Radar target spherical projection method for maritime formation

Abstract

The present invention discloses a radar target spherical projection method for maritime formation. The method comprises the steps of converting the height of a radar target into an altitude and converting the position of the radar target into a spherical position, can be used for pre-processing radar data, supports multi-platform composite tracking based on a data chain, and contribute to generating a sharable single integrated picture (SIP) among formation members. The present invention can be widely applied to oceanic area formation operations such as coastguard patrol, sea escort, deep sea far sighting and maritime formation fight.

Claims

1. A radar target spherical projection method for generating and using a single integrated picture (SIP) in a maritime formation comprising executing following steps: step 1, performing a projection modeling of a target at each of a plurality of platforms; step 2, calculating in the each platform an altitude of the target wherein the calculating comprises a specific process as follows: substituting D= cos , h= sin into a spherical projection model of the target, to obtain:
Z(Z+2R)=2(a+R) sin +a(a+2R)+.sup.2, namely, $\frac{Z\left(Z+2R\right)}{2a+2R}=\frac{\left(2a+2R\right)\sin }{2a+2R}+\frac{a\left(a+2R\right)}{2a+2R}+\frac{{}^2}{2a+2R}$ converting the above formula as R>>a, R>>Z, to obtain an altitude calculation formula of the target as follows: $\begin{array}{cc}Z=h+a+\frac{{}^2}{2\left(a+R\right)}& \left(\mathrm{formula}1\right)\end{array}$ step 3, calculating a projection of the target on a radar plane in the each platform; step 4, calculating the projection of the target on an earth spherical surface in the each platform which comprises a specific process as follows: step 4-1, setting $d=2R.Math.\tan \frac{}{2}$ wherein represents a central angle formed by a target projection point Q on the earth spherical surface and a radar position at a point $S,\frac{}{2}$ is an angle of circumference, d is a side length of a part, tangent to the radar position, of an opposite side of $\frac{}{2},$ and supposing that a point P exists, the side length is SP=d; $\mathrm{as}\sin =\frac{D}{R+Z},\cos =\frac{h+a+R}{R+Z},\mathrm{and}\tan \frac{}{2}=\frac{\sin }{1+\cos },d=\frac{2\mathrm{RD}}{2R+Z+h+a};$ step 4-2, substituting h in d=2RD/2R+Z+h+a in the step 4-1 through the (formula 1), to obtain: $d=\frac{R}{R+Z-\frac{{}^2}{4\left(a+R\right)}}.Math.D;$ step 4-3, setting $\frac{R}{R+Z-\frac{{}^2}{4\left(a+R\right)}}=K_2,$ regarding K.sub.2 as a spherical projection coefficient, so that
d=K.sub.2.Math.D, substituting D in d=K.sub.2.Math.D above from
D=K.sub.1.Math.(formula 2),
to obtain
d=K.sub.1.Math.K.sub.2.Math.(formula 3); step 4-4, approximately substituting a projection point of the target on the earth spherical surface with the point P, and obtaining coordinates P(X.sub.Q,Y.sub.Q) of the spherical projection of the target according to a principle of a same proportion of sides of similar figures, namely: $\{\begin{array}{c}{X}_Q=K_1.Math.K_2.Math.x_{}\\ Y_Q=K_1.Math.K_2.Math.y_{}\end{array}$ wherein X.sub.Q represents an East coordinate of the projection of the target on the earth spherical surface, and Y.sub.Q represents a North coordinate of the projection of the target on the earth spherical surface; so, calculation formulas of spherical projection coordinates and the altitude of the radar target are as follows: $\{\begin{array}{c}{X}_Q=K_1.Math.K_2.Math.\sin \\ Y_Q=K_1.Math.K_2.Math.\cos \\ Z=h+a+\frac{{}^2}{2\left(R+a\right)}\end{array}.$ step 5, collecting obtained projections of the target on the earth spherical surface from multiple platforms for preprocessing radar data and generating a picture; and step 6, processing radar data including data of space-time consistency of the target from the multiple platforms, correcting projection errors by calculating data on the altitude, the projection on the earth spherical surface of the target from the multiple platforms, generating the single integrated picture (SIP), and using the SIP for supporting a load control of the platform or a collaborative control over the maritime formation.

