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Hi all

From about the beginning of 2017, the team at the SGF noticed some increased instability in our terrestrial range calibration values at the level of 2-3 mm.  It was particularly clear on the first calibration of the day being a low value and so we learnt to take at least two calibrations before starting an observing duty.

2 weeks ago we also saw an increase in the RMS of the calibrations and some periodic behaviour in the calibration range values.  We consequently took the kHz laser offline and began using our older 10Hz laser, which had very stable calibration values and RMS.

After some investigation and discussion with High-Q, the team found that the flow rate of the cooling water was much lower than it should have been.  The water used is a reservoir of distilled water, but after 10 years of use something had built up to block the waterways.

Temperatures in the laser bed were not being kept at a stabilised constant, causing energy fluctuations and range errors from the start diode. The temperature would change when the laser began firing after being off for a period (20+ minutes). It would stabilise after approximately 10 minutes, during which time calibration range differences were seen.

Running the flow backwards and using a descaler (Durgol was recommended) brought the flowrate up to specification levels.  Setting the best operating temperature removed the signals in the range values and now the calibration RMS and repeatability are now within acceptable levels.

Needless to say, we will be checking the flowrate more often from now on.

Matt
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Telescopes / Re: CCTV/ICCD/EMCCD cameras for tracking
« Last post by Matt Wilkinson on February 22, 2017, 03:23:26 PM »
Hi Kalvis

I've been testing one of these cameras https://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=4024, which are rebranded uEye cameras from IDS https://en.ids-imaging.com/home.html (more to choose from at IDS site!).

It is very adaptable and affordable with an extensive API with example software. If you don't need a top of the range camera, these could be worth a look, depending on the job you have in mind.

Matt
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Open a Discussion / Site Log
« Last post by CurtisEmerson on February 21, 2017, 06:40:04 PM »
I notice in the ILRS site log fields exist to identify Model and Manufacturer for:

Tracking Camera
Detector
Signal Processing
Time of Flight Observ.
Frequency Standard
GPS Timing Rcvr
Meteorological Instrumentation


but not for:

Laser
Receiving Telescope
Xmitting Telescope
Calibration Target
Aircraft Detection
Collocated Permanent Geodetic Systems (which would be identified in their own site logs).

Just an historical anomaly, or is vendor/model information useful for some but not others?
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Telescopes / Re: CCTV/ICCD/EMCCD cameras for tracking
« Last post by danielhampf on January 31, 2017, 12:56:46 PM »
Dear Kalvis,
we have been using the Andor Zyla sCMOS camera for about 3 years now and are quite happy with it. It comes as camera link or USB3 version, of which the latter was much more practical to use (we have 3 of these now, 2 USB and one older CL). To your questions:
1) Programming API is pretty good in my opinion, it's a C library that also exists in a precompiled form. I imported the DLL to python and went on from there.
2) There are a number of trigger options, which should enable you to do what you want. E.g. you can trigger via TTL input. The shutter is fully electronical, global or rolling. The camera is also pretty fast, up to some 50 Hz or so if you really push it hard.
3) Pixel size is 5,5 um, the sensor is 2560 x 2160 pixels, which gives us (at 3m focal length) a FoV of 0.3 deg and a scale of 0.5 arcsec per pixel. Pretty useful. And it's cmount.
4) No problems whatsoever so far in rather harsh outdoor conditions. The camera is also rather small and lightweight, which is also nice.
I can also mention that we tested two other cameras that were less useful in this context: First a FLI astro-CCD that had a gigantic chip and thus FoV, but a slow shutter and readout, so you could only take one picture every five seconds or so, and the timing was not accurate either (otherwise very good camera). And an Andor iXon emCCD which is very sensitive, but the camera is somewhat bulky and heavy and the chip is rather small. Unless you expect very low light levels I do not see much point in using any emCCD at the moment.
Ah, and maybe good to know: You'd pay something like eight to ten thousand Euro for it. Maybe a bit expensive for your needs, don't know.
If you need a rather cheap, reliable camera, I can recommend pretty much everything from PointGrey. Sturdy industrial cameras with a good interface, high frame rates, small size, cmount, ethernet or USB connection. Not very sensitive and not very large chip though. We use them for beam monitoring and occasionally on our transmitter telescope.
Hope that helps somewhat...
Daniel
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In-Sky Safety / Re: On telescope camera for plane spotting
« Last post by Matt Wilkinson on January 31, 2017, 12:20:20 PM »
Hi Kalvis

That's quite a narrow FOV.  We are wondering here @Hx what would be the best approach, either to use a wider image to spot approaching planes and take action when necessary or to have a narrower field to immediately shutoff when any plane like object appears in the frame (perhaps using a comparison to an earlier frame).

