Disclosure of Invention
The technical problem to be solved by the invention is to provide a multi-element ship target radar echo simulation method aiming at the defects of the prior art, wherein the multi-element ship target radar echo simulation method simulates the complex ship motion state through software, combines the radar principle and some characteristics of radar echo existing in actual detection, and provides real approaching test data for the research of a radar tracking algorithm.
In order to solve the technical problems, the invention adopts the technical scheme that:
a multi-element ship target radar echo simulation method comprises the following steps.
Step 1, setting target number and simulation of 6 elements of each target: the number n of target ships to be tracked is set, and 6 key elements are set for radar echoes of each target ship. Wherein, 6 key elements are respectively: center coordinates (xn, yn), ship length Ln, width Wn, echo intensity An, motion direction d (t), and motion velocity v (t). Then, the set 6 key elements are simulated in a rectangular coordinate system. Where n =1,2, … …, t denotes the movement time.
Step 2, adding a center coordinate random error Sn: and (3) adding the center coordinate random error Sn to the center coordinates (Xn, Yn) simulated in the step 1 to form corrected center coordinates (Xn, Yn), wherein Xn = Xn Sn and Yn = Yn Sn.
Step 3, adding a random error Wn of the motion speed: and (4) adding the random error Wn of the motion speed to the motion speed V (t) simulated in the step 1 to form a corrected motion speed Wn V (t).
Step 4, establishing a correction motion curve: and establishing a corrected motion curve of the reaction environment change factor according to the corrected central coordinates (Xn, Yn) in the step 2 and the corrected motion speed Wn V (t) in the step 3.
And 5, coordinate conversion: and (3) converting the rectangular coordinate system where the echo intensity An in the step (1) is located into a polar coordinate system.
Step 6, adding intensity random error Qn: for echo intensity An in a polar coordinate system, the echo intensity An has radial echo intensity An1 and tangential echo intensity An 2; adding a radial echo intensity error Qn1 to the radial echo intensity An1 to form a corrected radial echo intensity Qn1 An 1; adding a tangential echo intensity error Qn2 to the tangential echo intensity An2 to form a corrected radial echo intensity Qn2 An 2; the radial echo intensity error is used for simulating the influence of a range side lobe on the radar echo shape when two coordinate radars are detected; the tangential echo intensity error is used for simulating the influence of the azimuth side lobe on the radar echo shape when the two-coordinate radar is detected.
And 7, solving the real echo intensity Tn: the vector sum of the modified radial echo intensities Qn1 An1 and the modified radial echo intensities Qn2 An2 constitutes the true echo intensity Tn.
In step 2, the center coordinate random error Sn = Rand (min1, max1) x K1, wherein K1 represents a random influence reduction coefficient; min1 represents the minimum random error of the center coordinate, and max1 represents the maximum random error of the center coordinate.
K1 is related to the distance between the target ship and the radar station and the shape of the ship, and the closer the target ship is to the radar station, the smaller K1 is; the simpler the ship shape, the smaller K1; min1= -Ln/2, max1= Ln/2.
In step 3, the random error Wn =1+ Rand (min2, max2) x K2 of the movement speed, where K2 represents the random influence reduction coefficient, min2 represents the minimum random error of the movement speed, and max2 represents the maximum random error of the movement speed.
K2 is related to the degree to which the speed of the target vessel is influenced by the environment, the greater the influence degree, the greater K2; min2= -1, max2= 1.
And selecting a corresponding distribution function type according to the ship length Ln, the width Wn and the ship type simulated in the step 1 by the radial echo intensity error Qn1 and the tangential echo intensity error Qn 2. Wherein the distribution function types include normal distribution, positive bias distribution, negative bias distribution, multimodal distribution, and chi-squared distribution.
The invention has the following beneficial effects:
1. the complex ship motion state is simulated by software, and the radar principle and some characteristics of radar echo in actual detection are combined to provide real-approaching test data for the research of a radar tracking algorithm.
2. The random error Sn of the central coordinate, the random error Wn of the movement speed and the random error Qn of the echo intensity are adopted to simulate the detection errors of a real radar when the radar is influenced by factors such as the detection electromagnetic environment of the radar, the storm of the water surface, the weather condition and the like. Meanwhile, the three random factors are represented by three random numbers with different value ranges. The selection of the value range indicates the severity of the environmental factors under the simulation condition. The noise environment is indicated to be good or bad compared to the radar.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific preferred embodiments.
