On-orbit Test System and Test Method for Emissivity of Spaceborne Microwave Radiometer Antenna

Abstract

The present invention discloses an on-orbit test system and a test method for the antenna emissivity of a spaceborne microwave radiometer. The test system includes a radiance temperature receiving module, a radiance temperature calibration module, an on-orbit positioning module, a maneuvering module, and a data application module. It is mainly used to calculate the antenna emissivity parameter of the spaceborne microwave radiometer in orbit, so as to solve the problem that it is difficult to accurately measure the antenna emissivity and its time-varying situation in orbit. During the on-orbit flight of the satellite, by adjusting the satellite flight attitude, the antenna of the spaceborne microwave radiometer is made to observe the cold sky. By comparing the observed cold sky radiance temperature value obtained by the microwave radiometer with the theoretical cold sky radiance temperature value calculated by the radiative transfer model, the emissivity of the antenna is calculated. The accurate calibration of the antenna emissivity can eliminate the influence of the antenna self-radiation on the calibration accuracy of the microwave radiometer system, which is beneficial to evaluating the actual on-orbit calibration effect of the radiometer, can specifically improve the system calibration scheme, and further improve the radiation measurement accuracy of the spaceborne microwave radiometer.

Description

Technical Field

[0001] The present invention relates to the technical field of aerospace microwave passive remote sensing radiometers, and particularly relates to an on-orbit test system for the emissivity of a spaceborne microwave radiometer antenna and an on-orbit test method for the emissivity of a spaceborne microwave radiometer antenna. Background Art

[0002] By measuring the radiation information of the earth's surface and the atmosphere, a spaceborne microwave radiometer can retrieve parameters such as temperature, humidity, wind speed, sea ice, snow cover, soil moisture, and precipitation, and is widely used in environmental exploration fields such as the atmosphere, ocean, and land. Whether accurate and effective brightness temperature remote sensing data of the earth's surface and the atmosphere can be obtained during the on-orbit operation of the microwave radiometer mainly depends on the calibration accuracy of the microwave radiometer. Therefore, in order to obtain accurate and effective brightness temperature remote sensing data of the earth's surface and the atmosphere, it is necessary to greatly improve the calibration accuracy of the microwave radiometer.

[0003] In the traditional calibration process, the emissivity parameter of the antenna reflector surface is obtained through ground tests. However, the ground test accuracy is low and it cannot characterize the on-orbit time-varying characteristics of the antenna emissivity. Therefore, the main antenna emissivity parameter used in the current on-orbit calibration of the microwave radiometer is calculated according to the ideal formula, rather than the ground test result, and no on-orbit correction has been performed. In order to improve the on-orbit calibration accuracy of the spaceborne microwave radiometer, it is very necessary to accurately calculate the on-orbit emissivity of the antenna. Summary of the Invention

[0004] The purpose of the present invention is to provide an on-orbit test system and method for the emissivity of a spaceborne microwave radiometer reflector antenna, which can solve the problem that it is difficult to accurately measure the emissivity of the antenna reflector surface and its on-orbit time-varying characteristics, so as to improve the calibration accuracy of the on-orbit observed brightness temperature of the microwave radiometer.

[0005] The first aspect of the present invention provides an on-orbit test system for the emissivity of a spaceborne microwave radiometer antenna. The test system includes a radiance temperature receiving module, a radiance temperature calibration module, an on-orbit positioning module, a maneuvering module, and a data application module. The radiance temperature receiving module is used to receive the first radiance temperature signal of the observation target, convert the first radiance temperature signal into a voltage signal, and transmit the voltage signal to the radiance temperature calibration module. The radiance temperature calibration module is used to obtain the radiance temperature of the calibration source, simultaneously receive the voltage signal transmitted back by the radiance temperature receiving module, convert the voltage signal into a second radiance temperature signal according to the two-point calibration equation of the spaceborne microwave radiometer, and transmit the second radiance temperature signal to the data application module. The on-orbit positioning module is used to obtain the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer, and transmit the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer to the data application module. The maneuvering module analyzes the on-orbit maneuvering range of the spaceborne microwave radiometer according to the observation requirements, controls the spaceborne microwave radiometer to perform on-orbit maneuvers, and adjusts the flight attitude of the spaceborne microwave radiometer. The data application module determines the attributes of the observation target according to the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer, and calculates the on-orbit emissivity of the antenna reflector surface in combination with the temperature information of the spaceborne microwave radiometer and the second radiance temperature signal.

