Comparison of the accuracy of two UAV‐mounted uncooled thermal infrared sensors in predicting river water temperature

Abstract

Measurement by a unmanned aerial vehicles (UAV) equipped with thermal infrared sensors has great potential as a new technique for understanding the spatial heterogeneity of river water temperature; however, the measurement technique has not been established yet. Therefore, this study measured surface and water temperatures using two uncooled thermal infrared sensors, which are commercially available, for 7 months, to obtain knowledge to establish a method for predicting the river water temperature using uncooled thermal infrared sensors mounted on UAVs. The survey covered a 500 m section upstream from the confluence of the Inukai River in the Katsura River of the Yodo River system, in Japan. DJI Zenmuse XT2 and MicaSense Altum were mounted on a DJI Matrice 300 at the same time and took images seven times at intervals of approximately 1 month between June 2021 and January 2022. The water temperature and depth were measured at several locations within the study area within 1.5 hr after the UAV acquisition. Then, the relationship between the measured water temperature and the surface temperature extracted from the thermal infrared orthorectified mosaic image was analyzed. Altum was more suitable than XT2 for obtaining thermal infrared orthorectified mosaic images with less inconsistencies among courses in the surface temperature range, and the difference in water temperature was also smaller, making it suitable for understanding the river water temperature. To predict water temperature from surface temperature, actual measured data of water temperature is necessary, but I demonstrated that it is possible to measure the river water temperature in a spatially continuous manner.

Distribution analysis of adult and larval Calopteryx japonica using unmanned aerial vehicle acquired water temperature distribution

“…Following the method of Niwa (2022), the thermal infrared orthomosaic image created from Altum data was corrected using the measured water temperature. On 2 August 2022, the water temperature was measured at nine sites using CT-300WP (CUSTOM Corporation, Tokyo, Japan) within 1 h after the UAV shooting.…”

“…Therefore, thermal infrared sensors mounted on UAVs, which can measure surface temperature as an area with high spatial resolution, provide insights into the study of river water temperature. Niwa (2022) used a commercially available thermal infrared sensor mounted on a UAV and showed that river water temperature can be estimated as an area with high spatial resolution. Collas et al (2019) evaluated a suitable habitat for freshwater fish using UAV‐acquired water temperature distributions with high spatial resolution.…”

Real‐Time Monitoring and Postprocessing of Thermal Infrared Video Images for Sampling and Mapping Groundwater Discharge

“…Although TIR cameras can only measure the water temperature at the surface, it is much less labor‐intensive for surveys covering a large spatial scale than direct observation using thermometers or fiber‐optic distributed temperature sensing (FO‐DTS) systems (Hare et al., 2015). For surveys of wide rivers, the spatial distributions of groundwater discharge zones and the stream temperature can be mapped by using a TIR camera mounted on an unmanned aerial vehicle (UAV), helicopter, or aircraft (Dugdale et al., 2022; Niwa, 2022; Rautio et al., 2015; Wilbur et al., 2020). Even for fifth‐order river sites, however, UAV‐based TIR sensing is less suitable for locating groundwater discharge points than handheld TIR imaging owing to their submeter scale and position beneath the riparian tree canopy (Briggs et al., 2022).…”

“…• Real-time thermal imaging helps find suitable sampling points of groundwater discharge differing in chemistry from stream water • Postprocessing of thermal video can easily map springs with thermal anomalies and the spatial distribution of the stream temperature • The water temperature of springs is useful for inferring their sources when multiple groundwater sources contribute to a stream and the stream temperature can be mapped by using a TIR camera mounted on an unmanned aerial vehicle (UAV), helicopter, or aircraft (Dugdale et al, 2022;Niwa, 2022;Rautio et al, 2015;Wilbur et al, 2020). Even for fifth-order river sites, however, UAV-based TIR sensing is less suitable for locating groundwater discharge points than handheld TIR imaging owing to their submeter scale and position beneath the riparian tree canopy (Briggs et al, 2022).…”

Thermal video recording while walking: A simple method for mapping groundwater discharge points along forested headwater streams

“…Although thermal cameras can only measure the water temperature at the surface, it is much less labor-intensive for surveys with a large spatial scale than direct observation using thermometers or fiber-optic distributed temperature sensing (FO-DTS). For surveys of wide rivers, groundwater discharge zones can be mapped by using a thermal camera mounted on an unmanned aerial vehicle (UAV), helicopter, or aircraft (Dugdale et al, 2022;Niwa, 2022;Rautio et al, 2015;Wilbur et al, 2020). However, this remote sensing technique is difficult to utilize for headwater streams because their channels and riverbanks are often covered by dense riparian trees.…”