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> optical frequency comb "113 km absolute ranging with nanometer precision" (2024) https://arxiv.org/abs/2412.05542 https://arxiv.org/abs/2412.05542 : > two-

> optical frequency comb "113 km absolute ranging with nanometer precision" (2024) https://arxiv.org/abs/2412.05542 https://arxiv.org/abs/2412.05542 : > two-way dual-comb ranging (TWDCR) approach > The advanced long-distance ranging technology is expected to have immediate implications for space research initiatives, such as the space telescope array and the satellite gravimetry

mikewarot 2y ago
Note that the precision is very good, however the accuracy is nowhere near as close (fractions of a metre) in the atmosphere, due to the variable refractive index of air. Long term averages can help, of course.
- Aurornis 2y ago
  They talk about this technique for ranging between satellites, which wouldn't have to deal with atmospheric conditions. For ranging in an atmosphere they suggest dual-comb spectroscopy or two-color methods to account for the atmospheric changes.
  - westurner 2y ago
    From https://news.ycombinator.com/item?id=42330179 https://news.ycombinator.com/item?id=42330179 .. https://www.notebookcheck.net/University-of-Tokyo-researchers-prototype-optical-measurement-of-blood-pressure-and-glucose-levels.920305.0.html https://www.notebookcheck.net/University-of-Tokyo-researcher... : > multispectral [UV + IR] camera ... optical, non-contact method to detect [blood pressure, hypertension, blood glucose levels, and diabetes]." [ for "Non-Contact Biometric System for Early Detection of Hypertension and Diabetes" https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.4131796 https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.413... ] >> "Tongue Disease Prediction Based on Machine Learning Algorithms" (2024) https://www.mdpi.com/2227-7080/12/7/97 https://www.mdpi.com/2227-7080/12/7/97 : >>> new imaging system to analyze and extract tongue color features at different color saturations and under different light conditions from five color space models (RGB, YcbCr, HSV, LAB, and YIQ). [ and XGboost ]

mikewarot 2y ago

Note that the precision is very good, however the accuracy is nowhere near as close (fractions of a metre) in the atmosphere, due to the variable refractive index of air. Long term averages can help, of course.

Aurornis 2y ago
They talk about this technique for ranging between satellites, which wouldn't have to deal with atmospheric conditions. For ranging in an atmosphere they suggest dual-comb spectroscopy or two-color methods to account for the atmospheric changes.
- westurner 2y ago
  From https://news.ycombinator.com/item?id=42330179 https://news.ycombinator.com/item?id=42330179 .. https://www.notebookcheck.net/University-of-Tokyo-researchers-prototype-optical-measurement-of-blood-pressure-and-glucose-levels.920305.0.html https://www.notebookcheck.net/University-of-Tokyo-researcher... : > multispectral [UV + IR] camera ... optical, non-contact method to detect [blood pressure, hypertension, blood glucose levels, and diabetes]." [ for "Non-Contact Biometric System for Early Detection of Hypertension and Diabetes" https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.4131796 https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.413... ] >> "Tongue Disease Prediction Based on Machine Learning Algorithms" (2024) https://www.mdpi.com/2227-7080/12/7/97 https://www.mdpi.com/2227-7080/12/7/97 : >>> new imaging system to analyze and extract tongue color features at different color saturations and under different light conditions from five color space models (RGB, YcbCr, HSV, LAB, and YIQ). [ and XGboost ]