Question about ground station position for mobile setup


#1

Hello,

I searched for posts regarding to my topic, but found nothing useful. So sorry if this was answered before but I didn’t found it.
I’m traveling a lot for my job (working 50% at home and 50% at two or three different places in Germany). When I’m traveling I used to live in my camper van (self converted old fire truck) close to my work. Mostly I’m 2 or 3 weeks at the same location. I want to setup my ground station on the van so that it is online most of the time, but at different locations. I can set (and update) the position of the ground station in the config and also on the SatNOGS network page. But what happens to already filed observations? What I assume is, that an observation is related to the ground station as a reference. So if I change the location of my ground station later, also the location for the observation would be changed causing wrong data for this observation?
What would be the best way to overcome this (if it is the case)? Should I create several ground stations for the different locations and then use the appropriate one for the local config when it goes online?
Thanks in advance for every hint and tip,
Mario.


#2

The networks keeps information about your station location in each observation under meta-data

https://network.satnogs.org/observations/810886/

(Ignore the fact that this failed :frowning: my station is being flaky.)

The metadata doesn’t change. :slight_smile:


#3

Hi Mario!

The client fetches jobs (future / scheduled observations) from network which includes the orbital elements for tracking (rotator & radio/Doppler). If the client configuration (location) is always up-to-date observations will be performed correctly.

That said, @drid added location retrieval support using gpsd in the development branch of satnogs-client.

Possible Steps:

  • Get a compatible GPS receiver
  • Install master branch of satnogs-client
  • Install & Configure gpsd
  • Set GPSD_ENABLED=True in satnogs-setup

#4

For position update i would suggest using the GPS feature, this will automate things and reduce any chance of having the wrong location.

Regarding already scheduled observations, it depends on the distance travelled since the observation calculation. I am guessing that you will not be using a rotator for a mobile setup so for relatively short distances i would expect that the observations will still be valid.


#5

OK, thanks for the replies. So I’m safe changing the location of my station and old observation that are already finished and sent to the database still have the location where they were recorded. But I have to care for observations that have been scheduled and that are already calculated for a specific position if I have moved since then. The GPS feature should update the position to a correct value but will not trigger a recalculation? Is the calculation done by the SatNOGS client or is it done when a observation is scheduled over the website?
I will not use a rotator on the mobile setup, I will just start with a simple antenna and then play around with different types of antennas to find the best compromise between size, performance and flexibility. The longest distance I currently travel is about 700km (north to south). I checked with a NOAA 18 fly-by and the elevation changed from 37.8° to 43° for the same time and a difference of about 2 minutes for the highest elevation on both location. So I think it should be ok for this setup, but would it be possible to retrigger the calculations?


#6
  • Tracking & Doppler correction is done by the client during the observation.
  • Observation times are calculated by the network when scheduling the observation.

In case of a wrong location during scheduling in network, worst case the observation will be started slightly too late into the pass or ends slightly too early.


#7

Yes, personally I would choose this option to avoid observations with wrong coordinates. However, if the locations are within 100 km or so from each other, it doesn’t matter that much.


#8

Currently it is a triangle with about 500km, 600km and 700km edges. So I think the position should matter in fact of the observation timings.
Using different ground stations for this would in fact prevent scheduled observations that have an offset because of the shifted location.
Is it a good practice or at least OK to have ground stations that are switched off for some weeks and then switched on for the next weeks, switched off again … and so on?
Because this would happen to this several stations. Also all the scheduled observations that are still scheduled when the station is switched off for a location will be gone.


#9

There is no problem with stations going off and on.
In either case, separate stations or one station, you can always delete future observations that are scheduled on the old location.

Every time that client asks network for jobs, it sends also its location, if this is different from the one in network, then station’s location is updated in network. Changing location in client can be done automatically with GPS as @drid suggested or manually in satnogs-setup.

Currently in case of location changes in network, there is no recalculation of the observations, however client uses its own location for the observation which also upload it in the metadata of the observation. So the only problem is that client will perform the observation with the initial start and end times.