Re: Cold anomaly in NE Portugal
David J Taylor GM8ARV 🏴 🇪🇺
Unless you are using an inverted palette, black on a IR image
translates into hot, not cold. It looks to me as a small hot spot,
probably a fire as suggested by Terence, but it is odd that it shows up
best in Ch4 and much less so in Ch9.
Best regards - Alan S
It's not really "odd". Channel 4 is most sensitive in the 3-5 um waveband, corresponding to temperatures around 600K (~327C) as found in fires. Channel 10 is optimised for radiation at 300K (~27C), that of the natural ground around us. See:
Note that one issue with channel 4 is that there is also significant reflected solar radiation from the Earth in that waveband, so that the image differs between day and night. Black hot is often used for thermal images, as that makes the colder clouds show up in white. Channel 4 is used for fire detection, perhaps using channel 10 as a reference to the expected background temperature so that hotspots can be detected.
I hope no-one has been injured in the fires.
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