CN107526066A - A kind of echo simulation method and device - Google Patents

Abstract

The present disclosure relates to an echo simulation method and device, which are used to solve the problem that moon-based radar simulation cannot be performed in related technologies. The method includes: calculating lunar orbit parameters according to lunar ephemeris data; setting radar system parameters according to lunar orbit parameters and observation requirements; determining the central time of echo simulation and the corresponding beam irradiation position at this time according to lunar ephemeris data; A point target is set within the range of the beam irradiation position corresponding to the center moment of the wave simulation, and the point target is the target irradiated during the echo simulation process; the echo data of the point target is obtained based on the radar system parameters. Echo simulation of base radar.

Description

Echo simulation method and device

technical field

The present disclosure relates to the technical field of radar simulation, and in particular, to an echo simulation method and device.

Background technique

With the gradual deepening of research in the field of natural sciences, human beings have gradually realized the existence of "solid tides", and discovered that the large-scale dynamic changes in the long-term natural evolution of the earth directly affect the climate and environment of the earth. At present, the SAR (Synthetic Aperture Radar, Synthetic Aperture Radar) system cannot meet the measurement scale requirements at the crustal plate level due to various reasons, and considering the performance characteristics of artificial satellites, it is not difficult to find The idea of improving the radar observation capability is not the most reasonable way to solve the problem. There must be a new form of carrier platform to break through the bottleneck faced by the artificial satellite platform.

As the only natural satellite of the earth, the moon's special "tidal locking" phenomenon makes it possible to realize the idea of establishing a moon-based ground observation radar on the moon's surface using the moon as a carrier platform. The average observation slant distance of the moon exceeds 370,000 kilometers, so that the radar azimuth beam width of only 2 degrees on the lunar surface can cover the entire earth. At the same time, the average radius of the moon reaches 1737 kilometers, and the deployment of multiple sensors at different positions on the surface of the moon makes the moon-based interferometric radar have the potential to be realized. The huge mass of the moon, which is close to 7.3×10 ²² kg, is also a strong guarantee for the stability of the platform.

In recent years, the conception of moon-based SAR applications in related fields has become more and more diverse, but the analysis of the echo characteristics of moon-based SAR is still in the initial stage based on spaceborne SAR theory. The large slant distance characteristic of moon-based SAR makes its simulation algorithm very different from that of traditional spaceborne SAR. Many approximate conditions are no longer applicable, and the unique geometric relationship indicates that the echo results will show completely different properties. Nutation and libration of the star will also have a great impact on the actual echo, and the simple two-body model is not suitable for moon-based radar simulation.

Contents of the invention

The purpose of the present disclosure is to provide an echo simulation method and device to solve the problem in the related art that moon-based radar simulation cannot be performed.

The present disclosure provides a radar echo data acquisition method, including: calculating lunar orbit parameters according to lunar ephemeris data; setting radar system parameters according to the lunar orbit parameters and observation requirements; determining the lunar orbit parameters according to the lunar ephemeris data The central moment of the echo simulation and the beam irradiation position corresponding to the moment; setting a point target within the range of the beam irradiation position, the point target being the target irradiated during the echo simulation process; based on the system The parameter gets the echo data of the point target.

Optionally, the determining the center moment of the echo simulation and the beam irradiation position corresponding to the moment according to the lunar ephemeris data includes: according to the position of the antenna phase center in the lunar astral coordinate system and the position of the moon in the simulation Determine the position of the aiming point of the beam in the rotating earth-centered coordinate system at the center moment in the rotating earth-centered coordinate system; obtain the coordinates of the center point of the beam according to the position of the aiming point of the beam in the rotating earth-centered coordinate system, and the The longitude and latitude corresponding to the center point coordinates; select the position corresponding to the beam center, and determine the time corresponding to the position as the simulation center time.

Optionally, setting a point target within the range of the beam irradiation position includes: determining the first position of the antenna phase center in the rotating earth coordinate system at the start of the echo simulation; The second position of the point target in the rotating earth coordinate system at the beginning of the simulation; judge whether the point target is irradiated by the beam according to the relative vector of the first position and the second position; obtain the irradiated beam The echo phase of the point target.

