CN101551457A - A construction method of forward looking linear array three-dimensional synthetic aperture radar system - Google Patents

Abstract

The invention discloses a construction method of a forward-looking three-dimensional synthetic aperture radar system, which utilizes the characteristics of high control precision of the single-excitation linear array three-dimensional synthetic aperture radar antenna phase center and the ability of the forward-looking synthetic aperture radar system to obtain terrain information ahead of time , using the mode of combining the single-excitation linear array 3D SAR system and the forward-looking SAR system, so that the beam of the single-excitation linear array 3D SAR is forward-looking. Then we use the standard back projection algorithm to process the received echo data in real time to obtain the three-dimensional imaging results of the front surveying and mapping area. The three-dimensional terrain information in front of the aircraft can be obtained in advance and in real time, which provides a new method for precise guidance and aircraft navigation, approach landing and blind landing.

Description

A Construction Method of 3D Synthetic Aperture Radar System with Forward Line-of-Sight Array

Technical field:

The technical invention belongs to the technical field of radar, and in particular relates to the technical field of synthetic aperture radar (SAR) imaging.

Background technique:

Synthetic Aperture Radar (SAR) is a high-resolution microwave imaging system, which relies on the relative motion between the radar and the target to form a synthetic array to obtain horizontal high resolution, and uses large bandwidth signals to achieve vertical high resolution. SAR is based on the conventional SAR horizontal dimension and longitudinal dimension with an additional tangential horizontal dimension, and it also relies on the relative motion between the radar and the target to obtain the tangential horizontal resolution. 3D imaging is an important feature that distinguishes 3D SAR from other remote sensing imaging systems. Because of its all-weather, all-time, and long-distance characteristics, it plays an irreplaceable role in terrain mapping, environmental detection, and disaster forecasting.

The emergence of forward-looking SAR has expanded the application range of SAR. At present, the German Aerospace Agency (DLR) has done a good job in forward-looking SAR. A new type of airborne forward-looking synthetic aperture radar system for high-resolution imaging -- "New Area Imaging Radar for Vision Enhancement (SIREV)", the theoretical research, forward-looking imaging algorithm, computer simulation and prototype of SIREV have been completed so far Developed and flight tested on DLR's E-SAR airborne test platform. The system is analyzed and described in related literature. However, this kind of forward-looking SAR can only obtain two-dimensional SAR images, and the three-dimensional information of the terrain cannot be obtained.

Our forward-looking 3D SAR combines the advantages of 3D SAR and forward-looking SAR. In addition to the role played by 3D SAR, because the beam is forward-looking illumination, it can obtain surveying and mapping terrain information in advance and in real time, so it can also Realize the navigation and blind landing of the aircraft, so the forward-looking three-dimensional synthetic aperture radar has broad application prospects.

Invention content:

The purpose of the present invention is to provide a method for constructing a forward line-of-sight array three-dimensional synthetic aperture radar system (SAR system) in order to overcome the shortcoming that the existing synthetic aperture radar system (SAR system for short) cannot obtain real-time three-dimensional terrain information ahead. The system adopts the single-array element excitation method of the linear array system, and the forward-looking beam can obtain the three-dimensional terrain information in front of the aircraft in advance and in real time, providing a new method for precise guidance, aircraft navigation, approach landing and blind landing.

In order to describe content of the present invention conveniently, at first do following term definition:

Definition 1. Linear array 3D imaging synthetic aperture radar

The linear array three-dimensional imaging synthetic aperture radar is a synthetic aperture radar system that fixes the linear array antenna on the moving platform, combines the movement of the moving platform to synthesize a two-dimensional planar array, and performs three-dimensional imaging.

Definition 2. Single incentive mode

In a flight aperture, for a linear array antenna fixed on a moving platform, at each slow time n, n=1...N, use a control switch to turn on a specific array element in the linear array antenna to transmit signals or Receive echo. For details, please refer to the literature: "APC Trajectory design for'one-active'linear array 3-D imaging SAR", Shi Jun et al.

Definition 3. Beam front angle of view

The beam front angle of view refers to the acute angle between the center of the synthetic aperture radar beam and the flight speed direction of the aircraft. Generally, the aircraft flies along a straight line, so the beam angle can be considered as the angle between the center of the radar beam and the straight line along the track. When the beam front angle of view is 0°-20°, it is called hypertropia, and when it is 20°-90°, it is called microstrabismus.