In the description of the present invention, it is to be understood that the terms "left side", "right side", "upper part", "lower part", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and that "first", "second", etc., do not represent an important degree of the component parts, and thus are not to be construed as limiting the present invention. The specific dimensions used in the present example are only for illustrating the technical solution and do not limit the scope of protection of the present invention.
As shown in fig. 1, a multi-element ship target radar echo simulation method includes the following steps.
Step 1, setting target number and simulation of 6 elements of each target: the number n of target ships to be tracked is set, and 6 key elements are set for radar echoes of each target ship. Wherein, 6 key elements are respectively: center coordinates (xn, yn), ship length Ln, width Wn, echo intensity An, motion direction d (t), and motion velocity v (t).
The invention uses rectangle to simulate the ship echo, so the length Ln and the width Wn of the target ship become two important factors. Then, the set 6 key elements are simulated in a rectangular coordinate system. Where n =1,2, … … denotes a ship number, and t denotes a movement time.
The motion direction and the motion speed are all functions changing along with time, and can be a regular curve or any motion track customized by a user, but it is emphasized that the motion direction and the motion speed are smooth curves in consideration of the reality of the ship motion; v (t) and D (t) together form the motion curve of the ship target.
And 2, adding a central coordinate random error Sn.
Any ship, even if anchored and parked, continuously changes in the scanning echo of each circle of the radar, because the shape of the echo obtained by each circle of the radar is different, the coordinates of a target are calculated when the radar echo is processed, each circle slightly changes, and in order to describe the change, a central coordinate random error is introduced.
After the central coordinate is influenced by random factors, the motion direction after calculation naturally changes randomly, so that the random factors of the motion direction are not considered. The length and width of the target are closely related to the intensity distribution function in the next calculation and are not considered here.
And (3) adding the center coordinate random error Sn to the center coordinates (Xn, Yn) simulated in the step 1 to form corrected center coordinates (Xn, Yn), wherein Xn = Xn Sn and Yn = Yn Sn.
The random error of the center coordinates Sn = Rand (min1, max1) K1, wherein K1 represents a random influence reduction coefficient, K1 is related to the distance of a target ship from a radar station and the shape of the ship, and the closer the target ship is to the radar station, the smaller K1 is; the simpler the ship shape, the smaller K1; here, it is preferably 0.1; min1 represents the minimum random error of the center coordinates, max1 represents the maximum random error of the center coordinates, min1= -Ln/2, max1= Ln/2.
Since the change in direction is calculated from the change in coordinates, the direction of motion d (t) is expressed by the following equation:
D(t)=arctan[(Yn(t+2)-Yn(t+1))/(Xn(t+2)-Xn(t+1))]-arctan[(Yn(t+1)-Yn)/(Xn(t+1)-Xn)])
in the above formula, if Xn and Yn are the corrected central coordinates of the nth target ship at time t, Xn (t +1) and Yn (t +1) are the corrected central coordinates of the nth target ship at time t + 1; xn (t +2) and Yn (t +2) are the corrected center coordinates of the nth target vessel at time t + 2.
Step 3, adding a random error Wn of the motion speed: the moving speed of the ship is easily influenced by the environment such as water flow, wind speed and the like, therefore, the real speed of the ship with fixed speed is always changed along with the conditions such as water speed, wind speed and the like, and in order to describe the change, a random speed error Wn is introduced.
And (4) adding the random error Wn of the motion speed to the motion speed V (t) simulated in the step 1 to form a corrected motion speed Wn V (t).
The above-mentioned random error Wn =1+ Rand (min2, max2) × K2 of the movement speed, where min2 represents the minimum random error of the movement speed and max2 represents the maximum random error of the movement speed. K2 represents a random influence reduction factor, K2 is related to the degree to which the speed of the target vessel is influenced by the environment, the greater the influence degree, the greater K2. In general, the speed influence of the environment on ships varies from ship to ship, and for a yacht, K2 is smaller and may be set to 0.1 or less, and for a kayak, it may be set to 0.5 or more.
The random motion speed error Wn is usually between 0 and 2, so min2= -1, and max2= 1.
Step 4, establishing a correction motion curve: and establishing a corrected motion curve of the reaction environment change factor according to the corrected central coordinates (Xn, Yn) in the step 2 and the corrected motion speed Wn V (t) in the step 3.