[0006] Further, the radiance temperature receiving module includes an antenna subsystem and a receiver subsystem. The antenna subsystem is used to reflect the radiance temperature TB of the observation target into the receiver subsystem. The radiance temperature reflected and transmitted by the antenna subsystem is expressed as TA = TB·(1 - ε)+Tphy·ε, where Tphy is the physical temperature of the antenna reflector surface, TB represents the actual radiance temperature of the observation target, and ε is the emissivity of the antenna reflector surface. The receiver subsystem is used to receive the radiance temperature TA reflected and transmitted by the antenna subsystem and convert the observed temperature into a voltage signal.

[0007] Further, the radiance temperature calibration module includes a calibration source subsystem and a calibration calculation subsystem. The calibration source subsystem includes a cold calibration source structure and a hot calibration source structure. The calibration source subsystem is used to provide a calibration radiance temperature signal for the radiance temperature receiving module and the calibration calculation subsystem. The calibration calculation subsystem obtains the voltage signal transmitted from the receiver subsystem, and uses the two-point calibration formula to convert the voltage value into a temperature value TA = G(VA - VH)+TH, where TA represents the radiance temperature of the observation target after two-point calibration, VA represents the output voltage of the antenna when observing the target, the system gain G = (TH - TC)) / (VH - VC), TH represents the hot source radiance temperature, VH represents the output voltage of the antenna when observing the hot calibration source, TC represents the cold source radiance temperature, and VC represents the output voltage of the antenna when observing the cold calibration source.

[0008] Further, the maneuver module is used to analyze the on-orbit maneuver angle requirements of the spaceborne microwave radiometer, design the maneuver scheme of the spaceborne microwave radiometer, and control the spaceborne microwave radiometer to perform on-orbit maneuvers according to the analysis results of the on-orbit maneuver angles.

[0009] Further, the on-orbit positioning module includes an on-orbit positioning subsystem and an attitude control subsystem; the on-orbit positioning subsystem is used to receive satellite navigation positioning signals and obtain the payload position and the observation pixel position; the attitude control subsystem is used to receive the on-orbit flight attitude information of the spaceborne microwave radiometer, and the on-orbit flight attitude information includes the roll angle, pitch angle, and yaw angle of the spaceborne microwave radiometer.

[0010] Further, the data application module is used to receive the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer transmitted by the on-orbit positioning module, obtain the observation target attributes of the spaceborne microwave radiometer, and calculate the simulated brightness temperature of the observation target in combination with the radiation transfer model. At the same time, it receives the observed brightness temperature TA transmitted by the radiation brightness temperature calibration module, and calculates the on-orbit emissivity parameter of the antenna reflector surface according to the antenna radiation brightness temperature formula.

[0011] The second aspect of the present invention provides an on-orbit test method for the emissivity of a spaceborne microwave radiometer antenna, which is used for the on-orbit test system of the emissivity of a spaceborne microwave radiometer antenna provided in the first aspect of the present invention. The on-orbit test method for the emissivity of a spaceborne microwave radiometer antenna includes the following steps:

[0012] S1. Determine the observation target of the spaceborne microwave radiometer antenna, establish an orbital simulation model for the on-orbit operation of the spaceborne microwave radiometer, and simulate and analyze to obtain the maneuver angle range [θ1, θ2]. Within the maneuver angle range, the observation target of the spaceborne microwave radiometer meets the requirements.

[0013] S2. When the spaceborne microwave radiometer observes the cold source, obtain the first output voltage VC and the radiation brightness temperature TC of the cold source. When the spaceborne microwave radiometer observes the heat source, obtain the second output voltage VH and the radiation brightness temperature TH of the heat source. Use the radiation brightness temperature TC of the cold source, the radiation brightness temperature TH of the heat source, the first output voltage VC, and the second output voltage VH to calculate the system calibration gain G of the spaceborne microwave radiometer. The calculation formula of G is as follows:

[0014] G = (TH - TC) / (VH - VC);

[0015] S3. According to the system calibration gain G, calibrate the observation voltage VA of the spaceborne microwave radiometer to the brightness temperature. The brightness temperature observation value TA is:

[0016] TA = G(VA - VH) + TH;

[0017] S4. Using the radiative transfer model, obtain the simulated brightness temperature values of the antenna observing the target within the maneuvering angle range [θ1, θ2].

