A rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar

Abstract

This invention discloses a rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar, belonging to the field of sea surface backscattering coefficient measurement technology. The method includes the following four steps: S1, determining the rubbing angle interval and the number of measurements, and performing measurements sequentially; S2, compressing the range pulses of the echo signal to obtain a one-dimensional high-resolution range image of the sea surface that varies over time; S3, calculating the local rubbing angle of each pulse in each range unit of the range image, and classifying them according to small step intervals of the rubbing angle; S4, calculating the sea surface backscattering coefficient for each category, obtaining the measurement results at small step intervals of the rubbing angle. This invention employs the above-mentioned rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar, requiring only a few measurements with large step intervals of the rubbing angle to obtain the sea surface backscattering coefficient measurement results at small step intervals of the rubbing angle, which helps reduce the cost and time of sea clutter measurement.

Description

Technical Field

[0001] This invention relates to the field of sea surface backscattering coefficient measurement technology, and in particular to a rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar. Background Technology

[0002] The sea surface backscattering coefficient is an important physical quantity describing the electromagnetic scattering characteristics of the sea surface. It reflects the strength of backscattered energy per unit area of ​​sea surface and is affected by many factors such as radar operating frequency band, polarization, ground-scratching angle, sea state, and seawater dielectric constant. Research on the sea surface backscattering coefficient is a technological prerequisite for monitoring territorial waters and identifying naval targets against a sea surface background in modern technological warfare. Under conditions of large ground-scratching angles or high sea states, the intensity of the backscattered electromagnetic echo from the sea surface is very close to that of the target echo, easily causing false alarms during sea surface target detection. To ensure accurate target detection and tracking under strong sea clutter interference, a systematic and in-depth study of the sea surface backscattering coefficient across all sea states and various radar bands is necessary.

[0003] Conducting sea clutter measurement experiments (see reference [1] Ding Hao, Liu Ningbo, Dong Yunlong, et al. Review and prospect of radar sea clutter measurement experiments [J]. Journal of Radar, 2019, 8(3): 281-302.) is an efficient, accurate and widely used research method. Through actual sea clutter data, the electromagnetic scattering mechanism of the sea surface under various conditions can be studied in a relatively comprehensive manner, and a semi-empirical model of the sea surface backscattering coefficient can be constructed, which directly serves the study of sea clutter characteristics cognition and sea surface target detection methods. However, measurement experiments to obtain real data of the sea surface backscattering coefficient generally need to be completed through dedicated test platforms such as airborne and spaceborne platforms, which makes data acquisition both complex, time-consuming and costly. In addition, due to limitations such as the flight time and wind zone length of a single flight of the carrier aircraft, it is difficult to obtain the measurement results of the sea surface backscattering coefficient with small step intervals of the ground grazing angle in airborne tests (see reference [2] Little MO and Berry W P. Real-time multichannel airborne radar measurements [C]. Proceedings of 1997 IEEE National Radar Conference, Syracuse, NY, USA, 1997: 138-142. Reference [3] Crisp DJ, Stacy NJS, and Goh A S. Medium-high incidence angle polarimetric sea clutter measurements and analysis [R]. Technical Report DSTO-TR-1818, 2006. Reference [4] Berginc G. Small-slope Approximation method: a future study of vector wave scattering from two-dimensional surface and comparison with experimental data [J]. Progress in Electromagnetics Research, 2002, PIER 37: 251-287.). Summary of the Invention

[0004] The purpose of this invention is to provide a rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar, so as to solve the problems existing in the background art. For airborne radar sea surface backscattering coefficient measurement experiments, it can improve measurement efficiency and reduce measurement cost.

[0005] To achieve the above objectives, this invention provides a method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar, comprising the following steps:

[0006] S1. Determine the rubbing angle interval for measuring the sea surface backscattering coefficient, determine the number of measurements based on the antenna beamwidth, and use radar rubbing angle large step interval to measure the sea surface echo signal under different rubbing angles within the rubbing angle interval one by one.

