CN103217686B - Computing method of azimuth focusing position in SAR (Synthetic Aperture Radar) image simulation process - Google Patents
Computing method of azimuth focusing position in SAR (Synthetic Aperture Radar) image simulation process Download PDFInfo
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Abstract
The invention provides a computing method of an azimuth focusing position in an SAR (Synthetic Aperture Radar) image simulation process. The influence of synthetic aperture factors on the azimuth focusing position can be effectively expressed, and SAR image characteristics in a simulated image, generated by a synthetic aperture, are fully shown. The computing method comprises the following steps of: 1, confirming an initial equiphase surface and a ray starting point: on one side ,close to a radar, of an object, selecting the initial equiphase surface according to a radar beam incidence direction, and confirming coordinates of the ray starting point on the surface; 2, computing the coordinates of the ray starting point under an object coordinate system, and transforming a matrix T according to the coordinates; 3, tracking a ray, and computing a position of an eyepoint B of the ray at the equiphase surface according to the coordinates of the ray starting point obtained through the step 2 and according to a ray theory; and 4, computing an approximate azimuth focusing position of the ray.
Description
Technical field
The present invention relates to a kind of synthetic-aperture radar (Synthetic Aperture Image, SAR) in image simulation process, orientation, to the computing method of (azimuth) focal position, relates to High frequency scattering and calculates and two fields of synthetic aperture radar image-forming.
Background technology
In recent years, SAR equipment and imaging technique development, the understanding of SAR image and decipher problem receive much attention.For inverting target information, set up the relation between SAR image and target, the current research means generally adopting is to utilize scattering mechanism and SAR principle of work to carry out the emulation of SAR image.SAR image simulation has become one of the study hotspot in SAR field.SAR image simulation mainly comprises scene modeling, scattering calculating, three steps of picture construction.Orientation to distance be the process of picture construction to the definite of position.
Traditional SAR image simulation need to carry out multi-angle to investigated scene according to observation condition, two-dimensional scattering under multi-frequency condition calculates, such simulation process effectively simulated target radar in-flight the variation of scattering and synthetic aperture factor on the impact of SAR characteristics of image because complicacy and the two-dimensional scattering calculated amount of electromagnetism Scattering Calculation are huge, the method simulation velocity is slow, in picture construction, need according to simulation echo utilize imaging algorithm determine target azimuth to distance to position [Li Renjie etc., the target SAR image simulation calculating based on Electromagnetic Scattering Characteristics, radar science and technology, 8 (5): 395-405, 2010.].In actual applications, conventionally do not need the scattering mechanism of considering target with position angle and incident frequency change, cause thus: the emulation mode based on projection mapping principle becomes the main flow [Xu Feng etc. in SAR image simulation field gradually, complicated ground scene polarization SAR Imaging Simulation based on projection mapping, 16 (11): 1459-1471, 2006], the method has been simplified the process that SAR image generates, be similar to and think that the scattering of target does not change with the synthetic aperture time, ignore the process of synthetic aperture and imaging, in picture construction process, think that when target scattering finally returns to radar, corresponding coordinate is that target azimuth is to the position focusing on.
SAR image simulation method based on projection mapping has been simplified the process of target scattering, calculating for from orientation to focal position, the method is not considered the process of synthetic aperture, while directly utilizing target scattering finally to return to radar, replacement orientation, corresponding position is to the position focusing on, and the emulation SAR image obtaining like this and actual SAR image can there are differences on a lot of characteristics of image.
The basic reason that this species diversity exists is, in the time of target generation multiple scattering, due to the impact of synthetic aperture, when target scattering returns to radar, corresponding position exists difference with the actual orientation focusing on to position, need to find a kind of method to consider the impact that synthetic aperture process is brought to focusing to multiple scattering orientation.In a word, at present, in the SAR image simulation method based on projection mapping, the synthetic aperture process of SAR has been ignored in orientation to the step focusing on, and the SAR image that emulation obtains and actual SAR image exist difference, should improve.
