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Cold anomaly in NE Portugal


nick <dctower@...>
 

Evening all,

Any one else see the _very_ cold (black) area in NE Portugal in the last few IR images? Very obvious in Channel 4 from about 18:30 to 19:15?

Also on several other wave-lengths but not so obvious.

Any ideas as to what/why?

Regards

Nick


Terence O'Hanlon Smith
 

--- In MSG-1@yahoogroups.com, nick <dctower@...> wrote:

Evening all,

Any one else see the _very_ cold (black) area in NE Portugal in the last
few IR images? Very obvious in Channel 4 from about 18:30 to 19:15?

Also on several other wave-lengths but not so obvious.

Any ideas as to what/why?

Regards

Nick
Nick,
it looks rather as though it's a quite serious fire near the border. It shows up very well on the fire-monitoring animation.
Regards,
Terence


Alan Sewards
 

Nick,

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

On 22/09/2012 9:59 PM, nick wrote:
Evening all,

Any one else see the _very_ cold (black) area in NE Portugal in the last
few IR images? Very obvious in Channel 4 from about 18:30 to 19:15?

Also on several other wave-lengths but not so obvious.

Any ideas as to what/why?

Regards

Nick

--
Alan Sewards
�mail: alan@asewards.net
web site: http://asewards.free.fr


nick <dctower@...>
 

On 23/09/2012 08:34, Alan Sewards wrote:
Nick,

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

On 22/09/2012 9:59 PM, nick wrote:
Evening all,

Any one else see the _very_ cold (black) area in NE Portugal in the last
few IR images? Very obvious in Channel 4 from about 18:30 to 19:15?

Also on several other wave-lengths but not so obvious.

Any ideas as to what/why?

Regards

Nick

Yes, not sure how I got hot/cold inverted :-)

Regards

Nick


Simon Proud <simon.proud@...>
 

Are you converting the data into an imprecise data type (such as 8bit int)?
Depending on the scaling you apply it could be that the values in that
region (~350K) are too high for the data type and so 'roll over' into a
very low value. This happens to us occasionally when calculating
reflectance in the twilight region.

/random guess

Cheers,
Simon

On Sun, Sep 23, 2012 at 11:07 AM, nick <dctower@nildram.co.uk> wrote:

On 23/09/2012 08:34, Alan Sewards wrote:
Nick,

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

On 22/09/2012 9:59 PM, nick wrote:
Evening all,

Any one else see the _very_ cold (black) area in NE Portugal in the last
few IR images? Very obvious in Channel 4 from about 18:30 to 19:15?

Also on several other wave-lengths but not so obvious.

Any ideas as to what/why?

Regards

Nick

Yes, not sure how I got hot/cold inverted :-)

Regards

Nick


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David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

Nick,

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:

http://en.wikipedia.org/wiki/Black-body_radiation

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.

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk


David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

Are you converting the data into an imprecise data type (such as 8bit int)?
Depending on the scaling you apply it could be that the values in that
region (~350K) are too high for the data type and so 'roll over' into a
very low value. This happens to us occasionally when calculating
reflectance in the twilight region.

/random guess

Cheers,
Simon
=====================================

Simon,

Likely the guys are using the images from the MSG Data Manager software. The thermal scaling applied to the images avoids wrap-around artefacts such as you mention.

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk