A phased array weather radar calibration method based on generalized metal sphere calibration theory

Abstract

The application discloses a phased array weather radar calibration method based on generalized metal ball calibration theory. The method comprises the following steps: collecting two-dimensional antenna pattern data of a phased array weather radar under at least one working mode and multiple different beam directions in a microwave darkroom; performing numerical integration on the two-dimensional antenna pattern data, calculating a combined beam main lobe real solid angle of a transmitting antenna and a receiving antenna, and calculating an equivalent beam width product; calculating a calibration theory reflectivity factor of a metal ball based on a radar scattering cross section of the metal ball and the equivalent beam width product; acquiring actual detection echo data of the phased array radar on the metal ball under different working modes and beam directions, and calculating an actual reflectivity factor; and comparing the actual reflectivity factor with the calibration theory reflectivity factor, thereby completing calibration of the phased array weather radar. The application can quantitatively evaluate the reflectivity factor of the phased array weather radar in a non-Gaussian working mode, and improves radar detection performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weather radar data processing and calibration, and relates to a method for quantitatively calibrating a phased array weather radar with a metal ball, and more particularly to a phased array weather radar calibration method based on a generalized metal ball calibration theory. BACKGROUND

[0002] Weather radar is the core equipment for meteorological monitoring, short-term forecasting and disaster weather warning. The accuracy and reliability of radar detection data directly determine the effectiveness of key services such as precipitation estimation, typhoon monitoring, and severe convective identification. In order to ensure that the radar system maintains high precision throughout its life cycle, it must be calibrated absolutely and accurately on a regular basis. As a method of evaluating the performance of the entire link using a target with a known radar cross section (RCS), metal ball calibration has the advantages of clear principle and reliable results, and has become one of the standard methods for calibrating the performance of operational weather radar.

[0003] Currently, the widely used metal ball quantitative calibration method in business is mainly aimed at traditional mechanical scanning parabolic weather radar. The principle is to use a standard metal ball suspended under a balloon or unmanned aerial vehicle as a point target, and based on the radar equation, combined with the radar system parameters and the precise RCS theoretical value of the metal ball, the theoretical expected value of the radar receiving power or reflectivity factor is calculated. By comparing the theoretical value with the actual observed value of the radar, the overall performance deviation of the radar system can be quantitatively evaluated.

[0004] However, the theoretical formula derivation of the above-mentioned traditional method is based on the assumption that the antenna pattern of the radar can be approximated as a Gaussian function model. Under this assumption, the energy distribution of the antenna can be approximately described by the 3dB beam width parameter, thereby simplifying the complex beam integration into an analytical expression. For example, the calculation formula of the metal ball reflectivity factor theoretical value Z is simplified as:

[0005]

[0006] In the formula, Z represents the theoretical value of the metal ball reflectivity factor, with the unit of mm 6 / m 3 ; λ represents the wavelength of the radar working, with the unit of meters (m); σ represents the radar cross section (RCS) of the metal ball used for calibration, with the unit of square meters (m²), which is a physical quantity determined by the metal ball material, radius and radar wavelength, representing the scattering ability of the target; θ0 represents the beam width of the radar antenna in the horizontal direction, i.e. the azimuth dimension, with the unit of radians (rad). φ0 represents the beam width of the radar antenna in the vertical direction, i.e. the elevation dimension, with the unit of radians (rad); c represents the speed of light in vacuum; τ represents the pulse width of the radar transmission signal, with the unit of seconds (s). |K| 2The square of the modulus of the complex refractive index factor of a meteorological target. R represents the straight-line distance from the phase center of the radar antenna to the geometric center of the metal sphere, in meters (m).

[0007] This formula has good effect in the calibration of parabolic antenna. However, with the application of phased array technology in the field of meteorological detection, the new generation of phased array weather radar is gradually put into operation. Unlike parabolic radar, phased array radar (currently mainly one-dimensional phased array radar) often adopts wide transmission and narrow reception working mode to improve scanning speed. In this mode, its transmission beam is widened by beam forming algorithm, resulting in that its antenna pattern deviates from the Gaussian model and presents a complex non-Gaussian shape.

[0008] When the traditional calibration theory based on Gaussian assumption is directly applied to such non-Gaussian antenna, significant errors will be generated, mainly in the following aspects:

[0009] The 3dB beam width of non-Gaussian pattern can no longer accurately represent its energy distribution. Directly substituting it into the traditional formula will cause a fundamental deviation in the calculation of calibration theory value due to underestimation or overestimation of the actual energy integral in the beam.

