CN115128564A - Method and device for polarization calibration of lunar orbit synthetic aperture radar - Google Patents
Method and device for polarization calibration of lunar orbit synthetic aperture radar Download PDFInfo
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Abstract
The embodiment of the disclosure discloses a method and a device for polarization calibration of a lunar orbit synthetic aperture radar, wherein the method comprises the following steps: acquiring a first echo signal and a second echo signal; respectively carrying out matched filtering processing on the first echo signal and the second echo signal to obtain first pulse pressure data and second pulse pressure data after pulse compression; respectively extracting a data module value maximum value point from the first pulse pressure data and the second pulse pressure data to obtain first calibration data and second calibration data; calculating to obtain a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar, and the receiving end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radar.
Description
Technical Field
The disclosure relates to the technical field of radars, in particular to a method and a device for polarization calibration of a combined radio telescope lunar orbit synthetic aperture radar.
Background
Synthetic Aperture Radar (SAR) is an active microwave imaging Radar, has the characteristics of all-weather operation and certain ground surface penetration capacity, and is an important means for earth remote sensing and planet detection. For lunar exploration, since there are some regions where direct solar radiation cannot be obtained, also called permanent shadow regions, it is impossible to effectively observe such regions using sensors such as optical sensors. Therefore, the detection using SAR has the advantage of being unique, and more lunar orbit SAR (hereinafter referred to as lunar SAR) detection tasks are proposed.
Compared with a single-polarization SAR, the full-polarization SAR can acquire polarization scattering information with richer targets by transmitting and receiving electromagnetic waves with different polarization states. To obtain accurate polarization scattering information, the polarization SAR data needs to be scaled. The polarization SAR calibration means that distortion parameters of each link of a polarization SAR system are estimated by a proper means, and data of each observation channel are corrected to an ideal condition. If the SAR data is not subjected to polarization correction, the acquired SAR data cannot correctly reflect the scattering characteristics of the target, so that the polarization SAR calibration is a premise for SAR quantification application.
Conventional polar SAR scaling schemes require either a ground-based scaling target or a distributed target (e.g., amazon tropical rainforest) with known and stable scattering performance. For the lunar SAR, a calibrator cannot be arranged on the lunar surface at present, and the characteristics of the ground object on the lunar surface belong to an object needing to be detected by a remote sensing means, so that the characteristics are not known deeply enough at present. Therefore, the SAR calibration scheme matured on the earth cannot be directly applied to the monthly SAR, and a polarization calibration scheme for the monthly SAR needs to be explored urgently.
Disclosure of Invention
The embodiment of the disclosure provides a method and a device for polarization calibration of a lunar orbit synthetic aperture radar.
In a first aspect, an embodiment of the present disclosure provides a method for polarization calibration of a lunar orbit synthetic aperture radar, including:
acquiring a first echo signal and a second echo signal, wherein the first echo signal is a signal received by a first radio telescope with a receiving function after electromagnetic waves are respectively transmitted to the earth by a lunar orbit synthetic aperture radar to be polarized and calibrated; the second echo signal is a signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits electromagnetic waves to the lunar orbit synthetic aperture radar;
respectively performing matched filtering processing on the first echo signal and the second echo signal to obtain first pulse pressure data and second pulse pressure data after pulse compression;
respectively extracting a data module value maximum value point from the first pulse pressure data and the second pulse pressure data to obtain first calibration data and second calibration data;
calculating to obtain a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar, and the receiving end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radar.
And correcting the data acquired by the lunar orbit synthetic aperture radar during normal work based on the obtained transmitting end error parameter and/or receiving end error parameter.
Further, the transmission power and the effective aperture area of the second radio telescope satisfy the following limiting conditions:
wherein the content of the first and second substances,P t is the transmission power of the second radio telescope,A t in order to receive the effective aperture area of the antenna,N= kBT s the noise power level of a receiving system consisting of a receiving antenna and a receiver;λrepresents a wavelength;rrepresenting the transmission distance of the transmitted signal to the receiving antenna; the SNR represents the signal-to-noise ratio of the desired received signal.
Further, calculating a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data, including:
calculating the transmitting end error parameter by the following formula:
wherein the content of the first and second substances,f 2 representing amplitude-phase imbalance parameters between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar;δ 3 the crosstalk amount of a horizontal transmitting channel when the lunar orbit synthetic aperture radar transmits the vertically polarized electromagnetic waves is represented;δ 4 the method comprises the steps of representing the crosstalk amount of a vertical transmitting channel when a lunar orbit synthetic aperture radar transmits horizontal polarization electromagnetic waves;M xh andM yh when the lunar orbit synthetic aperture radar transmits horizontal polarization electromagnetic waves, the horizontal polarization antenna and the vertical polarization antenna of the first radio telescope receive obtained echo signals;M xv andM yv when the lunar orbit synthetic aperture radar transmits vertical polarization electromagnetic waves, the horizontal polarization antenna and the vertical polarization antenna of the first radio telescope receive obtained echo signals;θrepresenting an included angle between the lunar orbit synthetic aperture radar and a first radio telescope polarization coordinate system; and omega represents the Faraday rotation angle caused by the earth ionosphere corresponding to the lunar orbit synthetic aperture radar.
