The link to the poster (PDF; provisional): http://geo.science.hit-u.ac.jp/slr/bias/2022sp/20221107-poster-otsubo-systematic.pdf

Moimoi Arttu,

I presented in Stuttgart last year what you have in mind. 

https://cddis.nasa.gov/2019_Technical_Workshop/docs/2019/presentations/Session5/session5_Otsubo_presentation.pdf

Toshi

Are there any publicly available software that can produce the [Range, Az, El] time series from CPF for a given station position?  Toshi

Johann and Jens

Thank you very much.  Amazed to hear that you could track Etalon solidly with such a weak-energy laser.

I am still learning and a bit confused.

I applied the same procedure as Herstmonceux and Stuttgart to the WLRS-IR based on what you wrote.  It does not seem eye-safe in my quick computation.

(W) WLRS:  1064 nm, 0.4 mJ, 400 Hz, 10 ps FWHM, beam diameter 75 cm

The MPE per pulse in the first wikipedia graph is:
  MPE for (W) = 3e-8 J/cm^2 (where real (W) = 9e-8 J/cm^2)
which suggests WLRS-IR is NOT EYE-SAFE.  Am I right?

The MPE per 0.1 s and per 1.0 s in the second wikipedia graph is:
  MPE for (W) = 2e-3 J/cm^2 per 0.1 sec (where real (W) = 4e-6 J/cm^2)
  MPE for (W) = 1e-2 J/cm^2 per 1.0 sec (where real (W) = 4e-5 J/cm^2)
which looks ok.

The N^(-0.25) rule ("Rule 3" in the document from Jens message) will make the MPE simply lower, if I understand correctly.

The PDF document Jens suggested looks useful for visible (400-700 nm) wavelengths - thanks.  I would be glad to see the same thing for 1064 nm.

Toshi

Dear laser ranging colleagues,

On Thursday's session in Riga, we heard a few talks and comments on eye safety issues.  I knew almost nothing about MPE (Maximum permissible exposure) and want to learn a bit.

I was wondering how difficult/realistic it will be to make the energy density low enough (as intended in SLR2000).  But I have a question: in what time window(s) should we worry about our eyes?

I found it hard to understand IEC 60825 even in the Japanese translation, but some of the charts in this wikipedia page is partly understandable (but not sure if trustable).
  https://en.wikipedia.org/wiki/Laser_safety

Let me try to understand by assuming two lasers:
(H) Herstmonceux's:  532 nm, 0.5 mJ, 2 kHz, 10 ps FWHM, beam diameter 3 cm
(S) Stuttgart's:  1064 nm, 0.3 mJ, 10 kHz, 3 ns FWHM, beam diameter 7 cm

(1) Energy per pulse
I guess this chart
  https://en.wikipedia.org/wiki/Laser_safety#/media/File:IEC60825_MPE_J_nm.png
  caption: "MPE as energy density versus wavelength for various exposure times (pulse durations)"
is the one to look at.  We can read the MPEs at:
  MPE for (H) = 1e-8 J/cm^2 (where real (H) = 7e-5 J/cm^2)
  MPE for (S) = 2e-6 J/cm^2 (where real (S) = 8e-6 J/cm^2)
so Herstmonceux's pulse is far from eye safety but Stuttgart's is close to eye safety considering the fibre loss.

(2) Energy per longer time span (but how long?)
John Degnan commented that the IR could be dangerous because we cannot see it and the eyes can be exposed for a longer time. 
I am not sure but is this chart
  https://en.wikipedia.org/wiki/Laser_safety#/media/File:IEC60825_MPE_J_s.png
  caption: "Maximum permissible exposure (MPE) at the cornea for a collimated laser beam according to IEC 60825, as energy density versus exposure time for various wavelengths"
useful for this?  Then, we can read at 1 sec (correct?):
  MPE for (H) = 2e-3 J/cm^2 (where real (H) = 0.14e J/cm^2)
  MPE for (S) = 1e-2 J/cm^2 (where real (S) = 8e-2 J/cm^2)
again a similar story as above.