And 5, coordinate conversion: and (3) converting the rectangular coordinate system where the echo intensity An in the step (1) is located into a polar coordinate system.
Step 6, adding intensity random error Qn: for echo intensities An in a polar coordinate system, there are radial echo intensities An1 and tangential echo intensities An 2.
The intensity of each real radar echo is not invariable all the time, and random errors Qn of the target intensity are introduced along with the influences of the change of the equivalent reflection area of a moving target, the environmental change and the like.
The radial echo intensity error Qn1 is added to the radial echo intensity An1 to form a modified radial echo intensity Qn1 An 1. The tangential echo intensity error Qn2 is added to the tangential echo intensity An2 to form a modified radial echo intensity Qn2 An 2. The radial echo intensity error is used for simulating the influence of a range side lobe on the radar echo shape during the detection of the two-coordinate radar. The tangential echo intensity error is used for simulating the influence of the azimuth side lobe on the radar echo shape when the two-coordinate radar is detected.
And 7, solving the real echo intensity Tn: the vector sum of the modified radial echo intensities Qn1 An1 and the modified radial echo intensities Qn2 An2 constitutes the true echo intensity Tn.
And selecting a corresponding distribution function type according to the ship length Ln, the width Wn and the ship type simulated in the step 1 by the radial echo intensity error Qn1 and the tangential echo intensity error Qn 2. Wherein the distribution function types include normal distribution, positive bias distribution, negative bias distribution, multimodal distribution, and chi-squared distribution. In fig. 2, the left side shows four intensity profiles, and the right side shows the effect of the echo intensity profile corresponding to the four intensity profiles. The intensity distribution function can simulate a real ship as much as possible, for example, the 4 th component distribution function in fig. 2 can simulate the situation that the echo of the bow and the stern is weak, and two piles of goods with strong reflection are loaded on the ship (such as an LNG ship, a container ship and a special operation ship provided with a crane).
FIG. 3 shows a ship rectangular radar echo in which the radial echo intensity distribution function, the tangential echo intensity distribution function and the random error of the echo target intensity are considered simultaneously, and a rectangular radar echo in which any random factor and intensity distribution are not considered completely. The comparison of the two figures shows that the echo simulation effect of the device is closer to reality.
As shown in fig. 4, after the motion function of the target is combined, the multi-element ship target echo simulation method provided by the invention provides a more real radar video echo for the research of a ship target tracking algorithm.
The three random factors Sn, Wn and Qn are represented by three random numbers with different value ranges. The selection of the value range indicates the severity of the environmental factors under the simulation condition. The noise environment is indicated to be good or bad compared to the radar.
The present invention will be described in detail with reference to the following, meeting, crossing and circling states as specific embodiments.
1. Overtaking meeting state
The two states are similar, for example, the tracking is taken as an example, the state simulates that the A ship is in front of the B ship and is 200 meters away from the front and the back, the A ship moves in the same direction at a speed higher than that of the B ship, the A ship is required to be within 15 meters away from the B ship when the A ship passes through the B ship, and the simulation is finished after the A ship passes through the B ship by 200 meters, as shown in FIG. 5.
Let A, B be yachts 5m long and 2 m wide, with the other parameters shown in FIG. 5. Initially, the motion curves of the two vessels can be expressed as:
YA=15;XA=100+10t;
YB=30;XB=300+5t;
considering the random error of the motion direction detection, namely the random error Sn of the central coordinate, taking Rand (-2.5, 2.5) as random data in the range of (-2.5, 2.5), considering that the speed boat is small, the influence of the random error factor in the direction can be reduced, and the random influence is reduced to 0.1, so that the motion curves of the two boats can be expressed as follows:
YA=15+ Rand(-2.5,2.5)*0.1;XA=100+ Rand(-2.5,2.5)*0.1+10t;
YB=30+ Rand(-2.5,2.5)*0.1;XB=300+ Rand(-2.5,2.5)*0.1+5t。
considering the random error of the motion speed detection and then introducing the random error Wn of the motion speed, the motion curves of the two ships can be expressed as follows:
YA=15+ Rand(-2.5,2.5)*0.1;XA=100+ Rand(-2.5,2.5)*0.1+10*(1+ Rand(-1,1)*0.1)*t;
YB=30+ Rand(-2.5,2.5)*0.1;XB=300+ Rand(-2.5,2.5)*0.1+5*(1+ Rand(-1,1)*0.1)*t。
after the coordinate conversion is completed, the influence of the echo intensity distribution on the radial direction and the tangential direction is considered, and since the influence of the change of the echo in the Y direction of the radar on the tracking when two ships approach about 15 meters is concerned under the test condition, the radial intensity distribution function Qn1 can be ignored, and only the tangential intensity distribution function Qn2 is considered. Due to bilateral symmetry of the yacht, a standard normal distribution function can be selected as a tangential intensity distribution function. (there are many alternative distribution functions including, but not limited to, normal distribution, positive bias distribution, negative bias distribution, multi-peak distribution, chi-square distribution, etc., where the distribution function morphology can be changed by adjusting parameters, for example, a normal distribution, which can be selected to be "flat" for sand carriers, and "steep" for LNG). The preferred distribution is as shown in fig. 6-8.