Further, calculating a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data, including:
and calculating to obtain a receiving end error parameter by the following formula:
wherein the content of the first and second substances,f 1 representing amplitude-phase imbalance parameters between a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar;δ 1 the method comprises the steps of representing the crosstalk amount of a horizontal receiving channel when a vertical receiving channel of the lunar orbit synthetic aperture radar receives signals;δ 2 the method comprises the steps of representing the crosstalk amount of a vertical receiving channel when a horizontal receiving channel of the lunar orbit synthetic aperture radar receives signals;M hl andM vl signals received by a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar after the second radio telescope transmits the left-handed circularly polarized electromagnetic wave are respectively received;M hr andM vr respectively transmitting signals received by a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar after the second radio telescope transmits the right-hand circularly polarized electromagnetic wave;ϑis the included angle between the coordinate systems of the second radio telescope and the lunar orbit synthetic aperture radar; and omega represents the Faraday rotation angle caused by the earth ionosphere corresponding to the lunar orbit synthetic aperture radar.
Further, the step of correcting the data acquired by the lunar orbit synthetic aperture radar during normal operation based on the obtained transmitting end error parameter and/or receiving end error parameter includes:
acquiring four-channel data received by the lunar orbit synthetic aperture radar when the lunar orbit synthetic aperture radar works normally;
and obtaining corrected data by using the receiving end error parameter and the transmitting end error parameter according to the following formula:
wherein the content of the first and second substances,M hh 、M hv 、M vh andM vv is four-channel data;C hh 、C hv 、C vh andC vv representing the corrected four-channel data;f 1 representing the amplitude-phase unbalance parameter between a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar;δ 1 the method comprises the steps of representing the crosstalk amount of a horizontal receiving channel when a vertical receiving channel of the lunar orbit synthetic aperture radar receives signals;δ 2 the method comprises the steps of representing the crosstalk amount of a vertical receiving channel when a horizontal receiving channel of the lunar orbit synthetic aperture radar receives signals;f 2 representing amplitude-phase imbalance parameters between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar;δ 3 the method comprises the steps of representing the crosstalk amount of a horizontal transmitting channel when a lunar orbit synthetic aperture radar transmits vertical polarization electromagnetic waves;δ 4 and the crosstalk quantity of a vertical transmitting channel when the lunar orbit synthetic aperture radar transmits the horizontally polarized electromagnetic waves is shown.
In a second aspect, an embodiment of the present disclosure provides an apparatus for polarization calibration of a synthetic aperture radar for lunar orbit, including:
the system comprises an acquisition module and a control module, wherein the acquisition module is configured to acquire a first echo signal and a second echo signal, and the first echo signal is a signal received by a first radio telescope with a receiving function after a lunar orbit synthetic aperture radar to be polarized and calibrated respectively carries out electromagnetic wave to the first radio telescope with the receiving function; the second echo signal is a signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits electromagnetic waves to the lunar orbit synthetic aperture radar;
the processing module is configured to perform matched filtering processing on the first echo signal and the second echo signal respectively to obtain first pulse pressure data and second pulse pressure data after pulse compression;
an obtaining module configured to take out a data module maximum point from the first pulse pressure data and the second pulse pressure data respectively to obtain first calibration data and second calibration data;
a calculating module configured to calculate a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar, and the receiving end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radar.
And the correction module is configured to correct the data acquired by the lunar orbit synthetic aperture radar when the lunar orbit synthetic aperture radar works normally based on the obtained transmitting end error parameter and/or receiving end error parameter.
Further, the transmission power and the effective aperture area of the second radio telescope satisfy the following limiting conditions:
wherein the content of the first and second substances,P t is the transmission power of the second radio telescope,A t for the effective aperture area of the receiving antenna,N= kBT s a noise power level for a receiving system consisting of a receiving antenna and a receiver;λrepresents a wavelength;rrepresenting the transmission distance of the transmitted signal to the receiving antenna; the SNR represents the signal-to-noise ratio of the desired received signal.
The functions can be realized by hardware, and the functions can also be realized by executing corresponding software by hardware. The hardware or software includes one or more modules corresponding to the above-described functions.
In one possible design, the apparatus includes a memory configured to store one or more computer instructions that enable the apparatus to perform the corresponding method, and a processor configured to execute the computer instructions stored in the memory. The apparatus may also include a communication interface for the apparatus to communicate with other devices or a communication network.
