readme.html

ObsReduce is an MS Windows program that reduces observations of satellites relative to the backgroun

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- enter <a href="#Date&Time">date and time</a> of observation
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- enter zero in <a href="#Early/Late">Satellite Early / Late</a> text box
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- press <a href="#Plot">Plot Satellite</a> button. The satellite will be in the wrong place, but this step is required to load its elements.
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- in the <a href="#Move">Move Satellite</a> frame, select the "by changing" option Early/Late, which tells the program to vary the value in the Early/Late box instead of the time in the FOV Centre frame, when you move the satellite.
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- in the same frame, use either set of increment/decrement buttons to move the satellite. One set moves the satellite a specified percentage of the FOV diameter; the other moves it a specified number of seconds of time. Moving a percentage of FOV diameter is preferred, because it ensures that stars will not be skipped over when you increment or decrement.
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If the satellite was early, repeatedly click the decrement button to plot its track at the observed time, but for progressively earlier times relative prediction.
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If the satellite was late, repeatedly click the increment button to plot its track at the observed time, but for progressively later times relative prediction.
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With each click, watch the stars in the FOV change; when the stars you sketched come into view, you can proceed with the reduction.
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- <a href="#Select">select the displayed reference star(s)</a>
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- select the <a href="#Geometry">geometry</a> of the observation and enter the object's position relative the reference star(s)
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- if they were observed, enter the object's <a href="#Magnitude">magnitude</a> (brightness), <a href="#Period">period of variation</a> and <a href="#OpticalCode">optical code</a>
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- press the <a href="#Reduce">Reduce</a> button
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- briefly review the <a href="#Error">Obs - Pred</a> information. These differences have been computed relative to the object's orbital elements loaded earlier. The time difference is an accurate measurement of how early or late the object was relative your observation. The position cross-track difference should be fairly small, because the track has been compensated for Earth's rotation corresponding to the time difference.
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- now that the difference between the observed and predicted time is known, it can be used to easily find the reference stars of any additional observations of the same object still to be reduced, Simply press the <a href="#UseAs">Use As Early/Late button.</a> This has the effect of instantly updating the FOV display, and copying the prediction time difference into the "Satellite Early/Late text box.
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- you may save your observation using the <a href="#Save">Save button</a> near the lower right corner of the program's window. If you wish to discard it, press the Clear Position button.
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- to begin reducing another observation of the same object, edit the date and time. Do not change the value in the Satellite Early/Late box. Press Plot Satellite, which will display your new reference stars, and the satellite's track. From here, the reduction proceeds as any other reduction.
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<B><a name="C.2">C.2 &nbsp;Using ObsReduce Without Orbital Elements</B>
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If you do not have orbital elements for an object, or prefer not to use them, ObsReduce can still help reduce your stars, as long as you know their approximate coordinates.
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- select <a href="#Site">observation site</a>
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- enter <a href="#Desig">Desig</a>
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- IOD users must enter <a href="#SSN">SSN</a>
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- IOD users select site <a href="#Status">Status</a>
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- enter <a href="#Date&Time">date and time</a> of observation
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- in the <a href="#Centre">FOV Centre</a> frame (at lower right of the FOV), enter the RA and Dec (or the AZ and EL) approximately centred on the reference stars. Your reference stars should now be visible in the FOV, oriented as they were at the time of observation.
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- <a href="#Select">select the displayed reference star(s)</a>
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- select the <a href="#Geometry">geometry</a> of the observation and enter the object's position relative the reference star(s)
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- if they were observed, enter the object's <a href="#Magnitude">magnitude</a> (brightness), <a href="#Period">period of variation</a> and <a href="#OpticalCode">optical code</a>
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- press the <a href="#Reduce">Reduce</a> button
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- you may save your observation using the <a href="#Save">Save button</a> near the lower right corner of the program's window. If you wish to discard it, press the Clear Position button. If you have additional observations of the same object, then resume these steps at the point where the observed date and time are entered.
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<B><a name="C.3">C.3 &nbsp;Sketch-Free Observing</B>
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When I began making positional observations, and for many years thereafter, I always stopped after each observation and sketched my reference stars. I labelled them as A and B, and drew a line with an arrow to indicate the satellite's path, noting the fraction of its passage between them, for example 70 percent down from star A to B. I also sketched several of the surrounding stars, to aid in locating the star field in an atlas.
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This method ensured that I would not lose my observation, but I rarely made more than one per pass, because the satellite had moved on and was difficult to reacquire, especially if it was faint and fast-moving.
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Though my sketches were fairly detailed, the star fields were small, therefore difficult to find in a star atlas. Fortunately, I found that for well-predicted objects, or ones running early or late by a known interval, I could accurately estimate the location of my reference stars by computing the predicted location of the satellite at the time of my observation.
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This experience taught me that I did not have to sketch my stars, as long as I could remember the fraction of a satellite's passage between stars. As a result, my observing method evolved, so that by July 2000, I only rarely stopped to sketch reference stars.
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The sketch-free method relies upon the fact that accurate paths can be predicted for most of the objects we track, as long as we can compensate for Earth's rotation during the interval by which they are early or late.
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Of the more than 1100 observations I have made since July 2000, perhaps 5 percent have involved sketches - mainly long-lost objects, new launches, or recently manoeuvred objects, for which predicted paths tend to be inaccurate.
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I wrote ObsReduce to facilitate the sketch-free method, as described below.
