A method for measuring scene microwave emissivity based on reflection characteristics

Abstract

The present invention discloses a method for measuring microwave emissivity of a scene based on reflection, comprising: placing an observation target on a flat surface, receiving microwaves emitted from the observation target and cold air at the same emission angle #imgabs0#, reflecting from the observation target, and obtaining a first output voltage; placing the observation target on a flat surface, receiving microwaves emitted from the observation target and cold air at the same emission angle #imgabs1#, reflecting from a reference wall, then reflecting from the observation target, and then reflecting from the reference wall, and obtaining a second output voltage; receiving microwaves emitted from the cold air at an emission angle #imgabs2#, reflecting from the reference wall, and obtaining a third output voltage; receiving microwaves emitted from the cold air at an emission angle #imgabs3#, obtaining a fourth output voltage; and calculating the emissivity of the observation target at an emission angle #imgabs4#. This rapid emissivity measurement method can calculate the microwave emissivity of the observation target without absolute calibration, and has the advantages of low hardware requirements and simple process operations.

Description

Technical Field

[0001] The invention belongs to the field of passive microwave remote sensing and passive detection of microwave radiation, and in particular relates to a method for measuring scene microwave radiation based on reflection features. 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 and sea surface salinity, is a key task. It is an important theoretical basis for studying brightness temperature inversion models for various important Earth physical parameters. In the field of passive microwave radiation detection, accurately measuring the microwave emissivity of targets and scenes is also a key task. It is an important foundation for realizing target detection by utilizing the differences in microwave radiation characteristics between targets and scenes. Accurately knowing the microwave emissivity of targets and scenes is an important foundation for conducting research on feasibility analysis, system solution demonstration, target identification and classification, and other research in various application scenarios for passive microwave radiation detection of various types of targets.

[0003] Currently, in the field of passive microwave remote sensing and passive microwave radiation detection, measuring the microwave emissivity of a scene or target is accomplished using a precisely calibrated microwave radiometer. A microwave radiometer is a highly sensitive and stable passive receiver. After receiving the microwave thermal radiation signal from a target or scene through an antenna, the signal undergoes radio frequency amplification, filtering, down-conversion, intermediate frequency amplification, filtering, and DC detection, ultimately outputting a voltage signal. A microwave radiometer is a linear system. The intensity of the microwave thermal radiation signal from the natural scene or target at the receiver is proportional to the voltage signal output by the radiometer. A linear relationship between the microwave radiometer input and output is established, and a calibration equation is determined. The absolute brightness temperature of the target or scene is then calculated based on the measured output voltage and the calibration equation. The target's emissivity is then calculated based on the target's physical temperature. Calibration of a microwave radiometer requires both calibration equipment and a relatively complex process. 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 an absorbing material in cold air or immersed in liquid nitrogen. The calibration process requires that the high-temperature calibration source and the low-temperature calibration source, whose brightness temperature is known, be observed at the antenna port of the microwave radiometer, and the output voltage value be recorded. The calibration equation is then determined based on the recorded physical temperature and output voltage value of the calibration source. The above process is usually called external calibration. It is not difficult to understand that the calibration equipment and calibration process required for the external calibration of traditional microwave radiometers are relatively complex. In order to facilitate calibration at any time and simplify the calibration process, internal calibration has been proposed as another calibration solution. However, internal calibration also requires additional calibration equipment and cannot calibrate the antenna aperture. Therefore, the calibration accuracy is also greatly limited to a certain extent.

[0004] In summary, the current microwave radiometer process for measuring the microwave emissivity of a target or scene is relatively complex and requires additional calibration equipment. Therefore, there is an urgent need for a method that can achieve simple and rapid microwave emissivity measurement with low hardware requirements. Summary of the Invention

[0005] In view of the shortcomings of existing internal calibration methods and external calibration methods in terms of numerous hardware and complex processes, the present invention proposes a method for quickly measuring the emissivity of target microwave radiation based on reflection characteristics.

