Test-optical positions

From: Greg Roberts (grr@iafrica.com)
Date: Fri May 04 2001 - 07:32:11 PDT

  • Next message: Bruno Tilgner: "OIG down?"

    Hi All
    Herewith positional observations for USA81 made evening 03 May 2001 and
    reported in usual IOD format:( using my usual CoSaTrak setup)
    21949 92 023A   0433 F 20010503164625930 56 15 1344516-405832 57 S+070 05
    21949 92 023A   0433 F 20010503164500580 56 15 1236106-170228 57 S+072 05
    21949 92 023A   0433 F 20010503164631860 56 15 1350493-422005 57 S+065 05
    21949 92 023A   0433 F 20010503164705040 56 15 1426316-485025 57 S+065 05
    21949 92 023A   0433 F 20010503164710910 56 15 1433182-494854 57 S+065 05
    21949 92 023A   0433 F 20010503164726900 56 15 1452246-521201 57 S+065 05
    I am currently exploring new techniques for obtaining positional
    observations and this is the first try out of such. A lot remains to be
    done - ie making it somewhat more automated so as to increase efficiency
    but I am hopeful that at the end of the excercise the positions reported
    are as accurate as can be achieved.
    The time is now believed to be accurate to within a few milliseconds.The
    actual images are now being measured, using standard astrometric procedure
    - ie deriving plate constants and plate solution to give a position
    considerably better than previously achievable - typical rms errors appear
    to be under 30 arc seconds and are probably limited by the equipment used.
    Since this is the first tryout of the system I would be particularly
    interested in comments, especially if there are any obvious errors or some-
    thing that doesnt look quite right.
    The procedure used is as follows:
    The video image from the low light level surveillance camera is fed into a
    TV capture card that can receive and dispay composite video. The computer
    clock is "spot on" and drift is under 0.1 seconds per day at the moment.
    Time is displayed on the screen to 0.01 seconds. Since I have been unable,
    so far to superimpose the time display onto the camera video output I have
    to do a screen capture whenever the satellite passes through a suitable
    field. CoSaTRak is operated in the TRACK mode so that the image is
    centred in the field of view. I can do screen captures approximately once a
    second and the resultant image is 1024 x 768 pixels x 24 bits,giving an BMP
    image of 2.25 Mb.Using the program GUIDE I identify the star field for each
    capture and if I have done the job properly I have the satellite surrounded
    by at least three reference stars- the more the better, but with a field of
    view of only 3 degrees one does not get often get enough stars suitably
    placed. Using GUIDE I make a note of the RA and Dec of the reference stars
    chosen, measure the x and y coordinates of the images on the screen and then
    run a standard astrometric program to give the plate solution and answer.
    The weakness of the system is the problem of getting suitably placed
    stars - those who are familiar with astrometry know that the unknown should
    be surrounded by a minimum of three stars, and each having about the same
    dependency, so if three stars, the dependencies should be about 0.33 per
    ( would I be that lucky!). Because of the small camera aperture used I am
    currently limited to reference stars brighter than about 6.8 magnitude (
    figure comes from last nights observations when I had a bright moon and
    problems with the optics misting over-) hopefully I can get fainter under
    better conditions.
    Sorry if Ive been so detailed but this is a field relatively ignored by
    amateur satellite trackers and I am hoping that others may think about using
    similar techniques.
    I do have more observations to report but that will have to wait for another
    Cospar Site 0443. Long 18.5129E,Lat  33.9405S
    Near Cape Town, South Africa.
    Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
    in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org

    This archive was generated by hypermail 2b29 : Fri May 04 2001 - 07:49:22 PDT