Spectra of particulate backscattering in natural waters

Howard R Gordon,Kenneth J Voss,Michael S Twardowski,Scott D Mclean,Marlon R Lewis,G Chris Boynton,Scott A Freeman

doi:10.1364/oe.17.016192

Abstract

Hyperspectral profiles of downwelling irradiance and upwelling radiance in natural waters (oligotrophic and mesotrophic) are combined with inverse radiative transfer to obtain high resolution spectra of the absorption coefficient (a) and the backscattering coefficient (b(b)) of the water and its constituents. The absorption coefficient at the mesotrophic station clearly shows spectral absorption features attributable to several phytoplankton pigments (Chlorophyll a, b, c, and Carotenoids). The backscattering shows only weak spectral features and can be well represented by a power-law variation with wavelength (lambda): b(b) approximately lambda(-n), where n is a constant between 0.4 and 1.0. However, the weak spectral features in b(b)b suggest that it is depressed in spectral regions of strong particle absorption. The applicability of the present inverse radiative transfer algorithm, which omits the influence of Raman scattering, is limited to lambda < 490 nm in oligotrophic waters and lambda < 575 nm in mesotrophic waters.

Highlights

Space-borne sensors such as the Coastal Zone Color Scanner (CZCS), the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and the MODerate resolution Imaging Spectroradiometer (MODIS) have provided ocean color imagery from which the concentration of the phytoplankton photosynthetic pigment chlorophyll a (Chl a) has been estimated on a global scale since 1978
The hyperspectral apparent optical properties (AOPs) data we examine here consist of depth profiles of the downwelling spectral irradiance, Ed, and the upwelling spectral radiance toward the zenith, Lu, measured at 3.3 nm increments from 350 to 700 nm with a wavelength accuracy of ± 0.1 nm
The inherent optical properties (IOPs) data were averaged over 1 m depths to reduce noise

Summary

Introduction

Space-borne sensors such as the Coastal Zone Color Scanner (CZCS), the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and the MODerate resolution Imaging Spectroradiometer (MODIS) have provided ocean color imagery from which the concentration of the phytoplankton photosynthetic pigment chlorophyll a (Chl a) has been estimated on a global scale since 1978. “hyperspectral” reflectance measurements might enable a wide range of spectroscopic analyses of absorption and backscattering spectra to derive the phytoplankton species composition or community structure, an important determinant of the upper ocean carbon cycle and something that is not possible with the limited number of spectral channels available on most current satellite sensors. Such hyperspectral aircraft instruments have been developed [3], and space borne missions optimized for ocean color have been proposed

Results

Discussion

Conclusion