Hot Spots Gallery

In this section we will show you a gallery on how remote sensing helps to detect hots spots.

Fig. 5.7 - Meteosat 8 IR3.9 - 25 July 2004 17:15 UTC.

This Figure is an example of an IR3.9 image over Portugal and part of Spain, with hot spots in red, where the brightness temperature exceeds the threshold of 50 ºC.

Fig. 5.8 - Meteosat 8 IR3.9 - 4 August 2005 13:00 UTC.

Although it may seem a promising image for detecting fires, in fact it does not distinguish fires from hot land during the day as we see in the this example of a hot summer day (Fig 5.8).

Fig. 5.9 - Left image: Meteosat 8 IR3.9 - 3 August 2003 12:00 UTC (inverted grey scale - hot spots as darker pixels). Right image: Meteosat 8 NIR1.6 for the same instant (non-inverted grey scale - hot spots as white pixels). Click to enlarge.

Two Meteosat 8 images are shown here. On the left there is the 3.9 µm (inverted image) and to the right the near-infrared 1.6 µm. Most striking in the 3.9 µm image are the hotspots associated with the fires (darker pixels). A closer look even reveals some smoke swirling northward from those pixels. If fires are too hot they may even be detected using 1.6 µm. In this example, only a few pixels with high radiance values (white pixels) are identified at 1.6 µm, while the number of pixels in the 3.9 band is much larger (number of dark pixels). Note the hot spot color is different in the images, as the IR3.9 is inverted and the NIR1.6 is not!

Fig. 5.10 - Meteosat 8 Night Microphysical RGB - 5 August 2005 02:00 UTC. Pixels are depicted in magenta for fire hot spots. Source: Portuguese Met. Service.

Figure 5.10 shows the so-called Night Microphysical RGB where the range and gamma values are defined to depict fire pixels in magenta.

The magenta color results from high values on the red and blue beams and low values on the green beam. The key beam is in fact the green - less and less green is obtained when IR3.9 brightness temperature increases and steps away more and more from the IR10.8 brightness temperature (up to a maximum difference of 15 ºC). Also, the air has to be very dry, so the difference between the brightness temperatures of IR10.8 and IR12.0 is close to 0 (maximum of red), and the fire pixels have to have a brightness temperature of at least 20 ºC in IR10.8 (maximum of blue). These two final conditions are peanuts for a fire event, right?

Fig. 5.11 - Meteosat 8 IR3.9 - 21 August 2005 17:00 UTC.

In Figure 5.11 one can see the construction of the so-called Fire RGB which uses the VIS0.6, HRV and IR3.9 channels. In the ultimate RGB the fires themselves appear as red dots. A close look also shows the smoke which was swirling over the Atlantic Ocean on that day.

During the night there is no contamination of the IR3.9 band by solar radiation. Naturally, this is not the case during the day, which makes it more difficult to detect hot spots. However, there have been case studies where some RGBs have been successfully used to detect hot spots subjectively during the day. The image shows the hot spots over northern and central Portugal on a day during the devastating 2005 forest fire season.

Fig. 5.12 - Left Image: Meteosat 8 IR3.9 - 7 July 2003 (inverted grey scale - hot spots as darker pixels). Right Image: Meteosat 8 IR3.9-IR10.8 - 7 July 2003 (the brighter the pixels the higher the difference). Click to enlarge.

Here is a case of fire hot spots over Congo and Angola. The fires are depicted in both the single IR3.9 image and the difference IR3.9-IR10.8 image.

Fig. 5.13 - Metop AVHRR RGB composite channels 1, 2, 3 - 25 August 2007 09:55 UTC.

The following two examples are from Greece during the last week of August 2007, when large parts of the Greek countryside - from the island of Evia north of Athens to the Peloponnese in the south - were ravaged by some of the worst wildfires in living memory.

The locations of fires and smoke can also be seen with the METOP satellite using the AVHRR instrument.

Fig. 5.14 - Meteosat 9 Night Microphysics RGB (IR12.0-IR10.8, IR10.8-IR3.9, IR10.8) - 26 August 2007 03:00 UTC

Another RGB image which uses most of the thermal channel (which makes it possible to also monitor fires at night). The hot spots themselves are seen as small red dots in the center of the image.

Fig. 5.15 - EUMETSAT MPEF fire product for Meteosat 9 over Central Africa on 10 July 2008 12:15 UTC. Probability of fire in yellow squares and high probability of fire in red squares. Updated daily.

Figure 5.15 is again the EUMETSAT fire product which was also presented in the beginning of this chapter. In this case a zoom is made over western Africa, where pixels with a probability of fire are found over Senegal and Gambia during the summer of 2008.

Fig. 5.16 - Composite of LSASAF Fire Detection & Monitoring (FD&M) product for January 2007. Courtesy of LSA-SAF.