[0007] S2. Range pulse compression is performed on the time-domain sampled sea surface echo signal to obtain a time-varying one-dimensional high-resolution range profile (HRRP) of the sea surface.

[0008] S3. Calculate the local smear angle of each pulse in each distance cell of the sea surface HRRP that varies over time, and classify them according to the small step interval of the smear angle;

[0009] S4. Calculate the backscattering coefficient of the sea surface for each type to obtain the measurement results of the backscattering coefficient of the sea surface with small step intervals of the rubbing angle.

[0010] Preferably, step S1 specifically includes:

[0011] Determine the range of grazing angles for measuring sea surface backscattering coefficient. To measure the initial value of the floor rubbing angle, To measure the termination value of the rubbing angle, and When using radar to measure ground erosion angle with large step intervals, the required number of measurements N is:

[0012]

[0013] Where α is the main beamwidth of the measuring radar antenna; To round the real numbers in the range to positive infinity;

[0014] The ground rubbing angle at the center of the radar antenna beam during the nth measurement. for

[0015]

[0016] Due to limitations of radar range blind zone and maximum unambiguous range, the aircraft's flight altitude h is limited during the nth measurement. n satisfy

[0017]

[0018] Where c is the speed of electromagnetic wave propagation in vacuum; t p T is the pulse width; p The pulse repetition interval (PRI) of the radar is defined by its lower limit, which is determined by the radar's range blind zone, and its upper limit, which is determined by the radar's maximum unambiguous range.

[0019] Equation (3) ensures that the echoes of the main beam of the radar antenna can be collected without ambiguity. Due to the attenuation of radar receiving power caused by antenna pattern, atmospheric transmission and propagation distance, in order to ensure sufficient receiving clutter ratio (CNR), the flight altitude of the carrier aircraft should be as close as possible to the lower limit in equation (3).

[0020] During formal measurements, an offshore area should be selected to minimize the influence of near-shore waves on the measurement results. The aircraft flies in a straight line in a certain direction, the radar operates in forward-looking mode, and the ground-touching angle of the radar antenna beam center and the aircraft altitude are adjusted to complete N measurements, obtaining N two-dimensional sea clutter data matrices. One dimension of this two-dimensional sea clutter data matrix is ​​the range, i.e., the radar fast time; the other dimension is the pulse, i.e., the radar slow time. The sea clutter two-dimensional data matrix A obtained from the nth measurement is... n for

[0021] a n,lm =s r (τ,t) (4)

[0022] Where l represents the l-th sample of the radar fast time, l = 0, 1, 2, ..., L-1; τ represents the number of radar fast time samples; and τ = l / F represents the radar fast time. s ;F s t is the analog / digital sampling rate of the radar; m is the m-th pulse in the radar slow time, m = 0, 1, 2, ..., M-1; M is the number of pulses; t is the radar slow time, t = m / f p ;f p The pulse repetition frequency of the radar; s r The echo signal received by the radar;

[0023] In addition, an inertial measurement unit (IMU) is used to record the aircraft's heading angle, pitch angle, roll angle, altitude, north velocity, east velocity, sky velocity, longitude, and latitude; a servo system is used to ensure that the ground grazing angle of the antenna beam center is always at a set value, while simultaneously recording the azimuth and pitch angles of the radar antenna relative to the aircraft; and marine meteorological and hydrological information buoys or other auxiliary equipment are used to record wind and wave elements of the measurement sea area, including wind speed, wind direction, significant wave height, mean wave period, and wave direction.

