Hybrid Underwater Imaging System for 3D Reconstruction in Turbid Water
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Solution Overview
Problem
Current underwater robotic systems face limitations in visual perception due to photometric issues such as light attenuation, scattering, and turbidity, which affect the accuracy and density of 3D reconstructions in underwater environments.
Innovation Solution
A hybrid imaging system combining multiple light stripe range and photometric stereo techniques, using a range-gated imaging scheme to synchronize image acquisition and reduce backscattering noise, while employing a data-driven formulation to enhance image formation and processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional passive imaging uses ambient sunlight or light sources for underwater 3D acquisition, then the system can provide basic imaging capability, but the photometric limitations of underwater environments (light attenuation, scattering, turbidity) severely degrade image quality and 3D reconstruction accuracy
Solution Approach 1:
The patent applies preliminary action by projecting structured light patterns onto the underwater scene before capturing images. The structured light emitter projects known light patterns (lines, dots, or other geometries) onto the target object or environment, and the camera captures these illuminated scenes. This preliminary illumination action enables accurate 3D reconstruction by providing reference markers that can be detected and used for spatial calibration and depth estimation, overcoming the photometric limitations of underwater environments.
Solution Approach 2:
The patent utilizes color changes by employing structured light patterns with specific color characteristics. The structured light emitter projects light patterns that may have distinct color properties, and the camera captures these colored patterns. By analyzing the color information and spatial distribution of the projected light patterns, the system can differentiate between the projected structured light and the natural underwater scene, improving 3D reconstruction accuracy despite the challenging photometric conditions.
2Measurement precision
If active imaging uses projected light patterns for long and medium range acquisitions, then the quality of images perceived by the receiver is enhanced, but the electric power required by the projector reduces the autonomy of the robotic vehicle
Solution Approach 1:
The patent applies periodic action by using pulsed illumination instead of continuous illumination. The structured light emitter projects light patterns in periodic pulses, and the camera captures images during these pulse intervals. This periodic illumination approach reduces the average power consumption of the active imaging system while still providing sufficient illumination for accurate 3D reconstruction. The robotic vehicle can alternate between active imaging modes and passive imaging modes, further managing power consumption to extend operational autonomy.
Solution Approach 2:
The patent employs dynamics by making the illumination system adjustable and adaptable. The structured light emitter can dynamically adjust its projection parameters (intensity, duration, frequency, pattern type) based on the operational requirements and available power. The system can switch between different illumination modes (structured light projection, pulsed illumination, or passive imaging) depending on the task at hand, allowing optimization between image quality and power consumption to maximize robotic vehicle autonomy.
3Measurement precision
If stereoscopic systems use two industrial cameras for close and medium range acquisition, then the system can estimate stereo correspondence, but the sampling frequency is low and texture information is insufficient
Solution Approach 1:
The patent applies merging by combining multiple imaging techniques and multiple cameras into a unified system. The system integrates structured light projection, pulsed illumination, and stereoscopic imaging with multiple cameras. By merging these techniques, the system achieves both accurate stereo correspondence estimation and high sampling frequency with rich texture information. The combined system processes data from all cameras and illumination sources simultaneously, producing dense 3D point clouds with high spatial resolution and detailed texture information.
Solution Approach 2:
The patent utilizes another dimension by adding temporal dimension to the spatial dimension. Instead of relying solely on spatial sampling from multiple cameras, the system introduces temporal sampling through pulsed illumination and sequential image capture. This temporal dimension enables the system to gather additional information about the scene structure and texture by observing changes across multiple time frames, thereby increasing the effective sampling frequency and enhancing texture information density without adding more physical sensors.
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 dense and accurate 3D information in turbid underwater environments, improving the robustness and accuracy of 3D point extraction, and reducing power consumption, enabling real-time obstacle avoidance and texture data retrieval.
Implementation Method 1
a structured-light emitter for projecting light patterns onto the target
Implementation Method 2
The work presented in Bruno et al. (2011) [4] concludes that the structured light can be used in underwater environments and the authors have reported good results for a 3D reconstruction in low turbidity waters
Implementation Method 3
two optical image sensors for capturing reflected light from the target
Implementation Method 4
This category is based on photogrammetry where information of the scene taken from different viewpoints is used for underwater 3D acquisition
Implementation Method 5
a range-gated imaging scheme to synchronize image acquisition and reduce backscattering noise
Implementation Method 6
multiple light stripe range and a photometric stereo technique, respectively
Data Source
AI summary
Hybrid imaging system for 3D imaging of an underwater target, comprising: two optical image sensors for stereoscopic imaging; a switchable structured-light emitter having different wavelengths; a switchable spatially non-coherent light source; a data processor configured for alternating between operating modes which comprise: a first mode wherein the structured-light emitter is activated, the light source is deactivated and the image sensors are activated to capture reflected light from the structured-light emitter, and a second mode wherein the structured-light emitter is deactivated, the light source is activated and the image sensors are activated to capture reflected light from the light source; wherein the data processor is configured for delaying image sensor capture, on the activation of the structured-light emitter and on the activation of the light source, for a predetermined time such that light reflected from any point closer than the target is not captured.