Receiver noise coefficient testing method based on high-precision radiation measurement

Abstract

According to the receiver noise coefficient testing method based on high-precision radiation measurement, a calibration source outputs different brightness temperature signals to calibrate a receiver in real time, and high-precision measurement of the noise coefficient of the receiver can be achieved by calculating the equivalent noise temperature. An actual brightness temperature scene is integrally simulated, the radiation measurement method is more accurate, and the test precision is improved; the calibration source realizes accurate and stable cold source and heat source based on liquid nitrogen refrigeration and physical heating, and has the advantages of high output precision, long stabilization time and the like, and the long-time stabilization precision can reach 0.1 k / 3 days; and meanwhile, the output brightness temperature of the high-precision calibration source is between 90K and 330K and is closer to an actual brightness temperature scene, so that a relatively large nonlinear error caused by nonlinearity of an internal amplifier of the receiver can be avoided, and the test precision is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of space microwave remote sensing, and in particular relates to a receiver noise coefficient testing method based on high-precision radiation measurement. Background Art

[0002] Microwave radiometer is a passive remote sensing instrument used to measure the microwave radiation energy of an object. It obtains the characteristic information of the object by receiving the microwave noise radiation of the object itself, and inverts the output data to obtain specific target parameters (mainly brightness temperature), so as to understand the physical characteristics of the detected target. It is essentially a highly sensitive noise receiver. At present, there is no publicly reported research on the method of measuring the noise coefficient of microwave radiometer receiver using radiation measurement method.

[0003] The traditional method is to test the noise coefficient of the microwave radiometer receiver under laboratory conditions using a noise coefficient analyzer. The principle of the noise coefficient analyzer is to use an external noise head to generate hot and cold temperature noise respectively. The hot temperature noise is calculated based on the noise head's excess noise ratio (generally 1000K~10000K), and the cold temperature noise is based on the thermal noise generated by the attenuator inside the noise source (Tc≥273.15+T0), T0 represents the device ambient temperature, and finally the receiver noise coefficient is measured by the Y factor method. Since the working mode of the noise coefficient analyzer is frequency sweep, its hot temperature output noise selects the excess noise ratio value according to the frequency of the receiver to be tested, so the noise coefficient of the test receiver only represents the value at the corresponding frequency. When the microwave radiometer system is conducting ground observations, the target scene is a broadband signal. The measurement results of the noise coefficient analyzer cannot reflect the noise coefficient of the receiver when observing the real scene, and the test noise coefficient accuracy of the noise coefficient analyzer is generally 0.1dB, and the corresponding brightness temperature uncertainty is about 4K. More importantly, the noise coefficient analyzer measures the receiver noise coefficient using hot and cold temperature noise, which is generally between 290K and 1000K. The target scene observed by the satellite-borne microwave radiometer system is the self-energy radiation of the ground objects, which is generally between 3K and 350K. When the noise coefficient analyzer is used to measure the noise coefficient of the microwave radiometer receiver, the receiver will bring a large nonlinear error due to the nonlinearity of its internal amplifier, which will bring about a nonlinear error of about 0.2dB, corresponding to a brightness temperature of about 8K. In summary, the noise coefficient analyzer is far from meeting the requirements of microwave radiometer noise coefficient measurement (generally, the requirements for quantitative measurement of microwave radiometers are about 0.2K to 1K depending on the frequency band, and the corresponding power accuracy is 0.002dB to 0.01dB).

[0004] The disadvantages of the existing test methods for receiver noise coefficient are: first, the test accuracy is determined by the noise coefficient analyzer and can only be controlled at around 0.1dB, which cannot meet the increasingly high application requirements; second, when the noise coefficient analyzer uses cold temperature and hot temperature noise (290K~1000K) to measure the receiver noise coefficient, it is quite different from the actual ground radiation brightness temperature (3K~350K), which will cause relatively large nonlinear errors; third, the test working mode of the noise coefficient analyzer is frequency sweep, while the scene signal is a broadband signal, which will cause large test errors. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a receiver noise figure testing method based on high-precision radiation measurement to solve the technical problems of insufficient measurement accuracy and large errors in existing methods.