Optionally, the lunar orbit parameters include at least one of the following: orbital eccentricity, perigee position, ascending node position, ascending node equator, perigee angular distance, and orbital inclination.

Optionally, the radar system parameters include at least one of the following: transmit tone frequency, pulse duration, beam irradiation time, antenna angle of view, antenna size, and radar position.

The present disclosure also provides a radar echo data acquisition device, including: a calculation module, used to calculate the lunar orbit parameters according to the lunar ephemeris data; a first setting module, used to set the radar parameters according to the lunar orbit parameters and observation requirements System parameters; a determination module, used to determine the central moment of the echo simulation and the beam irradiation position corresponding to the moment according to the lunar ephemeris data; a second setting module, used to set within the range of the beam irradiation position A point target, where the point target is a target irradiated during the echo simulation process; an acquisition module, configured to acquire echo data of the point target based on the system parameters.

Optionally, the determining module includes: a first determining unit, configured to determine the position of the beam according to the position of the antenna phase center in the lunar astral coordinate system and the position of the moon in the rotating geocentric coordinate system at the time of the simulation center The position of the aiming point in the rotating earth-centered coordinate system; the first acquisition unit is used to obtain the coordinates of the center point of the beam according to the position of the aiming point of the beam in the rotating earth-centered coordinate system, and the longitude corresponding to the coordinates of the center point and latitude; a second determining unit, configured to select a position corresponding to the center of the beam, and determine the time corresponding to the position as the time of the simulation center.

Optionally, the second setting module includes: a third determination unit, configured to determine the first position of the antenna phase center in the rotating earth coordinate system at the start of the echo simulation; a fourth determination unit, configured to Determining a second position of the point target in the rotating earth coordinate system at the start of the echo simulation; a judging unit configured to judge the point target according to the relative vector of the first position and the second position Whether it is irradiated by the beam; the second acquisition unit is used to acquire the echo phase of the point target irradiated by the beam.

Optionally, the lunar orbit parameters include at least one of the following: orbital eccentricity, perigee position, ascending node position, ascending node equator, perigee angular distance, and orbital inclination.

Optionally, the radar system parameters include at least one of the following: transmit tone frequency, pulse duration, beam irradiation time, antenna angle of view, antenna size, and radar position.

Through the above technical scheme, calculate the lunar orbit parameters and determine the central moment of the echo simulation and the corresponding beam irradiation position at this time according to the lunar ephemeris data; set the radar system parameters according to the lunar orbit parameters and observation requirements; within the range of the beam irradiation position The point target is set inside, and the echo data of the point target is obtained based on the set system parameters, and the echo simulation of the moon-based radar is realized. Based on the obtained echo data, the echo characteristics of the moon-based radar can be analyzed.

Other features and advantages of the present disclosure will be described in detail in the detailed description that follows.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present disclosure, and constitute a part of the description, together with the following specific embodiments, are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the attached picture:

Fig. 1 is a flow chart of an echo simulation method according to an exemplary embodiment.

Fig. 2 is a schematic diagram showing the geometric relationship between the relative positions of the earth and the moon according to an exemplary embodiment.

Fig. 3 is a schematic diagram showing the position of the moon in the ephemeris according to an exemplary embodiment.

Fig. 4 is a schematic diagram showing echo results of a single point target according to an exemplary embodiment.

Fig. 5 is a schematic diagram of imaging of a single-point target echo simulation according to an exemplary embodiment.

Fig. 6 is a schematic diagram of simulated imaging of a nine-dot matrix according to an exemplary embodiment.

Fig. 7 is a structural block diagram of an echo simulation device according to an exemplary embodiment.

detailed description

Specific embodiments of the present disclosure will be described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

In order to solve the above problems, this disclosure provides and introduces an echo simulation method, using this method to simulate the working process of the moon-based radar, and by adjusting the parameters of the radar system to obtain echo simulation data under different conditions to verify the system Performance under different system parameters.

Fig. 1 is a flowchart of an echo simulation method according to an exemplary embodiment. As shown in Fig. 1, the echo simulation method provided by the present disclosure includes the following processing:

S101: Calculate lunar orbit parameters according to lunar ephemeris data;

Exemplarily, in the present disclosure, the lunar ephemeris data may adopt JPL ephemeris parameters, and the radar may be SAR.

