Availability of volcanic ash observations
Wednesday 28, April 2010
There are a range of instruments and techniques that can be used to help identify the likely presence of volcanic ash. Each has its strengths and weaknesses and by combining all of them we can produce a better picture of the likely locations and concentrations.
Observation types
Satellite
Different types of products capable of detecting airborne aerosols and trace gases (e.g. sulphur dioxide), most effectively where features are of high density. Clouds can mask signals.
LIDAR
Optical sensing of atmospheric aerosol up to approximately 10 km in non-cloudy conditions, some instruments are capable of providing information on aerosol type, size and distribution (which can help to distinguish volcanic ash from other types of aerosols).
LCBR
Equipment designed to observe cloud base height, which can be used to aid observation of aerosol layers in non-cloudy conditions up to approximately 3 km.
Manual surface observations
Reports of ash/dust seen by trained observers who continuously monitor weather and atmospheric phenomena (e.g. haze) and use other information such as LCBRs to assist in identification of the height of any aerosol layer observed. Can be affected by cloud cover and visibility.
ATD lightning detection
Locates lightning strokes, including those generated by volcanic ash plumes, but weak strokes may be missed. Can help to identify the strength of the eruption and the height of the emissions.
Aerosol weather balloon
Aerosol sampling instrument carried by a weather balloon up through the atmosphere, which can detect concentration and size of particles within that specific location.
Research aircraft
Downward facing LIDAR and other instruments attached to an aircraft can detect the presence of aerosol layers below the aircraft, size of particles, total mass of material and concentration of trace gases such as sulphur dioxide.
Sun photometer
Spectral analysis of sunlight giving an indication of aerosol concentration through the depth of the atmosphere at that location.
Aerosola suspension of fine solid particles or liquid droplets in a gas, which in the atmosphere can include volcanic ash, dust (e.g. Saharan dust), industrial pollution.
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