Optical Attenuation Meter Using LIDAR Backscatter
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Solution Overview
Problem
Existing meters for measuring optical beam and diffuse attenuation coefficients in water are limited by short optical paths, leading to non-repeatable and inaccurate measurements in clear water due to stringent cleanliness and calibration requirements.
Innovation Solution
An attenuation meter with a transmitter and receiver system that uses a pulsed laser to focus light at specific locations in water, filters backscattered light, and adjusts its output to calculate beam and diffuse attenuation coefficients over extended paths, eliminating the need for precise calibration and minimizing scattering effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If short optical paths are used to limit meter size, then device compactness is improved, but measurement precision deteriorates in clear water
Solution Approach 1:
The patent transitions from confined short-path measurements to extended-range measurements by utilizing the spatial dimension of water column. The LIDAR system measures backscattered light from multiple ranges (e.g., 10m, 20m, 30m) vertically in the water column, effectively using the depth dimension to achieve long optical paths without increasing lateral device size. This resolves the contradiction by decoupling measurement path length from device physical dimensions.
Solution Approach 2:
The patent introduces backscattered light as an intermediary signal carrier. Instead of requiring direct transmission through the entire optical path, the system uses backscattered light from intermediate points at various ranges to infer attenuation coefficients. This intermediary approach enables measurement of long-path attenuation without requiring a physically continuous optical path of that length, thus maintaining compact device size while achieving high measurement precision.
2Measurement precision
If long optical paths are used to improve measurement accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical optical path management systems with a LIDAR-based electromagnetic sensing system. Instead of using physical optical benches, mirrors, and lenses arranged in long mechanical paths, the system uses laser pulses and electronic timing to achieve virtual long-path measurements. The complexity is reduced from mechanical optical alignment to electronic signal processing, achieving high precision with simpler device architecture.
Solution Approach 2:
The patent employs periodic laser pulsing to probe the water column at different ranges. By sending repeated laser pulses at known intervals and measuring the time-of-flight of backscattered light, the system achieves multiple measurements at different depths. This periodic action enables statistical averaging and improves precision without requiring a single complex long optical path, thereby reducing overall device complexity.
3Device complexity
If short optical paths are used to simplify device structure, then device complexity is reduced, but reliability deteriorates in clear water measurements
Solution Approach 1:
The patent performs preliminary range selection and optical focusing before the actual attenuation measurement. The LIDAR system pre-establishes measurement ranges (e.g., 10m, 20m, 30m) and focuses laser energy at these predetermined depths. This preliminary action ensures that measurements are taken at optimized ranges where signal-to-noise ratio is maximized, improving reliability without requiring complex adaptive optics or real-time range adjustment mechanisms.
Solution Approach 2:
The patent uses feedback from measured backscattered light intensity and time-of-flight data to calculate and verify attenuation coefficients at multiple ranges. The system continuously monitors the returned signal strength and uses this feedback to adjust measurement parameters and ensure data quality. This feedback mechanism improves measurement reliability by detecting and correcting for anomalies, while the device structure remains relatively simple.
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
Enables accurate and repeatable measurements of optical beam and diffuse attenuation coefficients by averaging multiple scattering realizations and adjusting focal ranges, providing more reliable data than conventional meters with short paths.
Implementation Method 1
the transmitter produces a laser pulse of a duration and in-water wavelength that is focused to a sized location at a range from the attenuation meter. As the laser pulse propagates thru water, some of the light becomes back scattered.
Implementation Method 2
As the laser pulse propagates thru water, some of the light becomes back scattered
Implementation Method 3
A lens of the transmitter collimates the light and a half wavelength plate rotates the polarization of the light until the light polarization is horizontal. The light output passes through a quarter waveplate that converts the light to a circular polarization. Light that is back scattered in a region about the sized location is reflected back to the receiver. To the extent that the circular polarization is preserved; the back scattered light is converted to linear polarization by the quarter waveplate
Implementation Method 4
When the back scattered light reaches a polarized beam splitter, the light is reflected toward a mirror
Implementation Method 5
the transmitter produces a laser pulse of a duration and in-water wavelength that is focused to a sized location at a range from the attenuation meter
Data Source
AI summary
An attenuation meter is provided for use in a water environment. In operation, a transmitter of the meter transmits a laser pulse focused to a size at a predetermined range. A receiver of the meter images a focused spot to minimize unwanted light back scattering and avoid diffractive spreading within the back scattering region. Filtering the angular region can further reject scattered light. The filtered light is received, measured and processed by a oscilloscope as pulse averages. The meter also includes a photodetector to measure a diffuse attenuation coefficient. The output voltage of the photodetector is measured and processed by the oscilloscope that produces an average voltage over a preset number of pulses. A controller best fits voltage to time dependence to produce the diffuse attenuation coefficient. Only the shape of the receiver time dependence is required to provide the diffuse attenuation coefficient measurement.