[0018] S5. Use the temperature sensor to obtain the physical temperature Tphy of the antenna reflector surface. By comparing the observed brightness temperature value TA and the simulated brightness temperature value calculate the emissivity parameter of the antenna reflector surface:

[0019]

[0020] Technical effects of the present invention:

[0021] The present invention provides an on-orbit test system and method for the emissivity of the reflector antenna of a spaceborne microwave radiometer. This method is mainly applied to calculate the antenna emissivity parameter of the spaceborne microwave radiometer in orbit, so as to solve the problem that it is difficult to accurately measure the antenna emissivity and its time-varying situation in orbit. During the on-orbit flight of the satellite, by adjusting the flight attitude of the satellite, the antenna of the spaceborne microwave radiometer observes the cold sky. By comparing the observed brightness temperature value of the cold sky obtained by the microwave radiometer with the theoretical value of the brightness temperature of the cold sky calculated by the radiative transfer model, calculate the emissivity of the antenna. The accurate calibration of the antenna emissivity can eliminate the influence of the antenna self-radiation on the calibration accuracy of the microwave radiometer system, which is beneficial to evaluating the actual on-orbit calibration effect of the radiometer, can specifically improve the system calibration scheme, and further improve the radiation measurement accuracy of the spaceborne microwave radiometer. Based on the traditional two-point calibration method, the present invention provides an on-orbit test system and method for the emissivity of the reflector antenna of a spaceborne microwave radiometer. By adjusting the attitude of the satellite during on-orbit flight, the antenna reflector is aligned with the cold sky for observation, and then the on-orbit emissivity of the antenna is accurately calculated.

[0022] Furthermore, the calculation method for the on-orbit emissivity of the antenna of the spaceborne microwave radiometer of the present invention is scientific, reasonable and easy to implement. It can solve the problem that it is difficult to accurately measure the emissivity parameter of the antenna reflector surface and its time-varying characteristics in orbit, so as to effectively and accurately obtain the on-orbit antenna emissivity of the spaceborne microwave imager. Accurately calculating the on-orbit emissivity of the antenna reflector surface of the spaceborne microwave radiometer is beneficial to evaluating the actual on-orbit calibration effect of the instrument, can specifically improve the system calibration scheme, and further improve the radiation measurement result of the spaceborne microwave imager. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] By reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects and advantages of the present invention will become more apparent:

[0024] Figure 1 It is a process diagram of the on-orbit test system for the emissivity of the antenna of the spaceborne microwave radiometer in an embodiment of the present invention;

[0025] Figure 2The flowchart of the on-orbit test method for the emissivity of the spaceborne microwave radiometer antenna in an embodiment of the present invention. Detailed implementation manners

[0026] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several deformations and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0027] As Figure 1 shown, one aspect of the present invention provides an on-orbit test system for the emissivity of the spaceborne microwave radiometer antenna. The test system includes a radiation brightness temperature receiving module, a radiation brightness temperature calibration module, an on-orbit positioning module, a maneuvering module, and a data application module. The radiation brightness temperature receiving module is used to receive the first radiation brightness temperature signal of the observation target, convert the first radiation brightness temperature signal into a voltage signal, and transmit the voltage signal to the radiation brightness temperature calibration module. The radiation brightness temperature calibration module is used to obtain the radiation brightness temperature of the calibration source, simultaneously receive the voltage signal transmitted back by the radiation brightness temperature receiving module, convert the voltage signal into a second radiation brightness temperature signal in combination with the two-point calibration equation of the spaceborne microwave radiometer, and transmit the second radiation brightness temperature signal to the data application module. The on-orbit positioning module is used to obtain the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer, and transmit the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer to the data application module. The maneuvering module analyzes the on-orbit maneuvering range of the spaceborne microwave radiometer according to the observation requirements, and controls the spaceborne microwave radiometer to perform on-orbit maneuvers to adjust the flight attitude of the spaceborne microwave radiometer. The data application module determines the attributes of the observation target according to the on-orbit position of the spaceborne microwave radiometer and the flight attitude information of the spaceborne microwave radiometer, and calculates the on-orbit emissivity of the antenna reflector in combination with the temperature information of the spaceborne microwave radiometer and the second radiation brightness temperature signal.

