2:15 PM - 2:30 PM
[STT39-08] Crustal deformation of Azuma volcano detected by a portable radar interferometer for volcano observation (SCOPE)
Keywords:SAR, SCOPE, Azuma volcano, crustal deformation
Spaceborne SAR can investigate spatially detailed crustal deformation without field observations, making it an effective tool for detecting crustal deformation around craters that are difficult to access. However, the temporal resolution of spaceborne SAR is limited to the satellite recurrence period, making it difficult to understand crustal deformation transitions that progress over several days. Then we are developing a portable radar interferometer for volcano observation (sensor name: SCOPE) that can observe crustal deformation illuminating radar waves from the ground, which can be used for mobile observations when increase of volcanic activity is observed (Ozawa et al., JDR, 2019; Ozawa et al., 2022).
To detect crustal deformation of Azuma-yama, we conducted observations using SCOPE with the car-borne observation type on Oct. 28 and 29, 2021, Jul. 1, 2022, and Nov. 11, 2022. Azuma-yama is located in the northern part of Fukushima Prefecture in the Tohoku region, and active fumarolic activity is observed in the Oana Crater located at about 1700 m on the southern flank of Mt. Issaikyo. Himematsu and Ozawa (the volcanological society of Japan 2021 fall meeting) reported that expansion and contraction deformations have occurred repeatedly around the Oana crater from spaceborne SAR analysis. A road runs south of the Oana crater at an elevation of 1600 m, which provides a panoramic view of the Oana Crater, and it was used in the observations. The distance from the observation point to the crater is about 1 km. In an observation, a frame was fixed on the roof of car using suction cups and a radar antenna and GNSS/INS for positioning were mounted on it, and radar waves were transmitted and received while driving at low speed on the road. Another vehicle was parked approximately 300 m away from the observation point, and the GNSS antenna was fixed to its roof as a reference site for the positioning of the radar antenna. In the SAR processing, the antenna trajectory was set as a 20 m straight line. The antenna position obtained from the GNSS kinematic analysis was used to correct the fluctuation of antenna trajectory from the set trajectory to produce SAR images. As a result, an interferometric image was obtained without applying the image matching in the interferometric processing. Sufficient coherence for crustal deformation detection was obtained even for the interferometric pairs at approximately 1-year intervals. Atmospheric delay noise was reduced by applying a method for estimating atmospheric delay from the results of a numerical meteorological model (mesoscale model) published by the Japan Meteorological Agency (Ozawa and Shimizu, Journal of geodetic society of Japan, 2010; Ozawa et al., JDR, 2019). This resulted in a relatively flat phase distribution for the short-term pairs, suggesting that the atmospheric delay noise was well reduced by this method. On the other hand, in the interferometric pair of Oct. 29, 2021 and Nov. 11, 2022, a slant-range contraction was obtained in the southeast area of the Oana crater, and its maximum was about 3 cm. We analyzed PALSAR-2 data pair observed on Sep. 2, 2021 to Jun. 23, 2022 from the descending orbit of ALOS-2 (path 18, right-looking mode) and obtained that crustal deformation was insignificant. On the other hand, a slant range contraction of about 3 cm was obtained around the Oana crater from a data pair of Sep. 2, 2021 and Sep. 1, 2022. Assuming this slant-range change due to inflation, these results are consistent. We attempted to explain this crustal deformation using the elastic half-space dislocation model (Okada, BSSA, 1985), assuming a rectangular tensile fault, and obtained the 500 m x 600 m fault geometry that tilts slightly to the southeast just 400m below the Oana crater. The opening value was 15 cm. The obtained fault geometry is roughly consistent with the source of crustal deformation related to the past inflation estimated by Himematsu and Ozawa (2021).
To detect crustal deformation of Azuma-yama, we conducted observations using SCOPE with the car-borne observation type on Oct. 28 and 29, 2021, Jul. 1, 2022, and Nov. 11, 2022. Azuma-yama is located in the northern part of Fukushima Prefecture in the Tohoku region, and active fumarolic activity is observed in the Oana Crater located at about 1700 m on the southern flank of Mt. Issaikyo. Himematsu and Ozawa (the volcanological society of Japan 2021 fall meeting) reported that expansion and contraction deformations have occurred repeatedly around the Oana crater from spaceborne SAR analysis. A road runs south of the Oana crater at an elevation of 1600 m, which provides a panoramic view of the Oana Crater, and it was used in the observations. The distance from the observation point to the crater is about 1 km. In an observation, a frame was fixed on the roof of car using suction cups and a radar antenna and GNSS/INS for positioning were mounted on it, and radar waves were transmitted and received while driving at low speed on the road. Another vehicle was parked approximately 300 m away from the observation point, and the GNSS antenna was fixed to its roof as a reference site for the positioning of the radar antenna. In the SAR processing, the antenna trajectory was set as a 20 m straight line. The antenna position obtained from the GNSS kinematic analysis was used to correct the fluctuation of antenna trajectory from the set trajectory to produce SAR images. As a result, an interferometric image was obtained without applying the image matching in the interferometric processing. Sufficient coherence for crustal deformation detection was obtained even for the interferometric pairs at approximately 1-year intervals. Atmospheric delay noise was reduced by applying a method for estimating atmospheric delay from the results of a numerical meteorological model (mesoscale model) published by the Japan Meteorological Agency (Ozawa and Shimizu, Journal of geodetic society of Japan, 2010; Ozawa et al., JDR, 2019). This resulted in a relatively flat phase distribution for the short-term pairs, suggesting that the atmospheric delay noise was well reduced by this method. On the other hand, in the interferometric pair of Oct. 29, 2021 and Nov. 11, 2022, a slant-range contraction was obtained in the southeast area of the Oana crater, and its maximum was about 3 cm. We analyzed PALSAR-2 data pair observed on Sep. 2, 2021 to Jun. 23, 2022 from the descending orbit of ALOS-2 (path 18, right-looking mode) and obtained that crustal deformation was insignificant. On the other hand, a slant range contraction of about 3 cm was obtained around the Oana crater from a data pair of Sep. 2, 2021 and Sep. 1, 2022. Assuming this slant-range change due to inflation, these results are consistent. We attempted to explain this crustal deformation using the elastic half-space dislocation model (Okada, BSSA, 1985), assuming a rectangular tensile fault, and obtained the 500 m x 600 m fault geometry that tilts slightly to the southeast just 400m below the Oana crater. The opening value was 15 cm. The obtained fault geometry is roughly consistent with the source of crustal deformation related to the past inflation estimated by Himematsu and Ozawa (2021).