Due to the influence of the moon's nutation, the moon's orbit around the earth changes periodically, and the relative geometric relationship between the earth and the moon is shown in Figure 2. Echo simulation first needs to determine the orbital parameters at the time of irradiation based on the lunar ephemeris data used. The requirements for the lunar ephemeris data are as follows:

The lunar ephemeris data should reflect the nutation and balance information of the moon; the overall time span of the lunar ephemeris data must be greater than 27.4 days but not longer than 30 days, and the maximum time interval between adjacent data is 1h, and it is interpolated to seconds; The ephemeris data must contain the position and velocity information of the moon; the reference system of the ephemeris data should be selected as a non-rotating geocentric reference system, that is, the earth's center is the origin, the earth's center points to the vernal equinox as the positive direction of the X axis, and the earth's center points to the earth's north pole as In the positive direction of the Z axis, the Y axis is perpendicular to the X and Z axes and constitutes a right-hand reference system; according to the lunar ephemeris data, the lunar orbit parameters obtained can include: the eccentricity of the lunar orbit, perigee position, ascent Parameters such as the equator of the intersection point and the angular distance of the pericentric point.

The above lunar ephemeris data can be obtained in the following ways:

Among them, the JPL ephemeris data contains a lot of other information besides the position and velocity of the star, and the orbital eccentricity e is one of them; the JPL lunar ephemeris includes the position information of the moon in the non-rotating geocentric coordinate system, and the earth is A focal point of the moon's elliptical orbit, calculate the moon's vector radius r(n) relative to the earth's center at each moment:

|r(n)|＝r _min (1)

The |r(n)| position is the perigee position.

According to the position of the moon in the ephemeris, traverse the plus and minus of the moon's Z axis along the direction from west to east. When the following conditions are met, n is obtained.

Among them, position n is the ascending node position.

After obtaining the position of the ascending node, calculate the angle between the point and the positive direction of the X-axis to obtain the equator of the ascending node.

According to the position of perigee and the position of ascending node, calculate the angle between the two relative to the center of the earth to obtain the angular distance of the pericentric point of the lunar orbit.

Orbital inclination can be obtained directly from ephemeris data.

S102: Set radar system parameters according to lunar orbit parameters and observation requirements;

Set the system parameters of the radar according to the observation requirements such as the required surveying and mapping bandwidth, resolution, and irradiation time. The system parameters can include: antenna size, carrier frequency f ₀ of the transmitting wave, modulation frequency K _r , PRF (Pulse Recurrence Frequency, pulse repetition frequency ), antenna viewing angle, radar position, etc. The setting of these parameters has the following requirements: the radar beam must cover the earth without generating sub-satellite point echoes; the PRF is high enough to ensure that the echo azimuths do not alias; the radar is deployed on the lunar equator, and the simulation center is always facing the center of the earth. Among them, the transmit wave modulation frequency K _r and the pulse duration T _r determine the transmit wave bandwidth, that is, the range resolution. The accumulation time T _a determines the azimuth resolution. The angle of view θ _a of the antenna and the size of the antenna determine the direction and coverage of the beam, and at the same time, the beam cannot deviate from the earth. It is considered that the radar is facing the center of the earth at all times in the simulation center. However, there is an included angle between the lunar equator and the lunar orbit, and the equivalent lunar carrier yaw angle yaw=0, pitch angle pitch=0, and roll angle roll=6.67°.

S103: Determine the central moment of the echo simulation and the beam irradiation position corresponding to this moment according to the lunar ephemeris data;

This step S103 may include the following processing procedures:

Determine the position of the aiming point of the beam in the rotating earth-centered coordinate system according to the position of the antenna phase center in the lunar astral coordinate system and the position of the moon in the non-rotating earth-centered coordinate system at the target moment; Rotate the position in the geocentric coordinate system to obtain the coordinates of the center point of the beam, and the longitude and latitude corresponding to the coordinates of the center point; select the position corresponding to the center of the beam, and determine the time corresponding to the position as the simulation center time.

As an example, the above processing procedure may be implemented in the following manner.

Interpolate the lunar ephemeris data to PRI (Pulse Repetition Interval, pulse repetition period), take the time when the moon is at the perigee of the orbit as 0 time, and at the same time think that the earth's prime meridian just passes through the vernal equinox at 0 time, the moon position information in the ephemeris is shown in the figure 3 shown.

Take any moment t, and calculate the lunar eccentricity E and pericentric angle θ at that moment;

Calculate the eccentric angle E and pericentric angle θ of the moon at this moment according to the formulas (11) (12) (13) in turn;

M=nt (3)

Among them, M is the average pericentric angle of the moon, and n is the average orbital angular velocity of the moon.

Assume that the position of the antenna phase center (the origin of the antenna coordinate system) relative to the lunar star coordinate system is (x _e , y _e , z _e ); according to the interpolated ephemeris data, the time when the moon is in the non-rotating geocentric coordinate system is obtained The position of t (x _os , y _os , z _os ), that is, the position of the origin of the satellite platform coordinate system in the fixed geocentric coordinate system; any point (x _a , y _a , z _a ) in the antenna coordinate system is established at The expression of the coordinates (x _g , y _g , z _g ) in the rotating geocentric coordinate system, namely:

Among them, A _go , A _ov , A _vr , A _re , A _ea are the matrices used for coordinate system conversion as follows:

Transform the coordinates from the non-rotating geocentric coordinate system to the rotating geocentric coordinate system, H _G is the Greenwich mean time angle.

Transform the coordinates from the orbit plane coordinate system to the non-rotating geocentric coordinate system, Ω is the equator of the ascending node, _i is the orbit inclination, and ω is the angular distance of the pericentric point.

Convert the coordinates from the satellite platform coordinate system to the orbital plane coordinate system, |γ|≤90°.

Convert the coordinates from the satellite star coordinate system to the satellite platform coordinate system.

Converting the coordinate antenna coordinate system to the satellite star coordinate system, it is considered that the yaw angle yaw = 0, the pitch angle pitch = 0, and the roll angle roll = 6.67° at the time of the simulation center.

Since the Y-axis of the antenna coordinate system coincides with the antenna aiming line, the coordinates (0, y, 0) of the aiming point in the coordinate system are substituted into the expression (1), and the antenna aiming point in the rotating earth-centered coordinate system is obtained coordinate:

Bring Equation (7) into the earth model shown in Equation (8), solve for y (take a small value) and substitute it back into Equation (7), and obtain the coordinates of the aiming point in the rotating geocentric coordinate system (x _go , y _go , z _go );

Then the longitude Λ and latitude φ of the center point of the beam at this moment are shown in equations (9) and (10) respectively:

From time t, traverse all lunar positions according to the PRF step, and obtain the coordinates of the corresponding beam center point; take the desired latitude and longitude of the beam center position, and use the corresponding time t ₀ as the simulation center time.

S104: Set a point target within the range of the beam irradiation position, where the point target is the irradiated target during the echo simulation process;

This step S104 may include the following processing procedures:

Determine the first position of the antenna phase center in the rotating earth coordinate system at the beginning of the echo simulation; determine the second position of the point target in the rotating earth coordinate system at the beginning of the echo simulation; according to the first position and the second position Determine whether the point target is irradiated by the beam relative to the vector; obtain the echo phase of the point target irradiated by the beam, and according to the simulation needs, lay out points or lattices at different positions around the center of the beam at the time of the simulation center, for example, using The target layout form can be a single point target and a nine-point lattice perpendicular to the azimuth direction and the distance direction respectively.

S105: Acquire echo data of point targets based on system parameters.

Assuming that the radar irradiation time length is T _a , it is necessary to traverse along the PRI step from the starting moment of irradiation, and the echo simulation process at any time t _P is as follows:

Suppose the position of the moon in the non-rotating earth-centered coordinate system at time t _P is (x _ps , y _ps , z _ps ), find the position of the antenna phase center in the rotating earth coordinate system at time t _P (x _ap , y _ap , z _ap ):

Wherein, the yaw angle yaw required for calculating A _re is not 0 at this time due to the influence of longitude balance movement.

yaw=ρ ₁ -ρ ₂ (12)

In _formula (12), ρ1 is the revolution angle of the moon from this moment to the simulation center moment, and _ρ2 is the moon rotation angle from this moment to the simulation center moment.

