Re: Nanosail-D flash pattern, and images of yesterday

From: Marco Langbroek (marco.langbroek@wanadoo.nl)
Date: Thu Aug 18 2011 - 12:17:01 UTC

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    Op 17-8-2011 13:49, alain.figer@club-internet.fr schreef:
    > Hi Marco,
    >
    > Last night I took a series of 6 consecutive photos in a field in Aquila. All
    > photos were of 4 sec duration.
    >
    > In all the photos, a same flashpattern seems rather obvious : 1 bright maximum
    > followed by 2 secondary maxima. At times both secondary maxima merge together.
    > The brightest flash is very sharp and also variable in magnitude. It can be at
    > times definitely fainter. I derived a photometric period of 0.73 sec,
    > respectively : 0.727 ; 0.729 ; 0.728 ; 0.723 for the 4 photos with a complete
    > 4-sec track.
    
    Hi Alain,
    
    Those are cool images! And you are so right in the periods you derive!
    
    Going back to my data (see http://www.satobs.org/seesat/Aug-2011/0088.html), I 
    get a result *exactly* like yours...!
    
    With only two exceptions (where secondary peaks are missing/not pronounced), if 
    I take each third peak in the sequence, I get a period of 0.73 +- 0.03 seconds, 
    exactly what you found.
    
    The two exceptions (marked * in below table) , themselves are intervals close to 
    this: 0.77 and 0.68 seconds. This suggest two submaxima are missing inbetween 
    two major peaks in these cases.
    
    table: peak nr ; seconds after 20:51:00 UTC ; interval between these peaks (s).
    --------------------------------------
    > 3   18.15	0.76
    > 5   18.9	0.75
    > 7   19.63	0.73
    > 8   20.4	0.77 *
    > 10  21.14	0.74
    > 12  21.88	0.74
    > 14  22.62	0.74
    > 16  23.32	0.70
    > 18  24.06	0.74
    > 20  24.81	0.75
    > 21  25.49	0.68 *
    > 23  26.22	0.73
    > 25  26.91	0.69
    ---------------------------------------
    
    secondary maxima tend to have intervals of about 0.27s and 0.46s, (see the full 
    list of intervals here: http://www.satobs.org/seesat/Aug-2011/0088.html),in that 
    stereotype order: so a "main" peak in the 0.73 cycle, followed by a 0.27s 
    separated peak, followed by a 0.46s separated peak (the both together creating 
    the 0.73s cycle). Neat!
    
    In June, it became very apparent from my photographs that the "regularity" of 
    the flash pattern is, as it is dependant on the exact viewing angle, changing 
    over the course of a pass:
    
    http://sattrackcam.blogspot.com/2011/06/nanosail-d-evolution-of-flash-pattern.html
    
    Early June, a very regular longer period was gradually added upon by smaller 
    secondary peaks, creating a seemingly more chaotic pattern - see the URL above.
    
    I guess the results of this mid-august show something similar: a main longer 
    periodicity "hidden" because of smaller subperiodicities on it. Your images show 
    the sequence perfectly though!
    
    - Marco
    
    -----
    Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
    e-mail: sattrackcam@wanadoo.nl
    
    Cospar 4353 (Leiden):   52.15412 N, 4.49081 E (WGS84), +0 m ASL
    Cospar 4354 (De Wilck): 52.11685 N, 4.56016 E (WGS84), -2 m ASL
    SatTrackCam: http://home.wanadoo.nl/marco.langbroek/satcam.html
    Station (b)log: http://sattrackcam.blogspot.com
    -----
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