[0010] The traditional calibration process relies on the complete fixation of the pointing direction of the radar antenna in azimuth and elevation, so as to stably align the metal sphere for a long time. However, the current mainstream one-dimensional phased array weather radar usually only realizes electronic scanning in the elevation direction, and the azimuth direction still needs to be driven mechanically, so it is difficult to realize the full fixation of the precise pointing direction like parabolic radar, which leads to the fact that the traditional calibration operation process cannot be directly executed.

[0011] Therefore, how to provide a calibration method capable of accurately calibrating the non-Gaussian working mode of phased array weather radar is a technical problem urgently needed to be solved by those skilled in the art. SUMMARY

[0012] In view of the above problems, the present application is proposed in order to provide a phased array weather radar calibration method based on generalized metal ball calibration theory, which can overcome the above problems or at least partially solve the above problems, and can quantitatively evaluate the reflectivity factor of the non-Gaussian working mode of phased array weather radar, so as to improve the radar detection performance and ensure accurate prediction of weather processes.

[0013] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0014] The embodiment of the present application provides a phased array weather radar calibration method based on generalized metal ball calibration theory, comprising the following steps:

[0015] S1: In a microwave anechoic chamber, collect two-dimensional antenna pattern data of a phased array weather radar in at least one working mode and at multiple different beam pointing directions;

[0016] S2: Numerically integrating the two-dimensional antenna pattern data to obtain a combined beam main lobe real solid angle of the transmitting antenna and the receiving antenna, and calculating an equivalent beam width product based on the combined beam main lobe real solid angle;

[0017] S3: Calculating a calibration theoretical reflectivity factor of the metal sphere based on a theoretical radar scattering cross section of the metal sphere and the equivalent beam width product;

[0018] S4: Obtaining actual detection echo data of the metal sphere by the phased array radar under different working modes and beam pointing directions, and calculating an actual reflectivity factor;

[0019] S5: Comparing the actual reflectivity factor with the calibration theoretical reflectivity factor to complete calibration of the phased array weather radar.

[0020] Preferably, the working modes in step S1 include at least one of a narrow transmission and narrow reception mode and a wide transmission and narrow reception mode; and the beam pointing directions include a normal alignment direction and at least one normal deviation direction.

[0021] Preferably, step S1 further includes: for a predetermined beam pointing direction under each mode, controlling the antenna to move according to a serpentine scanning path to obtain near-field intensity distribution data, and converting the near-field intensity distribution data into two-dimensional antenna pattern data in ° units in the azimuth dimension and the elevation dimension.

[0022] Preferably, step S2 includes the following steps:

[0023] The combined beam main lobe real solid angle is calculated according to the following formula:

[0024]

[0025] wherein, is a normalized transmitting antenna pattern function; is a normalized receiving antenna pattern function; is an azimuth beam width; is an elevation beam width; and Ω is a solid angle integration region.

[0026] The equivalent beam width product is calculated according to the following formula:

[0027]

[0028] wherein, is the equivalent beam width product.

[0029] Preferably, in step S3, the formula for calculating the calibration theoretical reflectivity factor of the metal sphere is:

[0030]

[0031] wherein Z is a reflectivity factor; λ is a wavelength; σ is a radar cross section of the metal sphere; is an equivalent beam width product; c is a speed of light; τ is a pulse width; K is a dielectric constant; R is a range between the radar and the metal sphere.

[0032] Preferably, after calculating the equivalent beam width product, the method further comprises:

[0033] For a one-dimensional phased array radar, obtaining a fixed azimuth beam width thereof ;

[0034] calculating an equivalent elevation beam width according to the following formula:

[0035]

[0036] wherein, is the equivalent elevation beam width; is the equivalent beam width product.

[0037] Preferably, in step S3, a formula for calculating the calibration theoretical reflectivity factor of the metal sphere is:

[0038]

[0039] wherein Z is a reflectivity factor; λ is a wavelength; σ is a radar cross section of the metal sphere; c is a speed of light; τ is a pulse width; K is a dielectric constant; R is a range between the radar and the metal sphere.

[0040] Preferably, the radar cross section σ of the metal sphere is obtained by calculation according to the following formula:

[0041]

[0042]

[0043]

[0044]

[0045] wherein λ is a wavelength; r is a radius of the metal sphere, and k is a wave number; is a first kind of spherical Bessel function, is a second kind of spherical Bessel function.