After a rectangular ship is processed by an intensity distribution function in the length direction and the width direction or the radial direction and the tangential direction after coordinate conversion, the echo shape of the rectangular ship is not rectangular any more after processing but is closer to the echo of a real ship because the intensity distribution function is selected according to different ship shapes.
2. Cross state
The state A ship and the state B ship run on a 90-degree vertical route. Sailing in the south and east directions, respectively, at the same speed. Requiring a distance of less than 15 meters at the crossover.
Suppose that ship a is a river crossing yacht with the length of 5 meters and the width of 2 meters, ship B is a cargo ship in a river channel (the middle section of the front section of the ship is lower, and the cockpit is higher at the back of the ship), and other parameters are as shown in fig. 9. Initially, the motion curves of the two vessels can be expressed as:
XA=190;YA=200-10t;
YB=100;XB=100+10t;
considering the random error of the motion direction detection, the direction stability of the yacht is good, the influence of the random error factor (namely, the random error Sn of the central coordinate) in the direction can be reduced, the random influence is reduced to 0.1, and then the motion curves of the two ships can be expressed as follows:
XA=190+ Rand(-2.5,2.5)*0.1;YA=200+ Rand(-2.5,2.5)*0.1-10t;
YB=100+ Rand(-2.5,2.5)*0.1;XB=100+ Rand(-2.5,2.5)*0.1+10t;
considering the random error of the motion speed detection and then introducing the random error Wn of the motion speed, the motion curves of the two ships can be expressed as follows:
XA=190+ Rand(-2.5,2.5)*0.1;YA=200+ Rand(-2.5,2.5)*0.1-10*(1+ Rand(-1,1)*0.1)t;
YB=100+ Rand(-2.5,2.5)*0.1;XB=100+ Rand(-2.5,2.5)*0.1+10*(1+ Rand(-1,1)*0.1)t;
after the coordinate conversion is completed, the influence of the echo intensity distribution on the radial direction and the tangential direction is considered, and under the test condition of intersection, the influence of the change of the radar echo at the intersection point on tracking is concerned when two ships are close to about 15 meters, so that the ship A can only consider the tangential echo intensity distribution Qn2, and the ship B can only consider the radial echo intensity distribution function Qn 1. At the moment, because the ship A is a yacht, the standard normal distribution can be selected as a tangential intensity distribution function; the B-ship is a cargo ship and a "flat" negative bias profile is selected as a function of the radial intensity profile.
3. State of revolution
A ship, a speed boat 5 meters long and 2 meters wide, takes a circle with a diameter of about 200 meters as a path and has a speed of 5 m/s.
Initially, the motion curves of the two vessels can be expressed as:
X=100*cos(5t/200/pi*360);
Y=100*sin(5t/200/pi*360);
considering the random error of direction and speed, the motion curves of the two ships can be expressed as:
X=100*cos(5t/200/pi*360)*(1+ Rand(-1,1)*0.1)+ Rand(-2.5,2.5)*0.1;
Y=100*sin(5t/200/pi*360)*(1+ Rand(-1,1)*0.1)+ Rand(-2.5,2.5)*0.1。
after the coordinate transformation is completed, the influence of the echo intensity distribution on the radial direction and the tangential direction is considered, at the moment, the distribution on the radial direction and the tangential direction is considered, and the standard normal distribution can be selected as the intensity distribution function in both directions.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the embodiments, and various equivalent modifications can be made within the technical spirit of the present invention, and the scope of the present invention is also within the scope of the present invention.