In-water Spectral Radiative Transfer Modeling using Photon Mapping

In contrast to spectroscopic observation of deep ocean waters, measurement of coastal waters is often influenced by inhomogeneous surroundings. An accurate model of light propagation in coastal regions must therefore take into account spatially variant phenomena, such as the distribution of inherent optical properties in the water, bottom structure, in-water objects, and wind-driven wave surfaces. In order to account for the influence of these multi-dimensional structures effectively, this work adapts and develops efficient Monte Carlo based ray tracing techniques to simulate radiative transfer in natural waters. The basis of this work is a two-pass ray tracing process that generates a stored map of the in-water light field. This concept, called photon mapping and originally developed by Henrik Warm Jensen, is re-derived in the context of spectral radiative transfer in coastal waters and has been implemented to allow for arbitrary scene definition. Novel techniques and approaches have been introduced that relate to volumetric efficiency, spectral considerations, and wave modeling, among other areas. A detailed treatment of practical Monte Carlo and Quasi-Monte Carlo techniques provides the motivation and justification for the particular sampling and propagation algorithms that are implemented and used within (he model. The final product is a modular, generic light propagation algorithm for water and other media that can be used within an existing synthetic image generation environment known as DIRSIG. A detailed validation study and full scene renderings demonstrate the usefulness and fidelity of the model, forming the capstone of the project