Detecting clear-air turbulence via beam broadening in a Rayleigh-scattering lidar system

The volume of clear-air turbulence (CAT) in the atmosphere at flight cruising altitudes is increasing rapidly, posing a growing problem for civil aviation and resulting in reduced confidence in aviation safety. There are limited remote detection capabilities for CAT, since clear air produces no measurable radar return. Lidar has been proposed as a viable detection methodology, and several systems have been demonstrated. However, these systems have to date demonstrated limited detection ranges of less than 15 km. In this work, we propose what is believed to be a novel lidar-based CAT detection methodology that uses Rayleigh scattering and relies on a differential detector measurement to quantify beam spread and thereby estimate the eddy dissipation rate (EDR), which is the international aircraft-independent metric for quantifying aviation turbulence strength. Additionally, we present laboratory measurements illustrating range-resolved molecular-scattering returns consistent with the modeled collection behavior. We show that, under modest assumptions, a size, weight, and power (SWAP) constrained system that implements this method can detect moderate CAT at ranges in excess of 30 km, equating to two minutes of flight time at typical commercial aviation cruising speeds, which represents a substantial range improvement over prior approaches. This is an important advance because—for what is believed to be the first time—it potentially allows the cabin to be secured before the turbulence is encountered, reducing the injury risk to passengers and flight attendants.