Pulse Finding Apparatus for DIAL Gas Detection
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Solution Overview
Problem
Differential absorption LIDAR (DIAL) systems face challenges in detecting ON-line pulse samples due to low signal/noise ratios when gases of interest are present, leading to ambiguities and degraded detection performance.
Innovation Solution
A method is introduced to determine the temporal location of ON-line and OFF-line pulse samples by transmitting a pulse burst, capturing and analyzing the reflected signal, and measuring the inter-pulse separation to accurately locate the pulses, using techniques such as peak-based and semi-matched filter algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the DIAL system uses conventional pulse detection methods, then the system structure remains simple, but the detection performance degrades due to low signal-to-noise ratios when gases are present
Solution Approach 1:
The patent applies preliminary action by capturing a copy of the transmitted pulse burst before it interacts with the target scene. This captured copy is processed to determine inter-pulse separation and temporal locations in advance, which then guides the analysis of the reflected signal. This preliminary processing step enables the system to accurately locate weak ON-line pulses even when they are buried in noise, thereby improving detection performance without requiring complex real-time signal processing hardware.
Solution Approach 2:
The patent introduces an intermediary approach by using the captured copy of the transmitted pulse burst as a reference signal. This reference serves as an intermediary between the transmitted pulse and the reflected signal, allowing the system to determine temporal locations of received pulses by comparing with the known transmitted pulse structure. This intermediary reference enables accurate pulse detection in low signal-to-noise conditions without directly complicating the main detection path.
2Measurement precision
If the system transmits pulse bursts with equal intensities for both ON-line and OFF-line lasers, then the transmission process remains simple, but the ON-line pulse detection becomes ambiguous when gases are present due to signal attenuation
Solution Approach 1:
The patent replaces direct mechanical/intuitive pulse detection with a computational approach. Instead of relying on simple threshold-based detection of pulse amplitudes, the system uses algorithms that analyze temporal locations and inter-pulse separations. This substitution of computational methods for direct detection enables precise gas concentration measurements even when ON-line pulses are significantly attenuated by absorbing gases, as the algorithm can identify the attenuated pulses through their temporal characteristics rather than their amplitude alone.
Solution Approach 2:
The system performs preliminary analysis on a captured copy of the transmitted pulse burst to establish the expected temporal structure and inter-pulse separation. This preliminary information is then used to guide the detection process in the reflected signal, enabling the system to accurately locate ON-line pulses even when their intensities are reduced due to gas absorption. This preliminary preparation eliminates the need for complex real-time adjustments during detection.
3Productivity
If the system processes millions of samples per second without preprocessing, then real-time processing is maintained, but the computational complexity and processing burden increase significantly
Solution Approach 1:
The patent applies segmentation by dividing the signal processing into distinct stages: first capturing a copy of the transmitted pulse burst for preliminary analysis, then using the derived temporal location information to process the reflected signal. This segmentation allows the system to process millions of samples per second efficiently by focusing computational resources on relevant signal portions identified through the preliminary analysis, rather than uniformly processing all samples with equal computational intensity.
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 detection performance of DIAL systems by accurately determining the presence and location of pulses, even in scenarios with low signal intensities, allowing for precise measurements of gas concentrations and improving the signal-to-noise ratio.
Implementation Method 1
The present invention relates, in general, to differential absorption LIDAR (DIAL) systems used to remotely measure characteristics of gases in the atmosphere.
Implementation Method 2
One laser may have a wavelength selected to coincide with a strong absorption feature of the gas to be detected. The other laser may have a wavelength selected in the wing (non-absorption region) of this absorption feature.
Implementation Method 3
The intensity of the ON-line pulse is smaller than the intensity of the OFF-line pulse, because energy of the ON-line pulse is attenuated upon passing through the gas.
Implementation Method 4
The generated composite signal, which is a combination of the two laser pulses, is transmitted by a transmitter of the DIAL system to a target scene, where it reflects off the ground (or any other surface).
Data Source
AI summary
A method of finding a temporal location of a reflected pulse in a system for remotely measuring characteristics of a target scene. The method includes steps of: (a) transmitting a pulse burst of two or more pulses toward the target scene; (b) capturing a copy of the pulse burst transmitted in step (a); (c) measuring an inter-pulse separation between at least two pulses in the pulse burst captured in step (b); (d) receiving a signal reflected from the target scene; (e) determining a temporal location of a first pulse in the signal received in step (d); and (f) determining a temporal location of a second pulse in the signal received in step (d) based on the inter-pulse separation measured in step (c). Step (a) may include transmitting an OFF-line pulse and at least one ON-line pulse in the pulse burst toward the target scene from a differential absorption LIDAR (DIAL) system, where the OFF-line pulse and the ON-line pulse are combined pulses, each individually generated from a separate pulsed laser transmitter and each having a different wavelength.