A method and system for measuring complex dielectric constant based on millimeter wave radiation

Abstract

The present invention discloses a method and system for measuring the complex dielectric constant based on millimeter-wave radiation, belonging to the field of passive microwave remote sensing and detection technology. The method comprises utilizing the horizontally polarized brightness temperature and vertically polarized brightness temperature of a target measured at multiple incident angles, analyzing the data to obtain the PDoP at each incident angle, and finally inverting the complex dielectric constant based on the PDoP measurement values. The present invention can obtain the complex dielectric constant of a target without measuring the target's physical temperature and ambient brightness temperature; non-ideal factors such as radiometer measurement noise, calibration error, atmospheric radiation, and attenuation do not cause measurement distortion in this method.

Description

Technical Field

[0001] The present invention belongs to the technical field of passive microwave remote sensing and detection, and more specifically, relates to a method and system for measuring complex dielectric constant based on millimeter wave radiation. Background Art

[0002] All objects with a physical temperature above 0K spontaneously radiate electromagnetic energy into space in the form of electromagnetic waves. This phenomenon is called thermal radiation. Millimeter-wave radiometers achieve remote sensing and detection of targets by receiving thermal radiation signals in the millimeter-wave frequency band. This technology is often referred to as passive millimeter-wave radiometry. Millimeter-wave radiometry offers the advantages of 24 / 7 and near-all-weather operation, concealment, and the ability to penetrate the atmosphere, clothing, and smoke to a certain extent. Therefore, it has been applied to fields such as remote sensing, security inspection, target detection, and astronomy. The complex dielectric constant is an important material characteristic of a target. Obtaining this through millimeter-wave radiometry is crucial for target classification and even identification.

[0003] In the field of millimeter-wave radiation, existing methods measure the target's horizontally polarized brightness temperature, vertically polarized brightness temperature, ambient brightness temperature, and physical temperature, and then invert the complex dielectric constant based on the millimeter-wave radiation model. However, in most applications, especially remote sensing, obtaining the target's physical temperature and ambient brightness temperature presents challenges. Furthermore, calibration errors and atmospheric radiation and attenuation can distort the measurement of the target's brightness temperature, making it impossible to accurately invert the complex dielectric constant. Therefore, how to accurately and conveniently measure the complex dielectric constant in real-world applications remains to be explored. Summary of the Invention

[0004] In response to the shortcomings of the prior art, the present invention aims to provide a method for measuring the complex dielectric constant based on millimeter-wave radiation. This method utilizes the horizontally and vertically polarized brightness temperatures of a target measured at multiple incident angles to determine the PDoP at each incident angle through data analysis. Finally, the complex dielectric constant is inverted based on the PDoP measurements. This invention aims to address the current issues of complex dielectric constant measurement in millimeter-wave radiation, such as the large number of measurements and susceptibility to imperfections, thereby removing the limitations of measuring complex dielectric constant in real-world environments.

[0005] To achieve the above object, the present invention provides a method for measuring complex dielectric constant based on millimeter wave radiation, comprising the following steps:

[0006] (1) In a period of time t∈[0,T], the physical temperature of the measurement target is kept constant, and the ambient brightness temperature T incident on the target surface at an incident angle θ1 is controlled by controlling the illumination source or utilizing the changes in the natural scene. inc The millimeter wave radiometer is used to measure the target horizontal polarization brightness temperature T within the time [0, T] at an incident angle θ1. h(t) and vertical polarization brightness temperature T v (t).

[0007] (2) Using the target horizontal polarization brightness temperature T measured in step (1) h (t) and vertical polarization brightness temperature T v (t) Calculate the target’s millimeter wave radiation characteristic quantity PDoP value.

[0008] (3) At the incident angles θ2,…,θ N Repeat steps (1) to (2) to finally obtain the incident angles θ1, θ2, ..., θ N The millimeter wave radiation characteristic quantity PDoP value on the N .

[0009] (4) According to the measured incident angles θ1, θ2,…, θ N Upper PDoP measurement values ​​PDoP1, PDoP2,…, PDoP N , solve for the target complex dielectric constant.

[0010] Furthermore, in step (2), the calculation formula of PDoP is:

[0011]

[0012] Among them, cov means calculating covariance, T E (t) and T R (t) are the emission brightness temperature and the reflection brightness temperature, T E (t) and T R The calculation formula for (t) points is:

[0013]

[0014]

[0015] Among them, p e is the transmit polarization degree, which can take any value between (0,1) without affecting the estimation of RDoP. N is the radiometer measurement noise correction term, C N The calculation formula is:

[0016]

[0017] Among them, p e The value of p in formula (2) e The value of remains consistent. is the sensitivity of the radiometer horizontal polarization channel, is the sensitivity of the vertical polarization channel of the radiometer.

[0018] Preferably, p e Generally, it is taken as 0.5.

[0019] Furthermore, in step (3), the selected incident angles include at least 60°, and the total number of incident angles N is ≥ 3.

[0020] Furthermore, in step (4), the system of equations is solved:

[0021]

[0022] Get an estimate of the target complex permittivity ∈.