Definition 4. The theoretical resolution of 3D imaging SAR

Theoretical resolution of 3D SAR refers to the maximum resolution that 3D SAR can achieve based on the parameters of the 3D SAR system, including the transmitted signal bandwidth, the length of the synthetic aperture and the length of the linear array antenna. For details, see the document "Synthetic Aperture Radar Imaging - Algorithm and Implementation", edited by Frank H. Wong et al., published by Electronic Industry Press.

Definition 5. Standard back projection algorithm

The back projection algorithm is a synthetic aperture radar imaging algorithm based on the principle of matched filtering. For details, please refer to the literature: "Research on A novel fast back projection algorithm for strip map bistaticSAR imaging", Huang Yulin, etc.

Definition 6. Transmitting/receiving antenna phase center locus

The phase center trajectory of the transmitting/receiving antenna refers to the trajectory formed by the positions of the transmitting/receiving antenna elements opened by the forward line-of-sight array 3D imaging synthetic aperture radar in different pulse repetition periods, which can be regarded as a random variable that obeys a certain distribution;

Definition 7. Synthetic Aperture Radar Transmitter

Synthetic aperture radar transmitter refers to the system used by synthetic aperture radar to transmit electromagnetic signals to the observation area, mainly including signal generators, mixers, amplifiers and other modules

Definition 8. Synthetic Aperture Radar Receiver

The synthetic aperture radar receiver refers to the system used by the current synthetic aperture radar to receive the echo of the observation area, mainly including mixers, amplifiers, analog/digital converters, storage devices, etc.

Definition 9, flight aperture and slow time

The flight aperture of the dual-station linear array 3D synthetic aperture radar system refers to the distance traveled by the center of the transmitting and receiving beam for a scattering point in the surveying and mapping scene from the common irradiation of the transmitting and receiving beams to the beginning to the end when either the transmitting beam or the receiving beam cannot be illuminated.

The slow time of the dual station linear array 3D SAR system refers to the time required for the transceiver platform to fly through a flight aperture. Since the radar transmits and receives pulses with a certain repetition period _Tr , the slow time can be expressed as a discretized time variable t _s =nT _r , n=1L N, N is the discrete number of slow times in a flight aperture, and T _r is the repetition period.

The invention provides a method for constructing a forward line-of-sight array three-dimensional synthetic aperture radar system, which comprises the following steps:

Step 1: Construction of transmitting system and receiving system

The transmitting system and the receiving system include: a transmitter, a receiver, a T/R switch, a feeder control switch, M feeders and M linear array feeders; M is a natural number, and the size of M is determined by the previous The line-of-sight array three-dimensional synthetic aperture radar system is determined by the pulse repetition frequency within a flight aperture, M=v×Na/L, where v is the speed of the flying platform, Na is the number of sampling points in the direction of the synthetic aperture radar, and L is the linear array Antenna length; the transmitter and receiver are connected to the control switch with a T/R switch, one side of the T/R switch is connected to the control switch, and the other side is connected to the transmitter and receiver respectively, as shown in Figure 1 The control switch is connected to form a linear array antenna through M feeders and M linear array feed elements, as shown in Figure 2; the length L of the linear array antenna is determined by the resolution required by the forward line-of-sight array three-dimensional synthetic aperture radar system , L=λ/ρ, where λ is the forward line-of-sight array 3D SAR system carrier frequency, ρ is the system resolution; the transmitter and the receiver share a linear array antenna, and a T/R switch is used to control the transmitter and The receiver works in different periods, that is, it adopts a single excitation mode.

Step 2: Determination of the phase center locus of single excitation linear array antenna

For slow time n, n=1...N, N is a positive integer, when n=1, the control switch opens any linear array feed element M=M ₁ in the linear array antenna according to the triangular periodic function, M ₁ is M lines The mark of any linear array feeder in the array feeder, write down the mark M ₁ of the linear array feeder working when the slow time n=1;

When n=2, the control switch opens a linear array feed element M=M ₂ in the linear array antenna, M ₂ ≠ M ₁ , and write down the mark M ₂ of the linear array feed element working when the slow time n=2;

When n=3, the control switch opens a linear array feed element M=M ₃ in the linear array antenna, M ₃ ≠M ₂ ≠M ₁ , write down the line array feed element mark M ₃ that works when the slow time n=3;

...;

By analogy, when n=N, the control switch opens a linear array feed element M=M _N in the linear array antenna, M ₁ , M ₂ , M ₃ ,..., M _N are all different, record the slow time n= The line array feed element mark M _N of work at N; Like this, just obtain the corresponding relation of slow time and the line array feed element mark corresponding to this slow time work, namely line array antenna phase center locus, described line array antenna phase center locus The composed random variables obey the uniform distribution.

