http://www.pa.op.dlr.de/wirbelschleppe/publ/PAS.pdf

Commercial aircraft wake vortices

Ladar is becoming more prominent due to the maturation of its component technologies, especially lasers. There are many forms of ladar. There is simple two-dimensional (2-D) ladar, similar to a passive electro-optic sensor, but with controlled illumination and the ability to see at night even at short wavelengths. There is three-dimensional (3-D) ladar, with angle/angle/range information. 3-D images are very powerful because shape is an invariant. 3-D images can be easily rotated to various perspectives. You can add gray scale or color, just like passive, or 2-D ladar, imaging. You can add precise velocity measurement, including vibrations. Ladar generates orders of magnitude higher frequency change then microwave radar for velocity measurement, because frequency change is proportional to one over the wavelength. Orders of magnitude higher frequency change means you can measure a given velocity orders of magnitude quicker, in many cases making an accurate measurement possible. Polarization can be used. With an active sensor you control both the illumination and the reception, so you can pattern the illumination. Also, because ladar can use narrow band illumination it is easier to easier to coherently combine sub-aperture images to obtain the higher resolution of an array.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-51/issue-8/089801/Errata--Review-of-ladar--a-historic-yet-emerging/10.1117/1.OE.51.8.089801.pdf

Review of ladar: a historic, yet emerging, sensor technology with rich phenomenology

In this paper we report on diode pumped single mode Tm:LuAG and Tm,Ho:LuAG lasers which are developed as master oscillators for an airborne LIDAR system. Using a new fourfold pump setup 51 mW of output power with a Tm(10%):LuAG laser were reached at room temperature. The Tm(10%),Ho(0.4%):LuAG laser proved to be more temperature sensitive than the Tm laser. 18 mW and 30 mW of single mode laser output could be achieved at room temperature and 0°C, respectively. In multi mode laser operation 130 mW output power at room temperature (slope efficiency 36%) were achieved.

https://iopscience.iop.org/article/10.1002/lapl.200410067/pdf

Single mode Tm and Tm,Ho:LuAG lasers for LIDAR applications

A system for observing a field of view including a light transmitter and a light detector. A path is defined between the transmitter and the detector. The light transmitter generates substantially coherent light onto a transmit portion of a light path and the light detector is positioned in a receive portion of the light path defined by reflected light from some of the target locations. The system includes a component for configuring at least a portion of the light path such that a subset of the plurality of potential target points are included in the light path.

Efficient lidar with flexible target interrogation pattern

Coherent lidar/laser radar systems have been used for the remote measurement of atmospheric wind velocity since 1966. Both CW and pulsed coherent lidars have been developed and applied to a variety of ground-based and airborne applications. In recent years, most efforts have concentrated on pulsed CO/sub 2/ and solid-state Doppler lidars for the remote measurement of atmospheric wind velocities. Issues associated with the design and application of coherent lidars to atmospheric wind measurement are discussed. Coherent lidar/laser radar systems have been applied to detection and tracking of aircraft wake vortices, measurement of atmospheric wind fields during the space shuttle takeoff and landing, airborne windshear detection, ground-based airport microburst windshear monitoring, meteorological research, and environmental monitoring. Numerous examples of measurement results are presented. An assessment of the status of coherent lidar technology as practical devices for operational and research uses is addressed.

Remote sensing of atmospheric wind velocities using solid-state and CO/sub 2/ coherent laser systems

Pulsed solid-state coherent laser radar (lidar) systems can measure radial wind velocity to precisions well below 1 m s−1 at spatial scales on the order of 30–50 m and to ranges of several kilometres. This capability is appropriate for a variety of measurement objectives in the airport terminal area. Wake vortex detection and tracking is one of the primary objectives currently being evaluated by regulatory agencies in the United States and elsewhere. Up to now, non-invasive measurement of wake vortex properties has been limited to short-range continuous-wave lidar systems. This paper discusses this application and presents theoretical analysis and experimental results for pulsed 2 μm coherent lidar. Detection, tracking, and measurement results are presented for sample DC10, 757, and 727 aircraft landings from a laser radar wake vortex database compiled in 1993 at Denver Stapleton International Airport.

Aircraft Wake Vortex Detection and Measurement with Pulsed Solid-state Coherent Laser Radar

In a laser radar (lidar) system a Doublet Pulse (M1(t), M2(t)) is generated by injection-seeded aborted cavity dumping of a solid-state laser. The doublet pulse provides coherent Doppler lidar systems a substantial time bandwidth product (TB) with a very modest processing requirement. The waveform format comprises a pair of pulselets, each of duration τ, separated by T seconds. The range resolution is governed by the pulselet duration τ, while the velocity precision is governed by one over the pulselet separation, T. Ambiguities in the velocity measurement arise as a result of the periodic structure of the waveform and occur every μ/2T m/sec, where μ is the operating wavelength. These ambiguities are removed by conventional de-aliasing algorithms as well as through the generation and processing of higher order pulse waveforms.

Doublet pulse coherent laser radar for precision range and velocity measurements

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.

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

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.

Autonomous lidar wind field sensor: performance predictions

Lidar remote sensing of micro-Doppler signals is important for a large number of civilian and military applications. The single most important performance metric of these sensors is their velocity measurement precision. The velocity precision of a micro-Doppler lidar is limited by any one of various noise sources, which include shot-noise, local-oscillator frequency noise, speckle decorrelation noise, refractive turbulence advection noise and pointing jitter. In this paper, we present a theory, which describes these noise sources and their wavelength dependence. For example, it will be shown that the turbulence advection noise is wavelength independent while speckle decorrelation noise is proportional to the illumination wavelength and that the noise sources are, to a first-order, independent of the interrogation waveform classification (i.e., pulsed or CW). The results from recent field measurements using a doublet-pulse lidar will be compared with theory.

J. Alex L. Thomson

Papers

Aircraft Wake Vortex Detection and Measurement with Pulsed Solid-state Coherent Laser Radar

Doublet pulse coherent laser radar for precision range and velocity measurements

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

Autonomous lidar wind field sensor: performance predictions

Micro-Doppler lidar signals and noise mechanisms: theory and experiment