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Trying to Understand How Sensors Work


pottyprof

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Posted
  • Location: Swallownest, Sheffield 83m ASL
  • Location: Swallownest, Sheffield 83m ASL

    But, and it's a very big but, why don't infrared-imaging satellites pick up on all these 'mysterious' and undiscovered eruptions?

    That'll be the CO2 absorbing the infrared, as it does...........

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    Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

    That'll be the CO2 absorbing the infrared, as it does...........

     

    Infrared has quite a large rage, from short wave reflected near infrared, to long wave emitted thermal infrared. Only sections of the IR spectra are absorbed by CO2, other parts are absorbed by methane, water vapour, ozone, etc, while some isn't absorbed at all.

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    Posted
  • Location: Derbyshire Peak District South Pennines Middleton & Smerrill Tops 305m (1001ft) asl.
  • Location: Derbyshire Peak District South Pennines Middleton & Smerrill Tops 305m (1001ft) asl.
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    Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

    What, in an isolated patch surrounding an individual volcano? Forensic experts can use IR imaging satellites to monitor underground missile silos...I think that such technology would be capable of noticing an undersea Krakatau...

     

    Shortwave infrared acts very much like visible light, and cannot penetrate ocean water to any usable depth. With thermal infrared, it could only be detected by heating of the overlying water, not from the volcano itself. 

    I do think that large underwater eruptions would be detected seismically though.

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.

    Shortwave infrared acts very much like visible light, and cannot penetrate ocean water to any usable depth. With thermal infrared, it could only be detected by heating of the overlying water, not from the volcano itself. 

    I do think that large underwater eruptions would be detected seismically though.

    I think I see what you mean, BFTV...So all that hot water ought to be detectable?

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    Posted
  • Location: Swallownest, Sheffield 83m ASL
  • Location: Swallownest, Sheffield 83m ASL

    Infrared has quite a large rage, from short wave reflected near infrared, to long wave emitted thermal infrared. Only sections of the IR spectra are absorbed by CO2, other parts are absorbed by methane, water vapour, ozone, etc, while some isn't absorbed at all.

    Makes you wonder how the sensors function properly at all.....

     

    I know, I know...  Different molecules reflect/absorb different wavelengths and the whole IR spectrum is huge when looked at in detail.  It's interesting stuff but with everything absorbing it's own frequency 'bandwidth', how do they know what they are seeing/missing?

     

    Is there a chart somewhere with the wavelengths for absorption?

     

    My original comment was in jest but it's a good thing to learn about.....

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    Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

    I think I see what you mean, BFTV...So all that hot water ought to be detectable?

     

    Depends on a lot of things, but mainly the mass of the oceans would require some massive and sustained eruptions to cause much any measureble warming, which I think we might have noticed. Also, the underwater eruptions would cause more warming of the deep waters than the surface, which is not the trend we're seeing.

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    Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

    Makes you wonder how the sensors function properly at all.....

     

    I know, I know...  Different molecules reflect/absorb different wavelengths and the whole IR spectrum is huge when looked at in detail.  It's interesting stuff but with everything absorbing it's own frequency 'bandwidth', how do they know what they are seeing/missing?

     

    Is there a chart somewhere with the wavelengths for absorption?

     

    My original comment was in jest but it's a good thing to learn about.....

     

    A semi interactive chart is here http://commons.wikimedia.org/wiki/File:Atmospheric_Transmission.png

     

    Can you phrase your first question a little differently? I'm not entirely sure what you're asking.

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    Posted
  • Location: Beccles, Suffolk.
  • Weather Preferences: Thunder, snow, heat, sunshine...
  • Location: Beccles, Suffolk.

    Depends on a lot of things, but mainly the mass of the oceans would require some massive and sustained eruptions to cause much any measureble warming, which I think we might have noticed. Also, the underwater eruptions would cause more warming of the deep waters than the surface, which is not the trend we're seeing.

    So, if I've gotten everything right, if there were any ongoing enormous eruptions, there's a fair chance we'd know about them...

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    Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

    So, if I've gotten everything right, if there were any ongoing enormous eruptions, there's a fair chance we'd know about them...

     

    That would be my thinking. But also, if there were any large volcanic cones/mountains under the ocean, they could be detected by their gravitation pull directly, and also on the overlying water too as the increased pull would cause a slight doming effect.

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    Posted
  • Location: Swallownest, Sheffield 83m ASL
  • Location: Swallownest, Sheffield 83m ASL

    Can you phrase your first question a little differently? I'm not entirely sure what you're asking.

     

    I think the link sort of answers my question.  I was wondering if some molecules absorb similar wavelengths and how do they differentiate between them?

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    Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

    I think the link sort of answers my question.  I was wondering if some molecules absorb similar wavelengths and how do they differentiate between them?

     

    Ah right. As you saw in the chart, many of them do absorb similar wavelengths. I suppose they can determine what parts are absorbed within lab conditions too.

    But these kind of things need to be understood pretty well to get effective satellite imagery. In the chart you can also see why we can't do any imaging with UV light too.

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