  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.
