The Technical Concept of Differential Optical Absorption Spectroscopy for SO2 Gas Spectrum Monitoring on Volcanic Ash of Gunung Anak Krakatau volcano

Gunung Anak Krakatau is one of the active volcanoes in Indonesia. In October – December 2018, it erupted 156 times by releasing incandescent materials and toxic gases in the form of sulphur dioxide (SO2), carbon dioxide (CO2), and hydrogen sulphide (H2S) at 2 km radius. The release of SO2 gas indicates that magma is approaching the surface and puts the volcano on alert status. Finally on 22 December 2018 the continued eruption caused the flank collapse on some part of the volcano, triggered a tsunami that stroke the coastal of Lampung and Banten. This work investigated the SO2 gas monitoring technology using Differential Optical Absorption Spectroscopy (DOAS). The study specifically concerns on the working principles of DOAS, optimization of DOAS with optical bandpass filters and amplifiers, as well as the implementation architecture design of DOAS from Gunung Anak Krakatau Volcano to Hargo Pancuran Monitoring Station. Based on this study, the DOAS can be used to monitor SO2 gas by using a catadioptric telescope and the optimization works for UG11 as an optical bandpass filter and Raman Amplifier as the amplifier.