Assuming that the position vector of the point target in the rotating geocentric coordinate system at this moment is (x _tar , y _tar , z _tar ), the relative vector between the point target and the antenna phase center in the same coordinate system can be calculated as:

Whether the point target is within the 3dB width of the beam at this moment can be judged according to ΔR; for a point target within the 3dB coverage of the beam, its echo phase information can be expressed as:

In formula (14), c is the speed of light, and t is the time for the electromagnetic wave to go back and forth; record the echo data at this moment, and carry out the next step of simulation. After completing the simulation results at all times in T _a , save the echo data and key parameters.

The echo data obtained by the radar echo data acquisition method provided in the present disclosure is verified by point target simulation, and the single-point echo result is shown in FIG. 4 . And carry out imaging verification on the single-point and nine-point echo results. Table 1 shows some radar parameters of the simulation process.

Fig. 5 is a schematic imaging diagram of a single-point target echo simulation according to an exemplary embodiment, based on which the correctness of the echo can be verified. Among them, the black star-shaped part shown in Figure 5 is a point target, and the white part in the figure is a part without a point target. It should be noted that in the imaging image obtained by actual detection, the part without a point target is black. The portion where the point target exists has a certain brightness, and FIG. 5 is only a schematic diagram for highlighting the point target. Fig. 6 (the representation method of the part of the point target in this Fig. 6 is consistent with that of Fig. 5) is a schematic diagram of a nine-point lattice simulation imaging according to an exemplary embodiment, according to the simulation imaging result of a nine-point lattice It can be seen that point targets at different positions can obtain effective energy compression, which verifies that the echo simulation method provided by the present disclosure has high correctness and effectiveness.

Table 1

The present disclosure also provides an echo simulation device. FIG. 7 is a structural block diagram of an echo simulation device according to an exemplary embodiment. As shown in FIG. 7 , the device 70 includes the following components:

Calculation module 71, is used for calculating lunar orbit parameter according to lunar ephemeris data;

Wherein, the lunar orbit parameters include at least one of the following: orbital eccentricity, perigee position, ascending node position, ascending node equator, pericentric angular distance, and orbital inclination.

The first setting module 72 is used to set the system parameters of the radar according to the lunar orbit parameters and observation requirements;

Wherein, the system parameters of the radar may include at least one of the following parameters:

Transmit tone frequency, pulse duration, beam exposure time, antenna viewing angle, antenna size, and radar position.

Determining module 73, is used for determining the central moment of echo simulation and the corresponding beam irradiation position of this moment according to lunar ephemeris data;

The second setting module 74 is configured to set a point target within the range of the beam irradiation position, where the point target is the irradiated target during the echo simulation process;

An acquisition module 75, configured to acquire echo data of point targets based on system parameters.

Exemplarily, the above-mentioned determination module 73 may include: a first determination unit, configured to determine the aiming of the beam according to the position of the antenna phase center in the lunar astral coordinate system and the position of the moon in the rotating geocentric coordinate system at the time of the simulation center The position of the point in the rotating geocentric coordinate system; the first acquisition unit is used to obtain the coordinates of the center point of the beam according to the position of the aiming point of the beam in the rotating geocentric coordinate system, and the longitude and latitude corresponding to the coordinates of the center point; The second determination unit is configured to select a position corresponding to the center of the beam, and determine the time corresponding to the position as the simulation center time.

Exemplarily, the above-mentioned second setting module 74 may include: a third determination unit, configured to determine the first position of the antenna phase center in the rotating earth coordinate system at the start of echo simulation; a fourth determination unit, configured to determine The second position of the point target in the rotating earth coordinate system at the start of the wave simulation; the judging unit is used to judge whether the point target is irradiated by the beam according to the relative vector of the first position and the second position; the second acquisition unit is used to Get the echo phase of the point target hit by the beam.

The preferred embodiments of the present disclosure have been described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure. These simple modifications all belong to the protection scope of the present disclosure.

In addition, it should be noted that the various specific technical features described in the above specific implementation manners may be combined in any suitable manner if there is no contradiction. In order to avoid unnecessary repetition, various possible combinations are not further described in this disclosure.

