A description of an AVHRR volcanic ash detection product and examples of its application
Watkin Sarah
Volcanic ash clouds are a threat to aircraft safety. The London Volcanic Ash Advisory Centre, based at the Met Office, has a responsibility to issue advice to the aviation industry about the presence of volcanic ash in its designated area. To aid this task a volcanic ash detection product has been developed. This product displays the brightness temperature difference between two channels at 10.8 and 12.0 microns, on the Advanced Very High Resolution Radiometer (AVHRR). Negative brightness temperature differences are expected for semi-transparent volcanic ash and positive brightness temperature differences for semi-transparent water and ice clouds. Images are produced for three areas including the London Volcanic Ash Advisory Centre area of responsibility. These are displayed on an internal web page and are updated throughout the day as data from AVHRR passes are received. This report provides a description of the volcanic ash detection product and examples of situations that can affect the spectral signal in the imagery. Successful and failed detection of volcanic ash are discussed using examples from the eruptions of Mt. Spurr, Alaska in 1992, Soufriere Hills, Monserrat in 1997 and Hekla, Iceland in 2000. Several situations that cause false alarms have been identified and these are also discussed. A summary and ideas for future development of the volcanic ash product conclude this report.
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