Gas-Filter Correlation Radiometer Surface Reflectivity Correction
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Solution Overview
Problem
Nadir-viewing gas detection systems face significant noise and error due to spatial and temporal variations in surface reflectivity and emissivity, which complicates the measurement of trace gases in the lower atmosphere, particularly at shorter wavelengths where solar radiation becomes a dominant component.
Innovation Solution
The method involves determining the surface reflectivity spectral profile using multi-spectral measurements and an atmospheric radiative transfer model to correct gas-filter correlation radiometer signals, allowing for the accurate detection of target gases by accounting for variations in surface reflectivity and thermal emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurements are made at shorter wavelengths to detect trace gases, then detection capability is improved, but noise from surface variations and solar radiation increases
Solution Approach 1:
The measurement spectrum is segmented into multiple spectral channels, each targeting specific absorption features of the trace gas. By dividing the broad spectral range into narrower bands, the system can selectively measure gas absorption while minimizing interference from broad-band surface variations and solar radiation
Solution Approach 2:
A spectral library of known gas absorption features serves as an intermediary reference. The measured spectrum is compared against this library to identify and quantify trace gas concentrations, effectively separating gas signals from background noise through pattern recognition
2Use of energy by moving object
If a nadir viewing geometry is used to maximize energy gathering, then signal strength is improved, but sensitivity to surface variations increases
Solution Approach 1:
The field of view is effectively segmented spectrally, with different spectral channels measuring different atmospheric paths and surface interactions. This allows the system to maintain nadir viewing for maximum energy collection while using spectral differentiation to isolate atmospheric signals from surface effects
Solution Approach 2:
The system changes spectral parameters across multiple channels, measuring radiance at different wavelengths. This spectral parameter variation allows differentiation between atmospheric absorption (which affects specific wavelengths) and surface reflectivity (which has broader spectral characteristics)
3Measurement precision
If multi-spectral measurements and radiative transfer modeling are used to correct surface reflectivity, then measurement accuracy is improved, but system complexity increases
Solution Approach 1:
Surface reflectivity characteristics are determined in advance through multi-spectral measurements and radiative transfer modeling. These pre-determined surface parameters are then used to correct the gas detection measurements, separating the surface effect calculation from the gas concentration retrieval process
Solution Approach 2:
The system uses feedback from multi-spectral measurements to iteratively refine surface reflectivity estimates and gas concentration retrievals. By continuously comparing measurements against radiative transfer model predictions and adjusting parameters accordingly, the system achieves accurate gas detection despite the complexity of surface-atmosphere interactions
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 significantly reduces errors in gas detection, improving the accuracy of trace gas measurements by up to two orders of magnitude by accounting for surface reflectivity variations and thermal emission effects.
Implementation Method 1
A gas-filter correlation radiometer (GFCR) has a field of view (FOV) oriented towards the target area. The GFCR receives reflected radiation in a passband and produces GFCR signals from the received reflected radiation.
Implementation Method 2
The main sources of spatial and temporal variations include, variations in {a} surface reflectivity and emissivity, {b} surface temperature... The emission of the surface and gases in atmosphere are a function of their temperatures and their emissivities.
Implementation Method 3
Reflected solar energy—The amount of solar energy reflected from a surface is dependent on the flux of solar energy incident on the surface... The GFCR receives reflected radiation in a passband
Data Source
AI summary
A method of detecting a target gas includes the step of traversing a target area with a gas-filter correlation radiometer having a field of view oriented towards the target area. The gas-filter correlation radiometer receives reflected radiation in a passband from the target area and produces gas-filter correlation radiometer signals from the received reflected radiation. A surface reflectivity spectral profile of the target area is determined. The presence of the target gas in the target area is then determined based upon the received reflected radiation and the surface reflectivity spectral profile of the target area.