Millimetre wave FMCW radar as a tool for 3D Terrain mapping of volcanic topography

Since the start of eruptive activity in 1995 the lava dome at the Soufrière Hills Volcano, Montserrat has grown and collapsed repeatedly with many of the larger rockfall collapse events producing hazardous pyroclastic flows. Monitoring the timing, direction and magnitude of these avalanches remains a major difficulty due to the fundamental problem of being able to continuously observe the changing topography of the lava dome during periods of low or zero visibility. Cloud cover can last for weeks at a time, during which the location and magnitude of significant changes (tens of metres) to the dome topography can remain undetected. Since 2002 the Millimetre Wave and High Filed ESR group in St Andrews have developed portable ground based FMCW millimetre wave radar for use as a practical field tool for the remote sensing of volcanic terrain at active lava domes. The primary aim of the All-weather Volcano Topography Imaging Sensor (AVTIS) instruments is to record 3D topography at safe ranges of up to 7km to enable round-the-clock monitoring of lava dome bulk growth, i.e. detect topographic changes on the order of meters per day. The original AVTIS prototype developed between 2002 and 2008 proved the viability of low power millimetre wave radar for remote sensing of volcanoes, combining active active and passive measurement modes to record the 3D shape, reflectivity and brightness temperature of target topography in most viewing conditions. There currently exist two instruments: AVTIS2, a long range (7km) portable rover designed for quick and practical field deployment and AVTIS3, a smaller autonomous unit deployed in 2011 under telemetered control at a fixed site at the Soufrière Hills Volcano, Montserrat. We will describe the how the AVTIS instruments are deployed in the field, the quality of the primary ranging and radiometric measurements, and the post processing techniques used to derive the geophysical products of the target terrain, surface temperature, and reflectivity. We will also discuss the estimation of volume change and lava extrusion rate from these data products.eft: AVTIS-2 rover (top) and AVTIS-3 installationat the Soufriere Hills Volcano. Centre: AVTIS-temperature image draped over an AVTIS-DEM of 2005 lava dome. Right: Photo of SHV from Windy Hill obscured by cloud (top) and contemporary AVTIS radar reflectivity image (bottom) in 2011.