CN108614248B - Frequency modulation detection target echo simulation method based on fractal theory - Google Patents

Frequency modulation detection target echo simulation method based on fractal theory Download PDF

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CN108614248B
CN108614248B CN201810320545.9A CN201810320545A CN108614248B CN 108614248 B CN108614248 B CN 108614248B CN 201810320545 A CN201810320545 A CN 201810320545A CN 108614248 B CN108614248 B CN 108614248B
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ground
grid
frequency modulation
echo
fractal theory
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CN108614248A (en
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赵惠昌
邢姣
刘倩云
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Nanjing University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/40—Means for monitoring or calibrating
    • G01S7/4052—Means for monitoring or calibrating by simulation of echoes

Abstract

The invention relates to a fractal theory-based frequency modulation detection target echo simulation method, which comprises the following steps of: generating a triangular wave chirp signal; obtaining DEM data of a three-dimensional terrain by adopting a fractal theory; establishing a scattering unit model by using DEM data as topographic data through an equal Doppler ring-equal distance method, and simulating an echo of a scattering unit; and (3) superposing the echoes of all scattering units in the radar antenna beam irradiation area, thereby realizing the simulation of the ground echoes. The method not only solves the problems of long time consumption and high capital consumption of the external field test, but also considers the influence of the three-dimensional terrain on the echo simulation compared with other echo simulation methods, and the data is more real and effective.