[0024] Preferably, the pulse compression in step S2 specifically involves:

[0025] The time-domain expression for the linear frequency modulated waveform transmitted by the radar is:

[0026]

[0027] Where β is the bandwidth of the linear frequency modulated waveform;

[0028] Pulse compression technology is used to process linear frequency modulated signals to obtain high range-direction resolution radar transmitted signals. t (τ t The frequency domain representation of ) is S t (f), the frequency domain representation of the matched filter H(f) is S t The conjugate of (f) is

[0029]

[0030] The superscript * indicates the conjugate of the complex number;

[0031] Range pulse compression is performed on the two-dimensional sea clutter data matrix obtained from a single measurement in step S1. Let the time-domain representation of the received signal of one radar pulse be s. r (τ), its frequency domain representation is Sr ( f), the signal spectrum after matched filtering is

[0032] S(f)=S r (f)·H(f) (7)

[0033] After performing an inverse fast Fourier transform (IFFT) on S(f), the time-domain signal is obtained after pulse compression, and is expressed as follows:

[0034]

[0035] The sea surface HRRP over time is represented as:

[0036] P(τ,t)=|s(τ,t) 2 (9)

[0037] Preferably, the classification process based on local wiping corners in step S3 is as follows:

[0038] The local smear angle of each pulse in each distance cell of HRRP varies with time.

[0039]

[0040] Where H is the aircraft's flight altitude recorded by the IMU;

[0041] During measurement, the radar grazing angle is measured with a large step interval of α. The measurement results are then classified to obtain the small step interval of θ for the grazing angle. r The refined sea surface backscattering coefficient results are obtained by using the echo from the main beam of the antenna illuminating the sea surface during each measurement to calculate the sea surface backscattering coefficient. Therefore, the range of local rubbing angle variation of the sea surface element in the nth measurement is as follows: Therefore, the number of classes obtained by N measurements with small step intervals for the wiping angle is:

[0042]

[0043] Then the radar grazing angle corresponding to the i-th type is

[0044]

[0045] Since the sea surface backscattering coefficient varies little within a small range of rubbing angles, it is assumed that the rubbing angle interval [ψ] i -θ r / 2,ψ i +θ r The data within [ / 2] is used to calculate the rubbing angle ψ. i The sea surface backscattering coefficient, the elements contained in the i-th class are:

[0046]

[0047] in, Let be the local rubbing angle of the sea surface element at (τ,t) during the nth measurement.

[0048] Preferably, the calculation of the sea surface backscattering coefficient in step S4 is as follows:

[0049] For a single measurement, the radar cross section of the sea surface element (τ,t) is:

[0050]

[0051] Where L represents the antenna pattern attenuation and atmospheric transmission loss at (τ,t); C is the scaling factor, calculated using the following formula:

[0052]

[0053] Among them, P rC The power of the compressed echo signal pulse measured by the radar receiver when measuring the calibration body; σ C R is the maximum backscattering radar cross section of the calibration body. C L is the slant range from the calibration object to the radar during calibration. C This is to account for the attenuation of the antenna pattern and atmospheric transmission loss during calibration;

[0054] Because the measuring radar uses a pulse compression system, the pulse width resolution cell after pulse compression is much smaller than the antenna beamwidth resolution cell. Therefore, the illuminated area of ​​the sea surface at (τ,t) is...

[0055]

[0056] Therefore, the sea surface backscattering coefficient at (τ,t) is

[0057]

[0058] For the nth measurement, let the sea surface backscattering coefficient at (τ,t) be denoted as . The measured result of the sea surface backscattering coefficient at small step intervals of the rubbing angle is:

[0059]

[0060] Among them, |B i | represents set B i The number of elements in the middle.

[0061] Therefore, the present invention employs the above-mentioned method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar, which has the following beneficial effects:

[0062] (1) When measuring the backscattering coefficient of the sea surface using existing technologies, after determining the flight altitude of the carrier aircraft and the ground rubbing angle of the radar beam center, the measurement result of the ground rubbing angle can usually only be obtained. The measurement method proposed in this invention can improve the measurement efficiency and reduce the measurement cost.

[0063] (2) Wide-beam airborne radar is used to make the local rubbing angle of the sea surface element change more widely during a single measurement; a large-bandwidth linear frequency modulated waveform is used to obtain higher range resolution and make the effective illumination area of ​​each element as small as possible.

[0064] (3) By using only a few measurements with large step intervals of radar rubbing angle, the refined measurement results of sea surface backscattering coefficient with small step intervals of rubbing angle were obtained, which reduced the cost and time of sea clutter measurement and improved the quality of measurement data.