In a third aspect, the disclosed embodiments provide an electronic device, comprising a memory, a processor, and a computer program stored on the memory, wherein the processor executes the computer program to implement the method of any one of the above aspects.
In a fourth aspect, the disclosed embodiments provide a computer-readable storage medium for storing computer instructions for use by any one of the above apparatuses, the computer instructions, when executed by a processor, being configured to implement the method of any one of the above aspects.
In a fifth aspect, the disclosed embodiments provide a computer program product comprising computer instructions that, when executed by a processor, implement the method of any one of the above aspects.
The technical scheme provided by the embodiment of the disclosure can have the following beneficial effects:
the scheme innovatively provides a method for polarization calibration of the lunar orbit synthetic aperture radar by combining the earth radio telescope, the requirements for on-orbit performance monitoring and correction of the lunar orbit synthetic aperture radar are met, the method can be effectively applied to actual radars, and a foundation is laid for accurate measurement of the radars. The feasibility of the scheme is shown by analyzing the signal-to-noise ratio and selecting an example of the actual radio telescope in China.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.
Drawings
Other features, objects, and advantages of the present disclosure will become more apparent from the following detailed description of non-limiting embodiments when taken in conjunction with the accompanying drawings. In the drawings:
fig. 1 shows a schematic flow diagram of a method of polarization scaling of a lunar orbit synthetic aperture radar according to an embodiment of the present disclosure;
FIG. 2 illustrates a flow diagram for one implementation of a method for polarization scaling of a lunar orbit synthetic aperture radar in accordance with an embodiment of the present disclosure;
fig. 3 shows a schematic diagram of a monthly SAR and FAST antenna polarization coordinate system correspondence according to an embodiment of the present disclosure;
4(a) -4 (f) are schematic diagrams illustrating the estimation error of the transmission distortion parameter under different received signal-to-noise ratios according to an embodiment of the present disclosure;
FIG. 5 is a schematic diagram of an electronic device suitable for implementing a method for polarization scaling of lunar orbit synthetic aperture radar in accordance with an embodiment of the present disclosure.
Detailed Description
Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. Furthermore, parts that are not relevant to the description of the exemplary embodiments have been omitted from the drawings for the sake of clarity.
In the present disclosure, it is to be understood that terms such as "including" or "having," etc., are intended to indicate the presence of the disclosed features, numbers, steps, actions, components, parts, or combinations thereof, and do not preclude the possibility that one or more other features, numbers, steps, actions, components, parts, or combinations thereof are present or added.
It should be further noted that the embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict. The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
The radio telescope on the earth is considered to be an effective ground deep space observation means, and can sensitively detect weak and small signals from deep space. By establishing a transmission link between the radio telescope and the monthly SAR, system distortion parameters of the monthly SAR can be acquired by a proper means. Therefore, the present disclosure proposes a method for polarization calibration of lunar synthetic aperture radar by using a radio telescope with orthogonal polarization receiving function (for example, FAST radio telescope) for calibration of lunar SAR transmitting end, and another radio telescope with orthogonal polarization transmitting function (for example, goos radio telescope) for calibration of lunar SAR receiving end. When taking the FAST radio telescope and the jianus radio telescope as examples, the present disclosure can be applied to a lunar orbit SAR with an operating frequency of 70MHz to 3GHz in consideration of the operating frequency of the radio telescope. The method requires the assistance of satellite attitude data and total ionospheric electron content TEC data. To achieve the above purpose, the technical solution of the present disclosure is shown in fig. 1.
Fig. 1 shows a flow diagram of a method for polarization scaling of a lunar orbit synthetic aperture radar according to an embodiment of the present disclosure. As shown in fig. 1, the method comprises the steps of:
in step S101, a first echo signal and a second echo signal are obtained, where the first echo signal is a signal received by a first radio telescope with a receiving function after a lunar orbit synthetic aperture radar to be polarized and calibrated transmits a horizontally polarized electromagnetic wave signal and a vertically polarized electromagnetic wave signal to the first radio telescope with the receiving function; the second echo signal is a signal which is received by the lunar orbit synthetic aperture radar to be polarized and calibrated after a second radio telescope with a transmitting function respectively transmits a left-handed circularly polarized electromagnetic wave and a right-handed circularly polarized electromagnetic wave to the lunar orbit synthetic aperture radar;
in step S102, performing matched filtering processing on the first echo signal and the second echo signal respectively to obtain first pulse pressure data and second pulse pressure data after pulse compression;
in step S103, extracting a data module maximum point from the first pulse pressure data and the second pulse pressure data, respectively, to obtain first calibration data and second calibration data;
in step S104, calculating a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radarf 2 And crosstalk amount, wherein the receiving end error parameters comprise amplitude-phase imbalance parameters between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radarf 1 And the amount of crosstalk.
