Microwave radiometer and methods for sensing atmospheric moisture and temperature
First Claim
1. A multi-channel, passive microwave radiometer for determining the water vapor content and the liquid content in the atmosphere, comprising:
- antenna means for receiving atmosphere signals having frequencies in two separate ITU protected bands, a first of which frequencies being above a given frequency of relative maximum water vapor absorption and a second of which frequencies being near a relative minimum in the water vapor absorption spectra; and
a single radiometer responsive alternately to said received atmospheric signals from said antenna means at the first frequency and at the second frequency for generating output signals alternately representing such water vapor and such liquid content in the atmosphere from which such atmospheric signals were received.
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Accused Products
Abstract
A passive, multi-channel microwave radiometer includes an antenna-lens assembly for receiving, and a first waveguide designed to provide a common path for propagating, 23.8 GHz and 31.4 GHZ atmospheric signals. The 23.8 GHz signal is above the frequency of relative maximum water vapor absorption and the 31.4 GHz signal is near a relative minimum in the water vapor absorption spectrum. Circuitry is responsive to the atmospheric signals for generating output signals representing the respective water vapor and liquid content in and the temperature of the atmosphere. For realtime calibration a blackbody assembly is mounted in the near field of the antenna-lens assembly. The blackbody assembly emits known blackbody microwave signals at 23.8 GHz, 31.4 GHz and in the V band. The radiometer is calibrated during its normal operation by causing a mirror to select the blackbody signals for propagation along the common path. The circuitry responds to the blackbody signals to represent them as first blackbody reference signals. A factory calibrated noise diode assembly adds a known noisy microwave signal to the first waveguide when a blackbody signal is being processed. The circuitry separately responds to such combined blackbody and noisy signals to separately generate a second blackbody reference signal. These first and second blackbody reference signals and the known temperature of the blackbody assembly are used to provide realtime calibration data that is used in realtime to obtain the output signals in response to the atmospheric signals.
65 Citations
37 Claims
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1. A multi-channel, passive microwave radiometer for determining the water vapor content and the liquid content in the atmosphere, comprising:
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antenna means for receiving atmosphere signals having frequencies in two separate ITU protected bands, a first of which frequencies being above a given frequency of relative maximum water vapor absorption and a second of which frequencies being near a relative minimum in the water vapor absorption spectra; and a single radiometer responsive alternately to said received atmospheric signals from said antenna means at the first frequency and at the second frequency for generating output signals alternately representing such water vapor and such liquid content in the atmosphere from which such atmospheric signals were received. - View Dependent Claims (2, 3, 4, 7)
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5. A multi-channel passive radiometer for determining the water vapor content and the liquid content in the atmosphere, comprising:
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antenna means for receiving atmospheric signals having frequencies in the two separate ITU protected bands, a first of which frequencies being above a given frequency of relative maximum water vapor absorption and a second of which frequencies being near a relative minimum in the water vapor absorption spectra; radiometer means responsive to said received atmospheric signals at the first and second frequencies for generating output signals representing such water vapor and such liquid content in the atmospheric from which such atmospheric signals were received; said antenna means including unitary waveguide means for guiding to said radiometer means signals having said first frequency and signals having said second frequency, both of said first and second frequencies being within the band pass of said unitary waveguide means; and a single microwave lens for focusing said atmospheric signals at said first and second frequencies into said unitary waveguide means. - View Dependent Claims (6)
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8. A multi-channel, passive microwave radiometer for determining the water vapor content and the liquid content in the atmosphere, wherein the microwave absorption coefficients of water vapor and liquid vary with frequency and wherein attenuation vs. frequency curves for water vapor at different altitudes each have a peak and cross each other at first and second pressure invariant frequencies, a first pressure invariant frequency being above the frequency corresponding to such peaks, comprising:
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a single antenna for receiving atmospheric signals having said first frequency and a third frequency, said first frequency being substantially in one of two separate ITU protected bands, said third frequency being substantially in the other of said ITU bands and being near a relative minimum in the water vapor absorption spectra; and a single radiometer responsive alternately to said received atmospheric signals at the first frequency and at the third frequency for generating successive output signals representing such water vapor content and such liquid content in the atmosphere from which such atmospheric signals were received.
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9. A multi-channel, passive microwave radiometer for determining the water vapor content and the liquid content in the atmosphere, comprising:
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unitary waveguide means for guiding such microwave signals as are received from the atmosphere and as have first and second microwave frequencies, said first frequency being above the microwave frequency of relative maximum water vapor absorption, said second frequency being near a relative minimum in the microwave water vapor absorption spectrum; and means responding alternately to said first and second frequency signals from said unitary waveguide means for generating first and second output signals representing respectively the water vapor content and the liquid content of the atmosphere from which said microwave signals were received. - View Dependent Claims (10)
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11. A passive microwave radiometer, comprising:
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feed horn means having a relatively small area for receiving microwave signals having first and second frequencies, said first frequency being above the frequency of relative maximum water vapor absorption and said second frequency being near a relative minimum in the water vapor absorption spectra; means for receiving broadband microwave signals and for focusing into said feed horn means such of said signals as have said first and second frequencies; unitary waveguide means for guiding such microwave signals as are received from said feed horn means and as have said first and second microwave frequencies; and means for selectively processing said first and second frequency signals from said unitary waveguide means to selectively generate first and second output signals representing respectively the water vapor content and the liquid content of the atmosphere from which said microwave signals were received. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A multi-channel, passive microwave radiometer for determining at least one selected characteristic of the atmosphere comprising;
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housing means for containing said radiometer, said housing means having a first section and a microwave transparent window for admitting microwave signals from the atmosphere to said first section said housing means having a second section adjacent said first section; blackbody means in said first section of said housing means adjacent said window for emitting blackbody microwave signals in the spectral region corresponding to said selected characteristics; signal selecting means for directing either said blackbody microwave signals or said atmospheric microwave signals into said second section of said housing means; and antenna means in said second section of said housing means for selectively receiving said blackbody microwave signals or said microwave signals. - View Dependent Claims (20, 21, 22, 23)
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24. A method of determining the water vapor content and the liquid content in the atmosphere, comprising the steps of:
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receiving atmospheric signals having frequencies substantially in two separate ITU protected bands, a first of which frequencies being above a peak frequency of relative maximum water vapor absorption and at a frequency at which attenuation by water vapor is substantially pressure invariant and a second of which frequencies is near a relative minimum in the water vapor absorption spectra; and in response to said received atmospheric signals at said first and second frequencies, generating output signals representing such water vapor and such liquid content in the atmosphere from which such atmospheric signals were received. - View Dependent Claims (25, 26, 27)
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28. The method according to claim 28, wherein
said atmospheric signals at said first and second frequencies are guided in the same waveguide prior to being used to generate said output signals; - and
said atmospheric signals at said first and second frequencies are focused into said waveguide.