[0065] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0066] Figure 1 This is a flowchart of the rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar according to the present invention;

[0067] Figure 2 This is a schematic diagram of the airborne radar sea clutter measurement method of the present invention;

[0068] Figure 3 This is a schematic diagram showing the variation of the sea surface backscattering coefficient with the rubbing angle, measured using traditional methods.

[0069] Figure 4 This is a schematic diagram showing the variation characteristics of the sea surface backscattering coefficient with the rubbing angle, measured using the method of this invention. Detailed Implementation

[0070] Example

[0071] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0072] like Figure 1 As shown, a rapid measurement method for sea surface backscattering coefficient based on airborne high-resolution radar includes the following steps:

[0073] S1. Determine the rubbing angle interval for measuring the sea surface backscattering coefficient. Based on the antenna beamwidth, determine the number of measurements. Use a radar rubbing angle with large step intervals to successively measure the sea surface echo signal at different rubbing angles within the rubbing angle interval. Specifically:

[0074] Determine the range of grazing angles for measuring sea surface backscattering coefficient. To measure the initial value of the floor rubbing angle, To measure the termination value of the rubbing angle, and When using radar to measure ground erosion angle with large step intervals, the required number of measurements N is:

[0075]

[0076] Where α is the main beamwidth of the measuring radar antenna; To round the real numbers in the range to positive infinity;

[0077] The ground rubbing angle at the center of the radar antenna beam during the nth measurement. for

[0078]

[0079] Due to limitations of radar range blind zone and maximum unambiguous range, the aircraft's flight altitude h is limited during the nth measurement. n satisfy

[0080]

[0081] Where c is the speed of electromagnetic wave propagation in vacuum; t p T is the pulse width; p The pulse repetition interval (PRI) of the radar is defined by its lower limit, which is determined by the radar's range blind zone, and its upper limit, which is determined by the radar's maximum unambiguous range.

[0082] Equation (3) ensures that the echoes of the main beam of the radar antenna can be collected without ambiguity. Due to the attenuation of radar receiving power caused by antenna pattern, atmospheric transmission and propagation distance, in order to ensure sufficient receiving clutter ratio (CNR), the flight altitude of the carrier aircraft should be as close as possible to the lower limit in equation (3).

[0083] During formal measurements, an offshore area should be selected to minimize the impact of near-shore waves on the measurement results. The aircraft flies in a straight line in a certain direction, the radar operates in forward-looking mode, and the ground-touching angle of the radar antenna beam center and the aircraft altitude are adjusted to complete N measurements, obtaining N two-dimensional sea clutter data matrices. One dimension of this sea clutter data matrix is ​​the radar fast time; the other dimension is the radar slow time. The sea clutter two-dimensional data matrix A obtained from the nth measurement is... n for

[0084] a n,lm =s r (τ,t) (4)

[0085] Where l represents the l-th sample of the radar fast time, l = 0, 1, 2, ..., L-1; L represents the number of radar fast time samples; τ represents the radar fast time, τ = l / F s ;F s t is the analog / digital sampling rate of the radar; m is the m-th pulse in the radar slow time, m = 0, 1, 2, ..., M-1; M is the number of pulses; t is the radar slow time, t = m / f p ;f p The pulse repetition frequency of the radar; s r The echo signal received by the radar;

[0086] In addition, an inertial measurement unit (IMU) is used to record the aircraft's heading angle, pitch angle, roll angle, altitude, north velocity, east velocity, sky velocity, longitude, and latitude; a servo system is used to ensure that the ground grazing angle of the antenna beam center is always at a set value, while simultaneously recording the azimuth and pitch angles of the radar antenna relative to the aircraft; and marine meteorological and hydrological information buoys or other auxiliary equipment are used to record wind and wave elements of the measurement sea area, including wind speed, wind direction, significant wave height, mean wave period, and wave direction.

