Re: IOD Format - Please, some help with a few questions (applied to Starlink observations)

From: C. Bassa via Seesat-l <seesat-l_at_satobs.org>
Date: Fri, 22 May 2020 21:09:05 +0200
Hi Andreas,


On Fri, May 22, 2020 at 8:50 PM Andreas Hornig via Seesat-l
<seesat-l_at_satobs.org> wrote:
> 1) What is a good way to fill the "Object number and international
> designation" when you do not know the satellite that you observed?

This is always tricky. Some of us use a 99XXX code for the object
number, i.e. 99123, to signify an object that has not been identified
yet. For the international designations of unknowns we use a format
like 20501ABC, where the first two digits indicate the year of the
observation, the next three the day of year + 500 of the observations,
with the letters indicating which unknown you saw, A for the first, B
for the second unknown etc. The crucial bit is to keep the object
number and international designation of measurements of the same
object the same. In otherwords, if you saw two unknown Starlink
objects today (day of year 143), you'd use, e.g. 99123 20 643A for the
first, and 99124 20 643B for the second.

However, in this case you are specifically targeting Starlink
satellites, which frequently maneuver. So while it may be unclear
which satellite you observed at the time of the observation, new TLEs
may help you identify it.

> 2) Is there a way to quantify the "Sky condition codes", because maybe my
> poor will your bad condition.

Use what ever describes your conditions.

> 3) What does "Time uncertainty" mean?
> This is one of te more interesting questions for me, because I have a few
> time uncertainties in a range of seconds.
> The GPS of the gopro is only used by the second, not sub second.
> So +-0.5sec could be possible.
> The storing itself seems to variying. I set the integration time to 10
> seconds and that I can see n the data, but the time gaps between the photos
> seems to jitter between 2 and 4 seconds. So I would use MX = 18: 1*10E(8-8)
> =   1     sec but I am not sure.
> For what will this be important?

This is indeed the accuracy of the timestamp you provide. I think 1
second should be used in your case, but it can be checked against
other satellites in your images.

> 4) the "Angle format code" I use 2 because I saw a few more of you using
> it. Does it make a difference?

No, this does not really make a difference. If you are referencing
positions with astrometry.net, use the RA/Dec formats, so either 1, 2,
3 or 7.

> 5) Is the "Epoch code" related to J2000?

Yes, code 5 is J2000 to reference the positions. This is what
astrometry.net would reference to.

> 6) I am not sure yet how precise my way in determinatig the RA/DEC is, so I
> used MX = 56: 5*10E(6-8) =  0.05   deg/min/sec of arc as the "Positional
> uncertainty", good idea?

Note the unit of the positional uncertainty is linked to the position
format. I.e. format 1 has uncertainty in seconds of arc, while format
2 has it in minutes of arc. What is your positional accuracy in
degrees?

> 7) Where do I find an explanation of how I can determine the "Optical
> behavior code"? As before, I would like to able to help, but I don't know
> how to rate that. This is also for the related code sthat follow.

The majority of the satellites will be steady so have code S. Some
will regular flashing during one or more images, indicating R, while
others only flash or flare once, so you can use I.

> 8) And last but not least, the "Flash period in seconds". Is that from the
> observed satellite?

Yes.

Regards,
    Cees
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Received on Fri May 22 2020 - 14:10:13 UTC

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