CN114636980A - Polarized signal satellite-ground full link transmission model establishing method and system - Google Patents

Abstract

The present invention provides a method and system for establishing a polarized signal satellite-to-ground full link transmission model. In the third step, mathematical abstraction is performed on the system model to obtain the mathematical model of the satellite-to-ground full-link transmission of polarized signals. The invention establishes a model of satellite-to-ground full link transmission of multi-polarization SAR satellite polarization signals, the theoretical model unifies wired link and wireless link, and its system model realizes the chain of multi-polarization SAR satellite polarization signal transmission. Through the analysis of the influencing factors of the road, its mathematical model realizes the quantitative calculation of the influencing factors of each link in the multi-polarization SAR satellite polarization signal transmission process. The present invention is generally applicable to multi-polarization SAR satellites with "alternate transmission and simultaneous reception".

Description

A method and system for establishing a satellite-to-ground full-link transmission model for polarized signals

technical field

The invention relates to the field of multi-polarization synthetic aperture radar, and in particular, to a method and system for establishing a satellite-ground full-link transmission model of polarized signals.

Background technique

Synthetic Aperture Radar (SAR) has been widely used in various fields due to its all-weather, all-weather high-resolution earth observation capability, such as flood monitoring, ocean monitoring, agricultural census, and terrain mapping. Multi-polarization SAR can obtain richer polarization information of the target, so the application advantages of polarization SAR image interpretation and quantification are more obvious.

For multi-polarization SAR images, the accurate measurement of the target polarization scattering matrix is a fundamental problem in the field of polarization SAR research, and its correct acquisition can provide a strong guarantee for subsequent applications such as polarization detection and target recognition. Under ideal conditions, there is no energy leakage between the polarization channels of the polarization SAR system, and they do not affect each other, and the amplitude and phase characteristics of the two polarization channels are consistent. However, due to the insufficient isolation between the polarization channels of the multi-polarization SAR system, it is impossible to achieve complete consistency in engineering, and the complex transmission characteristics of electromagnetic waves in the space link are affected by various factors, and the polarimetric SAR system measured by the polarization SAR system. Scattering matrices introduce distortion. Therefore, it is necessary to establish the transmission model of the polarized signal in the whole satellite-ground link to analyze, decompose and control the errors introduced in each link.

Comparison of the intellectual achievement of this position with the existing technology at home and abroad, as well as with the closest existing technology achievement:

Document 1 is an article on Polarimetric SAR Internal Calibration Scheme Based on TRModule Orthogonal Phase Coding, Document 2 is an article on a distributed dual-polarization satellite mobile MIMO channel model, and Document 3 is an article on simultaneous full-polarization measurement and calibration technology for polarimetric radars Related technologies are disclosed. However, document 1 only analyzes the system model related to the TR component in the radio frequency link of the SAR system; document 2 establishes a model for the mobile MIMO channel of distributed dual-polarization satellites, and analyzes the MIMO system composed of polarization diversity and space diversity. The theoretical model analysis is different from that of the polarimetric SAR system. In view of the polarimetric measurement error existing in the traditional simultaneous full polarimetric measurement technology, Reference 3 introduces a new simultaneous full polarimetric measurement method based on the ambiguity function matrix, which is aimed at polarimetric measurement. The research on the end-to-end measurement of polarization error, and the analysis of the polarization signal transmission link is not carried out.

SUMMARY OF THE INVENTION

In view of the defects in the prior art, the purpose of the present invention is to provide a method and system for establishing a satellite-to-ground full-link transmission model of polarized signals.

According to a method for establishing a polarized signal satellite-to-ground full-link transmission model provided by the present invention, the method includes the following steps:

Theoretical model unification steps: unify the theoretical model of wired link and wireless link polarized signal transmission;

System model establishment steps: establish a system model for the polarimetric SAR system of "alternate transmission and simultaneous reception";

Mathematical abstract model establishment steps: perform mathematical abstraction on the system model to obtain the mathematical model of polarized signal satellite-to-earth full link transmission.