The Fire Detection & Monitoring product from the LSA SAF (Fig. 5.16) is a pre-operational procedure that allows detecting active fires based on information from MSG-SEVIRI. The procedure takes advantage of the temporal resolution of SEVIRI (one image every 15 minutes), and relies on information from SEVIRI channels (namely 0.6, 0.8, 3.9, 10.8 and 12.0 μm) together with information on illumination angles. The method is based on heritage from contextual algorithms designed for polar, sun-synchronous instruments, namely NOAA/AVHRR and MODIS/TERRA-AQUA. A potential fire pixel is compared with the neighbouring ones and the decision is made based on relative thresholds as derived from the pixels in the neighbourhood.

Fig. 5.17 - MODIS fire product (polygons in red) on 25 September 2007 over Bolivia. Source: NASA Earth Observatory - Natural Hazards.

Hundreds, possibly thousands of fires (locations marked in red) were burning in South America when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite passed overhead on 25 September 2007 and captured this image. The most intense fire activity was in Bolivia, where fires are concentrated in the Santa Cruz Department, in the southeastern part of the country. Thick smoke hangs over much of the scene. The towering Andes mountains (lower left) partially block the flow of smoke to the west.

Fig. 5.18 - MODIS fire product (polygons in red) on 8 July 2008 over Turkey and Cyprus. Source: NASA Earth Observatory - Natural Hazards.

The MODIS fire product mentioned earlier is very well suited for the detection of hotspots in a higher resolution than those obtained from geostationary platforms such as the MSG. This is an example of the MODIS fire product in southern Turkey, in which the hotspots are plotted in red polygons. These are superposed on a composite image using three bands from the visible region of the spectrum. In the image, the smoke generated by the fire is also clearly visible as it is being driven southward and reaches Cyprus.

Although it might be easier to identify small/weak forest fires with a polar orbiter satellite, like is the case of MODIS, the high temporal frequency provided by geostationary observations enables to follow the life cycle of the identified fires. An example of this is provided by fig. 5.19 showing the temporal behaviour of the wild fires over the Sahel region for 2 weeks in 2004 as captured by a fire product derived from Meteosat 9, the Fire Radiative Power (in short, FRP) (on the left axis). This product is also being computed by the LSA SAF. As you can see, the temporal behaviour of the fire activity is very well captured by the high SEVIRI revisiting time (15 minutes). The colors represent different land covers; Mosaic Forest, Savanna and Deciduous woodland have the most pronounced diurnal cycle of the fire activity.

Fig. 5.19 - Daily variations of the FRP (Fire Radiative Power produced by the LSA SAF) and the combustion rate over the Sahel region, averaged from 1 to 15 February 2004. (In: Yves Govaerts et al., The operational MSG/SEVIRI fire radiative power product generated at the LAND SAF. Proceedings of 2008 EUMETSAT Meteorological Satellite Conference, Darmstadt, Germany, 8 - 12 September 2008). Click to enlarge.

The previously mentioned Fire Radiative Power (FRP) product from LSA SAF corresponds to the amount of radiant heat energy of a fire per unit time. It is measured in megawatts every 15 minutes on a pixel basis, being currently in a pre-operational status. The example showed in Figure 5.20 is for the fires over Greece on 25th August 2007 at 09:45 UTC. Note that this product can be extremely useful as it was found to be related to the amount of fuel consumed by fires.

There is another related product that will become available in 2012: the FRP grid, which will estimate hourly averages of FRP within 1º longitude times 1º latitude boxes. The FRP grid will also benefit from a correction for small fires that go undetected by SEVIRI and for potential cloud contamination. These corrections are based on statistical analysis performed for each box and the user will access both the end product and all correction factors applied. Other main ancillary pieces of information stored in the product include the percentage of burnt area and the average number of detected fires per grid box.

Fig. 5.20 - Fire radiative power on 12 October 2011, derived from SEVIRI (LSA SAF) and MODIS (NASA) data averaged over 125 km grid cells [mW/m2], for the MACC (Monitoring Atmospheric Composition & climate) D-Fire subproject. Click to enlarge.

Figure 5.20 presents the thermal radiation coming from actively burning vegetation and other open fires for 12 October 2011. The data is derived from SEVIRI (LSA SAF) and MODIS (NASA) and calculated as daily averages of FRP in 125 km grid cells [mW/m2]. This (daily average) FRP areal intensity data is computed within the D-Fire subproject, which provides data of global emissions from biomass burning that are used as model input for smoke distribution forecasts (organic matter, black carbon and sulfate aerosols). The emissions are calculated in real time and retrospectively from satellite-based observations of open fires (for example wildfires and human-ignited grassland and forest fires).

Fig. 5.21 - Modelled organic matter plus black carbon AOD [-] (left, blue) and MODIS visual images (right) for an Aqua overpass on 25 August, 12:05 UTC, (top) and a Terra overpass on 26 August, 09:35 UTC (bottom). Overlaid with SEVIRI FRP [W/m2] interpolated to model resolution (left, orange) and MODIS hot spots in (right, red). Click to enlarge.

The left panel shows the fire intensity observed by the SEVIRI instrument in terms of fire radiative power (FRP per unit area at 25 km resolution, reddish color bar) and the optical depth of the simulated resulting smoke aerosols (AOD, bluish color bar) for 26 and 27 August. Images on the right show concurrent MODIS observations; the simulations and observations of the Greek fire plumes display very similar shapes. (source: landsaf.meteo.pt)