Lidar Polarization Analysis for Shallow Water Depth Resolution
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Solution Overview
Problem
Current lidar technologies face limitations in resolving range between closely spaced targets in shallow water environments due to system bandwidth constraints, leading to ambiguities between surface, volume, and floor scatterings, and are unable to accurately measure depths shallower than tens of centimeters.
Innovation Solution
A lidar system that achieves sub-pulse width resolution by using polarized light and polarizing beam splitters to separate and analyze scattered light components, allowing for precise distance measurement within the duration of a laser pulse or system dead time, and dynamically adjusts parameters to maintain accurate data sampling without physical contact with the medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional lidar systems use pulse width resolution to measure depth, then the system structure remains simple, but the range resolution is insufficient to distinguish closely spaced targets in shallow water
Solution Approach 1:
The patent segments the scattered light into multiple polarization components using polarizing beam splitters. By separating the light based on polarization states (s-polarized and p-polarized components), the system can resolve multiple scattering events that occur within a single pulse width, achieving sub-pulse width range resolution without requiring shorter pulses or higher bandwidth electronics.
Solution Approach 2:
The patent transitions from temporal resolution (pulse width) to polarization dimension resolution. Instead of relying solely on time-of-flight differences, the system uses polarization state analysis to distinguish between surface scattering, volume scattering, and floor scattering, effectively adding a new dimension for resolving closely spaced targets.
2Measurement precision
If the laser pulse width is reduced to improve range resolution, then the measurement precision increases, but the system bandwidth requirements increase and complexity increases
Solution Approach 1:
The patent changes the measurement parameter from temporal (pulse width) to polarization state. By maintaining a fixed pulse width and using polarization analysis, the system achieves high depth measurement precision without increasing bandwidth requirements. The polarization state of scattered light provides additional information that enables precise depth measurement with standard pulse widths.
3Loss of information
If conventional lidar systems measure total intensity of backscattered light, then the system operation is simple, but ambiguities exist between surface, volume, and floor scatterings
Solution Approach 1:
The patent segments the total backscattered light signal into multiple polarization components. Surface scattering, volume scattering, and floor scattering have different polarization characteristics, and by analyzing these components separately, the system can identify the source of each scattering event, eliminating ambiguities present in total intensity measurements.
Solution Approach 2:
The patent uses polarization state as an intermediary to distinguish between different scattering sources. The polarization characteristics of scattered light serve as a mediator that carries information about the scattering source, enabling the system to resolve ambiguities without directly analyzing the complex temporal waveform.
4Measurement precision
If lidar systems attempt to measure very shallow depths, then the measurement capability improves, but system bandwidth limitations prevent accurate measurement
Solution Approach 1:
The patent uses polarization dimension to achieve shallow depth measurement capability without increasing temporal bandwidth. By analyzing polarization components of scattered light, the system can resolve depth information for very shallow water where traditional time-of-flight methods fail due to pulse width limitations.
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
The system provides enhanced range resolution and accurate measurement of shallow water depths and surface topography, enabling precise characterization of semi-transparent media thickness and turbidity, and supports navigation through semi-transparent media without requiring knowledge of the lidar system's platform position.
Implementation Method 1
Portions of the laser pulse scatter from the air/water interface, the water volume, and the floor of the water body back to and are collected by the instrument
Implementation Method 2
A polarized laser light is transmitted from the lidar instrument to the body of water. The polarization of the laser light is preserved by surfaces and the water column and altered by polarization altering targets, e.g., the water surface in certain geometries, the water floor, and objects on or near the water floor
Implementation Method 3
The times of flights of the detected signals are converted into range measurements and, upon consideration of viewing geometry, propagation paths, and associated errors, permit determination of the probed water depth
Data Source
AI summary
Through discrimination of the scattered signal polarization state, a lidar system measures a distance through semi-transparent media by the reception of single or multiple scattered signals from a scattering medium. Combined and overlapped single or multiple scattered light signals from the medium can be separated by exploiting varying polarization characteristics. This removes the traditional laser and detector pulse width limitations that determine the system's operational bandwidth, translating relative depth measurements into the conditions of two surface timing measurements and achieving sub-pulse width resolution.