Background Light Rejection Filter for Laser Air-Data Systems
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Solution Overview
Problem
Existing laser air-data systems face challenges in accurately measuring air data metrics due to the presence of unwanted background light, which can obscure the Doppler-shifted reflected portion of the projected beam.
Innovation Solution
The system employs a background-light rejection filter and a vapor cell filter to separate the received light into a beam sampling portion and a complementary non-beam portion, allowing for the estimation and excision of background light from the beam sampling portion, thereby isolating the Doppler-shifted reflected portion for air data metric calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If background light is received along with the Doppler-shifted reflected portion, then the optical receiver captures all relevant light signals, but the measurement precision deteriorates due to background light obscuring the Doppler-shifted signal
Solution Approach 1:
The patent segments the received light into two distinct portions using a background-light rejection filter: a beam sampling portion containing the Doppler-shifted reflected portion, and a complementary non-beam portion containing background light. This segmentation allows separate processing and estimation of background light levels, which can then be subtracted from the beam sampling portion to improve measurement precision.
Solution Approach 2:
The patent introduces a background-light rejection filter as an intermediary optical element that selectively transmits or blocks different portions of the received light based on their origin (beam vs. background). This intermediary enables the system to distinguish between signal and noise without requiring direct measurement of the Doppler-shifted portion alone.
2Measurement precision
If a background-light rejection filter is introduced to separate beam and background light, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into the background-light rejection filter: it simultaneously separates beam light from background light, directs them to different detectors, and enables background light estimation. This merging reduces the need for additional separate components and simplifies the overall system architecture despite the increased functional requirements.
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 effectively reduces the impact of background light, enabling more accurate determination of air data metrics such as airspeed, air particle concentration, and air temperature, by isolating the Doppler-shifted reflected signal.
Implementation Method 1
The vapor cell filter has a narrow stop-band characterized by a characteristic wavelength
Implementation Method 2
The background-light rejection filter is configured to separate the received light into a beam sampling portion and a complementary non-beam portion
Implementation Method 3
A Doppler-shifted reflected portion of each of the projected beams of light is then backscattered by aerosols (small particles that are suspended in the atmosphere)
Implementation Method 4
A wavelength spectrum (or frequency spectrum) of the Doppler-shifted reflected portion can be different from that of the projected beam of light
Data Source
AI summary
Apparatus and associated methods relate to improving measurement of metrics determined by laser air-data systems subject to unwanted background light. Such measurements are improved by estimating and excising the unwanted background light from the total light received by an optical receiver which receives a Doppler-shifted reflected portion of a projected beam of light backscattered by aerosols and air molecules of an atmosphere. The background light is estimated using a background-light rejection filter that receives the light received by the optical receiver after it has been filtered by a vapor cell filter and separates the light received by the optical receiver into a beam sampling portion and a complementary non-beam portion. The non-beam sampling portion is used to estimate the background light portion within the beam sampling portion, which also contains the Doppler-shifted reflected portion of the projected beam used for calculating the metrics of air data.