In step S105, the data acquired when the lunar orbit synthetic aperture radar is operating normally is corrected based on the obtained transmitting end error parameter and/or receiving end error parameter.
In this embodiment, the first echo signal includes a first signal received by the first radio telescope after the lunar orbit synthetic aperture radar transmits a horizontally polarized electromagnetic wave signal, and a second signal received by the first radio telescope after the lunar orbit synthetic aperture radar transmits a vertically polarized electromagnetic wave signal.
The first signal comprises a signal received by a horizontal polarization antenna and a signal received by a vertical polarization antenna of the first radio telescope respectively; the second signal also includes a signal received by a horizontally polarized antenna of the first radio telescope and a signal received by a vertically polarized antenna, respectively.
The second echo signal comprises a third signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits the horizontally polarized electromagnetic wave to the lunar orbit synthetic aperture radar, and a fourth signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits the vertically polarized electromagnetic wave to the lunar orbit synthetic aperture radar.
The third signal comprises a signal received by a horizontal receiving channel and a signal received by a vertical receiving channel which are received by the lunar orbit synthetic aperture radar; the fourth signal also includes a signal received by a horizontal receive channel and a signal received by a vertical receive channel received by the lunar orbit synthetic aperture radar. The details of the implementation of the present disclosure will be described in detail below by taking the first radio telescope as a goos radio telescope and the second radio telescope as a FAST radio telescope, and the details flow is shown in fig. 2. It is to be understood that the first radio telescope and the second radio telescope are not limited to the aforementioned google radio telescope and FAST radio telescope, and any radio telescope having a function of receiving radar signals may be used as the first radio telescope and any radio telescope having a function of transmitting electromagnetic waves may be used as the second radio telescope.
The signal-to-noise ratio satisfies the condition:
for a transmission power ofP t The transmission distance of the transmitted signalrThe received power at the time of arrival at the receiving antenna can be represented by:
wherein the content of the first and second substances,A r is the effective aperture area of the receiving antenna.G t Represents the transmission gain, and is calculated by the following formula:
whereinA t For the effective aperture area of the receiving antenna,λindicating the wavelength. A receiving system comprising an antenna and a receiver, equivalent to the noise power level at the input:
N=kBT
s
wherein K is Boltzmann's constant of 1.380649X 10-23J/K.BIn order to receive the noise-equivalent bandwidth of the system,T s to receive the noise temperature of the system, 293K was taken.
The calculation that yields the required signal-to-noise ratio of the received signal is therefore:
assume lunar orbit SAR antenna size of 1.100m×0.870mThe peak power is 720W and the antenna efficiency is 85%. Working frequency of 1.25GHz, effective bandwidth 300 MHz. During lunar orbit SAR transmission, the FAST radio telescope receives at an effective aperture of 300 meters in diameter. The propagation distance between earth months is 38 kilometres. The resulting calculated received signal-to-noise ratio is about 33dB, taking into account the 3dB noise figure.
Similarly, for the transmission of the radio telescope, assuming that the received signal-to-noise ratio needs to be achieved to be SNR, the ground radio telescope is required
. Assuming that the received signal-to-noise ratio needs to be greater than 35dB,P t A t >3.2703×10 7 W·m 2 . For the Jia Musi radio telescope, the diameter is 66m, so the antenna needs to be modified, and the transmitting power is not lower than 9.6KW by adding the feed source. Secondly, other dual circularly polarized transmitting antennas can be selected to meet the transmitting power requirement
For example, a Minampian radio telescope.
Calibrating a lunar SAR emission channel by combining the FAST radio telescope:
the FAST radio telescope has a double-circular polarization or double-linear polarization electromagnetic wave receiving function and has sky coverage of a zenith angle of 40 degrees. Therefore, the main lobe of the antenna beam of the moon SAR satellite is aligned to the ground FAST through the moon SAR satellite in-orbit attitude control system and the beam scanning control system, meanwhile, the spatial angle of the incident electromagnetic wave reaching the FAST is calculated according to the moon SAR orbit information, and the main beam of the FAST antenna is aligned to the moon SAR antenna array surface, so that a signal transceiving link between the moon SAR and the FAST is formed. The method can realize the calibration of the error of the transmitting channel of the monthly SAR by transmitting specific electromagnetic wave signals through the monthly SAR and analyzing the signals received by the FAST. The specific implementation steps are as follows:
the first step is as follows: the lunar SAR respectively transmits horizontal and vertical polarization electromagnetic waves (linear frequency modulation signals), the FAST receives corresponding signals, and one-dimensional complex data of two channels can be obtained. After the received signal is subjected to pulse compression processing, one-dimensional complex data after pulse compression, namely a first pulse pressure signal, can be obtained. Data at the maximum point of the data, i.e., two complex data, are taken out from the first pulse pressure signal as first calibration data. According to the first calibration data, the related calibration can be performed. It should be noted that, the lunar SAR transmits a horizontal electromagnetic wave and a vertical polarized electromagnetic wave respectively, the transmitted horizontal electromagnetic wave corresponds to one received signal, the transmitted vertical polarized electromagnetic wave corresponds to one received signal, and after pulse pressure, a maximum point is taken out from the two received signals respectively to obtain two complex data.