Preferably, the unified theoretical model of wired link and wireless link polarized signal transmission, the four-port network transmission model of radio frequency signal in wired link and the Jones vector model of electromagnetic wave in space wireless link, in mathematics Formally equivalent.

Preferably, for the polarization SAR system of "alternate transmission and simultaneous reception", the system modeling of the polarization signal on-board transmit link, the space wireless link and the on-board receive link is carried out respectively, and the link for polarized signal transmission is carried out. Analysis of influencing factors.

Preferably, mathematical abstraction is performed for each link in the system model according to the theoretical model, and the polarized signal transmission matrix of each link is obtained, and the mathematical model corresponding to the satellite-ground full link system model is the product operation of the polarized signal transmission matrix of each link.

Preferably, for the system model of "alternate transmission and simultaneous reception", when performing mathematical abstraction, the mathematical abstraction of each link is obtained by alternately transmitting H and V signals, and a pair of "H-V" signals together form the complete polarization scattering matrix of the target characterization.

A system for establishing a polarized signal satellite-to-ground full-link transmission model provided according to the present invention includes the following modules:

Theoretical model unified module: unifies the theoretical model of polarized signal transmission in wired and wireless links;

System model establishment module: establish a system model for the polarimetric SAR system of "alternate transmission and simultaneous reception";

Mathematical abstract model building module: Mathematically abstract the system model to obtain the mathematical model of polarized signal satellite-to-earth full-link transmission.

Preferably, the unified theoretical model of wired link and wireless link polarized signal transmission, the four-port network transmission model of radio frequency signal in wired link and the Jones vector model of electromagnetic wave in space wireless link, in mathematics Formally equivalent.

Preferably, for the polarization SAR system of "alternate transmission and simultaneous reception", the system modeling of the polarization signal on-board transmit link, the space wireless link and the on-board receive link is carried out respectively, and the link for polarized signal transmission is carried out. Analysis of influencing factors.

Preferably, mathematical abstraction is performed for each link in the system model according to the theoretical model, and the polarized signal transmission matrix of each link is obtained, and the mathematical model corresponding to the satellite-ground full link system model is the product operation of the polarized signal transmission matrix of each link.

Preferably, for the system model of "alternate transmission and simultaneous reception", when performing mathematical abstraction, the mathematical abstraction of each link is obtained by alternately transmitting H and V signals, and a pair of "H-V" signals together form the complete polarization scattering matrix of the target characterization.

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

1. The present invention can be universally applied to multi-polarization SAR satellites that "alternately transmit and receive simultaneously". After the model of the present invention is established, the error factors in the whole process of polarized signal transmission can be quantitatively analyzed based on the model, so as to determine its accuracy. be controlled.

2. The system model of the present invention realizes the analysis of the link influencing factors of the multi-polarization SAR satellite polarization signal transmission, and its mathematical model realizes the quantitative calculation of the influence factors of each link in the multi-polarization SAR satellite polarization signal transmission process.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a schematic flow chart of the present invention.

Figure 2 shows the signal four-port network transmission model.

FIG. 3 is a system model of a polarized signal transmission link proposed by the present invention.

FIG. 4 is a polarization signal transmission model introduced by the rotation of the polarization plane proposed by the present invention.

FIG. 5 and FIG. 6 are mathematical models of polarized signal transmission links proposed by the present invention.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the inventive concept. These all belong to the protection scope of the present invention.

As shown in FIG. 1 to FIG. 6 , according to a method and system for establishing a polarized signal satellite-to-ground full-link transmission model provided by the present invention, the method includes the following steps:

Step 1, unify the theoretical model of polarized signal transmission of wired link and wireless link;

Step 2, establish a system model for the polarimetric SAR system of "alternate transmission and simultaneous reception";

In step 3, mathematical abstraction is performed on the system model to obtain a mathematical model of satellite-to-ground full-link transmission of polarized signals.

