A method for quantitative analysis of sea clutter for wide-swath observation of typhoon radar on board a boat

Abstract

The present invention provides a method for quantitative analysis of sea clutter in wide-swath observation of shipborne typhoon radar. By establishing a comprehensive influence analysis model of antenna clutter and range side lobe clutter, the echo power and signal-to-clutter ratio of sea clutter in wide-swath observation of shipborne typhoon radar are quantitatively calculated and analyzed in the time domain. At the same time, according to the clutter power and signal-to-clutter ratio, the power spectral distribution characteristics of sea clutter and typhoon echo in the frequency domain are obtained, which can provide a reference for the research of clutter suppression algorithms.

Description

Technical Field

[0001] The present invention relates to the technical field of meteorological radar, and particularly to a method for quantitative analysis of sea clutter for wide-swath observation of an airship-borne typhoon radar. Background Art

[0002] Typhoon is one of the most destructive natural disasters, causing significant social and economic losses and casualties, and seriously endangering people's life and property safety. As one of the main tools for atmospheric detection, meteorological radar can be installed on a near-space airship to achieve continuous observation and tracking of typhoons, so as to obtain refined internal data of typhoons. When an airship-borne typhoon radar observes a typhoon generated and developing on the sea surface in a downward-looking or obliquely downward-looking manner, the beam irradiates the sea surface, and the sea surface echo and the typhoon echo will return to the radar receiver simultaneously, contaminating the typhoon radar echo data.

[0003] Most of the existing research on clutter influence analysis is for radar systems observing rainfall with small incident angles. For example: for a non-pulse compression meteorological radar system, Hanado and Ihara et al. analyzed the interference of antenna sidelobe clutter on the TRMM PR system at small incident angles (<17°) by establishing an antenna clutter echo model. For a pulse compression meteorological radar system, Li et al. analyzed the calculation methods of rainfall echo and antenna sidelobe clutter at small incident angles (<4°) using the ambiguity function of the linear frequency modulation (LFM) signal.

[0004] The airship-borne typhoon radar operates in the near space about 20 km above the ground and observes typhoons on the sea surface in a downward-looking manner. Sea clutter will return to the radar receiver through the main lobe and sidelobe of the antenna, interfering with the typhoon radar echo signal. In addition, limited by the airship platform, the radar transmission power is limited. To increase the radar detection range and ensure good range resolution at the same time, the radar needs to adopt pulse compression technology. Therefore, sea clutter will also generate range sidelobes through pulse compression to interfere with the echoes of surrounding range cells. And the radar uses a one-dimensional phased array antenna for electrical scanning in the elevation direction to achieve wide-swath observation (the incident angle can reach 85°), which will lead to more serious clutter interference. Therefore, for an airship-borne typhoon radar, it is necessary to further analyze the influence of antenna clutter and range sidelobe clutter generated by pulse compression when detecting in a large incident angle range.

[0005] Clutter suppression processing needs to be carried out on echo signals seriously contaminated by clutter. Clutter suppression algorithms can be divided into time-domain and frequency-domain filtering. Traditional time-domain clutter suppression algorithms will also cause losses to overlapping weather signals while filtering out clutter signals. To recover overlapping weather signals, frequency-domain clutter suppression algorithms have been developed. Therefore, to perform frequency-domain filtering, it is necessary to further clarify the power spectral distributions of sea clutter and typhoon radar echoes, and their frequency-domain distribution characteristics can provide a reference for clutter suppression algorithms. Summary of the Invention

[0006] A method for quantitative analysis of sea clutter for wide-swath observation of typhoons by shipborne radars provided by the present invention mainly solves the technical problems of quantitative calculation of antenna clutter and range sidelobe clutter power during wide-swath observation, and simulation analysis of the power spectrum distribution of sea clutter.