We've not tested our camera at night yet.

Matt
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In-Sky Safety / Re: On telescope camera for plane spotting
« Last post by kalvis on January 17, 2017, 07:56:17 PM »
We are using Mintron CCTV attached to telescope,  approx 2x4 deg FOV, plane navigation lights are visible in night.   
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Telescopes / CCTV/ICCD/EMCCD cameras for tracking
« Last post by kalvis on January 17, 2017, 07:08:59 PM »
Any ideas or suggestions for ICCD/EMCCD/CCTV camera for tasks like  visual tracking and star models? In a few SLR publications ICCD cameras are mentioned, like  https://cddis.nasa.gov/lw14/docs/presnts/atm1_zzp.pdf, but no details on specific models. The options are like starting from CCTV cameras used also  in astronomy like Watec http://wateccameras.com/productline/cameras/910HXEIA and ending like Andora Zyla 4.2 PLUS sCMOS(?).
Requirements besides the obvious to see as much as possible:
1) Programming API, e.g. we should be able to define and display reference marks
2) Gating - we should able to shut down  camera/close shutter at certain moments
3) Pixel size, sensor size and mount are important but here we have some freedom, px count is not so important. C-mount and 1/2" CCTV like sensor size should do fine.
4) Expected lifetime - should handle regular use in tracking
Applications:
Visual tracking, mount models, and optionally experiments like described in "Optical Characteristics of the Retroreflector in Space on the ADEOS Satellite in Orbit", where ICCD was used.   
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Open a Discussion / Re: Leap Second 01-01-2017: a place to post issues and tips
« Last post by Dan OGara on January 04, 2017, 03:27:09 AM »
Tracking at TLRS-4. For day 003/004UT have needed to use +/-2us range biases for Ajisai (SGF#5022) and LAGEOS1/2(SGF35021).

The LAGEOS would range bias would drift from +2us to -2us during the pass. On a 78 degree STELLA we got 20 returns at culmination, but none before or after culmination. This is very unusual.
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Open a Discussion / Re: Leap Second 01-01-2017: a place to post issues and tips
« Last post by Matt Wilkinson on January 02, 2017, 07:58:24 PM »
Happy New Year everyone

So far today at Herstmonceux, we had a mixed experience from SLR cpf predictions after the leap second. There were time bias issues with the Jason satellites using the CNES cpf predictions.  Also Galileo205 was off by 1 second using the ESA predictions, I've not yet seen if this holds for all Galileo. HY2A and Kompsat5 were also off on the MCC predictions. Most other satellites are well predicted. Successfully tracking Lageos with JAXA cpfs.

CPF predictions are compared here http://sgf.rgo.ac.uk/qualityc/cpf_qc_resids.html each day and it is clear that there are conflicting predictions
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Below is the "official" notice of the ILRS Leap Second Procedure" sent several times this year.

Dear Prediction, Station, and Analyst Colleagues,

As you are probably aware, there is a leap second at the end of December 31 this year. Our last couple of leap second experiences could have been better. This time, the ILRS has adopted the following simplified policy approved by the Data Formats and Procedures Standing Committee and the ILRS Central Bureau.

1) Stations:

    - On December 31, track as normal up until the end of the UTC day.

    - On January 1 UTC, be sure your stations clock is updated, and switch to the CPF files that start on

        January 1. Do NOT use CPF files that start in December.

    - Tracking a satellite pass through the December 31/January 1 crossover will probably not work

        properly.

2) Prediction providers:

    - Most of you do not need to change anything. It does not matter whether you are setting the leap

        second flag or not, as long as it it is set consistent with the CPF document.

    - The CPF files starting on January 1 and thereafter MUST NOT have the leap second flag set to '1'.

        After the last leap second, one or two providers did not reset the flag for a few days into January.

    - Be sure to have your leap second files updated properly.

3) Analysts:

    - Be sure to update your leap second files!

This procedure should be easier than dealing with leap second flags, although some passes that span the leap second will be lost. Let us know if you have any issues with this procedure.

Best regards,
Randall Ricklefs
For the ILRS Central Bureau
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