The first step unifies the theoretical models of polarized signal transmission in wired links and wireless links. In the process of full-link transmission of polarized signals from satellite to ground, the signal is embodied in two forms: one is the signal in the wired link of the system, which is represented by the amplitude and phase of the electrical signal; the other is the space wireless link The signal in the path is characterized by the amplitude and phase of the electric field in the electromagnetic wave.

In the wired signal transmission link of the polarimetric SAR system, the transmission model of the four-port network is usually used for analysis, as shown in Figure 2. Denote the input signals of the two channels as H ^t and V ^t respectively, and the output signals as H ^r and V ^r respectively. The signal transfer coefficients from the two input ports to the two output ports are respectively: α _HH - from the H ^t port to the H ^r Port transfer coefficient, α _VH — transfer coefficient from H ^t port to V ^r port, α _HV — transfer coefficient from V ^t port to H ^r port, α _VV — transfer coefficient from V ^t port to V ^r port. Then the two-channel output signal and the two-channel input signal satisfy the transmission relationship shown in formula (1), that is, the transmission model of the four-port network.

The above-mentioned signals are all complex signals (including amplitude and phase), and the transfer coefficients are all complex transfer coefficients (including gain to signal amplitude and time delay to signal phase).

即为一个简谐电场，可以表示为两个归一化正交基

和

下的复分量E_h和E_v的线性组合。For an electromagnetic wave excited by a point-frequency signal, its electric field

is a simple harmonic electric field, which can be expressed as two normalized orthonormal bases

and

A linear combination of the complex components E _h and E _v under .

It is represented by Jones vector as:

The Jones vector reflects the complex component of the (H, V) projection of the electric field vector on two orthonormal bases.

雷达回波(目标散射波)的Jones矢量为

则这一线性变换过程可以表示为公式(4)：Since the electromagnetic scattering process of the radar target is a linear process, the scattering space coordinate system and the corresponding polarization base are selected, so there is a linear transformation relationship between the polarization components of the radar irradiation wave and the target scattered wave, so the target The variable polarization effect can be represented in the form of a complex two-dimensional matrix, which is the polarization scattering matrix [S] of the target. If the Jones vector of the radar illumination wave (target incident wave) is recorded as

The Jones vector of the radar echo (target scattered wave) is

Then this linear transformation process can be expressed as formula (4):

即

which is

where hh is the coefficient with which the target scatters the H-polarized incident wave into an H-polarized echo, vh is the coefficient with which the target scatters the H-polarized incident wave into a V-polarized echo, and hv is the target scatters the V-polarized incident wave into a V-polarized echo. The coefficient of the H-polarized echo, vv represents the coefficient of the target to scatter the V-polarized incident wave into the V-polarized echo, and they are all complex coefficients.

For a multi-polarization SAR system using the "alternate transmit and receive" mode, H-polarized waves and V-polarized waves are alternately transmitted, and H and V-polarized waves are received simultaneously, respectively, and the Jones vector is transmitted without considering any errors. The relationship between the received Jones vector and the received Jones vector is shown in formulas (5) to (7):

H transmits, H and V receive simultaneously:

即

which is

V transmits, H and V receive simultaneously:

即

which is

Since the alternately transmitted H and V signals are the same except for the orthogonal polarization directions, there are:

To sum up, it can be seen from the four-port network transmission model equation (1) of the system wired link signal transmission and the electromagnetic scattering model equation (4) of the space wireless link signal transmission that the entire satellite working in the spaceborne multi-polarization SAR works. In the ground link, the mathematical forms of the two models are equivalent and can be used as the basic model for the full-link signal transmission analysis. In addition, through the analysis of the multi-polarization SAR system in the working mode of "alternate transmission and simultaneous reception", it can be seen that a pair of H-V signals can completely describe the polarization scattering matrix of the target.

The second step is to establish a system model for the polarization SAR system of "alternately transmitting and receiving simultaneously". The satellite-ground full-link polarization signal transmission model is established when the SAR system works in multi-polarization imaging, as shown in Figure 3.

