Based on the analysis of the principle of lidar ranging and speed measurement, this paper derives the continuous laser pulse digital ranging and Doppler frequency shift speed measurement methods, and gives the basic schematic diagram of the vehicle-mounted lidar, which is the distance measurement and speed measurement of the vehicle-mounted lidar system Provides basic methods.
Keywords: Lidar, ranging, speed measurement
1 Introduction
"Lidar" (Light Detection and Range, Lidar, laser scanner, laser rangefinder) is an electronic device that uses electromagnetic waves to detect the location of a target. Its functions include searching and finding targets; measuring its distance, speed, position and other motion parameters; measuring target reflectivity, scattering cross-section and shape and other characteristic parameters. Like traditional radars, lidar is composed of three parts: transmitting, receiving and post-signal processing, and a mechanism that makes these three parts work in coordination. However, the traditional radar is a radar that uses microwave and millimeter wave band electromagnetic waves as the carrier. Lidar uses laser as the carrier wave, which is electromagnetic radiation in the optical waveband, and the wavelength is much shorter than microwave and millimeter wave. Has the following advantages:
(1) Work around the clock, not restricted by day and night light conditions.
(2) The laser beam has a small divergence angle, concentrated energy, and has better resolution and sensitivity.
(3) Information such as amplitude, frequency and phase can be obtained, and the Doppler frequency shift is large, which can detect targets from low speed to high speed.
(4) Strong anti-interference ability and good concealment; the laser is not interfered by radio waves, can penetrate the plasma sheath, and is insensitive to multipath effects on the ground when working at low elevation angles.
(5) The laser radar has a short wavelength, can detect targets at the molecular weight level, and the structure size of the detection system can be made small.
Of course, Lidar also has the following disadvantages:
(1) The laser is greatly affected by the atmosphere and weather.
(2) The laser beam is narrow and it is difficult to search and capture the target.
With its unique advantages, lidar has been widely used in remote sensing detection of the atmosphere, ocean, land and other targets. The automotive laser radar collision avoidance system is designed based on the advantages of laser radar while using advanced digital technology to overcome its shortcomings. The following will briefly introduce the principle of laser radar ranging and speed measurement, and on this basis, research and discuss the methods of automotive laser collision avoidance radar ranging and speed measurement.
2. Measuring principle of target distance
The transmitter in the automotive laser radar collision avoidance system emits a series of narrow laser pulses with a certain repetition period, which is a typical incoherent ranging radar. The requirement for it is high ranging accuracy, which has nothing to do with the distance of the measurement. ; The system is small in size, light in weight, quick to measure, and can be digitally displayed; simple to operate, easy to train, and has a communication interface, which can be connected to a measurement network or connected with other equipment for digital information processing and transmission.
2.1 Ranging principle
When the lidar is working, the transmitter emits a series of high-frequency narrow pulses with a certain repetition period into the space. If there is a target in the path of electromagnetic wave propagation, then the lidar can receive the echo reflected by the target. Since the echo signal travels back and forth between the radar and the target, it will lag behind the transmitted pulse by a time, as shown in Figure 1.
