A Simple Method to Minimize Orientation Effects in a Profiling Radiometer

Abstract

Marine optical parameters required for ocean color satellite applications need to be measured with high accuracy and errors within the permissible limits. These stringent requirements demand careful measurements of optical parameters. Though the free fall radiometer is found to be a better option for measuring underwater light parameters as it avoids the effects of ship shadow and is easy to operate, the measurements however demand profiling the radiometer vertical in water with minimum tilt. Here we present the results of our observations on the tilts of the radiometer from the measurements in the Arabian Sea. Since there is hardly any study carried-out on the tilt of the profiling radiometer, the result of this study will help in the better design of such marine instruments. The tilt of the radiometer near the surface of water is attributed to the mode of deployment and environment parameters, while the tilt at depth of water is influenced by the density variations of the water. Here we also demonstrate a method of deploying the instrument that minimize the tilt of the instrument at the surface layer of water.

Biogeochemical research with an Autonomous Underwater Vehicle: Payload structure and arctic operations

“…The inclination angle can be derived from the scalar product of the vertical vector and the direction vector of the PAR sensor . Within a tolerance limit of 5° for the inclination angle following Sturesh et al [24], this yields to:…”

Comparison of remote sensing reflectance from above-water and in-water measurements west of Greenland, Labrador Sea, Denmark Strait, and west of Iceland

“…It eliminates the major external effects namely sunglint and fog effects. However, the in-water free falling deployment does have its drawbacks, namely the tilt changes driven by upper layer turbulence, which therefore have to be accounted for in estimating error sources [7]. Nevertheless, a better understanding of uncertainties in abovewater optical sensing can be achieved by optical closure with in-water measurements and solving radiative transfer equations.…”

“…Above-water radiometry is sensitive to meteorological conditions and sea state which makes it obligatory to perform effective glint correction [5,6]. In-water profile radiometric quantities are used to approximate light just below the sea surface, but they are influenced by illumination changes with depth, sensor deployment, self-shading, ship shadow, air bubbles and wave-induced perturbations [4,7]. Additionally, in polar regions there are more external effects; the constant low solar elevation, ice reflectance contribution to remote sensing reflectance, colored dissolved organic matter (CDOM) absorption decoupling with chlorophyll a abundance, and continued presence of cloud and fog [3].…”