CN113075252A - Method and system for measuring passive millimeter wave radiation characteristic quantity and classification method - Google Patents
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- 230000005855 radiation Effects 0.000 title claims abstract description 38
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- 238000005259 measurement Methods 0.000 claims abstract description 28
- 230000010287 polarization Effects 0.000 claims abstract description 26
- 230000035945 sensitivity Effects 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 4
- 238000001514 detection method Methods 0.000 abstract description 4
- 238000007689 inspection Methods 0.000 abstract description 3
- 239000007788 liquid Substances 0.000 abstract description 2
- 238000007405 data analysis Methods 0.000 abstract 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000005286 illumination Methods 0.000 description 3
- 239000013077 target material Substances 0.000 description 3
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Abstract
The invention discloses a method and a system for measuring radiation characteristic quantity of passive millimeter waves and a classification method, and belongs to the technical field of passive microwave remote sensing and detection. The method comprises the following steps: the measured horizontal polarization brightness temperature and vertical polarization brightness temperature of the target are utilized, millimeter wave radiation characteristic quantity RDoP is obtained through data analysis, meanwhile, a formula for calculating other radiation characteristic quantities through the RDoP is given, and classification of the target can be achieved through the characteristic quantities. The millimeter wave radiation characteristic quantity of the target can be obtained without measuring the physical temperature of the target; undesirable factors such as radiometer measurement noise, calibration error, atmospheric radiation and attenuation cannot cause measurement distortion of the method. The technical scheme of the invention can be used for recognizing and classifying ground object targets in remote sensing, recognizing and classifying various hidden objects in human body security inspection, detecting liquid and the like.
Description
Technical Field
The invention belongs to the technical field of passive microwave remote sensing and detection, and particularly relates to a method and a system for measuring passive millimeter wave radiation characteristic quantity and a classification method.
Background
All objects with physical temperatures above 0K spontaneously radiate electromagnetic energy into space in the form of electromagnetic waves, a phenomenon known as thermal radiation. Millimeter wave radiometers achieve remote sensing and detection of targets by receiving thermal radiation signals in the millimeter wave frequency band, and this technology is generally called passive millimeter wave radiometry. Millimeter wave radiometry has the advantages of all-time, quasi-all-weather operation, invisibility and penetration to a certain extent through the atmosphere, clothes, smoke, etc., and thus has been applied to fields such as remote sensing, security inspection, target detection, astronomy, etc.
The brightness temperature observed by the radiometer is related to a plurality of factors such as the environment brightness temperature, the target temperature and the like, so that the radiometer cannot be directly applied to the classification and identification of the target. In the existing method, characteristic quantities are calculated through the horizontal polarization brightness temperature, the vertical polarization brightness temperature and the physical temperature of a target, and then the characteristic quantities are utilized to realize the classification and identification of the target. Common feature quantities are PDoP (passive clearance of Polarization), LPR (linear Polarization ratio), LPDR (linear Polarization Difference ratio), etc., wherein LPR and LPDR have been used for identification of metal targets and PDoP has been used for classification of land objects (e.g., cement, land, water surface, etc.). However, in most applications, particularly remote sensing applications, there is some difficulty in obtaining the physical temperature of the target. In addition, calibration errors and atmospheric radiation and attenuation can cause measurement distortion of the target brightness temperature, resulting in calculation errors of the characteristic quantity. Therefore, how to achieve accurate measurement of the feature quantity in real applications has yet to be studied.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method and a system for measuring the radiation characteristic quantity of passive millimeter waves and a classification method, aiming at solving the problems of more measurement quantity and easy influence of non-ideality in the current millimeter wave radiation characteristic quantity measurement technology and breaking the limitation of measuring the millimeter wave radiation characteristic quantity in the real environment.
In order to achieve the above object, an aspect of the present invention provides a method for measuring a characteristic quantity of passive millimeter wave radiation, including the following steps:
(1) for a period of time T ∈ [0, T]Keeping the physical temperature of the measurement target constant, and controlling the illumination source or utilizing the change of natural scene to make the ambient light temperature T incident to the target surface at the incident angle thetaincIn a changed state. Measuring time [0, T ] at an angle of incidence [ theta ] with a millimeter wave radiometer]Inner target horizontal polarization bright temperature Th(T) and vertical polarization luminance temperature Tv(t)。
(2) Using formulas
An estimate of RDoP is obtained, where cov denotes the calculated covariance, TE(T) and TR(t) emitted light temperature and reflected light temperature, respectively, CNA noise correction term is measured for the radiometer.
(3) Conversion from RDoP to other common feature quantities can be achieved by the following formula:
PDoP=-pr,
LPER, PDoP and LPR are characteristic quantities commonly used in the field of passive millimeter wave radiation measurement, and target material classification can be realized based on the characteristic quantities.