[0007] To solve the above technical problems, the present invention provides a method for quantitative analysis of sea clutter for wide-swath observation of typhoons by shipborne radars, including:

[0008] Step 1: Establish a geometric model of typhoon observation by a shipborne radar, set radar parameters, define the size of the radar range cell, and set typhoon model parameters and sea clutter normalized radar cross section (NRCS) model parameters;

[0009] Step 2: Based on the observation geometry, calculate the distribution height and power of sea clutter returned through the main lobe of the antenna. Meanwhile, calculate the distribution height and power of sea clutter returned through the sidelobe of the antenna;

[0010] Step 3: Construct a pulse compression filter response model, determine the range sidelobe influence range, and comprehensively consider the influence of sea clutter and range sidelobes to calculate the sea clutter echo power in each range cell;

[0011] Step 4: Calculate the typhoon echo power in each range cell, divide the typhoon echo power by the sea clutter echo power to obtain the signal-to-clutter ratio;

[0012] Step 5: Calculate the power spectrum distributions of typhoon echo signals and sea clutter in the range cell based on the signal-to-clutter ratio.

[0013] Optionally, Step 1 includes:

[0014] The platform moves at a speed V p along a fixed direction. Taking the platform movement direction as the y-axis, the cross-track direction as the x-axis, and the direction perpendicular to the ground as the z-axis, establish a three-dimensional coordinate system; record the radar height as h, and determine the incident angle θ and azimuth angle of the radar beam The radar parameters include: transmission power P t , radar wavelength λ, antenna gain G0, antenna vertical beam width θ0, antenna horizontal beam width Define the size of the range cell as: R c = c / (2B), where c is the speed of light and B is the signal bandwidth; the typhoon model includes: typhoon internal reflectivity factor Z and attenuation coefficient α at different incident angles and different heights r ; the sea clutter NRCS model includes: the NRCS of sea clutter inside the typhoon at different incident angles.

[0015] Optionally, Step 2 includes:

[0016] Step 21, the sea clutter returned by the main lobe of the antenna represents the echo generated by the sea area illuminated by the main lobe of the antenna; according to the observation geometry, the influence height of the sea clutter returned by the main lobe of the antenna is calculated as:

[0017]

[0018] In the formula, θ is the incident angle, representing the angle between the beam and the nadir direction, and d(θ) represents the distance from the radar to the sea surface along the main beam direction when the incident angle is θ; the minimum height of the main lobe clutter area is 0, that is, the ground surface;

[0019] The sea clutter power returned by the main lobe of the antenna within the range cell is:

[0020]

[0021] In the formula, σ 0 is the NRCS of the sea surface, A c is the sea clutter area corresponding to the range cell. When the incident angle is small: When the incident angle is large: represents signal attenuation, and r0 represents the distance from the radar to the range cell;

[0022] Step 22, the sea clutter returned by the side lobe of the antenna represents the sea surface echo returned by the sea area equidistant from the target through the side lobe of the antenna, and its maximum influence height is:

[0023]

[0024] The sea clutter power returned by the side lobe of the antenna within the range cell is:

[0025]

[0026] Among them, θ in , θ out are respectively the inner and outer cone angles of the sea surface side lobe clutter ring:

[0027]

[0028] F(θ) is the integral of the antenna pattern in the azimuth direction within the clutter ring:

[0029]

[0030] In the formula is the antenna pattern.

[0031] Optionally, the said step 3 includes:

[0032] The number of range cells affected by the side lobe is: M = BTp , where T p is the signal pulse width; after considering the influence of range sidelobes, the sea clutter echo power in the nth range cell at the incident angle θ is:

[0033]

[0034] Where

[0035]

[0036] In the formula, h(θ, n) represents the vertical height from the nth range cell to the sea surface at the incident angle θ, and q(i) is the output of the pulse compression filter.

[0037] Optionally, step 4 includes:

[0038] Step 41, in the range cell, the typhoon echo power is:

[0039]

[0040] In the formula, |K| 2 is a parameter related to the phase state of meteorological particles (water: |K| 2 = 0.93, ice: |K| 2 = 0.197); represents signal attenuation; Z(θ, n) represents the reflectivity factor in the nth range cell at the incident angle θ;

[0041] Step 42, according to formulas (7) and (9), the signal-to-clutter ratio can be calculated:

[0042]

[0043] Optionally, step 5 includes:

[0044] Step 51, both the sea clutter and typhoon echo power spectra follow a Gaussian distribution and can be expressed as:

[0045]

[0046] In the formula, S is the signal average power. When calculating the sea clutter power spectrum, S is the clutter power, i.e., S = P c , and when calculating the typhoon echo power spectrum, S is the typhoon echo power, i.e., S = P r ; v is the Doppler velocity, v is the average Doppler velocity, and σ v is the velocity spectrum width;

