De-focusing Optic for Solar Spectrometer Calibration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing radiometric calibration methods for space-based remote sensors face challenges due to degradation of diffuser panels and geometrical issues with transmissive diffusers, leading to measurement distortions and difficulties in calibrating over various angles and preventing saturation when viewing the sun.
Innovation Solution
A system employing a de-focusing optic and convolution integrals allows direct in-flight calibration of spectrometers, enabling them to stare at the sun without saturating, and uses a de-focusing optic to calibrate both wide and narrow field-of-view optics, ensuring accurate radiometric measurements by integrating spectral throughput and accounting for point spread functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffuser panel is used as a reference source for radiometric calibration, then the remote sensor can be calibrated using solar radiation, but the spectral characteristics of the diffuser panel change with time due to degradation, resulting in measurement distortion
Solution Approach 1:
The patent removes the diffuser panel from the calibration system entirely and replaces it with direct viewing of celestial bodies (sun, moon, planets). This extraction eliminates the degradation problem by eliminating the intermediate diffuser component that was causing measurement distortion over time.
Solution Approach 2:
The patent introduces a beam splitter as an intermediary component that enables simultaneous calibration measurements using celestial bodies while the instrument operates. The beam splitter directs a portion of the incoming radiation to a reference detector, allowing continuous calibration without requiring a physical diffuser panel.
2Ease of operation
If transmissive diffusers (screen or pinhole arrays) are used for calibration, then radiation can be distributed, but screens cause internal shadowing and are difficult to calibrate over ranges of angles, and pinholes are subject to clogging
Solution Approach 1:
The patent eliminates transmissive diffusers (screens and pinhole arrays) from the system and replaces them with direct celestial body viewing. This removes the problems of internal shadowing, angular calibration difficulties, and pinhole clogging by using the natural radiation sources in space directly.
3Measurement precision
If the spectrometer stares directly at the sun for calibration, then solar radiation can be used as a reference source, but the detector arrays become saturated
Solution Approach 1:
The patent divides the incoming solar radiation into multiple paths using a beam splitter. One path goes to the reference detector for calibration measurements, while the other path continues to the main instrument detectors. This segmentation prevents saturation by controlling the radiation distribution among different detectors.
Solution Approach 2:
The patent uses only a portion of the incoming solar radiation for calibration purposes through the beam splitter, rather than directing all radiation to the reference detector. This partial action allows calibration measurements without overwhelming the detector arrays, maintaining operational balance.
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 provides stable and accurate radiometric calibration, reducing measurement distortions and allowing for precise spectral measurements of celestial bodies like the sun and earth, with increased signal-to-noise ratio through integration over thousands of samples.
Implementation Method 1
A de-focusing optic is selectively positioned in the first or second light paths
Implementation Method 2
wide field-of-view (WFOV) optics providing a first light path to a first spectrometer, and narrow field-of-view (NFOV) optics providing a second light path to a second spectrometer
Implementation Method 3
spectral characteristics of a diffusive reflector, or diffuser panel
Data Source
AI summary
A system for calibrating a spectrometer includes wide field-of-view (WFOV) optics providing a first light path to a WFOV spectrometer, and narrow field-of-view (NFOV) optics providing a second light path to a NFOV spectrometer. A de-focusing optic is selectively positioned in the first or second light paths. A scan controller selectively controls the WFOV or NFOV optics to scan a celestial body. A processor is configured to calibrate the de-focusing optic, while the WFOV optics scan the celestial body. First, the WFOV optics scan the celestial body without the de-focusing optic positioned in the first light path. Second, the WFOV optics scan the celestial body with the de-focusing optic positioned in the first light path. Next, the processor calibrates the NFOV spectrometer, while the NFOV optics and the de-focusing optic scan the celestial body. After the NFOV spectrometer is calibrated, the NFOV spectrometer may be used to measure the albedo of the earth.