A new method to reconstruct the 3D ground surface temperature from aerial TIR and visible images: application to the active crater of Aso volcano, Japan

Abstract

At active volcanoes, the surface temperature and its spatial distribution can indicate changes in the underlying magmatic and hydrothermal system. Surface temperature monitoring has been widely performed using thermal remote sensing with thermal infrared (TIR) cameras. One of the drawbacks of this method is that the unknown viewing orientation of TIR images inhibits quantitative evaluations of the spatial extent and distributions of thermal anomalies. Therefore, many studies have performed 3D temperature-field reconstructions by processing TIR images photogrammetrically. However, these studies have not included the correction of TIR wave atmospheric attenuation and viewing-angle variation in emissivity in the reconstruction procedure, which can result in significant temperature misestimation. We propose a simple method that incorporates the correction into the reconstruction process, which can improve the estimation of surface temperature, especially in rugged terrains. We demonstrate our method for the active crater of Aso volcano in Japan. We create digital elevation models by applying the Structure from Motion–Multi-view Stereo algorithm to aerial visible images taken at the same time as the TIR images and then project the TIR images onto the DEM with the direct georeferencing method. The correction is carried out using the geometric parameters acquired in the process. We create 1-m resolution orthorectified thermal images of the crater on two separate dates (18 August 2020 and 16 March 2022) and calculate the heat discharge rates from steaming grounds and a volcanic lake. We find that the heat discharge rate from the fumarolic field on the south crater wall showed a sevenfold increase after the phreatic explosions that occurred on 14 and 20 October 2021. Graphical Abstract

Heat transport process associated with the 2021 eruption of Aso volcano revealed by thermal and gas monitoring

“…We speculate that the plume HDR was < 300 MW because the lower limit of our analyzed period was ~ 300 MW. This speculation is consistent with the HDR of ~ 100 MW of volcanic gas injected in the lake bottom in March 2022, estimated from thermal modeling of the crater lake (Nashimoto and Yokoo 2023).…”

“…1b). The HDRs of vent plumes ranges from 300 to 5000 MW, whereas the total of the FF and SF is up to ~ 20 MW (Nashimoto and Yokoo 2023). Thus, the heat discharge over the crater is dominated by plume-laden heat (> 93% of the total).…”

“…Cigolini et al (2018) analyzed satellite TIR images over the crater during the 2014-2016 eruption, but they did not provide absolute values of the plume heat discharge. Nashimoto and Yokoo (2023) analyzed aerial TIR imagery in 2020-2022, but they only targeted the fumarolic fields. Considering active plume discharge, these plumes were probably the primary form of heat discharge at the crater during 2020-2022.…”