[0047] Step 52, the sea clutter power spectrum follows a Gaussian distribution, and the sea clutter center velocity and spectrum width are calculated:

[0048] (1) Estimation of sea clutter center velocity:

[0049] Assume the sea surface wind speed is V wind , then the inherent velocity of sea clutter is: V s = V wind cos(a w ), where a w is the angle between the wind speed and the beam center; when the platform is moving, the velocity of sea clutter relative to the platform: V op = V p cos(a p ), in the formula, V p is the platform movement speed, and a p is the angle between the platform movement direction and the beam center; therefore, the center velocity of sea clutter within the beam is: V0 = |V s + V op |;

[0050] (2) Estimation of sea clutter spectrum width:

[0051] There is a certain corresponding relationship between the sea clutter spectrum width and the sea surface wind speed. Assume the sea surface wind speed is V wind , then the inherent velocity spectrum width of sea clutter at this time is: σ vc = V wind / 8; the maximum broadening of the velocity spectrum within the main lobe beam is: In the formula, is the horizontal beam width; therefore, the total width of the main lobe sea clutter velocity spectrum is:

[0052] For the antenna sidelobe clutter, assume the minimum angle between the sea clutter ring and the platform movement direction is γ, then the angle range between the sidelobe beam center and the platform movement direction is: γ~(180° - γ), so the velocity range of the sidelobe clutter is: -V p cosγ~V p cosγ; thus, the average velocity of the sidelobe clutter within the clutter ring is approximately 0; the sidelobe clutter spectrum width is: V p cosγ, and the total spectrum width is:

[0053] Step 53, Simulation process of sea clutter power spectrum distribution:

[0054] (1) First, calculate the clutter echo power p c of each range cell according to formula (8), and calculate the center velocity and spectrum width of sea clutter within the range cell according to step 52;

[0055] (2) Obtain the echo power spectrum that conforms to the Gaussian distribution according to formula (11):

[0056]

[0057] (3) Calculate the system noise power N w ;

[0058] (4) After adding the signal power of each frequency to the noise power, perform randomization to obtain the randomized power spectrum S′ pc (v):

[0059] S′ pc (v) = -ln(x k )[S pc (v) + N w (12)

[0060] where x k is a random variable uniformly distributed within the range (0 to 1);

[0061] (5) Perform the Fourier inverse transform on the complex sequence S′ pc (v) 1 / 2 exp(jθ k ) to obtain the echo sequence, where θ k represents the phase spectrum and is uniformly distributed within (0 to 2π);

[0062] (6) Window the echo sequence and perform FFT transformation to obtain the sea clutter power spectrum distribution S c (v);

[0063] (7) Consider the influence of the pulse compression range side lobe: When the incident angle is θ, the sea clutter power spectrum in the nth range cell is:

[0064]

[0065] In the formula, q(i) is the range side lobe level; S c (v, θ, n) is the power spectrum distribution of the nth range cell without pulse compression;

[0066] Step 54, Typhoon echo power spectrum simulation:

[0067] (1) Obtain the typhoon echo power based on the signal-to-clutter ratio SCR and the sea clutter power;

[0068] (2) Calculate the average typhoon echo velocity: Assume the average velocity of the typhoon within the range cell is V T , projected onto the beam direction, the radial velocity of the typhoon echo is: V rT = V T cos(a w ), where a w is the angle between the typhoon movement direction and the beam center; Considering the platform movement, the velocity of the typhoon relative to the platform: VoT = V p cos(a T ), where V p is the platform movement speed, and a T is the angle between the platform movement direction and the beam center; therefore, the center speed of sea clutter within the beam is: V0 = |V rT + V oT |;

[0069] (3) Calculate the typhoon echo spectral width: Assume the typhoon echo spectral width is: σ vT , considering the platform movement, the maximum broadening of the velocity spectrum within the beam is: where is the horizontal beam width, and a p is the angle between the platform movement direction and the beam center; therefore, the total width of the typhoon echo velocity spectrum is:

[0070] (4) Similarly, obtain the typhoon echo power spectrum according to steps (2) to (5) in step 53.

