Hyperspectral Camera Slit Illumination Uniformity
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Solution Overview
Problem
Hyperspectral cameras of the push broom type suffer from striping artefacts due to mechanical imperfections in the slit, which cause variations in illumination, leading to dark and light stripes in the image, and these imperfections can change over time due to slight movements or dust accumulation, rendering previous calibration invalid.
Innovation Solution
An optical system comprising a first optical element that defocuses light in the direction parallel to the slit and a second optical element that compensates for this defocus, effectively blurring and reducing the impact of slit imperfections, using astigmatic elements or cylindrical lenses to maintain focus in the perpendicular direction and correct for slit variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow slit is used to define the instantaneous field of view, then the spectral resolution is improved, but mechanical imperfections of the slit cause striping artefacts in the image
Solution Approach 1:
The patent transforms the point-source illumination into an extended line source by introducing cylindrical lenses that focus light along the slit direction. This dimensional change from point to line allows the slit to be illuminated uniformly across its entire length, eliminating the striping artefacts caused by mechanical imperfections while preserving the narrow slit geometry needed for spectral resolution
Solution Approach 2:
The patent modifies the illumination parameters by using cylindrical lenses with specific focal lengths to create a line focus that matches the slit geometry. By changing the spatial distribution of light from a point source to a line source, the system achieves uniform illumination across the slit while maintaining the narrow aperture required for high spectral resolution
2Device complexity
If the slit position is fixed, then the optical system is simpler, but slight movements or dust accumulation cause calibration to become invalid over time
Solution Approach 1:
The patent implements a self-calibrating system where the extended line source continuously illuminates the entire slit uniformly, making the system insensitive to small positional variations or dust accumulation. The uniform illumination pattern automatically compensates for minor misalignments, eliminating the need for frequent manual recalibration while keeping the mechanical structure simple and fixed
3Length of moving object
If a point source is used for illumination, then the light path is shorter, but the slit is not uniformly illuminated causing striping artefacts
Solution Approach 1:
The patent uses cylindrical lenses to transform the point source illumination into a line source that extends along the slit direction. This creates an extended illumination path that uniformly covers the entire slit length, eliminating striping artefacts while keeping the overall instrument compact through efficient optical folding
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 solution significantly reduces the occurrence of dark and light stripes in the image, maintaining image quality by minimizing the influence of slit imperfections and ensuring consistent calibration across the image sensor.
Implementation Method 1
a first optical element before the slit, having a form that defocuses light in a direction parallel to the tangent of the stripe while keeping focus in a direction perpendicular to the tangent of the stripe at each point of the centre
Implementation Method 2
a second optical element after the slit, which is compensating for the defocus introduced by the first element
Implementation Method 3
relay optics with dispersive element - optical subsystem that projects an image of the very narrow area of the scene onto an image sensor with the light being spectrally dispersed in the direction perpendicular to the slit
Data Source
Figure 1~1b
Figure 2~2b
Figure 3~3b
AI summary
An optical system for a hyperspectral camera and a hyperspectral camera comprising such an optical system are disclosed. The optical system comprises fore optics (1000), an image sensor (1800), a slit (1500), relay optics (1200), a first optical element (2000) positioned before the slit (1500), where the first optical element (2000) is defocusing light in a direction parallel to the slit (1500) while keeping focus in a direction perpendicular to the slit (1500); and a second optical element (2100) positioned after the slit (1500), where the second optical element (2100) is compensating the defocus of the depicted scene introduced by the first element (2000).