Re: Standard Magnitude Calculation

From: Bjoern Gimle@GlocalNet (Gimle@GlocalNet)
Date: Tue Oct 14 2008 - 22:25:07 UTC

  • Next message: Ralph McConahy: "Re: Standard Magnitude Calculation"

    I made a quick check for a "random" object #32378, now at std mag +2.0, at a 
    position where I searched, gave +9.2 at phase 115 degrees.
    Changing it to RCS=1.0 gave +15.2, so in SkyMap 1.0 m2 is std.mag=+8.0 ?
    
    Changing #01804 Alouette 2 from std=+8.2 to rcs=1  doesn't change +8.4 at 
    phase 150,
    so Skymap (Rob Matson) uses about +8.1 for 1 m2 RCS at 1000 km
    
    With +8.2 at 90 degrees and  range 3734 km it gives +10.6, which would be 
    +7.7 at 1000 km, so this confuses me (neither 90 nor 180 phase !?)
    
    For #6993 with std=+5.5 it gave +7.2 at 90 d and 2181 km, 90 d phase, which 
    indeed would be +5.5 at 1000 km,
    
    so it confirms what I believed - SkyMap uses 90 d for STD MAG definiton
    
    
    ----- Original Message ----- 
    From: "Phelps Williams" <phelpsw@gmail.com>
    To: "B Gimle @ComHem" <bg_26934@glocalnet.net>
    Cc: "seesat-l" <seesat-l@satobs.org>
    Sent: Tuesday, October 14, 2008 7:54 PM
    Subject: Re: Standard Magnitude Calculation
    
    
    It is this radar cross section to standard magnitude conversion that I
    am interested in.  I will look into SkyMap later this evening.
    
    On Tue, Oct 14, 2008 at 1:30 AM, B Gimle @ComHem <b.gimle@comhem.se> wrote:
    > Most standard magnitudes are derived from actual observations, after
    > (approximate) conversion to 90 or 180 degrees phase, probably using
    > ln(1-cos(phase) and 5*log10(range) as correction terms.
    > Also there are different preferences re using max or average magnitude.
    > See http://www.io.com/~mmccants/tles/intrmagdef.html
    > Rob Matson's SkyMap can use the standard magnitude on elset Line0 or in 
    > its
    > SKYMAP.DAT file.
    > The SKYMAP.DAT can also contain Radar Cross Sections, which are converted 
    > to
    > standard magnitudes internally.
    >
    > From dimensions, surface form and properties "conversion" is very 
    > difficult,
    > but I believe that a white sphere of  1 m2 cross-section is +6.4
    >
    > /Björn
    >
    > ----- Original Message -----
    >>
    >> I am interested in how standard magnitude is calculated.  I have been
    >> unable to find information on this exact calculation beyond the fact
    >> that it is based on the surface area of the spacecraft and some
    >> assumptions about the surface properties.
    >>
    >> I cannot find further definition beyond what is mentioned here:
    >> http://www.io.com/~mmccants/tles/mccdesc.html
    >
    >
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