[0087] S2. Range pulse compression is performed on the time-domain sampled sea surface echo signal to obtain a time-varying one-dimensional high-resolution range profile (HRRP) of the sea surface. The pulse compression is as follows:

[0088] The time-domain expression for the linear frequency modulated waveform transmitted by the radar is:

[0089]

[0090] Where β is the bandwidth of the linear frequency modulated waveform;

[0091] Pulse compression technology is used to process linear frequency modulated signals to obtain high range-direction resolution radar transmitted signals. t (τ t The frequency domain representation of ) is S t (f), the frequency domain representation of the matched filter H(f) is S t The conjugate of (f) is

[0092]

[0093] The superscript * indicates the conjugate of the complex number;

[0094] Range pulse compression is performed on the two-dimensional sea clutter data matrix obtained from a single measurement in step S1. Let the time-domain representation of the received signal of one radar pulse be s. r (τ), its frequency domain representation is S r (f), the signal spectrum after matched filtering is:

[0095] S(f)=S r (f)·H(f) (7)

[0096] After performing an inverse fast Fourier transform (IFFT) on S(f), the time-domain signal is obtained after pulse compression, and is expressed as follows:

[0097]

[0098] The sea surface HRRP over time is represented as:

[0099] P(τ,t)=|s(τ,t) 2 (9)

[0100] S3. Calculate the local smear angle for each pulse of each distance cell in the time-varying HRRP of the sea surface, and classify them according to the small step interval of the smear angle, specifically:

[0101] The local smear angle of each pulse in each distance cell of HRRP varies with time.

[0102]

[0103] Where H is the aircraft's flight altitude recorded by the IMU;

[0104] During measurement, the radar grazing angle is measured with a large step interval of α. The measurement results are then classified to obtain the small step interval of θ for the grazing angle. r The refined sea surface backscattering coefficient results are obtained by using the echo from the main beam of the antenna illuminating the sea surface during each measurement to calculate the sea surface backscattering coefficient. Therefore, the range of local rubbing angle variation of the sea surface element in the nth measurement is as follows: Therefore, the number of classes obtained by N measurements with small step intervals for the wiping angle is:

[0105]

[0106] Then the radar grazing angle corresponding to the i-th type is

[0107]

[0108] Since the sea surface backscattering coefficient varies little within a small range of rubbing angles, it is assumed that the rubbing angle interval [ψ] i -θ r / 2,ψ i +θ r The data within [ / 2] is used to calculate the rubbing angle ψ. i The sea surface backscattering coefficient, the elements contained in the i-th class are:

[0109]

[0110] in, Let be the local rubbing angle of the sea surface element at (τ,t) during the nth measurement.

[0111] S4. Calculate the sea surface backscattering coefficient for each type, and obtain the measurement results of the sea surface backscattering coefficient at small step intervals of the rubbing angle, specifically:

[0112] For a single measurement, the radar cross section of the sea surface element (τ,t) is:

[0113]

[0114] Where L represents the antenna pattern attenuation and atmospheric transmission loss at (τ,t); C is the scaling factor, calculated using the following formula:

[0115]

[0116] Among them, P rC The power of the compressed echo signal pulse measured by the radar receiver when measuring the calibration body; σ C R is the maximum backscattering radar cross section of the calibration body. C L is the slant range from the calibration object to the radar during calibration. C This is to account for the attenuation of the antenna pattern and atmospheric transmission loss during calibration;

[0117] Because the measuring radar uses a pulse compression system, the pulse width resolution cell after pulse compression is much smaller than the antenna beamwidth resolution cell. Therefore, the illuminated area of ​​the sea surface at (τ,t) is...

[0118]

[0119] Therefore, the sea surface backscattering coefficient at (τ,t) is

[0120]

[0121] For the nth measurement, let the sea surface backscattering coefficient at (τ,t) be denoted as . The measured result of the sea surface backscattering coefficient at small step intervals of the rubbing angle is:

[0122]

[0123] Among them, |B i | represents set B i The number of elements in the middle.

[0124] In summary, by conducting a small number of N measurements with a large step interval of α for the radar rubbing angle, the rubbing angle range was obtained. The inner small step interval is θ r The results of refined sea surface backscattering coefficient measurements.

