We report on the successful delivery of a 30 W solid-state sodium Guide Star Laser System (GLS) to the W. M. Keck
Observatory in 2009, and the demonstration of a 55 W GLS delivered to the Gemini South Observatory in 2010. This
paper describes the GLS performance results of both the Keck I and Gemini South GLSs with an emphasis on the system
design and delivered performance. The 589 nm output was generated via Sum Frequency Mixing (SFM) of 1064 nm
and 1319 nm Nd:YAG lasers in a LBO (Lithium Triborate) nonlinear crystal. The Keck GLS underwent extensive
testing and has demonstrated consistent performance with a CW mode-locked output of > 30 W and measured beam
quality of M2 < 1.2 while locked to the sodium D2a transition. The Keck GLS was installed on the telescope in late 2009
and first light on the sky was achieved in early 2010. Factory testing of the Gemini South GLS shows a CW modelocked
output of > 55 W and measured M2 ~1.2 while locked to the sodium D2a line center. The Gemini South GLS has
produced a maximum power of 76 W at 589 nm with 85 W of 1319 nm and 110 W of 1064 nm as inputs to the SFM,
representing a single-pass conversion efficiency of 39%.
Numerous coherent lidar systems have shown the ability to make measurements of atmospheric winds over the past three decades. During the past decade a 2-micron-wavelength coherent lidar system for remote wind and aerosol backscatter measurements has been advanced from initial breadboard demonstration units to a turnkey coherent lidar product, the WindTracer"R" that can operate autonomously and reliably. In this paper, the instrument is described and recent examples of wind measurement capability are provided.
Pulsed coherent Doppler lidar systems have matured rapidly, especially at solid-state wavelengths. Turnkey systems are commercially available and are being deployed for various aviation applications. Doppler lidar data is used in the airport terminal area to map hazardous wind shear and turbulence levels and to detect and track wake vortices. Future applications could include slant path visibility monitoring. Several permanent installations and rapidly deployable instrument configurations have been achieved. The benefit of the infrared Doppler lidar relative to its microwave counterparts is the ability to sense clear air hazards, especially those in and around local terrain features. The fact that the lidar beam is quite narrow eliminates artifacts associated with sidelobe-induced ground clutter. This paper summarizes our autonomous pulsed lidar developments and reviews sample results.
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.
Doppler lidar sensors provide a unique capability to generate high resolution 3D distributions of wind and aerosol data. Appropriately processed, these data can yield useful detection, tracking and short-term prediction information relating to the extent, density and location of potentially dangerous isolated aerosol plumes. The aerosol data are analyzed to detect above-threshold inhomogeneities and the wind and turbulence data are used to provide short- term prediction of plume propagation. Broadcast of these data to plume dispersion models can enable robust prediction of dispersion and propagation over longer time periods. Performance predictions are given for both wind and aerosol measurements. Sample processed field data results are presented for Doppler lidars operating at the eyesafe 2 micron wavelength.
Solid-state coherent Doppler lidar sensors operating at eyesafe wavelengths have broad application to a variety of wind measurement scenarios. We have developed a modular, autonomous, high PRF, diode-pumped coherent lidar sensor that is appropriate for wind profiling at high temporal resolution. This paper describes the design of the sensor, provides examples of high-resolution wind data, and compares the performance with modeling.
Pulsed Doppler lidar sensors can provide accurate range-resolved wind velocity measurements with sufficient spatial resolution to detect turbulent wind features. Application of this technology to commercial airliners would enable much-needed advanced warning of moderate to severe turbulence ahead. CTI, with NASA/Dryden, has developed the Airborne Coherent Lidar for Advanced Inflight Measurements (ACLAIM) which was recently flight tested aboard a research aircraft. This paper presents results from these initial engineering flights, with validated demonstration of Doppler lidar wind turbulence detection using the observed spatial and temporal variations in the longitudinal component of the wind field.
KEYWORDS: Sensors, Turbulence, LIDAR, Signal to noise ratio, Monte Carlo methods, Polonium, Receivers, Device simulation, Coherence (optics), Backscatter
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 Force's 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.
Range-resolved crosswind measurements are required for improved ballistics accuracy in a variety of planetary boundary layer applications. In these environments, the effects wind turbulence can cause large errors in estimates derived using conventional Velocity Azimuth Display (VAD) lidar techniques. This paper presents the results from two recent measurement campaigns employing the VAD algorithm and Monte Carlo performance predictions of a novel velocity- pattern tracking concept for precision range-resolved crosswind sensing in the presence of wind turbulence.
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.
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.
Under NASA sponsorship, Coherent Technologies, Inc. (CTI) has designed and built the transceiver, and is developing the scanner, for an airborne scanning optical wind sensor. A scanning, single-aperture architecture was chosen for the CTI/NASA Optical Air Data System. Techniques for vector wind estimation form LOS scalar velocity measurements, the choice of scan patterns and wind models for various applications, and various other considerations that led to this decision are discussed within. Estimating wind vectors requires taking multiple scalar velocity projections along non- coplanar lines of slight. THis can be done from several apertures to the same field point, or vice versa, and may involve either fixed or scanned beams. For a scanning, interpolative systems, the choice of scan pattern and wind model are intimately related. Typically, more complicated models require more intricate scans to separate the fit parameters. Vector wind estimation error can arise from a variety of sources. Several effects can contribute to LOS velocity measurement noise, some of which stem form the scan itself. Inaccuracies in the scan deflection vector can also introduce error. Error can enter if the wind field model is not sufficiently sophisticated to account for small-scale turbulence. Finally, a surface-flux measurement technique is introduced, which promises to be less sensitive to noise and turbulence than wind vector estimation.
Solid-state coherent Doppler lidar sensors operating at the eyesafe 2 micrometers wavelength have experienced rapid development over the past five years. Several ground-based and airborne systems have been successfully demonstrated. CTI is currently making significant strides toward the development of an autonomous, modest-cost wind field sensor for boundary-layer profiling. High spatial resolution 3D coverage for several kilometers around the lidar location will be possible at update rates of about a minute-- depending on the scan volume and grid size. This paper summarizes the results of detailed sensor performance modeling for the boundary layer profiler and discusses preliminary scan concepts and issues.
KEYWORDS: LIDAR, Data modeling, Turbulence, Sensors, Wind measurement, Atmospheric modeling, Doppler effect, Signal to noise ratio, Systems modeling, Digital signal processing
Solid-state coherent Doppler lidar systems are rapidly emerging as useful tools for boundary layer wind profiling. These Doppler lidars provide sufficient temporal,s spatial and velocity resolution to serve as an adjunct sensor, providing both real-time hazard detection as well as large-area wind state data for input to predictive models. THis paper briefly reviews recent results produced with a mobile flashlamp-pumped 2.09 microns coherent lidar sensor for windshear detection and measurement and wind turbulence estimation at the site of the new Hong Kong airport. Wind state predictions based on a fine-mesh mesoscale model are compared with the lidar results.
KEYWORDS: LIDAR, Turbulence, Sensors, Solid state electronics, Doppler effect, Error analysis, Solid state lasers, Wind measurement, Digital signal processing, Oscillators
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.
Simulated signatures of aircraft wakes as detected by a scanning coherent short wavelength lidar are presented and characterized for a number of candidate surveillance scenarios. Ground based and airborne scanning configurations that emulate candidate operational detection and warning systems are compared for spatial coverage and detection capability as a function of system design parameters and atmospheric conditions. Examples of trailing geometries characteristic of onboard wake detection and warning systems are presented. The dependence of predicted detection capability on hydrodynamic parameters, such as vortex circulation, axial motion in the wake vortices, and ambient turbulence is discussed. Simulated wake signatures are compared to observations for wakes observed at Denver's Stapleton International Airport in 1993.
Multifunction laser radar systems can collect two-dimensional target images of intensity, range, or velocity, and many such systems augment their active-sensor channel with a FLIR channel. This paper addresses the problem of optimal target detection using such an active-passive sensor, focusing on the performance benefits that accrue when multidimensional data-active-sensor range, velocity, and intensity, plus passive-sensor intensity - are combined in the detection processor. Generalized likelihood ratio tests are derived for active-passive detection processing, and quantitative performance results - receiver operating characteristics - are obtained through computer simulation of pixel-level statistics. The performance predictions for the gamut of multidimensional, multipixel detection processors are confirmed via experiments performed using a multidimensional laser radar test bed.
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