(1) After the H signal is generated by the reference frequency source, it is modulated to the required frequency band by the frequency modulation source, and then the power of the signal is amplified by the pre-amplifier, and then enters the microwave combination. In this section of the link, the channel experienced by the signal is the shared channel of H and V, there is no polarization crosstalk, and there is no amplitude-phase imbalance between channels.

(2) When the signal passes through the polarization switch in the microwave combination, part of the signal will leak to the V transmission channel due to the switching of the polarization switch. At this time, the signal changes from a single H-polarized signal to a uniform signal in the H and V transmission channels. There is a signal present.

(3) After the polarization switch, before the signal reaches the antenna waveguide front, it must go through the antenna transmission channel composed of microwave switches, power dividers at all levels, delay amplification components, T/R components and interconnecting cables. Considering the H antenna The transmitting channel and the V antenna transmitting channel are two independent parts on the device, so the isolation of the polarized signals between each other is high, and there is no polarization crosstalk; however, the two will have their own differences due to the inconsistency of the engineering devices. The transfer coefficient (that is, the transmission gain and delay of the two channels to the signal are inconsistent). At the end of this transmission channel, due to the alternate transmission mode, when transmitting H-polarized signals, only the T/R component of the H channel works to amplify the signal; while the T/R component of the V channel is in a closed state, In this way, even if there is a signal leaked to the V channel at the front end, it will not be transmitted.

(4) When the signal reaches the antenna radiation front and is emitted, there will be a certain polarization crosstalk between the H-polarized radiation unit and the V-polarized radiation unit; It will also lead to the inconsistency of the amplitude and phase of the H-polarized signal and the V-polarized signal. Since the function of the antenna radiation front is to convert electrical signals into electromagnetic waves and emit them, the transfer coefficient of the antenna radiation front should be described in the electromagnetic waves, such as the antenna pattern.

(5) When the electrical signal in the wired link of the system is converted into the electromagnetic wave in the space wireless link, the H-V polarization plane formed by the H-polarized wave and the V-polarized wave should satisfy the H direction and the horizon direction in an ideal state. , the V and H directions are orthogonal. However, due to factors such as thermal deformation of the antenna radiating unit in engineering, the generated H-polarized waves and V-polarized waves have components in another polarization direction, and the antenna front surface rotation caused by the attitude change of the satellite platform, and the space The Faraday rotation caused by the ionosphere to the polarized electromagnetic wave will cause the overall rotation of the H-V polarization plane, which will cause the H (or V) polarized wave to have a projected component in the V (or H) direction, that is, the polar crosstalk. The polarization signal transmission model introduced by the rotation of the polarization plane is shown in Figure 4.

(6) In the process of the electromagnetic wave reaching the ground object and returning through the target scattering, since different targets will have a certain degree of polarization effect on the polarized wave, the polarization change caused by the characteristics of the target itself can be viewed as It is the transmission model of the target to the polarized electromagnetic wave, which is added to the full-link transmission model of the polarized signal.

(7) For the target echo, when it passes through the ionosphere again, reaches the antenna radiation front, and enters the H slot and the V slot, the same polarization plane rotation as that of the launch will occur, and in a very short time, the visible The same as the projection component for rotation.

(8) When the target echo passes through the antenna radiation front, there will also be the same polarization crosstalk and polarization signal amplitude inconsistency as when transmitting. In theory, according to the reciprocity of the antenna, the signal transfer coefficient of the antenna should be the same when it is received and when it is transmitted. However, in engineering, the transmitting and receiving patterns of the antenna should be measured separately, and the signal transfer coefficient should be obtained according to the measured parameters.

(9) After the target echo is converted into an electrical signal by the antenna radiation front, it reaches the microwave combination through the antenna receiving channel. Considering that the H and V antenna receiving channels are two independent parts on the device, the isolation of the polarized signals between each other is relatively high, and there is no polarization crosstalk; however, the two will be caused by the inconsistency of the engineering device. their respective transfer coefficients.

