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, scaleabl e to specific system configurations. The signal estimate is dependent on the calculation of the effective backscatter cross-section for the He 10 830 Angstrom resonant transition as well as an estimate of therm ospheric metastable helium densities obtained from a recent model. The peak backscatter cross-section is found to be 2.7(+/-0.3) x 10(-16) m (2) With an effective backscatter cross-section (assuming a 1 GHz rms laser linewidth centered at a wavelength of 10830.32 Angstrom) of 2.6( +/-0.3) x 10(-16) m(2). Measurements using the metastable He 3188 Angs trom and 3889 Angstrom lines are evaluated. Challenges in experimental design (i.e., laser characteristics, near infrared single photon dete ction, and background noise), as well as potential operation from a sp ace-borne platform, are also discussed. With current technology, profi les with relatively high temporal and vertical resolution are shown to be attainable under twilight conditions. (C) 1997 Elsevier Science Lt d.