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SUMMARY:Microwave remote sensing of volcanic ash clouds. - Dr Mario Montop
 oli\, Department of Geography\, University of Cambridge
DTSTART:20120521T131500Z
DTEND:20120521T143000Z
UID:TALK36310@talks.cam.ac.uk
CONTACT:Dr Alex Archibald
DESCRIPTION:Plinian and sub-Plinian volcanic explosive eruptions probably 
 represent one of \nthe most devastating natural events for the surrounding
  environment\, endangering people’s \nlives and property. Explosive volc
 anic eruptions can significantly influence climate as well as \ncloud form
 ation and global circulation through atmospheric transport. Volcanic ash c
 louds are \nalso an increasing hazard to aviation safety because of growin
 g airline traffic. From the first \nrudimental visual inspections at the t
 imes of Pliny the Elder\, the human curiosity and its needs \nto find effe
 ctive countermeasures to these extreme volcanic episodes has never ceased\
 , even \nthough their (fortunate) rarity makes the scientific research qui
 te challenging.\n\nNowadays\, visual inspections are accompanied by sophis
 ticated measurements made by \ndirect analysis and from remote sensors. Mi
 crophysical characterization of the Plinian volcanic \nash plumes is usual
 ly carried out by analyzing tephra deposits and ash sedimentation at groun
 d. \nThis analysis may only give indirect information on the ash cloud com
 position as several \nprocesses can take place during the ash fallout. On 
 the other hand\, real-time monitoring of a \nvolcano eruption is not alway
 s possible by conventional visual inspections due to the usual low \noptic
 al visibility. Finally\, airborne flights within ash plumes using sample p
 robes\, as done for \nwater clouds\, are considered too dangerous for the 
 safety reasons previously mentioned.\nRemote sensing techniques represent 
 a unique tool to be exploited for this scope. They \nallow observing the e
 volution of some key parameters of volcanic eruptions without a direct \ni
 nteraction between the measurement system and the target of the measure. E
 lectromagnetic or \nacoustic waves are usually used to this aim.  Among th
 e available remote sensing techniques\, \nsatellite-based approaches\, usi
 ng multi-frequency radiometers with visible and infrared \nchannels\, have
  demonstrated to be a valuable supports to the monitoring of ash clouds. \
 nMoreover\, measurements in the visible spectral window are not always ava
 ilable due to its \nsolar illumination dependence and the optical thicknes
 s of volcanic clouds can severely impair \nthe sounding of lower cloud lay
 ers. \n\nIn  contrast with satellite methodologies\, ground-based microwav
 e scanning weather \nradars can gather three-dimensional information of as
 h-cloud scattering volumes with ranges \nup to several hundreds of kilomet
 ers\, in all weather conditions\, at a fairly high spatial \nresolution (h
 undreds of meters) and with a repetition cycle of few minutes.  So far\, t
 hese\nsystems have been mainly used for meteorological operational forecas
 ts and for observing of \nsome small number  of volcanic areas which can b
 e  monitored by previously installed \ninstruments. There are also several
  open issues about microwave weather radar capabilities to \ndetect and qu
 antitatively retrieve ash cloud parameters.\n\nAfter a basic introduction 
 on remote sensing principles\, the presentation will focus  at \nillustrat
 ing and assessing the potential and limitation of microwave remote sensing
  of Plinian \nand sub-Plinian volcanic eruption. This will be done using e
 xamples from both ground based \nradar and satellite radiometers data\, co
 llected after the 2010 and 2011 eruptions in Iceland. \nSome quantitative 
 estimates of ash category and ash concentration will be shown  together wi
 th  \nexplanations of the algorithms used.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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