Interferometric Distance Meter Speckle Mitigation
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Solution Overview
Problem
Interferometric distance measurement techniques face challenges with speckle-induced measurement errors, particularly when measuring tilted targets, due to phase decorrelation effects that cause stochastic range fluctuations and measurement inaccuracies.
Innovation Solution
The method involves determining the pointing direction of the speckle field relative to the optical axis, using multiple detectors or scanning to resolve the speckle pattern, which allows for correction of phase decorrelation errors and improves measurement accuracy by accounting for the offset pointing direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric distance measurement is used to achieve high measurement accuracy, then measurement precision is improved, but phase decorrelation errors occur when measuring tilted targets causing measurement inaccuracies
Solution Approach 1:
The patent segments the speckle field into multiple measurement points by determining pointing directions to at least one point of the speckle field. This segmentation allows the system to capture spatial variations in the speckle pattern and compensate for phase decorrelation errors through statistical analysis of multiple points, thereby maintaining measurement reliability on tilted targets while preserving interferometric precision
Solution Approach 2:
The patent changes the parameter being measured from simple distance to distance plus pointing direction. By determining the pointing direction to points in the speckle field relative to the optical axis, the system transforms the problem of phase decorrelation into a solvable parameter estimation problem, enabling correction of measurement inaccuracies through the additional angular information
2Measurement precision
If speckle field is resolved using multiple detectors or scanning to determine pointing direction, then phase decorrelation errors are compensated, but device complexity increases
Solution Approach 1:
The patent makes the existing detector serve multiple functions: it simultaneously measures distance through interferometric phase and determines pointing direction through speckle field analysis. This multi-functionality allows the system to compensate for phase decorrelation errors without adding separate dedicated sensors, thereby reducing the increase in device complexity while achieving improved measurement precision
Solution Approach 2:
The patent uses the speckle field pattern itself as an intermediary carrier of pointing direction information. Rather than requiring complex additional hardware, the system extracts angular information from the natural speckle pattern formed by coherent light scattering, using the speckle field as a mediator that encodes both distance and directional information in its spatial distribution
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 measurement accuracy by compensating for phase decorrelation errors, reducing range fluctuations, and providing precise distance measurements even for tilted targets, thereby improving the reliability of interferometric distance sensors.
Implementation Method 1
a laser source (21) for emitting optical radiation with at least one wavelength λ
Implementation Method 2
wherein the optical radiation forms a speckle field
Implementation Method 3
a receiver optics (22) with a focal point F and an optical axis OA
Implementation Method 4
converting the received optical radiation into at least one received signal
Implementation Method 5
absolute or incremental interferometric distance measurements
Data Source
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AI summary
A method for speckle mitigation in an interferometric distance meter comprises the steps of transmitting optical radiation (12) with at least one wavelength ? to a target (11) to be surveyed, receiving a portion of the optical radiation (12) scattered back by the target (11) in an optical axis (OA), wherein the optical radiation (12) forms a speckle field, converting the received optical radiation (12) into at least one received signal, determining a true distance to the target (11) from the received signal by absolute or incremental interferometric distance measurements. In the method the true pointing direction relative to the optical axis (OA) is determined, wherein the distance error due to speckle effects is corrected.