Mid-infrared laser heterodyne radiometer for remote sensing and planetary applications

Laser heterodyne radiometry (LHR) is primarily used for remote sensing of atmospheric column and molecular densities, specifically trace gases. The technique utilizes the mixing of two radiations: one is sunlight, and the other is a local oscillator, typically a laser tuned to spectral line transitions of interest. In this paper, we demonstrate a mid-infrared coupled LHR system to quantify molecular rotational-vibrational line transitions of methane and water vapor in the spectral region of 3.7 μm and 6.8 μm. We used integrated wavelength-modulation spectroscopy to discriminate overlapping line transitions, thereby improving the fit of the speed-dependent Hartmann-Tran Profile (HTP) lineshape models. The laboratory-based instrumentation can be field-deployed for earth science and planetary applications by simply modifying the solar tracker modules.