Operational Satellite Analysis Techniques of Volcanic Ash Detection and Height Determination at the Washington Volcanic Ash Advisory Center (VAAC): Methods, Problems, and New Techniques

Volcanic ash poses a significant hazard to aviation safety, as it is extremely abrasive to sensitive aircraft sensors, engines and other aircraft parts and with the explosive nature of ejecting ash to typical flight cruising levels in less than 30 minutes and cruising speeds of jet aircraft over 600 mph; detection of and tracking volcanic ash needs to be carefully monitored and warned upon in the quickest and most accurate nature. Obviously, near environment visual detection by aircraft and ground based volcano observers provide the most helpful information in determining volcanic cloud content and height information but this data is all too often not available due to remoteness of volcano, economic costs to run an observatory or monitoring station, and communication of said information. The role of geostationary and polar orbiting satellites has aided in filling the gaps left by human detection. In 1997, the Satellite Analysis Branch of NOAA/NESDIS began serving as the Washington Volcanic Ash Advisory Center (VAAC) per the request by the International Civil Aviation Organization (ICAO). Along with the Washington VAAC, eight (8) other centers (Anchorage, Buenos Aires, Darwin, London, Montreal, Tokyo, Toulouse, and Wellington) where created with the goal of providing volcanic ash information (via the Volcanic Ash Advisory, or VAA), mostly using satellite analysis. Since the Washington VAAC's area of responsibility spans over half the globe, multiple geostationary and polar meteorological satellites are used. With timeliness a significant issue, the VAAC favors geostationary imagery, though the higher spatial and spectral resolution polar imagery is used to help verify the analysis. Visible imagery tends to be the preferred method of ash determination at the VAAC. However, after dark or when determining weather from volcanic ash clouds, other techniques are used to exploit the sensitivity of 12 μm IR for detecting volcanic ash, including: Split Window (11μm – 12μm), Principle Component Imagery (PCI) (Hillger and Clark, 2003), and Ellrod technique (Ellrod, 2004). Other channels and techniques, such as 3.9 μm and the CIRA (2-4-2) technique, exploit the heat generated by volcanic activity, and can alert the analyst to the potential for airborne ash. Ash detection and height determination using these techniques can vary by volcano, time of day, and atmospheric environment sometimes with the possibility of introducing large error and time delay. Additionally, the replacement of the 12μm IR with the13 μm IR on the GOES-12 and subsequent GOES series satellites, some of these techniques have become degraded or are no longer effective, which has been difficult for VAAC, considering most of the active volcanoes fall under the GOES-EAST footprint.