[0023] The present invention also provides a complex dielectric constant measurement system based on millimeter wave radiation, comprising: a computer-readable storage medium and a processor;

[0024] The computer-readable storage medium is used to store executable instructions;

[0025] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the above-mentioned complex dielectric constant measurement method based on millimeter wave radiation.

[0026] Compared to existing technologies, the above technical solution conceived by the present invention can obtain the target's complex dielectric constant without measuring the target's physical temperature or ambient brightness temperature. Imperfect factors such as radiometer measurement noise, calibration errors, atmospheric radiation, and attenuation do not cause measurement distortion in this method. The above technical solution conceived by the present invention can be used to measure the complex dielectric constant of various materials in the millimeter wave frequency band. The complex dielectric constant measurements can be used to analyze liquid composition, identify hidden objects, and more. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a measurement schematic diagram of the present invention;

[0028] Figure 2 is the change curve of ambient brightness temperature during the measurement period;

[0029] Figure 3 is the horizontal polarization brightness temperature measured during the measurement period;

[0030] Figure 4 is the vertical polarization brightness temperature measured during the measurement period. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0032] (1) Figure 1 As shown in the figure, the radiometer observes the calm water surface at an incident angle of 30°. The output brightness temperature of the variable noise source (i.e., the ambient brightness temperature T inc ), T inc The changing curve within the time [0,300ms] is as follows Figure 2 As shown, the measurement requirements are met. During the measurement time [0,300ms], the physical temperature of the water surface does not change, which meets the measurement requirements. The target horizontal polarization brightness temperature T is measured by the radiometer within the time [0,300ms]. h (t) and vertical polarization brightness temperature T v (t), the measurement results are as follows Figure 3 、 Figure 4 shown.

[0033] (2) The sensitivity of the horizontal polarization channel and the vertical polarization channel of the radiometer are both 1K, and the estimated PDoP is 0.1280.

[0034] (3) Repeat steps (1) to (2) at incident angles of 45°, 60°, and 75°, and finally obtain the PDoP measurement values ​​at incident angles of 30°, 45°, 60°, and 75°, which are PDoP1 = 0.1280, PDoP2 = 0.3050, PDoP3 = 0.5793, and PDoP4 = 0.8510, respectively.

[0035] (4) According to the measured incident angles θ1, θ2,…, θ N Upper PDoP measurement values ​​PDoP1, PDoP2,…, PDoP N , solve the system of equations:

[0036]

[0037] The target complex dielectric constant is obtained as ∈=7.6-13.1i.

[0038] In step (2), the calculation formula of PDoP is:

[0039]

[0040] Where cov means calculating covariance, T E (t) and T R(t) are the emission brightness temperature and the reflection brightness temperature, T E (t) and T R The calculation formula for (t) points is:

[0041]

[0042]

[0043] Among them, p e is the emission polarization degree, which is 0.5. N is the radiometer measurement noise correction term, C N The calculation formula is:

[0044]

[0045] Among them, p e The value of p in formula (2) e The value of remains consistent. is the sensitivity of the radiometer horizontal polarization channel, is the sensitivity of the vertical polarization channel of the radiometer.

[0046] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring complex dielectric constant based on millimeter wave radiation, characterized in that: The following steps are involved: (1) In a period of time t∈[0,T], the physical temperature of the measurement target is kept constant, and the ambient brightness temperature T incident on the target surface at an incident angle θ1 is controlled. inc In a changing state, the horizontal polarization brightness temperature T of the target within time [0, T] is measured using a millimeter-wave radiometer at an incident angle θ1. h (t) and vertical polarization brightness temperature T v (t); (2) According to the horizontal polarization brightness temperature T h (t) and vertical polarization brightness temperature T v (t) Calculate the target's millimeter wave radiation characteristic quantity PDoP value; (3) At the incident angles θ2,…,θ N Repeat steps (1) to (2) to finally obtain the incident angles θ1, θ2, ..., θ N The millimeter wave radiation characteristic quantity PDoP value on the N ; Wherein, N≥3; the selected incident angle includes 60°; (4) According to the characteristic quantities PDoP1, PDoP2,…, PDoP N Calculate the complex permittivity of the target; an estimate of the complex permittivity ∈ is obtained by solving the following system of equations: Where, i=1,2,···N.

2. The method for measuring complex dielectric constant according to claim 1, wherein: The calculation formula for the PDoP value is: Among them, cov means calculating covariance, T E (t) and T R (t) are the emission brightness temperature and the reflection brightness temperature, C N Correction term for radiometer measurement noise.

3. The method for measuring complex dielectric constant according to claim 2, wherein: T E (t) and T R The calculation formulas for (t) are: Among them, p e Any value between (0,1).

4. The method for measuring complex dielectric constant according to claim 2, wherein: C N The calculation formula is: in, is the sensitivity of the millimeter wave radiometer horizontal polarization channel, is the sensitivity of the millimeter wave radiometer vertical polarization channel.

5. A complex dielectric constant measurement system based on millimeter wave radiation, characterized in that: include: Computer-readable storage medium and processor; The computer-readable storage medium is used to store executable instructions; The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the complex dielectric constant measurement method based on millimeter wave radiation according to any one of claims 1 to 4.

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