Tweets on Tuesday 7 March 2017 highlighted the fast-moving fires over the High Plains (that began burning on 6 March), and they also highlighted different bands available from the GOES-16 ABI. For example, this tweet references the loop above, showing an animation of 3.9 µm temperatures; that shortwave infrared channel is used because it is more sensitive to hot temperatures than longer wavelength infrared channels. The Norman WFO also tweeted out imagery, shown below, that included the 0.86 µm ‘Veggie’ band and the 0.47 µm visible band. Why use those two channels?The 0.47 µm imagery is observing a part of the visible electromagnetic spectrum where scattering is largest, so smoke plumes are more apparent at that wavelength than at 0.64 µm. For a very obvious event such as this one, this might not be as important, but for a modest fire event over Florida, shown next, it can be. The 0.86 µm imagery is useful because it very distinctly shows fire burn scars; that is, the contrast at 0.86 µm between vegetated soil and adjacent burned regions is greater than occurs at other visible wavelengths. That is shown in the toggle below that steps through 0.47 µm, 0.64 µm, 0.86 µm, 1.61 µm and 3.9 µm imagery for one time on 7 March. The smoke plume is most distinct at the shortest wavelength 0.47 µm; it is very difficult to discern at 0.86 µm and especially at 1.61 µm because these near-infrared channels sense radiation at longer wavelengths that is unaffected by scattering of light by the small smoke particles. Note, however, that the small lakes do jump out at both wavelengths because of the very different reflectance properties of land and water at both 0.86 µm and 1.61 µm.
Finally, compare the 0.64 µm and 0.86 µm with special focus on the burn scars (here is a toggle between the two). Although the spatial resolution is greatest in the 0.64 µm visible imagery (0.5 km at the sub-satellite point, vs. 1 km at the sub-satellite point for the 0.86 µm imagery), the burn scars nevertheless are more distinct at 0.86 µm, in part because vegetated ground is more reflective at 0.86 µm than at 0.64 µm (See the figure in ‘Tim’s Topics’ on page 2 of the 0.86 µm fact sheet).
AWIPS Note: The default enhancement (“IR_COLOR_CLOUDS_WINTER”) for 3.9 µm results in imagery that shows too little gradation over Florida during the daytime; for fire detection, either modify the colormap (this changed the temperature range from the default [-109 to 55] to -70 to 75, and is shown above) or switch to the”IR_COLOR_CLOUDS_SUMMER” enhancement.