Re: daylight satellite viewing

From: Ed Davies (
Date: Fri Sep 03 2004 - 15:01:39 EDT

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    Alistair wrote:
    > Hello,
    > Let me introduce myself.  I'm a student working on my Master's in
    > Applied Physics.  My thesis is  on Daylight Detection of LEO Satellites
    > in Infrared.
    > I'm curious as to information about some of the daylight Iridium flares
    > that have been mentioned on some websites.  I've read the background on
    > most of these sites.  What I"m really looking for is information on sky
    > brightness, wavelengths and local sunset/sunrise times.
    > More generally, if anyone has some knowledge on non-Iridium flare
    > imaging of satellites in or near daylight conditions, that would be
    > greatly appreciated.
    I'm surprised that nobody's replied to this message, at least
    not publicly.
    IR observing of satellites in daylight is something I've been
    wondering about for a while.  I have vague recollections of
    rather speculative stuff about the US Air Force systems to 
    do this which were sort of confirmed by the picture of the 
    Columbia which seemed to have been taken, IIRC, at about 11am 
    local time from Hawaii.  Can't remember if that was explicitly 
    stated to be IR or if it was just my assumption.
    During the day, the sky is blue - something which might be news
    to the more nocturnal members of this list.  Red light doesn't get 
    scattered much.  Presumably, near IR gets scattered even less.
    The following is hearsay - but I got it from a pretty reliable
    source.  Webcams are quite sensitive in at least some IR.  If 
    you remove the manufacturer's lens to do, say, prime focus imaging 
    with a telescope, then you have to extract the IR filter from the 
    original lens and refit it somehow - otherwise the IR light which 
    is out of focus blurs the image.  The same source also told me
    that exposed colour film can be used as an IR filter.
    Therefore, it should be quite cheap and straightforward to look at 
    the daylight sky in IR to see what can be seen.  I need to find
    out a bit more about IR filters and IR transmission through the
    atmosphere first.
    It's on my to-do list, but quite a way down.  Has anybody else
    tried this sort of thing?
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