[0006] The technical solutions provided by the present invention are as follows:

[0007] A method for measuring target microwave emissivity based on reflection, comprising the following steps:

[0008] Build a first scenario, place the observation target on a flat surface, set the incident angle of the microwave radiometer, receive microwave electromagnetic signals from the observation target and the cold air reflected by the observation target through the microwave radiometer, and obtain a first output voltage;

[0009] A second scene is set up, where the observation target is placed on a flat surface, the incident angle of the microwave radiometer is set, and a reference wall is set up. The microwave radiometer receives microwave electromagnetic signals from the observation target, the cold air, which is reflected by the reference wall, then reflected by the observation target, and then reflected by the reference wall, and obtains a second output voltage.

[0010] Build a third scene, set up a reference wall, set the incident angle of the microwave radiometer, and the microwave radiometer receives microwave electromagnetic signals from the reference wall and the cold air reflected by the reference wall to obtain a third output voltage;

[0011] Build the fourth scenario, set the incident angle of the microwave radiometer, and the microwave radiometer directly receives the microwave electromagnetic signal from the cold air to obtain the fourth output voltage;

[0012] Calculate the incident angle of the observed target on the microwave radiometer The emissivity at ;

[0013] 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 mirror reflection when directly incident.

[0014] In a possible implementation manner, the observation target has at least one specular reflection plane and the reference wall has at least one specular reflection plane.

[0015] In a possible implementation manner, the observation target is a reflective surface with a certain area.

[0016] In one possible implementation, the reference wall is made of a non-metallic material.

[0017] Furthermore, within the range of optional materials for the reference wall, the higher the microwave emissivity thereof, the higher the calculation accuracy of the emissivity.

[0018] In one possible implementation, the first output voltage is calculated as follows:

[0019]

[0020] In the formula, in the formula, is the incident angle on the microwave radiometer θ The first output voltage when G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the first scenario θ The observed target radiation rate at is the physical temperature of the observed target, is the incident angle of the microwave radiometer in the first scenario θ The cold sky descending brightness temperature at that time, is the offset of the microwave radiometer.

[0021] In one possible implementation, the second output voltage is calculated as follows:

[0022]

[0023] In the formula, in the formula, is the incident angle on the microwave radiometer θ The second output voltage when G is the gain of the microwave radiometer, is the incident angle on the microwave radiometer θ The observed target radiation rate at 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 descending brightness temperature at that time, is the offset of the microwave radiometer.

[0024] In one possible implementation, the third output voltage is calculated as follows:

[0025]

[0026] Where, is the incident angle on the microwave radiometer θ The third output voltage whenG 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 descending brightness temperature at that time, is the offset of the microwave radiometer.

[0027] In one possible implementation, the fourth output voltage is calculated as follows:

[0028]

[0029] Where, is the incident angle on the microwave radiometer θ The fourth output voltage, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the fourth scenario θ The cold sky descending brightness temperature at that time, is the offset of the microwave radiometer.

[0030] In a possible implementation, the calculation observation target is at the exit angle The method for the emissivity is:

[0031]

[0032] in, The incident angle of the observed target on the microwave radiometer θ The radiation rate, 、 、 and These are the first, second, third and fourth output voltage values ​​respectively.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The method of the present invention can quickly measure the microwave emissivity of a flat target by observing four different scenes. 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 measurement efficiency.

[0035] The method of the present invention can not only measure the radiance at a single incident angle, but also quickly measure the radiance at multiple different incident angles;

[0036] The method of the present invention does not require calibration of the radiometer, requires a simple site, and has a convenient and fast operation process;

[0037] The present invention can also re-estimate the target microwave emissivity for the historical microwave radiation image data containing information of four observation scenes. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the first scenario in the method of the present invention;

[0039] Figure 2 This is a schematic diagram of the second scenario in the method of the present invention;

[0040] Figure 3 This is a schematic diagram of the third scenario in the method of the present invention;

[0041] Figure 4 This is a schematic diagram of the fourth scenario in the method of the present invention;

[0042] Figure 1-4 Middle: 100-microwave radiometer, 200-observation target, 300-reference wall;

[0043] Figure 5 is the microwave radiation brightness temperature map calculated and simulated in this embodiment;

[0044] Figure 6 is the inversion result in this embodiment;

[0045] Figure 7 This is the error analysis result of this embodiment. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] like Figures 1-4 As shown, the present invention provides a method for measuring target microwave emissivity based on reflection characteristics, comprising the following steps:

[0048] S100, such as Figure 1 As shown, 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.