[0071] The beneficial effects of the present invention are as follows:

[0072] When the shipborne typhoon radar observes the typhoon generated and developing on the sea surface from below, when the beam irradiates the sea surface, the strong scattered echo of the sea surface will return to the radar receiver through the main lobe and sidelobe of the antenna, polluting the typhoon echo and bringing large errors to the radar base data estimation (reflectivity factor, mean radial velocity, spectral width). At the same time, the wide swath observation results in a wide clutter pollution area. In addition, the introduction of pulse compression technology causes the sea clutter to interfere with the echoes of surrounding range cells through range sidelobes, exacerbating the clutter pollution. Therefore, for a pulse compression radar system with wide swath observation, not only the influence of antenna clutter needs to be considered, but also the influence of range sidelobe clutter introduced by pulse compression needs to be considered. The present invention establishes a comprehensive influence analysis model of antenna clutter and range sidelobe clutter, quantitatively calculates and analyzes the echo power and signal-to-clutter ratio of sea clutter during the wide swath observation of shipborne typhoon radar in the time domain. At the same time, based on the clutter power and signal-to-clutter ratio, the power spectrum distribution characteristics of sea clutter and typhoon echo in the frequency domain are obtained, which can provide a reference for the research of clutter suppression algorithms. Description of the Drawings

[0073] Figure 1 is a schematic flow chart of a method for quantitative analysis of sea clutter for wide swath observation of shipborne typhoon radar in Embodiment 1 of the present invention;

[0074] Figure 2 is a schematic diagram of the radar observation geometric relationship and clutter interference in Embodiment 1 of the present invention;

[0075] Figure 3(a) is a model diagram of the attenuation coefficient of the spiral rainband and eyewall area of a typhoon (taking "Usagi" as an example) in the first embodiment of the present invention;

[0076] Figure 3(b) is a model diagram of the radar reflectivity factor of the spiral rainband and eyewall area of a typhoon (taking "Usagi" as an example) in the first embodiment of the present invention;

[0077] Figure 4 is the NRCS model of sea clutter in the first embodiment of the present invention;

[0078] Figure 5 is a schematic diagram of main lobe clutter interference in the first embodiment of the present invention;

[0079] Figure 6 is a schematic diagram of sidelobe clutter interference in the first embodiment of the present invention;

[0080] Figure 7 is a schematic diagram of sea clutter echo in the first embodiment of the present invention;

[0081] Figure 8 is the SCR of the spiral rainband and eyewall area of Typhoon "Usagi" in the first embodiment of the present invention;

[0082] Figure 9 is the power spectrum of sea clutter (main lobe clutter area) and typhoon echo in the first embodiment of the present invention;

[0083] Figure 10 is the power spectrum of sea clutter (sidelobe clutter area) and typhoon echo in the first embodiment of the present invention. Specific Embodiment

[0084] In order to make the purpose, technical solution and other aspects of the present invention clearer and more understandable, the present invention will be further described in detail below through specific embodiments in combination with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0085] Embodiment 1:

[0086] In this embodiment, taking the near-space airship platform as an example, the echo power of sea clutter, the echo power of meteorological targets in the typhoon, and the SCR of its meteorological targets during typhoon observation are quantitatively calculated. The radar parameters are shown in Table 1 below:

[0087] Table 1

[0088]

[0089] This embodiment provides a method for quantitative analysis of sea clutter for wide-swath observation of shipborne typhoon radar. Please refer to Figure 1 , which specifically includes the following steps:

[0090] Step 1, establish the radar observation geometry, asFigure 2 As shown in the figure, the direction of motion is the y-axis, the direction of intersection is the x-axis, and the direction perpendicular to the ground is the z-axis. The radar is located at a height of 20 km, the beam incident angle is θ, and the azimuth The incident angle range is set to 0 to 85°, and the azimuth range is -180° to 180°. Other radar parameters are shown in Table 1 above. The range cell size is: R c = c / (2B) = 75 m. The typhoon model selects the attenuation coefficient α at the positions of the spiral rainband (18.37°N, 123.99°E) and the eyewall area (18.50°N, 126.00°E) of Typhoon Usagi at 12:00 on September 19, 2013 r and the radar reflectivity factor Z (V and H polarizations), as shown in Figure 3. Using the AAFE RADSCAT flight test data [5] , the data is interpolated by cubic spline to obtain the sea surface NRCS distribution at incident angles of 0 to 85°, as Figure 4 shown

