CN114970213B - Sea clutter dynamic simulation method under soliton internal wave fluctuation effect - Google Patents
Sea clutter dynamic simulation method under soliton internal wave fluctuation effect Download PDFInfo
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Abstract
The invention belongs to the technical field of signal processing, and particularly discloses a dynamic simulation method of sea clutter under soliton internal wave fluctuation effect. Which comprises the following steps: step 1, establishing a dynamic sea wave spectrum model of a large-scale sea surface by using a linear superposition method; step 2, simulating soliton internal waves by taking an MITgcm mode as a core, and establishing a soliton internal wave propagation model; step 3, modulating the high-frequency spectrum part of the dynamic sea surface to correct the capillary wave of the sea surface; step 4, dividing sea surface elements on the sea surface, and calculating sea clutter electromagnetic scattering coefficients of the sea surface elements without soliton internal waves and modulated by the soliton internal waves according to whether soliton internal waves exist under the elements; and 5, substituting parameters such as the sea surface electromagnetic scattering coefficient value and the like into a sea surface echo signal formula, calculating the echo signals of all sea surface elements, and superposing to generate the sea clutter data at all times. The invention improves the authenticity and the accuracy of sea clutter simulation.
Description
Technical Field
The invention belongs to the technical field of signal processing, and relates to a dynamic simulation method of sea clutter under soliton internal wave fluctuation effect.
Background
Most of the traditional sea clutter simulation is simple simulation based on statistical characteristic extraction of limited measured data, such as a sea clutter amplitude distribution simulation model of Rayleigh distribution, logarithmic normal distribution, weibull distribution, K distribution and the like, and a classical sea clutter generation method of a zero memory nonlinear variation method (ZMNL), a ball invariant process method (SIRP) and the like. However, the method does not start from a physical mechanism generated by sea clutter, and for the influence of various natural factors such as sea surface wind power, sea surface environment humidity, surge and the like, radar sea surface echoes have serious multipath effect in a radar receiver, so that sea clutter signals have complex change and high intensity compared with other signals, therefore, simulated clutter data generated by the traditional method cannot be really matched with sea surface environment parameter change factors, and particularly has far difference with actual sea clutter characteristics under the complex change condition of an ocean internal power process.
The sea surface mainly comprises gravity waves of a large-scale structure and capillary waves of a small-scale structure, the medium-and small-scale fast-changing power process such as ocean soliton internal waves is fluctuation of density stabilization layer junctions in the ocean, and in the ocean, because density difference exists between sea water layer junctions, the small disturbance can cause the fluctuation in the ocean. In the ocean energy level, soliton internal waves are indispensable internal dynamic processes, which are very important roles in the processes of ocean substance, momentum and energy transfer, so that the soliton internal waves play an important role in the theoretical research of the whole ocean dynamics. In addition, soliton internal waves are observed in the synthetic aperture radar imaging and are represented as texture changes, and the fact that the soliton internal waves have certain influence on ocean remote sensing and formation of ocean clutter is proved. At present, a mainstream ocean forecast model mostly takes a large and medium scale dynamic process as core motion, and simulation of internal dynamic processes such as soliton internal waves and the like is not considered, so that dynamic change details of the ocean surface are difficult to show, the electromagnetic scattering coefficient of the sea clutter is influenced, and accurate and credible sea clutter data cannot be obtained finally.
Disclosure of Invention
The invention aims to provide a method for dynamically simulating sea clutter under the soliton internal wave fluctuation effect, which fully considers the influence of soliton internal waves on ocean surface details and further acts on an electromagnetic scattering coefficient of the sea clutter, thereby improving the accuracy and the authenticity of sea clutter simulation.
