**6. Infrared thermal cameras**

212 Solar Radiation

(Duthie et al., 1999). Even humans with varying levels of pigmentation in their skin, such as those of diverse racial descent, are affected differently when exposed to UVB (Coelho et al., 2009; Duthie et al., 1999). Langerhans cells, antigen-presenting cells within the epidermis, die due to membrane disruption and organelle damage in Celtic descendants while cells in the darker skin of Aboriginal or Asian Australians are depleted by apoptosis (Duthie et al., 1999). The melanin produced in the skin when humans are exposed to UV radiation is actually able to absorb UV, shielding nuclear DNA (Coelho et al., 2009). Long term exposure can lead to degeneration of skin cells, underlying fibrous tissue and/or blood vessels leading to premature skin aging and skin cancer. Other possible effects include ocular inflammation and cataracts that can cause blindness. Most tissue damage is due to high levels of UVB wavelengths while more indirect damage via reactive oxygen intermediates affecting DNA, proteins, and lipids is caused by UVA radiation (Figure 8)

Fig. 8. Relationship of exposure to UV-R and burden of disease. Source: WHO, Ultraviolet

Vitamin D is necessary for healthy growth and function of most terrestrial vertebrates. Exposure to direct sunlight allows UVB photons to enter the skin and begin a chain reaction resulting in the formation of vitamin D. This nutrient is essential for efficient intestinal absorption of calcium, especially in humans (Holick, 2008). However, an organism's diet is often a supplemental source of vitamin D in addition to providing the building blocks of vitamin D synthesis. In bats, diet strongly affects the levels of circulating vitamin D metabolite. Certain cave dwelling species, receiving little to no direct sunlight, actually have the highest recorded concentrations in vertebrate taxa. Unlike the plant visiting bats, which have levels not even sufficient for humans, sanguivorous and piscivorous species have access to dietary vitamin D, increasing their serum concentrations of the vitamin D metabolite (Southworth et al., 2009). Ectotherms, who often bask in sunlight, are able to use this behavior to regulate their own vitamin D levels when dietary intake is insufficient

radiation and the INTERSUN Programme in Rafanelli et al., 2010

(Rafanelli et al., 2010).

A specialized sensor in units of Watts/m2 normally measures solar radiation while a UV meter is needed to determine UV radiation either by wavelength or a UV index. The effects of solar and UV radiation on organisms are harder to quantify. Observed behaviors can be statistically associated with monitored solar intensity and/or UV radiation to calculate whether there is a significant effect. Physiological responses however, must be measured with other equipment or using procedures involving immobilization, radioactive tracers etc. Such methods can cause stress to the animal in question or establish a bias in some way as is often the case with attaching equipment to wild animals or bringing them into a laboratory setting. Often the variable being monitored is some form of temperature, be it core/body, skin, or intramuscular. Temperature is often the first physical measurement affected by solar radiation. Infrared radiation (IR), simply put, is the thermal emission of an object or organism. Thermal infrared cameras are able to detect various wavelengths in the infrared spectrum that can be accurately measured based on the temperature of a surface using the physical laws of radiative transfer.

The use of thermal cameras is relatively new to scientific field research. In the past, thermal cameras were expensive, large, bulky, and hindered by the need for a large external power source. As the technology has progressed, the IR detector itself has become smaller and thermal cameras have been used for military applications, on airplanes, helicopters, and today the individual soldier. Currently a handheld IR camera can be purchased for under \$2,000 and is often used by electricians, engineers, and construction companies to detect problem areas in work zones and other facilities. Scientists too, are now able to purchase high definition IR cameras that can be easily carried into the field and wirelessly linked with data loggers and tablets.

Thermal cameras allow for a non-invasive scrutiny of an organism's skin surface temperature, giving the ability to see temperature variability across the body rather than just one to a few individual areas recorded by a thermocouple or other device (Figure 9) (McCafferty, 2007; Norris et al., 2010). Clear links between heat loss and areas of the body such as the head and appendages have been established due to thermal imaging (McCafferty, 2007; McCafferty et al., 2011). Behavioral responses to solar radiation and other environmental variables can be paired with changes in skin surface blood circulation. The surrounding environment is imaged at the same moment as the organism being studied, allowing for temperature measurements of the substrate to be collected for future analysis. Thermograms of insects such as bees make measuring individual or hive temperatures quick and simple without having to use smoke or gaseous chemicals that take time and may affect the bees' thermoregulatory properties (Kovac et al., 2010). Thermal video of emerging bats can be recorded and their flight trajectories tracked using specialized computer analysis programs (Hristov et al., 2008). Thermal imaging can even be used for plant and crop research, measuring temperature in relation to solar radiation absorption and water treatment (Jones et al., 2009).

Fig. 9. Post combat thermal images sequence (A-F) of an alpha male northern elephant seal taken at intervals of ~1min immediately following a combat lasting 11 min. Skin temperature variability is clearly displayed over time. Source: Norris et al., 2010.

The use of thermal cameras for biological study has been well validated in the past for both individual studies and those involving groups of animals (McCaffery, 2007). Using either the IR camera or computer software paired with it, maximum, minimum, and mean temperatures can be measured and calculated rapidly and efficiently. However, distance from the organism, emissivity, relative humidity, and TA must be known to reduce errors in the camera's detection of surface temperature. Solar and UV radiation measurements can now be statistically paired with the temperature data, skin variability in temperature, thermal gradient between skin temperature and ambient/substrate temperature, and other environmental or physiological measurements. Use of IR cameras eliminates the need to capture or handle animals in physiological, behavioral, and ecological studies involving thermoregulation.