[0125] like Figure 2 As shown, the aircraft flew at a constant speed along a straight path. The radar operating mode was forward-looking, X-band, bandwidth 400MHz, A / D sampling rate 500MHz, HH and VV polarization, and antenna beamwidth 5°. A total of 5 measurements were performed, with the ground rubbing angle of the antenna beam center being 40°, 50°, 60°, 70° and 80° for each measurement. The aircraft altitude for each measurement was reasonably set according to equation (3). This embodiment did not determine the number of measurements and the radar ground rubbing angle for each measurement according to equations (1) and (2), but without loss of generality, this embodiment can still demonstrate the feasibility and effectiveness of using this method to obtain the sea surface backscattering coefficient with small step intervals of ground rubbing angle.

[0126] Figure 3 The variation characteristics of the sea surface backscattering coefficient with the rubbing angle are obtained by the traditional method, and the radar rubbing angle step interval is 10°.

[0127] Figure 4 To measure the variation characteristics of the sea surface backscattering coefficient with the rubbing angle using the method of this embodiment, the radar rubbing angle step interval is 1°.

[0128] Therefore, the present invention adopts the above-mentioned method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar. By using a wide-beam airborne radar and a large-bandwidth linear frequency modulated waveform, and only a few measurements with large step intervals of radar rubbing angle, the refined measurement results of sea surface backscattering coefficient with small step intervals within a set rubbing angle range are obtained. This reduces the cost and time of sea clutter measurement and improves the quality of measurement data.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar, employing a wide-beam airborne radar and a large-bandwidth linear frequency modulated waveform, characterized in that... Includes the following steps: S1. Determine the rubbing angle interval for measuring the sea surface backscattering coefficient, determine the number of measurements based on the antenna beamwidth, and use radar rubbing angle large step interval to measure the sea surface echo signal under different rubbing angles within the rubbing angle interval one by one. S2. Range pulse compression is performed on the time-domain sampled sea surface echo signal to obtain a one-dimensional high-resolution range image of the sea surface that varies with time. S3. Calculate the local smear angle of each pulse in each range cell of the time-varying one-dimensional high-resolution range image of the sea surface, and classify them according to the small step interval of the smear angle. S4. Calculate the backscattering coefficient of the sea surface for each type to obtain the measurement results of the backscattering coefficient of the sea surface with small step intervals of the rubbing angle.

2. The method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar according to claim 1, characterized in that, Step S1 is as follows: Determine the range of grazing angles for measuring sea surface backscattering coefficient. To measure the initial value of the wiping angle, To measure the termination value of the rubbing angle, and When using radar to measure ground erosion angle with large step intervals, the number of measurements N is: Where α is the main beamwidth of the measuring radar antenna; To round the real numbers in the range to positive infinity; The ground rubbing angle at the center of the radar antenna beam during the nth measurement. for Due to limitations of radar range blind zone and maximum unambiguous range, the aircraft's flight altitude h is limited during the nth measurement. n satisfy Where c is the speed of electromagnetic wave propagation in vacuum; t p T is the pulse width; p The pulse repetition interval of the radar; the lower limit is determined by the radar's range blind zone; the upper limit is determined by the radar's maximum unambiguous range. The aircraft flies in a straight line in a certain direction. The radar operates in forward-looking mode. The radar antenna beam center's ground-touching angle and the aircraft's altitude are adjusted to complete N measurements, resulting in N two-dimensional sea clutter data matrices. One dimension of these sea clutter data matrices represents the radar's fast time; the other dimension represents the radar's slow time. The sea clutter two-dimensional data matrix A obtained from the nth measurement is... n for a n,lm =s r (t,t) Where l represents the l-th sample of the radar fast time, l = 0, 1, 2, ..., L-1; L represents the number of radar fast time samples; τ represents the radar fast time, τ = l / F s ;F s t is the analog / digital sampling rate of the radar; m is the m-th pulse in the radar slow time, m = 0, 1, 2, ..., M-1; M is the number of pulses; t is the radar slow time, t = m / f p ;f p The pulse repetition frequency of the radar; s r The echo signal received by the radar; In addition, an inertial measurement unit is used to record the aircraft's heading angle, pitch angle, roll angle, altitude, north velocity, east velocity, sky velocity, longitude, and latitude; a servo system is used to ensure that the ground grazing angle of the antenna beam center is always at a set value, while simultaneously recording the azimuth and pitch angles relative to the radar antenna and the aircraft; and marine meteorological and hydrological information buoys or other auxiliary equipment are used to record wind and wave elements of the measurement sea area, including wind speed, wind direction, significant wave height, mean wave period, and wave direction.