[0028] The present invention provides an on-orbit test system for the emissivity of a satellite-borne microwave radiometer reflector antenna, which is mainly used to calculate the antenna emissivity parameters of the satellite-borne microwave radiometer on-orbit, thereby solving the problem that the antenna emissivity and its on-orbit time-varying conditions are difficult to measure accurately. During the on-orbit flight of the satellite, the satellite flight attitude is adjusted so that the antenna of the satellite-borne microwave radiometer observes the cold sky, and the cold sky brightness temperature observation value obtained by the microwave radiometer is compared with the cold sky brightness temperature theoretical value calculated by the radiation transmission model to calculate the emissivity of the antenna. The accurate calibration of the antenna emissivity can eliminate the influence of the antenna self-radiation on the calibration accuracy of the microwave radiometer system, which is conducive to evaluating the actual on-orbit calibration effect of the radiometer, and can improve the system calibration scheme in a targeted manner, thereby improving the radiation measurement accuracy of the satellite-borne microwave radiometer. Based on the traditional two-point calibration method, the present invention provides an on-orbit test system and method for the emissivity of the reflector antenna of a satellite-borne microwave radiometer. By adjusting the attitude of the satellite during on-orbit flight, the antenna reflector is aligned with the cold sky observation, thereby accurately calculating the on-orbit emissivity of the antenna.

[0029] Furthermore, the calculation method of the on-orbit emissivity of the satellite-borne microwave radiometer antenna of the present invention is scientific, reasonable, and easy to implement, and can solve the problem that the emissivity parameters of the antenna reflector surface and its on-orbit time-varying characteristics are difficult to measure accurately, thereby effectively and accurately obtaining the on-orbit antenna emissivity of the satellite-borne microwave imager. Accurately calculating the on-orbit emissivity of the satellite-borne microwave radiometer antenna reflector is conducive to evaluating the actual on-orbit calibration effect of the instrument, and can improve the system calibration scheme in a targeted manner, thereby improving the radiation measurement results of the satellite-borne microwave imager.

[0030] In some embodiments, the radiation brightness temperature receiving module includes an antenna subsystem and a receiver subsystem; the antenna subsystem is used to reflect the radiation brightness temperature TB of the observed target to the receiver subsystem, and the radiation brightness temperature reflected and transmitted by the antenna subsystem is expressed as TA=TB·(1-ε)+Tphy·ε, where Tphy is the physical temperature of the antenna reflection surface, TB represents the actual radiation brightness temperature of the observed target, and ε is the emissivity of the antenna reflection surface; the receiver subsystem is used to receive the radiation brightness temperature TA reflected and transmitted by the antenna subsystem, and convert the observed brightness temperature into a voltage signal.

[0031] In these embodiments, the radiation brightness temperature receiving module includes an antenna subsystem and a radiation receiver subsystem. The antenna reflector performs rotation scanning, and the observation field of one rotation includes three observation areas: the observation area, the cold calibration area, and the hot calibration area. The antenna observes the actual brightness temperature T B The radiation receiver receives the radiation brightness temperature signal T from the antenna. A =T B ·(1-ε)+T phy ·ε, after frequency selection, amplification, detection and other signal processing measures, the brightness temperature signal T AConverted to voltage signal V A Output.

[0032] In some embodiments, the radiometric brightness temperature calibration module includes a calibration source subsystem and a calibration calculation subsystem; the calibration source subsystem includes a cold calibration source structure and a hot calibration source structure, and the calibration source subsystem is configured to provide a calibration brightness temperature signal for the radiometric brightness temperature receiving module and the calibration calculation subsystem; the calibration calculation subsystem obtains the voltage signal transmitted from the receiver subsystem, and converts the voltage value into a brightness temperature value TA = G(VA - VH) + TH using the two-point calibration formula, where TA represents the observed target radiometric brightness temperature after two-point calibration, VA represents the output voltage when the antenna observes the target, the system gain G = (TH - TC)) / (VH - VC), TH represents the hot source brightness temperature, VH represents the output voltage when the antenna observes the hot calibration source, TC represents the cold source radiometric brightness temperature, and VC represents the output voltage when the antenna observes the cold calibration source.

