The general characteristics of Satellite Laser Ranging (SLR): The photons returning are usually fewer because the transmitting laser and retroreflectors both have a divergence. This means that the laser beam spreads out as it travels, which can affect the accuracy of the measurement. How can this divergence be minimized?
Abdelrahim Ruby
Hi ,
There are a few ways to minimize the divergence between the transmitting laser and the retroreflectors in Satellite Laser Ranging (SLR).
By following these tips, it is possible to minimize divergence in SLR and improve the accuracy of the measurements.
One way is to use a laser with a narrow beamwidth. This will reduce the amount of spreading that occurs as the laser beam travels.
Another way to minimize divergence is to use a retroreflector with a large reflective area. This will increase the chance that the laser beam will hit the retroreflector and be reflected back to the ground station.
Finally, it is also important to use a high-quality optical system. This will help to reduce the amount of aberrations that can occur in the laser beam, which can also lead to divergence.
By using these techniques, it is possible to minimize the divergence between the transmitting laser and the retroreflectors in SLR, which can improve the accuracy of the measurements.
Here are some additional tips for minimizing divergence in SLR:
- Use a laser with a wavelength that is well-matched to the atmospheric conditions.
- Use a laser with a high pulse energy. This will increase the signal-to-noise ratio of the measurements.
- Use a laser with a high repetition rate. This will increase the number of measurements that can be made in a given time period.
- Use a retroreflector that is made of a high-reflectivity material.
- Use a retroreflector that is mounted on a stable platform. This will reduce the amount of vibration that can affect the measurements.
- Use a high-quality optical system. This will help to reduce the amount of aberrations that can occur in the laser beam.
Please recommend my reply if it is useful .Thanks
Dear prof. Aahed Alhamamy
Thank you very much for this information
But at the present time, how to overcome this problem at ground laser stations. If you have any references for that, please share them here.
Greetings, Ruby
I am a bit puzzled by your question...
A robust design would _never_ expect 100% recovery of all emitted photons.
I don't understand how fewer photons would affect the accuracy of the measurement - unless there was such a significant loss of returned photons that detecting the rising/falling pulse times became compromised.
In terrestrial applications I could envision some measurement errors if one were measuring divergent side-beam energy instead of mid-beam,
but in the satellite context the error relative to the distance would be extremely small...
I assume that the emitted beam is both grossly and micro-tracked in order to ensure mid-beam max-intensity measurements
oh... I meant to add that I would expect that errors due to atmospheric refraction and absorption would eclipse any beam-divergence artifacts
I am curious how refraction effects are compensated ?
Multi-wavelength lasers and some arm-wavery algorithms ;-)?
Dear, Kurt Klingbeil
Apologies for any confusion caused.
The accuracy of Satellite Laser Ranging (SLR) is determined by the ability to detect and measure the precise time it takes for the laser pulses to travel to the target and return. In SLR, the goal is to reduce the spreading of the laser beam over long distances, resulting in a decrease in the number of photons per unit area at the target. The accuracy of the measurement is influenced by the signal-to-noise ratio, and if the received photon count is too low, it can introduce higher levels of noise and decrease the precision of the timing measurements.
For atmospheric propagation delays, you can refer to chapter 9 in the following reference for more details:
Petit G, Luzum B (2011) IERS Conventions 2010. IERS Technical Note 36. https://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn36.html-1.htm?nn=94912
Greetings, Ruby
I suggest you read my article "Millimeter Accuracy Satellite Laser Ranging: A Review" available on Researchgate .
John Degnan
Use the telescope to transmit AND receive the photons. My SLR2000 system (available on Researchgate ) did this by greatly reducing the transmit beam divergence and increased the measurement rate to 2 kHz.
Dear Prof. John J. Degnan , I hope you and your family are well and healthy.
Thank you very much for your answer.
Also, thanks for this suggestion.
Really, this paper is wonderful.
I have benefited from it.
Regards
Ruby
Larger reflectors don't necessarily help because of "velocity aberration" which causes the reflected beam to be deflected from the beam source. I just published an invited paper in the open access IEEE journal Photonics JOU
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