Target RCS statistical property calculation method under sea surface multipath effect

Abstract

The invention discloses a target RCS statistical property calculation method under a sea surface multipath effect, and belongs to the technical field of radar application, and the method comprises the steps: giving complex RCS data in a target pitch angle direction and sea surface mirror reflection coefficient data under a clean background; according to a target RCS statistical characteristic formula under the sea surface multipath effect, calculating a fluctuation mean value and variance of a target total RCS; according to a target total RCS function with the phase difference of the relative direct path as a variable, random testing is carried out through a Monte Carlo method, and statistics is carried out on a probability density function of the target total RCS in a numerical function form; according to the method for calculating the target RCS statistical characteristics under the sea surface multipath effect, the target RCS statistical characteristics under the sea surface multipath effect can be rapidly calculated according to the target complex RCS and the sea surface mirror reflection coefficient, and the total RCS probability density function of the target under the sea surface multipath effect is rapidly calculated through Monte Carlo simulation.

Description

Technical Field

[0001] The invention relates to the field of radar application technology, and in particular to a method for calculating target RCS statistical characteristics under sea surface multipath effects. Background Art

[0002] In the near-sea environment, the radar detection of targets needs to consider the influence of the sea surface multipath effect. The echo generated by the radar wave directly irradiating the target and the echo reflected by the sea surface are superimposed at the receiver, causing the RCS of the target to fluctuate. The classic model for studying the sea surface multipath effect is the "four-path" echo model. For the incident wave, there are two main paths, one is that the radar wave directly irradiates the target, and the other is that the radar wave irradiates the target after a single reflection from the sea surface; for the scattered wave, there are two main paths, one is that the radar wave directly returns to the radar, and the other is that the radar wave returns to the radar after a single reflection from the sea surface. Combining the two main paths of the incident wave and the two main paths of the scattered wave, we get the "four-path" signal model. In fact, in addition to the above four main paths, there are other high-order reflection paths, but the contribution of the high-order reflection paths to the target echo signal is very small and can be ignored. On this basis, using the single-double station equivalence theorem and assuming that the mirror reflection of the sea surface is mutually coupled, the model can be further simplified to a "three-path" model. The total RCS of the target under the sea surface multipath effect can be calculated based on the RCS corresponding to the three paths of the target, the mirror reflection coefficient of the sea surface and the distance of each path.

[0003] However, existing methods cannot further analyze the statistical characteristics of the target's RCS as it changes with distance, especially for sea-skimming aircraft, whose distance relative to the radar changes rapidly, causing the RCS to fluctuate continuously. The radar's detection performance for sea-skimming aircraft is closely related to the target's RCS statistical characteristics. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating the RCS statistical characteristics of a target under the sea surface multipath effect, which can quickly calculate the RCS statistical characteristics of the target under the sea surface multipath effect according to the target complex RCS and the sea surface mirror reflection coefficient, and can quickly calculate the total RCS probability density function of the target under the sea surface multipath effect through Monte Carlo simulation.

[0005] To achieve the above object, the present invention provides a method for calculating the statistical characteristics of target RCS under the sea surface multipath effect, comprising the following steps:

[0006] S1, complex RCS data of the target pitch angle direction under a given clean background and the sea surface specular reflection coefficient data at each grazing angle;

[0007] S2. Calculate the mean and variance of the target total RCS according to the target RCS statistical characteristic formula under the sea surface multipath effect;

[0008] S3. Based on the target total RCS function with the phase difference relative to the direct path as a variable, a random experiment is conducted by the Monte Carlo method to statistically calculate the probability density function of the target total RCS in the form of a numerical function.

[0009] Preferably, in S1, obtaining complex RCS data in the pitch angle direction of the target includes the following steps:

[0010] S11, simplifying the "four-path" signal model to a "three-path" signal model;

[0011] S12, calculating the distance of each path in the "three-path" signal model;

[0012] The radar, the sea surface reflection point and the target are located at the three vertices of the triangle, and the distance between the radar and the sea surface reflection point is r. 1 , the distance between the sea surface reflection point and the target is r 2 , the distance between the radar and the target is R, and the elevation angles of the radar and the target observed at the sea surface reflection point are The elevation angle of the radar at the target and the depression angle of the reflection point on the sea surface are both The target height from sea level is H 1 ;

[0013] Path 1 Distance L 1 =2R;

[0014] Path 2

[0015] Route 3

[0016] S13. The scattering field of each path is expressed by the scattering field of the target body:

[0017]

[0018] Where ρ is the sea surface specular reflection coefficient, K is the radar wave number, and the total scattered field is:

[0019]

[0020] S14, obtaining complex RCS data of the target in the pitch angle direction;

[0021] Normalized relative to the incident wave energy, the total complex RCS of the target is:

[0022]

[0023] Where K is the radar wave number, σ is the total complex RCS of the target under multipath effect, and σ 1 , σ 2 , σ 3 The corresponding target pitch angles are The directional complex RCS, horizontal complex RCS and target pitch angle are Direction complex RCS.

