Underwater 3D Imaging Using Range-Gated Laser Pulses
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Solution Overview
Problem
Current underwater imaging technologies face challenges in achieving precise, high-resolution three-dimensional imaging at video rates, especially in deep ocean environments where scattering and darkness hinder the detection of objects like unexploded ordnance and underwater structures.
Innovation Solution
The LIVESIGHT system employs a single camera with laser light at water-penetrating wavelengths and a range-gated ICMOS camera to eliminate the correspondence problem, allowing for millimeter-scale range resolution and high spatial resolution imaging across a wide field of view, capable of operating in 24/7 darkness with nanosecond timing, and rendering 3D imagery at 10 Hz or faster.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If point-cloud LIDAR systems are used for underwater 3D imaging, then depth information can be obtained, but the imaging speed is too slow to achieve video rates
Solution Approach 1:
The patent replaces mechanical scanning LIDAR systems with a snapshot imaging approach using a single camera and pulsed laser. Instead of mechanically scanning points in sequence, the system captures the entire field of view simultaneously using optical propagation time differences, achieving video-rate 3D imaging without moving parts.
Solution Approach 2:
The patent adds the time dimension to the spatial imaging by utilizing the time-of-flight of light. By measuring the time delay of light return from different depths and encoding it into the spatial image through range gating, the system converts 3D spatial information into 2D images with depth encoding, achieving rapid 3D reconstruction.
2Measurement precision
If stereo imaging methods are used for underwater 3D imaging, then depth perception can be achieved, but the computational complexity is too high due to solving the image correspondence problem
Solution Approach 1:
The patent replaces the complex computational matching process of stereo vision with a direct physical measurement approach. Instead of algorithmically matching features between two images, the system uses the physical principle of light time-of-flight to directly measure depth, eliminating the correspondence problem entirely.
Solution Approach 2:
The patent introduces light itself as the intermediary for depth measurement. By using the time-of-flight of light photons as the measuring medium, the system directly encodes depth information into the temporal profile of the returned light signal, bypassing the need for complex image matching algorithms.
3Measurement precision
If conventional LIDAR systems are used for underwater imaging, then range information can be obtained, but the systems are too immature for practical video-rate operation
Solution Approach 1:
The patent uses periodic pulsed laser illumination at video rates (e.g., 30 Hz or higher) to illuminate the scene. By synchronizing the camera's range-gated exposure with these periodic laser pulses, the system captures depth information at each frame rate, achieving continuous video-rate 3D imaging.
Solution Approach 2:
The patent performs preliminary synchronization between the laser pulsing and camera gating before actual imaging. The range gates are pre-configured to open and close at specific times relative to the laser pulse, ensuring that depth information is captured correctly at video rates without requiring complex real-time processing.
4Productivity
If a single imaging aperture is used to eliminate the correspondence problem, then 3D imaging speed improves, but achieving millimeter-scale range resolution becomes more difficult
Solution Approach 1:
The patent uses dynamic range gating with adjustable time windows to capture light return at different depths. By dynamically adjusting the gate timing and width, the system can resolve fine depth differences (millimeter-scale) even with a single aperture, while maintaining video-rate operation through rapid gating sequences.
Solution Approach 2:
The patent changes the temporal parameters of light detection by using ultrafast range gating with picosecond to nanosecond resolution. By precisely controlling the timing and duration of the detection window, the system achieves millimeter-scale depth resolution through time-domain discrimination, compensating for the lack of spatial baseline.
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 clear, precise 3D imaging of underwater objects and structures with low latency, overcoming limitations of point-cloud LIDARs and stereo imaging methods, enabling effective detection and manipulation of underwater threats and structures.
Implementation Method 1
a laser source to generate laser beam pulses
Implementation Method 2
a gating module to create gates... with nanosecond timing
Implementation Method 3
water-penetrating wavelengths... high spatial resolution imaging
Data Source
AI summary
An underwater imaging system is carried by a submersible platform to capture images that are processed into three-dimensional images stitched together to create a 3D dimensional video at video rate speeds that are transmitted to a control unit above the surface of the water. The imaging system utilizes a high speed image sensor or camera to capture sequential gated images that are synced via a gating module to two sequential laser beam pulses. The laser beam pulses illuminate an object in each gated image. When the object is within a gate overlap region, the two images may be processed using 3D imaging techniques to generate a 3D representation of the object in the overlap region of the two gates.