Imaging optical beam attenuation coefficient meter
Inventors
Assignees
US Department of Navy • Government of the United States of America
Publication Number
US-9816859-B1
Publication Date
2017-11-14
Expiration Date
2036-05-13
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Abstract
The present invention provides a meter and method of use for measuring an optical attenuation coefficient in a liquid medium. In operation, a collimated beam, produced by a laser of the attenuation meter apparatus, propagates thru the liquid medium with filtered back-scattered light arriving at a camera of the meter. A light image is formed at a focal plane of the camera. The light image is recorded and analyzed by a microcomputer to provide optical beam attenuations coefficients.
Core Innovation
The invention provides a meter and method of use for measuring an optical attenuation coefficient in a liquid medium. In operation, a collimated beam produced by a laser propagates through the liquid medium, with filtered back-scattered light arriving at a camera of the meter. A light image is formed at the camera's focal plane, which is recorded and analyzed by a microcomputer to provide optical beam attenuation coefficients.
The problem addressed is that existing commercially-available meters designed to measure an optical beam attenuation coefficient in water are limited by short optical propagation paths less than one meter, while attenuation lengths in clear water are often greater than eight meters. This results in challenges to maintain optical cleanliness, accuracy of measurement electronics and calibration, causing non-repeatable and unusable measurements in clear water.
To solve this, the invention measures optical attenuation in environments with comparatively low attenuation rates, such as clear water, by choosing a maximum water range to be one half of an expected maximum attenuation length and adjusting the laser beam diameter to maintain collimation but minimize forward scattering. The invention enables measurements over long propagation paths, improving accuracy of optical beam attenuation coefficient measurements in clear media.
Claims Coverage
The patent includes one independent claim describing the main components and operation of the attenuation meter apparatus for measuring optical attenuation in a liquid medium.
Integration of components to measure optical attenuation in a liquid medium
The apparatus comprises an optical window separating the interior of the meter from the liquid medium, a continuous wave laser producing a collimated laser beam through the window, an optical filter that passes only the laser wavelength, a measuring device producing a light image of backscattered light at a focal plane, sensors producing data based on the light image, and a microcomputer analyzing the data to determine the beam attenuation coefficient.
The independent claim covers an attenuation meter integrating a continuous wave laser, optical window, wavelength-selective filter, imaging measuring device with sensors, and microcomputer, configured to measure optical attenuation coefficients from backscattered light in a liquid medium.
Stated Advantages
Ability to obtain measurements over long propagation paths, providing accurate measurements of optical beam attenuation coefficients in clear media.
Use of relatively low cost continuous wave lasers instead of short duration pulsed lasers.
Capability to deploy the meter as a self-contained battery powered module and on vehicles such as unmanned underwater vehicles or from platforms using an umbilical cable.
Possibility to include more than one color light source to provide measurements at multiple wavelengths.
Documented Applications
Measurement of optical beam attenuation coefficients in clear water environments.
Measurement of optical beam attenuation coefficients in various liquid mediums where backscattering arises from thermodynamic index of refraction fluctuations and particles.
Deployment of the attenuation meter on unmanned underwater vehicles or from separate platforms for underwater optical measurements.
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