Development of a Helium Resonance Lidar for the Upper Thermosphere

Abstract

Resonance lidars targeting fluorescence lines of metallic layers in the mesosphere and lower thermosphere have long been used to measure profiles of wind and temperature [1], most recently achieving a maximum altitude of 300 km [2], but the rapidly decreasing densities of these metallic species prevents measurements at higher altitudes. An alternative, first proposed in 1997 [3], is an extension of this technique to metastable helium, which would increase the possible range of resonance lidar measurements to 1000 km or higher. Last year, for the first time, a helium resonance lidar system was realized at the German Aerospace Center (DLR) in southern Germany [4]. The initial measurements by this instrument, made last year between January and March, captured the first profiles of metastable helium density, extending to an altitude of 700 km. We present an overview of this lidar system; we report an update on its status, including the results of the second measurement campaign; and we discuss the potential for wind and temperature measurements given anticipated improvements to system performance. [1] Fricke, K. & von Zahn, U. (1985) Mesopause temperatures derived from probing the hyperfine structure of the D2 resonance line of sodium by lidar. J. Atmos. Terrestrial Phys. 47, 499–512. [2] Jiao, J., Chu, X., Jin, H., Wang, Z., Xun, Y., Du, L., et al. (2022). First lidar profiling of meteoric Ca+ ion transport from 80 to 300 km in the midlatitude nighttime ionosphere. Geophysical Research Letters, 49, e2022GL100537. https://doi.org/10.1029/2022GL100537 [3] Gerrard, A. J., Kane, T. J., Meisel, D. D., Thayer, J. P. & Kerr, R. B. (1997) Investigation of a resonance lidar for measurement of thermospheric metastable helium. J. Atmos. Sol. Terrestrial Phys. 59, 2023–2035 [4] Kaifler, B., Geach, C., Büdenbender, H.C. et al. (2022) Measurements of metastable helium in Earth’s atmosphere by resonance lidar. Nat Commun 13, 6042 https://doi.org/10.1038/s41467-022-33751-6