2. The method according to claim 1, characterized in that the step 1 comprises a specific process as follows: expressing a position of the target detected by a radar through polar coordinates (, , ) with a position of a radar antenna as an origin point, wherein specifically, is a slant distance to the target, a is an azimuth of the target relative to due north and is an elevation of the target; converting (, , ) into rectangular coordinates (x.sub., y.sub., h) as follows: $\{\begin{array}{c}{x}_{}=\sin .Math.\\ y_{}=\cos .Math.\\ h=\sin .Math.\end{array}$ wherein x.sub. represents an x-coordinate of the target, y.sub. represents a y-coordinate of the target, and represents a vertical coordinate of the target; and establishing a plane projection model and a spherical projection model of the target, wherein the plane projection model of the target is as follows: $D/=\sqrt{1-\frac{h^2}{{}^2}}$ the spherical projection model of the target is as follows:
(R+Z).sup.2=D.sup.2+[(a+R+h)].sup.2 in formulas, D represents a length of a projection of on the radar plane, Z represents the altitude of the target, R represents the earth radius, and a represents an altitude of the position of the radar antenna.

3. The method according to claim 1, characterized in that the step 3 comprises a specific process as follows: Setting $\sqrt{1-\frac{h^2}{{}^2}}=K_1,$ regarding K.sub.1 as a plane projection coefficient, so that a plane projection model of the target is converted into the (formula 2):
D=K.sub.1.Math. obtaining projection coordinates of the target on the radar plane according to a principle of a same proportion of sides of similar figures, $\{\begin{array}{c}x=K_1.Math.x_{}=K_1.Math.\sin \\ y=K_1.Math.y_{}=K_1.Math.\cos \end{array}$ wherein x represents an x-coordinate of the projection of the target on the radar plane, and y represents a y-coordinate of the projection of the target on the radar plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is further explained in detail with drawings and specific modes of execution, and the mentioned advantages of the present invention or the advantages in other aspects will be much clearer.

(2) FIG. 1 is a target plane projection schematic diagram.

(3) FIG. 2 is a target spherical projection schematic diagram.

(4) FIG. 3 is a brief flow chart of radar data distributed type processing for maritime formation.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention is further explained in combination with drawings and the embodiment.

(6) 1. Projection Modeling

(7) A radar generally regards the position of an antenna as an original point, polar coordinates (, , ) represent the position of a detected target, is the target slant distance, is the target azimuth relative to due north and is the target elevation. The polar coordinates (, , ) are converted into rectangular coordinates as follows:

(8) $\{\begin{array}{c}{x}_{}=\sin \\ y_{}=\cos \\ h=\sin \end{array}$

(9) Due to influence of the earth curvature and a certain height of the radar antenna, h in the formula does not represent the real height of a target, (x.sub., y.sub.) is far different from the projection position of the target on the ground. Influence caused by errors is large in actual application like verification of unknown targets and search and rescue. Therefore, in radar data distributed type processing, projection transformation needs to be performed on a target point trace firstly to obtain the projection position and the altitude of the target on the ground.

(10) In order to convert the coordinates of the radar target into the spherical projection coordinates, a plane projection model and a spherical projection model of the target are established, as shown in FIG. 1 and FIG. 2, wherein R represents the earth radius (6371.3 km), S represents the position of the radar, represents the altitude of the radar antenna, and T represents the aerial target.

(11) 2. Calculation of Altitude of the Target

(12) The relation between the altitude Z of the target and the measurement height h of the radar can be deduced according to FIG. 2.

(13) Through OS'T, the spherical projection model of the target can be expressed into:
(Z+R).sup.2=D.sup.2+[(+R+h)].sup.2

(14) D= cos , h= sin are substituted into the formula, obtain
Z(Z+2R)=2(a+R) sin +a(a+2R)+.sup.2, namely,

(15) $\frac{Z\left(Z+2R\right)}{2a+2R}=\frac{\left(2a+2R\right)\sin }{2a+2R}+\frac{a\left(a+2R\right)}{2a+2R}+\frac{{}^2}{2a+2R}$

(16) The above formula can be converted into the following formula as R>>a, R>>Z,

(17) $\begin{array}{cc}Z=h+a+\frac{{}^2}{2\left(a+R\right)}& \left(1\right)\end{array}$

(18) 3. Calculation of Projection of the Target on a Radar Plane

(19) The target is projected onto the radar plane, and the projection relation is shown as FIG. 1.

