CN1184939A - Real-time calibration microwave radiometer - Google Patents

Abstract

Real-time calibration microwave radiometer is composed of full power microwave radiometer, two reference sources and single chip processor, data acquisition and processing unit. Through periodically detecting the ouput voltage of high temp. reference source, low temp. reference source and antenna and inserting into antenna receiving target brightness equation, the equation eliminates the influence of main device's noise change by voltage difference, so as to attain real time calibration and precise measuring. The present invention is of simple method, easy to operate, of simple system, easy to assemble.

Description

Real-time calibration microwave radiometer

The invention belongs to high sensitivity radio receiver and application thereof.Be specifically related to the formation of real-time calibration microwave radiometer and reception atural object microwave radiation was calibrated and accurately stablized in realization to microwave radiometer method.

Since nineteen forty-six Dicke type microwave radiometer is born, development along with requirement of actual application and microwave, electronic component, the performance of microwave radiometer is also constantly improving, and the minimum detectable signal that makes microwave radiometer is near the uncertainty that is caused by system noise.Current microwave radiometer becomes the important microwave remote sensor of earth observation from the application development of radio astronomy.In surveying and control, metering also is used widely.The microwave radiometer development, use so far, can be summarized as five kinds of fundamental types: the total power microwave radiometer, Dicke type microwave radiometer [R.H.Dicke, The Review of scientific Instrument, Vol.17, No.7,1946], negative feedback zero balancing Dicke type microwave radiometer [Zhang Junrong, Changchun remote sensing test collection of thesis (2), PP18-31,1988, Science Press], two reference temperature automatic gain compensation microwave radiometer [J.P.Hach, IEEE Trans.Micro.Theory and Tech, NTT-16,9, PP629-696], the automatic offset-type microwave radiometer of digital gain [Chinese patent, application number 96220482.2].Total power type microwave radiometer is exactly the superhet microwave receiver of a sensitivity, is the basis of other type microwave radiometer.Its circuit structure is simple, it is bigger that output is influenced by gain fluctuation and own ship's noise, minimum detectable signal is big, in order to remove the influence of this machine gain fluctuation, adopt receiver inlet alternately to receive antenna port and reference source port, in the laggard line correlation detection of square law detection with subtract each other processing, Here it is Dicke radiometer.But this method only could all be eliminated the influence of system-gain fluctuation when antenna temperature equates with the reference source temperature.Because increased negative feedback loop, increased the active and passive element of several microwaves, make complex system, technical difficulty is big.Two reference temperature automatic gain compensation microwave radiometers are to make aerial signal and high and low temperature reference source signal successive cycle insert receiver, by detecting the difference of two reference sources after the system, change the judgement change in gain from difference, gain with this variable quantity control post amplifier, make it to produce the variation of opposite sign but equal magnitude, thereby compensated the variation of system-gain, but in signal output, can not eliminate the variation of system noise, thereby exigent feedback control loop, increased a reference source.Numeral is the offset-type microwave radiometer automatically, realized Gain Automatic compensation well, be by after the system in reference signal, in the digital compensation system, compare with benchmark, its result reflects radiometer system-gain fluctuation size, revise the signal value of coming one after the other in view of the above, thereby reach the constant purpose of system-gain, yet it can not eliminate the variation of system noise.

The objective of the invention is to make a kind of microwave radiometer of New System, eliminate the influence of gain fluctuation and system noise fully, realize receiving to the real-time calibration of system with to the accurately stable of atural object microwave radiation.Performance is better than the microwave radiometer of existing any kind.

Real-time calibration microwave radiometer of the present invention is counted the basis with total power type microwave radiation, adding single-chip microcomputer applies according to collection and processing and control section and inner two reference sources formation, the fixed end that it is characterized in that input switch (2) links to each other with the input end of total power microwave radiometer (6), two contacts link to each other with the fixed end of antenna (1) with reference source (3) respectively, two contacts of reference switch (3) link to each other with the output terminal of high temperature reference source (4) with low temperature reference source (5) respectively, the input end of A/D transducer (7) links to each other with the output terminal of total power microwave radiometer (6), output terminal links to each other with the input end of single-chip microcomputer (8), the output terminal of single-chip microcomputer (8) links to each other with the input end of bright temperature display, and two control signal output ends of single-chip microcomputer (8) link to each other with the control end with reference switch (3) of input switch (2) respectively.Be the output voltage of period measurement when being input as high temperature reference source (4), low temperature reference source (5) and antenna (1) in the course of the work.In data handling procedure, used voltage is the linear combination of above three voltage values.Eliminated the influence that own ship's noise changes by voltage difference, output is that voltage difference linear combination is divided by at last, the result of being divided by is the influence of having eliminated change in gain, can be whenever to carry out one-shot measurement, the new once standard signal of two reference sources of gathering, once calibrate, also can once calibrate real calibration when promptly having realized repeatedly measuring.Its course of work is actually the real-time calibration microwave radiometer that carries out signal measurement on system-gain and system noise change slowly.

