Lidar Aerosol Detection via Interferometric Mie-Rayleigh Separation
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Solution Overview
Problem
Existing lidar technologies face challenges in continuously measuring aerosol distributions due to the need for stringent control of laser wavelength and bandwidth to separate Mie and Rayleigh scattered light components, making long-term continuous measurements difficult.
Innovation Solution
A measurement apparatus using a light source with oscillation frequencies separated at equal intervals, an interferometer to produce interference in scattered light, and a signal processor to detect Mie scattered light components, allowing for separation without synchronizing the laser light with the spectroscope, enabling precise detection of aerosols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If filters are used to separate Mie and Rayleigh scattered light components by narrowing the laser band and adjusting the laser wavelength to the absorption spectrum or bandpass spectrum of a spectroscope, then the separation precision of scattered light components is improved, but the device complexity and control difficulty increase, making continuous measurements for a long period difficult
Solution Approach 1:
The patent changes the key parameter from laser wavelength to frequency interval. By using a frequency interval that is an integer divisor of the spectroscope's free spectral range, the system achieves automatic synchronization without complex wavelength control. This parameter transformation simplifies the control mechanism while maintaining separation precision.
Solution Approach 2:
The system employs multi-longitudinal-mode laser light where the frequency intervals automatically match the spectroscope's free spectral range. This self-synchronizing mechanism eliminates the need for external wavelength control systems, as the laser's inherent frequency structure naturally aligns with the spectroscope's transmission characteristics.
2Ease of operation
If multi-longitudinal-mode laser light is used with an interferometer to remove Mie scattered light components, then the ease of operation is improved by removing wavelength synchronization requirements, but the measurement precision of Rayleigh scattered light detection may be affected
Solution Approach 1:
The patent extracts only the Rayleigh scattered light components by using the interferometer to cancel out Mie scattered light. By setting the frequency interval appropriately, the interferometer selectively removes Mie components while preserving Rayleigh components, achieving both operational simplicity and measurement precision.
Solution Approach 2:
The system exploits the asymmetry in spectral characteristics between Mie and Rayleigh scattered light. Mie scattered light has a narrow spectral width matching the laser modes, while Rayleigh scattered light has a broader spectrum. This asymmetry allows selective removal of Mie components while retaining Rayleigh components through interferometric cancellation.
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 method allows for high-precision detection of Mie scattered light components without the need for complex wavelength synchronization, facilitating continuous and efficient aerosol measurement.
Implementation Method 1
The interferometer produces interference in scattered light generated as a result of the laser light being scattered by the scatterer
Implementation Method 2
Mie scattering is scattering of light by subjects to be measured, in other words, by particles of a size equal to or larger than the wavelength of laser light
Implementation Method 3
Rayleigh scattering is scattering of light by fine particles of a size smaller than the wavelength of laser light
Implementation Method 4
The full width at half maximum of the peak of Rayleigh scattered light resulting from molecules in the atmosphere is wider because of the Doppler effect by thermal motion
Data Source
AI summary
A measurement apparatus includes a light source, an interferometer, a light receiver, and a signal processor. The light source emits laser light to a scatterer in the atmosphere. The laser light has multiple oscillation frequencies separated from each other at equal frequency intervals. The interferometer produces interference in scattered light generated as a result of the laser light being scattered by the scatterer. The light receiver receives Mie scattered light included in the scattered light subjected to the interference produced by the interferometer and generates a signal. The signal processor detects the quantity of the Mie scattered light based on the signal. Each of the equal frequency intervals is smaller than the full width at half maximum of the peak of a frequency spectrum of Rayleigh scattered light. The Rayleigh scattered light is generated as a result of the laser light being scattered by molecules forming the atmosphere.