Stephen M. Hannon

Coherent laser radar at 2 mu m using solid-state lasers

The development of a coherent laser radar system using 2- mu m Tm- and Tm, Ho-doped solid-state lasers, which is useful for the remote range-resolved measurement of atmospheric winds, aerosol backscatter, and differential absorption lidar (DIAL) measurements of atmospheric water vapor and CO/sub 2/ concentrations, is described. Measurements made with the 2- mu m coherent laser radar system, advances in the laser technology, and atmospheric propagation effects on 2- mu m coherent lidar performance are discussed. Results include horizontal atmospheric wind measurements to >20 km. vertical wind measurements to >5 km, near-horizontal cloud returns to 100 km, and hard target (mountainside) returns from 145 km. >

Coherent Doppler Lidar Measurements of Wind Field Statistics

Coherent Doppler lidar measurements of wind statistics in the boundary layer are presented. The effects of the spatial averaging by the lidar pulse are removed using theoretical corrections and computer simulations. This permits unbiased estimates of velocity variance, spatial velocity structure functions, energy dissipation rate, and other point statistics of the velocity field.

Performance of a 2-µm Coherent Doppler Lidar for Wind Measurements

Abstract Measurements of boundary layer winds are presented using a 2-µm coherent Doppler lidar and the optimal performance of the maximum likelihood estimator. The systematic error for single-shot estimates was estimated as 3.6 cm s−1 using measurements from a stationary hard target. The estimation error for measurements of the radial component of the wind field was determined, as well as the fraction of the estimates that are randomly distributed over the velocity search space, when the signal power is low and speckle fading is important. The results from actual data are compared with the results from ideal simulations. The first direct estimation of the spatial structure function of the radial wind field and of the energy dissipation rate is presented for both horizontal and vertical directions of propagation. The rms estimation error of the velocity estimates is found to be within 30% of ideal performance based on simulation.

Coherent Doppler lidar measurements of winds in the weak signal regime.

In the weak signal regime coherent Doppler lidar velocity estimates are characterized by a localized distribution around the true mean velocity and a uniform distribution of random outliers over the velocity search space. The performance of velocity estimators is defined by the standard deviation of the good estimates around the true mean velocity and the fraction of random outliers. The quality of velocity estimates is improved with pulse accumulation. The performance of velocity estimates from two different coherent Doppler lidars in the weak signal regime is compared with the predictions of computer simulations for pulse accumulation from 1 to 100 pulses.

Windshear, turbulence, and wake vortex characterization using pulsed solid state coherent lidar

Coherent lidar systems based on eyesafe solid-state laser technology are rapidly emerging in ruggedized packages. The airport terminal area presents several measurement scenarios appropriate for application of pulsed coherent lidar sensors. This paper briefly reviews the status of coherent lidar technology and presents results produced with a mobile flashlamp- pumped 2.09 micrometers coherent lidar sensor for windshear detection and measurement, wind turbulence estimation, and wake vortex detection and tracking.

Assessment of Lockheed Martin's Aircraft Wake Vortex Circulation Estimation Algorithms Using Simulated Lidar Data

A new algorithm for estimating circulation strength of aircraft wake vortices is under development by Lockheed Martin and is being evaluated by NorthWest Research Associates, Inc. (NWRA) under the National Aeronautics and Space Administration Research Announcement (NASA-NRA) NextGen Airportal Program. The algorithm is being developed with the aid of Lockheed Martin’s Coherent Wind Lidar Simulator, developed under the same NASA-NRA program. A brief description of the simulator tool is presented. An overview of both the legacy estimation algorithm and the new algorithm under development is presented which highlights the differences between the two algorithms. The performance of both algorithms is assessed using simulated lidar data generated from analytic wake models and Large Eddy Simulation (LES) vortex wind fields with ambient turbulence eddy dissipation rates (EDR) of 4 x 10 -5 , 5 x 10 -4 and 1.45 x 10 -2 m 2 s -3 . Algorithm performance is quantified in terms of standard deviation and bias of estimates as a function of SNR.

Agile multiple-pulse coherent lidar for range and micro-Doppler measurement

A novel high time-bandwidth product waveform lidar has been developed. The lidar operates at the eyesafe 2 micrometers wavelength and produces a sequence of two or more cavity- dumped pulselets with a controllable intra-pulse spacing. The number of and spacing for the individual pulselets is adjusted to match the target and atmospheric characteristics. This waveform agility enables the sensor to operate at very long stand-off ranges. Performance predictions and results from recent field demonstrations are described.

Coherent laser radar atmospheric turbulence sensor

A single-ended, range-resolved, refractive turbulence sensor concept was investigated for ground-based and airborne platforms. This technology is of interest to the Air Forces Airborne Laser (ABL) program, because it will enable the determination of optimal engagement paths for the weapons laser. In this paper we describe the performance of a range- resolved refractive turbulence profiler which is based upon a coherent laser radar array receiver technology. We present Monte-Carlo simulation performance predictions for several sensor configurations, including a one micron ABL sensor and an eye-safe two micron ground-based sensor. In addition to its refractive turbulence sensing function, this innovative sensor will be capable of measuring wind velocity and characterizing wind turbulence.

Solid state coherent lidar technology for space-based wind measurement

Pulsed coherent solid-state 2 micron laser radar systems have been developed at Coherent Technologies, Inc. for ground- and airborne-based applications. Ground-based measurements of wind profiles and aerosol backscatter have been performed for several years. Examples of wind and aerosol backscatter coefficient measurements will be presented which cover a variety of weather conditions. Airborne measurements of wind profiles below the aircraft have been performed by Wright Laboratories, operating in a VAD measurement mode and will be reviewed. An engineered flight-worthy coherent lidar system is under development at CTI for flight on the SR-71 aircraft, in support of the High Speed Civil Transport program. Flights will be conducted by NASA-Dryden Flight Research Center at altitudes above 60,000 feet for the measurement of atmospheric turbulence ahead of the aircraft. Efforts are also underway at CTI for the development of high power coherent laser radar systems. Extensive detailed physical optics models of diode-pumped solid-state laser performance have been developed to characterize transient thermo-optic aberrations and the overall efficiency of lasers intended for space-based applications. We are currently developing a 2 micron 0.5 J/pulse transmitter with a 10 Hz PRF and a pulse duration of 400 - 500 ns. The status and expected space-based wind measuring performance for this system will be presented.

Eye-safe coherent lidar detection using a 1.5-um Raman laser

We present data on a novel short-pulse eyesafe lidar transceiver for utilization in high-resolution heterodyne detection Doppler wind sensing. Operating at 20 Hz, the transmitter is a 1.3 micrometers pumped solid state Raman laser running at 1.556 micrometers , and is injection seeded using a direct diode master oscillator. This system is coupled to a hemispherical scanner to measure atmospheric winds, with the data validated against a commercially-available 2 micrometers lidar system. We typically measured atmospheric returns from greater than 2 km, with range resolution less than 6 m.