author Affiliations +

Proceedings Volume 2963, Ocean Optics XIII; (1997) https://doi.org/10.1117/12.266396
Event: Ocean Optics XIII, 1996, Halifax, Nova Scotia, Canada

Abstract

There is growing interest in the development and utilization of optical instrumentation to measure water properties of coastal waters for ground-truthing satellite data. Current methods for determining above-water remote-sensing reflectance assume vertical homogeneity in the water column. In cases where in-water vertical structure and bottom reflectance confound standard algorithms, new methods must be developed to incorporate inhomogeneities. This paper addresses the available avenues for characterizing optical properties, color-correcting underwater imagery and determining bottom albedo values. The method begins by deriving backscatter from remote-sensing reflectance data collected near the red end of the visible spectrum near the surface where bottom reflectance is negligible and path radiance is maximal. Measured upwelling radiance is divided by measured downwelling irradiance yielding underwater remote sensing reflectance values. The backscattering coefficient is then modeled for each wavelength and the path radiance calculated and removed using measured attenuation coefficients. The above values are used to reduce the algorithm to an equation for bottom albedo by removing the bias associated with path radiance and the filter effects associated with the water path to and from the bottom. The calculated bottom reflectance is needed to interpret and correct above-water remote-sensing reflectance and satellite imagery. The results are illustrated using comparisons of color-corrected and non-color-corrected in-situ imagery of specific corals and their immediate surroundings. Imagery of a coral scene at various altitudes is also presented to illustrate spectral changes due to changes in thickness of the water column between the camera and the bottom.

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Patty D. Pratt, Kendall L. Carder, David K. Costello, and Zhongping Lee "Algorithms for path radiance and attenuation to provide color corrections for underwater imagery, characterize optical properties, and determine bottom albedo", Proc. SPIE 2963, Ocean Optics XIII, (6 February 1997); https://doi.org/10.1117/12.266396

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