Microwave radiometer and methods for sensing atmospheric moisture and temperature

A multi-channel passive radiometer for determining the water vapor content and the liquid content in the atmosphere, comprising:

• 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.

A passive microwave radiometer, comprising:

• 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.

A multi-channel, passive microwave radiometer for determining at least one selected characteristic of the atmosphere comprising;

• 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.

A method of determining the water vapor content and the liquid content in the atmosphere, comprising the steps of:

• 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.

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:

• 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.

A method of determining at least one selected characteristic of the atmosphere, comprising the steps of:

• 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.

A portable, microwave radiometer for indicating the water vapor content, the liquid content and the temperature of the atmosphere, comprising:

• 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.