Significance The technology known as the laser Doppler velocimeter (LDV) has gained widespread application in both scientific research and industrial production, following years of development. This technology offers an independent means of measuring velocity, which is especially useful for the navigation and localization of vehicles. Compared to traditional velocity measuring methods such as odometers, accelerometers, and global navigation satellite systems (GNSS), LDVs have high accuracy and reliability even in all-day, all-weather conditions. These features satisfy the requirement for precise navigation and localization, thus getting the focus of attention of the researchers in this field. In order to anticipate future progress, it is essential to review the current research.
Progress The frequency shift of the Doppler effect in the probe beam of LDVs depends on the velocity of the vehicle which is based on the optical Doppler effect. When LDVs are installed on vehicles, the angle between the probe beam and the road surface remains constant. By measuring the frequency shift, it is possible to determine the velocity of the vehicles with accuracy. LDVs can be classified into two types based on their optical structure of dual-beam and single-beam. For the dual-beam type, two probe beams intersect each other, and the point of intersection is referred to as the control volume. When traveling over a bumpy road, dual-beam LDVs often lose the signal due to the limited depth of the control volume. The researcher has proposed a multipoint layer-type LDV to address the limitations of dual-beam LDVs. This type of LDV consists of multiple dual-beam probes that are distributed in the vertical direction. Each probe's small depth of field is combined to form a larger depth of field. For the single-beam type, there is only one beam containing the Doppler frequency shift during the measurement, which is different from the dual-beam LDV. The reflected light of the probe beam is transmitted back to the detector after illuminating the uneven road surface and is mixed with the reference beam without any Doppler frequency shift. The single-beam LDV has a broad depth of field, ensuring accurate and stable measurements. It is particularly suitable for use in ground vehicles compared to the dual-beam LDV. Improvements have been made for single-beam LDV to enhance its performance. The reuse-type single-beam LDV utilizes part of the reference beam power to illuminate the road surface, which would otherwise be wasted by an attenuator in the traditional single-beam LDV. The Janus configuration single-beam LDV eliminates the effect of vertical velocity on the velocity parallel to the direction of the vehicle's heading when ground vehicles experience vertical jolts. The speed component in the direction of the vehicle's heading cannot accurately reflect the actual state of a moving vehicle, as there are two components in the vertical and lateral directions. To deal with this, two-dimension (2D) and three-dimension (3D) LDVs are investigated by researchers. There are two probes in 2D LDV and four probes in 3D LDV. Each probe in these two multi-dimensional LDVs can be either dual-beam or single-beam type. For years, researchers have been investigating the use of LDVs in the navigation and localization of ground vehicles. By integrating LDVs with inertial measurement units (IMUs), ground vehicles can achieve significantly improved localization and navigation precision. In particular, the highly accurate velocity data provided by LDVs can effectively suppress the measurement divergence of IMUs. As a result, the accuracy of dead reckoning has already reached an impressive 0.01%. However, to fully explore the potential of LDV technology for new applications such as high-speed trains, underwater vehicles, and aerial vehicles, further research is necessary. This will require optimization of LDV technology in terms of optical design, circuit design, and system architecture.
Conclusions and Prospects This paper reviews the current research on LDVs for the navigation and localization of ground vehicles. It demonstrates the process of development and concludes that LDV plays a significant role in achieving precise navigation and localization of vehicles. Additionally, the paper provides an outlook on the development trend of LDV and its potential applications for high-speed trains, underwater vehicles, and aerial vehicles. The perspectives provided here can serve as a guide for future LDV research.
DownLoad: