Signal simulation method of spaceborne conical scanning microwave scatterometer echo simulator

Abstract

The invention relates to a signal simulation method of a spaceborne conical scanning microwave scatterometer echo simulator, which provides single-point or multi-point target echo signal simulation based on a measured target of a spaceborne scatterometer, and comprises variable signal time delay and Doppler frequency compensation. Through echo signal simulation based on the satellite-borne conical scanning microwave scatterometer, the function and performance of the system can be effectively verified, the influence of different Doppler shifts of echo signals caused by satellite movement and earth rotation is eliminated, and the precision of the system on a wind vector inversion result subsequently is improved. Meanwhile, the signal simulation method has the advantages of being easy to implement and universal.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave remote sensing. For the echo simulator for verifying important functional and performance indicators of the Fengyun-3 series of wind field measurement radars and the new-generation ocean dynamic environment satellite microwave scatterometers based on the conical scanning system, a general algorithm for calculating the time delay and Doppler frequency of echo signals is designed. Background Art

[0002] The spaceborne microwave scatterometer is a typical radar system for measuring the backscattering coefficient σ° of a target, mainly used for measuring the sea surface wind field. It is currently the main remote sensing instrument capable of simultaneously measuring the sea surface wind speed and direction, and has the characteristics of all-weather, all-day, large swath width, high precision, and high resolution. The spaceborne microwave scatterometer adopts relatively complex signal processing methods, including transmitting signals with Doppler frequency pre-compensation and performing de-chirp pulse compression signal processing at the receiving end. How to conduct comprehensive functional and performance tests and verifications on the ground is a key point and a difficult point in the development of the spaceborne microwave scatterometer. The echo simulator can simulate the backscattering echo characteristics of the measured target and is one of the necessary means for verifying the functions and performance of the spaceborne microwave scatterometer. Summary of the Invention

[0003] The problem solved by the present invention is to overcome the deficiencies of the prior art and provide a general signal simulation method for the echo simulator of the conical scanning microwave scatterometer.

[0004] The technical solution of the present invention is as follows: A signal simulation method for the echo simulator of the spaceborne conical scanning microwave scatterometer, the steps are as follows:

[0005] Convert the satellite body coordinate system to the geocentric fixed coordinate system, and establish the transformation matrix between the satellite body coordinate system and the geocentric fixed coordinate system;

[0006] According to the characteristics of the conical scanning system of the spaceborne conical scanning microwave scatterometer, establish a calculation model for the intersection of the antenna beam and the earth based on the coordinates of the satellite position in the geocentric fixed coordinate system and the incident direction of the antenna beam center line;

[0007] Use the established calculation model for the intersection of the antenna beam and the earth to calculate the longitude and geocentric latitude of the beam center point and the slant range between the satellite and the beam center point;

[0008] According to the calculated longitude and geocentric latitude of the beam center point, establish a Doppler calculation model for the relative motion between the spaceborne conical scanning microwave scatterometer and the surface target, and calculate the Doppler frequency shift of the relative motion between the spaceborne conical scanning microwave scatterometer and the target;

[0009] Based on the typical eigenvalue of the transmitted signal of the spaceborne conical scanning microwave scatterometer, combined with the calculated slant range and Doppler frequency shift, a mathematical model of the echo of a point target or multiple point targets is established, and the echo spectrum with delay and Doppler frequency generated by the established mathematical model is modulated into the transmitted signal of the spaceborne conical scanning microwave scatterometer.

[0010] Preferably, the transformation matrix between the satellite body coordinate system and the geocentric fixed coordinate system is obtained by first transforming the satellite body coordinate system to the satellite orbit coordinate system, the satellite orbit coordinate system to the geocentric orbit coordinate system, the geocentric orbit coordinate system to the geocentric inertial coordinate system, and the geocentric inertial coordinate system to the geocentric fixed coordinate system.

[0011] Preferably, the calculation model of the intersection of the antenna beam and the Earth is established by the following method:

[0012] The unit vector of the antenna beam in the satellite body coordinate system is transformed into the direction vector in the geocentric fixed coordinate system according to the transformation matrix between the satellite body coordinate system and the geocentric fixed coordinate system;

[0013] According to the coordinates of the satellite position in the geocentric fixed coordinate system and the direction vector in the geocentric fixed coordinate system, the linear parameter equation of the beam center incidence is determined;

[0014] According to the intersection points of the linear parameter equation and the Earth ellipsoid, the calculation model of the intersection of the antenna beam and the Earth is obtained.

