Colored Noise Reduction in Optical Remote Airflow Measurement
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Solution Overview
Problem
Conventional Doppler LIDAR systems face challenges in measuring wind speed over a wide range of flying speeds due to limitations in noise reduction, particularly with colored noise, which affects measurement reliability and range, especially in remote regions with low signal strength.
Innovation Solution
The system employs a colored noise reduction method that calculates signal strength variation over distance to set a colored noise measurement region, modifies offset velocity based on flying speed, and estimates colored noise to remove it from measurement signals, enhancing precision and range without increasing laser output or light receiving area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional noise reduction methods (smoothing by integration) are used, then measurement reliability is improved, but colored noise cannot be reduced and useful signals cannot be distinguished
Solution Approach 1:
The patent performs preliminary measurement of the noise pattern before actual wind speed measurement. The reception system's noise characteristics are measured in advance when no signal is present, and this noise pattern is stored for subsequent subtraction from measurement signals, enabling both noise reduction and signal preservation
Solution Approach 2:
The patent implements a feedback mechanism where the measured noise pattern is continuously subtracted from incoming measurement signals. The system monitors signal strength and dynamically adjusts the noise subtraction process, ensuring that colored noise is reduced while useful wind speed signals are preserved
2Adaptability or versatility
If a fixed offset velocity is used, then the Doppler frequency range is limited, but the system cannot respond to variation in flying speed
Solution Approach 1:
The patent transitions from a fixed offset velocity to a dynamic offset velocity that varies with flying speed. The system calculates the appropriate offset velocity based on the current flying speed of the aircraft, allowing the Doppler frequency range to adapt to different flight conditions while maintaining accurate wind speed measurement capability
3Measurement precision
If laser transmission output is increased to improve signal strength, then measurement range is extended, but device complexity and energy consumption increase
Solution Approach 1:
The patent converts the harmful effect of colored noise into a beneficial process by measuring and characterizing the noise pattern, then using this knowledge to subtract the noise from measurement signals. This approach improves signal strength and measurement range without requiring increased laser transmission energy, as the noise reduction is achieved through signal processing rather than increased transmission power
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 measurement precision and extends the measurement range, enabling pilots to detect air turbulence reliably and preventing accidents by effectively reducing colored noise without conventional methods' limitations.
Implementation Method 1
measuring frequency variation (wavelength variation) therein due to the Doppler Effect
Implementation Method 2
receiving scattered laser light generated when an emitted light beam is scattered by minute aerosols floating in the atmosphere
Data Source
Figure 1~2
Figure 3~4
Figure 5(a)~6(b)
AI summary
An object of the present invention is to provide an optical remote airflow measurement apparatus with which even colored noise corresponding to an external environment of the apparatus can be reduced, thereby reducing measurement reliability deterioration and enabling long-distance measurement in a wide flying speed range. A colored noise reduction method for an optical remote airflow measurement apparatus according to the present invention, which emits laser light into the atmosphere as a transmission signal and measures a wind speed of an airflow in a remote region on the basis of a Doppler shift amount of a frequency between the transmission signal and a reception signal, includes: considering a signal strength of scattered light to be substantially non-existent in a remotest region and beyond; calculating a noise distribution by performing processing to average the signal strength in respective Doppler frequency components divided at intervals of a certain frequency in the remotest measurement region and beyond, and performing subtraction processing in each of the Doppler frequency components on all signal strength distributions of the measurement region, which are obtained by dividing the noise distribution at intervals of a certain distance.