Observing

1. Observing

2. Do you have any energy monitoring? YES Potsdam. During the pass, the instantaneous and the average return rate are displayed on the observer's screen as bar indicators, updated every second. YESSimosato. We always check the laser output by the oscilloscope and the power monitor, and adjust the gain of the amplifier. YESZimmerwald. Actual transmit energies (blue and IR) are displayedReceive energy (pulse generated by IR photomultiplier) displayed and stored NOGraz. With the full solid state kHz laser, it is not really an issue. It is sufficient to measure the output each week or so. In the few cases we had problems, we saw it immediately (we shot some small holes in the last output mirror ....). NOBorowiec Herstmonceux Transmit –NO Receive - YES

3. Do you have any energy monitoring? YES Potsdam. During the pass, the instantaneous and the average return rate are displayed on the observer's screen as bar indicators, updated every second. YESSimosato. We always check the laser output by the oscilloscope and the power monitor, and adjust the gain of the amplifier. YESZimmerwald. Actual transmit energies (blue and IR) are displayedReceive energy (pulse generated by IR photomultiplier) displayed and stored NOGraz. With the full solid state kHz laser, it is not really an issue. It is sufficient to measure the output each week or so. In the few cases we had problems, we saw it immediately (we shot some small holes in the last output mirror ....). NOBorowiec Herstmonceux Transmit –NO Receive – YES Yarragadee YES. We have a shot by shot receive energy indication. We have visual and audio indication. The audio indicator varies in pitch according to return energy level.

4. Do you have any energy control? YES Potsdam. The laser output energy can be controlled by selecting a single pulse or semitrain and by enabling/disabling the second amplifier. Additionally, the beam divergence can be remotely controlled. This is automatically set based on average sky and elevation conditions according to our experience and can be modified by the observer during the pass. We try to keep the average return rate below 50 per cent (30 per cent is optimum). YES Simosato. We attenuate the transmission power by using an aperture, and keep the level of return signals from satellites constant by adjusting the receiver attenuation. YES Zimmerwald Both transmit energy (polarizers) and ND filters in receive path (separate for blue and IR) ND filters are automatically adjusted to keep return rates between 10 and 25 percent. YES Borowiec.Percentage of good returns YES Herstmonceux. Software control of return rate with ND wheel (clear to ND4) to maintain 10% return rate. Observer control of Beam and Iris. All satellites have pre-determined starting values for beam and ND. YES Yarragadee. 6.0 ND wheel

5. Calibrations

6. Do you control the energy? YES Potsdam. For target calibrations the laser parameters (in connection with an attenuator) are set in a way that the average return rate is below 50 per cent (typical values 25 - 40 per cent. Average and instantaneous return rate are displayed in the same way as during a pass. YES Simosato. We attenuate the transmission power by using an aperture, and keep the level of return signals from satellites constant by adjusting the receiver attenuation. YES Zimmerwald. Both transmit energy (polarizers) and ND filters in receive path (separate for blue and IR) YESGraz. Attenuated by a factor of 5, using phase shifting of the last amplifier pumping; YES Borowiec. Percentage of good returns YES Herstmonceux. Realtime return rate + Software control of ND wheel YES Yarragadee. We try and make the calibration receive energy match the satellite’s.

7. Do you monitor any changes in calibration? YES Potsdam. We create EDF (Engineering Data Files) for every calibration run and look for obvious problems in the plotted mean and standard deviations. YES Simosato. We monitor the change of the amount of an internal delay. YES Zimmerwald YES Graz. Each cal delivers a full set of values that are stored/attached to a general CAL file. Each cal is compared to the previous one, differences shown to the observer .... Each cal produces also an XML file, sent to Kalvis in Riga. YES Borowiec. Control pre-post YES Herstmonceux. Checks on mean,rms,skew,kirtosis during reduction NPCHECK also checks mean when forming normal points. YES Yarragadee. We have limits on acceptable calibration rms and shift.

8. Do you have more than one target for comparisons? NOPotsdam. This is limited by the special design of our station. We are using a bistatic system, and the most simple way to perform a calibration is to direct the transmitter signal into the receiving telescope when both telescopes face each other (see the attached image). The receiver FOV intersects with the transmitted beam only after several kilometers, so a remote target would have to be VERY remote ... NOSimosato. We have only one target YES Zimmerwald. One internal, two externals NOGraz YES Borowiec. First (standard) 241m, second 1295m YES Herstmonceux. 2 targets at 600M (east) , 2 targets at 100m(west) , 1 internal target (south) YES Yarragadee. Close in azimuth though, about 10 degrees apart