[0006] To achieve the above object, the technical solution adopted by the present invention includes:

[0007] A receiver noise figure testing method based on high-precision radiation measurement specifically comprises the following steps:

[0008] S1, configure the calibration source and collector connected to the receiver; switch the calibration source to the cold source to provide cold source noise, and obtain the output brightness temperature T of the cold source noise at the current moment c and the collector output response V c , and obtain the temperature value t of the receiver at the current moment 01 ; The calibration source is switched to the heat source to provide heat source noise, and the output brightness temperature T of the heat source noise at the current moment is recorded h and the collector output response V h , and record the temperature value t of the receiver at the current moment 02 ;

[0009] S2, the receiver gain G and equivalent noise temperature T are calculated by equations (1) and (2) r ;

[0010] V h =G·(T h +T r )

[0011] V c =G·(T c +T r ) (1)

[0012] G=(V h -V c ) / (T h -T c )

[0013]

[0014] S3, the noise factor F of the receiver is calculated by formula (3);

[0015]

[0016] Among them, T 01 is the physical brightness temperature when the calibration source cuts off the cold source, T 01 =t 01 +273.15;T 02 is the physical brightness temperature when the calibration source cuts off the heat source, T 02 =t 02 +273.15.

[0017] Preferably, the time interval for the calibration source to switch from a cold source to a hot source or from a hot source to a cold source does not exceed 1 minute.

[0018] Preferably, the calibration source output brightness temperature is 90K to 330K.

[0019] Preferably, the calibration source in S1 is switched to a cold source, and the output brightness temperature is 90K.

[0020] Preferably, the calibration source in S1 is switched to a heat source, and the output brightness temperature is 330K.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) The receiver noise coefficient test method based on high-precision radiation measurement of the present invention simulates the actual brightness temperature scene. The radiation measurement method is more accurate and can improve the test accuracy.

[0023] (2) In the receiver noise coefficient test method based on high-precision radiation measurement of the present invention, the calibration source is based on liquid nitrogen refrigeration and physical heating to achieve accurate and stable cold source and heat source, which has the advantages of high output accuracy and long stabilization time. The long-term stability accuracy can reach 0.1k / 3 days; at the same time, the high-precision calibration source outputs a brightness temperature between 90K and 330K, which is closer to the actual brightness temperature scene, and can avoid the large nonlinear error of the receiver due to the nonlinearity of its internal amplifier, thereby greatly improving the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 It is a comparison chart of the noise coefficient test results of the present application method and the existing method;

[0026] Figure 2It is a comparison chart of the gain test results of the method of the present application and the existing method. DETAILED DESCRIPTION

[0027] The invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention. All components and devices in the present invention, unless otherwise specified, are all components and devices known in the prior art.

[0028] A microwave radiometer system is mainly composed of an antenna, a receiver and a data collector. The noise coefficient of the microwave radiometer system is mainly composed of two parts, one part is caused by the antenna, and the other part is caused by the receiver. Since the antenna is a passive device, its radiation efficiency will affect the noise coefficient of the antenna, which can be measured in an antenna darkroom. The noise coefficient of the microwave radiometer system is mainly determined by the receiver, and the performance index of the receiver is mainly determined by the gain and the noise coefficient. In particular, the noise coefficient is focused on for the microwave radiometer receiver. The present invention mainly proposes a receiver noise coefficient test method based on high-precision radiation measurement for the receiver noise coefficient of the microwave radiometer.

[0029] Example

[0030] This embodiment discloses a receiver noise figure testing method based on high-precision radiation measurement, which specifically includes the following steps:

[0031] S1, configures a calibration source and a collector connected to a receiver, the input port of the receiver is connected to the calibration source, and the output port of the receiver is connected to the collector; also includes a temperature measuring resistor connected to the receiver; also includes a host computer, and the collector finally transmits the collected data to the host computer for processing; also includes a power supply that provides stable power supply to the receiver and the collector;

[0032] Among them, the receiver disclosed in this embodiment uses an L-band microwave radiometer receiver; the preferred model of the temperature measuring resistor in this embodiment is a PT100 platinum resistor, which can be directly attached to the corresponding housing of the receiver amplifier when in use; the calibration source of this embodiment uses a high-precision calibration source of model Maury MT155J06, which achieves high-precision and stable cold source noise and heat source noise through liquid nitrogen refrigeration and physical heating; the collector of this embodiment uses model NI-PX1095, which digitally samples the signal amplified by the receiver, generates a clock signal through a highly stable clock chip, integrates the data in the FPGA, and then transmits it to the host computer at high speed through the serial port protocol to ensure the real-time and accuracy of the data.

[0033] Before testing, turn on the above equipment and preheat it for at least 1 hour, and then test it after it is working stably.