Step 3: Transmit/Receive Platform Construction

运动，运动平台的初始化飞行高度为H_t0；如图3所示；The forward line-of-sight array 3D synthetic aperture radar system transmitting/receiving platform is to place the linear array transmitting system/receiving system in step 1 on the moving platform, the arrangement direction of the feed elements in the linear array antenna is perpendicular to the moving direction of the moving platform, and the moving platform at constant vector velocity

Motion, the initial flight height of the motion platform is _Ht0 ; as shown in Figure 3;

Step 4: Synchronize the Transmitter and Receiver Systems

During the three-dimensional imaging process of the forward-looking array three-dimensional imaging synthetic aperture radar, the T/R switch is switched at a fixed delay time τ after the transmitting system transmits the electromagnetic signal, so that the receiving system receives the scene echo, so as to realize the transmission system and the receiving system. The time synchronization of , where the fixed delay time τ is determined by the distance R from the observation area to the linear array antenna, τ=0.8×2R/C, where C is the speed of light.

Step 5: Single-stimulus transmitting/receiving platform work of the forward-looking array 3D synthetic aperture radar system

Through the T/R conversion switch, the linear array transmitter and receiver continuously transmit electromagnetic wave signals and receive echo signals to the surveying scene according to the antenna phase center trajectory constructed in step 2. The forward line-of-sight array 3D synthetic aperture radar system uses a single excitation Working mode, that is, only one feeder works at each slow time, and in this slow time, the transmitter and receiver can only work through one feeder; the receiver obtains the echo signals of n surveying and mapping scenes at n slow times. Acquisition data of 3D synthetic aperture radar system with forward-looking array.

Through the above steps, the construction of the forward line-of-sight array three-dimensional imaging synthetic aperture radar system can be completed. The flow chart of the present invention is shown in FIG. 6 .

It should be noted,

Using the existing standard back projection algorithm, the data collected in step 4 of the forward line-of-sight array three-dimensional imaging synthetic aperture radar system can be used to reconstruct the three-dimensional scattering coefficient of the observation area;

The control switch described in step 2 opens any one of the linear array feed elements in the linear array antenna according to the triangular periodic function, and the described control switch can also open any one of the linear array feed elements in the linear array antenna according to the Gaussian function and the parabolic function, and finally The obtained distribution of the motion track of the antenna phase center can be a triangular periodic function distribution, a Gaussian function distribution or a parabolic function distribution, etc., which does not affect the effectiveness of the forward line-of-sight array three-dimensional imaging synthetic aperture radar system constructed by the present invention.

The innovation of the present invention is that the system uses the principle of synthetic aperture radar, combined with the high control precision of the phase center of the three-dimensional synthetic aperture radar antenna of single-excitation linear array and the existing forward-looking synthetic aperture radar system, which can obtain the front terrain information in advance to realize real-time acquisition. Knowing the three-dimensional information of the terrain surveyed and mapped ahead can realize the navigation and blind landing of the aircraft.

The basic principle of the present invention: the present invention utilizes the principle of synthetic aperture radar, combines the characteristics of high precision of phase center control of single-excitation linear array three-dimensional synthetic aperture radar antenna phase center and forward-looking synthetic aperture radar system that can obtain terrain information in advance, so we just adopt The combination mode of the single-excitation linear array 3D SAR system and the forward-looking SAR system makes the beam of the single-excitation linear array 3D SAR forward-looking. Then we process the received echo data in real time using the standard back projection algorithm (namely the 3D BP algorithm), and finally we can get the 3D imaging result of the front surveying and mapping area.

The technical problem solved by the present invention: the forward line-of-sight array three-dimensional synthetic aperture radar system proposed by the present invention is mainly proposed for the shortcoming that the existing synthetic aperture radar cannot obtain the front three-dimensional terrain information in real time. The radar antenna phase center control precision is high and the forward-looking synthetic aperture radar system can obtain the advantages of the front terrain information in advance. With the excitation method of the single array element of the linear array system and the forward-looking irradiation of the beam, the three-dimensional terrain information in front of the aircraft can be obtained in advance and in real time. , providing a new method for precision guidance and aircraft navigation, approach and landing, and blind landing.

