# Study and Realization of Dual-Mode Mobile Light Detection and Ranging Measurement System

## TL;DR

This paper introduces a dual-mode mobile LiDAR system that improves positioning accuracy in areas without GNSS signals by combining two positioning methods.

## Contribution

A dual-mode mobile LiDAR system with automatic mode switching and time synchronization for improved accuracy in GNSS-denied environments.

## Key findings

- The dual-mode system reduces trajectory error in the X-direction from 3 m to 1 m over 600 seconds.
- Positioning errors in Y and Z directions are significantly reduced compared to traditional GNSS/INS systems.
- The system performs well in GNSS-denied environments like tunnels and underground areas.

## Abstract

Most existing mobile LIDAR measurement systems use a GNSS/INS combination method for attitude positioning. This method requires a constant GNSS signal to correct the IMU’s positioning and attitude. In the absence of GNSS signals, the IMU’s positioning accuracy rapidly deteriorates from the centimeter to sub-meter, or even meter levels. To address the positioning limitations of mobile measurement systems without GNSS signals, this paper presents a dual-mode mobile lidar measurement system that combines the GNSS/INS and INS/wheel speed sensor positioning methods, with a time-synchronization controller that automatically switches between the two modes to cope with the loss of GNSS signals. The system uses a high-precision quartz crystal oscillator to simulate the GNSS time data and converts them to an NEMA standard time signal and a PPS signal to synchronize each sensor. The experimental results of the system show that the trajectory error of the dual-mode mobile measurement system reaches 3 m in the X-direction within 600 S compared with that of the ordinary mobile measurement system with GNSS/INS integration mode, and the dual-mode mobile measurement system controls the trajectory error within 1 m, reduces the error in the Y-direction from 2 m to less than 1 m, and reduces the error in the Z-direction from 3 m to less than 2 m. The dual-mode mobile LiDAR measurement system is not only suitable for outdoor road measurement, but also can effectively correct the positioning and attitude errors in the environment without GNSS signals, such as underground and tunnel, showing significant advantages in a variety of measurement scenarios.