In order to achieve the purpose, the invention adopts the following technical scheme:
a sea clutter dynamic simulation method under soliton internal wave fluctuation effect comprises the following steps:
establishing a dynamic sea wave spectrum model by linking the sea surface at each moment through a time function;
defining a first sampling period to start at time t =0;
step 3, modulating the high-frequency spectrum part in the dynamic wave spectrum model obtained in the step 1 through a wave-current interaction function of the soliton internal wave to obtain a modified wave spectrum containing the soliton internal wave action;
step 4, dividing a plurality of sea surface elements on the corrected sea wave spectrum, and calculating the sea clutter electromagnetic scattering coefficient of each sea surface element when soliton internal waves exist or do not exist on the sea surface by a double-scale method; the method specifically comprises the following steps:
if soliton internal waves exist under a certain sea surface element, calculating the sea clutter electromagnetic scattering coefficient of the modulated sea surface element; if soliton internal waves do not exist under a certain sea surface element, calculating a sea clutter electromagnetic scattering coefficient of the unmodulated sea surface element;
establishing a sea surface reference coordinate system by taking the central point of the irradiation range of the radar detection sea surface as an origin, and respectively calculating the distance between the radar and each sea surface element, namely the slope distance, according to the relative position between the radar and each sea surface element;
step 5, inputting the sea clutter electromagnetic scattering coefficient and the slope distance parameter of each sea surface element obtained in the step 4 based on a sea surface echo signal formula to obtain an echo signal of each sea surface element at the current moment;
superposing echo signals of all sea surface elements at the current moment to obtain an integral sea surface echo signal at the current moment, namely sea clutter data of the sea surface at the current moment;
step 6, enabling t = t +1, and entering the next sampling period;
and (5) repeating the steps 2 to 5 until the preset number of sea clutter data are obtained, and ending sampling.
The invention has the following advantages:
as described above, the invention relates to a dynamic simulation method of sea clutter under soliton internal wave fluctuation effect, which is based on sea surface dynamic sea wave spectrum modeling, realizes refined composite sea surface modeling under the action of small and medium-sized soliton internal waves, truly delineates a dynamic sea surface, takes the influence of the dynamic process of the sea soliton internal waves on the sea clutter numerical simulation into consideration, can perform high-precision refined dynamic simulation on a large area of radar sea surface echoes under different sea conditions in different sea areas, and combines large-sized sea information to enable the electromagnetic scattering coefficient of the sea clutter to more comprehensively reflect the parameter action of the sea surface. The invention brings the mutual coupling effect of the small and medium-scale marine power process into the sea clutter model calculation, considers the influence mechanism of soliton internal waves on the sea clutter, and improves the authenticity and the accuracy of the sea clutter simulation.
Drawings
Fig. 1 is a schematic flow chart of a dynamic simulation method of sea clutter under the soliton internal wave fluctuation effect in an embodiment of the present invention.
FIG. 2 is a schematic diagram of an ocean internal power process including a soliton internal wave model based on an MIT gcm mode in an embodiment of the present invention.
Fig. 3 is a flow chart of a sea clutter simulation method under the soliton internal wave fluctuation effect under one-time sampling in the embodiment of the present invention.
Fig. 4 is a schematic diagram of radar and dynamic physical sea surface geometry in an embodiment of the present invention.
Detailed Description
According to the method, dynamic sea clutter data are simulated in a refined mode under the influence of soliton internal waves on electromagnetic scattering.
In order to accurately simulate the sea clutter data under the soliton internal wave fluctuation effect, the invention provides the following technical means:
on the basis of fusion of a linear superposition method, a sea wave spectrum Elfouhaily spectrum and sea surface electromagnetic scattering calculation, a soliton internal wave model is established to modulate a sea surface wave high frequency spectrum, a corresponding sea surface capillary wave part is corrected, the problems of single sea wave spectrum parameter and coarseness are solved, and sea clutter data containing a soliton internal wave effect are simulated through electromagnetic scattering characteristics of the sea surface.
The invention is described in further detail below with reference to the following figures and detailed description:
as shown in fig. 1, the method for dynamically simulating sea clutter under soliton internal wave fluctuation effect includes the following steps:
The sea wave can be represented by a random process eta (x, y, t) about t, and the sea surface at a certain moment is formed by generating cosine waves with different frequencies, different propagation directions, different initial phases and different wave heights and then overlapping the cosine waves.
The step 1 specifically comprises the following steps:
according to sea condition parameters and a random process theory of sea waves, based on a Longuest-Higgins sea wave spectrum wave height model in a linear superposition method, a plurality of cosine waves with different frequencies, different propagation directions, different initial phases and different wave heights are generated.
