Tuned Lidar Modulation for Accurate Methane Detection

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Solution Overview

Problem

Current gas detection methods using laser-based optical devices face challenges in achieving fast spatial scanning and distinguishing backscattered radiation from noise, particularly in single photon detection systems where the signal-to-noise ratio is low.

Innovation Solution

The method involves modulating radiation of different wavelengths using orthogonal modulation codes with inserted gaps, allowing for interleaving of codes and enabling faster scanning by transmitting radiation of other wavelengths during gap periods, which improves the differentiation of backscattered radiation from noise through time correlation analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If radiation of different wavelengths is transmitted sequentially without gaps, then the scanning speed is maximized, but the backscattered radiation cannot be differentiated from noise

Engineering Contradiction:

Improvescanning speedVSAvoidsignal differentiation accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent applies periodic action by using orthogonal modulation codes with inserted gaps transmitted at regular intervals. Each wavelength is modulated with a unique code pattern that includes periodic gaps, allowing the system to maintain fast scanning while enabling correlation-based detection to distinguish backscattered radiation from noise through the characteristic periodic signal structure.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent uses orthogonal modulation codes as an intermediary between the transmitted radiation and the detection process. These codes embed unique temporal signatures in each wavelength's signal, and the inserted gaps act as mediators that create distinguishable patterns in the backscattered radiation, enabling the receiver to differentiate signals from noise through correlation analysis.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If gaps are inserted between bits of modulation codes for different wavelengths, then the backscattered radiation can be differentiated from noise, but the scanning speed decreases

Engineering Contradiction:

Improvesignal differentiation accuracyVSAvoidscanning speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent merges multiple wavelength transmissions by interleaving them during the gap periods. While one wavelength is in its gap period, other wavelengths transmit their modulated signals, allowing parallel transmission that compensates for the time lost due to gap insertion. This combining approach maintains overall scanning efficiency while enabling signal differentiation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent ensures continuity of useful action by utilizing the gap periods of one wavelength to transmit signals from other wavelengths. This continuous interleaved transmission pattern ensures that the system remains productive throughout the entire modulation cycle, minimizing idle time and maintaining high scanning speed despite the presence of gaps in individual code sequences.

Inventive Principle:

Principle #20Continuity of useful action

3Reliability

If orthogonal modulation codes with gaps are used for multiple wavelengths, then the signal-to-noise ratio improves, but the device complexity increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidmodulation system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex hardware differentiation mechanisms with optical modulation and correlation-based detection. Instead of using complex mechanical or electronic filtering systems to distinguish wavelengths, the system uses orthogonal modulation codes with gaps that can be differentiated through signal processing and correlation analysis, simplifying the overall device architecture while improving signal-to-noise ratio.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 speed of gas detection by allowing faster scanning of the wavelength spectrum, reduces low-frequency noise, and improves the signal-to-noise ratio, enabling more accurate and efficient gas identification and imaging.

Implementation Method 1

A laser source is provided which is arranged to emit radiation having a first wavelength

Methodology Applied

Scientific EffectLaser: Laser

Implementation Method 2

emitting radiation of different wavelengths across the absorption spectrum of a gas towards a target area

Methodology Applied

Scientific EffectAbsorption spectroscopy: Absorption Spectroscopy

Data Source

PatentUS12253466B2Accurate methane detection using tuned lidar modulation

Publication Date: 2025.03.18 QLM TECH LTD

AI summary

A method of gas detection comprises emitting radiation of different wavelengths across the absorption spectrum of a gas towards a target area; and analysing the spectrum of returned radiation from the target area to identify the gas in the target area using the time correlation of the emitted radiation and the returning radiation. The radiation is modulated using respective modulation codes for the different wavelengths and the modulation codes are modified by the insertion of a gap between each bit of the modulation code, the gap having a duration of at least n−1 bits where n is the number of different wavelengths.