Active Mode Sensor NUC via Laser Spot Scanning
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Solution Overview
Problem
Active mode imaging sensors face non-uniformity issues due to manufacturing defects and environmental variations, leading to varying sensor responses across the field of view, especially with changing angles of incidence, which conventional correction methods either require additional sources or computationally intensive post-processing, causing noise scaling and loss of scene visibility.
Innovation Solution
An active mode sensor uses a laser illuminator to scan a smaller laser spot over the field of view, simultaneously performing non-uniformity correction and providing illumination, using a liquid crystal waveguide to form and position the laser spot in an overlapping pattern that compensates for angle-dependent irradiance, eliminating the need for additional sources and maintaining scene visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional NUC methods use a black body source to provide flat field illumination, then uniform sensor response is achieved, but additional sources are required and scene visibility is lost during correction
Solution Approach 1:
The laser illuminator is designed to perform dual functions: providing illumination for active mode imaging and serving as the correction source for non-uniformity correction. By scanning the laser spot across the FOV and modulating its intensity based on the desired correction profile, the same component that illuminates the scene also performs the NUC function, eliminating the need for a separate black body source
Solution Approach 2:
The system uses its own laser illuminator to perform self-correction. The laser spot is scanned across the FOV and its intensity is modulated according to the inverse of the measured non-uniformity pattern, allowing the sensor to correct its own response non-uniformities using its existing illumination source rather than requiring external correction equipment
2Manufacturing precision
If conventional NUC methods scale pixel responses to correct non-uniformity, then uniform sensor response is achieved, but noise is amplified
Solution Approach 1:
Instead of measuring non-uniformity and then scaling responses (which amplifies noise), the system pre-modulates the laser illumination intensity according to the inverse of the desired correction profile. This preliminary action compensates for non-uniformity at the source, allowing uniform sensor response without the need for noisy scaling operations on the captured signals
3Ease of operation
If scene-based NUC is used to maintain scene visibility, then visibility is maintained, but computational demands increase and errors are introduced
Solution Approach 1:
The system performs preliminary correction by pre-modulating the laser illumination pattern according to the inverse non-uniformity profile before the scene is even captured. This approach maintains scene visibility during correction while avoiding the need for computationally intensive post-processing of scene images, as the correction is applied optically in real-time during illumination
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 enhances signal-to-noise ratio by limiting noise scaling and maintaining scene visibility during correction, achieving uniform sensor response without additional black body sources and reducing computational demands.
Implementation Method 1
an active mode sensor uses a laser illuminator to scan a smaller laser spot over the field of view, simultaneously performing non-uniformity correction and providing illumination, using a liquid crystal waveguide to form and position the laser spot
Implementation Method 2
Active mode sensors use a broad beam laser illuminator to illuminate the scene within the FOV of the sensor with laser energy in the spectral band
Data Source
AI summary
Optical non-uniformity correction (NUC) of an active mode image sensor scans a spot over a portion of the sensor's FOV within a frame time so that the net response of the sensor is approximately uniform. Scanning the laser spot simultaneously performs the NUC and provides the illumination of the FOV for imaging the scene. The laser spot is suitably scanned in an overlapping geometrical pattern relative to a line-of-sight of the sensor's imager while modulating a spacing between overlapping laser spots, the size of the spot, a dwell time of the laser spot or the energy of the laser spot or combinations thereof as a function of the scan position of the laser spot so that the laser illumination is inversely proportional to the imager response at the scan position of the laser spot. A liquid crystal waveguide may be used to form and scan the small laser spot over the FOV within the frame time.