[0033] In these embodiments, the radiometric brightness temperature calibration module includes a calibration source subsystem and a calibration calculation subsystem. The calibration source subsystem includes a cold calibration source structure and a hot calibration source structure, where the hot calibration source provides a stable and known thermal radiometric brightness temperature T H , and the cold calibration source is the cosmic background brightness temperature (cold sky brightness temperature), providing a stable and known cold radiometric brightness temperature T C . The calibration calculation subsystem first receives the voltage data from the radiometric receiver, and then calculates the microwave radiometer system gain G = (T C - T H ) / (V H - V C ) according to the corresponding voltages V H and V C when observing the hot and cold calibration sources, and finally calibrates the voltage data into brightness temperature data T A = G(V A - V H ) + T H according to the two-point calibration equation.

[0034] In some embodiments, the maneuver module is configured to analyze the on-orbit maneuver angle requirements of the spaceborne microwave radiometer, design the maneuver plan of the spaceborne microwave radiometer, and control the spaceborne microwave radiometer to perform on-orbit maneuvers according to the analysis results of the on-orbit maneuver angles.

[0035] In these embodiments, the maneuver module includes an orbit simulation subsystem and a maneuver implementation subsystem. The orbit simulation subsystem uses the orbit parameters of the spaceborne microwave radiometer to establish an orbit simulation model of the microwave radiometer, and determines a suitable range of maneuver angles [θ1, θ2] such as roll angle, pitch angle or yaw angle in combination with the observation area target requirements for calculating the on-orbit emissivity. The maneuver implementation subsystem directly controls the microwave radiometer to perform on-orbit maneuvers and obtains the observed target radiation information required for maneuver calibration.

[0036] In some embodiments, the on-orbit positioning module includes an on-orbit positioning subsystem and an attitude control subsystem; the on-orbit positioning subsystem is configured to receive satellite navigation positioning signals and obtain the payload position and the observed pixel position; the attitude control subsystem is configured to receive the on-orbit flight attitude information of the spaceborne microwave radiometer, and the on-orbit flight attitude information includes the roll angle, pitch angle, and yaw angle of the spaceborne microwave radiometer.

[0037] In these embodiments, the on-orbit positioning module includes an on-orbit positioning subsystem and an attitude control subsystem. The on-orbit positioning subsystem receives satellite navigation positioning signals and obtains the payload position and the observed pixel position. The attitude control subsystem receives the on-orbit flight attitude information of the radiometer, including the roll angle, pitch angle, and yaw angle of the microwave radiometer.

[0038] In some embodiments, the data application module is configured to receive the on-orbit position of the spaceborne microwave radiometer and the on-orbit flight attitude information of the spaceborne microwave radiometer transmitted by the on-orbit positioning module, obtain the observed target attributes of the spaceborne microwave radiometer, and the data application module uses the ARTS (Atmospheric Radiative Transfer Simulator) model to simulate the observed brightness temperature of the microwave radiometer. This model is a radiative transfer model applicable to the millimeter wave and sub-millimeter wave frequency bands. In the case of inputting the atmospheric profile and ground-related parameters, the atmospheric radiative transfer process can be simulated, and at the same time, the simulation of the observed brightness temperature of the radiometer can be combined with parameters such as the passband response and antenna pattern of the microwave radiometer. Therefore, it is applicable to calculating the spaceborne microwave radiometer and calculating the simulated brightness temperature of the observed target in combination with the radiative transfer model. At the same time, the data application module will receive the observed brightness temperature TA transmitted by the radiometric brightness temperature calibration module, and calculate the on-orbit emissivity parameter of the antenna reflector surface according to the antenna radiometric brightness temperature formula

[0039] The name of the radiative transfer model is The Atmospheric Radiative Transfer Simulator (abbreviated as ARTS), which is a radiative transfer model applicable to the millimeter wave and sub-millimeter wave frequency bands. In the case of inputting the atmospheric profile information and ground-related parameters, the atmospheric radiative transfer process can be simulated, and at the same time, the simulation of the observed brightness temperature of the radiometer can be combined with parameters such as the passband response and antenna pattern of the microwave radiometer.

