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Topics - Toshimichi Otsubo

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1
Open a Discussion / MPE
« on: October 11, 2017, 12:55:37 PM »
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

2
Station Performance / Station Performance 2016-2017 (Riga Workshop Spoiler)
« on: September 16, 2017, 03:42:40 PM »
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.


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


3
Station Performance / Station performance charts (Potsdam Workshop Spoiler)
« on: September 20, 2016, 05:03:20 PM »
Hello from Tokyo.

Just 2 weeks before the Potsdam workshop, we have generated a huge number of station-by-station charts so as to assess+assist the productivity and the quality of every SLR station. 

The details are introduced in the 'systematics' session and the 'clinic' session, but you will be able to directly get to the points if you look at them in advance.

This year, in addition to the usual tests, we look into the calibration (= system delay measurement) - frequency, stability, etc.

// Data span: 1 year = July 2015 to June 2016
// POD: software c5++ R874

Hit-rate (observation success rate) over all fly-over observation chances (El > 20 deg)
(Pages 3 and 5 are just rescaled-without-Yarragadee version of Pages 2
and 4 resp)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/SlrDataDensity.2016.pdf


LAGEOS-1+2 NP Post-POD 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/2016sp/DelayVsLag.pdf


System delay time series
(1 year span)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/CalTimeSeries1y.pdf
(5 day span; one of densely observed periods)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/CalTimeSeries5d.pdf


System delay measurement frequency
= Interval between calibration record with different time tags
(blue parts: not a unique measurement? Identical records with different time tags found.)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/CalInterval.pdf
(X-axis extended for 1824, 1873, 1884 and 7820)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/CalIntervalLong.pdf


Range bias vs System delay
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/SortDelay6.pdf


Range bias vs Intensity (# of returns per NP)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/SortIntensity6.pdf


Range bias vs Single-shot RMS
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/SortRms6.pdf


Range bias vs Sun Elevation (day vs night)
http://geo.science.hit-u.ac.jp/slr/bias/2016sp/SortSunEl6.pdf

See you soon in Potsdam,
Toshi
-----
The charts are created by:
Toshimichi Otsubo <t.otsubo@r.hit-u.ac.jp> and Akihisa Hattori
Hitotsubashi University


4
Station Performance / SLR Hit Rate 2015
« on: May 11, 2016, 04:38:42 AM »
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


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