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MODELING THE ANATOMICAL DISTRIBUTION OF SUNLIGHT
Citation:
Streicher, J J., W. C. Culverhouse Jr., M. S. Dulberg, AND R. J. Fornaro. MODELING THE ANATOMICAL DISTRIBUTION OF SUNLIGHT. PHOTOCHEMISTRY AND PHOTOBIOLOGY 79(1):40-47, (2004).
Impact/Purpose:
To understand and characterize the factors, including optical transmission properties of aerosols, which affect the intensity of UV-B radiation measured at the earth's surface in order to improve our estimates of ecosystem and human exposures to UV-B radiation; to understand the relationship between UV radiation and total column ozone; to model UV-B exposures at different locations, conditions, and times in order to estimate UV-B exposures throughout the US. This objective is achieved by maintaining a strict quality assurance program for both the Brewer Spectrophotometers in the network and the UV data obtained from the Brewers.
Description:
One of the major technical challenges in calculating solar irradiance on the human form has been the complexity of the surface geometry (i.e. the surface normal vis a vis the incident radiation. Over 80 percent of skin cancers occur on the face, head, and back of the hands. The quantification, as well as the mapping of the anatomical distribution of solar radiation on the human form is essential if we are to study etiology of skin cancers or cataracts or immune system suppression. Utilizing advances in computer graphics, including high-resolution 3-dimensional mathematical representation of the human form, the calculation of irradiance has been attained in sub-centimeter precision. Lighting detail included partitioning of direct beam and diffuse sunlight, shadowing effects, and gradations of model surface illumination depending on model surface geometry and incident light angle. With the incorporation of ray tracing and radiosity algorithms, the results are not only realistic renderings, but also accurate representations of the distributions of light on the subject model. The calculation of light illumination various receptor points across the anatomy provides information about differential radiant exposure as a function of subject posture, orientation relative to the sun and sun elevation. The integration of a geodesic sun-tracking model into the lighting module enabled simulation of specific sun exposure scenarios, with instantaneous irradiance, as well as the cumulative radiant exposure, calculated for a given latitude, date, time of day, and duration. Illustration of instantaneous irradiance or cumulative radiant exposure is achieved using a false color rendering-mapping light intensity to color-creating irradiance or exposure isopleths. This approach may find application in the determination of the reduction in exposure that one achieves by wearing a hat, shirt, or sunglasses. More fundamentally, such as analysis could provide improved estimates of scenario-specific dose (i.e. absorbed radiant exposure) needed to develop dose-response function for sunlight-induced diseases.
The United States Environmental Protection Agency through its Office of Research and Development partially funded and collaborated in the research described here under ct or assistance agreement number R829432010 to North Carolina State University. It has been subjected to Agency review and approved for publication.