Improved detection of airborne volcanic ash using multispectral infrared satellite data

Abstract

[1] A technique for improved detection of airborne volcanic ash has been developed that uses three infrared (IR) bands from meteorological satellites. The three IR bands are centered near 3.9, 10.7, and 12.0 mm wavelength. The technique is based on the sum of two brightness temperature differences (BTDs), scaled to maximize the brightness and contrast of volcanic ash in the output image. The physical effects attributed to the observed BTDs that help distinguish the volcanic ash from various meteorological cloud types are (1) differential absorption by volcanic ash or sulfur dioxide at 3.9 mm, 10.7 mm, and 12.0 mm and (2) strong solar reflectance by ash at 3.9 mm, which varies diurnally. On the basis of two examples using data from the Geostationary Operational Environmental Satellite (GOES) the three-band IR technique is shown to provide better discrimination of volcanic ash from meteorological clouds than is possible using existing two-band methods. This conclusion is supported by comparisons of brightness count profiles and estimation of false ash detection rate statistics. The best results from the three-band IR technique are obtained during daylight hours over any surface, and at night when the ash cloud is over the ocean or other large body of water. The three-band IR technique is one of the tools currently being employed operationally at the Washington Volcanic Ash Advisory Center.

An evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ‘Ring of Fire’

“…The net effect of these improvements will be to reliably sense more of each ash cloud, and to sense the ash clouds to a greater distance and time from their source. In addition, the availability of a 3.7 µm channel on MTSAT will enable implementation of 3-channel techniques (Ellrod et al, 2003) to better detect volcanic clouds, as well as further research into improved uses of short-wave IR channels for future satellite sensors.…”

Assessment and validation in time domain of a Robust Satellite Technique (RSTASH) for ash cloud detection

“…The local variation index T11-T12 (x, y, t) takes into account the reverse absorption of volcanic ash clouds at spectral wavelengths of 11 mm and 12 mm in comparison with meteorological ones (Prata 1989a, b). The local variation index T3-T11 (x, y, t), instead, considers the potential of the different behaviour in the mid-infrared band (MIR) of weather clouds and ash plumes (Ellrod et al 1999(Ellrod et al , 2003, contributing to better ash particle identification and discrimination. Negative values of the T11-T12 (x, y, t) index are generally expected in the presence of volcanic ash, whereas positive values of the T3-T11 (x, y, t) should characterize the same features with a different intensity, on the basis of the observational conditions .…”

“…However, these traditional satellite techniques, although performing quite well under specific conditions (e.g. low water vapour or ice concentration inside the plume, suitable temperature contrast between surface background and ash clouds), generally show unstable behaviour, with performances depending on local conditions as well as on the nature and features of erupted ash clouds (Ellrod and Connel 1999, Simpson et al 2000, Prata et al 2001, Simpson et al 2001, Ellrod et al 2003.…”

“…Ellrod and Connel 1999, Ellrod et al 2003, Bonfiglio et al 2005, Pavolonis et al 2006, although satellite methods capable of automatically identifying volcanic ash clouds under different observational conditions, assuring a full reliability (i.e. ash detection with very low false positive rate), are still required for effective monitoring of such volcanic phenomena.…”

A new simplified approach for simultaneous retrieval of SO<sub>2</sub> and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano

“…Because of the sporadic nature of volcanic eruptions and their large geographic extents, satellite remote sensing provides the most suitable technique for detecting and assessing volcanic emissions. The detection and assessment of volcanic ash clouds has been performed using different multispectral polar satellite instruments, including the Advanced Very High Resolution Radiometer (AVHRR, Prata, 1989a, b;Wen and Rose, 1994;Krotkov et al, 1999;Yu et al, 2002;Corradini et al, 2010), the Moderate Resolution Imaging Spectroradiometer (MODIS, Hillger at al., 2002;Ellrod et al, 2003;Watson et al, 2004;Corradini et al, 2008Corradini et al, , 2009Corradini et al, , 2010 aboard the Terra/Aqua NASA satellites, and multispectral geostationary satellite systems like for example the Geostationary Operational Environmental Satellite (GOES, Rose and Mayberry, 2000;Yu et al, 2002;Ellrod et al, 2003) and the Spinning Enhanced Visible and Infrared Imager radiometer (SEVIRI, Prata and Kerkmann, 2007) on board Meteosat Second Generation (MSG) satellites.…”