UV protection and shade structures

[Abstract]: Broadband field measurements were conducted beneath three different sized public shade structures at a sub-tropical Southern Hemisphere site for relatively clear skies and for a changing solar zenith angle (SZA) of 13o to 76o. These data were compared to the diffuse UV to quantify the relationship between diffuse UV and the UV in the shade of the structures. On the horizontal plane, the ultraviolet protection factors (UPF) for the shade structures ranged from 1.5 to 18 for a decreasing SZA. The data from this research is significant, because it shows that as the SZA of the sun increases so does the relative proportion of scattered UV beneath the shade structures which in turn decreases the shade structures UPF. In Australia, erythemal UV in full sun can reach levels of approximately 2.5 MED/h or more in the middle of the day during winter. Therefore, it is necessary for people that live in similar latitudes to minimise UV exposure in all climatic conditions throughout the year. Based on this research, a standard for reporting the UV protection provided by shade structures is essential for the public to make an informed decision on the efficacy of particular structures in reducing personal UV exposure

Effect of cloud on UVA and exposure to humans

The daily autumn and winter UVA exposures and 6-minute UVA irradiance data for a Southern Hemisphere, subtropical site (Toowoomba, Australia, 27.6 S, 151.9 E) are presented. This data is used to quantify the effect of cloud on UVA using an integrated sky-camera and radiation system. Additionally, an estimate of the effect of enhanced UVA exposure on humans is made. The measurement system consisted of broadband visible-infrared and UVA sensors together with a sun tracking, wide-angle video camera. The mean daily June exposure was found to be 409 kJm-2. Under the constraints of the uncertainty of both the UVA measurement system and clear-sky model, one case of enhanced UVA irradiance was found. Three cases of cloud enhancement of daily UVA exposure, approaching clear-sky levels, were also determined using a calculated clear-sky envelope. It was also determined that for a fulltime outdoor worker, the additional UVA exposure could approach approximately that of one third of a full winter's day. For indoor workers with an outside lunch break of noon to 1 pm, the additional UVA exposure was on average 6.9 kJm-2 over three cloud enhanced days. To the authors' knowledge this is the first paper to present some evidence of cloud enhanced UVA human exposure

Improved ground based sky camera for studies of enhanced spectral UV irradiance

A recent World Meteorological Organisation report discussed the importance of continued study of the effect of clouds on the solar UV radiation reaching the earths surface. The report mentions that the use of all-sky imagery offers the potential to understand and quantify cloud effects more accurately. There are an increasing number of studies investigating the enhancement of surface UV irradiance, and UV actinic flux, using automated CCD and sky cameras. This paper describes image-processing improvements and new algorithms applicable to a commercially available, relatively low cost all-sky camera (TSI-440), we use for investigating cloud enhanced spectral UV irradiance. Specifically, these include improved shadow band masking, and the addition of three new algorithms relating to cloud amount at different spatial positions and the visible brightness of clouds surrounding the sun. We also present a summary of 5-minute resolution cloud enhanced UV index and spectral UV irradiance over a 5-month period at a Southern Hemispheric sub-tropical latitude site using these new techniques, as well as how these findings relate to the current literature on this topic

Cloud observations for the statistical evaluation of the UV index at Toowoomba, Australia

The development of a unique statistical model for the estimation of the UV index for all sky conditions with solar zenith angles of 60 degrees or less is reported. The model was developed based on available data from an integrated whole-sky automated sky camera and UV spectral irradiance measurement system that was collected every five minutes when the equipment was operational over a period of one year. The final model does not include terms directly associated with solar radiation, but rather employs terms, and interactions between these terms, including the parameters of sky cover, solar obstruction, and cloud brightness. The correlation between the estimations of the model and the measured values was 0.81. The developed model was evaluated on a data set spanning five months that had not been employed in the development of the model. The correlation for this new data set was 0.50 which increased to 0.65 for the cases when the clouds were considered to be a contributor to UV enhancement above that of a cloud free day

Cloud effects on evaporation at a sub-tropical site

Water usage impacts the management of our water resources. It is believed that accurate information on the hydrological cycle disseminated to the public, will considerably alter consumer usage behaviour. Evapotranspiration is one of the most variable and sensitive of the hydrological components and it is imperative that we fully understand what environmental factors directly or indirectly affect evapotranspiration. The objective of this study was to confirm the indirect affect of clouds on evaporation by examining how clouds affect variables used by the Penman-Monteith equation. As expected, during the day or night it was found that clouds had a negative correlation with solar radiation and temperature, and a positive correlation with humidity all at the earth's surface. There was no significant relationship between wind speed and clouds except during the night. Correlation coefficients, with respect to cloud, for temperature and humidity varied only slightly from day to night, but interestingly wind speed showed a significant change from 0.077 to 0.264. These findings may suggest that there are some occasions when 'water-wise' activities, for example watering the garden at night to decrease potential evaporation, may not be as beneficial as previously thought

Retrieving cloud characteristics from ground-based daytime color all-sky images

A discussion is presented of daytime sky imaging and techniques that may be applied to the analysis of full-color sky images to infer cloud macrophysical properties. Descriptions of two different types of sky-imaging systems developed by the authors are presented, one of which has been developed into a commercially available instrument. Retrievals of fractional sky cover from automated processing methods are compared to human retrievals, both from direct observations and visual analyses of sky images. Although some uncertainty exists in fractional sky cover retrievals from sky images, this uncertainty is no greater than that attached to human observations for the commercially available sky-imager retrievals. Thus, the application of automatic digital image processing techniques on sky images is a useful method to complement, or even replace, traditional human observations of sky cover and, potentially, cloud type. Additionally, the possibilities for inferring other clou

Physics concepts: Engineering PBL at USQ

Problem based learning (PBL) has been incorporated into the curriculum of programs offered by the Faculty of Engineering and Surveying at the University of Southern Queensland (USQ) since 2001. This paper examines student learning in a team-based PBL course offered in 2006. The study checks students’ understanding of 10 fundamental physics concepts using computer administered quizzes conducted at the beginning and end of the semester. Pre-course results indicate that there is no difference in students’ general understanding of physics concepts between those entering PBL and those entering the more traditional physics course. Neither was there a difference based on the type of physics curriculum they had undertaken at secondary level. It was found that this PBL course is ‘pitched’ at the physics concepts in which students have the greatest prior knowledge. At the completion of the course only one question resulted in greater than 50% incorrect answers by those who had not previously studied physics, with the same question also being the least correctly answered by those that had previously studied physics. Further, students with less than 1 year of physics in year 11 and 12 are benefiting most from the physics content of this PBL course