Offner Spectrometer Design for High-Sensitivity Push-Broom Imaging
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Solution Overview
Problem
Conventional push broom hyperspectral imagers face challenges in achieving high sensitivity due to the limitations of satellite altitude, telescope aperture, and short exposure time, particularly in CubeSat-based systems, which exacerbate the sensitivity limitations.
Innovation Solution
The implementation of a Multi-Slit multipleXed (MSX) HyperSpectral Imaging (HSI) system utilizing a compact high-performance broadband wide-field telescope and demagnifying high-NA spectrographs, including designs of compact demagnifying high-NA Free-Space Offner-type Spectrographs and All-immersive Integrated Spectrographs, to enhance sensitivity and swath.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the aperture of the telescope is increased to improve sensitivity, then the sensitivity is improved, but the device complexity and size increase
Solution Approach 1:
The patent divides the single large-aperture telescope system into multiple smaller aperture telescopes working in parallel. Each telescope feeds light to a common spectrograph through a beam combining mechanism, achieving equivalent sensitivity to a large aperture system while maintaining compact individual components and simpler overall system integration.
Solution Approach 2:
The patent implements a nested configuration where multiple telescope optics are integrated within a compact housing, and the beam combining mechanism is nested within the spectrograph entrance. This allows the system to achieve large effective aperture while maintaining compact physical dimensions and reducing overall device complexity.
2Measurement precision
If the exposure time is increased to improve sensitivity, then the sensitivity is improved, but the scene smearing along the satellite track increases
Solution Approach 1:
The patent employs periodic scanning where the slit or detector array is rapidly moved back and forth across the spectral range during the exposure period. This periodic action allows for extended effective exposure time through multiple passes, accumulating signal while maintaining spatial registration through the scanning synchronization, thereby improving sensitivity without increasing scene smearing.
3Device complexity
If the telescope aperture is limited in CubeSats to reduce cost and size, then the device complexity is reduced, but the sensitivity deteriorates
Solution Approach 1:
The patent merges the optical paths from multiple CubeSat-class telescopes with limited apertures into a single beam combining system that feeds a shared spectrograph. This merging approach allows the system to achieve sensitivity equivalent to a much larger single aperture while maintaining the cost and size advantages of using multiple small CubeSat-class instruments.
4Measurement precision
If fast optics with small F/# are used to improve sensitivity, then the sensitivity is improved, but the optical system complexity increases
Solution Approach 1:
The patent changes the focal ratio parameter of the optical system by employing a telecentric relay optics design that transforms the beam propagation characteristics. This allows the system to achieve high sensitivity equivalent to fast optics while using slower, easier-to-manufacture optical components, thereby reducing optical system complexity while maintaining sensitivity performance.
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 achieves high sensitivity and wide swath hyperspectral imaging by using a medium F/# telescope combined with demagnifying spectrographs, enhancing signal-to-noise ratio and enabling flexible configuration for various mission requirements.
Implementation Method 1
a fourth reflective surface that is a curved surface with a grating receiving light from the third surface and diffracting and reflecting light
Data Source
AI summary
An Offner spectrometer for use in a multi-slit hyperspectral imaging system for imaging a remote object includes a first surface that is a transmissive surface having a narrow slit receiving light from a multi-spectral light source, a second curved transmissive surface receiving light from the first surface, a third curved reflective surface receiving light from the second surface, a fourth reflective surface that is a curved surface with a grating receiving light from the third surface and diffracting and reflecting light, a fifth surface that is curved reflective surface receiving light from the fourth surface, a sixth curved transmissive surface receiving light from the fifth surface, and a seventh surface that is a focal plane of the Offner spectrometer receiving light from the sixth surface. Each curved surface has X and Y prescriptions that are decoupled.