[0015] Preferably, the calculation model of the intersection of the antenna beam and the Earth is:

[0016]

[0017] where, (x se , y se , z se ) are the coordinates of the satellite position in the geocentric fixed coordinate system, and the direction vector of the antenna beam in the geocentric fixed coordinate system (x te , y te , z te ) are the intersection points of the beam center line and the Earth, u is the slant range from the satellite to the intersection point of the beam center line and the Earth, and a, b are the semi-major axes of the Earth ellipsoid equation.

[0018] Preferably, the Doppler calculation model is:

[0019] If the scanning azimuth angle is within 0° to 180°, the Doppler frequency calculation formula:

[0020]

[0021] If the scanning azimuth angle is within 180° to 360°, the Doppler frequency calculation formula:

[0022]

[0023] In the above formula, V sc is the satellite orbital velocity, γ is the viewing angle of the beam towards the target point, a is the scanning azimuth angle, ω e is the average angular velocity of the Earth's rotation, H is the distance measured from the center of the Earth to the satellite, β is the satellite latitude argument, and ψ is the satellite orbital inclination angle.

[0024] Preferably, the signal emitted by the spaceborne microwave scatterometer is a chirp signal, and its mathematical model is as follows:

[0025]

[0026] The echo of a point target is expressed as follows:

[0027]

[0028] The echo of a multi-point target is expressed as follows:

[0029]

[0030] In the above formula, T p is the pulse width of the transmitted signal, f c is the center frequency, f dc is the pre-compensated Doppler frequency, k is the chirp slope; C is the radar constant, σ 0 i is the backscattering coefficient, ΔA i is the area of the observation unit, R i is the slant range between the satellite and the center point of the i-th beam, c is the speed of light, f' dc,i is the difference between the Doppler frequency f d of the echo of the i-th point target and the pre-compensated Doppler frequency; t is the time, and N is the number of target points.

[0031] An echo simulator includes a receiving channel, a transmitting channel, a frequency synthesizer, and a baseband processor; the receiving channel receives the signal emitted by the scatterometer under the trigger pulse given by the spaceborne conical scanning microwave scatterometer. It is characterized in that the baseband processor executes the signal simulation method of the spaceborne conical scanning microwave scatterometer echo simulator to generate an echo signal with delay and Doppler frequency, and returns it to the scatterometer through the transmitting channel.

[0032] A verification system for signal simulation of a spaceborne conical scanning microwave scatterometer echo simulator includes a signal source, an echo simulator, a spectrum analyzer, and an oscilloscope,

[0033] The signal source is used to simulate the transmitted signal of the spaceborne conical scanning microwave scatterometer. The signal source is connected to the receiving channel. The spectrum analyzer and the oscilloscope are respectively used to detect the Doppler frequency shift and delay of the signal simulation method of the spaceborne conical scanning microwave scatterometer echo simulator described in claims 1-6 executed in the echo simulator. Compare the detected Doppler frequency shift and delay time with the index requirements to complete the verification, and input the echo simulation signal output by the verified echo simulator into the spaceborne conical scanning microwave scatterometer for the verification of the scatterometer.

[0034] A verification method implemented by a verification system for signal simulation of a spaceborne conical scanning microwave scatterometer echo simulator, including:

[0035] Connect the output of the signal source to the receiving channel of the radar echo simulator, and connect the spectrum analyzer to the transmitting channel of the radar echo simulator;

[0036] Set the frequency and power of the signal source;

[0037] Set the working band and working mode of the echo simulator. The working mode includes a point target mode and a surface target mode, corresponding to the echo mathematical models of point targets and multi-point targets respectively;

[0038] Input the Doppler dynamic lookup table and echo delay table of the point target simulation signal in the set working mode to the echo simulator; the Doppler dynamic lookup table and echo delay table are the Doppler frequency shift calculated by using the signal simulation method of the spaceborne conical scanning microwave scatterometer echo simulator and the delay time calculated according to the slant range;

[0039] Set the triggering mode. The receiving channel receives the transmitted signal of the signal source under the triggering pulse. The echo simulator generates an echo simulation signal according to the Doppler dynamic lookup table and echo delay table in combination with the working mode, and outputs it to the transmitting channel, and the spectrum analyzer tests the Doppler frequency shift;

[0040] Connect the oscilloscope to the transmitting channel, and observe the delay time of the I and Q channel outputs relative to the triggering time to test the delay compensation;

[0041] Compare the detected Doppler frequency shift and delay time with the index requirements to complete the verification of the method of the present invention;

[0042] Input the echo simulation signal transmitted by the verified echo simulator to the spaceborne microwave scatterometer, and use the echo simulation signal to complete the verification of the functions and performance of the spaceborne microwave scatterometer.

[0043] The advantages of the present invention compared with the prior art are as follows: Regarding the simulation of the echo signal of a conical scan microwave scatterometer, there are no relevant articles or materials on the simulation methods of delay and Doppler frequency. The solution proposed by the present invention for this problem solves the signal simulation of the target characteristics of a spaceborne scatterometer with a conical scan system, has certain generality and ease of implementation, and provides a strong guarantee for the verification of the functions and performance of the payload. Description of the Drawings

[0044] Figure 1 It is a schematic diagram of the principle of the signal simulation method of the echo simulator;

[0045] Figure 2 It is a schematic diagram of the relationship between satellite coordinates and earth coordinates;

[0046] Figure 3 It is a timing diagram of the distributed calibration of the spaceborne scatterometer.

[0047] Figure 4 It is a timing diagram of the trigger signal of the spaceborne scatterometer;

[0048] Figure 5 It is a self-test block diagram of the signal simulation of the echo simulator;

[0049] Figure 6 It is a loading interface for the echo signal simulation. Detailed Embodiment

[0050] The main function of the echo simulator is to generate an echo with variable delay and Doppler frequency according to a specific backscattering echo model and modulate and forward it into the transmitted signal, so as to provide an approximate real echo signal to verify the working mode of the scatterometer, the characteristics of the transmitted signal, and the functions and performance of the de-chirp pulse compression method. Since the scatterometer adopts a conical scan system, when the radar antenna beam scans at different positions, the Doppler frequency shift of the echo signal caused by satellite motion and earth rotation is different. However, after the satellite altitude and the antenna beam incident angle are determined, the Doppler frequency shift at different scanning positions of the radar antenna is fixed. The present invention is designed based on the above considerations during the echo simulation process.

[0051] The present invention revolves around the geocentric coordinate system. First, the position vector and velocity vector of the satellite are converted into the geocentric fixed coordinate system to establish a conversion matrix model; secondly, a general delay and Doppler frequency compensation algorithm is proposed based on the model. The result is applied to the echo simulator to provide an approximate real echo signal to verify the working mode of the scatterometer, the characteristics of the transmitted signal, and the functions and performance of the de-chirp pulse compression method.

[0052] 1) Establishment of the coordinate system

[0053] When describing the satellite space orbit using the orbital element method, it is more convenient in the geocentric orbit coordinate system. However, the position vector and velocity vector of the satellite must be converted to the geocentric fixed coordinate system in order to establish a connection with the ground position.

[0054] The geocentric fixed coordinate system is a coordinate system that is fixedly connected to the Earth and rotates simultaneously with the Earth's rotation. Therefore, it is also called the Earth-fixed coordinate system, and the geocentric fixed coordinate system is denoted as O e X e Y e Z e . The origin of this coordinate system is located at the geocenter. The X e axis is located in the equatorial plane and points to the intersection of the Greenwich meridian and the equatorial plane. The Z e axis points along the Earth's rotation axis to the North Pole. The Y e axis is perpendicular to the Z e axis in the equatorial plane. The X e , Y e , Z e The three coordinate axes satisfy the right-hand coordinate system rule. This method is divided into 4 steps to convert the satellite body coordinate system to the geocentric fixed coordinate system, laying a foundation for the next algorithm implementation.

[0055] As Figure 2 shown, S is the satellite position [x se , y se , z se determined by GPS at the current moment T , and S o is the satellite position [x' s0e , y' s0e , z' s0e determined by GPS at the nearest time before S T . Due to the Earth's rotation, in the inertial space, there is an angle of ω o t between S e and the x e axis of the Earth coordinate system where S is located, and the z e axis coincides. Then the Earth coordinate system where the S o point is located rotates by an angle of ω e t around the Z e axis to the Earth coordinate system where the S point is located. The position of S o in the Earth coordinate system where S is located is:

[0056]

[0057] (a) The transformation matrix M from the satellite body coordinate system to the satellite orbit coordinate system bso

[0058] The transformation matrix M from the satellite orbit coordinate system to the satellite body coordinate system sob is:

[0059]

[0060] Then M bso is the transpose of M, ψ is the yaw angle, θ is the pitch angle, and γ is the roll angle. sob The conversion from the satellite orbit coordinate system to the geocentric orbit coordinate system

[0061] (b) The conversion from the satellite orbit coordinate system to the geocentric orbit coordinate system

[0062]

[0063] In the above formula, [x o y o z o T is the coordinate vector in the geocentric orbit coordinate system, and [x so y so z so T is the coordinate vector in the satellite orbit coordinate system, and ξ is the track angle.

[0064] (c) The conversion matrix M from the geocentric orbit coordinate system to the geocentric inertial coordinate system oi

[0065]

[0066] In the above formula, Ω is the right ascension of the ascending node, i is the orbital inclination, ω is the argument of perigee, and f is the true anomaly.

[0067] (d) The conversion matrix M from the geocentric inertial coordinate system to the geocentric fixed coordinate system ie

[0068]

[0069] In the above formula, S is the Greenwich sidereal time angle at the current moment.

[0070] 2) Slant range simulation between the spaceborne scatterometer and the point target

[0071] The coordinates of the beam center point in the earth-fixed coordinate system can be obtained through the intersection of the incident direction of the beam center and the earth ellipsoid equation, and the slant range between the satellite and the beam center point can be calculated. Similarly, the slant ranges of other target points can be calculated.

[0072] The unit vector of a satellite beam (viewing angle φ s , azimuth angle ) in the satellite body coordinate system is:

[0073]

[0074] The vector in the satellite body coordinates​​ Convert the direction vector in the satellite orbit coordinate system to be:

[0075]

[0076] Convert the vector in the satellite orbit coordinates to the direction vector in the geocentric orbit coordinate system to be:

[0077]

[0078] Convert the vector in the geocentric orbit coordinates to the direction vector in the geocentric inertial coordinate system to be:

[0079]

[0080] Convert the vector in the geocentric inertial coordinates to the direction vector in the geocentric fixed coordinate system to be:

[0081]

[0082] Given the coordinates of the beam starting point (satellite position) in the geocentric fixed coordinate system and the incident direction of the beam center line the parametric equation of the straight line where the beam center is incident can be determined as:

[0083]

[0084] where u is the parameter. This straight line has two intersections with the Earth ellipsoid surface, and two coordinates can be calculated from the ellipsoid equation (i.e., the calculation model of the intersection of the antenna beam center and the Earth):

[0085]

[0086] The intersection point of the beam center line and the Earth that is closer to the satellite is [x te ,y te ,z te T , and this point is the coordinate of the beam center point. Then the longitude and geocentric latitude of the beam center are respectively:

[0087]

[0088] The slant range from the current satellite to the intersection point of the beam center line and the Earth can be calculated from the longitude and latitude of the beam center obtained by formulas (16) and (17).

[0089] ​3) Doppler Frequency Calculation of the Relative Motion between Spaceborne Scatterometer and Earth Surface Targets

[0090] For any radar measurement geometry, the Doppler shift between the radar and the observed target is:

[0091]

[0092] where r is the distance vector between the radar and the observed target (the distance vector can be calculated using the longitude and latitude obtained from Equations 16 and 17), is the first derivative of r, i.e., the relative velocity vector between the radar and the observed target. This relative motion is caused by two motions: the satellite orbital velocity vector and the Earth's rotation velocity vector R = r is the distance between the radar and the observed target point. The negative sign indicates that the Doppler frequency is negative when the radar is moving away from the target and positive when the radar is approaching the target. The distance vector is r = H - R e and the relative velocity vector is Then in Equation (18) can be expressed in terms of the satellite position vector H, the local position vector R of the target point e , the orbital velocity vector and the Earth's rotation velocity vector as:

[0093]

[0094] For a circular orbit or an approximately circular orbit, the satellite position vector and the satellite orbital velocity vector are orthogonal, i.e., the local position vector of the target point and the Earth's rotation velocity vector are orthogonal, i.e., Then Equation (19) can be expressed as:

[0095]

[0096] Substituting Equation (20) into Equation (18) gives:

[0097]

[0098] There is a dot product in Equation (21). The calculation process of the Earth's rotation velocity vector at the local position of the target point is as follows:

[0099] The vector pointing due east at the target (in the Earth-fixed coordinate system) is:

[0100]

[0101] The unit vector pointing due east at the target is:

[0102]

[0103] In the formula, (x target , y target , z target ) are the coordinates of the target point in the earth-fixed coordinate system. Then where ω e is the average angular velocity of the earth's rotation, R e is the local earth radius of the target point, and l is the geocentric latitude of the target point.

[0104] It can be deduced from Equation (21):

[0105] If the scanning azimuth angle is within 0° to 180°, the Doppler frequency calculation formula is:[[]]

[0106]

[0107] If the scanning azimuth angle is within 180° to 360°, the Doppler frequency calculation formula is:[[]]

[0108]

[0109] In the above formula, V sc is the satellite orbital velocity, γ is the angle of view of the beam towards the target point, a is the scanning azimuth angle, ω e is the average angular velocity of the earth's rotation, H is the distance measured from the earth's center to the satellite, β is the latitude argument, and ψ is the orbital inclination.

[0110] The invention gives an example where the signal emitted by the spaceborne microwave scatterometer is a linear frequency modulation signal, and the mathematical model is as follows:[[]]

[0111]

[0112] In the above formula, T p is the time width of the transmitted signal, f c is the center frequency, f dc is the pre-compensated Doppler frequency, and k is the frequency modulation slope.

[0113] Then, the echo of the point target after echo delay and frequency offset compensation is expressed as follows:[[]]

[0114]

[0115] In the above formula, C is the radar constant, σ 0 i is the backscattering coefficient, ΔA i is the observation unit area, R i is the slant range between the satellite and the center point of the i-th beam, c is the speed of light, f' dc,i is the difference between the Doppler frequency of the i-th point target echo and the pre-compensated Doppler frequency, and each beam center point and the point where it hits the target correspond one by one.

[0116] The echo representation of multi-point targets with echo delay and frequency offset compensation is as follows:

[0117]

[0118] As Figure 3 shown, the transmitted signal of the microwave scatterometer based on the FY-3E satellite, after inputting its orbital parameters and transmitted signal characteristics, is substituted into the algorithm model of the present invention to calculate the time delay and Doppler simulation of the measured point target and multi-point targets. After a certain power attenuation control through the transmitting channel, it is sent to the scatterometer. Specifically, the present invention further provides an echo simulator, including a receiving channel, a transmitting channel, a frequency synthesizer, and a baseband processor; the receiving channel receives the scatterometer transmitted signal under the trigger pulse given by the spaceborne conical scan microwave scatterometer, and the baseband processor executes the above steps 1)-3) to generate an echo signal with time delay and Doppler frequency, and returns it to the scatterometer through the transmitting channel.

[0119] As Figure 4 , taking the timing characteristics of the transmitted signal of a certain type of microwave scatterometer as an example, the compensation verification of the present invention is carried out.

[0120] As Figure 5 , the simulation signal obtained from the calculation model of the present invention is self-verified.

[0121] 1) Connect the output of the signal source to the RF_IN of the receiving channel of the radar echo simulator, and connect the spectrum analyzer to the RF_OUT of the transmitting channel of the radar echo simulator;

[0122] 2) Set the signal source, with a frequency of 5.401 GHz and a power of -5 dBm;

[0123] 3) Open the display and control software of the radar echo simulator, and select "C band" in the "band selection" box;

[0124] 4) Click the "surface target" option to switch to the surface target mode (i.e., multi-point target);

[0125] 5) Import the time delay parameter file in the "parameter file download" selection box (obtain the longitude and latitude information according to different multi-point targets according to formulas 16 and 17, and then obtain the slant range, and then obtain the time delay according to the slant range combined with the speed of light), and download it to the echo simulator.

