Heterodyne LiDAR Phase Modulation for Background Interference
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Solution Overview
Problem
Monostatic LIDAR devices with heterodyne detection face challenges in selectively measuring velocimetric characteristics due to interference from background objects, which hampers spatial resolution and measurement accuracy, especially when used on vehicles or aircraft where precise installation is difficult and target volume selection is critical.
Innovation Solution
A method that involves modulating the phase characteristic of the optical wave using specific multiplication factors during successive time slots, combined with spectral analysis and accumulation techniques, to isolate the target volume signal from background noise, enhancing spatial resolution and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If monostatic LIDAR device is used for velocimetric measurement, then device mobility and ease of installation are improved, but measurement precision deteriorates due to background interference
Solution Approach 1:
The measurement process is segmented into multiple successive time slots, with phase modulation applied differently in each slot. This temporal segmentation allows separation of target signals from background interference through cumulative processing, resolving the contradiction between mobility and measurement precision.
Solution Approach 2:
The phase characteristic of the optical wave is modulated with specific multiplication factors across successive time slots. By changing the phase parameter dynamically and applying spectral analysis, the system enhances target signal detection while suppressing background interference, thereby maintaining measurement precision in a mobile monostatic configuration.
2Measurement precision
If phase modulation with multiplication factors is applied, then spatial resolution is improved, but device complexity increases
Solution Approach 1:
Phase modulation is applied periodically across successive time slots with specific multiplication factors. This periodic modulation pattern, combined with spectral analysis, enhances spatial resolution by distinguishing target signals from background based on their temporal-phase characteristics, while the regularity of the modulation simplifies the processing algorithm.
Solution Approach 2:
The patent uses computational processing of temporary signal data in each time slot, where individual time-slot data can be discarded after processing. This approach achieves high spatial resolution through software-based spectral analysis rather than hardware complexity, effectively using 'disposable' temporal signal segments to build the final measurement.
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 improves the spatial resolution and selectivity of velocimetric measurements by effectively separating the target volume signal from background interference, allowing for precise velocimetric or vibrometric characterization without increasing the device's mass or complexity.
Implementation Method 1
producing a modulation of a phase characteristic of the optical wave in the transmission signal, such as frequency modulation or phase modulation
Implementation Method 2
the collected portion of the scattered wave is subjected to heterodyne detection. The speed measurement is deduced from a Doppler shift which is measured in a heterodyne detection signal
Implementation Method 3
The speed measurement is deduced from a Doppler shift which is measured in a heterodyne detection signal
Implementation Method 4
combining a spectral analysis of the demodulated heterodyne detection signal with an accumulation for successive splitting time windows
Data Source
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Figure 2a~2b
Figure 3a~3b
AI summary
A method for measuring velocimetric or vibrometric characteristics using a LiDAR-type device allows for the separation of a useful contribution (RV) from a parasitic contribution (RP) in a backscattered signal. This is achieved by modulating the phase characteristic of an optical wave emitted towards a target volume. The parasitic contribution, originating from a source distant from the target volume, appears with varying phase shifts in a heterodyne detection signal. Accumulation then isolates the useful contribution, from which a result is obtained for the velocimetric or vibrometric measurement. The method can be implemented with either frequency modulation or phase modulation of the optical wave.