Airborne Laser Scanner Pulse Modulation for Blind Point Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Airborne laser scanners experience regular patterned 'blind points' or dropouts when flying over flat surfaces due to the modulation of laser pulses, leading to prominent stripes or circles in surveyed 3D point clouds, caused by the sensor being 'blind' during pulse transmission and internal reflections.
Innovation Solution
An airborne laser scanner with a computer-controlled system that modifies pulse spaces between emitted laser pulses using a second pulse space variation overlaying the first, allowing for periodic changes in pulse emission patterns, such as sinusoidal, zig-zag, or random variations, to reduce blind points and internal reflection interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the sensor emits laser pulses at regular intervals to survey the ground surface, then the survey coverage and data collection efficiency are improved, but the sensor creates regular patterned blind points and dropouts due to being blind during pulse transmission and internal reflections
Solution Approach 1:
The patent applies periodic action by modulating the pulse spaces between laser pulses emitted during the first period of the periodically repeating movement differently from subsequent periods. The computer is configured to trigger the emitter with a first pulse space variation and a second pulse space variation overlaying the first, where according to the second pulse space variation, pulse spaces between pulses emitted during a first period are at least in part modified relative to pulse spaces between pulses emitted during any of subsequent periods. This periodic modulation disrupts the regular pattern of blind points while maintaining systematic survey coverage.
2Area of stationary object
If the optical element moves periodically to deflect laser pulses along different paths, then the survey area coverage is improved, but regular stripes or circles appear in the surveyed cloud due to blind points occurring in regular patterns
Solution Approach 1:
The patent applies asymmetry by creating asymmetric pulse spacing patterns between the first period and subsequent periods of the periodically repeating movement. The second pulse space variation modifies pulse spaces during the first period differently from subsequent periods, breaking the symmetry that causes regular stripes or circles in the point cloud. This asymmetric modulation ensures blind points do not occur in predictable regular patterns while maintaining comprehensive area coverage.
3Productivity
If the pulse emission rate is increased to improve survey speed, then the productivity is improved, but the sensor blind period causes more significant data gaps and measurement errors
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the pulse spaces between laser pulses based on the period of the periodically repeating movement. The computer dynamically triggers the emitter with varying pulse space variations - a first pulse space variation and a second pulse space variation overlaying the first - where pulse spaces during the first period differ from subsequent periods. This dynamic pulse spacing optimization allows higher overall pulse rates while strategically positioning pulses to minimize blind point impact on measurement precision.
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 solution reduces and distributes dropout points unrecognizably in the 3D point cloud, improving survey accuracy and completeness by minimizing ranging bias and internal reflection noise, especially over flat surfaces.
Implementation Method 1
an emitter configured for emitting a plurality of consecutive laser pulses towards the ground surface
Implementation Method 2
the distance to the target is determined on based on the travel times of the pulses, i.e. the time difference between the transmission of a laser pulse (outgoing pulse) and the reception of its echo (return) coming back from a surface
Data Source
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 moving the optical element to cause a periodically repeating movement of the pulse paths, 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, determining directions of the pulse paths, and triggering the emitter to emit the laser pulses.