Scene microwave radiance measurement method based on inverted image characteristics

Abstract

The invention discloses a scene microwave radiance measurement method based on an inverted image, and the method comprises the steps: placing an observation target on a flat surface, receiving microwaves which are emitted at the same emission angle # imgabs0 #, come from the observation target and are reflected by cold air through the observation target through a microwave radiometer, and obtaining a first output voltage; the observation target is placed on a flat surface, the microwave radiometer receives microwaves which are emitted at the same emergence angle # imgabs1 #, come from the observation target, are reflected by the observation target after cold air is reflected by the reference wall and are reflected by the reference wall through the observation target, and second output voltage is obtained; the microwave radiometer receives the microwaves which are reflected by the reference wall and are emitted by the cold air at the emitting angle # imgabs2 #, and third output voltage is obtained; the microwave radiometer receives the microwaves of the cold air emitted at the emission angle # imgabs3 #, and fourth output voltage is obtained; and calculating the radiance of the observation target at the exit angle # imgabs4 #. The rapid radiance measurement method can calculate the microwave radiance of the observation target without absolute calibration, and has the advantages of low hardware requirement, simple process operation and the like.

Description

Technical Field

[0001] The present invention belongs to the fields of passive microwave remote sensing and passive microwave radiation detection, and particularly relates to a method for measuring microwave radiation of a scene based on reflection characteristics. Background Art

[0002] In the field of passive microwave remote sensing of the Earth, accurately measuring the microwave emissivity of natural scenes, such as soil moisture, sea surface salinity, etc., is one of the important tasks, which is an important theoretical basis for studying the brightness temperature inversion models of various important physical parameters of the Earth. In the field of passive microwave radiation detection, accurately measuring the microwave emissivity of targets and scenes is also one of the important tasks, which is an important basis for realizing target detection by using the differences in microwave radiation characteristics between targets and scenes. Accurately knowing the microwave emissivity of targets and scenes is an important basis for carrying out research work such as feasibility analysis of passive microwave radiation detection of various types of targets, system scheme demonstration, target recognition and classification in various application scenarios. Currently, in the research fields of passive microwave remote sensing and passive microwave radiation detection, measuring the microwave emissivity of a scene or a target is achieved by using a precisely calibrated microwave radiometer. A microwave radiometer is a passive receiver with high sensitivity and high stability. After receiving the microwave thermal radiation signal of a target or a scene through an antenna, it goes through processes such as radio frequency amplification, radio frequency filtering, down-conversion, intermediate frequency amplification, intermediate frequency filtering, and direct current detection of the microwave radiometer, and finally outputs a voltage signal. A microwave radiometer is a linear system, and the intensity of the microwave thermal radiation signal of the natural scene or target received by the receiver is proportional to the voltage signal output by the radiometer. By constructing the linear relationship between the input and output of the microwave radiometer and determining the calibration equation, and then according to the measured output voltage and the calibration equation, the absolute brightness temperature of the target or scene is obtained, and then the emissivity of the target is calculated according to the physical temperature of the target or scene. The calibration of a microwave radiometer requires both the provision of calibration equipment and the implementation of the calibration process, and the whole process is relatively complex. The calibration equipment includes a high-temperature calibration source and a low-temperature calibration source. The high-temperature calibration source mainly includes a constant-temperature absorbing material, and the low-temperature calibration source includes cold air or an absorbing material immersed in liquid nitrogen. The calibration process requires observing the high-temperature calibration source and the low-temperature calibration source with known brightness temperatures at the antenna port of the microwave radiometer, recording the output voltage values, and then determining the calibration equation according to the physical temperatures and output voltage values of the recorded calibration sources. The above process is customarily called external calibration. It is not difficult to know that the calibration equipment and calibration process required for the traditional external calibration of a microwave radiometer are relatively complex. In order to facilitate calibration at any time and simplify the calibration process, internal calibration is proposed as another calibration scheme, but internal calibration also requires additional calibration equipment and cannot calibrate the antenna aperture surface, so the calibration accuracy is also greatly limited to a certain extent.

[0003] In summary, the current process of using a microwave radiometer to measure the microwave emissivity of a target or scene is complex and requires additional calibration equipment. Therefore, there is an urgent need for a method with a low hardware threshold that can achieve simple and rapid measurement of microwave emissivity. Summary of the Invention

[0004] Aiming at the deficiencies of the existing internal calibration method and external calibration method in terms of numerous hardware and complex processes, the present invention proposes a rapid measurement method for the microwave emissivity of a target based on reflection characteristics.

