Advanced human heat exposure sensing using two cylinder anemometer and radiometer: introducing CARla

The negative health impacts of extreme heat exposure can be mitigated by incorporating hyperlocal biometeorological observations into heat action planning, emergency responses, and heat-reducing urban design. A significant portion of outdoor human heat exposure is radiative, but it is often overlooked due to the absence of affordable, accurate, and user-friendly sensors. We developed a two cylinder anemometer and radiometer (CARla) consisting of unheated and heated gray components, which quantifies wind speed and the total radiation absorbed by the human body. The spectral properties of the gray coating match the standard short- and longwave absorptivity used in mean radiant temperature (MRT) calculations. We optimized the geometrical parameters of the cylinders, including height, wall thickness, and side-mounting, to minimize errors in MRT and wind speed measurements. Experiments were conducted across 15 outdoor sites in Tempe, Arizona, during the record-setting heat wave from August to October 2024. Results demonstrated that the MRT measured using CARla closely matched those measured using 3-way net radiometers. The average error in MRT using the new compact system was 1.3 ± 2.2 °C across a wide MRT range (20 to 75 °C). CARLa represents a significant improvement compared to other low-cost radiometers. The average difference between the CARla and ultrasonic anemometers for wind speed was - 0.05 ± 0.36 m·s^-1 in the 0.25 to 3 m·s^-1 range, comparable to standard low-cost anemometers. We integrated the CARla sensor with an Arduino-based logger, creating a cost-effective and accurate tool for broadly characterizing human exposure to extreme heat.