Thermal imaging and heat islands: Cross-discipline learning in optics and meteorology

There are many interesting ways in which optics and meteorology intersect and provide cross-discipline learning opportunities. One example is the use of thermal imaging to illustrate the principles underlying urban heat islands (UHIs), found on scales from the mesoscale to the microscale, which give rise to increased temperatures in urban settings. The most common way of documenting such phenomena is through traditional meteorological measurements. This presentation describes the use of a thermal infrared imager to document and help explain micro-scale UHIs observed initially as a persistent difference in air temperature measured by two nearly identical weather stations separated by 2.79 km in Bozeman, Montana. Mobile meteorological measurements from a backpack-mounted weather station, carried throughout the surrounding area at different times of year and compared with the stationary campus weather station, verified the presence and scale of a micro-heat island. This also identified one such micro UHI that existed when the immediate surroundings contained man-made materials such as concrete and asphalt adjacent to natural vegetation. Thermal images from the radiometrically calibrated imager recorded the diurnal thermal signature of manmade and natural surfaces. The thermal images help to explain process that are occurring, whereas most traditional meteorological instrumentation may not provide process-based information. Time-series plots of the infrared brightness temperatures show that the man-made materials emit elevated levels of thermal radiation long after the end of direct solar heating, while natural vegetation quickly comes into thermal equilibrium with the ambient air. The combination of traditional and nontraditional instrumentation document and explain processes occurring in micro UHIs that vary rapidly in space with changing ground cover.