Laser Radar Coherence Length Adaptation
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Solution Overview
Problem
Conventional laser radar devices face a decrease in heterodyne efficiency and measurement precision of wind speed when the coherence length shortens due to environmental fluctuations, causing it to be shorter than the width of the FFT gate.
Innovation Solution
A laser radar device with a setting changer that calculates the coherence length based on the received signal's spectrum and adjusts the range gate width to match the coherence length, ensuring the FFT gate width and pulse width are adjusted accordingly to maintain optimal heterodyne efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the width of the FFT gate is increased to enhance SNR, then the Signal-to-Noise ratio is improved, but the heterodyne efficiency decreases when the coherence length is shorter than the gate width
Solution Approach 1:
The patent implements dynamic adjustment of the FFT gate width based on real-time coherence length measurements. The system continuously monitors environmental conditions and adapts the gate width parameter to match the current coherence length, ensuring optimal heterodyne efficiency under varying atmospheric conditions while maintaining adequate SNR through appropriate gate width selection.
Solution Approach 2:
The patent changes the operational parameter (FFT gate width) based on the measured coherence length. By calculating the coherence length from the spectral width and adjusting the gate width to match it, the system optimizes the balance between SNR and heterodyne efficiency. This parameter adaptation allows the system to maintain high measurement precision across different environmental conditions.
2Adaptability or versatility
If the coherence length shortens due to environmental fluctuations, then the adaptability to environmental changes is improved, but the measurement precision of wind speed decreases
Solution Approach 1:
The patent employs a feedback mechanism where the coherence length is continuously calculated from the received signal spectrum and used to adjust the FFT gate width. This closed-loop control ensures that the system automatically adapts to environmental changes while maintaining optimal measurement conditions, thereby preserving wind speed measurement precision despite variations in coherence length.
Solution Approach 2:
The patent performs preliminary calculation of the coherence length from the spectral width before conducting wind speed measurements. By determining the appropriate gate width in advance based on the measured coherence length, the system prepares optimal measurement conditions that maintain high precision even when environmental conditions cause coherence length variations.
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 configuration enhances heterodyne efficiency and measurement precision of wind speed even under fluctuating environmental conditions by reducing noise power and improving Signal-to-Noise ratio.
Implementation Method 1
laser light being radiated in the atmosphere from a laser light radiator that radiates laser light in the atmosphere and reflected by a measurement target existing in the atmosphere to be returned
Implementation Method 2
a spectrum calculator that performs frequency analysis on a received signal outputted from the laser light receiver by a unit of a range gate to calculate a spectrum of the received signal
Implementation Method 3
a setting changer that calculates a coherence length based on a spectrum of the received signal calculated by the spectrum calculator, and performs a setting change to shorten a width of the range gate in case where the coherence length is shorter than the width of the range gate
Implementation Method 4
The laser radar device performs heterodyne detection on the scattered light and transmitted pulsed light to find a Doppler shift that occurs with the movement of the aerosol
Implementation Method 5
performs heterodyne detection on the scattered light and transmitted pulsed light to find a Doppler shift that occurs with the movement of the aerosol
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
There is provided a coherence length measurement device 10 that calculates a coherence length Lc based on a spectrum v calculated by an FFT device 9 and performs, in case where the coherence length Lc is shorter than an FFT gate width Gw, a setting change to shorten the FFT gate width Gw and a pulse width Pw, and the FFT device 9 performs frequency analysis on a received signal outputted from an A/D converter 8 by a unit of an FFT gate following the setting change to calculate the spectrum v of the received signal.