Calculating the wave height of the three-dimensional sea wave spectrum by a linear superposition method, and establishing a wave height equation by using the parameters, wherein the formula is as follows:
η(x,y,t)= Σ M i=1 Σ N j=1 a ij cos(w i t-k i [xcosθ j +ysinθ j +ε ij ])。
wherein η (x, y, t) represents a wave height equation established by a linear superposition method and is used for calculating the wave height of the three-dimensional sea wave spectrum.
M, N represents the number of frequency divisions and the number of direction divisions, respectively; a is ij 、w i 、k i 、θ j 、ε ij Respectively representing the amplitude, angular frequency, wave number, direction angle and initial phase of the component wave of the ith frequency and the jth direction.
Wherein, the direction angle is the included angle between the propagation direction of the sea waves and the shaft.
(x, y) is the sea wave position vector, t is the time vector, ε ij Are random numbers uniformly distributed in the range of 0-2 pi.
Amplitude a of component wave at ith frequency and jth direction ij The wave spectrum is obtained by carrying out inversion theory, and the calculation method comprises the following steps:
a ij = 
。
wherein, delta theta j And Δ w i Respectively represent theta j And w i The increment of (c).
Angular frequency interval Δ w i Is divided by frequency division with a directional interval delta theta j The division of (2) adopts a direction equipartition method.
S(w i ,θ j ) Is a wave spectrum, which represents the distribution of waves in frequency and direction; s (w) i ,θ j ) As the ith wave frequency spectrum function S (w) i ) And a jth wave direction development function D (theta) j ) Product of, i.e. S (w) i ,θ j )= S(w i ) D(θ j )。
Wave frequency spectrum function S (w) i ) An Elfouhaily spectrum is selected and consists of a low-frequency part corresponding to a large-scale gravity wave and a high-frequency part corresponding to a small-scale capillary wave, namely S (w) i )=(B L +B H )/(w i 2 /g) 3 。
Wherein, B L And B H Respectively representing the low-frequency part and the high-frequency part of the wave frequency spectrum, and g is the gravity acceleration.
Wave direction expansion function D (theta) j ) And selecting a bilateral direction expansion function for calculation.
And projecting any point (x, y, z) on the generated sea surface to a reference level point (x, y), describing the sea surface height z of the point (x, y) at the time t by using a wave height equation eta (x, z, t), and establishing a sea wave model of the sea surface as z = eta (x, y, t).
And establishing a dynamic wave spectrum model by relating the sea surface at each moment through a time function.
It is defined that at time t =0, the first sampling period starts.
And 2, establishing a generation and propagation model of soliton internal waves in the marine internal power process based on the MIT gcm mode, acting the marine internal power process of the soliton internal waves on the sea surface, and considering the change of the wave spectrum model.
MITgcm, short for MIT General Circulation Model, was developed by the American Massachusetts institute of technology, and can be used for the research of atmosphere, sea and climate. The mode is characterized in that a vertical momentum equation adopts non-static force approximation, so that the model is suitable for simulating various small-scale dynamic processes, such as soliton internal waves and small-scale frontal surfaces.
By using the MITgcm, an ultra-high resolution ocean numerical model in the north of the south China sea is established.
The model adopts orthogonal grids in the horizontal direction, the latitudinal direction resolution is 1/3 '(about 0.52 km), the longitudinal direction resolution is 1' (1.85 km), the vertical direction resolution is divided into 110 layers, and the resolution is gradually transited from 10 m of the surface layer to 200 m of the bottom layer.
As shown in fig. 2, the soliton internal wave can induce a strong vertical flow velocity, so that the surface flow field generates radiation and divergence, and finally the sea surface roughness is changed, and therefore, the peak line of the soliton internal wave corresponding to the significant high value region of the sea surface height gradient (as shown in the solid line box in fig. 2) is obtained.
And 3, considering the influence of the dynamic process of the soliton internal wave in the ocean on the sea clutter generation mechanism, and modulating a high-frequency spectrum part in the dynamic sea wave spectrum model through a wave-current interaction function of the soliton internal wave to obtain the modified sea wave capillary wave containing the soliton internal wave action.
