Characterizing atmospheric turbulence using the covariance and temporal intensity fluctuations of an optical source
Inventors
Wayne, David T. • Cauble, Galen D.
Assignees
Publication Number
US-10942119-B2
Publication Date
2021-03-09
Expiration Date
2038-03-09
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Abstract
A system and method are provided for receiving light that has traveled from an optical source through an atmosphere along a distance. The system includes: a receiver lens system having an aperture and being arranged to receive the light from the optical source; a beam splitter; an imaging lens; an image processing component; a photodetector system; and a refractive index structure parameter component. The photodetector system outputs data associated with averaged scintillation data of the aperture. The image processing component generates a normalized covariance curve based on a first portion of the received light. The refractive index structure parameter component generates a refractive index structure parameter, Cn2, of the atmosphere along the distance based on the data associated with averaged scintillation data of the aperture and the normalized covariance curve.
Core Innovation
The invention provides a system and method for characterizing atmospheric turbulence using the covariance and temporal intensity fluctuations of an optical beam propagating through an atmosphere. The system includes a receiver lens system with an aperture to receive light from an optical source, a beam splitter that divides the received light into two portions, an imaging lens, an image processing component that generates a normalized covariance curve from the first portion of the light, a photodetector system that outputs data associated with averaged scintillation of the aperture from the second portion, and a refractive index structure parameter component that generates the refractive index structure parameter, Cn2, of the atmosphere based on these data.
The problem addressed by the invention arises from the effects of atmospheric turbulence on coherent light beams, such as lasers, used in communication systems. Atmospheric turbulence, characterized by refractive-index fluctuations, causes intensity fluctuations at the receiver, leading to signal dropouts and distortions. Prior-art methods for characterizing turbulence often rely on assumptions about turbulence conditions and propagation path lengths, limiting accuracy especially with increased turbulence or non-idealized aperture receivers. There exists a need for a system that accurately characterizes atmospheric turbulence along the path between an optical source and receiver without these assumptions.
This invention directly measures the spatial intensity covariance function using the image processing component and photodetector data, avoiding assumptions required by prior methods. The photodetector system calculates the aperture averaged scintillation index, while the image processing component obtains a normalized covariance curve from spatial intensity measurements. These quantities are combined by the refractive index structure parameter component to calculate turbulence strength parameters such as the aperture averaging factor, point aperture scintillation index, Rytov variance, and ultimately the refractive index structure parameter Cn2. This approach provides a robust and more accurate characterization of atmospheric turbulence for dynamic measurement paths.
Claims Coverage
The patent includes three independent claims presenting inventive features of a system and method for characterizing atmospheric turbulence using light received from an optical source through an atmosphere.
System for characterizing atmospheric turbulence using covariance and averaged scintillation data
A system comprising a receiver lens system with an aperture to receive light, a beam splitter to split the received light into two portions directed to an imaging lens and a photodetector system, respectively. The photodetector system outputs data associated with averaged scintillation data of the aperture, the image processing component generates a normalized covariance curve based on the first portion of the received light, and the refractive index structure parameter component generates a refractive index structure parameter Cn2 based on these data.
Calculation of aperture averaged scintillation index and related factors
The photodetector system calculates an aperture averaged scintillation index σI2(DG) of the received light. The refractive index structure parameter component calculates an aperture averaging factor A from the normalized covariance curve, derives a point aperture scintillation index σI2(0), calculates a factor β0, computes a Rytov variance σR2, and finally generates the refractive index structure parameter Cn2 using defined mathematical relations.
Method for receiving and processing light to determine atmospheric turbulence
A method that includes receiving light from an optical source via a receiver lens system, splitting the light into two portions, providing one to an imaging lens and the other to a photodetector system. Then outputting data associated with averaged scintillation from the photodetector system, generating a normalized covariance curve from the imaging path, and calculating the refractive index structure parameter Cn2 of the atmosphere using these data. The method includes calculating the aperture averaged scintillation index, aperture averaging factor, point aperture scintillation index, factor β0, Rytov variance, and finally Cn2.
The independent claims collectively define a system and method that use a combination of spatial covariance of intensity and scintillation indices derived from split optical signals to calculate the refractive index structure parameter characterizing atmospheric turbulence, improving on prior methods by avoiding assumptions about turbulence and propagation conditions.
Stated Advantages
The invention reduces errors caused by assumptions in prior-art methods by directly measuring the spatial intensity covariance, leading to more accurate characterization of atmospheric turbulence.
It provides a robust system that can be applied to dynamic measurement paths without relying on specific atmospheric turbulence or propagation path assumptions.
Documented Applications
Characterizing atmospheric turbulence in optical communication systems that employ coherent light beams, such as lasers, propagating through the Earth's atmosphere.
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