In addition, various implementations of the present disclosure can be combined arbitrarily, as long as they do not violate the idea of the present disclosure, they should also be regarded as the content disclosed in the present disclosure.

Claims (10)

1. An echo simulation method, characterized in that, comprising: Calculate lunar orbit parameters based on lunar ephemeris data; Setting radar system parameters according to the lunar orbit parameters and observation requirements; determining the central moment of the echo simulation and the beam irradiation position corresponding to the moment according to the lunar ephemeris data; Setting a point target within the range of the beam irradiation position, the point target being the target to be irradiated during the echo simulation process; Acquiring echo data of the point target based on the system parameters. 2. The method according to claim 1, wherein the determining the central moment of the echo simulation and the beam irradiation position corresponding to the moment according to the lunar ephemeris data comprises: Determine the position of the aiming point of the beam in the rotating earth-centered coordinate system according to the position of the antenna phase center in the lunar astral coordinate system and the position of the moon in the rotating earth-centered coordinate system at the time of the simulation center; Acquiring the coordinates of the center point of the beam according to the position of the aiming point of the beam in the rotating geocentric coordinate system, and the longitude and latitude corresponding to the coordinates of the center point; Select the position corresponding to the center of the beam, and determine the moment corresponding to the position as the moment of the simulation center. 3. The method according to claim 1, wherein said setting a point target within the range of said beam irradiation position comprises: determining a first position of the antenna phase center in a rotating Earth coordinate system at the start of said echo simulation; determining a second position of the point target in a rotating Earth coordinate system at the start of the echo simulation; judging whether the point target is irradiated by the beam according to the relative vector radius of the first position and the second position; Get the echo phase of the point target hit by the beam. 4. The method according to claim 1, wherein the lunar orbit parameters include at least one of the following: Orbital eccentricity, perigee position, ascending node position, ascending node equator, perigee angular distance, and orbital inclination. 5. The method according to any one of claims 1 to 4, wherein the system parameters of the radar include at least one of the following: Transmit tone frequency, pulse duration, beam exposure time, antenna viewing angle, antenna size, and radar position. 6. An echo simulation device, characterized in that, comprising: Calculation module, for calculating lunar orbit parameter according to lunar ephemeris data; The first setting module is used to set the system parameters of the radar according to the lunar orbit parameters and observation requirements; A determining module, configured to determine the central moment of the echo simulation and the beam irradiation position corresponding to the moment according to the lunar ephemeris data; A second setting module, configured to set a point target within the range of the beam irradiation position, where the point target is a target to be irradiated during the echo simulation process; An acquisition module, configured to acquire echo data of the point target based on the system parameters. 7. The device according to claim 6, wherein the determining module comprises: The first determining unit is used to determine the position of the aiming point of the beam in the rotating earth-centered coordinate system according to the position of the antenna phase center in the lunar astral coordinate system and the position of the moon in the rotating earth-centered coordinate system at the time of the simulation center ; The first acquisition unit is configured to acquire the coordinates of the center point of the beam according to the position of the aiming point of the beam in the rotating geocentric coordinate system, and the longitude and latitude corresponding to the coordinates of the center point; The second determining unit is configured to select a position corresponding to the center of the beam, and determine the time corresponding to the position as the simulation center time. 8. The device according to claim 6, wherein the second setting module comprises: A third determining unit, configured to determine the first position of the antenna phase center in the rotating earth coordinate system at the start of the echo simulation; A fourth determining unit, configured to determine a second position of the point target in the rotating earth coordinate system at the start of the echo simulation; A judging unit, configured to judge whether the point target is irradiated by the beam according to the relative vector radius between the first position and the second position; The second acquisition unit is configured to acquire the echo phase of the point target irradiated by the beam. 9. The device according to claim 6, wherein the lunar orbit parameters include at least one of the following: Orbital eccentricity, perigee position, ascending node position, ascending node equator, perigee angular distance, and orbital inclination. 10. The device according to any one of claims 6 to 9, wherein the system parameters of the radar include at least one of the following: Transmit tone frequency, pulse duration, beam exposure time, antenna viewing angle, antenna size, and radar position.