[0049] In a possible implementation manner, the observation target has at least one mirror reflection plane.

[0050] It should be noted that 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, such as Figure 1-3 shown.

[0051] In a possible implementation manner, the observation target is a reflective surface with a certain area.

[0052] In one possible implementation, the first output voltage is calculated as follows:

[0053]

[0054] Where, is the incident angle on the microwave radiometer θ The first output voltage when G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the first scenario θ The observed target radiation rate at is the physical temperature of the observed target, is the incident angle of the microwave radiometer in the first scenario θ The cold sky descending brightness temperature at that time, is the offset of the microwave radiometer.

[0055] It should be noted that the microwave radiometer is a high-stability and high-sensitivity linear receiver, and its output voltage With input brightness temperature Satisfy the linear relationship ,in represents the gain of the microwave radiometer, Represents the offset of the microwave radiometer. It is generally assumed that the gain and offset of a microwave radiometer remain constant throughout the measurement process. A microwave radiometer observes a flat target in an open field.

[0056] S200, such as Figure 2 As shown, a second scene is built, the observation target is placed on a flat surface, the incident angle of the microwave radiometer is set, and a reference wall is set. The microwave radiometer receives microwave electromagnetic signals from the observation target, the cold air reflected by the reference wall, and then reflected by the observation target and the reference wall, and obtains a second output voltage.

[0057] In one possible implementation, the reference wall is made of non-metallic material, such as wood, foam, or absorbing material.

[0058] Furthermore, the reference wall has at least one mirror reflection plane.

[0059] Furthermore, within the range of optional materials for the reference wall, the higher the microwave emissivity thereof, the higher the calculation accuracy of the emissivity.

[0060] In one possible implementation, the second output voltage is calculated as follows:

[0061]

[0062] Where, is the incident angle on the microwave radiometer θ The second output voltage when G is the gain of the microwave radiometer, is the incident angle on the microwave radiometer θ The observed target radiation rate at 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 descending brightness temperature at that time, is the offset of the microwave radiometer.

[0063] S300, such as Figure 3 As shown, a third scene is built, a reference wall is set, and the incident angle of the microwave radiometer is set. The microwave radiometer receives microwave electromagnetic signals from the reference wall and the cold air reflected by the reference wall to obtain a third output voltage.

[0064] In one possible implementation, the third output voltage is calculated as follows:

[0065]

[0066] Where, is the incident angle on the microwave radiometer θ The third output voltage when 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 descending brightness temperature at that time, is the offset of the microwave radiometer.

[0067] S400, such as Figure 4 As shown, a fourth scenario is constructed, and the incident angle of the microwave radiometer is set. The microwave radiometer directly receives the microwave electromagnetic signal from the cold air to obtain a fourth output voltage.

[0068] In one possible implementation, the fourth output voltage is calculated as follows:

[0069]

[0070] Where, is the incident angle on the microwave radiometer θ The fourth output voltage, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the fourth scenario θ The cold sky descending brightness temperature at that time, is the offset of the microwave radiometer.

[0071] S500, calculate the observation target at the exit angle The radiation rate at .

[0072] In a possible implementation, the calculation observation target is at the exit angle The method for the emissivity is:

[0073]

[0074] in, The incident angle of the observed target on the microwave radiometer θ The radiation rate, 、 、 and are the incident angles of the microwave radiometer θ The first, second, third and fourth output voltage values ​​when

[0075] In the four scenarios, the following relationships exist:

[0076] ;

[0077] , ; and Transformation through reciprocal relations;

[0078] and Transformation through complementary relationships.

[0079] 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:

[0080]

[0081] in, Indicates the incident angle on the microwave radiometer θ The accuracy of the radiation rate calculation is 、 、 and Respectively represent the standard deviation of voltage fluctuation of the microwave radiometer output in the first, second, third and fourth scenarios.

[0082] Output voltage fluctuation standard deviation The calculation formula is as follows:

[0083]

[0084] Where, represents the antenna temperature, represents the equivalent noise temperature of the receiver, represents the system equivalent bandwidth, Indicates the integration time.

[0085] The following is a further explanation with reference to specific embodiments.

