Washington Volcanic Ash Advisory Center: Utilization of Satellites in Operations

Volcanic ash is an extreme hazard, not just locally, but due to size and weight is easily transported by winds affecting large areas. Its abrasive nature and low melting point, also, make it a severe hazard to the aviation community, particularly jet engines. Meteorological satellites provide a unique perspective for the detection and tracking of volcanic ash clouds. Since 1981, the Satellite (Synoptic) Analysis Branch (SAB) has provided analysis of large eruptions utilizing its focus of satellite techniques within a 24 by 7, 365 operational setting. Following 2 significant ash encounters with Boeing 747 aircraft in 1982 and 1989, the International Civil Aviation Organization (ICAO), developed a nearly world wide network of nine (9) Volcanic Ash Advisory Centres (VAAC) to provide detection, analysis, forecasting and communication of this hazard to the aviation community. In 1997, the Washington VAAC was officially established within SAB and was given areal responsibility of US airspace (except Alaska), Central and South America (to 10S) and the Caribbean. Text-based Volcanic Ash Advisories are issued containing analysis from satellite-derived imagery and products along with reports of ash from various sources, such as volcano observatories and pilots. A graphical depiction of current and forecasted ash cloud location or Volcanic Ash Graphic (VAG) can also generated utilizing output from the National Weather Service (NWS) HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model, as well as, other non-NOAA dispersion model sources. As jet aircraft can cover a large distance in a very short period, it is imperative to provide volcanic ash detection as soon as possible, so geostationary imagery continues to provide the best temporal resolution for rapid response to the initial eruption and the most current state of the ash cloud. Along with the conventional visible and IR imagery, utilizing the volcanic ash response at 12 um portion of the spectrum through differencing with 11 um, or the split window technique along with variations of this method including the Ellrod technique (1998) and Principle Component Imagery (PCI, Hillger and Clark, 2002), have become staples of volcanic ash detection, particularly at night. However, a large portion of the area of responsibility and most of the active volcanoes in the Washington VAAC fall under the GOES-East footprint; which is without channel 5 (12 um). Channel 6 (13.3 um) has filled the void and is serviceable but does not lend itself to the confidence with the availability of the 12 um band. Numerous polar orbiting instruments: MODIS, AVHRR, OMI, and GOME2 and their derived products have provided additional information such as ash cloud height, SO₂ location, particle size and distribution; which is used to confirm and/or aid in adjustment to eruption parameters to dispersion model runs with eventual use in the issuance of an update VAA or VAG.