Volcanic gas measurements using a compact mid-wave infrared hyperspectral imager

Abstract

Gases released from a volcano, such as sulfur dioxide (SO2) and carbon dioxide (CO2), present hazards to the environment and local populations as well as providing a means to monitor volcanic activity and study pre-eruptive signatures. In the Mid-Wave InfraRed (MWIR) from 3 to 5 microns both the aforementioned volcanic gases exhibit characteristic absorptions. Remote sensing in the MWIR, however, is challenging due to the limited amount of signal available to measure. This presents technical challenges on achieving high signal-to-noise ratios; therefore, acquiring adequate data in the MWIR has been difficult without cryogenically cooling the instrument. However, ecent improvements to microbolometer technology and emerging interferometric techniques have allowed us to acquire good thermal infrared data without the need for cooling. By utilizing the advantages of an imaging interferometer paired with an uncooled microbolometer, we demonstrate the use of a MWIR compact, hyperspectral imager for volcanic gas detection. The instrument, the Miniaturized Infrared Detector of Atmospheric Species (MIDAS), is representative of an instrument that could feasibly be flown on a small satellite in low earth orbit for the detection and monitoring of volcanic gases. Recently MIDAS was deployed to Kilauea’s Halema’uma’u pit crater which during the deployment had an active lava lake that was continuously releasing volcanic gases. Sources like the Kilauea lava lake provide high background temperatures that aid MWIR measurements of volcanic gases. We present hyperspectral analysis of volcanic gases from the Kilauea lava lake using data from the MIDAS instrument and line by line radiative transfer analysis. Brightness temperature maps of the lake surface show values consistent with direct thermocouple measurements and point radiometer measurements. Here we present resolved images of spectral radiance, brightness temperature, and CO2 concentrations. The map of CO2 is relatively uniform, but show subtle variation at the 2553 - 3313+/- 167 ppm level.