resoluton of observable objects, camera color balance, observing satellites is fun (or maybe just addictive)

From: George Roberts (
Date: Sat May 28 2011 - 17:23:32 UTC

  • Next message: alberto rango: "4542 SATOBS 25 - 27 MAY 2011."

    The goal here by everyone including Thierry and Ralph isn't to whine, 
    complain, belittle, show off, brag, lie, or deceive (well maybe a little 
    The goal here is to observe satellites, share observations, and try to draw 
    conclusions from those observations.  When Ted asks y'all to share more 
    please don't get mad, you don't have to share but we would love it if you 
    For example I've been tempted to discuss Thierry's conclusion of resolution 
    limits and the ability to see something 2 meters tall using Ralph's 
    equipment (an astronaut).
    Although I partly agree with Thierry's points I think he has a 
    misunderstanding.  That white spot on Ralph's image indeed might  (might!) 
    be an astronaut.  Thierry hasn't yet convinced me otherwise despite his 
    educational composite of an astronaut to scale against the ISS.
    I think a simple example will illustrate my point.
    Currently Ralph's equipment is insufficient to image the Lunar Modules left 
    behind by Apollo missions on the moon (hopefully this will change, lol!). 
    There is a commonly used equation from Rayleigh that draws conclusions about 
    resolution that only needs to take into account aperture.  I beleive this 
    formula was originally co-opted for the specific case of observing binary 
    stars of equal brightness.  The formula  doesn't necessarily apply to this 
    If I put a laser next to that lunar module, make it bright enough (maybe a 
    million watts? a billion?) and shine it back at Ralph's telescope, Ralph 
    will see a tiny dot on the moon.  That dot should be the size of a star or 
    airy disk image of a point source.  So clearly it is possible to image 
    something "beyond the possible resolution" of a given set of equipment.  The 
    key here is contrast.  The object imaged needs to be so bright that even if 
    it is only one inch across on the surface of the moon, it is brighter than 
    all the reflected light from the portion of the moon at Ralph's equipment's 
    "imaging limit".  So if for example the limiting resolution on the moon is 
    an area 1 mile across, then the laser needs to noticeably brighten 1 square 
    mile of lit up moon as seen from the earth.  In the shadowed part of the 
    moon, the energy needed is much less.
    Similarly, an astronaut working on the ISS, if lit up significantly brighter 
    than the area around him (sunlit astronaut, midnight dark stuff around him) 
    might be visible even if he is beyond the resolution limit of Ralph's 
    equipment.  Now the shape of that astronaut is probably noise, but one might 
    be correct in guessing that a certain region of the image is a particular 
    astronaut (or it might be a nearby part of the ISS also in bright sunlight 
    or it might be both objects merged into one).  Careful analysis of the 3D 
    shape of the ISS, the position of the arm and astronaut, and how sunlight 
    would fall on different parts of these objects might provide strong evidence 
    one way or the other.  Ralph did some of this analysis.  I don't think 
    Thierry did.  I'd love to see someone create a 3D model of the ISS and then 
    put a light source exactly the same angle as when Ralph photographed it and 
    then look at it from the angle Ralph did.  But this is a ton of work.  I 
    don't know if anyone will ever do this although I've heard there is software 
    that does this already.  One would need to know within a few seconds when 
    the image was taken and where Ralph was.  Ralph only included the time to 
    the nearest minute but that might be good enough as you can probably infer 
    the time and light angle by comparing 3D model lighting with Ralph's image 
    if you have software that allows you to quickly change the light source 
    position and see results in real time.
    But we have to be careful about the "canals on mars" phenomena which fooled 
    some very smart people!  Like Percival Lowell:
    Regarding the color of the nanosail, Thierry makes some okay and some not 
    okay points.  I'm particularly interested in this claim about color balance 
    for certain cameras in low light conditions and I would think Ralph would be 
    delighted to do a few controlled tests.  If someone accused my photos of 
    having bad color balance I wouldn't get pissed off at the person, I would 
    thank them (yes, really - I've learned to thank people for advice although 
    when I was younger...) and asked that person to help me set up some 
    experiments.  If one used the same camera indoors at night - light up some 
    very very small angular objects with a very dark background in a room.  See 
    if the camera gets it's color balance out of wack or if it indeed has just 
    as good color balance with dark backgrounds as with light backgrounds. 
    There might be some auto color balance setting (software) in the camera that 
    gets confused by large "black" areas or quite likely Thierry could be wrong. 
    An experiment could settle this.  Ideally I'd like to see Thierry design the 
    experiments and Ralph do them over and over until Thierry is satisfied that 
    Ralph's images don't have color error introduced by the camera color balance 
    or Ralph finds a setting on his camera that disables color correction. 
    Ralph and Thierry should be best friends excited on working on this project 
    together!  Even if only by phone and email.
    I think Thierry and Ralph are contributing great stuff here and I wish 
    people would bask in this great, interesting jumble of thoughts and 
    experiments and results and not feel personally attacked.  We are talking 
    about *ideas* here.  We aren't rooting for teams like in sports.  With ideas 
    the best and correct idea *always* wins.  And all the people win also.  We 
    all lose if Thierry claims the pictuers are bad and Ralph replies with "they 
    speak for themselves".  In that case I don't learn much.  Ralph and Thierry 
    aren't fighting each other.  Or they shouldn't think of it that way.  They 
    just have a disagreement about conclusions.  Thierry would like to see more 
    data.  Ralph doesn't want to supply it.  Regardless I think Thierry brings 
    up interesting points, some right and some wrong.  And Ralph also brings up 
    some interesting points - especially the concept that it might be possible 
    to photograph something as small as a human on the ISS.  What an amazing 
    feat if this really is possible!  It's great to try to push our technology 
    to new limits.
    - George Roberts
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Sat May 28 2011 - 17:24:12 UTC