(10) When the target echo signal is combined by microwave, it is no longer selected by the polarization switch, but is directly input to two independent radar receivers by the circulator in parallel, and then input to the two independent radar receivers respectively. ADCs of independent channels perform analog-to-digital conversion. Considering the independence of the devices, the polarization signals between them have a high degree of isolation, and there is no polarization crosstalk. Only due to the inconsistency of the devices in engineering, they have their own transfer coefficients.

(11) When the target echo signal undergoes ADC analog-to-digital conversion, the quantization of the two channels will be inconsistent due to the jitter of the sampling clock, resulting in inconsistent amplitude and phase between the two channels.

(12) When the analog signal becomes a digital signal, there is no longer the problem of polarization crosstalk and amplitude-phase imbalance between polarization channels. So far, the satellite-to-ground full-link transmission system model of the polarization signal has been established.

In the third step, mathematical abstraction is performed on the system model to obtain a mathematical model of polarized signal satellite-to-ground full-link transmission. According to the system model and theoretical model of polarized signal link transmission, a mathematical model corresponding to the engineering system model can be established. In order to simplify the mathematical model, the links with the same transfer model in the system model can be combined, and the simplified mathematical model is shown in Figure 5.

According to the mathematical model shown in Figure 5, it can be seen that each link in the entire polarized signal transmission chain conforms to the basic theoretical model. According to this model, the transmission mathematical model of H and V signals is obtained as:

When transmitting H and receiving H and V:

When transmitting V and receiving H and V:

According to the associative law of the matrix, the above model formula can be further combined and simplified:

When transmitting H and receiving H and V:

When transmitting V and receiving H and V:

For the working mode of alternating transmission and simultaneous reception, when H and V signals are transmitted alternately, the signal transmission model of the receiving channel and the rotation transmission model of the polarization plane are the same, and only the transmission model of the transmitting channel is different. According to the matrix distribution law, formulas (10) and ( 11) The transmission model of a pair of H-V signals can be obtained by adding the following formula.

则一对H-V信号对目标的极化回波矩阵模型可以表征为公式(13)所示。Considering that the amplitude and phase of the alternately transmitted H and V signals in the common channel are the same, there are

Then the polarization echo matrix model of a pair of HV signals to the target can be expressed as shown in formula (13).

Since the polarization accuracy is concerned with the relative characteristics between the H and V polarization channels, the absolute amplitude and phase of the signal can be ignored. In this case, the above formula can be written as:

A more simplified version can be written as:

[S ^m ] _ij = [R] _ij · [θ] · [S] · [θ] · [T] _ij (15)

Among them, [S] represents the real polarization scattering matrix of the target, [S ^m ] _ij represents the polarization echo matrix of the target corresponding to the jth pair of pulses at the ith frequency, [R] _ij represents the ith frequency at the ith frequency The polarization error matrix of the receive link corresponding to the j pair of pulses, [T] _ij represents the polarization error matrix of the transmit link corresponding to the jth pair of pulses at the ith frequency, and [θ] represents the polarization error caused by the rotation factor of the polarization plane Error matrix (one-way, and the same for sending and receiving).

The second step is to establish a system model for the polarimetric SAR system of "alternate transmission and simultaneous reception", that is, to systematically model the radio frequency link of the polarimetric SAR system of the multipolarization SAR satellite, covering from the signal source to the end of the formation of received signal data. The RF signal flow in the whole process identifies the common branch and independent branch of the polarized signal, and judges the polarized crosstalk signal according to the working mode of the single machine in the RF link. The on-board transmit link, space wireless link and on-board receive link of polarized signal are systematically modeled respectively, so as to analyze the link influencing factors of polarized signal transmission.

