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Oxford University team measure ash fall
20 April 2010
As part of efforts to understand the impact of the ash cloud from Iceland, Oxford University graduate student Adam Povey was sent off to STFC's Chilbolton Observatory in Hampshire to use a LIDAR system, jointly operated by both Oxford University and Hovemere Ltd, to see if any sign could be detected of the ash cloud passing over southern England.
A LIDAR system (Laser Direction and Ranging) sends pulses of coherent light up into the sky and measures scattered and reflected light from any particles or debris floating in the air. From timing the 'echoes' it can determine not only the presence of material but also measure its height and thickness.
Adam began operating the LIDAR late on Thursday of last week. By Friday lunchtime, his measurements could detect a thin layer of material at around 3 km altitude (around 10,000 feet up), part of which slowly descended over the following couple of hours before merging with echoes from other debris at the top of a convection layer (the 'Planetary Boundary Layer') around 3,000 feet up. Below that height, the air is full of all sorts of other debris, including human-generated pollution, so is difficult to untangle from the volcanic ash.
This prompted the Head of Hovermere Ltd, Professor David Rees, to take to the air himself on Saturday in a light aircraft near Dover, and fly up to heights of 6,500 feet (the bottom of the currently closed airspace), during which he could see continued clear evidence for debris and fall-out from the ash cloud at heights around 6,000 feet, though he could not see any evidence for ash at higher altitudes.
Adam Povey is continuing to measure the ash cloud as it develops, and further data are being processed. But this clearly shows the presence of the ash gradually settling out over parts of the UK, even at relatively low levels.
For further information contact Dr Andy Sayer of Oxford University's Department of Physics at email@example.com or mobile: 07734 859851 (he is at the Rutherford Appleton lab today)
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