A useful application of ATSR data is the detection of forest fires and other hotspots on the Earth's surface.
Numerous bush fires are visible as tiny yellow spots in this nighttime image of the West African Coast.
Most of the bush fires are in the southeast of the image which is Sierra Leone. In this false-colour representation the coldest areas (clouds) are blue, with purple and yellow representing increasingly warmer temperatures.
In this night-time image, the large yellow area is the Atlantic Ocean with the cooler land appearing red. The average temperature of the fire pixels is about 300K, but this is not representative of the fire temperature as only a small fraction of the 1 square kilometer pixel is actually on fire.
An ATSR-1 image of the West African coast.
An ATSR-2 image of Forest Fires (US)
The 1980's were the worst decade for volcanic disasters this century, with 24000 - 28000 fatalities each associated with two particularly devastating eruptions, that of El Chichón (Mexico, 1982) and Nevado del Ruiz (Columbia, 1985).
Such tragedy clearly shows that active volcanoes continue to represent extreme hazards, despite advances in the technology available for ground-based monitoring of pre-eruptive volcanic phenomena (McGuire et al., 1995). This is particularly true in developing countries, where the presence of highly fertile volcanic soils often leads to large populations close to active volcanoes but where budgetary and logistical constraints most hinder monitoring efforts (Stoiber and Willams, 1990; Clarke, 1991).
To add to these difficulties, there is the problem of the sheer number of potentially active volcanoes whose monitoring needs to be addressed. The Catalogue of Active Volcanoes (CAVW, 1951-1975) documents over 500 volcanoes that have had recently dated eruptions and, on average, more than 50 eruptions occur annually. With a such a huge number of potentially active volcanoes, traditional monitoring techniques such as seismic and microgravity require assistance if all these targets are to be kept under surveillance.
Spaceborne remote monitoring is one method by which this may be achieved and the Along Track Scanning Radiometer, mounted onboard the European Remote Sensing Satellite, is well placed to assist in the development of such techniques since it views all of Earth's terrestrial volcanoes once every three days under nighttime conditions (the ideal time for such measurements to be made).
ATSR measures the amount of thermal energy being emitted from the Earth's surface, including all terrestrial volcanoes, and these volcanic measurements can be related to the amount of high temperature activity occurring at centres of known eruptive activity. This poster gives a brief introduction to the techniques used and presents some case studies using test-site volcanoes around the world.
This 'thermal' image taken from an aircraft shows the summit of Mt. St Helens Volcano, which famously erupted very explosively in 1980. The situation here is similar to that at Lascar in that hot gas escaping from fumaroles is heating the surrounding rock surfaces to very high temperatures
Measure of Radiance
During nighttime observations (i.e. in the absence of sunlight) ATSR measures the amount of thermal radiation arriving at the instrument in four different wavebands (1.6, 3.7, 11 and 12 µm), making measurements on a 1 x 1 km grid over the entire Earth surface.
The relationship between the temperature of the Earth's surface and the amount of emitted radiant energy is governed by a theoretical relationship known as the Planck Equation (Figure 1). Understood simply this relationship indicates that the wavelength of peak energy emission decreases as the temperature of the surface increases.
So, whilst ATSR's longer wavelength channels are good for looking at energy emitted from ambient temperature surfaces such as the ocean, ATSR's short wavelength channel (1.6 µm) can be used to observe the significant amounts of energy emitted from very hot surfaces such as those found at active volcanoes.
Since surfaces at temperatures less than around 300 °C do not emit significantly at 1.6 µm, any nighttime signal at this wavelength is evidence of high temperature activity at the location of interest. By monitoring this volcanic signal over time these measurements can be used to deduce changes in the nature of the high temperature activity and these inferences used to assist monitoring of the eruptive and pre-eruptive phenomena.
The Planck function showing the theoretical relationship between the energy (spectral radiance) emitted by the Earth surface at different temperatures. The bars indicate the four 'thermal' channels of ATSR, with the bar width indicating the wavelength range of the channel and the bar height the range of energies that the channel can measure. The 3.7, 11, 12 µm channel can measure Earth-surface temperatures up to around 50 °C, whilst the 1.6 µm channel can measure temperatures up to around 500 °C. Since the hot surfaces of active volcanoes are often much smaller in area than the 1 km² size of the ATSR measurements, the 1.6 µm channel can actually be used to monitor changes in surfaces significantly hotter than this.
Courtesy of Rutherford Appleton Laboratory