Dual Pulse Frequency Laser Scanner MTA Ambiguity Resolution
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Solution Overview
Problem
Current terrestrial scanning and profiling instruments face challenges in resolving multiple-time-around (MTA) ambiguity, particularly when high pulse repetition rates cause echoes to mix and assign incorrectly, leading to inaccurate range measurements, especially in environments with distance jumps like urban or forested areas.
Innovation Solution
The implementation of a terrestrial scanning instrument using two pulse trains with different repetition rates, where the second pulse train is a proper fraction of the first, allowing for the identification of echoes through pattern recognition and correlation with emission sequences, and utilizing anchor points to determine ambiguity zones, thereby improving ambiguity resolution efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pulse repetition rates are used to increase scanning speed, then productivity is improved, but multiple-time-around (MTA) ambiguity occurs causing measurement precision to deteriorate
Solution Approach 1:
The patent segments the pulse train into multiple ambiguity zones by using different pulse repetition frequencies. Each frequency creates distinct ambiguity zones, allowing the system to identify and resolve MTA ambiguity by analyzing patterns across these segmented zones rather than treating all returns uniformly.
Solution Approach 2:
The patent changes the pulse repetition frequency parameter to resolve MTA ambiguity. By varying the PRF and observing how ambiguity zones shift with different frequencies, the system can identify correct range measurements versus false returns, thereby maintaining measurement precision at high scanning speeds.
2Measurement precision
If traditional MTA resolution methods are used, then ambiguity zones can be resolved, but computational complexity increases reducing processing efficiency
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing ambiguity zone patterns for multiple pulse repetition frequencies before actual scanning. During operation, the system simply compares measured returns against these pre-computed patterns, dramatically reducing real-time computational complexity while maintaining accurate ambiguity resolution.
Solution Approach 2:
The patent creates simplified copies of the complex MTA resolution problem by generating ambiguity zone maps for different PRFs. These copied patterns serve as reference templates that guide the resolution process, transforming a computationally intensive real-time problem into a simpler pattern-matching operation.
3Measurement precision
If pseudo-randomized number code generators are used for distance measurement, then measurement precision is improved, but device complexity increases due to large duty cycle codes
Solution Approach 1:
The patent replaces complex pseudo-randomized number code generators with simpler, disposable-like pulse trains at different repetition frequencies. Each pulse train serves its purpose for a specific measurement interval and can be independently controlled, eliminating the need for complex code generation hardware while maintaining measurement precision through frequency-based discrimination.
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 enhances the accuracy of range measurements by reducing computational complexity and effectively resolving ambiguity zones, even in environments with rapid distance changes, without increasing noise or requiring longer codes, thus improving the flexibility and efficiency of ambiguity resolution.
Implementation Method 1
The scanning or profiling instrument is configured to provide the point cloud by measuring a time of flight of an electromagnetic pulse, in particular a laser pulse, reflected from a plurality of object points in the environment
Implementation Method 2
The transmission unit comprises a beam deflection element for varying the transmission direction at least by a rotation around a rotation axis
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 2a~2b
AI summary
An MTA scanner for providing a point cloud comprising 1.) a light pulse source for generating a first pulse train with a first repetition rate, such that first ambiguity distance is less than an envisaged measurement range, and a second pulse train with a second repetition rate, such that second repetition rate is a proper fraction of the first repetition rate, 2.) a transmission unit to transmit the first scanning pulses and the second scanning pulses to respective transmission directions, 3.) an acquisition unit to acquire first and second scanning pulses reflected from object points in the environment, and 4.) an evaluation unit to assign the acquisition events to the respective first and second transmission events, using an MTA disambiguation based on the first and second repetition rates.