Systems and methods for detecting thermodynamic phase of clouds with optical polarization
Inventors
Shaw, Joseph A. • ESHELMAN, Laura M.
Assignees
Montana State University Bozeman
Publication Number
US-11499911-B2
Publication Date
2022-11-15
Expiration Date
2040-11-13
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Abstract
A method and system for imaging thermodynamic phase of clouds includes obtaining a spatially-resolved polarimetric image of a region of the sky containing a cloud using a multipixel image sensor having multiple channels corresponding to different wavelength bands, determining a value of the Stokes S1 polarization parameter of incident light on each pixel corresponding to a portion of the image containing the cloud for multiple channels corresponding to different wavelength bands, and determining the thermodynamic phase of the cloud within the image based on the values of the Stokes S1 polarization parameter. The Stokes S1 polarization parameter values determined for a first channel corresponding to a first wavelength band is used to determine a liquid thermodynamic phase, and the Stokes S1 polarization parameter values determined for a second channel corresponding to a second, shorter wavelength band is used to determine an ice thermodynamic phase.
Core Innovation
The invention describes a method and system for imaging the thermodynamic phase of clouds using optical polarization measurements. This approach utilizes a multipixel image sensor that has multiple channels corresponding to different wavelength bands to obtain spatially-resolved polarimetric images of regions of the sky containing clouds. For each pixel in these images that contains a cloud, the value of the Stokes S1 polarization parameter is determined across multiple wavelength bands.
The determined Stokes S1 values in a first channel corresponding to a first, longer wavelength band are used to indicate the presence of a liquid thermodynamic phase, while Stokes S1 values in a second, shorter wavelength band are used to indicate an ice thermodynamic phase. The method also involves referencing the Angle of Polarization (AoP) to the unique scattering plane for each pixel to ensure accurate phase detection across the sky. The thermodynamic phase is then deduced based on the S1 values, with thresholds distinguishing liquid from ice phase, and can further differentiate multi-layered ice and liquid clouds.
The problem addressed by this invention is the need for improved methods to remotely sense the thermodynamic phase of clouds, which is important for climate modeling, weather prediction, and interpreting cloud radiation interactions. Traditional methods either require active measurements such as lidar or rely on passive radiance detection that may not be as spatially resolved or directly indicative of the cloud's phase state. This invention proposes a novel passive imaging polarimetric approach that provides spatial phase discrimination using the spectral and angular dependencies of the Stokes S1 polarization parameter.
Claims Coverage
The claims present three main inventive features covering methods and systems for imaging cloud thermodynamic phase using polarization information.
Imaging cloud thermodynamic phase using Stokes S1 parameter across multiple wavelength bands
A method of obtaining a spatially-resolved polarimetric image of a sky region containing at least one cloud with a multipixel image sensor having multiple channels for different wavelength bands. For each pixel with a cloud, the Stokes S1 polarization parameter is determined for each wavelength band, and the thermodynamic phase of the cloud is determined based on these S1 values. Specifically: - S1 values from a first channel (longer wavelength) identify liquid phase. - S1 values from a second channel (shorter wavelength) identify ice phase. - The first wavelength band has a longer average wavelength than the second. The method measures the AoP in the instrument plane, transforms it to the scattering plane at each pixel, and references S1 to that scattering plane.
Phase discrimination using a threshold varying with scatter angle
A method in which the cloud thermodynamic phase is determined by comparing the Stokes S1 value to a threshold. For each pixel, if S1 is greater than the threshold, it indicates liquid phase; if less, ice phase. The key feature is: - The threshold varies as a function of the scatter angle of incident light for different pixels of the multipixel image sensor.
System for cloud phase imaging with polarimeter and processor referencing scattering plane
A system comprising a polarimeter with a multipixel image sensor having channels for multiple wavelength bands that captures spatially-resolved polarimetric images of the sky containing at least one cloud. A processor is coupled to the sensor and determines S1 values for each pixel for each wavelength band, and determines the phase (liquid or ice) based on S1: - S1 (from longer wavelength) indicates liquid phase. - S1 (from shorter wavelength) indicates ice phase. - The system determines S1 by measuring AoP in the instrument plane, transforming it to the scattering plane for each pixel, and referencing S1 accordingly.
The inventive features claimed comprise methods and systems for detecting cloud thermodynamic phase by measuring and interpreting the Stokes S1 polarization parameter across spectral channels, transformation of AoP to the scattering plane per pixel, and using variable thresholds based on scatter angle for phase determination.
Stated Advantages
Enables accurate and spatially-resolved detection of cloud thermodynamic phase (liquid or ice) across different regions of the sky based on optical polarization measurements.
Allows improved remote sensing methods for cloud phase determination without requiring active lidar or mm-wave radar instruments.
Documented Applications
Remotely sensing the thermodynamic phase (liquid or ice) of clouds for improved weather and climate modeling.
Simulating and interpreting cloud radiation measurements to understand the role of clouds in climate, weather, and optical propagation.
Retrieving cloud properties from satellite, airborne, or ground-based measurements where phase information is required.
Environmental remote sensing using ground-based, airborne, or spaceborne polarimeters.
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