Airborne LiDAR Pulse Rate Modulation for Uniform Point Distribution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Airborne LiDAR systems face issues with uneven point distribution and pulse pile-up at the edges of the scan swath, affecting data quality and eye-safety, due to high scanning rates and varying pulse energy in existing systems.
Innovation Solution
The airborne laser scanner modulates pulse rate based on the position and orientation of the scanning device to maintain constant pulse energy, varying pulse spacing to achieve a more even point distribution and reduce pulse overlap, thereby improving eye-safety and data quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high scanning rate is used to achieve fast surveying, then productivity is improved, but point distribution becomes uneven with pulse pile-up at edges
Solution Approach 1:
The pulse rate is dynamically adjusted based on the instantaneous scan angle. The system transitions from a static constant pulse rate to a dynamic variable pulse rate that adapts to the scanning position, emitting fewer pulses at edges and more pulses at the center to achieve uniform point distribution while maintaining high overall scanning speed
Solution Approach 2:
The pulse repetition frequency parameter is changed as a function of the scan angle. The system modifies the pulse rate parameter dynamically during scanning, using the relationship pulse_rate = base_rate / (1 + k * cos²(θ)) to transform the constant parameter into a position-dependent parameter that compensates for the cosine effect
2Use of energy by moving object
If constant average power is maintained while varying pulse rate, then energy efficiency is improved, but pulse energy varies significantly
Solution Approach 1:
Two parameters are simultaneously adjusted: pulse rate and pulse energy. The system changes the pulse repetition frequency based on scan angle while also modulating the energy of each individual pulse to maintain constant total energy per unit time, transforming from a single-parameter control to a dual-parameter coordinated control system
Solution Approach 2:
The system implements a feedback mechanism where the pulse energy is continuously adjusted based on the instantaneous pulse rate. The laser controller monitors the scan angle, calculates the required pulse rate, and automatically compensates the pulse energy to maintain constant average power output, creating a closed-loop control system
3Productivity
If pulse rate is increased to improve surveying speed, then productivity is improved, but eye-safety deteriorates due to pulse overlap
Solution Approach 1:
The pulse rate is dynamically reduced at scan edges where the effective ground coverage is minimal. By adapting the pulse rate to the instantaneous scanning geometry, the system prevents pulse pile-up in stationary regions while maintaining high pulse rates in moving regions, thereby improving eye-safety without sacrificing overall surveying speed
Solution Approach 2:
Different pulse rates are applied to different regions of the scan swath. The system implements local quality control by using higher pulse rates at the center where ground coverage is maximum and lower pulse rates at the edges where coverage is minimal, optimizing both safety and efficiency in different spatial locations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a more even spatial distribution of laser pulses, enhanced eye-safety, higher laser power, and improved signal-to-noise ratio, leading to better sensitivity and data quality in LiDAR scanning.
Implementation Method 1
an emitter (21) configured for emitting a plurality of consecutive laser pulses (4) towards the ground surface (3)
Implementation Method 2
a receiver (25) configured for receiving the laser pulses backscattered from the ground surface (3)
Implementation Method 3
determining distances from the airborne laser scanner to the ground surface based on the time of flight of the emitted and received laser pulses
Data Source
Figure 1
Figure 2a~4b
Figure 5a~5b
AI summary
The invention relates to an airborne laser scanner configured to be arranged on an aircraft for surveying a target along a flight path, wherein the airborne laser scanner comprises an emitter configured for emitting a plurality of consecutive laser pulses towards the ground surface, at least one optical element configured for deflecting the laser pulses along pulse paths towards the target, a motor configured for altering the pulse paths by moving the optical element, a receiver configured for receiving the laser pulses backscattered from the target, and a computer configured for controlling the emitter, the motor, and the receiver, for determining directions of the pulse paths, and for triggering the emitter to emit the laser pulses with a varying pulse spacing based on the directional component of the pulse paths in a horizontal direction perpendicular to a direction of the flight path.