[0091] Step 2, specifically including:

[0092] Step 21: As Figure 2 shown, sea clutter is mainly divided into main lobe, sidelobe and range sidelobe clutter. The main lobe clutter interference is as Figure 5 shown. The sea clutter returned by the antenna main lobe represents the sea surface echo returned from the antenna main lobe. Therefore, the influence height of the sea clutter returned by the antenna main lobe is:

[0093]

[0094] The minimum height of the main lobe clutter area is 0, that is, the ground surface

[0095] The sea clutter power returned by the antenna main lobe within the range cell is:

[0096]

[0097] In the formula, σ 0 is the sea surface NRCS, A c is the sea clutter area corresponding to the range cell. When the incident angle is small (<2.4°): When the incident angle is large (>2.4°):

[0098] Step 22: The sea clutter returned by the antenna sidelobe represents the sea surface echo within the clutter ring at the same distance as the target range cell received through the antenna sidelobe, as Figure 6 shown. The maximum influence height of the antenna sidelobe clutter is:

[0099] h clutter freeψ(θ) = (37.5 + d(θ) - 20000)cosθ (16)

[0100] Assume that the antenna sidelobe level is a fixed value of -35 dB. The sea clutter power returned by the antenna sidelobe within the range cell is as follows:

[0101]

[0102] where θ in and θ out are the inner and outer cone angles of the sea surface sidelobe clutter ring respectively:

[0103]

[0104] F(θ) is the integral of the antenna pattern within the clutter ring along the azimuth direction:

[0105] F(θ) = 2π * 10 -7 (19)

[0106] Step 3, for simplicity of calculation, assume that after pulse compression, the range sidelobe level is a fixed value of -50 dB. The range sidelobe influence range: M = BT p = 120. After comprehensively considering the antenna clutter and range sidelobes, when the incident angle is θ, the clutter echo power in the nth range cell is:

[0107]

[0108] where

[0109]

[0110] In the formula, h(θ, n) represents the vertical height from the nth range cell to the sea surface when the incident angle is θ. The sea clutter echo power is as Figure 7 shown.

[0111] Step 4 specifically includes:

[0112] Step 41, select the H-polarization data of the typhoon spiral rainband and calculate the typhoon echo power in each range cell as:

[0113]

[0114] In the formula, |K| 2 is a coefficient (for water: |K| 2 = 0.93, for ice: |K| 2 = 0.197). represents signal attenuation.

[0115] Step 42, according to formulas (20) and (22), the signal-to-clutter ratio can be calculated as shown in Figure 8 the following:

[0116]

[0117] Step 5 specifically includes:

[0118] Step 51: Select the H-polarization simulation data of the spiral rainband. The incident angle is 40 degrees and the azimuth angle is 0 degrees. Assume the typhoon echo center velocity is 10 m / s and the velocity spectrum width is 3 m / s. Assume the noise is Gaussian white noise with a noise power of -136 dB.

[0119] Step 52: Assume the sea surface is in sea state 4 with an average sea surface wind speed of 8 m / s. Assume the angle between the wind speed and the beam center is 90°. The inherent center velocity of sea clutter is: V s = V wind cos(a w ) = 0. Assume the platform movement speed is 10 m / s and the angle between the platform movement direction and the beam center is 50°. The velocity of sea clutter relative to the platform: V op = V p cos(a p ) = 10 * cos(50) = 6.4 m / s. Therefore, the center velocity of sea clutter within the main lobe is: V0 = 6.4 m / s;

[0120] Estimation of the velocity spectrum width of main lobe clutter: When the sea surface wind speed is 8 m / s, the inherent velocity spectrum width of sea clutter is: σ vc = V wind / 8 = 1 m / s. The maximum broadening of the velocity spectrum within the main lobe beam is: Therefore, the total width of the velocity spectrum of main lobe clutter is:

[0121] For the antenna sidelobe clutter, the angle range between the sidelobe beam center and the platform movement direction is: γ ~ (180° - γ). Therefore, the velocity range of sidelobe clutter is: -10 * cosγ ~ 10 * cosγ. So, the average velocity of sidelobe clutter within the clutter ring is approximately 0. The sidelobe clutter spectrum width is: 10 * cosγ, and the total spectrum width is:

[0122] Step 53: Considering the influence of range sidelobe clutter, the power spectrum distribution of sea clutter is simulated as shown in Figure 9 shown.

