Gas Filter Correlation Radiometry for Planetary Gas Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for determining gas concentrations near a planetary surface, such as Earth's surface, using passive sensors face challenges due to thermal contrast difficulties, water absorption, and variability in spectral and Bi-directional Reflectance Distribution Function (BRDF) characteristics, leading to limited success in detecting gases like carbon dioxide and methane, especially when they are present in the upper atmosphere.
Innovation Solution
A Gas Filter Correlation Radiometry (GFCR) system is employed, utilizing a processor and a GFCR sensor with a first gas cell containing the target gas and a second gas cell without the target gas, generating ratio images based on images captured through both cells, which are insensitive to albedo and BRDF variations, and incorporating altitude variations and zenith angle measurements to determine gas concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If modulation of gas cell condition is used to modulate sensitivity to target gas, then sensitivity to target gas is improved, but temporal noise increases due to combination with scene variability
Solution Approach 1:
The patent uses periodic modulation of the gas cell condition (filling/emptying) to create temporal variation in the correlation signal. This periodic action allows the system to modulate sensitivity to the target gas while using ratio imaging to eliminate the resulting temporal noise by comparing synchronized images from both gas cell states
Solution Approach 2:
The patent introduces ratio imaging as an intermediary processing step that mediates between the modulated gas cell signals and the final concentration measurement. By forming the ratio of images from filled and empty gas cell states, the system eliminates temporal noise while preserving the modulated sensitivity to target gas absorption
2Measurement precision
If gas spectral features in near infrared are used with scattered sunlight, then detection capability is improved, but measurement interpretation becomes difficult due to spectral and BRDF variability
Solution Approach 1:
The patent uses ratio imaging as an intermediary that eliminates the need to interpret complex spectral and BRDF variations. By forming the ratio of images through filled and empty gas cells, common variations in surface reflectance and illumination are canceled out, leaving only the gas-specific absorption signal
Solution Approach 2:
The patent changes the parameter being measured from absolute radiance (which requires complex interpretation of spectral and BRDF properties) to a ratio of radiances under different gas cell conditions. This parameter transformation simplifies the measurement interpretation while maintaining detection capability
3Measurement precision
If static hyperspectral imaging instruments are used, then spectral scanning problems are overcome, but difficulty in stitching spectra from measurement samples increases
Solution Approach 1:
The patent extracts only the necessary spectral information at the specific absorption wavelengths of the target gas using narrowband filters, rather than capturing full hyperspectral data. This extraction approach eliminates the need for complex spectral stitching while retaining the ability to measure gas concentrations accurately
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 allows for accurate determination of gas concentrations near the planetary surface, even in regions with high variability, and can detect gases present both near and above the surface, providing robust and precise results despite challenging atmospheric conditions.
Implementation Method 1
a first gas cell containing a target gas and a second gas cell where the second gas cell does not contain the target gas. Using the GFCR sensor, first images of a region of the planetary surface are generated via capture through the first gas cell and second images of the region are generated via capture through the second gas cell
Data Source
AI summary
A method and system are provided for determining gas concentration at a region of a planetary surface. A gas filter correlation radiometry (GFCR) system, provided at a location above a planetary surface, includes a processor and a GFCR sensor having a first gas cell containing a target gas and a second gas cell that does not contain the target gas. Using the GFCR sensor, first images of a region of the planetary surface are generated via capture through the first gas cell and second images of the region are generated via capture through the second gas cell. Using the processor, ratio images are generated using the first images and the second images. Concentration of the target gas over known altitude variations of the region is determined where the concentration of the target gas is a function of the ratio images and the altitude variations of the region.