Reference-beam Laser Doppler Velocimeter Research Articles

Laser Doppler velocimeter and its calibration system

A high-precision calibration system for laser Doppler velocimeter (LDV) is designed to calibrate the reference-beam LDV. Larger velocity range, lower velocity uncertainty and smaller alignment error can be provided in calibration process by employing a rotary cylinder with 600 mm radius in the calibration system. Experiments are carried out for detailed analysis. The results show that the relative measurement precision of the LDV under calibration is 0.1% (1σ) in the velocity range from 0 to 200 km/h. The main sources of uncertainty in the calibration system are discussed. The expanded uncertainty of the proposed system is 0.03%. The proposed calibrating method can be used in the calibration process for the reference-beam LDV, the dual-beam differential LDV, the self-mixing LDV and the spatial filtering velocimeter.

A novel laser Doppler velocimeter

The idea of using a reference-beam laser Doppler velocimeter (LDV) to measure the velocity of a vehicle for an inertial navigation system is proposed. In order to reduce the measurement error produced by the vehicle's jolt, a novel laser Doppler velocimeter (LDV) based on the Janus configuration is presented. The system mounted at the bottom of the vehicle is composed of two single reference-beam subsystems, one of the laser probes looks forward and the other looks backward. Each of the subsystems transmits a laser at 532 nm with the same inclination angle and detects its own Doppler frequency from the scattered light. The pitch angle of the vehicle is calculated by the two detected Doppler frequencies and the inclination angle, and then the measured velocity of the vehicle is compensated. The results of the theory analysis and experiments show that the vehicle's jolt affects conventional reference-beam LDV strongly. LDV with a Janus configuration is insensitive to the inclination angle, and its measurement accuracy is much better than that of a conventional reference-beam LDV. Comparing with the DZL-1 electronic speedometer, the measurement mean error is less than 0.9%, so it is suitable to offer the parameter of velocity for a vehicle self-contained inertial navigation system.

Research on laser Doppler velocimeter for vehicle self-contained inertial navigation system

An idea of using laser Doppler velocimeter (LDV) to measure the velocity for the vehicle inertial navigation system was put forward. The principle of measuring its own velocity with laser Doppler technique was elaborated and reference-beam LDV was designed. Then Doppler signal was processed by tracking filter, frequency spectrum refinement and frequency spectrum correction algorithm. The result of theory and experiment showed that the reference-beam LDV solved the problem that dual-beam LDV cannot be used for measuring when the system was out of focus. Doppler signal was tracked so that signal-to-noise ratio was improved, and the accuracy of the system was enhanced by the technology of frequency spectrum refinement and correction. The measurement mean error was less than 1.5% in velocity range of 0–30 m/s.

Combined differential and reference beam LDV for 3D velocity measurement

A prototype near-backscatter reference beam laser Doppler velocimeter was developed for measuring the component of velocity along its line-of-sight. It was used in combination with a previously commissioned single colour rotatable differential Doppler velocimeter for the simultaneous measurement of axial and radial velocities near a model mounted in a large water tunnel. This paper describes the reasons for adopting the reference beam method and the design principles that were employed. Sensitive signal processors were used and alignment problems were solved by means of optical fibres. Line-of-sight velocities of up to 2 m/s were measured with the same precision as that in the transverse directions. Future detailed attention to the optical system would increase the signal light flux and, thereby, enable faster flows to be measured.

Fibre optic based reference beam laser Doppler velocimetry

A compact reference beam laser Doppler velocimeter is described, constructed using semiconductor laser diodes, optical fibre components and semiconductor detectors. The design of the device overcomes many of the problems commonly associated with reference beam configurations. The system is demonstrated for the laser diode operating in cw and pulsed modes, to demonstrate its applicability to wavelength and time division multiplexing schemes for 3D laser Doppler velocimetry. The performance of the probe is investigated by measuring the velocity of a spinning disk in the range −20 m/s to +20 m/s.