In general, the horizontal and vertical polarization directions of the lunar SAR and FAST antenna wavefronts do not coincide. As shown in fig. 3, the horizontal polarization direction of the lunar SAR is h, and the vertical polarization direction is v. FAST has a horizontal polarization direction x and a vertical polarization direction y. Let the included angle between the two coordinate systems beθ. The corresponding relationship between the monthly SAR and the FAST antenna polarization coordinate system is shown in fig. 3.
Then there are:
in practical cases, both the monthly SAR and FAST antenna polarization coordinate systems are known, and a representation of the FAST antenna polarization coordinate system in the monthly SAR antenna polarization coordinate system can be obtained, that is:
wherein the content of the first and second substances,p i ,i=1,2,3,4 are coefficients. Based on this, the included angle between the two polarization coordinate systems can be estimated:
note the bookM xh AndM yh receiving echo signals by FAST horizontal and vertical polarized antennas when horizontal polarized electromagnetic waves are transmitted by a lunar SAR respectively, and considering FaradayThe relationship between the rotation effect and the projection between the coordinate systems can be obtained as follows.
Wherein A represents an absolute amplitude coefficient introduced in the entire signal transmission path,φrepresenting the phase delay of the signal transmission path.δ 4 Which represents the amount of cross-talk in the vertically polarized channel when transmitting horizontally polarized electromagnetic waves. Ω represents the faraday rotation angle induced by the earth ionosphere, which can be estimated from the total path ionosphere electron content TEC (which can be measured directly with other sensors):
in the above-mentioned formula, the compound has the following structure,frepresents the operating frequency of the monthly SAR,B 0 =4e -5 ~5e -5 Which represents the magnetic induction of the earth's magnetic field in tesla.φRepresenting the angle between the magnetic field and the radar signal (angle between magnetic signal),αIs the radar down view.
When SAR emits vertical polarization electromagnetic waves in the month, the echo signals received by FAST receiving horizontal and vertical polarization antennas are respectivelyM xv AndM yv the following relation holds.
Wherein the content of the first and second substances,f 2 representing the amplitude-phase imbalance parameter between the horizontal transmission channel and the vertical transmission channel of the lunar SAR,δ 3 which represents the amount of cross-talk in the horizontally polarized channel when vertically polarized electromagnetic waves are transmitted. Two equations are written as a matrix expression:
wherein the content of the first and second substances,ψ=θ+ Ω. The left side of equal sign isM xh 、M yh 、M xv AndM yv is signal data directly measured by FAST, which has been obtained previouslyθAnd can further obtainψ. Therefore, there are:
it is thus possible to obtain:
therefore, parameters representing the amplitude-phase imbalance between the horizontal transmitting channel and the vertical transmitting channel can be calculatedf 2 And amount of crosstalkδ 3 、δ 4 The calibration precision is consistent with the polarization isolation and amplitude consistency precision of the FAST radio telescope system.
Calibrating a lunar SAR receiving channel by the joint Jia Mus radio telescope:
similar to the lunar SAR system emission calibration, the wave beam main lobes of the lunar SAR and the Jia Mus radio telescope are mutually aligned to form a receiving and transmitting link, and then the special polarized electromagnetic wave signals are emitted through the Jia Mus radio telescope to calibrate the distortion parameters of the SAR receiving end. Because the Jia Musi radio telescope can only transmit left-handed or right-handed circularly polarized electromagnetic waves, the calibration process is slightly different.
The unit vector of the right hand direction of the memory wood radio telescope isrUnit vector of left-hand direction oflThe conversion relation between the unit vectors a and b and the corresponding horizontal and vertical polarization base is as follows:
where j represents a pure imaginary number. The horizontal polarization direction synthesized by the above formula is
In the direction of perpendicular polarization of
。
Similarly, the included angle between the Jia-Mus radio telescope and the horizontal and vertical polarization coordinate system of the lunar SARϑThen, the following relationship holds:
wherein h and v represent unit vectors in the horizontal and vertical directions of the monthly SAR horizontal-vertical polarization coordinate system. In practical cases, both the monthly SAR and the goodness radio telescope antenna polarization coordinate system are known, and the representation of the goodness radio telescope antenna polarization coordinate system in the monthly SAR antenna polarization coordinate system can be obtained, that is:
wherein the content of the first and second substances,q i ,i=1,2,3,4 are coefficients. Based on this, the angle between the two polarization coordinate systems can be estimated:
wherein the content of the first and second substances,
is the angle between two polar coordinate systemsϑAn estimate of (d).
