Reflected solar radiation from horizontal, vertical and inclined surfaces: Ultraviolet and visible spectral and broadband behaviour due to solar zenith angle, orientation and surface type

Abstract

Ultraviolet (UV) radiation affects human life and UV exposure is a significant everyday factor that individuals must be aware of to ensure minimal damaging biological effects to themselves. UV exposure is affected by many complex factors.Albedo is one factor, involving reflection from flat surfaces. Albedo is defined as the ratio of reflected (upwelling) irradiance to incident (downwelling) irradiance and is generally accepted only for horizontal surfaces. Incident irradiance on a non horizontal surface from a variety of incident angles may cause the reflectivity can change. Assumptions about the reflectivity of a vertical surface are frequently made for a variety of purposes but rarely quantified. As urban structures are dominated by vertical surfaces, using albedo to estimate influence on UV exposure is limiting when incident (downwelling) irradiance is not normal to the surface. Changes to the The RRG shows variability in reflective capacities of surface according to the above mentioned factors and present a more realistic influence on UV exposure than albedo for future investigations. Errors in measuring RRG at large solar zenith angles is explored, which equally highlights the errors in albedo measurement at large solar zenith angles.

Measuring the influence of UV reflection from vertical metal surfaces on humans

“…The albedo measurements from Lester and Parisi 15 suggest a non-Lambertian surface, where irradiance incidence does have an influence on reflectance measured. A recent study on determining if UV reflectivity differs according to horizontal, inclined or vertical planes of the reflecting surface 17 did not use albedo as the UV reflectance measurement. To compare the reflective capacity of surface position (vertical, horizontal or inclined), the authors decided that the incident irradiance would have to be consistent for any surface position.…”

Influence of reflected UV irradiance on occupational exposure from combinations of reflective wall surfaces

“…There are paint coatings available that additionally insulate against thermal radiation and have been shown to have comparable UV reflection to standard paint coated metallic surfaces. 32 Using the reflective ratios obtained in this study, the ability to determine a UV reflective factor should be possible and will be similar to cloud modification factors 33,34 or mean protection factors. 35 UV reflective factors could be disseminated to outdoor workers, who could use this knowledge to assist managing their personal UV exposure.…”

Improved method of ultraviolet radiation reflection measurement for non-horizontal urban surfaces

“…However, by considering seasonal reflective measurements made by Rosenthal et al, [30] reflectance on a horizontal surface is shown to be not consistent through seasons with differing reflective measurements obtained for grass and water. Weihs [12] through modeled data and bi-directional reflection measurements supports this variability, leading to work carried out to show that reflectance is not constant for more urbanised surfaces [13] where reflection of UV radiation in a solar UV environment is dependent on solar zenith angle (SZA), solar azimuth angle (SAA), orientation and of course, surface type.…”

“…As albedo is supposed to be considered constant from a surface, it is no longer pertinent to describe UV radiation reflection using albedo. Having established changing reflective ratios in Turner, Parisi & Turnbull [13] the next question of the method of reflection measurement arose from investigating the effects on humans due to UV reflected from non-horizontal surfaces [5] therefore implying non-natural surfaces.…”

“…Additionally, UV radiation reflection is variable depending on the orientation of the surface, the solar zenith angle and solar azimuth angle and the surface type [13]. Computer models that incorporate reflection information in order to create realistic images also provide significant information on radiation reflection behaviour [14][15][16][17][18], namely specular reflection, diffuse reflection and combinations of the two types.…”