[0024] Preferably, in S11, the “four-path” signal model is specifically as follows: Path 1 is a direct echo path, the radar transmits electromagnetic waves directly to the target, and generates scattered waves that directly return to the radar. The scattering field generated by Path 1 is recorded as E 01 Path 2 and path 3 are single reflection echoes. Path 2 is when the radar emits electromagnetic waves and directly irradiates the target, generating scattered waves that reflect once on the sea surface and then return to the radar. Path 3 is when the radar emits electromagnetic waves that reflect once on the sea surface and then irradiate the target, generating scattered waves that directly return to the radar. The scattering fields generated by path 2 and path 3 are respectively denoted as E 02 and E 03 Path 4 is the secondary reflection echo. The radar transmits electromagnetic waves that are reflected once by the sea surface and then illuminate the target, generating scattered waves that are reflected once by the sea surface and then return to the radar. The scattering field generated by path 4 is recorded as E 04 ; The scattering field at the radar receiving antenna is the superposition of the four-path scattering fields, that is, E s =E 01 +E 02 +E 03 +E 04 .

[0025] Preferably, in S11, the “three-path” signal model is specifically as follows: in the “four-path” signal model, path 2 and path 3 are bistatic scatterings to the target, and the bistatic angles are the same. According to the single-bistatic equivalence theorem, when the bistatic angle is small, the bistatic scattering is approximately equivalent to the single-bistatic scattering on the bistatic angle bisector, that is, the target scatterings of path 2 and path 3 are both set to target scatterings along the horizontal direction; at the same time, the mirror reflection coefficient of the rough sea surface is set to be mutually coupled, that is, the mirror reflection coefficients of the sea surface in path 2 and path 3 are the same; therefore, it is considered that the scattering fields of path 2 and path 3 are the same, that is, E 02 =E 03 , the total scattered field is simplified to E s =E 01 +2E 02 +E 04 ;

[0026] Redefine path 1 as the direct path, and its scattered field is E 1 =E 01 Path 2 is a single reflection path, and its scattered field is E 2 =2E 02 Path 3 is the secondary reflection path, and its scattering field is E 3 =E 04 ; The total scattered field is E s =E 1 +E 2+E 3 .

[0027] Preferably, in S2, the calculation process of the fluctuation mean and variance of the target total RCS includes the following steps:

[0028] S21. The phase of the scattered field under each path changes with the change of distance R. The total RCS of the target fluctuates with the change of distance R. The total complex RCS phase factor is extracted to obtain:

[0029]

[0030] S22. Taking the direct path phase as a reference, other phases are expressed as phase differences relative to the direct path:

[0031]

[0032] S23. Simplify the phase difference in S22 and let:

[0033] θ 1 =-K(L 2 -L 1 );

[0034] θ 2 =-K(L 3 -L 1 );

[0035]

[0036] Among them, θ 1 ,θ 2 It represents the phase difference between the first reflection path and the second reflection path relative to the direct path due to the path difference, Δθ 1 , Δθ 2 It represents the phase difference between the primary reflection path and the secondary reflection path relative to the direct path caused by the scattering of the target body in different directions. According to the path relationship, θ 2 =2θ 1 , the simplified phase difference is:

[0037]

[0038] S24. The total RCS of the target under multipath effect is regarded as the vector sum of the RCS of each path. According to the geometric relationship, the total RCS of the target is:

[0039]

[0040] S25. For a certain target, during a radar detection process, the sea surface is assumed to be stationary, the radar irradiation angle of the target remains unchanged, and the total RCS of the target is regarded as the phase difference θ caused by the path difference. 1As a function of the independent variable, θ 1 As a random variable, the total RCS has the following mean and variance:

[0041]

[0042] Preferably, in S2, the method for calculating the target RCS statistical characteristics is to substitute the target complex RCS data and the sea surface specular scattering coefficient into the mean and variance formula to calculate the statistical characteristics of the target total RCS under the sea surface multipath effect.

[0043] Preferably, in S3, the random variable θ is expressed according to the target total RCS 1 Perform Monte Carlo simulation.

