Development of a Sodium Lidar for Space-Borne Missions

Abstract:

Layers of neutral metal atoms, such as Iron (Fe), Magnesium (Mg), Calcium (Ca), Potassium (K) and Sodium (Na), which peak between 85 and 95 km and are ~20 km in width, are produced by the daily ablation of billions of Interplanetary Dust Particles (IDPs). As these metallic species are ionized during ablation, by sunlight’s ultraviolet photons, or by charge exchange with existing atmospheric ions, meteoroids affect the structure, chemistry, dynamics, and energetics of the Mesosphere and Lower Thermosphere (MLT). The strong optical signals that some of these metal layers produce, in particular the Na layer, makes them an optimal tracer of atmospheric dynamics and circulation and enabling the measurement of quantities, such as composition, temperature and winds, that are critical to address several compelling scientific questions related to the Earth's Upper Atmosphere and the Geospace Environment. In recent years, remote-sensing satellites have obtained the first global characterization of the basic structure of the MLT region in terms of large-scale temperature and wind climatologies, resulting in a much richer picture of the structure and variability of the mesosphere. Although these measurements have shown the high temporal variability of both the zonal mean state as well as large scale organized perturbations, such as planetary waves and atmospheric tides, they failed at providing information required for the fundamental characterization of how the basic state is established and maintained. Thus there is a pressing need in the Ionosphere-Thermosphere-Mesosphere (ITM) community to be able to perform high-resolution measurements that can be used to characterize the small-scale variability in the MLT on a global basis. Such measurements must include highly resolved, in space and time, global temperatures profiles, which will add to the understanding of key indicators of radiative cooling in the mesosphere. We present in this paper initial efforts to develop and demonstrate an integrated ground-based operational sodium lidar science instrument using key “space-flight-precursor” components. In this way, a ground-based Na lidar will demonstrate the spaceflight instrument viability in a cost-efficient approach and will serve as the core for the future planning of a Heliophysics space mission.