Summary of the invention
For solving the problems of the technologies described above, the invention provides in a kind of SAR image simulation process orientation to the computing method of focal position, the impact to focal position on orientation of energy effectively expressing synthetic aperture factor, fully shows the SAR characteristics of image producing due to synthetic aperture in emulating image.
Technical solution of the present invention is as follows:
In this SAR image simulation process, orientation, to the computing method of focal position, comprises the following steps:
The first step, determines initial constant phase front and ray starting point: in nearly radar one side of target, according to the selected initial equiphase plane of the direction of radar beam incident, and in this plane, determine ray starting point coordinate;
Second step, the coordinate of ray starting point under calculating target-based coordinate system, according to transformation matrix of coordinates T, supposes that A, 2 of B are respectively the incidence point of certain ray and eject point, establishes the coordinate of A point under target-based coordinate system to be: [x
a, y
a, z
a]=[X
a, Y
a, Z
a] T, [X
a, Y
a, Z
a] be the coordinate of A point under imaging coordinate system;
The 3rd step, ray tracking: ray is from A point, and sequence ejection is through C, D point, finally return to radar at the B of constant phase front point, according to the ray starting point coordinate of second step, calculate ray in the position of the eye point B of constant phase front according to ray theory, make the coordinate [X under its imaging coordinate system
b, Y
b, Z
b];
The 4th step, the apparent azimuth that calculates this ray is to focal position: while making radar beam center through A point, corresponding oblique distance is R
a, when the process B point of radar beam center, corresponding oblique distance is R
b; The apparent azimuth of this ray to focal position η is:
In the first step, selected equiphase plane adopts following methods:
1.1 determine target-based coordinate system and imaging coordinate system, obtain the transformation matrix of coordinates T that is tied to target-based coordinate system by imager coordinate; Wherein target-based coordinate system: radar trajectory direction is y direction of principal axis is z direction of principal axis perpendicular to ground direction upwards; Imaging coordinate system: X, Z is respectively radar bearing to, radar incident wave direction;
1.2 taking radar emission electromagnetic wave incident direction vector as normal vector, determines equiphase plane in imaging coordinate system;
1.3 determine the coordinate of initial ray according to equation.
Beneficial effect of the present invention:
The present invention combines scattering mechanism and synthetic aperture principle, provide in a kind of SAR image simulation process orientation to the computing method of focal position, the approximate synthetic aperture process of having considered in SAR imaging of the method, the method makes the factor that the SAR image of emulation can effectively expressing synthetic aperture, in SAR image simulation process, utilize the method can make the SAR image that emulation obtains more meet real physical process, the feature of emulating image is more similar to real feature.
Brief description of the drawings
Fig. 1 orientation is to focal position computation process schematic diagram;
Fig. 2 triangle corner reflector observation geometric representation.
Embodiment
Taking corner reflector as example, this explanation is described further below.
The first step, determines initial constant phase front and ray starting point.In nearly radar one side of target, according to the selected initial equiphase plane of the direction of radar beam incident, and in this plane, determine ray starting point coordinate.
1.1 determine target-based coordinate system and imaging coordinate system, obtain the transformation matrix of coordinates T that is tied to target-based coordinate system by imager coordinate.Target-based coordinate system: radar trajectory direction is y direction of principal axis is z direction of principal axis perpendicular to ground direction upwards; Imaging coordinate system: X, Z is respectively radar bearing to, radar incident wave direction;
1.2 taking radar emission electromagnetic wave incident direction vector as normal vector, determines equiphase plane in imaging coordinate system;
1.3 determine that according to this equation the coordinate of initial ray is, Fig. 1 is the schematic diagram of orientation to focal position computation process, as shown in Figure 1, investigate the ray from A point, and the coordinate of A point under imaging coordinate system is: [X
a, Y
a, Z
a].
Second step, the coordinate of ray starting point under calculating target-based coordinate system.According to transformation matrix of coordinates T, the coordinate of A point under target-based coordinate system is: [x
a, y
a, z
a]=[X
a, Y
a, Z
a] T, [X
a, Y
a, Z
a] be the coordinate of A point under imaging coordinate system; .