[0044] Therefore, the present invention adopts the above-mentioned method for calculating the statistical characteristics of the target RCS under the sea surface multipath effect, and further derives a statistical characteristic calculation formula of the target RCS based on the classic sea surface multipath model, and can quickly calculate the target RCS statistical characteristics under the sea surface multipath effect according to the target complex RCS and the sea surface mirror reflection coefficient. The total RCS function of the sea surface multipath effect derived by the present invention takes the relative phase difference as the independent variable, and can quickly calculate the total RCS probability density function of the target under the sea surface multipath effect through Monte Carlo simulation.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of an embodiment of a method for calculating the statistical characteristics of target RCS under the sea surface multipath effect of the present invention;

[0047] Figure 2 It is a "four-path" signal model diagram of an embodiment of a method for calculating target RCS statistical characteristics under sea surface multipath effect of the present invention;

[0048] Figure 3 It is a schematic diagram of each path distance and target scattering in a "three-path" model of an embodiment of a method for calculating target RCS statistical characteristics under sea surface multipath effect of the present invention;

[0049] Figure 4 It is a schematic diagram of RCS vectors of each path in an embodiment of a method for calculating RCS statistical characteristics of a target under sea surface multipath effect of the present invention;

[0050] Figure 5 It is a probability density function of the total RCS of a target under the sea surface multipath effect in an embodiment of a method for calculating the statistical characteristics of the target RCS under the sea surface multipath effect of the present invention. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0052] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0053] Embodiment 1

[0054] The present invention provides a method for calculating the statistical characteristics of target RCS under the sea surface multipath effect. The overall process is as follows: Figure 1 As shown, the following steps are included:

[0055] S1. Given the complex RCS data of the target in the pitch angle direction under a clean background and the sea surface mirror reflection coefficient data under each ground-grazing angle, obtaining the complex RCS data of the target in the pitch angle direction includes the following steps:

[0056] S11. Simplify the "four-path" signal model into a "three-path" signal model. The "four-path" signal model is as follows: Figure 2 As shown. Path 1 is the direct echo path. The radar transmits electromagnetic waves that directly illuminate the target, generating scattered waves that directly return to the radar. Paths 2 and 3 are single-reflection echoes. Path 2 is the radar transmitting electromagnetic waves that directly illuminate the target, generating scattered waves that reflect once on the sea surface and then return to the radar; Path 3 is the radar transmitting electromagnetic waves that reflect once on the sea surface and then illuminate the target, generating scattered waves that directly return to the radar. Path 4 is a secondary reflection echo. The radar transmits electromagnetic waves that reflect once on the sea surface and then illuminate the target, generating scattered waves that reflect once on the sea surface and then return to the radar. The scattering fields generated by paths 1 to 4 are denoted as E 01 , E 02 , E 03 , E 04 , the scattering field at the radar receiving antenna is the superposition of the four-path scattering fields, that is, E s =E 01 +E 02 +E 03 +E 04 .

[0057] Among the four paths, path 1 and path 4 are single-station scattering for the target, and path 2 and path 3 are double-station scattering for the target, and the double-station angle is the same. According to the single-station and double-station equivalence theorem, when the double-station angle is small, the double-station scattering is approximately equivalent to the single-station scattering on the bisector of the double-station angle, that is, the target scattering of path 2 and path 3 is set as the target scattering along the horizontal direction. At the same time, the mirror reflection coefficient of the rough sea surface is set to be mutually coupled, that is, the mirror reflection coefficient of the sea surface in path 2 and path 3 is the same. Therefore, it can be considered that the scattering field of path 2 and path 3 is the same, that is, E 02 =E 03 , the total scattered field is E s =E 1 +E 2 +E 3 .

[0058] The “four-path” signal model is simplified to a “three-path” signal model, and path 1 is redefined as a direct path, whose scattered field is E 1 =E 01 Path 2 is a single reflection path, and its scattered field is E 2 =2E 02 Path 3 is the secondary reflection path, and its scattering field is E 3 =E 04 ; The total scattered field is E s =E 1 +E 2 +E 3 .

[0059] S12. Calculate the distance of each path in the "three-path" signal model. The distance of each path in the "three-path" signal model and the target scattering diagram are as follows: Figure 3 The distances of each path are:

[0060] L 1 =2R;

[0061]

[0062] S13. The scattering field of each path is expressed by the scattering field of the target body:

[0063]

[0064] Where ρ is the sea surface specular reflection coefficient, K is the radar wave number, and the total scattered field is:

[0065]

[0066] S14, obtaining complex RCS data of the target in the pitch angle direction;

[0067] Normalized relative to the incident wave energy, the total complex RCS of the target is:

[0068]

[0069] Where K is the radar wave number, σ is the total complex RCS of the target under multipath effect, and σ 1 , σ 2 , σ 3 The corresponding target pitch angles are The directional complex RCS, horizontal complex RCS and target pitch angle are Direction complex RCS.

