Re: atmospheric extinction for low altitude flares T

From: Ed Cannon (
Date: Wed Jun 16 2004 - 02:31:14 EDT

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    Tom Wagner wrote:
    >Two questions:
    >(1) Does H-A consider atmospheric extinction when making 
    >their flare magnitude predictions?
    Someone ... asked that question in 2001, and at that time 
    Chris Peat replied -- if I understand correctly -- "No." 
    I don't find any update on that.  Of course it's really 
    tough, because the atmosphere can vary so much -- humidity, 
    haze, dust, smoke, thin fog, etc.  However, in the Iridflar 
    2.21 documentation Rob Matson wrote the following -- which 
    I don't fully understand -- about Iridflar (and SkyMap):
    >Improved calculation of satellite lighting condition.  Now 
    >calculates lighting the same way that SkyMap does -- 15 km 
    >or 20 km tangent height extinction (depending on season), 
    >with 0.2 or 0.1 degrees of refraction respectively.
    Tom also asked:
    >(2) Does anyone know the lowest in the sky someone has 
    >observed an Iridium flare?
    I don't know, but I've seen some pretty low ones.  Just two
    nights ago (4:23:46 June 14 UTC), I (and Mike also I think)
    saw Iridium 40 (97-069C, 25041) at altitude 7, azimuth 255.  
    It was predicted -1 by Iridflar, but I think it was actually 
    fainter.  However, the weather, though nice, was not pristine.
    Ed Cannon - - Austin, Texas, USA
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