The 3rd step, ray tracking.As shown in Figure 1, ray is from A point, and sequence ejection, through C, D point, is finally returned to radar at the B of constant phase front point.According to the ray starting point coordinate of second step, calculate ray in the position of the eye point B of constant phase front according to ray theory, make the coordinate [X under its imaging coordinate system
b, Y
b, Z
b].
The 4th step, calculates the apparent azimuth of this ray to focal position.While making radar beam center through A point, corresponding oblique distance is R
a, when the process B point of radar beam center, corresponding oblique distance is R
b.: the apparent azimuth of this ray to focal position η is:
As shown in Figure 2: target is triangle corner reflector, the length of side is 1m.Corner reflector apex coordinate is [000], the shortest oblique distance 5000m in summit, radar incident angle: 135 degree.Scene geometric relationship as shown in Figure 2.
Select initial equiphase plane, this plane chosen distance initial point 1m.Target-based coordinate system and imaging coordinate system are as shown in Figure 2.According to geometric parameter, the coordinates of targets of trying to achieve to the transition matrix of imager coordinate is:
Investigate 8 initial rays, their origin coordinates respectively the following table is:
Ray sequence number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
x(m) | 0.7776 | 0.6776 | 0.5776 | 0.7362 | 0.3948 | 0.2948 | 0.1948 | 0.2534 |
y(m) | 0.4524 | 0.3524 | 0.2524 | 0.6938 | 0.6352 | 0.5352 | 0.4352 | 0.7766 |
z(m) | 0.5445 | 0.6859 | 0.8273 | 0.4031 | 0.6859 | 0.8273 | 0.9687 | 0.6859 |
The orientation that classic method calculates is to focal position:
Ray sequence number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Orientation is to focusing on the moment | 0.23 | 0.23 | 0.23 | 0.03 | -0.17 | -0.17 | -0.17 | -0.37 |
The orientation that this paper method calculates is to focal position:
Ray sequence number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Orientation is to focusing on the moment | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
According to scattering mechanism and Principles of Radar, under this scene, the orientation of every ray is 0 to the theoretical value that focuses on the moment.Above result verification validity of the present invention and superiority.
Claims (2)
- In 1.SAR image simulation process, orientation, to the computing method of focal position, is characterized in that, comprises the following steps:The first step, determines initial constant phase front and ray starting point: in nearly radar one side of target, according to the selected initial equiphase plane of the direction of radar beam incident, and in this plane, determine ray starting point coordinate;Second step, the coordinate of ray starting point under calculating target-based coordinate system, according to transformation matrix of coordinates T, supposes that A, 2 of B are respectively the incidence point of certain ray and eject point, establishes the coordinate of A point under target-based coordinate system to be: [x a, y a, z a]=[X a, Y a, Z a] T, [X a, Y a, Z a] be the coordinate of A point under imaging coordinate system;The 3rd step, ray tracking: ray is from A point, and sequence ejection is through C, D point, finally return to radar at the B of constant phase front point, according to the ray starting point coordinate of second step, calculate ray in the position of the eye point B of constant phase front according to ray theory, make the coordinate [X under its imaging coordinate system b, Y b, Z b];The 4th step, the apparent azimuth that calculates this ray is to focal position: while making radar beam center through A point, corresponding oblique distance is R a, when the process B point of radar beam center, corresponding oblique distance is R b; The apparent azimuth of this ray to focal position η is:
- 2. in SAR image simulation process as claimed in claim 1, orientation, to the computing method of focal position, is characterized in that, in the first step, selected equiphase plane adopts following methods:1.1 determine target-based coordinate system and imaging coordinate system, obtain the transformation matrix of coordinates T that is tied to target-based coordinate system by imager coordinate; Wherein target-based coordinate system: radar trajectory direction is y direction of principal axis is z direction of principal axis perpendicular to ground direction upwards; Imaging coordinate system: X, Z is respectively radar bearing to, radar incident wave direction;1.2 taking radar emission electromagnetic wave incident direction vector as normal vector, determines equiphase plane in imaging coordinate system;1.3 determine the coordinate of initial ray according to equation.
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