Development of a Cooled Infrared Camera for Measuring Volcanic SO2 Gas Concentration and Temperature Distributions

Abstract

The volcanic surface phenomena (e.g., ground-surface brightness temperature distribution, volcanic gases, and volcanic ashes) provide useful information to evaluate the current status of volcanic activities. We are planning to develop a new observation device called a surface phenomena imaging camera with a cooled longwave infrared camera (SPIC-C (LWIR)). The SPIC-C (LWIR) is a multiband camera (multi-spectral camera) system used to measure the temperature and SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas concentration. To realize the SPIC-C (LWIR), we prototype cooled LWIR camera (SPIC-C (LWIR) Camera 3) by adopting a VGA ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$640\times 512$</tex> ) cooled T2SL sensor head unit. The performance evaluations indicate that this system can achieve a NETD of approximately 0.1 K. The evaluation of SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> measurement accuracy by simulation using the same SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas concentration distribution conditions as our original airborne hyperspectral sensor's (ARTS) actual observation on Apr. 8 2008 reveals that the developed cooled LWIR camera can detect SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas concentration distributions ranging approximately 0.2 - 0.4 ppmv in the background conditions at a temperature of 50 °C with errors of ±0.1 ppmv. These results indicate that the developed cooled LWIR camera can be a sensor head unit for the prototype SPIC-C (LWIR) system.