[0070] S2. Calculate the mean and variance of the target total RCS based on the target RCS statistical characteristic formula under the sea surface multipath effect.

[0071] The calculation process of the mean and variance of the target total RCS includes the following steps:

[0072] S21. The phase of the scattered field under each path changes with the change of distance R. The total RCS of the target fluctuates with the change of distance R. The total complex RCS phase factor is extracted to obtain:

[0073]

[0074] S22. Taking the direct path phase as a reference, other phases are expressed as phase differences relative to the direct path:

[0075]

[0076] S23. Simplify the phase difference in S22 and let:

[0077] θ 1 =-K(L 2 -L 1 );

[0078] θ 2 =-K(L 3 -L 1 );

[0079]

[0080] Among them, θ 1 ,θ 2 It represents the phase difference between the first reflection path and the second reflection path relative to the direct path due to the path difference, Δθ 1 , Δθ 2 It represents the phase difference between the primary reflection path and the secondary reflection path relative to the direct path caused by the scattering of the target body in different directions. According to the path relationship, θ 2 =2θ 1 , the simplified phase difference is:

[0081]

[0082] S24, the total RCS of the target under multipath effect is regarded as the vector sum of the RCS of each path, such as Figure 4 As shown, according to the geometric relationship, the total RCS of the target is:

[0083]

[0084] S25. For a certain target, during a radar detection process, the sea surface is assumed to be stationary, the radar irradiation angle of the target remains unchanged, and the total RCS of the target is regarded as the phase difference θ caused by the path difference. 1 As a function of the independent variable, θ 1 As a random variable, the total RCS has the following mean and variance:

[0085]

[0086] The target complex RCS data and the sea surface specular scattering coefficient are substituted into the mean and variance formulas to calculate the statistical characteristics of the target total RCS under the sea surface multipath effect.

[0087] S3. According to the target total RCS function, the random variable θ 1 By performing Monte Carlo simulation and statistically analyzing the results, we can obtain the target RCS probability density function in the form of a numerical function. 1 =σ 2 =σ 3 =1m 2 ,ρ=0.5,Δθ 1 =Δθ 2 = 0, the target total RCS probability density function can be obtained as follows Figure 5 shown.

[0088] Therefore, the present invention adopts the above-mentioned method for calculating the statistical characteristics of the target RCS under the sea surface multipath effect, and further derives a statistical characteristic calculation formula of the target RCS based on the classic sea surface multipath model, and can quickly calculate the target RCS statistical characteristics under the sea surface multipath effect according to the target complex RCS and the sea surface mirror reflection coefficient. The total RCS function of the sea surface multipath effect derived by the present invention takes the relative phase difference as the independent variable, and can quickly calculate the total RCS probability density function of the target under the sea surface multipath effect through Monte Carlo simulation.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the statistical characteristics of target RCS under sea surface multipath effect, characterized by: The following steps are involved: S1, complex RCS data of the target pitch angle direction under a given clean background and the sea surface specular reflection coefficient data at each grazing angle; S2. Calculate the mean and variance of the target total RCS according to the target RCS statistical characteristic formula under the sea surface multipath effect; S3. Based on the target total RCS function with the phase difference relative to the direct path as a variable, a random experiment is conducted by the Monte Carlo method to statistically calculate the probability density function of the target total RCS in the form of a numerical function.

2. The method for calculating the target RCS statistical characteristics under the sea surface multipath effect according to claim 1, characterized in that: In S1, obtaining the complex RCS data of the target pitch angle direction includes the following steps: S11, simplifying the "four-path" signal model to a "three-path" signal model; S12, calculating the distance of each path in the "three-path" signal model; The radar, the sea surface reflection point and the target are located at the three vertices of the triangle. The distance between the radar and the sea surface reflection point is R1, the distance between the sea surface reflection point and the target is R2, the distance between the radar and the target is R, and the elevation angles of the radar and the target at the sea surface reflection point are The elevation angle of the radar at the target and the depression angle of the reflection point on the sea surface are both The target height from sea level is H1; Path 1 distance L1 = 2R; Path 2 Route 3 S13. The scattering field of each path is expressed by the scattering field of the target body: Where ρ is the sea surface specular reflection coefficient, K is the radar wave number, and the total scattered field is: S14, obtaining complex RCS data of the target in the pitch angle direction; Normalized relative to the incident wave energy, the total complex RCS of the target is: Among them, K is the radar wave number, σ is the total complex RCS of the target under the multipath effect, and σ1, σ2, and σ3 correspond to the target pitch angles respectively. The directional complex RCS, horizontal complex RCS and target pitch angle are Direction complex RCS.

