Communications: directive radio wave systems and devices (e.g. – Directive – Including a radiometer
Patent
1997-09-26
1999-12-07
Tarcza, Thomas H.
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a radiometer
73 2901, 324640, G01R 2704
Patent
active
059991216
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The objective of the invention is a radiometer and a method for indicating water content, for example, water content change caused by water vapor and/or liquid water.
The radiometer is a sensitive receiver for small power level measurement. The radiometer deviates from a conventional receiver in two ways. Its input signal is phase-incoherent and broadband, which means that it has noise character; in the receivers generally phase-coherent and almost monochromatic. Secondly, conventional receivers require to operate as signal and noise ratio a considerably higher value than one. The actual radiometric `signal` effect is generally much lower than the receiver's own noise level. The radiometer measures the receiving equipment's system noise temperature, which consists of the antenna noise temperature and the receiver noise temperature. The antenna noise temperature is formed of the noise effect coming via the main beam and the side lobes according to diagram 1.6.
BACKGROUND OF THE INVENTION
The essential atmospheric agents for microwave radiometry are oxygen and water vapor. The atmospheric oxygen and water vapor emit on a cloudless sky thermal noise and provide the so called clear sky radiometric brightness temperature T.sub.sky. Inspected from the ground, the atmospheric brightness temperature at clear weather is a function of both frequency and elevation. The frequency dependence is due to the resonant absorption/emission spectrum of water and oxygen molecules. Due to the atmospheric pressure the spectral lines are spread on a broader frequency range. The lowest spectral line of the water molecule absorption/emission resonance is at approx. 22 GHz frequency (FIG. 6a). The elevation angle dependence of the clear sky brightness temperature results from geometry. The transmission path length of the layer formed on the ground by the atmosphere is considerably shorter in the zenith direction than closer to the horizon (FIG. 6b). The radiometric brightness temperature of the atmosphere is to a certain extent dependent on the amount of effective agent in the radiometer beam, at clear sky on the so called effective path length of the inspection direction. The clear sky brightness temperature in zenith direction is thus considerably lower than close to the horizon (FIG. 6a).
Water is present in the atmosphere in water vapor and liquid form and as ice in clouds and rains. Atmospheric water content changes: air humidity, clouds and rain occur in the microwave region as changes in the sky brightness temperature.
Atmospheric property observations with a radiometric scanner and rain indication with a rain detector are presented as examples of the fields of embodiment of the method and device according to the invention.
Atmospheric and ground properties have been measured by microwave radiometers both from satellites (weather and remote sensing satellites) and from the ground.
Atmospheric microwave radiometric measurements from the ground have been utilized for example, in meteorological applications, in measurements relating to interferometric and electromagnetic wave propagation studies, e.g.: Elgered et al./Chalmers University of Technology, Sweden, propagation study; T. Kokkila, thesis for diploma, University of Technology 1988, measurements; Stutzman, Haidara, Reklus, IEEE Proceedings.-Microwaves. Antennas. Propagation, Vol 141 No.1 Feb 1994, Pratt, Stutzman, Snider IEEE Proceedings.- Microwaves. Antennas. Propagation, Vol 141 No.5 Oct 1994.
The measuring device used in the above references are radiometers of Dicke-type (i, ii, iii) and a total output radiometer (iv, v). The radiometers are multichannel or connected to a measuring system utilizing radiometric measurements was to determine atmospheric properties by brightness temperature absolute values. The measuring of the brightness temperature absolute values requires stabilization of the radiometer amplification, measuring result calibration, accurate knowledge of the antenna side lobe properties and ambient radiation properties. The st
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Drummond Devin
Tarcza Thomas H.
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