A microwave radiometer blackbody emissivity measurement system and measurement method

Abstract

The present invention discloses a microwave radiometer blackbody emissivity measurement system and method, the system comprises a reflector antenna driven to rotate by a servo system, a calibration box is arranged on the top of the reflector antenna, a blackbody is installed in the calibration box, a calibration blackbody is arranged on the bottom of the reflector antenna, a blackbody temperature sensor is installed on the calibration blackbody, a K / V feed source receives the signal of the reflector antenna, and the K / V receiver comprises a noise source, a switch, a coupler and a signal processing circuit. The measurement system and method disclosed by the present invention solve the problems of poor accuracy of the blackbody emissivity of the existing ground-based microwave radiometer, inability to measure the blackbody emissivity during normal operation, and inaccurate brightness temperature caused by the change of the blackbody emissivity over time during real-time calibration.

Description

Technical Field

[0001] The invention belongs to the technical field of passive atmospheric microwave remote sensing, and in particular relates to a microwave radiometer blackbody emissivity measurement system and a measurement method in the field. Background Art

[0002] Microwave radiometer is a passive remote sensing instrument used to measure atmospheric microwave radiation. It does not emit electromagnetic waves itself, but detects target characteristics by passively receiving microwave energy radiated by the observed scene. Since the microwave radiation signal of an object is an incoherent and extremely weak signal, the power of this signal is much smaller than the noise power of the radiometer itself, so the radiometer is essentially a highly sensitive receiver.

[0003] Microwave radiometers are mainly used to receive atmospheric microwave radiation signals. The signals received by the antenna enter the receiver system through the feed source. The receiver amplifies, filters, detects and re-amplifies the signals, and then converts them into voltage to enter the data acquisition unit. After the equipment is calibrated, the data acquisition unit converts the corresponding voltage output into brightness temperature, thereby realizing real-time monitoring of atmospheric radiation brightness temperature. The vertical profile output under different brightness temperatures is obtained through the localized model.

[0004] In order to obtain accurate brightness temperature data, the microwave radiometer needs to be calibrated to obtain the quantitative relationship between the microwave radiometer output voltage and the atmospheric radiation signal received by the antenna. The calibration accuracy determines the accuracy and application value of the radiometer measurement data.

[0005] Common calibration methods include liquid nitrogen calibration, tilt curve calibration, noise source calibration, etc. At present, the most commonly used ground calibration method is liquid nitrogen calibration. When calibrating with liquid nitrogen, low-temperature sources generally use black bodies immersed in liquid nitrogen, and high-temperature sources use normal temperature or high temperature black bodies. If the black body material of the calibration source is not an ideal black body and the emissivity is less than 1, directly using its physical temperature as the brightness temperature of the black body will cause certain errors. Several commonly used emissivity measurement methods are generally limited to specific laboratory conditions, and the accuracy is limited. As the black body ages, the emissivity changes, but the emissivity cannot be updated in time, resulting in large errors in real-time calibration. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a blackbody emissivity measurement system and a measurement method based on a microwave radiometer.

[0007] The present invention adopts the following technical solution:

[0008] A microwave radiometer blackbody emissivity measurement system, the improvement of which lies in: comprising a reflector antenna driven to rotate by a servo system, a calibration box arranged on the top of the reflector antenna, a blackbody installed in the calibration box, a calibration blackbody arranged at the bottom of the reflector antenna, a blackbody temperature sensor installed on the calibration blackbody, a K / V feed source receiving a signal from the reflector antenna, a K / V receiver comprising a noise source, a switch, a coupler and a signal processing circuit, wherein the coupler is electrically connected to the K / V feed source, the switch and the signal processing circuit, the noise source is electrically connected to the switch, and a central signal processing system is electrically connected to the above-mentioned servo system and the K / V receiver.

[0009] Furthermore, liquid nitrogen is contained in the calibration box, and the black body in the calibration box is immersed in the liquid nitrogen.