The Jia Musi radio telescope can alternatively transmit left-handed and right-handed circularly polarized electromagnetic waves (linear frequency modulation signals), and the lunar SAR receives corresponding signals. After the pulse compression processing is performed on the received signal, image data along the azimuth direction can be obtained. And taking out data at the maximum point of the data, and carrying out relevant correction work according to the data.
When the Jia Musi radio telescope transmits the left-handed circularly polarized electromagnetic wave, the echo signals received by the horizontal and vertical polarized antennas of the lunar SAR are respectivelyM hl AndM vl when the Jia Musi radio telescope transmits the right-handed circularly polarized electromagnetic wave, the echo signals received by the horizontal and vertical polarized antennas of the lunar SAR are respectivelyM hr AndM vr . The following relationship holds:
wherein the content of the first and second substances,χ=ϑ+Ω。f 1 representing the amplitude-phase imbalance parameter between the horizontally polarized channel and the vertically polarized channel.δ 1 Which represents the amount of crosstalk in the horizontally polarized channel when the vertically polarized channel receives electromagnetic waves.δ 2 Which represents the amount of crosstalk in the vertically polarized channel when the horizontally polarized channel receives electromagnetic waves. According to an estimate
The value and Ω calculated by TEC can be foundχ. Therefore, there are:
it is thus possible to obtain:
from the analysis, the method is mainly used for calibrating the polarization isolation degree and the amplitude phase consistency of the SAR receiving end, and the calibration precision is consistent with the polarization isolation degree and the amplitude phase consistency precision of the Jia Mus radio telescope system.
To this end, the transmitting end error parameters have been obtained by separately scaling the transmitting end and the receiving end of the lunar SARNumber ofδ 3 、δ 4 、f 2 And receiving end error parametersδ 1 、δ 2 、f 1 。
And (3) polarization data correction:
suppose that the four-channel data acquired in the normal working stage of the lunar SAR are respectivelyM hh 、M hv 、M vh AndM vv the system equation after the distortion influence of the transmitting and receiving channels is as follows:
wherein the content of the first and second substances,S hh 、S hv 、S vh andS vv representing four channels of data in the ideal case. The polarization scaling may be accomplished by compensating the distortion parameters into the polarized SAR image data as follows.
Wherein the content of the first and second substances,C hh 、C hv 、C vh andC vv representing the corrected four-channel data.
An example transmit parameter estimation will be described in this section. Fig. 4(a) -4 (f) are schematic diagrams illustrating transmission distortion parameter estimation errors for different received signal-to-noise ratios according to an embodiment of the present disclosure. As can be seen from the figure, the above method proposed by the present disclosure can well estimate the distortion parameter.
The following are embodiments of the disclosed apparatus that may be used to perform embodiments of the disclosed methods.
The apparatus for polarization scaling of lunar orbit synthetic aperture radar according to an embodiment of the present disclosure may be implemented as part or all of an electronic device by software, hardware, or a combination of both. For example, the apparatus for polarization scaling of lunar orbit synthetic aperture radar comprises:
the system comprises an acquisition module and a control module, wherein the acquisition module is configured to acquire a first echo signal and a second echo signal, and the first echo signal is a signal received by a first radio telescope with a receiving function after a lunar orbit synthetic aperture radar to be polarized and calibrated respectively carries out electromagnetic wave to the first radio telescope with the receiving function; the second echo signal is a signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits electromagnetic waves to the lunar orbit synthetic aperture radar;
the processing module is configured to perform matched filtering processing on the first echo signal and the second echo signal respectively to obtain first pulse pressure data and second pulse pressure data after pulse compression;
an obtaining module configured to take out a data module maximum point from the first pulse pressure data and the second pulse pressure data, respectively, to obtain first calibration data and second calibration data;
a calculating module configured to calculate a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar, and the receiving end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radar.
And the correction module is configured to correct the data acquired by the lunar orbit synthetic aperture radar during normal operation based on the obtained transmitting end error parameter and/or receiving end error parameter.
Fig. 5 is a schematic diagram of an electronic device suitable for implementing a method for polarization scaling of lunar orbit synthetic aperture radar according to an embodiment of the present disclosure.
As shown in fig. 5, the electronic device 500 includes a processing unit 501, which may be implemented as a CPU, GPU, FPGA, NPU, or the like processing unit. The processing unit 501 may perform various processes in the embodiments of any one of the methods described above of the present disclosure according to a program stored in a Read Only Memory (ROM) 502 or a program loaded from a storage section 508 into a Random Access Memory (RAM) 503. In the RAM503, various programs and data necessary for the operation of the electronic apparatus 500 are also stored. The processing unit 501, the ROM502, and the RAM503 are connected to each other by a bus 504. An input/output (I/O) interface 505 is also connected to bus 504.