The advantage of the present invention is that it adopts the characteristic of combining single-excitation linear array 3D SAR and forward-looking SAR, utilizes lower hardware cost, and realizes forward-looking array 3D synthetic aperture radar imaging with small data processing capacity, the most important thing is to realize The three-dimensional imaging of the mapping area in front of the aircraft can obtain the three-dimensional terrain information in front of the aircraft in advance and in real time.

Description of drawings

Fig. 1 is a structural block diagram of transmitting system/receiving system of the present invention

Fig. 2 is the structural block diagram of the line array antenna of transmitter/receiver of the present invention

Fig. 3 is the motion geometric structure diagram of the forward line-of-sight array three-dimensional imaging synthetic aperture radar adopted in the present invention

为飞行器的速度矢量，θ_f为前视角；X、Y、Z为三维坐标系；in,

is the velocity vector of the aircraft, θ _f is the front viewing angle; X, Y, Z are the three-dimensional coordinate system;

Fig. 4 is the imaging result diagram of the specific embodiment of the present invention to the three-dimensional point target

The abscissa is the direction tangent to the track, the ordinate is the direction along the track, the vertical coordinate is the height direction, and 1 is the imaging of the three-dimensional point target.

Fig. 5 is the parameter table used when emulating the specific embodiment of the present invention

Fig. 6 is a flowchart of the present invention

Detailed ways

The present invention mainly uses the simulation experiment method to verify the feasibility of the system model, and all steps and conclusions are verified correctly on VC++ and MATLAB7.0. The specific implementation steps are as follows:

Step 1: Construction of line array transmitting/receiving system

i＝1L 1000，水平波束宽度分别为

单位为弧度，i＝1L 1000。The linear array transmitter/receiver on the moving platform of the forward line-of-sight array three-dimensional synthetic aperture radar system includes the following parts: a transmitter, a receiver, a T/R switch, a feeder control switch, 800 feeders and 800 linear array feed elements, the system block diagram is shown in Figure 1, the transmitter and receiver are connected to the control switch with a T/R switch, and the transmitter and receiver are respectively connected to the T/R switch for control The switch is connected to the receiver, and the control switch is connected to 800 line array feeders through 800 feeders, and the length of the line array is 20. In a flight aperture, the T/R switch controls the switching between the transmitter and the receiver, and the control switch controls the position of the feed element opened by each slow time n, n=1L N, and at each slow time n Only one feed is opened. The azimuth beamwidth of the linear array feed is

i=1L 1000, the horizontal beam widths are

The unit is radian, i=1L 1000.

Step 2: Construction of the phase center locus of the single excitation array antenna

Because the forward line-of-sight array 3D synthetic aperture radar adopts a single-excitation working mode, at each slow time n, n=1...N, use the control switch to select any feed element in the single-excitation array antenna according to the triangular periodic function. Transmit and receive signals, and record the position of each open feed element, then all the slow times, the positions of all working feed elements constitute a trajectory, which is defined as the antenna phase center of the forward line-of-sight array three-dimensional synthetic aperture radar trajectory.

Step 3: Transmit/Receive Motion Platform Construction

The forward line-of-sight array 3D synthetic aperture radar system transmits/receives the moving platform by placing the linear array transmitter/receiver in step 1 on the moving platform, the arrangement direction of the linear array antenna is placed along the vertical direction of the transmitting platform’s moving direction, and the moving platform is set with a constant vector Speed [01000] motion, the initial flight height of the motion platform is 1000m.

Use the T/R switch to make the line array transmitter and receiver continuously transmit electromagnetic wave signals and receive echo signals to the surveying and mapping scene according to the antenna phase center trajectory constructed in step 2.

The flight geometric structure diagram of the forward line-of-sight array three-dimensional synthetic aperture radar is shown in Figure 3.

The system parameters adopted in this specific embodiment are shown in FIG. 5 for details. Finally, we simulate and image the surveying and mapping points, and the obtained 3D imaging is shown in FIG. 4 .

Through the simulation and testing of the specific embodiments of the present invention, the 3D synthetic aperture radar system provided by the present invention can realize the 3D imaging synthetic aperture radar imaging of the forward line of sight array. Compared with the existing 3D synthetic aperture radar system, this The invention overcomes the shortcomings of the existing system, obtains the three-dimensional terrain information in front of the aircraft in advance, and provides a new method for precise guidance, aircraft navigation, approach landing and blind landing.