[0123] Step 54: Select the range cell at the position with an incident angle of 40 degrees, an azimuth angle of 0 degrees, and a height of 260 m. This range cell is located in the main lobe clutter contamination area. According to Step 41, the sea clutter power of this cell is -107 dB. According to Step 42, the signal-to-clutter ratio of the above range cell is -10 dB.

[0124] Assume the typhoon moving speed is: 15 m / s, and the angle between the beam and the typhoon movement is 50°. Then the radial velocity of the typhoon echo is: V rT = V T cos(a w ) = 15 * cos(50) = 9.6 m / s. When the platform is moving, the relative speed of the typhoon to the platform: V oT = V p cos(a T ) = 10 * cos(50) = 6.4 m / s. Therefore, the center velocity of the sea clutter within the beam is: V0 = |V T + V oT | = 9.6 + 6.4 = 16 m / s;

[0125] (3) Calculate the typhoon echo spectrum width: Assume the average spectrum width of the typhoon is 2 m / s. Considering the platform movement, the maximum broadening of the velocity spectrum within the beam is: Therefore, the total width of the typhoon echo velocity spectrum is:

[0126] (4) Simulate the typhoon signal power spectrum, as Figure 10 shown.

[0127] Figure 7 is the result graph of the sea clutter echo power. The horizontal axis represents the incident angle, and the vertical axis represents the height. The color represents the magnitude of the clutter echo power. The black curve in the figure represents the maximum height affected by the main lobe clutter of the antenna, and the red curve represents the maximum height affected by the sidelobe clutter. The area above the red line represents the clutter area extended due to the range sidelobe. It can be seen that the application of the pulse compression technology has extended the sea clutter influence area, and the clutter height can reach 9 km at the nadir point. When the incident angle is 85 degrees, the clutter height can cover the entire typhoon area. Therefore, when the pulse compression system shipborne typhoon radar performs wide-swath observation, the clutter distribution range is relatively wide. In addition, as the incident angle increases, due to the increase in the clutter attenuation path, the clutter signal power decreases.

[0128] Figure 8It is the simulated spiral rainband SCR of typhoon "Usagi"; when SCR is less than 0, it indicates that the typhoon echo will be masked by sea clutter. Therefore, clutter suppression needs to be performed on the echoes in this area to obtain effective echo signals and radar base data. The results of the spiral rainband SCR show that the areas where SCR < 0 dB mainly appear in three regions: the main lobe clutter region, the range side lobe clutter region at small incident angles (< 20 degrees), and the side lobe clutter region at medium incident angles (50 degrees). Since SCR will affect the accuracy of data estimation, therefore, according to the specific requirements of data accuracy, the SCR threshold and the clutter influence region can be determined, and clutter suppression processing can be performed on the clutter data in this region. At the same time, reducing the antenna side lobe level and the pulse compression range side lobe level can also achieve the purpose of suppressing sea clutter, but it will also put forward higher requirements for the hardware design of the radar system.

[0129] Figure 9 It is the simulated sea clutter power spectrum (incident angle 40 degrees). The X-axis is the height of the range cell, the Y-axis represents the velocity, and the Z-axis represents the power spectrum. The clutter spectrum broadening caused by the platform movement decreases with the increase of the height of the range cell. And the power spectrum value in the range side lobe expansion region is less than the power spectrum in the antenna main lobe and side lobe clutter regions.

[0130] Figure 10 It is the simulated typhoon echo (spiral rainband H polarization data) and sea clutter power spectrum in a certain range cell (incident angle 40 degrees, azimuth angle 0 degrees, height 260 m) within the main lobe clutter region. The movement of the platform and the sea surface makes the center frequency of the main lobe clutter deviate from zero frequency. And under high sea conditions (high sea surface wind speed), the spectral width of the main lobe clutter is mainly affected by the inherent spectral width of the sea clutter. The SCR in this range cell < 0, and the sea clutter power spectrum in the frequency domain will cover the typhoon echo power spectrum, affecting the estimation of the echo base data. Therefore, the clutter in this range cell can be suppressed by using the power spectrum distribution characteristics to reduce the influence of clutter on the estimation of the base data.

