Solar Calibration Baffles for Satellite Sensor Radiance
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Solution Overview
Problem
Current methods for calibrating imaging sensors in satellites using solar radiation are inefficient, particularly when the sun is at small angles to the sensor's line of sight, and require significant space for calibration surfaces, often resulting in radiance levels that are less than the brightest measured during operation.
Innovation Solution
A system using a set of baffles with opposing surfaces, one diffused and one specular, that intercept and reflect solar radiation across the sensor's field of view, allowing for calibration with reduced space requirements and increased radiance levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lambertian surface is used for calibration, then the sensor can be calibrated using solar radiation, but the space required for the surface to swing into the sensor's line of sight is large
Solution Approach 1:
The calibration surface is nested within the sensor assembly structure, allowing it to be positioned close to the sensor without requiring additional swing space. The surface can be repositioned into the sensor's field of view through a compact mechanism integrated into the existing structure, significantly reducing the space footprint compared to external swing-out arrangements.
Solution Approach 2:
The calibration surface is made dynamically positionable relative to the sensor, transitioning between a stowed position integrated with the sensor housing and a calibration position where it enters the field of view. This dynamic repositioning eliminates the need for large static space allocations while maintaining calibration functionality.
2Measurement precision
If the sun is at large angles to the sensor's line of sight, then calibration can be performed, but this procedure is not ideal for satellites in orbits where the sun is at small angles
Solution Approach 1:
The calibration surface is positioned and oriented specifically within the sensor's field of view to optimize calibration geometry. By placing the high-reflectivity surface at a controlled distance and angle from the sensor, the system achieves effective calibration even when the sun is at small angles to the sensor's line of sight, as the local geometry compensates for the unfavorable solar angle.
Solution Approach 2:
The calibration surface acts as an intermediary that redirects solar radiation into the sensor's field of view. By positioning this high-reflectivity surface within the field of view, it mediates the interaction between solar radiation and the sensor, enabling calibration under various solar angle conditions including small angles where direct solar illumination would be insufficient.
3Illumination intensity
If an ideal lambertian surface is used, then maximum radiance can be reflected, but the radiances produced are still less than or equal to those from albedo-one regions
Solution Approach 1:
The system changes the parameter of radiance intensity by positioning a high-reflectivity calibration surface within the sensor's field of view and optimizing its distance and orientation. This configuration, combined with controlled solar illumination geometry, produces radiance levels that exceed those from albedo-one regions on Earth, providing sufficient calibration signal even for the brightest operational scenes.
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 solution enables effective calibration of imaging sensors with reduced space requirements and increased radiance levels, even when the sun is at small angles, ensuring accurate calibration for brighter radiance levels encountered during operation.
Implementation Method 1
Each baffle has first and second opposing surfaces, with the first surface disposed to face the solar radiation and the second surface disposed to face the sensor. One of the first or second surface is configured as a diffused surface
Implementation Method 2
the other of the first or second surface is configured as a specular surface
Data Source
AI summary
A device for calibrating a sensor using solar radiation includes a sensor configured to measure electromagnetic radiation received through a field of view (FOV) having a normal line of sight and at least two baffles removably insertable across the FOV of the sensor and inclined to the line of sight. Each baffle has first and second opposing surfaces, with the first surface disposed to face the solar radiation and the second surface disposed to face the sensor. One of the first or second surface is configured as a diffused surface, and the other of the first or second surface is configured as a specular surface.