CN103217686A - Computing method of azimuth focusing position in SAR (Synthetic Aperture Radar) image simulation process - Google Patents

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

The orientation is to the computing method of focal position in a kind of SAR image simulation process

Technical field

(Synthetic Aperture Image, SAR) orientation relates to two fields of high frequency scattering calculating and synthetic aperture radar image-forming to the computing method of (azimuth) focal position in the image simulation process to the present invention relates to a kind of synthetic-aperture radar.

Background technology

In recent years, SAR equipment and imaging technique constantly develop, and the understanding of SAR image and decipher problem receive much attention.For the inverting target information, set up the relation between SAR image and the target, the current research means that generally adopts is to utilize scattering mechanism and SAR principle of work to carry out the emulation of SAR image.The SAR image simulation has become one of the research focus in SAR field.The SAR image simulation mainly comprises scene modeling, scattering calculating, three steps of picture construction.The orientation is to determining it is the process of picture construction with distance to the position.

Traditional SAR image simulation need carry out multi-angle to the scene of being investigated according to observation condition, two-dimensional scattering under the multi-frequency condition calculates, such simulation process effectively simulated target radar in-flight the variation of scattering and synthetic aperture factor to the influence of SAR characteristics of image because the complicacy and the two-dimensional scattering calculated amount of electromagnetism Scattering Calculation are huge, this method simulation velocity is slow, need in the picture construction according to the simulation echo utilize imaging algorithm determine the target azimuth to the distance to position [Li Renjie etc., target SAR image simulation based on the electromagnetic scattering property calculation, radar science and technology, 8 (5): 395-405,2010.].In actual applications, usually do not need to consider that the scattering mechanism of target is with position angle and incident frequency change, cause thus: the main flow [Xu Feng etc. that become SAR image simulation field based on the emulation mode of projection mapping principle gradually, complicated ground scene polarization SAR imaging simulation based on projection mapping, 16 (11): 1459-1471,2006], this method has been simplified the process that the SAR image generates, be similar to and think that the scattering of target does not change with the synthetic aperture time, ignore synthetic aperture and imaging process, in the picture construction process, think that pairing coordinate was that the target azimuth is to the position that focuses on when target scattering finally returned radar.

Simplified the process of target scattering based on the SAR image simulation method of projection mapping, at the calculating of orientation to focal position, this method is not considered the process of synthetic aperture, pairing position replaces the orientation to the position that focuses on when directly utilizing target scattering finally to return radar, and the emulation SAR image that obtains like this can there are differences on a lot of characteristics of image with the SAR image of reality.

The basic reason that this species diversity exists is, when target generation multiple scattering, because the influence of synthetic aperture, pairing position existed difference with the actual orientation that focuses on to the position when target scattering returned radar, need find a kind of method to consider the synthetic aperture process brings for influence from the multiple scattering orientation to focusing.In a word, at present, ignored the synthetic aperture process of SAR based on orientation in the SAR image simulation method of projection mapping to the step that focuses on, the SAR image that emulation obtains exists difference with actual SAR image, 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 the orientation to the computing method of focal position, can effectively expressing the synthetic aperture factor to the influence of orientation to focal position, make in the emulating image because the SAR characteristics of image that synthetic aperture produces fully shows.

Technical solution of the present invention is as follows:

The orientation may further comprise the steps to the computing method of focal position in this SAR image simulation process:

The first step is determined 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 determine the ray starting point coordinate on this plane;

In second step, the coordinate of ray starting point under the calculating target-based coordinate system according to transformation matrix of coordinates T, supposes that A, B are respectively the incidence point of certain bar ray and eject point at 2, 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;

In the 3rd step, the ray tracking: ray is from the A point, and sequence ejection is through C, D point, at last return radar at the B of constant phase front point, according to the ray starting point coordinate in 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];

In the 4th step, the apparent azimuth that calculates this ray is to focal position: the oblique distance of correspondence is R when making the radar beam center through the A point _A, the radar beam center is through the oblique distance R of out-of-date correspondence _BThen the apparent azimuth of this ray is to focal position _ηFor:

$\mathrm{\η}=\frac{R_B{X}_A+R_A{X}_B}{R_A+R_B}.$

Following method is adopted on selected equiphase plane in the first step:

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 wherein: the radar trajectory direction is the y direction of principal axis, and the direction that makes progress perpendicular to ground is the z direction of principal axis; Imaging coordinate system: X, Z are respectively radar bearing to, radar incident wave direction;

1.2 with radar emission electromagnetic wave incident direction vector is normal vector, determines the 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, provided in a kind of SAR image simulation process the orientation to the computing method of focal position, the approximate synthetic aperture process of having considered in the SAR imaging of this method, this method makes the factor that the SAR image of emulation can the effectively expressing synthetic aperture, the SAR image that utilizes this method that emulation is obtained in SAR image simulation process more meets real physical process, and the feature of emulating image is more similar to real feature.

