Lidar sounding of volcanic plumes

ABSTRACT Accurate knowledge of gas compositionin volcanic plumeshas high scientific and societal value. On the one hand, it gives information on the geophysical processes taking place inside volcanos; on the other hand, it provides alert on possible eruptions. For this reasons, it has been suggested to monitor volcanic plumesby lidar. In particular, one of the aims of the FP7 ERC project BRIDGE is the measurement of CO 2 concentration in volcanicgases by differential absorption lidar. This is a very challenging task due to the harsh environment, the narrowness and weakness of the CO 2 absorption lines and the difficulty to procure a suitable laser source. This paper, after a review on remote sensing of volcanic plumes, reports on the current progress of the lidarsystem. Keywords: lidar, differential absorption, aerosol load, water vapor, carbon dioxide, volcanic plumes1. INTRODUCTION The composition of volcanicgases gives information on the processes inside volcanosand on the transition from quiescence to eruption. Up to now, coupled gas-geophysical studies are sparse, due to the difference in their typical sampling frequency (> 1 Hz for seismic signals and < 10