Objective  Lidar technology offers significant advantages in speed measurement, particularly due to its short-wavelength characteristics. Recent advancements have raised the bar for lidar, demanding higher laser ranging resolution and extended detectable distances. This has led to challenges in designing laser emission waveforms. To address this, frequency modulation (FM) signal modulation is applied to laser pulses, enhancing the capabilities of pulsed laser coherent radar for long-distance, high-precision speed and ranging measurements, especially for maneuvering targets. However, a challenge arises with the single-chirp FM signal of a moving target, where velocity-distance coupling issues can result in ranging errors due to Doppler mismatch. The existing dual-chirp matched filter method faces limitations in distinguishing the radial velocity direction. In response, a proposed solution involves the use of a dual-chirp V-shaped FM triangle filter. This innovative filter, coupled with a sophisticated data processing method, facilitates the measurement of single-pulse speed direction, value, and target distance, overcoming the limitations posed by conventional approaches.

  Methods   The introduction highlights the limitations of both the single-chirp FM and double-chirp V-type FM matched filter methods in speed measurement. Theoretical calculations are then performed using the double-chirp V-type FM triangular filtering method to establish the relationship between speed and the filtered double peak value. The measurable speed value range is determined, considering the performance of existing devices, and a feasible waveform is designed accordingly. To validate the proposed approach, a laser coherence experimental platform is employed, utilizing a 1.55 μm laser for turntable speed measurement. The system incorporates a dual-lens structure for transmitting and receiving, with a 17.618 km delay fiber simulating long-distance targets to assess the impact of the system's components on actual ranging. The measurement effects of the double-chirped V-type matched filter and double-chirped triangular filter are then compared. Finally, the study includes the measurement of rotating disks with varying speeds of optical fibers, from which relevant data are obtained. Precision and accuracy analyses are conducted to evaluate the effectiveness of the proposed double-chirp V-type FM triangular filtering method (Tab.1 and Tab.2) for speed measurement. The results are presented in figures (Fig.6 and Fig.7) to illustrate precision and accuracy aspects.

  Results and Discussions   Using the coherent laser measurement experiment platform, actual sampling data with 17.618 km time-delay optical fibers are analyzed. The dual-chirp V-shaped FM matched filtering scheme is compared and verified, demonstrating its advantages in radial velocity direction measurement. The results of distance measurements with multiple pulses are illustrated in Fig.6 (a), showcasing a precision of 0.33 m. In the wheel speed range from −0.91 m/s to −3.67 m/s with a 0.92 m/s step, the speed measurement precision ranges are 0.055 m/s, 0.061 m/s, 0.058 m/s, and 0.045 m/s (Fig.6 (b)). Concurrently, the speed measurement results are fitted with the set values in Fig.6 (c), achieving fitting coefficients of 0.997 1. The accuracy of speed measurement is effectively verified.

  Conclusions  The single-pulse double-chirp V-type frequency modulation waveform is designed to meet the requirements of extending the farthest detection distance, improving distance resolution, and achieving high-precision radial velocity measurement. The triangular filtering method employed in this waveform enables the measurement of target distance, velocity value, and velocity direction. This approach accurately reflects changes in the target's movement, providing a valuable reference for determining the motion vector of a three-beam target. The application prospects for this methodology are promising, particularly in fields such as ship navigation trajectory measurement, unmanned aerial vehicle flight measurement, airborne measurement, and other related domains.