Tuesday, 11 February 2003: 9:15 AM
Development of volcanic ash image products using MODIS multi-spectral data
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua and Terra spacecraft provides 1 km resolution Infrared (IR) data in twenty spectral bands, with sixteen additional, higher resolution visible and near-IR bands available during daytime. Several of the MODIS spectral bands have previously been shown to be useful for the detection of airborne volcanic ash clouds that pose hazards to aircraft. Due to some degradation in the volcanic ash detection capability of the Geostationary Operational Environmental Satellite (GOES) Imager series, beginning with GOES-M (2002) through GOES-Q (late 2008 launch) there is a need for polar orbiting satellite image products to augment GOES in support of the operational aviation volcanic ash warning system. Work has begun within NOAA/NESDIS to develop prototype volcanic ash products from MODIS to support the Volcanic Ash Advisory Centers, as well as to prepare for advanced satellite systems such as the National Polar Orbiting Environmental Satellite System (NPOESS), and the GOES Advanced Baseline Imager that will have similar capabilities.
Initial analysis of MODIS data has been completed for two volcanic eruptions: (1) Cleveland volcano in the Aleutian Islands on 19 February 2001, and (2) Popocatepetl volcano near Mexico City on 19 December 2000. Two data sets were analyzed for each case (one daytime, one nighttime) using Man-computer Interactive Data Access System (McIDAS) image processing software on PC workstations.
Various combinations of MODIS IR bands have been evaluated. The best results obtained so far utilize Band 32 (12.0 µm), Band 31 (11.0 µm) and Band 29 (8.6 µm). The latter channel is sensitive not only to silicate ash, but also to sulfur dioxide gas and sulfates. Experiments with Red-Green-Blue color composite techniques have also resulted in a daytime image product that combines information from the three-band IR volcanic ash image with visible (0.6 µm) and near-Infrared (1.6 µm) data. The latter two channels help distinguish ice versus water clouds. Future efforts will involve the near real-time processing of MODIS data in native netCDF format, which will soon be available via a high speed data line from NASA to NOAA/NESDIS in Camp Springs, Maryland.