A study on the combined method to grasp volcanic hot spots using Terra/ASTER and Himawari-8/AHI data

Abstract:

Satellite-based thermal observations focused on volcanos detect high-temperature objects of eruption which provides detail information of the volcanic activity. It enables periodic observations over a wide area, cost reduction of installing observation equipment and sustainable safe surveys instead of in-situ observations. In order to make use of high-spatial/-temporal resolutions of multiple satellite sensors integrally, we aim to clarify effective observation methods on volcanic hot spots utilizing multiple satellite sensors and to make near-real-time monitoring system.

We used images of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) 11.3-μm band and those of the Advanced Himawari Imager (AHI) 3.9-μm and 11.2-μm bands. They were analyzed to evaluate the analytical performance of ASTER and AHI with respect to the recent activities of Mt. Sakurajima, Southern Japan, and the associated heat sources. As a result of ASTER TIR data analysis, a thermal anomaly of about 0.2 km² at the Showa crater side and that of about 0.3 km² at the Minami-dake summit cater side were identified. Results of ASTER data suggest that the AHI sometimes misses the small-scale heat sources of Mt. Sakurajima.

Next, we investigated a time series change of the brightness temperature of the 3.9-μm band of AHI and the differential brightness temperature between 3.9 -μm and 11.2-μm bands of AHI. We focused on four volcanoes in Japan, Mt. Sakurajima, Kuchinoerabujima island, Mt. Kirishima, and Nishinoshima island and used the data obtained by the AHI from 1 January 2017 to 31 October 2019, 00:00 JST. Heat sources associated with volcanic activities was confirmed in Mt. Sakurajima, Mt. Kirishima, and Nishinoshima island. In the analysis using the differential temperature, its increase for 20K or less was periodically observed due to the influence of clouds. Therefore, appropriate cloud removal is required for the use in small-scale heat source detection to obtain more robust hot-spot information from the AHI differential temperature.