Applicability of UAV-based Thermal Monitoring System for the Survey of Warm Water Dispersion Discharged from Thermal Power Plant

Rapidly spreading UAV-based observing system is expected for the efficient use of environmental monitoring. In this study, the applicability of UAV system equipped with thermal camera for the surface sea temperature survey was investigated through the field observation in the front sea area of thermal power plant, the rated output of over 2GW. The flight observations were conducted 6 times in the morning on October 19th in 2016. The research domain is configured about 1km alongshore direction by 600m offshore direction, where the large amount of heated water is discharged initially with 7ºC higher than the environmental sea temperature from the surface outlet in the middle of the coast. Then the sea surface temperature varies apparently from the outlet to the offshore boundaries and it is expected that the UAV thermal survey can detect the sea temperature variation in the domain. The thermal camera was set up in the right below direction of the UAV. The flight height was set up at 80m and each flight time was about 8 minutes with the aerial speed of 20m/s. The thermal image and visible image were simultaneously obtained every 3 seconds with the unit size of thermal image is about 45m width and 34m height with pixel resolution of 14cm. In conformity to the UAV flights the ship-based measurement of sea temperature was conducted and the vertical profile of sea temperature at six fixed-points was observed every flight time. In the beginning of the flight survey the oceanic condition was calm, however after 4th flight the wave gradually became high due to the strong wind. As the result, the comparison result of sea surface temperature by the UAV system with that by ship-based measurement is characterized into two groups by the data in the calm condition from 1st to 4th flight and that in the wavy condition from 5th to 6th flight. In the calm oceanic condition, the correspondence between UAV-based sea surface temperature and ship-based temperature is good with the correlation coefficient of 0.79 and standard deviation of 0.37ºC. On the contrary in the wavy condition, the correspondence between two temperature values is worse with the correlation coefficient of 0.44 and standard deviation of 0.84ºC. The main reason of this discrepancy is inferred that the direction of the surface thermal radiation varies with the sea surface perturbation against the right direction by the UAV-based measurement.