[0086] The above method was used to test the concrete floor as the observation target and the concrete wall as the reference wall. The same concrete was used for both, and its dielectric constant is , j represents an imaginary number.

[0087] Figure 5 The figure shows the brightness temperature diagram of microwave radiation calculated and simulated when the microwave radiation operating frequency is 94G. Figure 5 In FIG. 4 , the four black rectangular boxes represent the microwave radiation rates of the respective steps calculated using the method described in this embodiment.

[0088] Figure 6 This is the inversion result of the application example in this invention.

[0089] This embodiment is Figure 5 The microwave emissivity obtained using this microwave emissivity measurement method in four scenarios, where the red star-shaped dashed line is the microwave emissivity value inverted using the method described in this embodiment, and the black circular dashed line is the original ideal microwave emissivity value. The microwave emissivity value inverted in the figure is very close to the original ideal microwave emissivity value.

[0090] Figure 7 is the error analysis result of this embodiment, that is, Figure 7 The relative error between the inverted emissivity and the ideal emissivity is calculated by subtracting the ideal emissivity from the inverted emissivity divided by the inverted emissivity times 100%. Figure 7It can be seen that the relative error is less than 1% when the incident angle is lower than 70°, and the relative error does not exceed 5% when the incident angle is higher than 70°. The calculation results show that the microwave emissivity measurement method proposed in this embodiment is feasible and has good measurement accuracy.

[0091] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0092] It should be understood that the above description of the preferred embodiment is relatively detailed and cannot be regarded as limiting the scope of protection of the patent of the present invention. Under the guidance of the present invention, ordinary technicians in this field can also make substitutions or modifications without departing from the scope of protection of the claims of the present invention, which all fall within the scope of protection of the present invention. The scope of protection requested by the present invention shall be based on the attached claims.

Claims

1. A method for measuring target microwave emissivity based on reflection, characterized in that: The following steps are involved: Build a first scenario, place the observation target on a flat surface, set the incident angle of the microwave radiometer, receive microwave electromagnetic signals from the observation target and the cold air reflected by the observation target through the microwave radiometer, and obtain a first output voltage; A second scene is set up, where the observation target is placed on a flat surface, the incident angle of the microwave radiometer is set, and a reference wall is set up. The microwave radiometer receives microwave electromagnetic signals from the observation target, the cold air, which is reflected by the reference wall, then reflected by the observation target, and then reflected by the reference wall, and obtains a second output voltage. Build a third scene, set up a reference wall, set the incident angle of the microwave radiometer, and the microwave radiometer receives microwave electromagnetic signals from the reference wall and the cold air reflected by the reference wall to obtain a third output voltage; Build the fourth scenario, set the incident angle of the microwave radiometer, and the microwave radiometer directly receives the microwave electromagnetic signal from the cold air to obtain the fourth output voltage; Calculate the incident angle of the observed target on the microwave radiometer The radiation rate when the calculated observation target is at the incident angle of the microwave radiometer θ The method of the emissivity when is: in, is the incident angle of the observed target on the microwave radiometer θ The radiation rate, 、 、 and are the incident angles of the microwave radiometer θ The first, second, third and fourth output voltage values ​​when ; 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 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 has at least one specular reflection plane and the reference wall has at least one specular 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. The higher the microwave emissivity of the reference wall 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 first output voltage is calculated as follows: Where, is the incident angle on the microwave radiometer θ The first output voltage when G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the first scenario θ The observed target radiation rate at is the physical temperature of the observed target, is the incident angle of the microwave radiometer in the first scenario θ The cold sky descending 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: Where, is the incident angle on the microwave radiometer θ The second output voltage when G is the gain of the microwave radiometer, is the incident angle on the microwave radiometer θ The observed target radiation rate at 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 descending 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 third output voltage is calculated as follows: Where, is the incident angle on the microwave radiometer θ The third output voltage when 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 descending 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 fourth output voltage is calculated as follows: Where, is the incident angle on the microwave radiometer θ The fourth output voltage, G is the gain of the microwave radiometer, is the incident angle of the microwave radiometer in the fourth scenario θ The cold sky descending brightness temperature at that time, is the offset of the microwave radiometer.

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