Further, in the step (2), TE(T) and TRThe formula for calculation of (t) is:
wherein p iseFor the feature quantity edop (empirical dop), it can take any value between (0,1) without affecting the estimation of RDoP.
Further, in the step (2), CNThe calculation formula of (2) is as follows:
wherein,for the sensitivity of the horizontally polarized channel of the radiometer,is the sensitivity of the radiometer to the vertically polarized channel.
Preferably, p iseTypically 0.5.
In another aspect, the present invention provides a system for measuring a characteristic amount of passive millimeter wave radiation, including:
a bright temperature acquisition module for T ∈ [0, T ] in a period of time]Keeping the physical temperature of the measurement target constant, and controlling the illumination source or utilizing the change of natural scene to make the ambient light temperature T incident to the target surface at the incident angle thetaincIn a changed state. Measuring time [0, T ] at an angle of incidence [ theta ] with a millimeter wave radiometer]Inner target horizontal polarization bright temperature Th(T) and vertical polarization luminance temperature Tv(t);
A first characteristic amount calculation module for calculating a first characteristic amount according to the horizontally polarized light temperature Th(T) and vertical polarization luminance temperature Tv(t) calculating the characteristic quantity of the radiation of the millimeter waveAn estimate of RDoP is obtained, where cov denotes the calculated covariance, TE(T) and TR(t) emitted light temperature and reflected light temperature, respectively, CNMeasuring a noise correction term for the radiometer;
a second feature quantity calculation module for calculating a second feature quantity based on the feature quantity prCalculating the characteristic quantities LPDR, PDOP and LPR, the conversion from RDoP to other common characteristic quantities can be realized:
PDoP=-pr,
LPER, PDoP and LPR are characteristic quantities commonly used in the field of passive millimeter wave radiation measurement, and target material classification can be realized based on the characteristic quantities.
Further, TE(T) and TRThe formula for calculation of (t) is:
wherein p iseFor the feature quantity edop (empirical dop), it can take any value between (0,1) without affecting the estimation of RDoP.
Further, CNThe calculation formula of (2) is as follows:
wherein,for the sensitivity of the horizontally polarized channel of the radiometer,is the sensitivity of the radiometer to the vertically polarized channel.
Preferably, p iseTypically 0.5.
The invention further provides a target classification method based on millimeter wave polarization radiation measurement, and the material classification of the target is realized according to the characteristic quantity obtained by the measurement method of the passive millimeter wave radiation characteristic quantity.
Compared with the prior art, the technical scheme of the invention has the innovation points that: the millimeter wave radiation characteristic quantity of the target can be obtained without measuring the physical temperature of the target; undesirable factors such as radiometer measurement noise, calibration error, atmospheric radiation and attenuation cannot cause measurement distortion of the method. The technical scheme of the invention can be used for recognizing and classifying ground object targets in remote sensing, recognizing and classifying various hidden objects in human body security inspection, detecting liquid and the like.
Drawings
FIG. 1 is a schematic view of the measurement of the present invention;
FIG. 2 is a schematic illustration of measurements in an embodiment of the invention;
FIG. 3 is a graph showing the variation of ambient light temperature over a measurement period;
FIG. 4 is a graph of measured horizontal polarization bright temperature over a measurement period;
fig. 5 is a graph of the measured vertical polarization luminance temperature over the measurement period.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a method for measuring radiation characteristic quantity of passive millimeter waves, which comprises the following steps:
(1) as shown in FIG. 1, over a period of time T ∈ [0, T ∈]Keeping the physical temperature of the measurement target constant, and controlling the illumination source or utilizing the change of natural scene to make the ambient light temperature T incident to the target surface at the incident angle thetaincIn a changed state. Measuring time [0, T ] at an angle of incidence [ theta ] with a millimeter wave radiometer]Inner target horizontal polarization bright temperature Th(T) and vertical polarization luminance temperature Tv(t)。
(2) Using formulas
An estimate of RDoP is obtained, where cov denotes the calculated covariance, TE(T) and TR(t) emitted light temperature and reflected light temperature, respectively, CNA noise correction term is measured for the radiometer.
(3) Conversion from RDoP to other common feature quantities can be achieved by the following formula:
PDoP=-pr,
LPER, PDoP and LPR are characteristic quantities commonly used in the field of passive millimeter wave radiation measurement, and target material classification can be realized based on the characteristic quantities.
