CN102176011B - Method for realizing three-dimensional coherent imaging by ground penetrating radar under near field condition - Google Patents
Method for realizing three-dimensional coherent imaging by ground penetrating radar under near field condition Download PDFInfo
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- CN102176011B CN102176011B CN201110025100.6A CN201110025100A CN102176011B CN 102176011 B CN102176011 B CN 102176011B CN 201110025100 A CN201110025100 A CN 201110025100A CN 102176011 B CN102176011 B CN 102176011B
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Abstract
The invention belongs to the technical field of radar imaging, and particularly discloses a method for realizing three-dimensional coherent imaging by a ground penetrating radar under near field condition. The method is characterized by comprising the following steps of: 1) transmitting radar waves to a target at transmission frequency f, and performing difference frequency processing on a target echo signal received by the radar and a reference signal to obtain a difference frequency processed echo signal; 2) interpolating the difference frequency processed echo signal, and performing range direction compression; 3) dividing an imaging area into grids, and calculating delays of each grid point or pixel point, delayed by the radar, in the imaging area at each azimuthal position; 4) performing phase compensation on echoes of corresponding points according to the calculated delays; 5) performing coherence addition on each pixel point to obtain an addition result which is a value of the pixel point; and 6) traversing the whole imaging area by adopting the steps 4) and 5) to obtain an imaging function, and finishing the reconstruction of an image. In the method for realizing the three-dimensional coherent imaging by the ground penetrating radar under the near field condition, the three-dimensional imaging is performed on a near field target area, and relatively higher resolution is ensured.
Description
Technical field
The invention belongs to the radar imagery technical field, specifically the three-dimensional coherent imaging method of the ground penetrating radar under a kind of Near Field.The present invention is suitable for the back-projection algorithm of target area, near field imaging.
Background technology
In recent years, the radar near field Detection Techniques are because the traction of demand becomes one of hot issue of radar application research gradually, and the near field radar can be applied to different occasions, for example; The detection of detection through walls, mine detection, nondestructive highway inspection, bunker and archaeology excavate.At present, radar is operated in the near field pattern, is that to survey be main substantially.
The product of external and domestic ground penetrating radar is the signal form that the carrierfree of employing impacts mostly, the ground penetrating radar that adopts carrierfree to impact has the simple advantage of system, generally only need the impact signal generator, emitting antenna, receiving antenna, and the reception & disposal unit just can realize, but the radar that carrierfree impacts can not utilize the phase information of echo, and radar resolution can be subject to certain restrictions.And the ground penetrating radar resolution that its resolution of ground penetrating radar that adopts the linear frequency modulation system is impacted than carrierfree improves greatly.
Under the Linear Frequency Modulation system, the Near-Field Radar Imaging radar must adopt the coherent imaging technology to obtain high-resolution radar image, but at present relevant imaging technique is such as chirp scaling, the methods such as wavenumber domain all design for the far field model, under Near Field, some is approximate, perhaps interpolation is the restriction of supporting domain, and these algorithm application and the Near Field that make have some difficulties.
Summary of the invention
The purpose of this invention is to provide and a kind of three-dimensional imaging is carried out in the target area, near field, with the three-dimensional coherent imaging method of the ground penetrating radar under the Near Field that obtains better resolution.
The objective of the invention is to realize so bright, the three-dimensional coherent imaging method of ground penetrating radar under a kind of Near Field, the target echo signal that radar is received and reference signal are done difference frequency and are processed, obtain the echo after difference frequency, it is carried out to distance to compression, then according to radar each orientation on position to imaging region in the time delay of each pixel, carry out coherence stack after phase compensation, on actual target locations, form stronger signal, the signal formed in non-target location a little less than, travel through whole zone, thereby complete the reconstruction of image, it is characterized in that: concrete steps are as follows:
1) target echo signal radar received and reference signal are done difference frequency and are processed, and obtain the echo after difference frequency;
2) echo after difference frequency is carried out to distance to compression;
3) imaging region is divided into latticed, calculate radar in each orientation on position to the time delay of each net point (pixel) in imaging region;
4), according to the time delay that calculates, the echo of respective point is carried out to phase compensation;
5) each pixel is carried out to coherence stack, stack result had been both the value of this pixel;
6) applying step 4) and 5) travel through whole imaging region, complete the reconstruction of image.