[0046] Preferably, step S4 specifically comprises:

[0047] controlling the metal sphere to hover at a preset position and perform a serpentine scan to determine a position of the metal sphere relative to the radar;

[0048] adjusting the mechanical elevation angle of the phased array radar to make the normal of the transmitting beam align with the metal sphere, and performing multiple sets of RHI scans to obtain alignment data;

[0049] adjusting the mechanical elevation angle of the radar to make the normal of the transmitting beam deviate from the metal sphere, and performing multiple sets of RHI scans to obtain deviation data;

[0050] based on the alignment data and / or the deviation data, extracting radar detection parameters at the position of the metal sphere, and calculating the actual reflectivity factor.

[0051] Preferably, the scanning range of the serpentine scanning in step S4 is:

[0052] with the preset position (θ0, φ0) of the metal sphere as the center, the range in the azimuth direction is [θ0 4°, θ0+4°], and the range in the elevation direction is [φ0 4°, φ0+12°].

[0053] The above technical solutions provided by the embodiments of the present application have at least the following beneficial effects:

[0054] The present application can systematically solve the problem that the conventional parabolic metal sphere calibration method is not applicable to non-Gaussian antenna radars, and can further improve the metal sphere calibration accuracy.

[0055] By collecting antenna pattern data of different modes and directions in a microwave anechoic chamber, real and detailed parameters of the radar antenna are obtained; based on the generalized metal sphere calibration theory, the equivalent beam width of the non-Gaussian antenna is accurately calculated, and accurate phased array metal sphere calibration theoretical values are obtained; based on the developed phased array metal sphere calibration process, a large amount of metal sphere echo data is obtained.

[0056] The present application has good business applicability and promotion, helps to improve the calibration accuracy of the phased array weather radar, and is applicable to weather radar systems of different models, different working frequency bands and different antenna patterns, has wide business promotion value and application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0057] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0058] Figure 1 The present application provides a phased array weather radar calibration method flowchart based on the generalized metal sphere calibration theory.

[0059] Figure 2 A serpentine scanning path schematic diagram provided for an embodiment of the present application;

[0060] Figure 3 A Gaussian type two-dimensional antenna pattern provided for an embodiment of the present application;

[0061] Figure 4 A non-Gaussian type two-dimensional antenna pattern provided for an embodiment of the present application;

[0062] Figure 5 A non-Gaussian type antenna emission vertical pattern provided for an embodiment of the present application;

[0063] Figure 6 A phased array metal ball calibration result schematic diagram provided for an embodiment of the present application. DETAILED DESCRIPTION

[0064] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0065] The embodiment of the present application discloses a phased array weather radar calibration method based on generalized metal ball calibration theory. The complete technical process from data collection in a microwave darkroom, derivation of generalized metal ball calibration theory to establishment of a phased array radar metal ball calibration process is shown in FIG. Figure 1 and includes the following steps:

[0066] S1: In a microwave darkroom, collect two-dimensional antenna pattern data of a phased array weather radar in at least one working mode and multiple different beam directions.

[0067] In radar antenna parameter measurement, the beam width of an antenna is usually obtained through antenna far-field test or microwave darkroom data collection. To reduce the influence of multipath and obtain more accurate antenna pattern information, the radar antenna is usually tested in a microwave darkroom to collect data of the transmitting and receiving antennas.

[0068] In this embodiment, S1 collects phased array radar antenna data in different beam directions in a microwave darkroom, comprehensively considers the normal alignment and normal deviation conditions, realizes the acquisition of basic information of the antenna parameters of the phased array radar, and thus lays a foundation for the establishment of subsequent theoretical values.

[0069] S2: Numerically integrating the two-dimensional antenna pattern data to calculate the combined beam main lobe real solid angle of the transmitting antenna and the receiving antenna, and calculating the equivalent beam width product based on the combined beam main lobe real solid angle.

[0070] S3: Based on the theoretical radar scattering cross section of the metal sphere and the equivalent beam width product, the calibration theoretical reflectivity factor of the metal sphere is calculated.

[0071] When the antenna pattern is not Gaussian, its 3dB beam width cannot effectively reflect its energy distribution, so directly substituting the 3dB beam width into the traditional metal sphere calibration theoretical value formula will have a large error, which seriously affects the calibration accuracy.

