RE: Observing ICESat

From: k.t.mag@att.net
Date: Sun Oct 12 2003 - 15:59:03 EDT

  • Next message: Bjorn Gimle: "USA 129"

    Brian,
    
    To see ICESat laser light at this time requires a degree of determination and a 
    fair portion of luck.
    
    To get a view of the ICESat spots like those shown at www.gsfc.nasa.gov/
    topstory/2003/0920icesatfirst.html it is required to get nearly on the ground 
    track and be under suitable clouds.  This is quite hard to do at this time.  
    Anyone more than a few hundred meters away or less will probably not see spots 
    but may see flashes of green reflecting off of clouds much like an airport 
    beacon or search light reflects off of low clouds.  
    
    From what I have seen the observer probably needs to be within a mile or so of 
    the ground track under ideal conditions of good clouds and darkness to see 
    evidence of the laser beam.  It  will not be known how far away lit clouds can 
    be seen until more observations are reported.  I have seen ICESat illuminate 
    clouds twice now at elevations of about 50 degrees and estimate observers with 
    good clouds at 10,000 ft AGL may see something as much as one or two miles off-
    track.
    
    Getting fresh two line elements and using a good satellite tracking program 
    with 3 decimal places of longitude output is required to get the observer 
    within range.
    
    Here is a suggested process:
    
    First, run pass predictions out a few weeks using one of the satellite tracking 
    programs available and chose a candidate pass close enough to suit and passing 
    through a dark place.  (Note:  I think that ICESatís laser is planned to be 
    turned off around 12 November and turned back on March, 2004)
    
    Choosing an East-West running country road to observe from works well.  
    
    Determine the latitude of the road to the nearest 0.01 degree or better.
    
    From latitude and longitude ground track data returned by the satellite 
    tracking program determine the longitude where the ground track crosses the 
    road to the nearest 0.05 degree or better.  This may require some interpolation 
    of the data.  This crossing should be within a few miles of the best spot 
    depending on how old your elements are and how far in the future the pass will 
    be. It should be good enough to generally plan the trip.  (Mapquest, 
    www.mapquest.com/maps/latlong.adp is good for planning in the US at least as 
    detailed local maps can be generated from latitude-longitude input)
    
    A day or less before the pass get as recent a two-line element set as possible 
    and determine again the longitude of the ground track/road intersection.  This 
    time try to get the longitude of the crossing point calculated to better than 
    0.01 degrees.  ICESatís orbit is adjusted frequently and fresh elements are 
    necessary to get close.  Every 0.02 degree of error results in about mile of 
    offset at 40 degrees north.  I am not sure how accurate the NORAD determined 
    elements are but I suspect they may be a significant source of error
    
    Set your watch to within a second or so of UTC. 
     
    Get to the road crossing a bit before the appointed time.  (This could be a 
    chance to use that GPS receiver)
    
    Hope for some favorable atmospheric conditions, look straight up 30 seconds or 
    so before the predicted pass and maybe something will be seen within a few 
    seconds of the predicted pass time.  Do not blink as the spots are moving 5 
    miles per second
    
    The above process will challenge a novice but is a great exercise in using 
    satellite tracking tools, internet databases, land navigation skills, and 
    experiencing the astronomerís frustration with bad viewing conditions.
    
    In the future a more straightforward and/or accurate method may evolve if the 
    precision orbit determination information gathered by NASA for ICESat becomes 
    accessible. 
    
    Maybe Heavens-Above could help or people involved with the ďPublic OutreachĒ 
    portion of the ICESat program can put something together with an interactive 
    web site.
    
    Gregg Hendry
    
     
    > Hi All:
    > 
    > This is Brian Webb in southern California. I publish a newsletter* about
    > California astronomy and space news.
    > 
    > My newsletter has carried info about ICESat, so the idea of observing
    > flashes from the ICESat laser are interesting.
    > 
    > I'd like to add a one paragraph write-up on this topic for my newsletter.
    > Here are some questions:
    > 
    > 	- How bright are the flashes?
    > 
    > 	- Do you need to be at a dark site?
    > 
    > 	- Any observing tips for beginners?
    > 
    > By the way, I covered the ICESat launch from Vandenberg AFB in January. It
    > was great!
    > 
    > Regards,
    > 
    > Brian Webb
    > 
    > * http://home.earthlink.net/~kd6nrp/newsletter.htm
    > 
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