Investigation of a resonance Lidar for measurement of thermospheric metastable helium

Expected signal returns for a ground-based resonance Lidar system used for profiling metastable thermospheric helium are presented, scaleable to specific system configurations. The signal estimate is dependent on the calculation of the effective backscatter cross-section for the He 10 830 Å resonant transition as well as an estimate of thermospheric metastable helium densities obtained from a recent model. The peak backscatter cross-section is found to be 2.7( ± 0.3) × 10^-16 m² with an effective backscatter cross-section (assuming a 1 GHz rms laser linewidth centered at a wavelength of 10 830.32 Å) of 2.6(±0.3) × 10^-16 m². Measurements using the metastable He 3188 Å and 3889 Å lines are evaluated. Challenges in experimental design (i.e., laser characteristics, near infrared single photon detection, and background noise), as well as potential operation from a space-borne platform, are also discussed. With current technology, profiles with relatively high temporal and vertical resolution are shown to be attainable under twilight conditions.