[0126] 6) Import the frequency shift parameter file in the "parameter file download" selection box (what content in the Doppler frequency shift parameter file calculated according to different multi-point targets according to formula 25), and download it to the echo simulator.

[0127] 7) Set the center frequency of the spectrum analyzer to 5.4 GHz, Span to 5 MHz, and select maximum hold. Observe and record the frequency shift range. In the "Trigger" checkbox, select the trigger source as "Internal Trigger", set the number of external trigger pulses and internal trigger pulses according to the parameter file, and check the "Acquisition" checkbox;

[0128] 8) Connect the oscilloscope to the transmitting channel and observe the delay time of the I and Q channels (I+_out, Q+_out)

[0129] relative to the trigger time TRIG_IN and record it;

[0130] Fill in the self-verification measurement results of the echo signal simulation accuracy in Table 1.

[0131] Table 1 Echo Simulator Signal Simulation Test Form

[0132]

[0133]

[0134] Compare the detected Doppler frequency shift and delay time with the index requirements to complete the verification of the method of the present invention; if the verification fails, generally there is a problem with the verification system setup, and the method itself is okay. After checking and correcting, it can be verified again.

[0135] Such as Figure 6 , after the verification is passed, the echo simulator can generate at least 10 point target echo signals in real time and send them to the scatterometer under the control of the synchronization pulse, which can verify the function and performance of the on-board signal processing compensation result (the focus of the present invention is to provide an echo simulation signal for verification to the scatterometer, and how to verify is well-known technology in the industry), improving the measurement accuracy.

[0136] The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A signal simulation method for an echo simulator of a spaceborne conical scanning microwave scatterometer, characterized in that The steps are as follows: Convert the satellite body coordinate system to the geocentric fixed coordinate system, and establish the transformation matrix between the satellite body coordinate system and the geocentric fixed coordinate system; According to the characteristics of the conical scanning system of the spaceborne conical scanning microwave scatterometer, establish a calculation model for the intersection of the antenna beam and the earth by combining the coordinates of the satellite position in the geocentric fixed coordinate system with the incident direction of the antenna beam center line; Use the established calculation model for the intersection of the antenna beam and the earth to calculate the longitude, geocentric latitude of the beam center point, and the slant range between the satellite and the beam center point; According to the calculated longitude and geocentric latitude of the beam center point, establish a Doppler calculation model for the relative motion between the spaceborne conical scanning microwave scatterometer and the surface target, and calculate the Doppler frequency shift of the relative motion between the spaceborne conical scanning microwave scatterometer and the target; Based on the typical characteristic values of the signals emitted by the spaceborne conical scanning microwave scatterometer, combined with the calculated slant range and Doppler frequency shift, establish a mathematical model for the echo of a point target or multiple point targets, and use the established mathematical model to generate an echo spectrum with delay and Doppler frequency and modulate it into the signals emitted by the spaceborne conical scanning microwave scatterometer.

2. The method according to claim 1, wherein: The transformation matrix between the satellite body coordinate system and the geocentric fixed coordinate system is obtained by first converting the satellite body coordinate system to the satellite orbit coordinate system, the satellite orbit coordinate system to the geocentric orbit coordinate system, the geocentric orbit coordinate system to the geocentric inertial coordinate system, and the geocentric inertial coordinate system to the geocentric fixed coordinate system.

3. The method according to claim 1, characterized in that: The calculation model for the intersection of the antenna beam and the earth is established by the following method: Convert the unit vector of the antenna beam in the satellite body coordinate system into a direction vector in the geocentric fixed coordinate system according to the transformation matrix between the satellite body coordinate system and the geocentric fixed coordinate system; Determine the linear parameter equation of the straight line where the beam center is incident according to the coordinates of the satellite position in the geocentric fixed coordinate system and the direction vector in the geocentric fixed coordinate system; Obtain the calculation model for the intersection of the antenna beam and the earth according to the intersection points of the linear parameter equation and the earth ellipsoid surface.

4. The method according to claim 3, characterized in that: The calculation model for the intersection of the antenna beam and the earth is: where \((x se , y se , z se ) are the coordinates of the satellite position in the geocentric fixed coordinate system, and the direction vector of the antenna beam in the geocentric fixed coordinate system is (x te , y te , z te ) is the intersection point of the beam center line and the Earth, \(u\) is the slant range from the satellite to the intersection point of the beam center line and the Earth, and \(a\), \(b\) are the semi-major axes of the Earth ellipsoid equation.