9. Reductions

10. How is your initial data selection made? – do you use orbit or polynomial fits? Potsdam. We use orbital fits according to the recommendations by Appleby and Sinclair about how to form NPs. Simosato. We use the polynomial fits up to the 31st degrees. Zimmerwald. In real time:- Check of (obs - pred)- Check of (obs - pred) expressed as along track error- Predictions are corrected for confirmed along-track errors Before NP generation: - Data screening: - Least squares fit of constrained short arc to accepted ranges - 2.5 sigma rejection - Iteration - Daytime passes or problematic night time passes:   - Visual inspection (graphics)   - Interactive removal of outliers or portions of the pass

11. How is your initial data selection made? – do you use orbit or polynomial fits? Graz. We form residuals (measurements minus predicted orbit)- residuals are fitted with polynomials;- obvious noise is rejected;- 2.5 sigma iteration / poly fits / final 2.2 sigma rejections; - only returns from nearest retro used, returns from other retros rejected (if we can identify them ...) Borowiec. Polynomial fits Herstmonceux Initial selection by hand using a combination of automatic track detection, linear and polymonial fits. This selection uses the O-Cs for each point and as such is dependent on the quality of the predictions (more in software session) Selected data is used to get orbit corrections. This orbit is then used against raw data file and data rejected at 5sigma. This data then has a Gaussian fit and data is kept at 2.5sigma Yarragadee 3 sigma reiterative fit – irv + polynomials

12. Can you reject parts of the pass? NOPotsdam. No, unfortunately not yet. This is subject to upcoming S/W modifications. YES Simosato YES Zimmerwald. See above YES Graz. Any part; manually;- returns TOO CLOSE to RG begin are rejected automatically (< 50 ns); YES Borowiec. >2.5 sigma YES Herstmonceux Yes – any part manually and any of the semi-train pulses. Software also rejects any pulse in semitrain with too few points or peak-LEHM which does not comply to preset limits. Upper/Lower limits in the initial track selection are hardcoded into the software to avoid inconsistency between observers. YES Yarragadee Yes – any part manually

13. What error checking is carried out? Potsdam. Edit passes with unusually high RMS values. Target values which are outside a certain range are not accepted and the pass is edited as well. Simosato. After polynomial fits, remove outliers based on statistical criteria. In addition, we check whether the value is appropriate for all columns of the QL Data and the MRT Data by using a checking program when data is sent out. Zimmerwald. RMS of calibrations against standard value (color-dependent), RMS of post-fit residuals against standar value (satellite and color-dependent), average difference between blue and infrared, number of normal points, number of single shots per normal point. Graz. All we can think of .... Borowiec. Standard deviation, skew, kurtosis, normal distribution, normal points standard deviationHerstmonceux. RMS and Peak-LEHM (both satellites dependent). Orbit parameters. Shots/NP. Cal vals. Met values. Yarragadee. SS RMS (>7.5mm Lageos <13.0 mm). At least 30 accepted returns for lageos.

14. Post Reduction

15. Do you look at any of the following: Analysis reports? Potsdam Yes, preferably the Berne combined analysis report which shows the results from different analysis centres simultaneously. But the reports from single centres are checked as well as soon as they are available. Simosato We see the analysis report in the web page of NICT.We analyze tracking data of Lageos and Ajisai by using the Geodyn-II program on our own. Zimmerwald Weekly Range bias summary report Graz yes Borowiec Delft, NERC occasionally only Herstmonceux Yes Yarragadee Yes

16. Do you look at any of the following: Short arc? YES Potsdam. The NERC short arc analysis data is checked on a daily basisYES Zimmerwald. Occasionally YES Graz. Occasionally onlyYES Borowiec YES Herstmonceux. Daily NOYarragadee. Not usually Long arc? YES Potsdam. The NERC long arc analysis data is checked on a daily base.NOZimmerwald YES Graz. Occasionally only YES Borowiec YES Herstmonceux. Daily YES Yarragadee

17. Please give brief details of any QC carried out by your station not covered in above. Simosato. We measure the output of the start detector, and keep the output level constant. We adjust transmission beam divergence in real time and automatically according to the orbit altitude and the elevation of the satellite.We measure the relative position between the fixed point of the telescope and the reference monument once a year by GPS. Graz. We check distribution, all statistical values, shifts in all parameters (meteo, cals, etc.)- we check for all possible "formal" errors;- we check if NPs for this pass already have been tranmitted;- pressure measured with 1 main and 1 control device;- NPs are sent in parallel to a control address (so we can realize if our mail system works properly ...); (already gave as successful warnings in 2 cases ...) Herstmonceux In realtime we monitor our temp, pressure and hum Vs secondary device. We monitor the dye strength of the laser We monitor temp of laser bed and SR timer. Deviations on either close the system down.