When the radar detects the sea surface, the fluctuation of the soliton internal wave is small and steep, the growth process of the sea surface spectrum in a wave number space is described through a beam spectrum balance equation, and in soliton internal wave research, the influence of the soliton internal wave on the sea surface spectrum is mainly reflected on a wave-flow interaction source function, and other source functions are not considered temporarily.
The beam spectrum balance equation can be simplified as: [ ə/ə t + (c) g +U) ə/əx] ΔΨ= S cu (k)。
Wherein, c g Is the group velocity of sea surface waves, U is the velocity of water particles in the upper sea water, delta psi is the variation value of the sea surface wave height frequency spectrum influenced by soliton internal waves, S cu (k) For the wave-flow interaction source function, the formula is as follows:
S cu (k)=-(S αβ əU β /əx α ) Ψ original source 。
Wherein, U β Representing the velocity component, Ψ, of a large-scale flow field Original source Expressed as unmodulated wave spectrum values.
S αβ əU β /əx α Can be written as:
S αβ əU β /əx α =-(C 0 cos 2 φ/h l l) η 0 ▪sech 2 ((I- C 0 ＇t)/ l)th((I- C 0 ＇t)/ l)。
the embodiment of the invention only considers the modulation of the wave-current interaction on the frequency spectrum, and can be obtained by sorting, the wave-current interaction of the soliton internal wave generates the modulation quantity on the high-frequency spectrum part in the dynamic wave spectrum model as follows:
ΔΨ=-m 3 ω -1 k -4 η 0 (C 0 cos 2 φ/h l l) ▪sech 2 ((I- C 0 ＇t)/ l)th((I- C 0 ＇t)/ l)。
wherein, the delta psi is the variation value of the high frequency spectrum of the surface wave under the influence of soliton internal wave, omega is the space angular frequency of the sea spectrum, and omega is 2 = gk, g is acceleration of gravity, k is wave number, m 3 Is a coefficient, m 3 And phi is 0.13, and represents the included angle between the radar visual angle and the propagation direction of the soliton internal wave. Eta 0 The maximum amplitude of the soliton internal wave, which usually varies from a few meters to several tens of meters, C 0 For linear wave velocity, it is assumed that the seawater is composed of two layers of water, one above the spring layer, called the upper layer (or mixed layer) with depth h l L is the half-wave width of the internal wave, C 0 "is the inner wave phase velocity, and I represents the spatial position.
And 4, dividing a plurality of sea surface elements on the corrected sea wave spectrum, and calculating the sea clutter electromagnetic scattering coefficient of each sea surface element when soliton internal waves exist or do not exist on the sea surface by a double-scale method. The method specifically comprises the following steps:
if soliton internal waves exist under a certain sea surface element, calculating the sea clutter electromagnetic scattering coefficient of the modulated sea surface element; and if no soliton internal wave exists under a certain sea surface element, calculating the unmodulated sea clutter electromagnetic scattering coefficient of the sea surface element.
For example, as shown in fig. 3, a primary sea clutter sampling process is performed, the generated large-scale gravity wave rough sea surface profile is utilized to be divided into X sea clutter surface elements, and polarization factors F under horizontal polarization and vertical polarization are calculated HH And F VV ：
F HH =[1+R H (θ i )][1+R H (θ s )]cosφ s ；
F VV =[1+R V (θ i )][1+R v (θ s )]sinθ i sinθ s /ε-[1-R V (θ i )][1-R v (θ s )]cosθ i cosθ s cosφ s 。
Where H denotes horizontal polarization and V denotes vertical polarization.
R V ，R H Respectively being vertically polarizedAnd Fresnel reflection coefficient in horizontal polarization, θ i 、θ s The local incident angle and the reflection angle phi of the incident wave on each sea surface element s Epsilon is the dielectric constant of seawater, the azimuth of the local scattering angle.
Through a double-scale method, the electromagnetic scattering coefficient of each surface element of the sea surfaceσ 0 Calculated using the following formula:
σ 0 pq (k i ＇,k s ＇)= πk 4 |ε-1| 2 |F pq | 2 Ψ(d l )；
σ 0 pq (k i ＇,k s ') represents the electromagnetic scattering coefficients of various sea clutter bins of different polarization modes;
wherein k is i ' denotes the incident wave vector, k s "represents a scattered wave vector; p = (H, V) polarization mode of scattered wave, q polarization mode of incident wave, F pq Is the polarization factor, Ψ (d) l ) Is the high frequency spectrum part of the wave spectrum of the sea surface.
d l Is the scattering vector d = k (k) s ＇- k i ' on a sea surface bin.
