Relationship between the distribution of aquatic plants and the water surface temperature using UAV with thermal infrared sensor.

Abstract

We investigated a river section where spring water can be seen, the Katsura-gawa River of the Yodo-gawa River System (Kameoka-si, Kyoto-fu) and the Kuto-gawa River of the Kishida-gawa River System (Shin-onsen-cho, Mikata-gun, Hyogo-ken), as survey targets. Visible light and thermal infrared ortho-mosaic images were obtained using UAV （Unmanned Aerial Vehicles）. Based on the results of the field survey and visual interpretation of the ortho-mosaic images, we determined the distribution of aquatic plants. The thermal infrared ortho-mosaic images with high spatial resolution enabled us to determine the distribution of water surface temperatures. The distribution of water surface temperatures was spatially heterogeneous. Analysis of the relationship between the water surface temperature and the distribution of aquatic plants revealed that the water surface temperature of the distribution patch was significantly higher for alien species than for native species. In addition, the water surface temperature of the distribution patch was found to be significantly lower for endangered species, such as Sparganium japonicum and Ranunculus nipponicus than for other species. Application of thermal infrared ortho-mosaic images to the analysis of river ecosystems, as well as aquatic plants, is a potential method of revealing new relationships between organisms and water temperature. This study presents the possibility of applying thermal infrared ortho-mosaic images acquired by UAV to river ecosystem analysis.