Obstacles

This page is part of the UV Exposure Model (UVEM) documentation.
It contains a documentation about obstacles in the exposure model.
For an overview of all UVEM-related pages, see the UV Exposure Model main page.

3-dimensional UV Exposure Model in an Urban Environment

To calculate the biologically weighted human exposure in an obstructed environment, where for example buildings or vegetation are covering parts of the sky, information about the present obstructions for each considered location are needed. The additional parameter obstruction (obs) is included in the exposure model equation presented in section basic model? and is then given by:

The additional parameter obstruction depends on the azimuth φ and incident angle ϵ and contains the information to what percentage the sky is visible (unobstructed) for the corresponding solid angle Ω (direction). Due to the low reflectivity of most surfaces in the UV wavelength range, it is assumed that the radiance from obstructed sky regions can be neglected.

Determination of obstruction information

The obstruction information can be derived from topography data (voxel data). In the Figure on the left an exemplary imaginary three-way intersection is shown. The different colors indicate different building height and the red miniature block in the middle represents a human.

The obstruction information are derived by analyzing if obstructions are present in the direction of a specific vector. Exemplary vectors are shown in the Figure on the right, where solid lines indicate no obstructions with the direction of the vector. Dashed lines indicate that there are existing objects in the direction of the vector and that the Sky is obstructed in this direction and can therefore not be seen. Hence no sky radiation from this direction is reaching the human. To calculate the human exposure in an obstructed environment, several directions from different azimuth and zenith directions need to be analyzed. In the Figure on the right, red arrows show different horizontal directions (zenith angle 90°). Yellow arrows show exemplary directions with an lower zenith angle.

The Figure on the right shows the resulting obstruction information from the exemplary imaginary three-way intersection and is visualized as a polar plot. It should be noted, that similar to an astronomical map, the directions of east and west are inverted. If the obstruction information is derived for an city area, it is stored in a 3-dimesional array. The first two dimensions represent the x and y grid points of the model domain and the third dimension contains the obstruction information of the analyzed directions. Since the obstruction information needs quite a lot of disk space, the number of directions to be analyzed need to be choose carefully. A resolution with an azimuth and zenith interval 10° showed the best balance between high resolution and storage demand.

The Figure shows the topography data from Berlin Schöneberg and the resulting obstruction information for different locations within this area.

References:

• Seckmeyer, G., Schrempf, M.Wieczorek, A., Riechelmann, S., Graw, K., Seckmeyer, S., and Zankl, M. 2013. A Novel Method to Calculate Solar UV Exposure Relevant to Vitamin D Production in Humans, Photochem. Photobiol., 89(4), 974-983, DOI: 10.1111/php.12074.
• Schrempf, M., Thuns, N., Lange, K., and Seckmeyer, G. 2017a. Einuss der Verschattung auf die Vitamin-D-gewichtete UV-Exposition eines Menschen, Aktuelle Derm, DOI: 10.1055/s-0043-105258.
• Schrempf, M., Thuns, N., Lange, K., and Seckmeyer, G. 2017b. Impact of Orientation on the Vitamin D Weighted Exposure of a Human in an Urban Environment, Int. J. Environ. Res. Public Health, 14(8), 920, DOI: 10.3390/ijerph14080920.