Doppler Laser Radar Research Articles

Doppler laser radar for measuring range and speed simultaneously

For solving the problem that vehicle laser radar cannot measure range and speed simultaneously, we proposed a method of modulating amplitude of transmitting laser by pseudo-random noise code. At the receiving end, we measure target range by calculating correlation function of laser echoes and the local modulating codes, and target speed by analyzing spectrum of beat signal between laser echoes and local reference signal. Firstly, we show the schematic diagram, and discuss the inherent problem existing in the pseudo-random noise code modulated laser radar. Then, we proposed a novel spectrum analysis method for calculating beat signal. Finally, we verified the feasibility of the proposed method by numerical simulations. The results show that maximum speed that can be measured can be extended to 360 km/h without reducing the range measurement performance of current laser radar.

Demonstration of In-Car Doppler Laser Radar at 1.55 $ \mu\hbox{m}$ for Range and Speed Measurement

Laser radar provides better spatial resolution than millimeter-wave radar (MWR) due to the high directivity of the laser beam. However, commercial in-car laser radar approximates the target speed by a range differentiation method, which has the problems of excessive time consumption and the introduction of large errors. In this paper, a new Doppler laser radar scheme for simultaneously measuring target range and speed in automotive applications is presented. The scheme includes a new laser radar architecture, a new method to modulate the transmitted signal, and a method for calculating the range and speed from the signal returned from the target. The length of the transmitted signal is several microseconds, giving the possibility of realizing a high scan speed in automotive applications. In addition, simulations based on Simulink/Matlab were carried out to validate the proposed scheme. Finally, an experimental demonstration of simultaneous range and speed measurements was performed. The moving target for the experiment was a highly reflecting sheet attached to an electric grinder.

Laser Doppler radar for landing navigation

Precise determination of the relative velocity between the spacecraft and celestial body is necessary to ensure the secure landing in space exploration.An all-fiber linear frequency modulation continuous w ave(LFMCW)-continuous w ave(CW) Doppler laser radar w as developed for landing navigation.A narrow line w idth laser w as used as the seed laser.The laser frequency w as modulated by an acousto-optic modulator.Speed vector w as measured in real-time by means of balance coherent detection and digital signal processing based on FPGA.Experiments made on laser Doppler radar w ith a speed generator proved that 0.05cm/s or better accuracy can be achieved w hile the velocity direction can be discriminated.

Heterodyne Laser Doppler Radar Based on Er-Doped Fiber Laser

A low-cost, novel and robust heterodyne laser Doppler radar based on Er-doped fiber laser is presented in this paper. Reliable optical fiber components and instruments for the optical communication were used to build this system. All devices of optical circuit are connected by single-mode fibers making the system reliable and setup arrangement flexible. Spectrum estimation methods based on an efficient digital signal processing technique, fast Fourier transformation (FFT), was utilized to determine the location of the peak. Experiments were performed on a moving hard target with this developed prototype. The results are presented: the minimum velocity can be measured is below 0.5mm/s, and the resultant nonlinear of the measured curve calculated by least square method is below 100 ppm.

Amplitude-Modulated Laser Radar for Range and Speed Measurement in Car Applications

Doppler laser radar can improve the precision of speed measurement by about two orders of magnitude compared with time-of-flight range finders, which obtain target speeds by range differentiation. However, in a car environment, the usage of traditional Doppler laser radar schemes is limited, because they do not satisfy the requirement of simultaneously measuring the target range together with speed with high precision. First, in this paper, we describe a new in-car laser radar system and show a new modulation scheme that enables the in-car laser radar to simultaneously measure the target range and speed with high precision. Then, we perform simulations and experiments to verify the accuracy of the proposed method. In the Appendix, a brief review of current widely used laser radar schemes is given. The limitations of these schemes to their employment in car applications are also discussed.

能量重心校正法在提高激光多普勒测速精度中的应用

能量重心校正法在提高激光多普勒测速精度中的应用

Atmospheric-induced frequency spread in optical waves

This paper introduces analytic expressions for the long time average atmospheric-induced frequency spread of optical waves propagating through clear air turbulence. Spherical wave results are given for the horizontal double-pass case with reflection from a smooth target for bistatic and monostatic channels. The models presented are expected to be valid for weak-to-moderate scintillation environments. The results are discussed in the context of ‘micro’ Doppler laser radar (LIDAR) target detection systems.

