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Ground Target kHz Laser Ranging with Submillimeter Precision
Lukas Kral, Karel Hamal, Ivan Prochazka (1)
Georg Kirchner, Franz Koidl (2)
presented at
kHz SLR Meeting, Graz, Austria 27–29 October 2004
(1) Czech Technical University in Prague, Czech Republic
(2) Satellite Laser Station Graz Lustbuehel, Graz, Austria
L.Kral, K. Hamal, I. Prochazka, G. Kirchner, F. Koidl, Graz, October 2004
Goal & Philosophy
Goal: to achieve precision of <1 mm RMS together with high return rate during ground target calibration (purpose: investigation of atmospheric turbulence influence on the ranging jitter)
Method:• target selection and placing• adjusting return energy level• adjusting beam divergence etc.
Based on the authors’ personal experience from the SLR station Graz
L.Kral, K. Hamal, I. Prochazka, G. Kirchner, F. Koidl, Graz, October 2004
Target Selection & Placing
The best target for the ground calibration turned out to be a single cube-corner retroreflector: does not spread the reflected laser pulse in time provides high return energy
Must be distant enough to include theeffects of pass through the turbulent atmosphere (in our case 4.3 km from the observatory)
L.Kral, K. Hamal, I. Prochazka, G. Kirchner, F. Koidl, Graz, October 2004
Influences of Return Energy
100 101 102 103 104 1050
20
40
60
80
100
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Re
turn
ra
te [%
]
Return energy [rel. units]
Return Rate and Ranging Jitter vs. Signal Strength
Graz, 4.3 km ground target (retro), 2 kHz, attenuation by ND filters
strong signalweak signal prepulses dominate
ret. rate
L. Kral, 27th Oct 2004
SS
RM
S a
t 2.2
-sig
ma
[mm
]
jitter
optimum
L.Kral, K. Hamal, I. Prochazka, G. Kirchner, F. Koidl, Graz, October 2004
Ground Target Laser Ranging Energy SpectrumGraz, May 5, 2004, 2 kHz, 8 ps laser, C-SPAD, PET2k
dark countsprepulses
1 m ground target 1 - 10 PE, 15 ps rms
4 km ground target ~ 1000 PE, 6 ps rms
L.Kral, K. Hamal, I. Prochazka, G. Kirchner, F. Koidl, Graz, October 2004
Adjusting Divergence and FOVField-proven procedure at Graz observatory:1. Set the minimum beam divergence (~ 50 urad) to
concentrate the energy and make the target easily visible
2. Adjust laser/telescope to point exactly to the target (visual + CCD control of the reflected light intensity)
3. Set the maximum beam divergence (1 mrad) to stabilize the return rate (reduces the atmospheric fluctuation of returned light intensity)
4. Attenuate the laser beam to adjust the proper return energy (-> low jitter + high return rate)
The 4.3 km distant retro illuminated by the laser
Example of Results
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 60
5k
10k
15k
20k
25k
30k
35k
40k
45k
L. Kral, 27th Oct 2004
Graz, 4.3 km ground target, 2 kHz, 100k returns, 60% ret. rate
3.0*sigma iter. filter -> 0.9 mm RMS 2.2*sigma iter. filter -> 0.8 mm RMS
Re
turn
s
Range offset [mm]
dataset suitable for atmospheric influence extraction
Single shot RMS = 0.8 mm (2.2-sigma)Return rate = 1.2 kHz
L.Kral, K. Hamal, I. Prochazka, G. Kirchner, F. Koidl, Graz, October 2004
Conclusion Ground target 2–4 km ranging to a corner retro
reflector became routine with <1 mm instrumental precision at a signal strength ~ 1ooo phot/echo
Standard procedure developed and documented
Atmospheric fluctuation contribution to the laser ranging jitter budget extracted from this data for the first time
PROCHÁZKA, I. – HAMAL, K. – KRÁL, L. Atmospheric fluctuation induced laser ranging jitter. In Laser Radar Techniques for Atmospheric Sensing: Proceedings of SPIE, vol. 5575. ISBN 0-8194-5522-9.