[0010] Furthermore, the cone of the black body in the calibration box faces downward, and the cone of the calibration black body faces upward.

[0011] Furthermore, the noise source provides a high temperature noise signal.

[0012] Furthermore, the signal processing circuit includes an amplifier circuit, a power divider circuit, a filter circuit and a detector circuit.

[0013] A method for measuring blackbody emissivity using a microwave radiometer, using the above-mentioned measurement system, is improved in that it comprises the following steps:

[0014] Step 1, establish the microwave radiometer measurement system:

[0015] Install all components in the measurement system in place, pour liquid nitrogen into the calibration box, and cover the calibration box securely with a lid;

[0016] Step 2: Obtain calibration test data of the cold source:

[0017] The central signal processing system turns off the switch, controls the servo system to drive the reflector antenna to rotate to align with the calibration box, and the reflector antenna receives the radiation signal of the black body immersed in liquid nitrogen in the calibration box. The K / V feed source receives the power signal of the reflector antenna and sends it to the signal processing circuit through the coupler. The signal processing circuit conditions the input signal and outputs it as a voltage signal V1. The brightness temperature of the calibration box is T1.

[0018] The central signal processing system closes the switch, and the power signal of the reflector antenna is superimposed with the noise signal in the coupler and then sent to the signal processing circuit. The signal processing circuit conditions the input signal and outputs it as a voltage signal V2, and the equivalent brightness temperature is T2;

[0019] Step 3, calculate the calibration coefficient of the device:

[0020] The calibration equation for the microwave radiometer is:

[0021]

[0022] Where K is the slope and b is the intercept;

[0023] Since the microwave radiometer is linear, the slope K and intercept b can be obtained according to V1, V2, T1, T2 obtained in step 2 and equation (1):

[0024]

[0025]

[0026] Step 4: Correct the blackbody emissivity:

[0027] The central signal processing system turns off the switch, controls the servo system to drive the reflector antenna to rotate to align with the calibration black body, and the reflector antenna receives the radiation signal of the calibration black body. The K / V feed source receives the power signal of the reflector antenna and sends it to the signal processing circuit through the coupler. The signal processing circuit conditions the input signal and outputs it as a voltage signal V3. Substituting V3 into formula (1), the brightness temperature T3 of the calibration black body is obtained as:

[0028]

[0029] The slope K of formula (4) is obtained by formula (2), and the intercept b is obtained by formula (3);

[0030] The temperature of the calibration black body measured by the black body temperature sensor is T4;

[0031] The emissivity ε of the calibration blackbody can be obtained by dividing the brightness temperature T3 by the temperature T4:

[0032]

[0033] The emissivity ε is updated to the configuration file for use in real-time correction of the microwave radiometer.

[0034] The beneficial effects of the present invention are:

[0035] As a standard source for real-time correction of microwave radiometers, the emissivity of blackbody changes with time, resulting in calibration errors. The measurement system and measurement method disclosed in the present invention solve the problems of poor accuracy of blackbody emissivity of existing ground-based microwave radiometers, inability to measure blackbody emissivity during normal operation, and inaccurate brightness temperature caused by blackbody emissivity changing with time during real-time calibration. The blackbody emissivity can be measured while calibrating with liquid nitrogen. The blackbody emissivity is corrected by periodic liquid nitrogen calibration every quarter, which greatly improves the test efficiency of blackbody emissivity and the brightness temperature accuracy of calibrated blackbody, provides a more accurate standard source for real-time correction of microwave radiometers, increases the accuracy of real-time correction of microwave radiometers, provides the necessary basis for improving the brightness temperature measurement accuracy of microwave radiometers, and meets the application requirements of radiometer systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a block diagram of the composition of the measurement system disclosed in Embodiment 1 of the present invention;