Description of drawings

Fig. 1 orientation is to focal position computation process synoptic diagram;

Fig. 2 triangle corner reflector observation geometric representation.

Embodiment

Be example with the corner reflector below, this explanation is described further.

The first step is determined initial constant phase front and ray starting point.In nearly radar one side of target,, and on this plane, determine the ray starting point coordinate according to the selected initial equiphase plane of the direction of radar beam incident.

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: the radar trajectory direction is the y direction of principal axis, and the direction that makes progress perpendicular to ground is the z direction of principal axis; Imaging coordinate system: X, Z are respectively radar bearing to, radar incident wave direction;

1.2 with radar emission electromagnetic wave incident direction vector is normal vector, determines the equiphase plane in imaging coordinate system;

1.3 determine the coordinate of initial ray according to this equation be, Fig. 1 is the synoptic diagram of orientation to focal position computation process, as shown in Figure 1, investigates the ray from the 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 the 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.

The 3rd step, the ray tracking.As shown in Figure 1, ray is from the A point, and sequence ejection is returned radar at the B of constant phase front point at last through C, D point.According to the ray starting point coordinate in 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].

In the 4th step, the apparent azimuth that calculates this ray is to focal position.The oblique distance of correspondence is R when making the radar beam center through the A point _A, the radar beam center is through the oblique distance R of out-of-date correspondence _BThen: the apparent azimuth of this ray to focal position η is:

$\mathrm{\η}=\frac{R_B{X}_A+R_A{X}_B}{R_A+R_B}$

As shown in Figure 2: target is the triangle corner reflector, and the length of side is 1m.The corner reflector apex coordinate is [000], the shortest oblique distance 5000m in summit, radar incident angle: 135 degree.The 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:

$T=\left[\begin{array}{ccc}0.7071& -0.5& 0.5\\ 0.7071& -0.5& 0.5\\ 0& 0.7071& 0.7071\end{array}\right]$

Investigate 8 initial rays, their origin coordinates as following table is respectively:

The 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:

The ray sequence number	1	2	3	4	5	6	7	8
									The orientation is to focusing on constantly	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:

The ray sequence number	1	2	3	4	5	6	7	8
									The orientation is to focusing on constantly	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 focusing on theoretical value constantly.Above result verification validity of the present invention and superiority.

Claims (2)

1.SAR the orientation is characterized in that to the computing method of focal position in the image simulation process, may further comprise the steps:

The first step is determined 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 determine the ray starting point coordinate on this plane;

In second step, the coordinate of ray starting point under the calculating target-based coordinate system according to transformation matrix of coordinates T, supposes that A, B are respectively the incidence point of certain bar ray and eject point at 2, 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;

In the 3rd step, the ray tracking: ray is from the A point, and sequence ejection is through C, D point, at last return radar at the B of constant phase front point, according to the ray starting point coordinate in 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];

In the 4th step, the apparent azimuth that calculates this ray is to focal position: the oblique distance of correspondence is R when making the radar beam center through the A point _A, the radar beam center is through the oblique distance R of out-of-date correspondence _BThen the apparent azimuth of this ray to focal position η is:

$\mathrm{\η}=\frac{R_B{X}_A+R_A{X}_B}{R_A+R_B}.$

2. the orientation is characterized in that to the computing method of focal position in the SAR image simulation process as claimed in claim 1, and following method is adopted on selected equiphase plane in the first step:

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 wherein: the radar trajectory direction is the y direction of principal axis, and the direction that makes progress perpendicular to ground is the z direction of principal axis; Imaging coordinate system: X, Z are respectively radar bearing to, radar incident wave direction;

1.2 with radar emission electromagnetic wave incident direction vector is normal vector, determines the equiphase plane in imaging coordinate system;

1.3 determine the coordinate of initial ray according to equation.