More experimenting OBS

From: Greg Roberts (grr@iafrica.com)
Date: Wed May 30 2001 - 07:51:10 PDT

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    Hi All
    
    Herewith positional observations for Lacrosse 3 made evening 27 May 2001 and
    reported in usual IOD format:( using my usual CoSaTrak setup)
    
    25017 97 064A   0433 F 20010527172327615 26 15 0659011-223104 58  +030 05
    25017 97 064A   0433 F 20010527172328055 26 15 0659347-222540 58  +030 05
    25017 97 064A   0433 F 20010527172328545 26 15 0700134-221921 58  +030 05
    25017 97 064A   0433 F 20010527172328985 26 15 0700459-221350 58  +030 05
    25017 97 064A   0433 F 20010527172329485 26 15 0701227-220753 58  +030 05
    
    I am still experimenting with improving my system and it looks like the end
    is near :-))). The technique used has been improved, but I cant say its been
    speeded up- certainly I am virtually at the ultimate accuracy that one can
    expect to achieve with amateur equipment and perhaps Ive reached the point
    of
    an "overkill". Since the technique used is different from that previously
    described I will go into it in detail so it may aid others who want to
    follow
    the same path.
    
    As most of you know I am using a low sensitivity surveillance CCD camera
    coupled to a variety of small telephoto lenses - my favourite is an 80mm
    focal length f/2.0 lens which gives me a rectangular field of around 3
    degrees.
    Under my bright sky conditions (city lights of Cape Town) I can see stars to
    about mag 8.7 and track satellites down to about magnitude +7.5 to +7.9 or
    so.
    Whilst one can see stars etc on the video monitor down to this level of
    magnitude, it was impossible to do a frame capture and get anywhere near the
    magnitude seen. I think I have now achieved this - at least in recording
    stars
    down to the limit seen, but not yet satellites.
    
    I am using a process known as video integration.The camera is set on the
    expected field of view and when the satellite appears the camera shoots up
    to 10 frames in rapid succession, each frame having the time "stamped" on it
    to 0.01 seconds. I thus end with 10 frames with each one showing the
    satellite
    in a slightly different position. I then add the frames together- since they
    were shot in rapid succession the movement of the stars during the period
    is of no consequence and in this way get the star penetration I so
    desperately
    need in order to find sufficient stars to do astrometry as mentioned in my
    earlier report.If the satellite is bright enough I then have a string of up
    to 10 satellite images, fairly evenly spread across the frame ( the number
    of
    images depends on the angular velocity of the satellite which also affects
    the spacing between the images).
    
    Using astrometry I measure my selected reference stars and each satellite
    image ( or at least as many as I care to) and do an astrometric reduction to
    end up with (perhaps) 10 positions in the space of a short time.
    
    This is what I have done with the observation of Lacrosse 3 above, except
    that I only took 5 frames ( I meant to take 1 but by mistake took 5 and
    hence
    "discovered" this technique !).
    
    Prior to this video integration it was virtually a waste of time trying to
    do
    any image processing of the image - now it is possible to do so and gain
    about 2-3 magnitudes on the summed frame. I have not yet made use of
    darkframes of flatfields and I expect this to make a further improvement-
    will be tried next clear night .
    
    I am still experimenting with various programs to find the most efficient
    way - its amazing how many so called image processing programs cannot handle
    all versions (8,16,24 and 32 bit) of FITs or BMP images so I am constantly
    having to convert my picture formats from one program to the next- I do have
    a little control over the format of my images so now its basically deciding
    what software to concentrate on. Where possible I am concentrating on
    freeware
    or shareware software so everyone has access to this software as cheaply as
    possible.
    
    Tomorrow I will play with another multi-exposure frame of Lacrosse 3 secured
    on the same pass but only with three images this time.
    
    Cheers
    Greg
    
    
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