If soliton internal waves exist under a certain sea surface element, the influence of the soliton internal waves on a sea clutter generation mechanism is considered, the sea clutter electromagnetic scattering coefficient of the modulated surface element is calculated, and at the moment, the sea wave spectrum psi (d) is obtained l ) Is determined from the original wave spectrum value Ψ Original source Adding the sea surface high frequency spectrum modulation value obtained in the step 3, namely delta psi, and calculating according to the formula: Ψ (d) l )= Ψ Original source +ΔΨ。
Fig. 4 is a schematic diagram of radar and dynamic physical sea surface geometry. Establishing a reference coordinate system OXYZ by taking the central point of the irradiation range of the radar detection sea surface as the origin, wherein the radar is located at (x) L ,y L ,z L ) And calculating the slope distance R according to the relative position of the radar and each sea surface element: r (t) =
；
Wherein (x) p (t),y p (t),z p (t)) represents the center coordinates of any sea surface element, and R (t) is the distance between the radar and the center coordinates of any sea surface element at different sampling moments, namely the slope distance.
And 5, inputting the sea clutter electromagnetic scattering coefficient and the slope distance parameter of each sea surface element based on a sea surface echo signal formula to obtain the echo signal of each sea surface element at the current moment.
And overlapping the echo signals of all sea surface elements at the current moment to obtain the integral sea surface echo signal at the current moment, namely the sea clutter data of the sea surface at the current moment. The step 5 specifically comprises the following steps:
calculating a radar emission signal wave; setting a radar transmitting signal wave as a linear frequency modulation signal:
s(t＇,t m ) F =rect(t＇/T p )exp(2πf c t+πγt＇ 2 )。
wherein, rect (x) =1 when | x | > is less than or equal to 1/2, and rect (x) =0 when | x | > 1/2.
t' is called the fast time, i.e. the electromagnetic wave propagation time, t m For slow time, i.e. the moment of transmission of the pulse, T p Is the pulse width, f c The carrier frequency of the transmitted signal of the radar is gamma, and the frequency is adjusted.
And (4) inputting the electromagnetic scattering coefficient, the slope distance and other parameters of each sea surface element obtained in the step (4) based on a sea surface echo signal formula to obtain the echo signal of each sea surface element at the moment. The sea surface echo signal is calculated using the following formula:
s(t＇,t m )=Σ n σ n a n (t m )rect((t＇-2R n (t m )/c)/T p )exp(-jπγ(t＇-2R n (t m )/c) 2 )exp(-j4πR n (t m )/λ)。
wherein, s (t', t) m ) And representing the sea surface echo signals received by the radar to obtain sea clutter data.
c is the speed of light, σ n Electromagnetic scattering system for nth scattering sea surface elementNumber, R n (t m ) Is the sampling time t m Slope distance between radar and scattering sea surface elements, a n (t m ) Is the antenna two-way diagram gain of the radar.
And (3) superposing all sea surface element echo signals at the current moment to obtain the integral sea surface echo signal at the moment.
Step 6, letting t = t +1, and entering the next sampling period; and (5) repeating the steps 2 to 5 until the sea clutter data with the preset number (namely the number of the needed sea clutter which is artificially preset) is obtained, and ending the sampling.
Under the action of the dynamic process of the marine soliton internal wave, the dynamic time-varying sea wave spectrum is modulated, the influence of sea surface variation on sea clutter data when the soliton internal wave exists is considered, and the accuracy and the authenticity of sea clutter simulation are improved.
