Meteorological station

[Clement_GRSM]

Dear all,

we are thinking on the measurement of the meteorological parameters regarding systematic bias and accuracy of SLR station.

We would like to know:

1) on the choice of the equipment
what kind of equipment do you use ?
What parameters do you monitor ?
What metrological performances have your system ?

2) on the installation place and the corrections
Where do you place the sensors ?
Do you apply corrections (for example, on the pressure if the barometer is not at the same elevation as the cross-axis of the telescope)?

3) on calibrations
How often do you calibrate your equipment ?

Thanks

Clément 

[pywang]

In Graz, we are using  MET3A from Paroscientific.

And another pressure sensor--740-16B . Because pressure is the most critical met parameter, the 2 pressure sensor data are compared after each reading; a warning mesage is issued if the difference is > 0.3 hPa. Both are setup at different altitudes (not on the same as the reference point), and values are corrected to our invariant point.

All met devices are read by a dedicated PC in 1 Minute intervals. Any program in need for met data is accessing this data.

Unfortunately, since I am here(almost 4 years) never heard about somebody made any calibration.

[delpino@riga]

There is a point that was mentioned already by Kalvis Salmins in Annapolis:

the current log file do not have a dedicated line on the section 12 to report the difference height between the meteo sensors (in particular the barometric sensor) and the invariant point.
Anybody knows if and where this information is available for all the stations?

The pressure is reported on the CRD's in mbar in format 7.2, but according to the note on section 3.4.2. of the CRD format description, only the pressure changes by 0.1mB are significant enough to report.
what should be the recommended tolerance for measuring the height difference and/or maximum allowed height error if we want to set the sensor exactly at the invariant point level?

Another comment answering to pywang:
There is a work in progress from many years about having a traveling absolute barometer used to calibrate in-situ the SLR local barometers in Europe.

In this moment we have the GFZ Potsdam absolute barometer in Riga, and in July-August one intern from the bilateral Estonia-Latvia SpaceTEM Eslat project (https://estlat.eu/en/estlat-results/spacetem.html) will use it to calibrate our secondary Vaisala PTU300 sensor.
After that we will send it back to Potsdam during the autumn.

So if another station wants to do the same, contact Sven Bauer at GFZ about loaning the absolute barometer, and us for some practical hints on doing and processing the data.

[serna_yebes]

Good morning.
We are thinking about the optimum meteorological station for our new SLR system.
In the observatory we have a complete meteo station (pluviometer, anemometer, pyranometer, temp, pressure, humidity...).
Do you think we could use the data from this station for our SLR system? it is more or less 60m away from the planned SLR location.
Or could it be better to have a new station just close to the SLR station?
Perhaps we can share the data from the pluviometer, anemomenter, pyranometer...and install close to the SLR station in the optimum position-height the pressure-temp-humidity sensors + the rain detector on/off.
Thank you

[delpino@riga]

Serna Yebes

I think that all participants on the Networks and Engineering Standing Committee Forum will agree on the following points:

•   The coordinates and in particular the height difference between the barometric sensor in use and the telescope invariant point should be included, measured and known in the local geodetic network.

•   The sensors (and in particular the barometer, which is the most difficult to calibrate “in situ”) should be calibrated periodically, (how we define “periodic” will be another looooong discussion).

•   What is now the sampling data rate of the current Yebes meteorological station?
Most SLR and GPS stations works at 10 minutes (at sharp second) sampling rate.
Remember that the pressure resolution asked is 0.1 milibar, and most of time, the pressure change rate in 10 minutes is less or equal than that.

•   The meteodata should be time tagged and available immediately at the local network, not only the last measurement done, but also the proceeding ones.

•   This is because the best practice is to include both pre- and post- meteorological values on the Normal point and this Normal Point file should be generated and delivered as soon as possible.
But if you do the “batch filtering” every few hours, you need to have access to the data of at least the last couple of days (to have a monthly file is a good compromise)

•   If the “local microclimate” at Yebes is (more or less) the same at the meteorological and SLR places, for example both places are surrounded by grass, this distance is not a problem.
In Riga we are using a common meteorological station at a distance of 32m (GPS) and 50m (SLR)

•   Do the current meteorological station has an anemometer?
Do you have strong winds at Yebes?
Because for really strong winds, automatically closing the roof/cupola/clamshell will be a good security measure against flying objects.
At the new buildings at GFZ Potsdam, all the windows have external Venetian blinds connected to a central anemometer. When the wind reaches a limit all the blinds are automatically lowered to protect the windowpanes

•   Invest the money on the best clarity/rain sensor in which the rain/snow alarm can be used to automatically close the SLR roof AND on a high quality all-Sky camera!
When several satellites are visible and it is partially cloudy, the all-Sky camera is the best tool for the on-the-spot tracking optimization.

And if you have a LOT of money project, and buy the independent, well calibrated SLR basic meteorological station situated at the SLR invariant height, no one at the SLR community will complain!.

[serna_yebes]

Good morning Jorge, and thank you very much for your comments.
I need to verify the current sampling rate of the meteo station at Yebes.
The local microclimate is not also a problem here, as I told you the meteo station is about 60 meters from the planned SLR location. And yes, it has an anemometer. We will use the info from the anemometer (jointly with the rain on/off detector) to control the dome in case of risk.
We are buying a good all-sky camera and a rain detector to be installed in the SLR roof. We will buy also a cloud detector.
So I think we will install, in the SLR station optimum position, a new meteo station (JUST pressure, temp and RH) and share the other data from the meteo station in the observatory. This way we´ll also have redundant info from the barometers.