Digital back-end design considerations of a laser heterodyne radiometer

Laser Heterodyne Radiometry is a powerful technique that is becoming popular in atmospheric spectroscopy because of its ability to amplify signals and achieve high spectral resolution. Current designs employ a narrow-band analog radio design focused on time domain analysis combined with laser scanning to measure a spectrum. This study evaluates an alternative approach using a wideband radio design combined with digital processing focused on the frequency domain to generate a spectrum without laser scanning. A recorded signal is converted into the frequency domain using Fast Fourier Transform (FFT) and impacts of FFT length and number of time averages on the generated absorption spectrum are compared. Counterintuitively, longer FFT lengths decrease the signal fit while more averaging conveys better performance.