Fig. 1 is the real-time calibration microwave radiometer fundamental diagram.Form by antenna (1), input switch (2), reference switch (3), high temperature reference source (4), low temperature reference source (5), total power microwave radiometer (6), A/D transducer (7), single-chip microcomputer (8) and bright temperature display (9), antenna (1) receiving target microwave radiation signal, output switch (2) or antenna port, perhaps reference port is linked to each other with receiver, reference switch (3) is input switch (2) and have steady temperature T ₁And T ₂Two reference sources---high temperature reference source (4) and low temperature reference source (5)-one of link to each other, high temperature reference source (4) provides constant standard noise temperature T ₁, low temperature reference source (5) provides constant standard noise temperature T ₂Total power microwave radiometer (6) amplifies integration to the signal that is received, A/D transducer (7) is transformed into digital signal with the simulating signal of radiometer output, single-chip microcomputer (8) is pressed preset sequence gauge tap (2), (3) work, the data acquisition of control A/D transducer (7), data are handled computing, provide and show and output, bright temperature display (9) demonstrates the object brightness Temperature numerical that antenna (1) receives in real time, its concrete steps are as follows: (a) input switch (2) is connected reference switch (3), again reference switch (3) is connected high temperature reference source (4), record noise temperature T ₁, the output voltage of total power microwave radiometer (6) is V ₁(b) reference switch (3) is connected low temperature reference source (5), record noise temperature T ₂, the output voltage of total power microwave radiometer (6) is V ₂(c) input switch (2) is connected antenna (1), the output Shen of total power microwave radiometer (6) is pressed and is V _A'; (d) single-chip microcomputer (8) is pressed the bright temperature equation of receiving target ${T_A}^{\text{'}}=\frac{(V_A^{\&prime;}-V_2)T_1-(V_A^{\&prime;}-V_1)T_2}{V_1-{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="A9611460200081.png"\; state="\{\{state\}\}">V</figure-callout>}}_2}$ Calculate object brightness.In the course of the work, the sequential of two switches is as (a) of Fig. 2 with (b), and in a short period of time, the gain of receiver and own ship's noise are thought and remained unchanged substantially, then according to (a) of Fig. 1 and Fig. 2 with the switch work sequence (b), receiving output voltage is (seeing Fig. 2 (c)) Wherein G is the gain of total power microwave radiometer (6), T _RECFor being folded to the own ship's noise of total power microwave radiometer (6) front end.In any one calibration cycle, when the input noise temperature and the received signal of total power microwave radiometer (6) is respectively T ₁, T ₂, T _A' time, its output voltage is respectively V ₁, V ₂And V _A', then formula (1) can be write as following form:

V ₁＝G(T ₁+T _REC) …………(2a)

V ₂＝G(T ₂+T _REC) …………(2b)

V _A'=G (T _A'+T _REC) ... (2c) as can be known, because the input noise temperature and the output voltage of microwave radiometer are linear, use two known input noise temperature T like this from following formula ₁And T ₂And corresponding voltage V ₁And V ₂, just can determine the coefficient of calibration equation.As seen can determine the calibration equation coefficient that this signal measurement cycles is interior, the i.e. gain G of system and own ship's noise T by formula (2a) with (2b) herein _RECWith G and T _RECValue substitution (2c) formula in, calculate T _A': $T_A^{\&prime;}=\frac{(V_A^{\&prime;}-V_2)T_1-(V_A^{\&prime;}-V_1)T_2}{V_1-V_2}------\left(3\right)$ Whenever before carrying out one-shot measurement, newly gather V one time ₁And V ₂, once calibrate, even the gain G of system and own ship's noise T in next cycle like this _RECChange, its calibration equation also and then changes, and has promptly realized receiver system is carried out real-time calibration, reaches the accurate measurement to signal.Also can gather V one time ₁And V ₂, calibration once takes multiple measurements, and decides with specific requirement.By formula (3) as can be seen, real-time calibration microwave radiometer utilizes output voltage poor of antenna, high temperature reference source and low temperature reference source, eliminates own ship's noise T _RECInfluence, utilize the linear combination of voltage difference to be divided by again, eliminate the influence of gain G fluctuation, make complete machine have good stable.This course of work is actually at system-gain G and system noise T _RECSlowly carry out the measurement of echo signal on changing.