The third step is to perform mathematical abstraction on the system model to obtain the mathematical model of the polarized signal satellite-to-ground full-link transmission. For the system model established in the second step, the links with the same transfer model are merged, and the transfer coefficient is calculated for each link. The definition of the matrix finally abstracts the mathematics of the system model into the mathematical form of matrix multiplication, which is convenient for the subsequent quantitative analysis of errors in each link. When performing mathematical abstraction, the mathematical abstraction of each link is obtained by alternately transmitting H and V signals, and a pair of "H-V" signals together form the complete polarization scattering matrix of the target.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essential content of the present invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily, provided that there is no conflict.

Claims (10)

1. A polarized signal satellite-ground full link transmission model building method is characterized by comprising the following steps:

unifying theoretical models: unifying theoretical models of wired link and wireless link polarized signal transmission;

a system model establishing step: establishing a system model aiming at a polarized SAR system of 'alternate transmission and simultaneous reception';

establishing a mathematical abstract model: and (4) carrying out mathematical abstraction on the system model to obtain a mathematical model of the polarized signal satellite-ground full link transmission.

2. The method for establishing the polarized signal satellite-ground full link transmission model according to claim 1, wherein the theoretical model for polarized signal transmission of the unified wired link and the wireless link is mathematically equivalent to a four-port network transmission model of radio frequency signals in the wired link and a Jones vector model of electromagnetic waves in the space wireless link.

3. The polarized signal satellite-ground full link transmission model building method according to claim 1, characterized in that aiming at a polarized SAR system of 'alternately transmitting and simultaneously receiving', a polarized signal satellite-borne transmitting link, a space wireless link and a satellite-borne receiving link are respectively subjected to system modeling, and link influence factor analysis of polarized signal transmission is carried out.

4. The method for establishing the polarized signal satellite-ground full link transmission model according to claim 1, wherein mathematical abstraction is performed on each link in the system model according to a theoretical model to obtain a polarized signal transmission matrix of each link, and the mathematical model corresponding to the satellite-ground full link system model is a product operation of the polarized signal transmission matrix of each link.

5. The method for establishing the polarized signal satellite-ground full link transmission model according to claim 1, wherein for the system model of 'alternate transmission and simultaneous reception', mathematical abstractions are respectively obtained according to H, V signal alternate transmission when performing the mathematical abstractions, and a pair of 'H-V' signals jointly form a complete polarized scattering matrix representation of a target.

6. A polarized signal satellite-ground full link transmission model building system is characterized by comprising the following modules:

a theoretical model unifying module: unifying the theoretical models of wired link and wireless link polarized signal transmission;

a system model establishing module: establishing a system model aiming at a polarized SAR system of 'alternate transmission and simultaneous reception';

the mathematical abstract model building module comprises: and (4) carrying out mathematical abstraction on the system model to obtain a mathematical model of the polarized signal satellite-ground full link transmission.

7. The system for establishing the polarized signal satellite-ground full link transmission model according to claim 6, wherein the theoretical model for polarized signal transmission of the unified wired link and the wireless link is mathematically equivalent to a four-port network transmission model of radio frequency signals in the wired link and a Jones vector model of electromagnetic waves in a space wireless link.

8. The polarized signal satellite-ground full link transmission model building system according to claim 6, characterized in that aiming at a polarized SAR system of 'alternate transmission and simultaneous reception', a polarized signal satellite-borne transmission link, a space wireless link and a satellite-borne reception link are respectively subjected to system modeling, and link influence factor analysis of polarized signal transmission is carried out.

9. The polarized signal satellite-ground full link transmission model building system according to claim 6, characterized in that mathematical abstraction is performed on each link in the system model according to a theoretical model to obtain a polarized signal transmission matrix of each link, and the mathematical model corresponding to the satellite-ground full link system model is a product operation of the polarized signal transmission matrices of each link.

10. The polarized signal satellite-ground full link transmission model building system according to claim 6, characterized in that for the system model of "alternate transmission and simultaneous reception", when mathematical abstraction is performed, mathematical abstraction of each link is obtained according to H, V signal alternate transmission, and a pair of "H-V" signals jointly constitute a complete polarized scattering matrix representation of a target.

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