Laser Doppler Anemometry Aircraft Speed Measurement
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Solution Overview
Problem
Existing methods for measuring an aircraft's speed using laser Doppler anemometry are unreliable in inhomogeneous air masses, leading to false or unavailable speed determinations due to challenges in distinguishing between aerosol velocities and disturbances from clouds, turbulence, and ground echoes.
Innovation Solution
The method involves acquiring backscattered signals on multiple non-coplanar axes, selecting candidate velocity vectors based on spectral analysis, and calculating their coherences to determine the aircraft's speed vector, utilizing redundancy to improve reliability and availability while maintaining precision in homogeneous environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser Doppler anemometry is used to measure aircraft speed, then speed measurement can be obtained, but the measurement becomes unreliable in inhomogeneous air masses due to difficulty in distinguishing aerosol velocities from disturbances
Solution Approach 1:
The patent segments the backscattered signal spectrum into multiple frequency components and associates each with candidate velocity vectors. By analyzing the spectral structure and identifying distinct frequency peaks, the system separates useful aerosol velocity information from parasitic signals caused by clouds, turbulence, and ground echoes, enabling reliable speed measurement in complex atmospheric conditions
Solution Approach 2:
The patent introduces coherence analysis as an intermediary mechanism to evaluate and filter candidate velocity vectors. By calculating coherence values that assess the consistency between candidate vectors and the observed spectral structure, the system identifies and selects reliable velocity components while rejecting spurious signals from disturbances
2Measurement precision
If spectral analysis is performed to determine velocity components, then speed information can be extracted, but false determinations occur when multiple frequency components are present in the spectrum
Solution Approach 1:
The patent transforms the measurement approach by changing from direct frequency identification to a parameter-based selection process. By constructing multiple candidate velocity vectors from different frequency components and evaluating them through coherence calculations, the system selects the most reliable velocity components, preventing false determinations while maintaining precision
3Device complexity
If a single line of sight is used for measurement, then the system remains simple, but speed determination becomes unavailable when disturbances are present
Solution Approach 1:
The patent adds a redundancy dimension by measuring along multiple non-coplanar lines of sight in addition to the primary measurement axis. This dimensional expansion provides alternative measurement paths that can compensate for disturbances on any single line of sight, ensuring continuous speed determination availability while maintaining manageable system complexity through structured geometric arrangement
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 reliability and availability of aircraft speed measurements in inhomogeneous environments, allowing the system to differentiate between useful and parasitic signals, and provides a precise speed determination even in complex air mass conditions.
Implementation Method 1
a laser (from the Anglo-Saxon, 'Light Amplification by Stimulated Emission of Radiation') with continuous emission
Implementation Method 2
measuring the frequency shift between a reference wave emitted and a wave backscattered by natural air aerosols... The emitted beam is backscattered at a frequency shifted by a Doppler shift Δfi relative to the frequency of the emitted beam
Implementation Method 3
The backscattered signal is mixed with the reference wave to form a heterodyne beat on the photosensitive surface of a detector
Data Source
Figure 1
Figure 2a~2d
Figure 3a~4b
AI summary
A method for measuring the speed of an aircraft (1) at a given instant, by laser Doppler anemometry, said method comprising the following steps: • acquisition of a backscattered signal on at least four oriented sighting axes, and calculation of the spectrum of the backscattered signal on each of the sighting axes, characterized in that the method further comprises the following steps: • acquisition of an additional backscattered signal on at least one additional sighting axis (X4) not coinciding with one of the first three sighting axes (X1, X2, X3), • calculation of the spectrum of the backscattered signal on at least one additional sighting axis (X4), • calculation of several candidate velocity vectors (Vc), • calculation of the projections of the candidate vectors onto at least one sighting axis (X1, X2, X3, X4), referred to as the calculation axis.• Calculation of the consistency of the candidate vectors (Vc) based on their projection(s) onto the calculation axis(es) and based on the spectrum(s) of the signal(s) backscattered onto the calculation axis(es) (X1, X2, X3, X4), • Selection of the measured velocity vector (V) from among the candidate velocity vectors (Vc) by performing a likelihood analysis based on the consistency of said candidate velocity vectors (Vc).