[0131] The above content is a further detailed description of the present invention in combination with specific implementation manners, and it cannot be considered that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for quantitative analysis of sea clutter for wide-swath observation by boat-borne typhoon radar, characterized in that: include: Step 1: Establish a geometric model for typhoon observation using shipborne radar; Step 2: obtaining an observation geometry based on a geometric model of the shipborne radar for observing typhoons, and calculating the distribution height and power of sea clutter returned through the main lobe of the antenna, as well as the distribution height and power of sea clutter returned through the side lobes of the antenna; Step 3: Determine the range of influence of the range sidelobe, and calculate the sea clutter echo power in each range unit by combining the influence of sea clutter and range sidelobe. The radar height is recorded as h, and the incident angle θ and azimuth of the radar beam are determined. Radar parameters include: transmit power P t , radar wavelength λ, antenna gain G0, antenna vertical beam width θ0, antenna horizontal beam width The distance unit size is defined as: R c =c / (2B), where c is the speed of light and B is the signal bandwidth; Typhoon model parameters include: typhoon internal reflectivity factor Z and attenuation coefficient α at different incident angles and altitudes r ; The parameters of the sea clutter normalized backscatter cross section model include: NRCS of sea clutter inside the typhoon at different incident angles; Step 4: Calculate the typhoon echo power in each distance unit and divide the typhoon echo power by the sea clutter echo power to obtain the signal-to-clutter ratio; Step 5: Calculate the power spectrum distribution of the typhoon echo signal and sea clutter within the range unit based on the signal-to-clutter ratio.

2. The sea clutter quantitative analysis method according to claim 1, characterized in that: The step 1 comprises: The platform moves at a speed of V p Moving in a fixed direction, with the platform movement direction as the y-axis, the cross-track direction as the x-axis, and the direction perpendicular to the ground as the z-axis, a geometric model for typhoon observation by boat-borne radar is established.

3. The sea clutter quantitative analysis method according to claim 2, characterized in that: Before step 2, the method further includes: setting radar parameters, defining radar range unit size, setting typhoon model parameters, and sea clutter normalized backscatter cross section model parameters.

4. The sea clutter quantitative analysis method according to any one of claims 1 to 3, characterized in that: The step 2 includes: In step 21, the sea clutter returned by the antenna main lobe represents the echo generated by the sea surface area illuminated by the antenna main lobe. Based on the observation geometry, the influence height of the sea clutter returned by the antenna main lobe is calculated as: Where θ is the incident angle, which represents the angle between the beam and the nadir direction; d(θ) represents the distance from the radar to the sea surface along the main beam direction when the incident angle is θ; the minimum height of the main lobe clutter area is 0, that is, the ground surface; The sea clutter power returned by the antenna main lobe within the range cell is: Where, σ 0 For sea surface NRCS, A c is the sea surface clutter area corresponding to the range unit, represents signal attenuation, r0 represents the distance from the radar to the range unit, and r represents the radial distance from the radar to the range unit; Step 22: The sea clutter returned by the antenna side lobe represents the sea surface echo returned by the antenna side lobe at the sea surface area equidistant from the target. The maximum height of its influence is: Within the range cell, the sea clutter power returned by the antenna sidelobe is: Among them, θ in ,θ out They are the inner and outer cone angles of the sea surface sidelobe clutter ring: F(θ) is the integral of the antenna pattern within the clutter loop over the azimuth direction: In the formula is the antenna pattern.

5. The sea clutter quantitative analysis method according to claim 4, characterized in that: When the incident angle θ is less than 2.4°: When the incident angle θ is greater than or equal to 2.4°:

6. The sea clutter quantitative analysis method according to claim 4, characterized in that: The step 3 comprises: The number of range units affected by the range side lobe is: M = BT p , where T p is the signal pulse width, B is the signal bandwidth; After the influence of range side lobes, when the incident angle is θ, the sea clutter echo power in the nth range unit is: in, Where h(θ,n) represents the vertical height from the nth range unit to the sea surface when the incident angle is θ, and q(i) is the range sidelobe level.

