Coherent lidar airborne windshear sensor: performance evaluation

Abstract

National attention has focused on the critical problem of detecting and avoiding windshear since the crash on 2 Aug. 1985 of a Lockheed L-1011 at Dallas/Fort Worth International Airport. As part of the NASA/FAA National Integrated Windshear Program, we have defined a measurable windshear hazard index that can be remotely sensed from an aircraft, to give the pilot information about the wind conditions he will experience at some later time if he continues along the present flight path. A technology analysis and end-to-end performance simulation measuring signal-to-noise ratios and resulting wind velocity errors for competing coherent laser radar (lidar) systems have been carried out. The results show that a Ho:YAG lidar at a wavelength of 2.1 microm and a CO(2) lidar at 10.6 microm can give the pilot information about the line-of-sight component of a windshear threat from his present position to a region extending 2-4 km in front of the aircraft. This constitutes a warning time of 20-40 s, even in conditions of moderately heavy precipitation. Using these results, a Coherent Lidar Airborne Shear Sensor (CLASS) that uses a Q-switched CO(2) laser at 10.6 microm is being designed and developed for flight evaluation in the fall of 1991.

Intra-cavity side-pumped Ho:YAG laser

“…This is combined with a large emission cross-section and hence a low saturation fluence of ~6J/cm 2 in Ho:YAG, allowing efficient extraction of the stored energy in the form of short Q-switched pulses. These characteristics make Ho:YAG very attractive for applications such as coherent Doppler LIDAR, [2], and as a pulsed pump-source for mid-infrared optical parametric oscillators, [3].…”

<title>Lidar measurement of wind shear and turbulence and comparison with a predictive fine-mesh mesoscale model</title>

“…p-=--Vp+gkB+V•'r (1) dt and second-order centered differences for the anelastic mass continuity equation…”

“…Airborne applications include microburst windshear detection aboard commercial airliners [1], optical air data sensing [2-4J, and clear air turbulence and gust front detection for military and commercial aircraft [5]. Ground-based applications include windshear, gust front, and turbulence monitoring in the vicinity of airport terminals [6], wake vortex detection and tracking along airport approach corridors [7][8][9], and general wind profiling in support of objectives such as improved prediction of ballistic trajectories, and planetary boundary layer modeling [10][11][12].…”

<title>Doppler lidar measurement of the wind for a non-Gaussian signal in the turbulent atmosphere</title>

“…Considerable technological advances in the Doppler sounding are conditioned by a number of the factors among which is the use of the highpower lasers with the various wavelengths and the application of the original design [1][2][3][4][5][6][7][8][9]. As a result the Doppler lidar systems have been created for the wind velocity measurements with the high accuracy and high spatial resolution for the different platforms.…”