Abstract: A method includes emitting scanned reference laser light from a first tunable laser into a first atomic vapor filter to output filtered scanned reference laser light and receiving the filtered reference laser light with a first detector. The method includes emitting scanned outgoing signal laser light from a second tunable laser into an atmospheric space, receiving a return of the scanned signal laser light from Doppler shifted scattering from the atmospheric space into a second atomic vapor filter to output Doppler shifted filtered scanned signal laser light, and receiving the Doppler shifted filtered scanned signal laser laser light with a second detector. Each tunable laser wavelength scan is controlled independently using information from the wavelength scan received at the associated detector to maintain the center of the wavelength scan received at the detector as the bottom of an atomic absorption well.