Characteristics of the present invention are: the target echo signal that it receives radar and reference signal are done difference frequency and are processed, obtain the echo after difference frequency, it is carried out to distance to compression, then according to radar each orientation on position to imaging region in the time delay of each pixel, carry out coherence stack after phase compensation, on actual target locations, form stronger signal, the signal formed in non-target location a little less than, travel through whole zone, thereby complete the reconstruction of image.
The accompanying drawing explanation
Below in conjunction with the embodiment accompanying drawing, the present invention will be further described:
Fig. 1 is the signals of embodiment of the present invention Principles of Radar;
Fig. 2 is back-projection algorithm process flow diagram of the present invention;
Fig. 3 is last 3 d effect graph.
In figure: 1, radar signal circuit; 2, radar signal receiving circuit; 3, Radar Imaging Processing unit; 4, emitting antenna; 5, receiving antenna; 6, detection imaging district.
Embodiment
With reference to Fig. 1, with traditional the same radar signal circuit 1, radar signal receiving circuit 2 and Radar Imaging Processing unit 3 of comprising of radar system, reflected signal by radar antenna (emitting antenna 4 and receiving antenna 5) to target emission radar wave or receiving target, in detection imaging district 6 to buried petroleum pipe line in the present invention, requiring maximum investigation depth is 3.5 meters, namely the path length difference of target local oscillator and target echo is approximately 7 meters, and the intermediate frequency that therefore receives echo is that bandwidth is (ground dielectric constant is now estimated by 9):
In above formula
for receiving the bandwidth of signal,
for the frequency modulation rate of linear FM signal of emission,
the light velocity,
the earth electric medium constant,
it is maximum operating range.
This just requires transmitter that (4dBm) of the linear FM signal of input is amplified to 27dBm.
As shown in Figure 2, flowchart process of the present invention is as follows: comprise following process:
1) target echo signal radar received and reference signal are done difference frequency and are processed, and obtain the echo after difference frequency;
2) echo after difference frequency is carried out to distance to compression;
3) imaging region is divided into latticed, calculate radar in each orientation on position to the time delay of each net point (pixel) in imaging region;
4), according to the time delay that calculates, the echo of respective point is carried out to phase compensation;
5) each pixel is carried out to coherence stack, stack result had been both the value of this pixel;
6) applying step 4) and 5) travel through whole imaging region, complete the reconstruction of image.
As shown in Figure 3.
Wherein 1) echoed signal that step receives radar is done the difference frequency processing with reference signal, comprising: the linear FM signal form that provides emission:
Wherein
,
centered by frequency,
for pulsewidth,
for the frequency modulation rate.
Separating the line frequency modulation is to fix with the time, and the identical LFM signal of frequency, frequency modulation rate is done the difference frequency processing as the reference signal with it and echo.
Provide reference signal:
Wherein,
for reference distance.
for the reference pulsewidth.CF signal in reference signal
should be identical with the CF signal transmitted, to obtain good coherence.
Determine that certain point target to the distance of radar is
, this echo signal that radar receives
for:
Its difference frequency is output as:
Wherein
=
-
.
Adopted the double-basis radar in the present invention, the design that the single-shot list is received.If
for the position coordinates of subsurface scattering point,
be expressed as the coordinate of emitting antenna,
be expressed as the coordinate of receiving antenna.Omit for easy, will be less than phase effect
the factor save and consider specific inductive capacity
impact on velocity of wave.(4) formula after abbreviation is:
(5) formula is done to IDFT, is equivalent to echo is done to Range compress, obtain the echo function after compression:
In above formula,
Make the addition of echoed signal homophase need to compensate following three phase places:
The stack summation obtains finally becoming transform:
Three phase places in above formula are the phase factor that will compensate, and after compensation, making the signal from same pixel is homophase, thereby strengthened, make signal from other points due to the phase place difference, stack result is tending towards 0, therefore can think that final stack result is the value of this pixel.
