Spectroscopic thermometry for long-distance surveying.

Area of Science:

• Metrology
• Optical Sensing
• Atmospheric Science

Background:

• High-precision electronic distance meters (EDMs) require accurate air temperature data for refractive index compensation.
• Achieving relative measurement uncertainties of 10^-7 necessitates temperature knowledge within 100 mK.
• Traditional temperature measurement methods face challenges in accuracy and spatial coverage over long outdoor distances.

Purpose of the Study:

• To develop and validate a thermometer capable of accurate temperature measurements over distances up to a few kilometers.
• To provide spatially continuous air temperature data that aligns temporally with distance-measuring laser beams.
• To improve the refractive index compensation in high-performance EDMs.

Main Methods:

• Direct laser absorption spectroscopy of oxygen (O2) near 770 nm was employed.
• The thermometer was designed for long-distance, outdoor environmental monitoring.
• Field measurements were conducted at the 864-m Nummela standard baseline.

Main Results:

• The developed thermometer provides spatially continuous air temperature measurements.
• Data collected by the thermometer is temporally and spatially well-matched with distance-measuring laser beams.
• Demonstrated applicability for enhancing refractive index compensation in EDMs.

Conclusions:

• The laser absorption spectroscopy thermometer is effective for accurate long-distance temperature measurements.
• This technology can significantly improve the performance of high-precision electronic distance meters.
• The developed thermometer addresses the challenges of outdoor, kilometer-scale temperature monitoring.