The following components are connected to the I/O interface 505: an input portion 506 including a keyboard, a mouse, and the like; an output portion 507 including a display such as a Cathode Ray Tube (CRT), a Liquid Crystal Display (LCD), and the like, and a speaker; a storage portion 508 including a hard disk and the like; and a communication section 509 including a network interface card such as a LAN card, a modem, or the like. The communication section 509 performs communication processing via a network such as the internet. The driver 510 is also connected to the I/O interface 505 as necessary. A removable medium 511 such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, or the like is mounted on the drive 510 as necessary, so that a computer program read out therefrom is mounted into the storage section 508 as necessary.
In particular, according to embodiments of the present disclosure, any of the methods described above with reference to embodiments of the present disclosure may be implemented as a computer software program. For example, embodiments of the present disclosure include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program comprising program code for performing any of the methods of the embodiments of the present disclosure. In such an embodiment, the computer program may be downloaded and installed from a network through the communication section 509, and/or installed from the removable medium 511.
The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowcharts or block diagrams may represent a module, a program segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
The units or modules described in the embodiments of the present disclosure may be implemented by software or hardware. The units or modules described may also be provided in a processor, and the names of the units or modules do not in some cases constitute a limitation of the units or modules themselves.
As another aspect, the present disclosure also provides a computer-readable storage medium, which may be the computer-readable storage medium included in the apparatus in the above-described embodiment; or it may be a separate computer readable storage medium not incorporated into the device. The computer readable storage medium stores one or more programs for use by one or more processors in performing the methods described in the present disclosure.
The foregoing description is only exemplary of the preferred embodiments of the disclosure and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the invention in the present disclosure is not limited to the specific combination of the above-mentioned features, but also encompasses other embodiments in which any combination of the above-mentioned features or their equivalents is possible without departing from the inventive concept. For example, the above features and (but not limited to) the features disclosed in this disclosure having similar functions are replaced with each other to form the technical solution.
Claims (10)
1. A method for polarization scaling of a synthetic aperture radar for lunar orbits, comprising:
acquiring a first echo signal and a second echo signal, wherein the first echo signal is a signal received by a first radio telescope with a receiving function after electromagnetic waves are respectively transmitted to the earth by a lunar orbit synthetic aperture radar to be polarized and calibrated; the second echo signal is a signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits electromagnetic waves to the lunar orbit synthetic aperture radar;
respectively performing matched filtering processing on the first echo signal and the second echo signal to obtain first pulse pressure data and second pulse pressure data after pulse compression;
respectively extracting a data module value maximum value point from the first pulse pressure data and the second pulse pressure data to obtain first calibration data and second calibration data;
calculating to obtain a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar, and the receiving end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radar;
and correcting the data acquired by the lunar orbit synthetic aperture radar during normal work based on the obtained transmitting end error parameter and/or receiving end error parameter.
2. The method according to claim 1, wherein the transmitting power and the effective aperture area of the second radio telescope satisfy the following constraints:
wherein the content of the first and second substances,P t is the transmission power of the second radio telescope,A t for the effective aperture area of the receiving antenna,N=kBT s the noise power level of a receiving system consisting of a receiving antenna and a receiver;λrepresents a wavelength;rrepresenting the transmission distance of the transmitted signal to the receiving antenna; the SNR represents the signal-to-noise ratio of the desired received signal.
3. The method according to claim 1 or 2, wherein calculating a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data comprises:
calculating the transmitting end error parameter by the following formula:
wherein the content of the first and second substances,f 2 representing amplitude-phase imbalance parameters between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar;δ 3 the method comprises the steps of representing the crosstalk amount of a horizontal transmitting channel when a lunar orbit synthetic aperture radar transmits vertical polarization electromagnetic waves;δ 4 the method comprises the steps of representing the crosstalk amount of a vertical transmitting channel when a lunar orbit synthetic aperture radar transmits horizontal polarization electromagnetic waves;M xh andM yh when the lunar orbit synthetic aperture radar transmits horizontal polarization electromagnetic waves, the horizontal polarization antenna and the vertical polarization antenna of the first radio telescope receive obtained echo signals;M xv andM yv when the lunar orbit synthetic aperture radar transmits vertical polarization electromagnetic waves, the horizontal polarization antenna and the vertical polarization antenna of the first radio telescope receive obtained echo signals;θrepresenting an included angle between the lunar orbit synthetic aperture radar and a first radio telescope polarization coordinate system; omega represents lunar orbit synthetic aperture laserUp to a corresponding faraday rotation angle induced by the earth's ionosphere.