Description

Frequency modulation detection target echo simulation method based on fractal theory
Technical Field
The invention relates to a short-range detection technology, in particular to a frequency modulation detection target echo simulation method based on a fractal theory.
Background
At present, the traditional radar simulation technology has better application in a low-resolution radar system. However, with the increasing bandwidth of radar signals and the motion characteristics of most radar platforms, the characteristics of broadband radar echoes become more and more complex, the point echo model is no longer applicable, and a surface/volume echo model is used instead. Therefore, echo modeling and simulation under the study relief topography generate more real radar echo data, data can be provided for algorithm study in the radar system, actually measured data can be replaced to a certain extent, the working performance of the radar system is tested, and the radar echo modeling and simulation test system has important theoretical significance and practical value.
Zhouyi et al apply radar equations and target fluctuation simulation to echo simulation modeling in airborne radar echo signal simulation mathematic model research. However, the target fluctuation principle considered by the method is based on the swerlin model, does not consider a real terrain model, and cannot replace measured data to a certain extent.
Disclosure of Invention
In order to generate more real radar echo data, the invention provides a frequency modulation detection target echo simulation method based on a fractal theory.
The technical scheme for realizing the purpose of the invention is as follows: a frequency modulation detection target echo simulation method based on a fractal theory comprises the following steps:
step 1, generating a triangular wave linear frequency modulation signal;
step 2, performing three-dimensional terrain modeling by adopting a midpoint displacement method in a fractal theory to obtain terrain DEM data;
step 3, establishing a scattering unit model by using DEM data as topographic data through an equal Doppler loop-equal distance method, and calculating a ground normal vector, an included angle between an antenna beam and a topographic network according to the DEM data so as to simulate an echo of a scattering unit;
and 4, superposing the echoes of all scattering units in the radar antenna beam irradiation area to realize the simulation of the ground echoes.
Compared with the prior art, the invention has the following remarkable advantages:
(1) the radar echo data is more real: aiming at the inaccuracy caused by the fact that the existing radar echo simulation method does not consider topographic relief, the invention opens up a new idea for simulating the echo in a topographic scene, so that the radar echo data is more real; (2) the method has the advantages of real-time performance and controllability: compared with an actual measurement method, the method shortens the measurement period, saves manpower and financial resources, is not easily influenced by environmental factors, and improves the execution efficiency.
Drawings
FIG. 1 is a flow chart of a frequency modulation detection target echo simulation method based on a fractal theory.
FIG. 2 is a diagram of the steps of the point displacement method according to the present invention.
FIG. 3 is a three-dimensional modeling topographical map of the present invention.
FIG. 4 is a model diagram of a DEM-based scattering unit according to the present invention.
Fig. 5 is a waveform diagram of an echo signal.
Fig. 6 is a partial enlarged view of the waveform of the echo signal.
Detailed Description
With reference to fig. 1, a fractal theory-based frequency modulation detection target echo simulation method includes the following steps:
step 1, generating a triangular wave linear frequency modulation signal; the method comprises the following specific steps:
the transmitting signals of the up-and-down scanning frequency bands of the triangular wave linear frequency modulation signal are respectively as follows:
Figure BDA0001625172170000021
Figure BDA0001625172170000022
wherein A and
Figure BDA0001625172170000023
amplitude and random phase, respectively, of the transmitted signal, f0In order to transmit the center frequency of the signal,
Figure BDA0001625172170000024
to modulate the slope, FmTo modulate the frequency offset, T is the modulation period.
Assume that the initial distance of the target is R0With a radial velocity v, the instantaneous echo delay is
Figure BDA0001625172170000025
Wherein
Figure BDA0001625172170000026
In order to delay the time of the initial echo,
Figure BDA0001625172170000027
for normalized Doppler frequency, c is the speed of light.
Step 2, as shown in fig. 2, performing three-dimensional terrain modeling by adopting a midpoint displacement method in a fractal theory to obtain terrain DEM data; the concrete steps of generating the topographic data in the step 2 are as follows:
(21) the given area is subjected to grid division, a square grid is divided on an x-y plane by n, and initial height values of ha, hb, hc and hd are set in the z direction for four vertexes A, B, C, D of an original square.
(22) Calculating the height value he ═ of (ha + hb + hc + hd)/4+ Δ of the center E of the square ABCD from the four initial height values, where Δ is a random quantity;
(23) according to the height values of the three points A, B, E, adding a virtual point with the height value he which is the symmetric height value of the net and the point E, and calculating the height value of the midpoint G of the edge AB; according to the 3 points B, C, E and the virtual point with the grid outer and E point symmetric height value he, calculating the height value of the middle point H of the BC edge, and calculating the height value of the middle point I of the middle point F, DC of the AD edge in the same way;
