Saturation Effects in Narrowband Resonance Lidar Measurements, Part 1: Theoretical Consideration of Sodium, Iron, and Helium Lidar Systems

Abstract Atmospheric resonance lidars targeting metallic species in the mesosphere and lower thermosphere have yielded insights into the dynamics of the middle and upper atmosphere for over 50 years. Recently, the technique has been extended to the metastable helium layer, which reaches up to 1,000 km or above. It has long been recognized that high energy concentrations in the laser beam can lead to nonlinear behavior during the scattering process, a phenomenon known as saturation. Nonetheless, commonly used approaches to calculating the severity of saturation effects are not accurate for modern resonance lidar systems. Here, we present an approach to calculating saturation for sodium, iron, and helium resonance lidars and discuss the biases in wind and temperature that arise from neglecting saturation. The saturation calculators presented here are publicly available and can be adapted to estimate saturation for current or future resonance lidar systems.