Claims (2)
1. the three-dimensional coherent imaging method of the ground penetrating radar under a Near Field is characterized in that: comprise following process:
1) send radar wave to target with transmission frequency f, the target echo signal that radar is received and reference signal are done the difference frequency processing, obtain the echoed signal after difference frequency;
2) to the laggard row distance of echoed signal interpolation after difference frequency to compression;
3) imaging region is divided into latticed, calculate radar is the time delay of pixel to each net point in imaging region in each orientation on position;
4), according to the time delay that calculates, the echo of respective point is carried out to phase compensation;
5) each pixel is carried out to coherence stack, stack result is the value of this pixel;
6) applying step 4) and 5) travel through whole imaging region, obtain into transform, complete the reconstruction of image;
Wherein 1) described in step, signal is carried out to difference frequency, carries out according to following process:
The linear frequency modulation ripple of radar emission is:
The target echo that receiving antenna receives is:
Reference signal is:
Signal after difference frequency is processed is:
(x wherein
n, y
n, z
n) be the position coordinates of subsurface scattering point, u
t, v
tbe expressed as the coordinate of emitting antenna, u
r, v
rbe expressed as the coordinate of receiving antenna; R
reffor reference distance, R
tfor a certain point target distance in target area, f is transmission frequency, and γ is the frequency modulation rate of the linear FM signal of emission, and c is the light velocity, ε
rfor the earth electric medium constant, f
ccentered by frequency, T
pfor the reference pulsewidth.
2. the three-dimensional coherent imaging method of ground penetrating radar under Near Field according to claim 1, is characterized in that: step 3) described in the calculating of time delay, according to following process, carry out:
By the echo calculation delay carried out after interpolation and Range compress:
R
tfor the distance between emitting antenna and target, R
rfor the distance between receiving antenna and target, the time delay τ of required calculating is:
Wherein, R
reffor reference distance,
for the vertical direction range resolution, m is the interpolation multiple, and N is the sampling number after interpolation; (x wherein
n, y
n, z
n) be the position coordinates of subsurface scattering point, u
t, v
tbe expressed as the coordinate of emitting antenna, u
r, v
rbe expressed as the coordinate of receiving antenna; ε
rfor the earth electric medium constant, c is the light velocity.
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| CN102508205B (en) * | 2011-09-26 | 2013-07-31 | 中南大学 | Calculation method for propagation delay of electromagnetic waves in planar three-layered dielectrics |
| CN102540184B (en) * | 2011-12-30 | 2014-04-30 | 陕西延长石油(集团)有限责任公司研究院 | Frequency domain imaging method of ground penetrating radar |
| CN102736080B (en) * | 2012-04-27 | 2014-03-12 | 中国人民解放军国防科学技术大学 | Imaging method used for ground penetrating radar concentric circle echo data |
| CN104793195B (en) * | 2015-04-23 | 2017-05-03 | 西北工业大学 | Near-field planar scanning three-dimensional imaging and phase error compensating method |
| EP3574340B1 (en) * | 2017-01-27 | 2024-06-26 | Massachusetts Institute of Technology | Method and system for localization of a vehicle using surface penetrating radar |
| CN108286654B (en) * | 2017-12-20 | 2020-03-27 | 北京华航无线电测量研究所 | Pipeline inspection device and method |
| CN109298418B (en) * | 2018-09-30 | 2022-08-05 | 湖南华诺星空电子技术有限公司 | Radar detection false alarm suppression method and device based on building internal structure characteristics |
| CN109298417B (en) * | 2018-09-30 | 2022-04-22 | 湖南华诺星空电子技术有限公司 | Building internal structure detection method and device based on radar signal processing |
| CN110646794B (en) * | 2019-11-05 | 2022-12-02 | 西安电子工程研究所 | Method for forming terrain detection data by radar |
| CN112649806B (en) * | 2020-11-02 | 2023-03-07 | 西安电子科技大学 | MIMO radar near-field three-dimensional imaging method |
| CN112834621B (en) * | 2020-12-31 | 2024-07-23 | 安徽理工大学 | Rock mass fracture three-dimensional reconstruction method based on ultrasonic technology |
| CN112924965B (en) * | 2021-02-01 | 2022-04-12 | 桂林电子科技大学 | Clustering coherent superposition-based frequency diversity array radar target imaging method |
| CN113238221B (en) * | 2021-05-11 | 2023-09-22 | 沈阳航空航天大学 | MIMO through-wall radar imaging method based on two-dimensional minimum phase coherence factor |
| CN114756045B (en) * | 2022-05-18 | 2023-03-14 | 电子科技大学 | Unmanned aerial vehicle control method for meteorological radar calibration |
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