Asymptotic optical depths in source-free ocean waters

Area of Science:

• Ocean optics
• Radiative transfer theory
• Inherent optical properties (IOPs)

Background:

• Underwater light fields are influenced by surface illumination and water properties.
• Asymptotic regime describes light field behavior at depth, independent of surface conditions.
• Understanding the transition to the asymptotic regime is key for accurate optical modeling.

Purpose of the Study:

• To determine the depth at which key diffuse optical properties become independent of surface incident illumination.
• To investigate how incident light characteristics and water IOPs affect this depth.
• To provide insights for solving inverse ocean optics problems assuming an asymptotic light field.

Main Methods:

• Analysis of depth dependence for downward diffuse attenuation coefficient.
• Examination of upward-to-downward plane irradiance ratio depth profiles.
• Calculation of vertically upward radiance-to-downward plane irradiance ratio and mean cosine of radiance.

Main Results:

• Identified specific depths where diffuse attenuation, irradiance ratios, and mean cosine become insensitive to surface illumination.
• Demonstrated that these depths are significantly influenced by the spectral characteristics of incident light.
• Showed a strong dependence on the inherent optical properties (IOPs) of the water column.

Conclusions:

• The depth at which the light field approaches its asymptotic state is not fixed but depends on illumination and water IOPs.
• This finding is critical for validating models and algorithms in underwater remote sensing and optical oceanography.
• Accurate estimation of these transition depths improves the reliability of inverse problem solutions in ocean optics.