Retroreflecting Object Detection Using Dual-Wavelength Laser Difference Imaging
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Solution Overview
Problem
Existing methods for detecting objects using retroreflection, such as the 'cat's-eye effect', suffer from false alarms due to scene variations and are ineffective during significant relative movement between the sensor and object, primarily caused by movement and solar flickering effects.
Innovation Solution
A method and system utilizing a series of laser pulses with two distinct but closely matched wavelengths for image capture, where one image captures the scene with the laser echo and the other without, forming difference images to eliminate movement and flickering effects, ensuring similar sensitivities and simultaneous capture in different spectral domains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If images are captured at different times to compare laser echo with background, then the object detection is achieved, but false alarms are generated due to scene variations and movements
Solution Approach 1:
The patent captures a reference image of the background scene before the laser illumination sequence. This preliminary action allows the system to establish a baseline of the scene state, enabling subsequent comparison with laser-illuminated images to distinguish true object reflections from scene variations and movements.
Solution Approach 2:
The patent employs periodic laser pulses for illumination rather than continuous lighting. This periodic action creates discrete time windows for capturing images, allowing the system to compare laser-illuminated images with the reference background image captured at a different time, thereby isolating the laser echo signal from ambient scene variations.
2Productivity
If the time interval between images is shortened to reduce scene changes, then detection speed is improved, but movement effects and flickering still cause false alarms
Solution Approach 1:
By capturing the reference background image before the laser pulse sequence, the system establishes a baseline that accounts for the scene state at that specific moment. This allows rapid subsequent comparisons without being misled by scene variations that occur between the reference capture and the laser-illuminated images.
3Device complexity
If a single wavelength filter is used for image capture, then the detection system is simple, but the system cannot distinguish between object reflection and scene variations
Solution Approach 1:
The patent uses a single wavelength filter tuned to the laser signal wavelength. This localized spectral filtering approach allows the system to selectively capture only the laser-illuminated light and its reflections, while blocking other ambient light sources. The local quality of the filter (narrow bandwidth at specific wavelength) enables clear separation of the laser echo signal from background scene variations.
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 effectively reduces false alarms by synchronizing image capture with laser pulses and using filters tuned to specific wavelengths, allowing for accurate detection of retroreflecting objects even with relative movement, by isolating the object from scene variations and solar backscattering effects.
Implementation Method 1
the detection of an object able to retroreflect light... which present retroreflection properties by virtue of the so-called 'cat's-eye effect' principle
Implementation Method 2
at least one first image of said scene in which said illuminated object is located is formed, through a first filter, the bandwidth of which is tuned to said first wavelength
Implementation Method 3
at least one second image of said scene, in which said illuminated object is located, is formed, through a second filter, the bandwidth of which is tuned to a second wavelength different from said first wavelength
Implementation Method 4
sensors provided with matrix detectors, of CCD type
Implementation Method 5
said second wavelength is sufficiently close to said first wavelength for the backscattering of the solar light by said scene to be at least approximately similar in a first image and in the corresponding second image
Data Source
AI summary
According to the invention, two simultaneous images with different wavelengths (λ1, λ2) are formed in synchronism with each illuminance laser pulse, one of the Images corresponding to the wavelength (λ1) of the laser pulses, and the difference between the two images is generated.