[0037] Figure 2 It is a flow chart of the measurement method disclosed in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] Embodiment 1, as Figure 1 As shown, this embodiment discloses a microwave radiometer blackbody emissivity measurement system, including a reflector antenna 2 driven to rotate by a servo system 1, a calibration box 3 is arranged on the top of the reflector antenna, a blackbody 31 is installed in the calibration box, a calibration blackbody 4 is arranged at the bottom of the reflector antenna, a blackbody temperature sensor 41 is installed on the calibration blackbody for measuring the temperature of the calibration blackbody, a K / V feed source 5 receives the signal of the reflector antenna, a K / V receiver 6 includes a noise source 61, a switch 62, a coupler 63 and a signal processing circuit 64, wherein the coupler is electrically connected to the K / V feed source, the switch and the signal processing circuit, the noise source is electrically connected to the switch, a central signal processing system 7 is electrically connected to the above-mentioned servo system and the K / V receiver, and the central signal processing system is used to control other components, collect signals, process data, etc.

[0040] In this embodiment, liquid nitrogen is contained in the calibration box, and the black body in the calibration box is immersed in the liquid nitrogen as a cold source for calibration. The cone of the black body in the calibration box faces downward, and the cone of the calibration black body faces upward, which serves as an internal standard source and is used for periodic calibration after test calibration. The noise source provides a high-temperature noise signal, which periodically enters the receiving path of the K / V receiver through the coupler by opening and closing the switch. The signal processing circuit includes an amplifier circuit, a power divider circuit, a filter circuit and a detector circuit.

[0041] This embodiment also discloses a method for measuring the blackbody emissivity of a microwave radiometer, using the above-mentioned measurement system, based on liquid nitrogen calibration, to measure the emissivity of the blackbody inside the microwave radiometer, providing a basis for real-time calibration of the accuracy of the room temperature source. Figure 2 As shown, the specific steps include:

[0042] Step 1, establish the microwave radiometer measurement system:

[0043] Install all components in the measurement system, including the ground-based microwave radiometer system and make it work stably. Slowly pour liquid nitrogen into the calibration box, cover the calibration box with a lid, and obtain the low-temperature standard source for calibration.

[0044] Step 2: Obtain calibration test data of the cold source:

[0045] Measure the low-temperature standard source of the calibration box: the central signal processing system turns off the switch, controls the servo system to drive the reflector antenna to rotate to align with the calibration box, and the reflector antenna receives the radiation signal of the black body immersed in liquid nitrogen in the calibration box. The K / V feed source receives the power signal of the reflector antenna and sends it to the signal processing circuit through the coupler. The signal processing circuit conditions the input signal and outputs it as a voltage signal V1. The brightness temperature of the calibration box is T1.

[0046] The low temperature standard source and noise source of the calibration box are measured: the central signal processing system closes the switch, the power signal of the reflector antenna is superimposed with the noise signal in the coupler and then sent to the signal processing circuit. The signal processing circuit conditions the input signal and outputs it as a voltage signal V2. The equivalent brightness temperature (brightness temperature of the calibration box plus the coupled noise of the noise source) is T2.

[0047] Step 3, calculate the calibration coefficient of the device:

[0048] The calibration equation for the microwave radiometer is:

[0049]

[0050] Where K is the slope and b is the intercept;

[0051] Since the microwave radiometer is linear, the slope K and intercept b can be obtained according to V1, V2, T1, T2 obtained in step 2 and equation (1):

[0052]

[0053]

[0054] Step 4: Correct the blackbody emissivity:

[0055] The central signal processing system turns off the switch, controls the servo system to drive the reflector antenna to rotate to align with the calibration black body, and the reflector antenna receives the radiation signal of the calibration black body. The K / V feed source receives the power signal of the reflector antenna and sends it to the signal processing circuit through the coupler. The signal processing circuit conditions the input signal and outputs it as a voltage signal V3. Substituting V3 into formula (1), the brightness temperature T3 of the calibration black body is obtained as:

[0056]

[0057] The slope K of formula (4) is obtained by formula (2), and the intercept b is obtained by formula (3);

[0058] The temperature of the calibration black body measured by the black body temperature sensor is T4;

[0059] The emissivity ε of the calibration blackbody can be obtained by dividing the brightness temperature T3 by the temperature T4:

[0060]

[0061] The emissivity ε is updated to the configuration file for use in real-time calibration and correction of the microwave radiometer, thereby obtaining accurate blackbody brightness temperature information.

