Polarimetric Calibration Using Mirror Array for Remote Sensors
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Solution Overview
Problem
Current methods for polarimetric calibration of remote sensors are costly and lack accuracy and reproducibility, especially when used in operational conditions, as they rely on vicarious references, non-Lambertian surfaces, or scattered sunlight, which are not effective in validating sensor performance under changing physical conditions.
Innovation Solution
A system utilizing a set of reflective mirrors with known polarimetric properties, arranged to form an array, which reflects radiation to the remote sensor, allowing for direct calibration and performance validation by determining Stokes vector elements and polarimetric metrics, thereby enabling accurate polarimetric calibration and validation during operational use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If vicarious polarimetric references (field campaigns, non-Lambertian surfaces, spotlights, or scattered sunlight) are used for calibration, then calibration can be performed under operational conditions, but the accuracy, reproducibility, and cost-effectiveness deteriorate
Solution Approach 1:
The patent uses artificial mirror targets that replicate known polarimetric properties (Stokes vectors) to serve as calibration references. These mirror targets are designed to reflect sunlight with precisely controlled polarization states, providing a stable, reproducible copy of reference polarimetric conditions that can be deployed in the field under operational conditions.
Solution Approach 2:
The patent modifies the physical parameters of calibration targets by using mirrors with specific reflectance properties and orientations. By controlling the mirror angles and positions, the system generates predictable variations in polarization parameters (Stokes vector elements) that enable accurate calibration without requiring complex field campaigns or scattered sunlight conditions.
2Adaptability or versatility
If vicarious polarimetric references (field campaigns, non-Lambertian surfaces, spotlights, or scattered sunlight) are used for calibration, then calibration can be performed under operational conditions, but the cost increases
Solution Approach 1:
The patent employs simple, inexpensive mirror targets that can be easily manufactured and deployed. These mirror targets serve as single-use or limited-use calibration references in the field, replacing expensive and complex field campaigns while maintaining calibration accuracy. The mirrors can be readily replaced if needed, providing a cost-effective solution for operational calibration.
3Adaptability or versatility
If physical conditions in the atmosphere or imaging system change from laboratory calibration settings, then the sensor may operate in the field, but calibration accuracy deteriorates
Solution Approach 1:
The patent incorporates a feedback mechanism where the sensor observes the known polarimetric properties of mirror targets in the field, and this information is used to update or validate the calibration coefficients. By continuously comparing sensor measurements against the known Stokes vectors of the mirror targets, the system can detect and correct for changes in atmospheric or instrument conditions, maintaining calibration accuracy during field operations.
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 reliable, low-cost, and accurate polarimetric calibration and performance validation for remote sensors, reducing errors and maintenance costs, and improving calibration accuracy by using high-contrast, full-spectrum targets that are easily deployable and maintainable.
Implementation Method 1
A mirror array for polarimetric calibration of a remote sensor, comprising: a plurality of reflective mirrors configured and arranged to reflect neutral or polarized radiation from a source of radiation onto the remote sensor
Implementation Method 2
The polarimetric properties of the mirrors may be modified in a known way by having polarimetric filters placed over their reflecting surfaces or coating their reflecting surfaces with birefringent materials
Data Source
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AI summary
Described are methods and systems for vicarious polarimetric calibration and performance validation of a remote sensor. The system includes a plurality of reflective mirrors configured and arranged to reflect radiation from a source of radiation onto the remote sensor with accurately known polarimetric properties. Each of the reflective mirrors are located so that the target images do not overlap. The remote sensor is configured to receive the radiation reflected from the plurality of reflective mirrors and store the received radiation as image data (e.g., the image of each mirror appears as a point target). The system includes a processor configured to process the received data to provide direct calibration and performance validation for each polarimetric or spectral channel of the remote sensor. In addition, the calibration method removes all atmospheric effects except for transmittance and provides reference targets that have high polarimetric contrast, full spectrum performance and easy to deploy.