hf＝(hd+ha+he+he)/4+△
hg＝(ha+hb+he+he)/4+△
hh＝(hb+hc+he+he)/4+△
hi＝(hc+hd+he+he)/4+△
(24) completing a complete Diamond-Square step, increasing from the initial 4 known points to 9 known points; the square grid can be continuously refined through recursion steps (22) and (23), and finally the required terrain is obtained.
Step 3, establishing a scattering unit model by using DEM data as topographic data through an equal Doppler loop-equal distance method, and calculating a ground normal vector, an included angle between an antenna beam and a topographic network according to the DEM data so as to simulate an echo of a scattering unit; the method comprises the following steps:
(31) computing ground normal vectors
Let four vertexes of the square grid cell be A respectively1(x1,y1,z1)、A2(x2,y2,z2)、A3(x3,y3,z3)、A4(x4,y4,z4) Taking A1A2Is at the midpoint of
Figure BDA0001625172170000031
With A3A4A5With three points' normal vectors replacing the grid cellsA normal vector;
Figure BDA0001625172170000032
wherein the content of the first and second substances,
Figure BDA0001625172170000033
angle between ground grid unit and horizontal plane
Figure BDA0001625172170000041
(32) Calculating included angle between radar antenna wave beam and terrain grid
Figure BDA0001625172170000042
Wherein the content of the first and second substances,
Figure BDA0001625172170000043
for the beam vector of the radar antenna,
Figure BDA0001625172170000044
is the normal vector of the ground, and beta is the angle of ground rubbing.
(33) Calculation of the Radar Cross-section
Calculating the radar irradiation area S of each grid unit2Then, according to the ground rubbing angle of the grid unit and a backscattering coefficient formula, the radar scattering sectional area of the unit can be obtained
Figure BDA0001625172170000045
Step 4, superposing the echoes of all scattering units in a radar antenna beam irradiation area to realize the simulation of ground echoes; the method comprises the following steps:
and dividing the ground by adopting a grid mapping method, and superposing the echoes of all the point composite scatterers in the radar antenna beam irradiation area, thereby realizing the simulation of the ground echoes.
The invention is described in further detail below with reference to the figures and examples.
Examples
The present embodiment employs the following system parameters: triangular wave linear frequency modulation system with center frequency of 1GHz and modulation period Tm0.32ms, 12.8MHz, 20-2 m of projectile motion height, 60 degree projectile falling angle, 300m/s of vertical falling speed and differential frequency sampling rate Fs＝5GHz。
As shown in fig. 1, the present invention comprises the steps of:
(10) generating a signal: generating triangular wave linear frequency modulation signals according to system parameters, and simulating the motion track of the projectile according to the motion parameters of the projectile;
(20) generating topographic data: carrying out three-dimensional terrain modeling by adopting a midpoint displacement method in a fractal theory to obtain terrain DEM data;
(30) constructing a scattering unit model: establishing a scattering unit model by using DEM data as topographic data through an equal Doppler ring-equal distance method, and simulating an echo of a scattering unit;
(40) simulating an echo signal: and (3) superposing the echoes of all scattering units in the radar antenna beam irradiation area, thereby realizing the simulation of the ground echoes.
As shown in fig. 3, in step (20), a midpoint displacement method in a fractal theory is adopted to perform three-dimensional terrain modeling, so as to obtain a final terrain map, wherein the terrain map comprises information such as the position, height and undulation degree of the terrain, and a scattering unit model can be constructed through the information.
As shown in fig. 4, according to the terrain data obtained in step (20), a ground normal vector, an included angle between a radar antenna beam and a terrain grid, and a radar scattering cross-sectional area are calculated.
1) Computing ground normal vectors
Let four vertexes of the square grid cell be A respectively1(x1,y1,z1)、A2(x2,y2,z2)、A3(x3,y3,z3)、A4(x4,y4,z4) Taking A1A2Is at the midpoint of
Figure BDA0001625172170000051
With A3A4A5The normal vectors of the three points replace the normal vectors of the grid cells.
Figure BDA0001625172170000052
Wherein the content of the first and second substances,
Figure BDA0001625172170000053
angle between ground grid unit and horizontal plane
Figure BDA0001625172170000054
2) Calculating included angle between radar antenna wave beam and terrain grid
Figure BDA0001625172170000055
Wherein the content of the first and second substances,
Figure BDA0001625172170000056
for the beam vector of the radar antenna,
Figure BDA0001625172170000057
is the normal vector of the ground, and beta is the angle of ground rubbing.
3) Calculation of the Radar Cross-section
Calculating the radar irradiation area S of each grid unit2Then combining the backscattering coefficient according to the ground rubbing angle of the grid unit
Figure BDA0001625172170000058
The radar scattering cross section of the unit can be obtained by formula
Figure BDA0001625172170000059
With reference to fig. 5 and 6, echo signals of the scattering units can be obtained according to the ground normal vector, the included angle between the radar antenna beam and the terrain grid, and the radar scattering cross-sectional area obtained through calculation, and the echo signals of the scattering units in the antenna irradiation area are superposed to obtain ground echo signals. The whole ground echo shows an amplification trend, and accords with the rule that the amplitude of an intermediate frequency signal of the echo has one-to-one correspondence with the height of the projectile no matter the descent speed of the projectile.