[0040] In these embodiments, the data application module includes a brightness temperature simulation subsystem and an emissivity calculation subsystem. The brightness temperature simulation subsystem determines the basic attributes of the observed target according to the radiometer position and attitude information transmitted back by the on-orbit positioning module, and combines the radiative transfer model to obtain the simulated brightness temperature of the observed target.​ The emissivity calculation subsystem calculates the on-orbit emissivity parameter of the antenna reflector surface by comparing and analyzing the simulated brightness temperature of the observation target and the observed brightness temperature T of the observation target transmitted back by the radiation brightness temperature calibration module A The difference between them is calculated to obtain the on-orbit emissivity parameter of the antenna reflector surface where the physical temperature T of the antenna phy can be directly obtained through the temperature sensor on the antenna reflector surface.

[0041] Figure 2 This is the flowchart of the on-orbit test method for the emissivity of the spaceborne microwave radiometer antenna in an embodiment of the present invention.

[0042] As Figure 2 shown, the second aspect of the present invention provides an on-orbit test method for the emissivity of a spaceborne microwave radiometer antenna, which is used for the on-orbit test system for the emissivity of a spaceborne microwave radiometer antenna provided in the first aspect of the present invention. The on-orbit test method for the emissivity of a spaceborne microwave radiometer antenna includes the following steps:

[0043] S1. Determine the observation target of the spaceborne microwave radiometer antenna, establish an orbital simulation model for the on-orbit operation of the spaceborne microwave radiometer, and simulate and analyze to obtain the maneuvering angle range [θ1, θ2]. Within the maneuvering angle range, the observation target of the spaceborne microwave radiometer meets the requirements;

[0044] S2. When the spaceborne microwave radiometer observes the cold source, obtain the first output voltage VC and the radiation brightness temperature TC of the cold source. When the spaceborne microwave radiometer observes the heat source, obtain the second output voltage VH and the radiation brightness temperature TH of the heat source. Use the radiation brightness temperature TC of the cold source, the radiation brightness temperature TH of the heat source, the first output voltage VC, and the second output voltage VH to calculate the system calibration gain G of the spaceborne microwave radiometer:

[0045] G = (TH - TC) / (VH - VC);

[0046] S3. According to the system calibration gain G, calibrate the observation voltage VA of the spaceborne microwave radiometer to the brightness temperature, and the brightness temperature observation value TA is:

[0047] TA = G(VA - VH) + TH;

[0048] S4. Use the radiation transfer model to obtain the simulated brightness temperature values of the antenna observation target within the maneuvering angle range [θ1, θ2]

[0049] S5. Use the temperature sensor to obtain the physical temperature Tphy of the antenna reflector surface, and calculate the emissivity parameter of the antenna reflector surface by comparing the brightness temperature observation value TA and the simulated brightness temperature value The emissivity parameter of the antenna reflector surface is calculated as:

[0050]

[0051] The present invention provides an on-orbit test method for the emissivity of the reflector antenna of a spaceborne microwave radiometer. This method is mainly used to calculate the antenna emissivity parameters of the spaceborne microwave radiometer in orbit, so as to solve the problem that it is difficult to accurately measure the antenna emissivity and its time-varying situation in orbit. During the on-orbit flight of the satellite, by adjusting the flight attitude of the satellite, the antenna of the spaceborne microwave radiometer observes the cold sky. By comparing the observed value of the cold sky brightness temperature obtained by the microwave radiometer with the theoretical value of the cold sky brightness temperature calculated by the radiative transfer model, the emissivity of the antenna is calculated. The accurate calibration of the antenna emissivity can eliminate the influence of the antenna self-radiation on the calibration accuracy of the microwave radiometer system, which is beneficial to evaluating the actual on-orbit calibration effect of the radiometer, can specifically improve the system calibration scheme, and further improve the radiation measurement accuracy of the spaceborne microwave radiometer. Based on the traditional two-point calibration method, the present invention provides an on-orbit test system and method for the emissivity of the reflector antenna of a spaceborne microwave radiometer. By adjusting the attitude of the satellite during on-orbit flight, the antenna reflector is aligned with the cold sky for observation, and then the on-orbit emissivity of the antenna is accurately calculated.