3. The method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar according to claim 2, characterized in that, The pulse compression in step S2 is specifically as follows: The time-domain expression for the linear frequency modulated waveform transmitted by the radar is: Where β is the bandwidth of the linear frequency modulated waveform; Pulse compression technology is used to process the linear frequency modulated signal to obtain a high-resolution range-direction radar transmitted signal. t (τ t The frequency domain representation of ) is S t (f), the frequency domain representation of the matched filter H(f) is S t The conjugate of (f) is The superscript * indicates the conjugate of the complex number; Range pulse compression is performed on the two-dimensional sea clutter data matrix obtained from a single measurement in step S1. Let the time-domain representation of the received signal of one radar pulse be s. r (τ), its frequency domain representation is S r (f), the signal spectrum after matched filtering is: S(f)=S r (f)·H(f) After performing a fast inverse Fourier transform on S(f), the time-domain signal is obtained after pulse compression, and is expressed as follows: A one-dimensional high-resolution distance image of the sea surface that varies over time is represented as follows: P(τ,t)=|s(τ,t)| 2 。 4. The method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar according to claim 3, characterized in that, The specific process of classifying by local wiping corner in step S3 is as follows: The local smear angle of each pulse in each range cell of a time-varying one-dimensional high-resolution range image is: Where H is the flight altitude of the carrier aircraft recorded by the inertial measurement unit; During measurement, the radar grazing angle is measured with a large step interval of α. The measurement results are then classified to obtain the small step interval of θ for the grazing angle. r The refined sea surface backscattering coefficient results are obtained by using the echo from the main beam of the antenna illuminating the sea surface for each measurement. Therefore, the range of local rubbing angle variation of the sea surface element in the nth measurement is as follows: Therefore, the number of classes obtained by N measurements with small step intervals for the wiping angle is: Then the radar grazing angle corresponding to the i-th type is Since the sea surface backscattering coefficient varies little within a small range of rubbing angles, it is assumed that the rubbing angle interval [ψ] i -θ r / 2,ψ i +θ r The data within [ / 2] is used to calculate the rubbing angle ψ. i The sea surface backscattering coefficient, the elements contained in the i-th class are: in, Let be the local rubbing angle of the sea surface element at (τ,t) during the nth measurement.

5. The method for rapid measurement of sea surface backscattering coefficient based on airborne high-resolution radar according to claim 4, characterized in that, The calculation of the sea surface backscattering coefficient in step S4 is as follows: For a single measurement, the radar cross section of the sea surface element (τ,t) is: Where L represents the antenna pattern attenuation and atmospheric transmission loss at (τ,t); C is the scaling factor, calculated using the following formula: Among them, P rC The power of the compressed echo signal pulse measured by the radar receiver when measuring the calibration body; σ C R is the maximum backscattering radar cross section of the calibration body. C L is the slant range from the calibration object to the radar during calibration. C This is for the attenuation of the antenna pattern and atmospheric transmission loss during calibration; Because the measuring radar uses a pulse compression system, the pulse width resolution cell after pulse compression is much smaller than the antenna beamwidth resolution cell. Therefore, the illuminated area of ​​the sea surface at (τ,t) is... Therefore, the sea surface backscattering coefficient at (τ,t) is For the nth measurement, let the sea surface backscattering coefficient at (τ,t) be denoted as . The measured result of the sea surface backscattering coefficient at small step intervals of the rubbing angle is: Among them, |B i | represents set B i The number of elements in the middle.

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