Claims (5)

1. A frequency modulation detection target echo simulation method based on a fractal theory is characterized by comprising the following steps:
step 1, generating a triangular wave linear frequency modulation signal;
step 2, performing three-dimensional terrain modeling by adopting a midpoint displacement method in a fractal theory to obtain terrain DEM data;
step 3, establishing a scattering unit model by using DEM data as topographic data through an equal Doppler loop-equal distance method, and calculating a ground normal vector, an included angle between an antenna beam and a topographic network according to the DEM data so as to simulate an echo of a scattering unit;
and 4, superposing the echoes of all scattering units in the radar antenna beam irradiation area to realize the simulation of the ground echoes.
2. The frequency modulation detection target echo simulation method based on the fractal theory as claimed in claim 1, wherein the signal generation of step 1 comprises the following specific steps:
the transmitting signals of the up-and-down scanning frequency bands of the triangular wave linear frequency modulation signal are respectively as follows:
Figure FDA0003453851790000011
Figure FDA0003453851790000012
wherein A and
Figure FDA0003453851790000013
amplitude and random phase, respectively, of the transmitted signal, f0In order to transmit the center frequency of the signal,
Figure FDA0003453851790000014
to modulate the slope, FmTo modulate the frequency offset, T is the modulation period.
Assume that the initial distance of the target is R0With a radial velocity v, the instantaneous echo delay is
Figure FDA0003453851790000015
Wherein
Figure FDA0003453851790000016
In order to delay the time of the initial echo,
Figure FDA0003453851790000017
for normalized Doppler frequency, c is the speed of light.
3. The frequency modulation exploration target echo simulation method based on the fractal theory as claimed in claim 2, wherein the specific steps of generating the topographic data in step 2 are as follows:
(21) carrying out grid division on a given area, dividing a square grid on an x-y plane by nxn, and setting initial height values of ha, hb, hc and hd for four vertexes A, B, C, D of an original square in the z direction;
(22) calculating the height value he ═ of (ha + hb + hc + hd)/4+ Δ of the center E of the square ABCD from the four initial height values, where Δ is a random quantity;
(23) according to the height values of the three points A, B, E, adding a virtual point with the height value he which is the symmetric height value of the net and the point E, and calculating the height value of the midpoint G of the edge AB; according to the 3 points B, C, E and the virtual point with the grid outer and E point symmetric height value he, calculating the height value of the BC edge midpoint H, and calculating the height value of the AD edge midpoint F, DC edge midpoint I in the same way:
hf＝(hd+ha+he+he)/4+Δ
hg＝(ha+hb+he+he)/4+Δ
hh＝(hb+hc+he+he)/4+Δ
hi＝(hc+hd+he+he)/4+Δ
(24) completing a complete Diamond-Square step, increasing from the initial 4 known points to 9 known points; and repeating the steps (22) and (23) to continuously refine the square grid, and finally obtaining the required terrain.
4. The frequency modulation detection target echo simulation method based on the fractal theory as claimed in claim 3, wherein the step 3 comprises the following steps:
(31) computing ground normal vectors
Let four vertexes of the square grid cell be A respectively1(x1,y1,z1)、A2(x2,y2,z2)、A3(x3,y3,z3)、A4(x4,y4,z4) Taking A1A2Is at the midpoint of
Figure FDA0003453851790000021
Namely A5(x5,y5,z5) With A3A4A5Replacing the normal vector of the grid unit by the normal vector of the three points;
Figure FDA0003453851790000022
wherein the content of the first and second substances,
Figure FDA0003453851790000023
angle between ground grid unit and horizontal plane
Figure FDA0003453851790000024
(32) Calculating included angle between radar antenna wave beam and terrain grid
Figure FDA0003453851790000031
Wherein the content of the first and second substances,
Figure FDA0003453851790000032
for the beam vector of the radar antenna,
Figure FDA0003453851790000033
is the normal vector of the ground, and beta is the angle of ground rubbing.
(33) Calculation of the Radar Cross-section
Calculating the radar irradiation area S of each grid unit2Then combining the backscattering coefficient according to the ground rubbing angle of the grid unit
Figure FDA0003453851790000034
Formula to obtain the radar scattering cross section of the unit
Figure FDA0003453851790000035
5. The frequency modulation detection target echo simulation method based on the fractal theory as claimed in claim 1 or 4, wherein the echo simulation of step 4 comprises the following steps:
and dividing the ground by adopting a grid mapping method, and superposing the echoes of all the point composite scatterers in the radar antenna beam irradiation area, thereby realizing the simulation of the ground echoes.
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