4. The method according to claim 1 or 2, wherein calculating a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data comprises:
and calculating to obtain a receiving end error parameter by the following formula:
wherein the content of the first and second substances,f 1 representing the amplitude-phase unbalance parameter between a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar;δ 1 the method comprises the steps of representing the crosstalk amount of a horizontal receiving channel when a vertical receiving channel of the lunar orbit synthetic aperture radar receives signals;δ 2 the method comprises the steps of representing the crosstalk amount of a vertical receiving channel when a horizontal receiving channel of the lunar orbit synthetic aperture radar receives signals;M hl andM vl respectively transmitting signals received by a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar after the second radio telescope transmits the left-handed circularly polarized electromagnetic wave;M hr andM vr respectively transmitting signals received by a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar after the second radio telescope transmits the right-hand circularly polarized electromagnetic wave;ϑis the included angle between the coordinate systems of the second radio telescope and the lunar orbit synthetic aperture radar; and omega represents a Faraday rotation angle caused by an earth ionosphere corresponding to the lunar orbit synthetic aperture radar.
5. The method according to claim 1 or 2, wherein the correcting the data acquired by the lunar orbit synthetic aperture radar during normal operation based on the obtained transmitting end error parameter and/or receiving end error parameter comprises:
acquiring four-channel data received by the lunar orbit synthetic aperture radar during normal work;
and obtaining corrected data by using the receiving end error parameter and the transmitting end error parameter according to the following formula:
wherein the content of the first and second substances,M hh 、M hv 、M vh andM vv is four-channel data;C hh 、C hv 、C vh andC vv representing the corrected four-channel data;f 1 representing the amplitude-phase unbalance parameter between a horizontal receiving channel and a vertical receiving channel of the lunar orbit synthetic aperture radar;δ 1 the crosstalk amount of a horizontal receiving channel when a vertical receiving channel of the lunar orbit synthetic aperture radar receives signals is represented;δ 2 the method comprises the steps of representing the crosstalk amount of a vertical receiving channel when a horizontal receiving channel of the lunar orbit synthetic aperture radar receives signals;f 2 representing amplitude-phase imbalance parameters between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar;δ 3 the method comprises the steps of representing the crosstalk amount of a horizontal transmitting channel when a lunar orbit synthetic aperture radar transmits vertical polarization electromagnetic waves;δ 4 and the crosstalk quantity of a vertical transmitting channel when the lunar orbit synthetic aperture radar transmits the horizontally polarized electromagnetic waves is shown.
6. An apparatus for polarization scaling of a synthetic aperture radar for lunar orbit, comprising:
the system comprises an acquisition module and a control module, wherein the acquisition module is configured to acquire a first echo signal and a second echo signal, and the first echo signal is a signal received by a first radio telescope with a receiving function after a lunar orbit synthetic aperture radar to be polarized and calibrated respectively carries out electromagnetic wave to the first radio telescope with the receiving function; the second echo signal is a signal received by the lunar orbit synthetic aperture radar to be polarized and calibrated after the second radio telescope with the transmitting function transmits electromagnetic waves to the lunar orbit synthetic aperture radar;
the processing module is configured to perform matched filtering processing on the first echo signal and the second echo signal respectively to obtain first pulse pressure data and second pulse pressure data after pulse compression;
an obtaining module configured to take out a data module maximum point from the first pulse pressure data and the second pulse pressure data respectively to obtain first calibration data and second calibration data;
a calculating module configured to calculate a transmitting end error parameter and a receiving end error parameter of the lunar orbit synthetic aperture radar based on the first calibration data and the second calibration data; the transmitting end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal transmitting channel and a vertical transmitting channel of the lunar orbit synthetic aperture radar, and the receiving end error parameters comprise amplitude-phase imbalance parameters and crosstalk amount between a horizontal polarization channel and a vertical polarization channel of the lunar orbit synthetic aperture radar;
and the correction module is configured to correct the data acquired by the lunar orbit synthetic aperture radar during normal operation based on the obtained transmitting end error parameter and/or receiving end error parameter.
7. The apparatus according to claim 6, wherein the transmitting power and the effective aperture area of the second radio telescope satisfy the following constraints:
wherein the content of the first and second substances,P t is the transmission power of the second radio telescope,A t for the effective aperture area of the receiving antenna,N=kBT s for noise in a receiving system comprising a receiving antenna and a receiverAn acoustic power level;λrepresents a wavelength;rrepresenting the transmission distance of the transmitted signal to the receiving antenna; the SNR represents the signal-to-noise ratio of the desired received signal.
8. An electronic device comprising a memory, a processor, and a computer program stored on the memory, wherein the processor executes the computer program to implement the method of any of claims 1-5.
9. A computer-readable storage medium having computer instructions stored thereon, wherein the computer instructions, when executed by a processor, implement the method of any one of claims 1-5.
10. A computer program product comprising computer instructions, characterized in that the computer instructions, when executed by a processor, implement the method of any of claims 1-5.
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