[0034] The calibration source is switched to the cold source to provide cold source noise, and the output brightness temperature T of the cold source noise at the current moment is obtained. c and the collector output response V c , and obtain the temperature value t of the receiver at the current moment 01 ; The calibration source is switched to the heat source to provide heat source noise, and the output brightness temperature T of the heat source noise at the current moment is recorded h and the collector output response V h , and record the temperature value t of the receiver at the current moment 02 ;

[0035] Among them, the output brightness temperature of the calibration source in this embodiment is 90K~330K. When the calibration source is switched to the cold source, the output brightness temperature is 90K, and when the calibration source is switched to the hot source, the output brightness temperature is 330K, and it is ensured that the time interval for switching the calibration source from the cold source to the hot source or from the hot source to the cold source does not exceed 1 minute.

[0036] S2, the receiver gain G and equivalent noise temperature T are calculated by equations (1) and (2) r ;

[0037] V h =G·(T h +T r )

[0038] V c =G·(T c +T r ) (1)

[0039] G=(V h -V c ) / (T h -T c )

[0040]

[0041] S3, the noise factor F of the receiver is calculated by formula (3);

[0042]

[0043] Among them, T 01 is the physical brightness temperature when the calibration source cuts off the cold source, T 01 =t 01 +273.15;T 02 is the physical brightness temperature when the calibration source cuts off the heat source, T 02 =t 02 +273.15.

[0044] like Figure 1As shown, the test method disclosed in the present application simulates the actual brightness temperature scene compared to the frequency sweep test method of the noise coefficient analyzer, and the radiation measurement method is more accurate, which can improve the test accuracy. The calibration source of the present application is based on liquid nitrogen refrigeration and physical heating to achieve accurate and stable cold and heat sources, with the advantages of high output accuracy and long stabilization time. The long-term stable accuracy can reach 0.1k / 3 days; at the same time, the high-precision calibration source outputs a brightness temperature between 90K and 330K, which is closer to the actual brightness temperature scene, and can avoid the receiver from causing large nonlinear errors due to the nonlinearity of its internal amplifier, greatly improving the test accuracy.

[0045] Meanwhile, the gain G is an important index for evaluating the performance of the receiver. Conventionally, it can only be measured by a vector network analyzer. However, the method of the present application can also measure it directly, and the result is more accurate. Figure 2 shown.

[0046] The above embodiments are only specific application examples of the present invention. In actual operation, corresponding adjustments can be made according to the on-site geological conditions, detection requirements and specific conditions of technical equipment to achieve the best detection effect.

[0047] Through the above steps, a new receiver noise coefficient test method based on high-precision radiation measurement is realized, which effectively solves the problems existing in the existing technology and plays a positive role in promoting atmospheric detection and application.

[0048] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0049] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0050] In addition, the various different implementation modes disclosed in this solution may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the content invented by the present disclosure.

Claims

1. A receiver noise figure test method based on high-precision radiation measurement, characterized in that: The specific steps include: S1, configure the calibration source and collector connected to the receiver; The calibration source is switched to the cold source to provide cold source noise, and the output brightness temperature T of the cold source noise at the current moment is obtained. c and the collector output response V c , and obtain the temperature value t of the receiver at the current moment 01 ; The calibration source is switched to the heat source to provide heat source noise, and the output brightness temperature T of the heat source noise at the current moment is recorded. h and the collector output response V h , and record the temperature value t of the receiver at the current moment 02 ; S2, the receiver gain G and equivalent noise temperature T are calculated by equations (1) and (2) r ; S3, the noise factor F of the receiver is calculated by formula (3); Among them, T 01 is the physical brightness temperature when the calibration source cuts off the cold source, T 01 =t 01 +273.15;T 02 is the physical brightness temperature when the calibration source cuts off the heat source, T 02 =t 02 +273.

15.

2. The receiver noise figure test method based on high-precision radiation measurement according to claim 1, characterized in that: The time interval for the calibration source to switch from a cold source to a hot source or from a hot source to a cold source does not exceed 1 minute.

3. The receiver noise figure test method based on high-precision radiation measurement according to claim 1, characterized in that: The output brightness temperature of the calibration source is 90K to 330K.

4. The receiver noise figure test method based on high-precision radiation measurement according to claim 3, characterized in that: The calibration source in S1 is switched to a cold source, and the output brightness temperature is 90K.

5. The receiver noise figure test method based on high-precision radiation measurement according to claim 4, characterized in that: The calibration source in S1 is switched to a heat source, and the output brightness temperature is 330K.

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