It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (6)
1. A dynamic simulation method of sea clutter under soliton internal wave fluctuation effect is characterized in that,
the method comprises the following steps:
step 1, generating a plurality of cosine waves with different frequencies, different propagation directions, different initial phases and different wave heights by using a linear superposition method, and superposing a sea wave frequency spectrum function and a direction expansion function to form a sea surface;
establishing a dynamic sea wave spectrum model by linking the sea surface at each moment through a time function;
defining a first sampling period to start at time t =0;
step 2, establishing a generation and propagation model of soliton internal waves in the marine internal power process based on the MIT gcm mode, acting the marine internal power process of the soliton internal waves on the sea surface, and considering the change of a dynamic wave spectrum model;
step 3, modulating the high-frequency spectrum part in the dynamic wave spectrum model obtained in the step 1 through a wave-current interaction function of soliton internal waves to obtain a modified wave spectrum containing soliton internal wave action;
step 4, dividing a plurality of sea surface elements on the corrected sea wave spectrum, and calculating the sea clutter electromagnetic scattering coefficient of each sea surface element when soliton internal waves exist or do not exist on the sea surface by a double-scale method; the method specifically comprises the following steps:
if soliton internal waves exist under a certain sea surface element, calculating a sea clutter electromagnetic scattering coefficient of the modulated sea surface element; if no soliton internal wave exists under a certain sea surface element, calculating the unmodulated sea clutter electromagnetic scattering coefficient of the sea surface element;
establishing a sea surface reference coordinate system by taking the central point of the irradiation range of the radar detection sea surface as an origin, and respectively calculating the distance between the radar and each sea surface element, namely the slope distance, according to the relative position between the radar and each sea surface element;
step 5, inputting the sea clutter electromagnetic scattering coefficient and the slope distance parameter of each sea surface element obtained in the step 4 based on a sea surface echo signal formula to obtain an echo signal of each sea surface element at the current moment;
superposing echo signals of all sea surface elements at the current moment to obtain an integral sea surface echo signal at the current moment, namely sea clutter data of the sea surface at the current moment;
step 6, letting t = t +1, and entering the next sampling period;
and (5) repeating the steps 2 to 5 until the preset number of sea clutter data are obtained, and ending sampling.
2. The method of dynamically simulating sea clutter under the soliton undulation effect according to claim 1,
the step 1 specifically comprises the following steps:
based on a Longuest-Higgins wave spectrum wave height model in a linear superposition method, a plurality of cosine waves with different frequencies, different propagation directions, different initial phases and different wave heights are generated, and a wave height equation is described as follows:
η(x,y,t)= Σ M i=1 Σ N j=1 a ij cos(w i t-k i [xcosθ j +ysinθ j +ε ij ])；
wherein eta (x, y, t) represents a wave height equation established by a linear superposition method and is used for calculating the wave height of the three-dimensional sea wave spectrum;
m, N represents the number of frequency divisions and the number of direction divisions, respectively; a is ij 、w i 、k i 、θ j 、ε ij Respectively representing the amplitude, angular frequency, wave number, direction angle and initial phase of the component wave in the ith frequency and the jth direction;
(x, y) is the sea wave position vector, t is the time vector, ε ij Is a random number uniformly distributed in the range of 0-2 pi;
amplitude a of component wave at ith frequency and jth direction ij The wave spectrum is obtained by carrying out inversion theory, and the calculation method comprises the following steps:
a ij =
；
wherein, delta theta j And Δ w i Respectively represent theta j And w i An increment of (d);
S(w i ,θ j ) Is a wave spectrum, which represents the distribution of waves in frequency and direction; s (w) i ,θ j ) As the ith wave frequency spectrum function S (w) i ) And a jth wave direction development function D (theta) j ) Product of, i.e. S (w) i ,θ j )= S(w i ) D(θ j )；
Wave frequency spectrum function S (w) i ) An Elfouhaily spectrum is selected and consists of a low-frequency part corresponding to a large-scale gravity wave and a high-frequency part corresponding to a small-scale capillary wave, namely S (w) i )=(B L +B H )/(w i 2 /g) 3 ；
Wherein, B L And B H Respectively representA low frequency portion and a high frequency portion of a sea wave frequency spectrum;
wave direction expansion function D (theta) j ) Selecting a bilateral direction expansion function for calculation;
and projecting any point (x, y, z) on the generated sea surface to a reference horizontal plane point (x, y), describing the sea surface height z of the point (x, y) at the time t by using a wave height equation eta (x, z, t), and establishing a dynamic wave spectrum model of the sea surface as z = eta (x, y, t).