[0005] The technical solution provided by the present invention is as follows: A method for measuring the microwave emissivity of a target based on reflection includes the following steps: Construct a first scene, place the observation target on a flat surface, set the incident angle of the microwave radiometer, and receive, through the microwave radiometer, the microwave electromagnetic signals from the observation target and the cold air reflected by the observation target to obtain a first output voltage; Construct a second scene, place the observation target on a flat surface, set the incident angle of the microwave radiometer, set a reference wall, and receive, through the microwave radiometer, the microwave electromagnetic signals that are reflected by the reference wall and then by the observation target and the signals that are reflected by the reference wall through the observation target to obtain a second output voltage; Construct a third scene, set a reference wall, set the incident angle of the microwave radiometer, and receive, through the microwave radiometer, the microwave electromagnetic signals reflected by the reference wall from the cold air to obtain a third output voltage; Construct a fourth scene, set the incident angle of the microwave radiometer, and directly receive, through the microwave radiometer, the microwave electromagnetic signals of the cold air to obtain a fourth output voltage; Calculate the incident angle of the observation target on the microwave radiometer at the time of emissivity;

[0006] In a possible implementation manner, at least one specular reflection plane is provided on the observation target and the reference wall.

[0007] In a possible implementation manner, the observation target is a reflective surface with a certain area.

[0008] In a possible implementation manner, the material of the reference wall is a non-metallic material.

[0009] Furthermore, within the range of optional materials for the reference wall, the higher the microwave emissivity of the reference wall, the higher the calculation accuracy of the emissivity.

[0010] In a possible implementation manner, the calculation method of the first output voltage is as follows:

[0011] In the formula, is the first output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the first scenario θ at which the radiation rate of the observation target is measured, is the physical temperature of the observation target, is the incident angle of the microwave radiometer in the first scenario θ at which the downwelling brightness temperature of the cold sky is measured, is the offset of the microwave radiometer.

[0012] In a possible implementation manner, the calculation method of the second output voltage is as follows:

[0013] In the formula, is the second output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer θ at which the radiation rate of the observation target is measured, is the physical temperature of the observation target, is the incident angle of the microwave radiometer in the second scenario θ at which the radiation rate of the reference wall is measured, is the physical temperature of the reference wall, is the incident angle of the microwave radiometer in the second scenario θ at which the downwelling brightness temperature of the cold sky is measured, is the offset of the microwave radiometer.

[0014] In a possible implementation manner, the calculation method of the third output voltage is as follows:

[0015] In the formula, is the third output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the third scenario θ at which the radiation rate of the reference wall is measured, is the physical temperature of the reference wall, is the incident angle of the microwave radiometer in the third scenarioθ The brightness temperature of the cold air descending at is the offset of the microwave radiometer.

[0016] In a possible implementation, the calculation method of the fourth output voltage is as follows:

[0017] In the formula, is the fourth output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the fourth scenario θ when the brightness temperature of the cold air descending, is the offset of the microwave radiometer.

[0018] In a possible implementation, the method for calculating the emissivity of the observation target at the emission angle is as follows:

[0019] Among them, is the emissivity of the observation target at the incident angle θ of the microwave radiometer, , , and are the first, second, third, and fourth output voltage values respectively.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The method of the present invention can realize the rapid measurement of the microwave emissivity of a flat target by observing four different scenarios. The only external auxiliary materials required are a flat reference wall, such as a metal plate and an absorbing material, which greatly reduces the equipment threshold and improves the measurement efficiency; The method of the present invention can not only measure the emissivity at a single incident angle, but also quickly measure the emissivities at multiple different incident angles; The method of the present invention does not require calibration of the radiometer, has simple requirements for the site, and the operation process is convenient and fast; The present invention can also re-evaluate the microwave emissivity of the target for the historical microwave radiation image data containing the information of four observation scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the first scenario in the method of the present invention; Figure 2 is a schematic diagram of the second scenario in the method of the present invention; Figure 3Schematic diagram of the third scenario in the method of the present invention; Figure 4 Schematic diagram of the fourth scenario in the method of the present invention; Figures 1-4 Wherein: 100 - microwave radiometer, 200 - observation target, 300 - reference wall; Figure 5 Microwave radiation brightness temperature map of the computational simulation in this embodiment; Figure 6 Inversion result in this embodiment; Figure 7 Error analysis result in this embodiment. Specific implementation manner

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] As Figures 1-4 shown, the present invention provides a method for measuring the microwave emissivity of a target based on reflection characteristics, including the following steps: S100, as Figure 1 shown, build the first scenario, place the observation target on a flat surface, set the incident angle of the microwave radiometer, and receive the microwave electromagnetic signals from the observation target and the cold air reflected by the observation target through the microwave radiometer to obtain the first output voltage.

[0024] In a possible implementation manner, the observation target has at least one specular reflection plane.

[0025] It should be noted that the incident angle of the microwave radiometer is the incident angle of the microwave electromagnetic signal on the last reflection plane or the incident angle equivalent to specular reflection when directly incident, as Figures 1-3 shown.

[0026] In a possible implementation manner, the observation target is a reflective surface with a certain area.