Claims

1. A microwave radiometer blackbody emissivity measurement method, using a microwave radiometer blackbody emissivity measurement system, including a reflector antenna driven to rotate by a servo system, a calibration box is arranged on the top of the reflector antenna, a blackbody is installed in the calibration box, a calibration blackbody is arranged at the bottom of the reflector antenna, a blackbody temperature sensor is installed on the calibration blackbody, a K / V feed source receives a signal from the reflector antenna, a K / V receiver includes a noise source, a switch, a coupler and a signal processing circuit, wherein the coupler is electrically connected to the K / V feed source, the switch and the signal processing circuit, the noise source is electrically connected to the switch, and a central signal processing system is electrically connected to the above-mentioned servo system and the K / V receiver, characterized in that: The steps include: Step 1, establish the microwave radiometer measurement system: Install all components in the measurement system in place, pour liquid nitrogen into the calibration box, and cover the calibration box securely with a lid; Step 2: Obtain calibration test data of the cold source: The central signal processing system turns off the switch, controls the servo system to drive the reflector antenna to rotate to align with the calibration box, and the reflector antenna receives the radiation signal of the black body immersed in liquid nitrogen in the calibration box. The K / V feed source receives the power signal of the reflector antenna and sends it to the signal processing circuit through the coupler. The signal processing circuit conditions the input signal and outputs it as a voltage signal V1. The brightness temperature of the calibration box is T1. The central signal processing system closes the switch, and the power signal of the reflector antenna is superimposed with the noise signal in the coupler and then sent to the signal processing circuit. The signal processing circuit conditions the input signal and outputs it as a voltage signal V2, and the equivalent brightness temperature is T2; Step 3, calculate the calibration coefficient of the device: The calibration equation for the microwave radiometer is: Where K is the slope and b is the intercept; Since the microwave radiometer is linear, the slope K and intercept b can be obtained according to V1, V2, T1, T2 obtained in step 2 and equation (1): Step 4: Correct the blackbody emissivity: The central signal processing system turns off the switch, controls the servo system to drive the reflector antenna to rotate to align with the calibration black body, and the reflector antenna receives the radiation signal of the calibration black body. The K / V feed source receives the power signal of the reflector antenna and sends it to the signal processing circuit through the coupler. The signal processing circuit conditions the input signal and outputs it as a voltage signal V3. Substituting V3 into formula (1), the brightness temperature T3 of the calibration black body is obtained as: The slope K of formula (4) is obtained by formula (2), and the intercept b is obtained by formula (3); The temperature of the calibration black body measured by the black body temperature sensor is T4; The emissivity ε of the calibration blackbody can be obtained by dividing the brightness temperature T3 by the temperature T4: The emissivity ε is updated to the configuration file for use in real-time correction of the microwave radiometer.

2. The method for measuring blackbody emissivity using a microwave radiometer according to claim 1, wherein: The calibration box contains liquid nitrogen, and the black body in the calibration box is immersed in the liquid nitrogen.

3. The method for measuring blackbody emissivity using a microwave radiometer according to claim 1, wherein: The cone of the black body in the calibration box faces downward, and the cone of the calibration black body faces upward.

4. The method for measuring blackbody emissivity using a microwave radiometer according to claim 1, wherein: The noise source provides a high temperature noise signal.

5. The method for measuring blackbody emissivity using a microwave radiometer according to claim 1, wherein: The signal processing circuit includes an amplifier circuit, a power divider circuit, a filter circuit and a detector circuit.

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