Real-time calibration microwave radiometer has been eliminated the influence that receiver gain changes, and the reference source instability is by (3) Shi Kede: $\mathrm{\&Delta;}{T}_{\mathrm{st}}=\sqrt{{(\frac{T_1-T_A^{\&prime;}}{T_1-{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A9611460200081.png"\; state="\{\{state\}\}">T</figure-callout>}}_2}\&CenterDot;\mathrm{\&Delta;}{T}_2)}^2+{(\frac{T_2-T_A^{\&prime;}}{T_1-{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A9611460200081.png"\; state="\{\{state\}\}">T</figure-callout>}}_2}\&CenterDot;\mathrm{\&Delta;}{T}_1)}^2}------\left(4\right)$ This radiometer high-temperature targets time stability is high as can be known by (4) formula, and stability is relevant with the temperature difference of two reference sources, and the temperature difference is big more, and then system stability is good more.Minimum detectable signal is determined by following formula: $\mathrm{\&Delta;}{T}_{\min }=\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="T\; N"\; filenames="A9611460200081.png"\; state="\{\{state\}\}">T</figure-callout>}}_N^{}+\mathrm{\&Delta;}{T}_{\mathrm{st}}^2----\left(5\right)$ Wherein $\mathrm{\&Delta;}{T}_N=\frac{T_{\mathrm{sys}}}{\sqrt{\mathrm{B\&tau;}}}$ The uncertainty that causes for system noise.Current technical conditions and well-designed constant temperature source can make the uncertainty that is caused by constant temperature source in (5) formula very little, and minimum detectable signal is by the uncertain decision of system noise.

In sum, the present invention has eliminated the influence of system-gain and system noise fluctuation, has realized the accurate measurement of real-time calibration and signal, and the easy easy operating of method, and system is simple, is easy to make and install, and is suitable for continental rise, airborne and space remote sensing.

Fig. 1 real-time calibration microwave radiometer fundamental diagram;

Fig. 2 switching sequence figure

(a) the connection sequential of input switch

(b) the connection sequential of reference switch

(c) output timing of total power microwave radiometer output voltage

Claims (2)

1, a kind of real-time calibration microwave radiometer is handled all to divide by total power microwave radiometer, two reference source and single-chip data acquisition and is constituted.The fixed end that it is characterized in that input switch (2) links to each other with the input end of total power microwave radiometer (6), two contacts link to each other with the fixed end of antenna (1) with reference switch (3) respectively, two contacts of reference switch (3) link to each other with the output terminal of high temperature reference source (4) with low temperature reference source (5) respectively, the input end of A/D transducer (7) links to each other with the output terminal of total power microwave radiometer (6), output terminal links to each other with the input end of single-chip microcomputer (8), the output terminal of single-chip microcomputer links to each other with the input end of bright temperature display (9), and two control signal output ends of single-chip microcomputer (8) link to each other with the control end of input switch (2) with reference switch (3).

2, a kind of calibration measuring method of real-time calibration microwave radiometer is characterized in that whole calibration and measurement and processing procedure all are by carrying out under the preset sequence of realizing the real-time calibration method, and its concrete steps are as follows:

(a) input switch (2) is connected reference switch (3), again reference switch (3) is connected high temperature reference source (4), record noise temperature T ₁, the output voltage of total power microwave radiometer (6) is V ₁

(b) reference switch (3) is connected low temperature reference source (5), record noise temperature T ₂, the output voltage of total power microwave radiometer (6) is V ₂

(c) input switch (2) is connected antenna (1), the output voltage of total power microwave radiometer (6) is V _A';

(D) single-chip microcomputer (8) is pressed the bright temperature equation of antenna receiving target $T_A^{\&prime;}=\frac{(V_A^{\&prime;}-V_2)T_1-(V_A^{\&prime;}-V_1)T_2}{V_1-V_2}$ Calculate the bright temperature of target.

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