[0027] In a possible implementation manner, the calculation method of the first output voltage is:

[0028] In the formula, is the first output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, For the incident angle of the microwave radiometer in the first scenario θ when the observed target emissivity is the physical temperature of the observed target is For the incident angle of the microwave radiometer in the first scenario θ when the downwelling brightness temperature of the cold sky is the offset of the microwave radiometer is

[0029] It should be noted that the microwave radiometer is a highly stable and sensitive linear receiver, and its output voltage and the input brightness temperature satisfy a linear relationship where represents the gain of the microwave radiometer, represents the offset of the microwave radiometer. Generally, it is considered that the gain and offset of the microwave radiometer remain unchanged during the entire measurement process. The microwave radiometer observes a flat target in an open scenario

[0030] S200, as Figure 2 shown, construct the second scenario, place the observed target on a flat surface, set the incident angle of the microwave radiometer, set the reference wall, and the microwave radiometer receives the microwave electromagnetic signals reflected by the cold sky through the reference wall and then reflected by the observed target and the signals reflected by the reference wall through the observed target to obtain the second output voltage

[0031] In a possible implementation, the material of the reference wall is a non-metallic material, such as wood board, foam, absorbing material, etc

[0032] Furthermore, the reference wall has at least one specular reflection plane

[0033] Furthermore, within the range of optional materials, the higher the microwave emissivity of the reference wall, the higher the calculation accuracy of the emissivity

[0034] In a possible implementation, the calculation method of the second output voltage is as follows

[0035] In the formula is the second output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the observed target emissivity at the incident angle θ of the microwave radiometer, is the physical temperature of the observed target, is the incident angle of the microwave radiometer in the second scenario θ when the reference wall emissivity is the physical temperature of the reference wall is The incident angle of the microwave radiometer under the second scenario θ is the downwelling brightness temperature of the cold air, and is the offset of the microwave radiometer.

[0036] S300, as Figure 3 shown, set up the third scenario, set the reference wall, set the incident angle of the microwave radiometer, and the microwave radiometer receives the microwave electromagnetic signal reflected by the cold air from the reference wall to obtain the third output voltage.

[0037] In a possible implementation, the calculation method of the third output voltage is:

[0038] In the formula, is the third output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the emissivity of the reference wall at the incident angle θ of the microwave radiometer under the third scenario, is the physical temperature of the reference wall, is the downwelling brightness temperature of the cold air at the incident angle θ of the microwave radiometer under the third scenario, and is the offset of the microwave radiometer.

[0039] S400, as Figure 4 shown, set up the fourth scenario, set the incident angle of the microwave radiometer, and the microwave radiometer directly receives the microwave electromagnetic signal of the cold air to obtain the fourth output voltage.

[0040] In a possible implementation, the calculation method of the fourth output voltage is:

[0041] In the formula, is the fourth output voltage at the incident angle θ of the microwave radiometer, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer under the fourth scenario θ and is the downwelling brightness temperature of the cold air, and is the offset of the microwave radiometer.

[0042] S500, calculate the emissivity of the observation target at the emission angle

[0043] In a possible implementation, the method for calculating the emissivity of the observation target at the emission angle is: ​

[0044] Among them, is the emissivity of the observation target at the incident angle of the microwave radiometer θ at time , , and are respectively the first, second, third, and fourth output voltage values at the incident angle θ of the microwave radiometer.

[0045] In the four scenarios, the following relationships exist: ; , ; and are converted through a complementary relationship; and are converted through a complementary relationship.

[0046] It should be noted that the calculation accuracy of the emissivity is affected by the microwave emissivity of the reference wall. The calculation accuracy of the emissivity is as follows:

[0047] Among them, represents the emissivity calculation accuracy at the incident angle θ of the microwave radiometer, , , and respectively represent the standard deviations of the voltage fluctuations output by the microwave radiometer in the four scenarios of the first scenario, the second scenario, the third scenario, and the fourth scenario.

[0048] The calculation formula for the standard deviation of the output voltage fluctuation is as follows:

[0049] In the formula, represents the antenna temperature, represents the equivalent noise temperature of the receiver, represents the equivalent bandwidth of the system, represents the integration time.

[0050] The following is further described in conjunction with specific embodiments.

[0051] Taking the concrete ground as the observation target and the reference wall as the concrete wall, the above method is used for testing. Among them, the same kind of concrete is used for both, and its dielectric constant is , where j represents the imaginary number.

[0052] Figure 5 It shows the microwave radiation brightness temperature map with a microwave radiation operating frequency of 94 GHz obtained by calculation and simulation. Figure 5 Among them, the 4 black rectangular frames are the microwave radiation rates of each step obtained by using the method described in this embodiment.

[0053] Figure 6 It is the inversion result of the application example in the present invention.

