Satellite Michelson Interferometer for Doppler Wind Measurement
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Solution Overview
Problem
Conventional space-based optical measurements of winds using Fabry-Perot or Michelson interferometers face challenges such as alignment tolerances, thermal drifts, and the need for large, heavy instruments due to high resolving power requirements, and require two-dimensional imaging sensors for altitude resolution.
Innovation Solution
A fixed-path Michelson interferometer with a plurality of fields of view and scanning azimuthal angles is used on a satellite, employing a standard attitude determination and control system to sweep through these views around the Earth horizon circle, utilizing two single-channel detectors to generate wind-induced fringe phase differences and providing altitude resolution without moving parts, thus reducing telemetry and thermal drifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high resolving power is used for Doppler measurements, then measurement precision is improved, but device complexity and weight increase due to larger interferometer aperture requirements
Solution Approach 1:
The patent introduces a moving mirror mechanism that dynamically changes the optical path difference between interferometer beams. This dynamic adjustment allows the system to achieve high resolving power through temporal modulation rather than requiring a statically large aperture, thereby reducing instrument weight while maintaining measurement precision
Solution Approach 2:
The patent changes the operating parameters of the interferometer by introducing a time-varying optical path difference through the moving mirror. This parameter change enables the system to achieve high spectral resolution through frequency modulation of the interferogram, avoiding the need for a large fixed aperture
2Measurement precision
If Fabry-Perot etalon alignment tolerances are tightened to improve spectral resolution, then measurement precision is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts the spectral resolution function from the etalon alignment mechanism and transfers it to the moving mirror optical path modulation. By removing the requirement for precise etalon alignment and replacing it with controlled mirror motion, the system achieves spectral resolution through a more manufacturable and maintainable mechanism
Solution Approach 2:
The patent replaces the mechanically sensitive etalon alignment system with a controlled mirror positioning system. The spectral resolution is achieved through precise control of the optical path difference via mirror motion rather than through static etalon alignment, substituting a more robust mechanical approach
3Measurement precision
If conventional limb-viewing geometry is used with orthogonal look directions, then horizontal wind vector determination is achieved, but measurement time and loss of time increase due to several minutes between measurements
Solution Approach 1:
The patent implements continuous scanning through all azimuthal angles around the Earth horizon circle, eliminating the discrete measurement gaps inherent in conventional orthogonal sampling. This continuous action allows complete wind field characterization to be achieved in a single orbital pass without waiting for satellite repositioning between measurements
Solution Approach 2:
The patent transitions from discrete orthogonal sampling in two dimensions to continuous sampling in three dimensions by scanning through all azimuthal angles. This dimensional expansion allows complete wind vector determination from a single continuous measurement sequence rather than requiring multiple discrete measurements over time
4Measurement precision
If two-dimensional imaging sensors are used for altitude resolution, then measurement precision is improved, but device complexity and data volume increase
Solution Approach 1:
The patent segments the altitude resolution function from the azimuthal scanning function by using multiple single-channel detectors, each dedicated to a specific tangent point height. This segmentation allows altitude information to be obtained through temporal separation of measurements at different scanning angles, eliminating the need for complex two-dimensional imaging sensors
Solution Approach 2:
The patent employs the satellite's existing attitude determination and control system to perform the scanning function, allowing the instrument to utilize already-available rotational capability. This self-service approach eliminates the need for separate scanning mechanisms while still achieving comprehensive angular coverage for wind field reconstruction
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 compact, robust, and sensitive wind measurements with improved etendue and simultaneous observations at different altitudes, reducing thermal effects and resource requirements, while providing atmospheric temperature information alongside wind field data.
Implementation Method 1
measure passive Doppler wind measurements using a satellite-based instrument
Implementation Method 2
fixed-path Michelson interferometer
Data Source
AI summary
An apparatus on a satellite includes a standard fixed-path Michelson interferometer. The Michelson interferometer includes an input, at least one first output detector, and at least one second output detector. The Michelson interferometer includes a plurality of respective fields of view and a corresponding plurality of scanning azimuthal angles relative to a satellite velocity vector. The plurality of respective fields of view corresponds to a plurality of tangent points with constant tangent point height arranged around an Earth horizon circle. The apparatus includes an attitude determination and control system on the satellite, or an actuator on the satellite. The apparatus includes an input mirror and/or input optics in optical communication with the input of the Michelson interferometer. The attitude determination and control system rotates the satellite or the actuator rotates the input mirror and/or the input optics, so as to sweep through the plurality of respective fields of view around the Earth horizon circle.