5. The method according to claim 1, characterized in that: The Doppler calculation model is: If the scanning azimuth angle is within 0° to 180°, the Doppler frequency calculation formula: If the scanning azimuth angle is within 180° to 360°, the Doppler frequency calculation formula: In the above formula, V sc is the satellite orbital velocity, γ is the viewing angle of the beam towards the target point, a is the scanning azimuth angle, ω e is the average angular velocity of the Earth's rotation, H is the distance measured from the center of the Earth to the satellite, β is the satellite latitude argument, and ψ is the satellite orbital inclination angle.

6. The method according to claim 1, wherein: The signals emitted by the spaceborne microwave scatterometer are linear frequency modulation signals, and the mathematical model is as follows: The echo of the point target is expressed as follows: The echo of the multiple point targets is expressed as follows: In the above formula, T p is the pulse width of the transmitted signal, f c is the center frequency, f dc is the pre-compensated Doppler frequency, k is the frequency modulation slope; C is the radar constant, σ 0 i is the backscattering coefficient, ΔA i is the area of the observation unit, R i is the slant range between the satellite and the center point of the i-th beam, c is the speed of light, f' dc,i is the difference between the Doppler frequency f d of the echo of the i-th point target and the pre-compensated Doppler frequency; t is time, and N is the number of targets.

7. An echo simulator, comprising a receiving channel, a transmitting channel, a frequency synthesizer, and a baseband processor; the receiving channel receives the scattered signal transmitted by the scatterometer under the trigger pulse given by the spaceborne conical scanning microwave scatterometer, characterized in that, The baseband processor executes the signal simulation method of the spaceborne conical scanning microwave scatterometer echo simulator described in claims 1-6, generates an echo signal with delay and Doppler frequency, and returns it to the scatterometer through the transmission channel.

8. A verification system for signal simulation of an on-board conical scanning microwave scatterometer echo simulator, characterized in that: It includes a signal source, the echo simulator described in claim 7, a spectrum analyzer, and an oscilloscope, The signal source is used to simulate the emission signal of the spaceborne conical scanning microwave scatterometer. The signal source is connected to the receiving channel. The spectrum analyzer and the oscilloscope are respectively used to detect the Doppler frequency shift and delay of the signal simulation method of the spaceborne conical scanning microwave scatterometer echo simulator described in claims 1-6 executed in the echo simulator. Compare the detected Doppler frequency shift and delay time with the index requirements to complete the verification, and input the echo simulation signal output by the verified echo simulator into the spaceborne conical scanning microwave scatterometer for the verification of the scatterometer.

9. A verification method for implementing the signal simulation of an echo simulator of a spaceborne conical scanning microwave scatterometer, characterized in that It includes: Connect the output of the signal source to the receiving channel of the radar echo simulator, and connect the spectrum analyzer to the transmitting channel of the radar echo simulator; Set the frequency and power of the signal source; Set the working band and working mode of the echo simulator. The working mode includes the point target mode and the surface target mode, corresponding to the point target and multi-point target echo mathematical models respectively; Input the Doppler dynamic lookup table and echo delay table of the point target simulation signal in the set working mode to the echo simulator. The Doppler dynamic lookup table and echo delay table are the Doppler frequency shift calculated by using the signal simulation method of the spaceborne conical scanning microwave scatterometer echo simulator described in claim 1 and the delay time calculated according to the slant range; Set the trigger mode. The receiving channel receives the emission signal of the signal source under the trigger pulse. The echo simulator generates an echo simulation signal according to the Doppler dynamic lookup table and echo delay table combined with the working mode and outputs it to the transmitting channel, and the Doppler frequency shift is tested by the spectrum analyzer; Connect the oscilloscope to the transmitting channel to observe the delay time of the outputs of the I and Q channels relative to the trigger time to test the time delay compensation; Compare the detected Doppler frequency shift and delay time with the index requirements to complete the verification of the method in claim 1; Input the echo simulation signal emitted by the verified echo simulator to the spaceborne microwave scatterometer, and use the echo simulation signal to complete the verification of the functions and performance of the spaceborne microwave scatterometer.

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