3. The method for calculating the target RCS statistical characteristics under the sea surface multipath effect according to claim 2, characterized in that: In S11, the "four-path" signal model is as follows: Path 1 is the direct echo path, where the radar emits electromagnetic waves that directly irradiate the target, generating scattered waves that directly return to the radar. The scattering field generated by Path 1 is recorded as E 01 Path 2 and path 3 are single reflection echoes. Path 2 is when the radar emits electromagnetic waves and directly irradiates the target, generating scattered waves that reflect once on the sea surface and then return to the radar. Path 3 is when the radar emits electromagnetic waves that reflect once on the sea surface and then irradiate the target, generating scattered waves that directly return to the radar. The scattering fields generated by path 2 and path 3 are respectively denoted as E 02 and E 03 Path 4 is the secondary reflection echo. The radar transmits electromagnetic waves that are reflected once by the sea surface and then illuminate the target, generating scattered waves that are reflected once by the sea surface and then return to the radar. The scattering field generated by path 4 is recorded as E 04 ; The scattering field at the radar receiving antenna is the superposition of the four-path scattering fields, that is, E s =E 01 +E 02 +E 03 +E 04 .

4. The method for calculating the target RCS statistical characteristics under the sea surface multipath effect according to claim 3, characterized in that: In S11, the "three-path" signal model is specifically as follows: In the "four-path" signal model, path 2 and path 3 are bistatic scattering to the target, and the bistatic angle is the same. According to the single-bistatic equivalence theorem, when the bistatic angle is small, the bistatic scattering is approximately equivalent to the single-bistatic scattering on the bisector of the bistatic angle, that is, the target scattering of path 2 and path 3 is set to be the target scattering along the horizontal direction; at the same time, the mirror reflection coefficient of the rough sea surface is set to be mutually coupled, that is, the mirror reflection coefficient of the sea surface in path 2 and path 3 is the same; therefore, it is considered that the scattering fields of path 2 and path 3 are the same, that is, E 02 =E 03 , the total scattered field is simplified to E s =E 01 +2E 02 +E 04 ; Redefine path 1 as the direct path, and its scattered field is E1 = E 01 Path 2 is a single reflection path, and its scattered field is E2 = 2E 02 Path 3 is a secondary reflection path, and its scattering field is e3 = e 04 ; The total scattered field is E s =E1+E2+E3.

5. The method for calculating the target RCS statistical characteristics under the sea surface multipath effect according to claim 4, characterized in that: In S2, the calculation process of the mean and variance of the target total RCS includes the following steps: S21. The phase of the scattered field under each path changes with the change of distance R. The total RCS of the target fluctuates with the change of distance R. The total complex RCS phase factor is extracted to obtain: S22. Taking the direct path phase as a reference, other phases are expressed as phase differences relative to the direct path: S23. Simplify the phase difference in S22 and let: θ1=-K(L2-L1); θ2=-K(L3-l1); Among them, θ1, θ2 represent the phase difference of the primary reflection path and the secondary reflection path relative to the direct path due to the path difference, Δθ1, Δθ2 represent the phase difference of the primary reflection path and the secondary reflection path relative to the direct path due to the scattering of the target body in different directions. According to the path relationship, θ2 = 2θ1, and the simplified phase difference result is: S24. The total RCS of the target under multipath effect is regarded as the vector sum of the RCS of each path. According to the geometric relationship, the total RCS of the target is: S25. For a certain target, during a radar detection process, the sea surface is assumed to be stationary, the radar irradiation angle of the target is unchanged, and the total RCS of the target is regarded as a function with the phase difference θ1 caused by the path difference as the independent variable. θ1 is regarded as a random variable, and the mean and variance of the total RCS are calculated as follows:

6. The method for calculating the target RCS statistical characteristics under the sea surface multipath effect according to claim 5, characterized in that: In S2, the method for calculating the statistical characteristics of the target RCS is to substitute the target complex RCS data and the sea surface specular scattering coefficient into the mean and variance formula to calculate the statistical characteristics of the target total RCS under the sea surface multipath effect.

7. The method for calculating the target RCS statistical characteristics under the sea surface multipath effect according to claim 6, characterized in that: In S3, a Monte Carlo simulation is performed on the random variable θ1 according to the target total RCS expression.

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