Quantitative estimation of the underwater radiance distribution

Abstract

[1] Within the Radiance in a Dynamic Ocean (RaDyO) program, we have created and deployed a high dynamic range camera that can resolve the full spherical radiance distribution at the ocean surface and at depth. We present here the first results from deployments of the camera in near-surface water in eutrophic, mesotropic, and oligotropic environments. The instrument resolves the dynamics and fine structure of both the downwelling and upwelling radiance distribution and its variation with depth in these optically diverse water types. The various irradiances (E d , E u , E o , E ou , and E od ) are computed by integration. The distribution functions (e.g., the average cosines) are computed directly, as are the various diffuse attenuation coefficients. The fully specified radiance field therefore provides all the pertinent information to derive not only all of the apparent optical properties but, in principle, the inherent optical properties such as the absorption coefficient and the phase function as well. Comparison of the measured radiance field to independent measurements has shown very good agreement.

Underwater Radiance Distributions Measured with Miniaturized Multispectral Radiance Cameras

“…The data shown here are among the first of that sort ever obtained [but see the concurrent development of Lewis et al (2011)]. Numerous research domains will benefit from such measurements, including optical closure [deriving IOPs and AOPs from a unique set of L(J, z)] and characterization of the bidirectionality of the ocean reflectance in Case-2 waters (where currently there are virtually no data).…”

“…Based on three NuRADS instruments in which linear polarizers have been installed, another system was developed to determine the polarization state of the upward light field just beneath the sea surface (PolRADS instrument; Voss and Souaidia 2010). The concept of a free-fall profiling system using two cameras head-to-tail configuration was actually also developed by Lewis et al (2011) in parallel to our work. The concept of a free-fall profiling system using two cameras head-to-tail configuration was actually also developed by Lewis et al (2011) in parallel to our work.…”

“…When only upwelling radiances are considered, the subscript u will be used (J u ). Measurements of L(J d ) have been carried out only recently with present developments (see also Lewis et al 2011). All the ''apparent'' optical properties (AOPs; sensu Preisendorfer 1961) depend on, and can be obtained from, the radiance distribution.…”

“…Important features that are emphasized in comparison to previously developed instruments (Voss and Chapin 2005;Lewis et al 2011) include 1) miniaturization, which allows the minimization of the unavoidable self-shading when measuring the upwelling radiances; 2) a specifically designed fore optics with very high angular resolution and low attenuation; 3) the use of a detector array whose characteristics allow up-and downward hemispheres to be simultaneously measured; and 4) absolute calibration that is often neglected for such radiance camera systems. The purpose is to show how this instrument has been conceived, built, characterized, and calibrated, and to present preliminary results from field deployments.…”

Spectral measurements of underwater downwelling radiance of inland water bodies

“…Some instrumentation was developed to measure the underwater radiance distribution on lakes, fjords and oceans (Sasaki et al, 1958;Jerlov and Fukuda, 1960;Tyler, 1960;Lewis et al, 2011;Antoine et al, 2013). In this article, the authors present a new apparatus to operate in an underwater environment composed of an optical cable attached to a portable spectroradiometer.…”