Novel Doppler laser radar for diagnostics in fusion reactors

We describe the development of a novel Doppler laser radar (DOLAR) for remote measurement of flow velocity (0–10 m/s) and film thickness of liquid metal walls, currently being studied for their superior heat handling and self-healing characteristics. Small fluctuations in flow velocity(∼mm/s) and flow thickness (∼50 μm) that may arise during plasma discharges can also be measured. The DOLAR is also designed for non intrusive mapping of features of plasma-facing solid surfaces with very high precision (∼50 μm). It can also measure the motion of structural components of a fusion reactor during plasma discharges and during plasma disruptions. The device utilizes frequency modulation laser radar principles for precision range measurements. Compensation of Doppler frequency shift is used to measure flow velocity. The DOLAR probe head is designed with acousto-optic and piezoelectric devices for operation in the harsh fusion environment.

The Multi-center Airborne Coherent Atmospheric Wind Sensor

Abstract In 1992 the atmospheric lidar remote sensing groups of the National Aeronautics and Space Administration Marshall Space Flight Center, the National Oceanic and Atmospheric Administration/Environmental Technology Laboratory (NOAA/ETL), and the Jet Propulsion Laboratory began a joint collaboration to develop an airborne high-energy Doppler laser radar (lidar) system for atmospheric research and satellite validation and simulation studies. The result is the Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS), which has the capability to remotely sense the distribution of wind and absolute aerosol backscatter in three-dimensional volumes in the troposphere and lower stratosphere. A factor critical to the programmatic feasibility and technical success of this collaboration has been the utilization of existing components and expertise that were developed for previous atmospheric research by the respective institutions. For example, the laser transmitter is that of the mobile ground-based Do...

Frequency stability of RF-excited CO/sub 2/ waveguide lasers in gain-switched and Q-switched regimes

The behavior of an RF-excited waveguide laser is analyzed in a gain-switched and a Q-switched regime measuring the frequency sweep during the optical pulse. This enables laser-induced medium perturbations (LIMP) to be directly distinguished from the effects of the discharge power loading. The experimental observations confirm that the main perturbation in the laser output frequency is to be attributed to thermal energy variations. This gives the result of a Q-switch chirp more than one order of magnitude smaller than in the pulsed current mode, suggesting the use of Q-switching waveguide lasers in applications such as long range or Doppler laser radar systems. The chirp behavior in the pulsed current mode can show overshot relaxation corresponding to the propagation of density waves in the guide. >

Determination of the direction of motion on the basis of cw-homodyne laser Doppler radar

Determination of the direction of motion on the basis of cw-homodyne laser Doppler radar

Remote measurement of the transverse wind velocity component using a laser Doppler velocimeter

The wind speed transverse to the line-of-sight of a laser Doppler radar has been measured using the intensity fluctuations of the returned signal. These measurements were made at a range of 100 m with a CO(2) cw laser Doppler velocimeter, which was simultaneously performing its design function of determining the radial velocity component. The transverse component measurements are compared with those obtained using a u, v, w Gill propeller anemometer.

Remote intensity fluctuation measurements with a laser Doppler radar

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text L Z. Kennedy and J. W. Bilbro, "Remote intensity fluctuation measurements with a laser Doppler radar," Appl. Opt. 15, 2008-2008 (1976) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

A Laser Velocimeter for Remote Wind Sensing

A continuous wave carbon dioxide laser Doppler radar has been developed and applied to remote measurement of atmospheric wind velocity and turbulence. The carbon dioxide laser illuminates residual particulate matter in the atmosphere. Radiation scattered by these particles is homodyned with a local oscillator to provide the Doppler signal. The performance of the instrument is verified by comparison of wind velocity data recorded simultaneously by the laser Doppler system and a cup-anemometer-wind-vane system. Data were recorded, for 45 min intervals, of a single component of the horizontal wind velocity at an altitude of 10 m above the ground. The principle of the laser Doppler system and the theory of the system configuration are presented first, followed by the evaluation of the system. Sample data of a 20 min duration test run of a laser Doppler system are compared with conventional anemometer data. Further comparisons are given of the power spectral densities derived from the two time histories. All data comparisons indicate very close agreement of the two systems. Data inconsistencies are within the accuracy limitations of the conventional anemometer system. The range of the laser Doppler system during these tests was confined to approximately 30 m. Laser Doppler wind velocity data were observed at ranges exceeding 300 m; however, no conventional anemometer was set up at these ranges for data comparisons. Tests are planned for the near future, at which time comparison data at extended ranges will be recorded. These tests will also incorporate an on-line data processing system.

Velocity Measurement of Slowly Moving Surfaces Using an He–Ne Laser Heterodyne System

A simple and compact laser Doppler radar system capable of high resolution velocity measurements of a slowly moving surface is described. The system is nondestructive and does not contact or interfere with the object whose speed is to be measured. All required beam splitting and reflective surfaces are integrated in a solid crystal block, greatly simplifying alignment. Experiments are performed using a rotating scattering wheel in which velocities as low as 0.21±0.02 mm/sec have been measured.