Precision Doppler Shift Measurements with a Frequency Comb Calibrated Laser Heterodyne Radiometer

TL;DR

This paper demonstrates high-precision atmospheric CO2 spectroscopy using a laser heterodyne radiometer calibrated with an optical frequency comb, achieving Doppler shift measurements with 15 cm/s accuracy for wind velocity detection.

Contribution

The study introduces a novel application of a frequency comb calibrated laser heterodyne radiometer for precise Doppler shift measurements in atmospheric spectroscopy.

Findings

Achieved 200 MHz spectral resolution in sunlight-based CO2 spectra.

Measured wind-induced Doppler shifts with 15 cm/s accuracy.

Validated measurements against atmospheric models.

Abstract

We report precision atmospheric spectroscopy of $CO_2$ using a laser heterodyne radiometer (LHR) calibrated with an optical frequency comb. Using the comb-calibrated LHR, we record spectra of atmospheric $CO_2$ near 1572.33 nm with a spectral resolution of 200 MHz using sunlight as a light source. The measured $CO_2$ spectra exhibit frequency shifts by approximately 11 MHz over the course of the five-hour measurement, and we show that these shifts are caused by Doppler effects due to wind along the spectrometer line of sight. The measured frequency shifts are in excellent agreement with an atmospheric model, and we show that our measurements track the wind-induced Doppler shifts with a relative frequency precision of 100 kHz (15 cm/s), equivalent to a fractional precision of a few parts in $10^{10}$. These results demonstrate that frequency-comb-calibrated LHR enables precision velocimetry that can be of use in applications ranging from climate science to astronomy.