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I use ObsReduce in conjunction with an ephemeris generator to determine where I will intercept each satellite. I use the ephemeris generator to find satellite passes suitable for observing. I use ObsReduce to simulate each pass, looking for the earliest suitable reference star(s) at which point I will intercept the satellite, and begin tracking.
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I always try to intercept at a star pair that is likely to produce an accurate observation, i.e. no more than 0.5 deg apart, with the satellite crossing at close to a right angle. Alternatively, I will use a single star that the satellite is predicted to very closely appulse.
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I take care to use stars sufficiently bright to be seen in the expected circumstances. I am mindful of local obstacles that could block my view.
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This method almost guarantees me at least one useful observation, and it frees me from having to stop and sketch any of the subsequent reference stars, since ObsReduce can always take me to them, based upon the difference in time between observation and prediction of that first position, which is key to making the method work.
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For example, if ObsReduce tells me that a satellite was 23.2 s late at my pre-selected intercept point, then I know it was 23.2 s late at all of the subsequent points I observed. So, I hit the "Use As Early/Late" button to instruct ObsReduce to compensate for the 23.2 s lateness. When I enter the time of my next observation, ObsReduce places its reference stars nearly dead-centre in its simulated FOV.
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Freeing myself of the need to stop and sketch each point, made it easy to obtain many accurate positions on a single pass, instead of struggling to make one or two.
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All I do is to memorize the geometry, for example, while tracking, I see the satellite about to cross the line between a good star pair. As is almost always the case, one star is noticeably higher than the other, as seen in my FOV. I observe the satellite to cross at 70 percent of the distance from the higher star to the lower star. As I hit the stopwatch, I memorize the event as "70 down", and continue tracking. Had the stars been at the same height in the FOV, I would instead remember "70 left" or "70 right", as the case may be. I use similar short forms for appulses.
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My powers of memory are not all that great, but I can easily memorize several such descriptions while tracking, and then quickly jot them down in my log immediately after I stop tracking that object. By repeating the descriptions aloud over and over, I can remember half a dozen reliably.
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Tape recording the comments is an alternative, which makes it easier to record additional information, such as brightness and period of variation, at the expense of having to sit through the playback later. A voice-activated recorder can help in that regard - only if the voice-activation is reliable!
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<H3><a name="Interface">D. &nbsp;Description of User Interface</H3>
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This section describes ObsReduce's <a href="ObsReduce.jpg">text boxes and other controls</a>, reading from top to bottom, left to right of the program's window.
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NOTE: Frequently mentioned in this section is ObsReduce.ini, a text initialization file, installed in the same directory as ObsReduce. It contains 34 entries used to configure the program, which you may edit with a text editor. The file contains explanations of each one of the 34 entries.
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<B><a name="Site">D.1 &nbsp;Site List Box</B>
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Site is the code number identifying your site. Permanent numbers are issued only to the sites of observers who make fairly frequent observations and share them with others.
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If you already have a site number, you can cause ObsReduce to load it automatically, by adding it and its coordinates to line 1 of ObsReduce.ini, after the colon. ObsReduce supports the selection from among multiple sites at run-time. For details, please the notes in ObsReduce.ini.
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It is perfectly acceptable for a beginning or very infrequent observer to share reports having a zero value for the site number - just be sure to include your site co-ordinates in your report. If you show signs of becoming a fairly frequent reporter of observations, then you are likely to be offered a permanent site number.
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<B><a name="Desig">D.2 &nbsp;Desig Text Box</B>
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Desig denotes International Designation, which is the unique identifier officially assigned to all regularly tracked objects. This information is required by all three supported report formats: IOD, UK and RDE.
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Formally, the designation is written as yyyy-nnn$$$, where yyyy is the year of the launch, nnn is the order of the launch that year, and $$$ is an uppercase alphabetic string, denoting the piece from the launch in question, The first object is A, followed by B, etc. The letters I and O are excluded due to their similarity to 1 and 0 respectively.
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To save space, the reporting formats use shorter forms of the designation. The format for entering it into ObsReduce is the same for all formats.
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You have two entry options.
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1. Enter yynnn$$$, where:
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 yy  are the final two digits of the year of launch; leading zeros must be entered
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nnn  is the order of the launch that year; leading zeros must be entered
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  $  is a one to three character string denoting the piece from the launch in question
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2. Enter yynnnpp, where:
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 yy  are the final two digits of the year of launch; leading zeros must be entered
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nnn  is the order of the launch that year; leading zeros must be entered
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 pp  is a one to two digit number denoting the piece from the launch in question; leading zeros need not be entered
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The second format is convenient because it enables exclusive use of the numeric keypad. When working in IOD format, which reports the piece alphabetically, numeric pp entries will be converted and displayed as their alphabetic equivalents.
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Regardless of input format, ObsReduce correctly formats the designation within the IOD, UK and RDE reports.
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<B><a name="SSN">D.3 &nbsp;SSN Text Box</B>
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SSN (aka NORAD number) is a five digit catalogue number issued by U.S. Strategic Command. The field is required by IOD.
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UK and RDE format users may enter the SSN, so that it may used to search the 2-line elements file, and/or be included in the log files that record details of each observation. Users of the UK and RDE format who prefer not to see this prompt, can make it disappear by entering n at line 22 of ObsReduce.ini
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<B><a name="Status">D.4 &nbsp;Status List Box</B>
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Status is a drop-down list that is displayed only for IOD users. It is an alphabetic code that reports on the observing conditions and availability of the site for observations.
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<B><a name="Date&Time">D.5 &nbsp;Observation Date and Time Text Boxes</B>
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