3. The method of dynamically simulating sea clutter under the soliton undulation effect according to claim 1,
the step 3 specifically comprises the following steps:
the wave-current interaction of soliton internal waves generates modulation quantity to a high-frequency spectrum part in the dynamic wave spectrum model as follows:
ΔΨ=-m 3 ω -1 k -4 η 0 (C 0 cos 2 φ/h l l) ▪sech 2 ((I- C 0 ＇t)/ l)th((I- C 0 ＇t)/ l)；
wherein, Δ Ψ is a variation value of the sea surface wave height spectrum influenced by the soliton internal wave;
omega is the spatial angular frequency of the sea spectrum, omega 2 = gk, g is acceleration of gravity, k is wave number, m 3 Is a coefficient, m 3 =0.13，η 0 Maximum amplitude of soliton internal wave, C 0 Is the linear wave velocity, phi represents the included angle between the radar visual angle and the soliton internal wave propagation direction, h l The depth of the upper layer of the seawater, l is the half-wave width of the soliton internal wave, C 0 "is the soliton internal wave phase velocity, and I represents the spatial position.
4. The method according to claim 3, wherein the method for dynamically simulating sea clutter under the soliton undulation effect,
in the step 4, the sea clutter electromagnetic scattering coefficient of the sea surface element is calculated by the double-scale methodσ 0 The formula of (1) is as follows:
σ 0 pq (k i ＇,k s ＇)= πk 4 |ε-1| 2 |F pq | 2 Ψ(d l )；
wherein the content of the first and second substances,σ 0 pq (k i ＇,k s ') represents the electromagnetic scattering coefficients of the sea surface bins of different polarization modes; k is a radical of i ' denotes the incident wave vector, k s ' represents a scattered wave vector;σ 0 pq representing the electromagnetic scattering coefficients under different polarization modes; p = (H, V) polarization mode of scattered wave, q polarization mode of incident wave, H horizontal polarization, V vertical polarization, ε dielectric constant of seawater, F pq Is the polarization factor, Ψ (d) l ) Is the high frequency part of the sea wave spectrum at the sea surface; d l Is the scattering vector d = k (k) s ＇- k i ') projection on sea surface bins;
wave spectrum Ψ (d) when soliton inner waves exist l ) Is determined from the original wave spectrum value Ψ Original source Adding the sea surface high frequency spectrum modulation value obtained in the step 3, namely delta psi, and calculating according to the following formula: Ψ (d) l )= Ψ Original source +ΔΨ。
5. The method of dynamically simulating sea clutter under the soliton undulation effect according to claim 1,
in the step 4, a reference coordinate system OXYZ is established by taking the central point of the irradiation range of the radar detection sea surface as an origin, and the position of the radar is defined as (x) L ,y L ,z L ) And calculating the slope distance according to the relative positions of the radar and each sea surface element:
R(t)= 
；
wherein (x) p (t),y p (t),z p (t)) represents the center coordinates of any sea surface element, and R (t) is the distance between the radar and the center coordinates of any sea surface element at different sampling moments, namely the slope distance.
6. The method of dynamically simulating sea clutter under the soliton undulation effect according to claim 1,
in step 5, the sea surface echo signal is calculated by the following formula:
s(t＇,t m )= Σ n σ n a n (t m )rect((t＇-2R n (t m )/c)/T p )exp(-jπγ(t＇-2R n (t m )/c) 2 )exp(-j4πR n (t m )/λ)；
wherein, rect (x) =1 when | x | > is less than or equal to 1/2, and rect (x) =0 when | x | > 1/2;
wherein, s (t', t) m ) Representing sea surface echo signals received by a radar to obtain sea clutter data;
T p is the pulse width, lambda represents the wave length, gamma is the frequency modulation rate, and c is the speed of light; t' is called the fast time, i.e. the propagation time of the electromagnetic wave, t m The slow time is the transmission time of the pulse; sigma n The electromagnetic scattering coefficient of the nth scattering sea surface element is obtained;
R n (t m ) Is the sampling time t m Slope distance between radar and scattering sea surface elements, a n (t m ) Is the antenna two-way diagram gain of the radar.
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