[0054] This embodiment is Figure 5 The microwave radiation rates obtained by using this microwave radiation rate measurement method corresponding to 4 scenarios. Among them, the red star dotted line is the microwave radiation rate value inverted by using the method described in this embodiment, and the black circular dotted line is the original ideal microwave radiation rate value. The microwave radiation rate value inverted in the figure is very close to the original ideal microwave radiation rate value.

[0055] Figure 7 It is the error analysis result of this embodiment, that is Figure 7 the relative error between the inverted radiation rate and the ideal radiation rate in it. The relative error calculation formula is (the difference between the ideal radiation rate and the inverted radiation rate) divided by the inverted radiation rate multiplied by 100%. From Figure 7 it can be seen that the relative error is less than 1% when the incident angle is less than 70°, and the relative error does not exceed 5% when the incident angle is greater than 70°. The calculation results show that the microwave radiation rate measurement method proposed in this embodiment is feasible and has good measurement accuracy.

[0056] It should be understood that the parts not elaborated in detail in this specification all belong to the prior art.

[0057] It should be understood that the above description of the preferred embodiment is relatively detailed, and it should not be considered as a limitation to the protection scope of the present invention patent. Under the inspiration of the present invention, those of ordinary skill in the art can also make substitutions or deformations without departing from the protection scope defined by the claims of the present invention, and all fall within the protection scope of the present invention. The scope of protection claimed by the present invention shall be subject to the appended claims.

Claims

1. A method for measuring target microwave emissivity based on reflection, characterized in that: The following steps are involved: A first scene is constructed, the observation target is placed on a flat surface, the incident angle of the microwave radiometer is set, and the microwave electromagnetic signal from the observation target and the cold air reflected by the observation target is received by the microwave radiometer to obtain a first output voltage; Build a second scene, place the observation target on a flat surface, set the incident angle of the microwave radiometer, set a reference wall, and the microwave radiometer receives the microwave electromagnetic signal reflected by the cold air, the reference wall, the observation target, and the reference wall, and obtains a second output voltage; Build a third scene, set a reference wall, set the incident angle of the microwave radiometer, and the microwave radiometer receives the microwave electromagnetic signal reflected by the reference wall from the cold air to obtain a third output voltage; Build the fourth scene, set the incident angle of the microwave radiometer, and the microwave radiometer directly receives the microwave electromagnetic signal of the cold air to obtain the fourth output voltage; Calculate the incident angle of the observed target on the microwave radiometer The radiation rate at Among them, the incident angles of the microwave radiometers in the four scenes are the same; the incident angle of the microwave radiometer is the incident angle of the microwave electromagnetic signal on the last reflecting surface or the incident angle equivalent to the mirror reflection when directly incident.

2. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The observation target and the reference wall have at least one mirror reflection plane.

3. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The observation target is a reflective surface with a certain area.

4. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The reference wall is made of non-metallic material.

5. The method for measuring target microwave emissivity based on reflection according to claim 4, characterized in that: The reference wall is within the range of optional materials, and the higher the microwave emissivity thereof is, the higher the calculation accuracy of the emissivity is.

6. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The calculation method of the first output voltage is: In the formula, is the incident angle on the microwave radiometer θ The first output voltage at G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the first scenario θ The observed target radiance at time , is the physical temperature of the observed target, is the incident angle of the microwave radiometer in the first scenario θ The cold sky downward brightness temperature at that time, is the offset of the microwave radiometer.

7. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The second output voltage is calculated as follows: In the formula, is the incident angle on the microwave radiometer θ The second output voltage at G is the gain of the microwave radiometer, is the incident angle on the microwave radiometer θ The observed target radiance at time , is the physical temperature of the observed target, is the incident angle of the microwave radiometer in the second scenario θ The reference wall emissivity at is the physical temperature of the reference wall, is the incident angle of the microwave radiometer in the second scenario θ The cold sky downward brightness temperature at that time, is the offset of the microwave radiometer.

8. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The calculation method of the third output voltage is: In the formula, is the incident angle on the microwave radiometer θ The third output voltage at G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the third scenario θ The reference wall emissivity at is the physical temperature of the reference wall, is the incident angle of the microwave radiometer in the third scenario θ The cold sky downward brightness temperature at that time, is the offset of the microwave radiometer.

9. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The calculation method of the fourth output voltage is: In the formula, is the incident angle on the microwave radiometer θ The fourth output voltage at G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the fourth scenario θ The cold sky downward brightness temperature at that time, is the offset of the microwave radiometer.

10. The method for measuring target microwave emissivity based on reflection according to claim 1, characterized in that: The calculation of the incident angle of the observed target on the microwave radiometer θ The method for the radiance at time is: in, is the incident angle of the observed target on the microwave radiometer θ The radiation rate at , , and are the incident angles of the microwave radiometer θ The first, second, third and fourth output voltage values ​​at .

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