Thermal distributions of discolored water around Osima and craters of Osima Miharayama by the airborne thermal infrared radiometer.

Abstract

As a part of the national program on the prediction of volcanic eruptions, the Hydrographic Department is conducting the investions by the remote sensing technique on the submarine volcanoes and the volcanic islands. After Miharayama erupted on Nov. 15, 1986, the Hydrographic Department made 14 time-observations of discolored waters around Osima and craters of Osima Miharayama by the airborne thermal infrared radiometer AGA 780 and the multiband camera MK-1 from Nov. 22, 1986 to Mar. 18, 1987. The results are ( 1)Temperature of discolored waters around Osima was lower than that of sea water surrounding discolored water of about l～ 2'C, and there was no higher-temperature discolored water. ( 2) If the discolored water was dense, the origin of it coincided with the lower temperature area of the seawater many times and correlation between the area of the discolored water and the isothermline was good. ( 3)There were many lower temperature areas without the discolored water目 ( 4)If the discolored water was thin, correlation between the area of the discolored water and the isotherm line was bad. ( 5) It was suitable to make thermal observations before sunrise to detect the distribution of the sea surface temperature in detail. ( 6) In the daytime observations, sea surface temperature was apt to show no thermal distribution pattern. ( 7)Temperature of the A crater (crater opened at the south wall of the old crater) had kept high. ( 8)Temperature of B craters (craters opened at the north rim of the old crater) showed a tendency to decrease, though samplings were few. Temperature of B craters on March 17 was rather high. (9) Temperature of C craters (craters opened on the flank of Miharayama) showed a strong tendency to decrease． Temperature of C craters on March 17 was nearly even to the ground temperature. (JO) Temperature of A crater, B craters and C craters became higher together before the small eruption on Dec. 18. As the observation condition was differed at every observation time, careful considerations should be required to discuss the relation between the volcanic activities and the temperature of the craters.