Examples
(1) As shown in fig. 2, the radiometer observes a calm water surface at an angle of incidence of 50 °. The sun is located at the position 1 at the time 0 and at the position 3 at the time T-100 s, and therefore, the ambient light temperature T at the incident angle of 50 ° is obtainedincAt time [0,100s]The inner variation curve is shown in fig. 3, and meets the measurement requirement. Measuring time [0,100s ]]And in addition, the physical temperature of the water surface is not changed, so that the measurement requirement is met. Time [0,100s ] was measured using a radiometer]Inner target horizontal polarization bright temperature Th(T) and vertical polarization luminance temperature Tv(t), the measurement results are shown in fig. 4 and 5, respectively.
(2) The sensitivity of the horizontal polarization channel and the vertical polarization channel of the radiometer are both 1K, and the formula is used
To obtain prThe estimate of (1) is-0.385, where cov denotes the calculated covariance, TE(T) and TR(t) are each independentlyEmission bright temperature and reflection bright temperature, CNA noise correction term is measured for the radiometer.
(3) Using the formula:
PDoP=-pr,
the other characteristic quantities are calculated as follows: LPDR ═ 0.799, PDoP ═ 0.385, and LPR ═ 2.252.
Wherein, in the step (2), TE(T) and TRThe formula for calculation of (t) is:
wherein p iseFor the feature quantity edop (empirical dop), it can take any value between (0,1) without affecting the estimation of RDoP. In this example, peTake 0.5.
Wherein, in the step (2), CNThe calculation formula of (2) is as follows:
wherein,for the sensitivity of the horizontally polarized channel of the radiometer,is the sensitivity of the radiometer to the vertically polarized channel.
TABLE 1
Measurement object | pr | LPDR | PDoP | LPR |
Water (W) | -0.385 | 0.799 | 0.385 | 2.252 |
Alcohol | -0.954 | 0.024 | 0.954 | 42.48 |
Gasoline (gasoline) | -0.816 | 0.113 | 0.816 | 9.870 |
Aluminium plate | -0.001 | 499.5 | 0.001 | 1.002 |
Repeating the above steps, respectively treating gasoline, alcohol and p of aluminum platerMeasurements are made and the respective characteristic quantities LPDR, PDoP and LPR are calculated. All results are shown in table 1. As can be seen from table 1, the LPDR values of the metal target (aluminum plate) are very different from those of other targets, and thus LPDR can be used to distinguish metal-nonmetal. PDoP and LPR are different for each material, and thus PDoP and LPR can be used for classification of materials.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A method for measuring passive millimeter wave radiation characteristic quantity is characterized by comprising the following steps:
(1) for a period of time T ∈ [0, T]In the method, the ambient light temperature T incident on the target surface at the incident angle theta is controlled while keeping the physical temperature of the measurement target constantincIn the change state, the time [0, T ] is measured at the incident angle theta by a millimeter wave radiometer]Horizontally polarized light temperature T of inner targeth(T) and vertical polarization luminance temperature Tv(t);
(2) According to the horizontally polarized light temperature Th(T) and vertical polarization luminance temperature Tv(t) calculating the characteristic quantity RDoPp of millimeter wave radiationr:
Wherein cov denotes the calculation covariance, TE(T) and TR(t) emitted light temperature and reflected light temperature, respectively, CNMeasuring a noise correction term for the radiometer;
(3) according to the characteristic quantity prThe feature quantities LPDR, PDoP and LPR are calculated.
3. The method for measuring the characteristic quantity of radiation of passive millimeter waves according to claim 2, characterized in that in the step (2), CNThe calculation formula of (2) is as follows:
5. A system for measuring a characteristic amount of passive millimeter wave radiation, comprising:
a bright temperature acquisition module for T ∈ [0, T ] in a period of time]In the method, the ambient light temperature T incident on the target surface at the incident angle theta is controlled while keeping the physical temperature of the measurement target constantincIn the change state, the time [0, T ] is measured at the incident angle theta by a millimeter wave radiometer]Horizontally polarized light temperature T of inner targeth(T) and vertical polarization luminance temperature Tv(t);
A first characteristic amount calculation module for calculating a first characteristic amount according to the horizontally polarized light temperature Th(T) and vertical polarization luminance temperature Tv(t) calculating the characteristic quantity of the radiation of the millimeter waveWherein cov denotes the calculation covariance, TE(T) and TR(t) emitted light temperature and reflected light temperature, respectively, CNMeasuring a noise correction term for the radiometer;
a second feature quantity calculation module for calculating a second feature quantity based on the feature quantity prThe feature quantities LPDR, PDoP and LPR are calculated.
7. The system for measuring a characteristic quantity of passive millimeter wave radiation according to claim 5, wherein CNThe calculation formula of (2) is as follows:
9. A target classification method based on millimeter wave polarization radiation measurement is characterized in that the characteristic quantity obtained by the method for measuring the passive millimeter wave radiation characteristic quantity according to any one of claims 1 to 4 realizes the material classification of the target.
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