Urban heat islands and cooler infrastructure - Measuring near-surface temperatures with hand-held infrared cameras

Infrared thermography is an essential tool for evaluating Urban Heat Islands (UHI). Hand-held thermal cameras, however, are only designed for measuring surface temperatures. Near-surface air temperatures are physically different, and although the two temperatures are expected and assumed to correlate, their relationship remains an important research question. It would be a methodological advance if thermal cameras could measure air temperatures too, as it would make mobile data collection more efficient, consistent, and precise. The authors address this by studying the camera temperature readings using a proxy for air temperature - shaded white test-sheets held aloft. The challenge is to minimize near-field absorption of infrared radiation that impinges upon the test-sheets, potentially raising surface temperatures significantly above ambient air temperatures bathing the sheets. The authors correct for the infrared effect using an adjacent sheet of aluminum foil to estimate background radiation impinging on the paper proxy. Results show that at a two-meter height, 86-87% of the measurements closely approximate (within ± 1 °C) of weather station data. Over hotter surfaces, the background infrared test is needed for the proxy temperature reading to be accurate.