DIAL Reflectivity Correction via Multi-Wavelength Interpolation

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Solution Overview

Problem

DIAL systems face challenges in accurately estimating concentration path length of target molecules due to ground surface cover type reflectivity variations, leading to errors in plume detection, especially in inhomogeneous environments.

Innovation Solution

A method using at least three pulsed laser beams with an online peak wavelength within the target molecule's absorption band and multiple offline laser beams with peak wavelengths outside the absorption band, measuring transmitted and received pulse energies to estimate reflectivity ratios and calculate concentration path length, thereby correcting for surface reflectivity variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If ground surface cover type reflectivity variations are not corrected, then the system operation is simple, but measurement precision of concentration path length deteriorates significantly

Engineering Contradiction:

Improveconcentration path length estimation accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary parameter (reflectivity ratio between online and offline wavelengths) that mediates the relationship between surface properties and measured signal. By measuring reflected energies at multiple wavelengths and calculating the reflectivity ratio, the system compensates for surface variations without requiring direct measurement or modeling of surface properties themselves.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the measurement parameters by introducing multiple offline wavelengths in addition to the online wavelength. This allows the system to measure and compensate for reflectivity variations by comparing signals at different wavelengths, thereby improving concentration path length estimation accuracy through parameter diversification.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If multiple offline laser beams are used to correct reflectivity variations, then measurement precision improves, but device complexity increases

Engineering Contradiction:

Improvereflectivity ratio estimation accuracyVSAvoidnumber of laser beams and processing steps

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses multiple offline wavelengths (excessive action) to ensure accurate reflectivity ratio measurement across varying surface conditions. While more than the minimum single offline wavelength would suffice, the multiple wavelengths provide redundant measurements that improve robustness and accuracy of the reflectivity correction.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If reflectivity variations are properly corrected using multiple wavelengths, then detection reliability improves, but loss of time increases due to additional measurements

Engineering Contradiction:

Improveplume detection reliabilityVSAvoidmeasurement time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent uses pulsed laser beams at multiple wavelengths in a periodic sequence. Each pulse measures the reflected energy at its specific wavelength, and by alternating between online and offline wavelengths in rapid succession, the system collects all necessary data points for reflectivity correction while minimizing total measurement time through time-multiplexed operation.

Inventive Principle:

Principle #19Periodic action

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 accuracy of detecting plumes containing target molecules by minimizing errors caused by ground surface cover type reflectivity variations, improving the probability of plume detection in diverse environments.

Implementation Method 1

an online laser beam having an online peak wavelength within an optical absorption band of the target molecule; and a number of offline laser beams, each having one of a corresponding set of offline peak wavelengths, each of which is outside of the optical absorption band of the target molecule

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Data Source

PatentUS7333184B2Ground surface cover type reflectivity variation correction in a differential absorption LIDAR system

Publication Date: 2008.02.19 HARRIS CORP

AI summary

A method for improving the accuracy of estimating concentration path length of a target molecule using a differential absorption LIDAR (DIAL) system. In particular, this method allows improved detection of plumes containing the target molecule against inhomogeneous background, such as uncovered ground or ground with various types of cover. In an embodiment of the present invention, spectral surface reflectivity variations are systematically corrected based on interpolation of surface reflectivity measurements of multiple offline beams of different wavelengths, which are relatively close to the online wavelength. In another embodiment, the signal to noise ratio of the received online pulse energy is improved by using multiple laser beams having the online wavelength and the signal to noise ratio of the received pulse energies at an offline wavelength is improved by using multiple laser beams having that offline wavelength.