[0052] Furthermore, the calculation method for the on-orbit emissivity of the antenna of the spaceborne microwave radiometer of the present invention is scientific, reasonable and easy to implement. It can solve the problem that it is difficult to accurately measure the emissivity parameters of the antenna reflector and its time-varying characteristics in orbit, so as to effectively and accurately obtain the on-orbit antenna emissivity of the spaceborne microwave imager. Accurately calculating the on-orbit emissivity of the antenna reflector of the spaceborne microwave radiometer is beneficial to evaluating the actual on-orbit calibration effect of the instrument, can specifically improve the system calibration scheme, and further improve the radiation measurement result of the spaceborne microwave imager.

[0053] In a specific embodiment of the present invention, as Figure 1 shown, the implementation process of an on-orbit test system and method for the emissivity of the reflector antenna of a spaceborne microwave radiometer provided by the present invention:

[0054] Step 1: The observation target of the antenna of the spaceborne microwave radiometer is the cold sky. An on-orbit observation model of the spaceborne microwave radiometer is established using orbit simulation software. By using the pitch maneuver mode, the antenna observation area is aligned with the cold sky area, and the maneuver angle range is θ1 = 33.19° and θ2 = 37.76°.

[0055] Step 2: Taking the cold sky as the cold source T C = 2.7K, and its corresponding output voltage V C = -0.798V, and taking the blackbody as the heat source with a radiation brightness temperature T H = 298K, and its corresponding output voltage V H = 5.971V, calculate the calibration gain G of the microwave radiometer system as G = (T H - T C ) / (V H - VC ) = 43.626 K / y.

[0056] Step 3: The output voltage V of the spaceborne microwave radiometer antenna observing the cold sky A，space = -0.546 V. After calibration, the brightness temperature T of the cold sky observed by the antenna is obtained A，space = G(V A，space - V H ) + T H = 13.689 K.

[0057] Step 4: The antenna observes the target as the cold sky, and its simulated brightness temperature value

[0058] Step 5: The physical temperature T of the antenna reflector is directly obtained by using a temperature sensor phy = 300 K. Comparing the observed value T A，space with the simulated value The emissivity parameter of the reflector antenna is calculated

[0059] The above is only the specific embodiment of the present invention and is not used to limit the present invention. It only further details the purpose, technical solution and beneficial effects of the present invention.

[0060] Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0061] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An on-orbit test system for the emissivity of a spaceborne microwave radiometer antenna, characterized in that The test system includes: An on-orbit positioning module, which is used for on-orbit positioning and attitude control, receives satellite navigation and positioning signals, obtains the position information of the spaceborne microwave radiometer, including the payload position and the observation pixel position, and at the same time obtains the flight attitude information of the spaceborne microwave radiometer, including the roll angle, pitch angle, and yaw angle; A maneuvering module, which is used to analyze the on-orbit maneuvering angle requirements of the spaceborne microwave radiometer, design the maneuvering scheme of the spaceborne microwave radiometer, control the spaceborne microwave radiometer to perform on-orbit maneuvers according to the maneuvering scheme, and maneuver the roll angle, pitch angle, and yaw angle to the target angles; A radiance temperature receiving module, which is used to receive the first radiance temperature signal of the observation target and the calibration radiance temperature signals of the cold and hot calibration sources provided by the radiance temperature calibration module by using the antenna subsystem, and transmit the first radiance temperature signal and the calibration radiance temperature signals to the receiver subsystem, and use the receiver subsystem to convert the first radiance temperature signal and the calibration radiance temperature signals into voltage signals respectively; A radiance temperature calibration module, which is used to provide the calibration radiance temperature signals of the cold and hot calibration sources for the radiance temperature receiving module, receive the voltage signals transmitted back by the radiance temperature receiving module for observing the calibration radiance temperature signals, obtain a two-point calibration equation, and use the calibration equation to convert the voltage signal corresponding to the first radiance temperature signal into a second radiance temperature signal; A data application module, which is used to determine whether the observation target is stable according to the on-orbit position and attitude information of the spaceborne microwave radiometer. If it is stable, calculate the simulated radiance temperature signal of the observation target through the radiative transfer model, and calculate the on-orbit emissivity of the antenna reflector surface in combination with the temperature information of the antenna subsystem of the spaceborne microwave radiometer, the second radiance temperature signal, and the simulated radiance temperature signal; The radiance temperature calibration module includes a calibration source subsystem and a calibration calculation subsystem; The calibration source subsystem is used to provide calibration radiance temperature signals for the radiance temperature receiving module and the calibration calculation subsystem. The calibration source subsystem includes a cold calibration source structure and a hot calibration source structure; The calibration calculation subsystem obtains the voltage signals transmitted from the receiver subsystem, and converts the voltage values into radiance temperature values by using the two-point calibration formula. The detailed content of the two-point calibration formula is as follows: TA = G(VA - VH) + TH, where TA represents the radiance temperature of the observation target after two-point calibration, VA represents the output voltage of the antenna when observing the target, G represents the system gain, and the calculation formula of G is as follows: G = (TH - TC) ⁄ (VH - VC), where TH represents the hot source radiance temperature, VH represents the output voltage of the antenna when observing the hot calibration source, TC represents the cold source radiance temperature, and VC represents the output voltage of the antenna when observing the cold calibration source; The data application module is configured to receive the on-orbit position of the spaceborne microwave radiometer and the on-orbit flight attitude information of the spaceborne microwave radiometer transmitted by the on-orbit positioning module, obtain the observed target attributes of the spaceborne microwave radiometer. The data application module uses a radiative transfer model to simulate the observed brightness temperature of the microwave radiometer, which is used to calculate the spaceborne microwave radiometer. Combining with the radiative transfer model, the simulated brightness temperature value of the observed target is calculated. At the same time, the data application module receives the observed brightness temperature TA transmitted by the radiative brightness temperature calibration module, and calculates the on-orbit emissivity parameter ε=(TA - ) ⁄ (Tphy - ) of the antenna reflector surface according to the antenna radiative brightness temperature formula TA=(1 - ε)• + ε•Tphy.