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29. A method of determining the water vapor content and the liquid content in the atmosphere, comprising the steps of:
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guiding in a single waveguide both such microwave signals as are received from the atmosphere and as have first and second microwave frequencies, said first frequency being above the microwave frequency of relative maximum water vapor absorption, said second frequency being near a relative minimum in the microwave water vapor absorption spectra; and alternately feeding said first and second frequency signals from said single waveguide to a common radiometer to generate first and second output signals representing respectively and successively the water vapor content and the liquid content of the atmosphere from which said microwave signals were received.
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30. A method of determining the water vapor content and the liquid content in the atmosphere, comprising the steps of:
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guiding in a common path both such microwave signals as are received from the atmosphere and as have first and second microwave frequencies, said first frequency being above the microwave frequency of relative maximum water vapor absorption, said second frequency being near a relative minimum in the microwave water vapor absorption responding alternately to said first and second frequency signals in said common path to generate first and second output signals representing respectively the water vapor content and the liquid content of the atmosphere from which said microwave signals were received; mixing said first and second frequency signals from said common path and successive signals having said first frequency and then said second frequency to provide an output that successively represents only said first frequency signal and only said second frequency signal; and after each such mixing performing said generating step in response to said output.
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31. A method of generating first and second output signals representing respectively the water vapor content and the liquid content of the atmosphere, comprising the steps of:
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receiving microwave signals having first and second frequencies, said first frequency being above the frequency of relative maximum water vapor absorption and said second frequency being near a relative minimum in the water vapor absorption spectra; using a lens for focusing said signals having said first and second frequencies toward a common waveguide; and using a single radiometer to successively process said first and second frequency signals from said common waveguide from which said microwave signals were received.
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32. A method of determining at least one selected characteristic of the atmosphere, comprising the steps of:
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admitting microwave signal from the atmosphere into a defined volume; emitting into said volume blackbody microwave signals in the spectral region corresponding to said selected characteristic, said emitting alternating with such said admitting; selecting ones of said atmospheric signals and said blackbody signals from said volume and propagating said selected signals along a common path; generating a first reference signal in response to said blackbody signals in said common path; adding a predetermined noisy signal to said blackbody signals in said common path to generate a second reference signal, said first and second reference signals forming calibration data; when said atmospheric signals are propagated in said common path, causing said noisy signal to stop so that said common path propagates said selected atmospheric signals without said added noisy signal; in response to said atmospheric signals, generating a first output; and comparing said first output to said calibration data to generate a second output representative of said selected characteristic of said atmosphere. - View Dependent Claims (33)
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34. A portable, microwave radiometer for indicating the water vapor content, the liquid content and the temperature of the atmosphere, comprising:
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a housing having first and second sections, each of said sections having a top and a bottom, said top of said first section being formed from a microwave signal--transparent window adapted to admit atmospheric microwave signals in the K and V bands to said first section; a blackbody mounted inside said first section on the bottom thereof, said blackbody being effective to emit known microwave signals in the K and V bands; a microwave signal mirror; means for mounting said mirror between said top and said bottom in said first section of said housing for movement into a first position for reflecting only said blackbody signals into said second section and into a second position for reflecting only said atmospheric signals into said second section; means having a central axis and being received in said second section of said housing adjacent said first section, said means being designed for focusing microwave signals having 23.8 GHz and 31.4 GHz frequencies toward a common path along said central axis and within said housing; a cylindrical microwave signal collar having a relatively small diameter and being received in said second section, said collar having a second axis coextensive with said central axis of said focusing means, said collar having a material therein for absorbing side lobes of said focused microwave signals; a horn mounted along said second axis for receiving said 23.8 GHz and 31.4 GHz focused signals; a first waveguide coupled to said horn, said first waveguide being effective to propagate both said 23.8 GHz and 31.4 GHz signals along said common path; a grid polarizer in said collar between said horn and said focusing means for deflecting some of said focused signals at an angle relative to said central axis, said deflected signals being at least in the V band; a second waveguide for receiving and propagating said deflected V band signals; heterodyne means for temporally separating said 23.8 GHz signal from said 31.4 GHz signal to form successive intermediate signals representing said 23.8 GHz and said 31.4 GHz signals; and means for separately processing each of said intermediate signals and said V band signals from said second waveguide for generating a first output signal representing said water vapor content, a second output signal representing said liquid content and a third output signal representing said temperature. - View Dependent Claims (35, 36, 37)
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Specification