Is my understanding correct?  Can Stuttgart SLR be declared as an eye-safe system by reducing the energy a bit and/or by making the beam aperture large?

Or, if you know the best MPE expert in this community, I would like to contact him/her.

Toshi

Matt, we all missed you in Riga.  This forum is widely known as Matt's forum or Wilkinson forum, rather than NE-something's.  Toshi

Dear Worldwide Laser Ranging Colleagues,

Hello from Tokyo.

In preparation for 2017 ILRS Technical Workshop in Riga http://www.ilrstw2017.lu.lv, I have just generated and uploaded a number of charts on station performance from various aspects.

• LAGEOS-1 & 2 "precision" charts:
  Single-shot RMS, NP RMS, Pass Range Bias (RB) RMS and Pass Time Bias (TB) RMS
  http://geo.science.hit-u.ac.jp/slr/bias/2017sp/variousrms.pdf
  (Single-shot RMS taken from CRD, NP RMS smoothed by a simple function (RB only, RB + TB, or RB + RB-dot + TB) per pass, RB/TB RMS taken from pass-by-pass biases)
  
• LAGEOS-1+2: Pass RB RMS vs Session-by-session system delay RMS
  (Page 1 >> ZOOM >> Page 2 >> ZOOM >> Page 3)
  http://geo.science.hit-u.ac.jp/slr/bias/2017sp/DelayVsLag7.pdf
  (Good performing stations are mostly stable in calibration too.)
  
• 6-Sat: POD residuals vs Applied system delay
  http://geo.science.hit-u.ac.jp/slr/bias/2017sp/SortDelay7.pdf
  (Negative 1:1 trend indicates untrue variation in calibration.)
  
• 6-Sat: POD residuals vs Intensity (returns per NP bin)
  http://geo.science.hit-u.ac.jp/slr/bias/2017sp/SortIntensity7.pdf
  (Negative trend indicates intensity dependence.)
  
• 6-Sat: POD residuals vs Single shot RMS
  http://geo.science.hit-u.ac.jp/slr/bias/2017sp/SortRms7.pdf
  (Positive trend indicates the mean being affected by the tail clipping.)
  
• 6-Sat: POD residuals vs Local time
  http://geo.science.hit-u.ac.jp/slr/bias/2017sp/SortHour7.pdf
  (Day-night observability and stability.)
  

Period: July 2016 to June 2017.
Satellites: LAGEOS-1, LAGEOS-2, AJISAI, STARLETTE, STELLA and LARES.
POD Software: c5++.  Station positions are solved for.  Atm + hyd loading displacements are applied.  Grav coeffs 5x5 are solved for with some empirical acceleration params.

I will be able to only present only a small part of them in my presentation (Session 2),
but I am willing to discuss these results with everyone. 

See you soon in Latvia,
Toshi
---
Toshimichi Otsubo (t.otsubo@r.hit-u.ac.jp)
Hitotsubashi University

Hello from Tokyo.

The following link contains the quantity (not the quality) statistics for the productive 20 SLR stations last year.  Please have a look.

  Pass-based hit rate and Normal-point(NP)-based hit rate.
  Average number of normal points per pass.
  Average pass duration, defined as the time between the 1st and the last NP.

http://geo.science.hit-u.ac.jp/2016/04/05/slr-hit-rate-2015/

Yarragadee's hit rates are really awesome.  Note that the hit rate of the microwave techniques will be almost 100%.

I would also like to point out that some stations do not (try to?) track a satellite for a long time as seen in Figure 3.  I think low orbiters should be observed from horizon to horizon unless there is a conflict with other low orbiters.

Toshi
-----
Toshimichi Otsubo <t.otsubo@r.hit-u.ac.jp>
Hitotsubashi University