(20) The plane projection model of the target is expressed as

(21) $D^2={}^2-h^2,\mathrm{namely}D/=\sqrt{1-\frac{h^2}{{}^2}}$

(22) $\sqrt{1-\frac{h^2}{{}^2}}=K_1$
is set and regarded as a plane projection coefficient, so
D=K.sub.1.Math.(2)

(23) According to the principle of the same proportion of sides of similar figures, the projection coordinates of the target on the radar plane can be obtained as follows:

(24) 0$\{\begin{array}{c}x=K_1.Math.x_{}=K_1.Math.\sin \\ y=K_1.Math.y_{}=K_1.Math.\cos \end{array}$

(25) 4. Calculation of Projection of the Target on the Earth Spherical Surface

(26) The projection of the target T on the ground is a point Q, and is approximately substituted with the point P according to FIG. 2.

(27) Through O'SP, it is known that

(28) $d=2R.Math.\tan \frac{}{2}$$\mathrm{As}\sin =\frac{D}{R+Z},\cos =\frac{h+a+R}{R+Z},\mathrm{and}$$\tan \frac{}{2}=\frac{\sin }{1+\cos },d=\frac{2\mathrm{RD}}{2R+Z+h+a}$

(29) h in the above formula is substituted with the formula (1), obtain

(30) $d=\frac{R}{R+Z-\frac{{}^2}{4\left(a+R\right)}}.Math.D$

(31) $\frac{R}{R+Z-\frac{{}^2}{4\left(+R\right)}}=K_2$
is set and regarded as a spherical projection coefficient, so
d=K.sub.2.Math.D

(32) The formula (2) is substituted into the above formula, so
d=K.sub.1.Math.K.sub.2.Math.(3)

(33) P(X.sub.Q, Y.sub.Q) can be obtained according to the principle of the same proportion of sides of similar figures as well, namely

(34) $\{\begin{array}{c}{X}_Q=K_1.Math.K_2.Math.x_{}\\ Y_Q=K_1.Math.K_2.Math.y_{}\end{array}$

(35) In conclusion, the algorithms of the spherical projection coordinates and the altitude of the radar target are as follows:

(36) $\begin{array}{cc}\{\begin{array}{c}{X}_Q=K_1.Math.K_2.Math.\sin \\ Y_Q=K_1.Math.K_2.Math.\cos \\ Z=h+a+\frac{{}^2}{2\left(R+a\right)}\end{array}& \left(4\right)\end{array}$

(37) wherein,

(38) $K_1=\sqrt{1-h^2/{}^2}$$K_2=\frac{R}{R+Z-{}^2/\left[4\left(a+R\right)\right]}$$h=\sin$

(39) the target slant distance of the radar

(40) the target azimuth of the radar

(41) the target elevation of the radar

(42) athe altitude of the position of the radar antenna

(43) Rthe earth radius

(44) 5. Application of a Radar Target Spherical Projection Method to Pre-Processing of Radar Data and to Generate a Picture

(45) The brief flow of radar data distributed type processing for maritime formation is shown as FIG. 3. Each platform that undertakes the task of a target surveillance task executes the same flow. Pre-processing of radar data mainly includes space-time consistency for multi-platform target data for formation. The projection error correction is achieved through calculation of the altitude, plane projection and spherical projection on the target data of the local radar. A far-end target report is subjected to coordinate conversion and accurate grid locking, to reach space unification of the local target data and the far-end target data. The local target data and the far-end target data are subjected to time alignment processing to achieve time unification. Then entering composite tracking processing that includes target correlation, fusion, smoothing, prediction, identification number consistency management and report obligation processing which generates the single integrated picture (SIP) for supporting load control over a local platform or collaborative control over formation.

(46) The present invention provides a radar target spherical projection method for maritime formation, there are many specific methods and ways for achieving the present technical scheme, and the above-mentioned is only a preferred mode of execution of the present invention. It should be noted that for general technicians in the technical field, various improvements and retouches may be made therein without departing from the principle of the present invention and should be regarded within the protection scope of the present invention. Components not specifically identified in the present embodiment may be implemented in accordance with the prior art.