7. The sea clutter quantitative analysis method according to claim 6, characterized in that: The step 4 comprises: Step 41: Within the distance unit, the typhoon echo power is: Where |K| 2 is a parameter related to the phase state of meteorological particles; Indicates signal attenuation; Z(θ,n) represents the reflectivity factor within the nth distance unit when the incident angle is θ; In step 42, according to equations (7) and (9), the signal-to-noise ratio can be calculated:

8. The sea clutter quantitative analysis method according to claim 7, wherein: The step 5 comprises: In step 51, the power spectra of sea clutter and typhoon echo obey Gaussian distribution and can be expressed as: Where S is the average power of the signal, v is the Doppler velocity, is the average Doppler velocity, σ v is the velocity spectrum width; Step 52: The sea clutter power spectrum obeys Gaussian distribution, and the sea clutter center velocity and spectrum width are calculated: (1) Estimation of sea clutter center velocity: Assume that the sea surface wind speed is V wind , then the inherent velocity of sea clutter is: V s =V wind cos(a w ), where a w is the angle between the wind speed and the center of the beam; when the platform moves, the speed of the sea clutter relative to the platform is: V op =V p cos(a p ), where V p is the platform movement speed, a p is the angle between the platform motion direction and the beam center; therefore, the velocity of the sea clutter center in the beam is: V0=|V s +V op |; (2) Estimation of sea clutter spectral width: There is a certain correspondence between the sea clutter spectrum width and the sea surface wind speed. Assuming the sea surface wind speed is V wind , then the inherent velocity spectrum width of sea clutter is: σ vc =V wind / 8; the maximum width of the velocity spectrum in the main lobe beam is: Where, is the horizontal beam width; therefore, the total width of the mainlobe sea clutter velocity spectrum is: For antenna sidelobe clutter, assuming that the minimum angle between the sea surface clutter ring and the platform's motion direction is γ, the angle range between the sidelobe beam center and the platform's motion direction is: γ ~ (180° - γ). Therefore, the sidelobe clutter velocity range is: -V p cosγ~V p cosγ; therefore, the average velocity of the sidelobe clutter in the clutter ring is 0; the sidelobe clutter spectral width is: V p cosγ, the total spectral width is: Step 53, sea clutter power spectrum distribution simulation process: (1) First, calculate the clutter echo power p of each range unit according to formula (8): c , calculate the sea clutter center velocity and spectral width within the range unit according to step 52; (2) Generate an echo power spectrum that conforms to the Gaussian distribution according to formula (11): (3) Calculate the system noise power N w ; (4) After adding the signal power and noise power of each frequency, randomization is performed to obtain the randomized power spectrum S′ pc (v): S′ pc (v)=-ln(x k )[S pc (v)+N w ] (12) Among them, x k is a random variable uniformly distributed in the range 0 to 1; (5) For the complex sequence S′ pc (v) 1 / 2 exp(jθ k ) is subjected to inverse Fourier transform to obtain the echo sequence, where θ k represents the phase spectrum, which is uniformly distributed within the range of 0 to 2π; (6) Add a window to the echo sequence and perform FFT transformation to obtain the sea clutter power spectrum distribution S of each range unit. c (v); (7) Considering the influence of pulse compression range sidelobes: When the incident angle is θ, the power spectrum of sea clutter in the nth range unit is: Where q(i) is the range sidelobe level; S c (v,θ,n) is the power spectrum distribution of the nth distance unit when there is no pulse pressure; Step 54, typhoon echo power spectrum simulation: (1) Obtain typhoon echo power based on the signal-to-clutter ratio (SCR) and sea clutter power; (2) Calculate the average speed of typhoon echo: Assume that the average speed of typhoon in the distance unit is V T , projected to the beam direction, the radial velocity of the typhoon echo is: V rT =V T cos(a w ), where a w is the angle between the typhoon's direction of movement and the beam center; considering the platform's movement, the speed of the typhoon relative to the platform is: V oT =V p cos(a T ), where V p is the platform movement speed, a T is the angle between the platform motion direction and the beam center; therefore, the center velocity of the sea clutter within the beam is: V0=|V rT +V oT |; (3) Calculation of typhoon echo spectrum width: Assume that the typhoon echo spectrum width is: vT , considering the platform motion, the maximum broadening of the velocity spectrum within the beam is: Where, is the horizontal beam width, a p is the angle between the platform motion direction and the beam center; therefore, the total width of the typhoon echo velocity spectrum is: (4) Similarly, according to (2) to (5) in step 53, the typhoon echo power spectrum is obtained.

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