2. The on-orbit test system for the emissivity of the spaceborne microwave radiometer antenna according to claim 1, wherein the radiative brightness temperature receiving module includes an antenna subsystem and a receiver subsystem; the antenna subsystem is configured to reflect the radiative brightness temperature of the observed target into the receiver subsystem, and the radiative brightness temperature reflected and transmitted by the antenna subsystem is expressed as: wherein, TA is the radiative brightness temperature reflected and transmitted by the antenna subsystem, TB represents the actual radiative brightness temperature of the observed target, Tphy is the physical temperature of the antenna reflector surface, and ε is the emissivity of the antenna reflector surface; the receiver subsystem is configured to receive the radiative brightness temperature reflected and transmitted by the antenna subsystem and convert the observed brightness temperature into the voltage signal.

3. An on-orbit test method for the emissivity of a spaceborne microwave radiometer antenna, characterized in that, For the on-orbit test system for the emissivity of the spaceborne microwave radiometer antenna according to any one of claims 1 to 2, the test method includes the following steps: S1, determine the observed target of the spaceborne microwave radiometer antenna, establish an orbital simulation model for the on-orbit operation of the spaceborne microwave radiometer, and simulate and analyze to obtain the maneuvering angle range [θ1, θ2]. Within the maneuvering angle range, the observed target of the spaceborne microwave radiometer meets the requirements; S2, when the spaceborne microwave radiometer observes the cold source, obtain the first output voltage VC and the radiative brightness temperature TC of the cold source. When the spaceborne microwave radiometer observes the heat source, obtain the second output voltage VH and the radiative brightness temperature TH of the heat source. Use the radiative brightness temperature TC of the cold source, the radiative brightness temperature TH of the heat source, the first output voltage VC and the second output voltage VH to calculate the system calibration gain G of the spaceborne microwave radiometer: G=(TH - TC) ⁄ (VH - VC); S3, according to the system calibration gain G, calibrate the observed voltage VA of the spaceborne microwave radiometer as the brightness temperature, and the brightness temperature observed value TA is: TA = G(VA - VH) + TH; S4, use the radiative transfer model to obtain the simulated brightness temperature value of the antenna observed target within the maneuvering angle range [θ1, θ2]; S5, use a temperature sensor to obtain the physical temperature Tphy of the antenna reflector surface. By comparing the brightness temperature observed value TA and the simulated brightness temperature value, calculate the emissivity parameter of the antenna reflector surface: ε=(TA - ) ⁄ (Tphy - ).

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