|MODIS wavelengths for volcanic cloud detection – a quick and dirty summary.
Many thanks to the authors of the listed references. Special thanks to A.T., BoM - Darwin VAAC.
|405-420 nm||8||Ocean colour band, normally saturated for cloud, but can be unsaturated for cloud with high aerosol content (Tupper et al, 2003). Close to SeaWIFS channel 1, used by Higurashi & Nakajima (2002) for sulphate/kosa/sea-salt discrimination near Miyakejima.|
|459-479 nm||3||Bands 1,4, & 3 are used in RGB ‘true colour’ images, easy to interpret for strong albedo features, but potentially misleading as diffuse ash can be invisible. Best prepared on ‘HDF Look’, which has atmospheric corrections and is free!|
|1628-1652 nm||6||Near-infrared bands. 3.X bands have been used extensively in ash cloud detection (Ellrod & Connell, 1999, Ellrod et al, 2003) as well as hot spot detection, and are now available on most geostationary satellites. 1.6 µm channel (not functioning on Aqua/MODIS, but 2.1 µm is an acceptable substitute) corresponds to NOAA/AVHRR 3A, which has been used successfully to distinguish ash-poor Miyakejima plumes from water/ice clouds because of reflectivity of different particle size (http://arist.edu.kagoshima-u.ac.jp/miyake/ and Kinoshita et al, (2003)). Ellrod et al (2003) used 4.5 µm band because of relative lack of reflectivity problems.|
|6.535-6.895 µm||27||Part of SO2 test used by Crisp (1995). Worth trying 27-28 or vice versa.|
|7.175-7.475 µm||28||Part of SO2 test used by Crisp (1995). Used by Rose et al (2003). Not so sensitive to volcanic ash as 8.6 µm, but more sensitive to water vapour and cloud height (Watson et al, 2003).|
|8.400-8.700 µm||29||Very useful for SO2 and sulphate aerosol detection, also sensitive to ash and water vapour (Realmuto et al, 1997). Used by Rose et al (2003). Most effective night-time band for sensing Miyakejima plumes (Kinoshita et al, 2003). Trialed by Meteo-France (2001) with mixed results.|
|9.580-9.880 µm||30||Possibly sensitive to O3, SO4. Meteo-France (2001) trialed for SO2 detection with mixed results. Used in Rose et al (2003). Observed response for Miyakejima eruption of Aug 29, 2000 (Kinoshita et al, 2003).|
|10.780-11.280 µm||31||‘Reverse absorption’ (Prata 1989) using 11-12 µm is most widely used and effective test for diffuse volcanic ash (Prata et al, 2001) and for estimating quantities (Wen & Rose, 1994). Affected by water vapour, underlying cloud & various factors (Rose et al, 1995, Rose et al, 2000, Prata et al, 2001).|
|14.085-14.385 µm||36||Part of SO2 test used by Crisp (1995)|