Claims (2)

1. A construction method of a forward looking linear array three-dimensional synthetic aperture radar system is characterized by comprising the following steps:

step 1: single excitation transmitting system and receiving system construction

The transmitting system and the receiving system include: the system comprises a transmitter, a receiver, a T/R change-over switch, a feed element control switch, M feeder lines and M linear array feed elements; m is a natural number, the size of M is determined by the size of pulse repetition frequency of a foresight linear array three-dimensional synthetic aperture radar system in a flight aperture, and M is v multiplied by Na/L, wherein v is the speed of a flight platform, Na is the number of sampling points of the synthetic aperture radar in the azimuth direction, and L is the length of a linear array antenna; the transmitter and the receiver are connected with the control switch by a T/R change-over switch, one side of the T/R change-over switch is connected with the control switch, the other side of the T/R change-over switch is respectively connected with the transmitter and the receiver, the control switch is connected with M linear array feed elements by M feeder lines to form a linear array antenna, the length L of the linear array antenna is determined by the resolution ratio required by the foresight linear array three-dimensional synthetic aperture radar system, L is lambda/rho, wherein lambda is the carrier frequency of the foresight linear array three-dimensional synthetic aperture radar system, and rho is the system resolution ratio; the transmitter and the receiver share a linear array antenna, and a T/R change-over switch is used for controlling the transmitter and the receiver to work at different time intervals, namely, a single excitation working mode is adopted;

step 2: determination of phase center trajectory for single-excitation antenna

For slow time N, N is 1. N is a positive integer, and when N is 1, the control switch opens any linear array feed element M in the linear array antenna according to a triangular periodic function₁，M₁Is the mark of any one of M linear array feed elements, and marks the linear array feed element mark M working when the slow time n is equal to 1₁；

When n is 2, the control switch opens one linear array feed element M in the linear array antenna₂，M₂≠M₁Recording linear array feed element mark M working when slow time n is 1₂；

When n is 3, the switch is controlled to open one linear array feed element M in the linear array antenna₃，M₃≠M₂≠M₁Recording linear array feed element mark M working when slow time n is 1₂；

……；

And so on, when N equals to N, the control switch opens one linear array feed element M equals to MN, M in the linear array antenna₁，M₂，M₃，…，M_NDifferent, recording the line array feed element mark M working when the slow time N is equal to N_N(ii) a Thus, the corresponding relation between the slow time and the linear array feed element mark working corresponding to the slow time is obtained, namely the phase center track of the linear array antenna, and the phase of the linear array antennaRandom variables formed by the central track are subjected to uniform distribution;

and step 3: transmit/receive platform construction

The forward looking linear array three-dimensional synthetic aperture radar system transmitting/receiving platform is characterized in that the linear array transmitting system/receiving system in the step 1 is arranged on a moving platform, the arrangement direction of feed elements in a linear array antenna is vertical to the moving direction of the moving platform, and the moving platform is at constant vector speed

Initial flying height of moving platform is H_t0；

And 4, step 4: transmission system and reception system synchronization

In the process of three-dimensional imaging of the front line-of-sight array three-dimensional imaging synthetic aperture radar, a T/R switch is switched at a fixed delay time tau after an emission system emits electromagnetic signals, and a receiving system is enabled to receive scene echoes to achieve time synchronization of the emission system and the receiving system, wherein the fixed delay time tau is determined by the distance R from an observation area to a linear array antenna, tau is 0.8 multiplied by 2R/C, and C is the speed of light;

and 5: single excitation transmitting/receiving platform work of forward looking linear array three-dimensional synthetic aperture radar system

Enabling the linear array transmitter and the receiver to continuously transmit electromagnetic wave signals and receive echo signals to a surveying and mapping scene according to the antenna phase center track constructed in the step 2 through a T/R (time to arrival) change-over switch, wherein the forward-looking linear array three-dimensional synthetic aperture radar system adopts a single excitation working mode, namely only one feed element works at each slow time, and the transmitter and the receiver can only work through one feed element at the slow time; the receiver obtains echo signals of n surveying and mapping scenes in n slow time, and the echo signals are acquired data of the forward looking linear array three-dimensional synthetic aperture radar system.

2. The method according to claim 1, wherein said control switch in step 2 opens any one of the linear array feed elements in the linear array antenna according to a triangular periodic function, said triangular periodic function is replaced by a gaussian function or a parabolic function, and the distribution obeyed by the antenna phase center motion trajectory obtained after replacement is gaussian function distribution or parabolic function distribution.

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