[0072] To accurately reflect the contribution of non-Gaussian antennas to the reflectivity factor, the embodiments S2-S3 give the derivation of the generalized metal sphere calibration theory, and the equivalent beam product is directly calculated based on the antenna pattern obtained in the microwave anechoic chamber, so as to inversely calculate the Gaussian equivalent contribution of non-Gaussian antennas and accurately calculate the metal sphere calibration theoretical value.

[0073] S4: Obtain the actual detection echo data of the metal sphere by the phased array radar in different working modes and beam pointing directions, and calculate the actual reflectivity factor.

[0074] S5: Compare the actual reflectivity factor with the calibration theoretical reflectivity factor to complete the calibration of the phased array weather radar.

[0075] The traditional parabolic weather radar has realized the function of fixed azimuth residence of the antenna, but the current phased array weather radar has not realized the function of full fixation of azimuth and elevation. According to the actual operation of the phased array weather radar, the embodiments S1-S5 develop an effective metal sphere calibration process for the operational phased array weather radar, effectively obtain a large amount of calibration data, and enhance the calibration accuracy.

[0076] In one embodiment, the working modes in step S1 include at least one of a narrow transmission and narrow reception mode and a wide transmission and narrow reception mode; and the beam pointing directions include a normal alignment direction and at least one normal deviation direction.

[0077] In one embodiment, step S1 further includes: for the predetermined beam pointing directions in each mode, controlling the antenna to move according to a snake-shaped scanning path to collect data at a preset azimuth angle interval and elevation angle interval, and obtaining two-dimensional antenna pattern data.

[0078] The data acquisition step of the multi-directional microwave anechoic chamber provided by S1 is different from the traditional parabolic antenna. The one-dimensional phased array weather radar quickly scans the target at different elevation angles through beam forming technology. However, the beam performance deviates from the normal direction at a cost, so it is necessary to collect multi-directional antenna data. Here, a microwave anechoic chamber data acquisition process is proposed to provide effective data support for one-dimensional phased array radar metal ball calibration. The specific execution steps are as follows:

[0079] Acquire the directional diagram data in the narrow transmit and narrow receive mode. In the microwave anechoic chamber, convert the near-field intensity distribution data into narrow Gaussian antenna directional diagram data in the azimuth dimension and the elevation dimension with 1° as the beam pointing interval. The elevation beam pointing is usually from -30° to 30°, with a large pointing coverage area. When collecting data, the horn antenna moves in a zigzag scanning manner. This scanning scheme can obtain detailed two-dimensional antenna directional diagram and metal ball intensity distribution, as shown in Figure 2 With 1° as the beam pointing interval, the data has high continuity, and has high accuracy when using the antenna directional diagram to invert the equivalent beam width. The range of azimuth angle and elevation angle: Since the one-dimensional phased array is Gaussian in azimuth, the converted data azimuth angle range is -60° to 60°; the center of the elevation angle changes with the beam pointing, and the beam elevation pointing is φ, then the range of the converted data elevation angle is [-60°+φ, 60°+φ].

[0080] Acquire the directional diagram data in the wide transmit and narrow receive 4 times beam widening mode. According to the business radar scanning mode and the metal ball test requirements, the beam pointing is selected with 4° as the interval, starting from -20° and ending at 20°. The same strategy as in the directional diagram data acquisition in the narrow transmit and narrow receive mode, the horn antenna moves in a zigzag scanning manner to obtain the near-field intensity distribution data. Convert the near-field intensity distribution data into antenna directional diagram data in the azimuth dimension and the elevation dimension with 4° as the beam pointing interval. The scanning range of azimuth angle and elevation angle: the same square scanning area with the beam pointing as the center and 120° long.

[0081] Acquire the directional diagram data in the wide transmit and narrow receive 8 times beam widening mode. According to the business radar scanning mode and the metal ball test requirements, the beam pointing is selected with 8° as the interval, and the starting range is arbitrary, which can be selected according to the metal ball test requirements. The same strategy as in the directional diagram data acquisition in the narrow transmit and narrow receive mode, the horn antenna moves in a zigzag scanning manner to obtain the near-field intensity distribution data. Convert the near-field intensity distribution data into antenna directional diagram data in the azimuth dimension and the elevation dimension with 6° as the beam pointing interval. The scanning range of azimuth angle and elevation angle: the same square scanning area with the beam pointing as the center and 120° long.

[0082] Data statistics. Collect the data after normal alignment and normal deviation in each mode, arrange the data into a two-dimensional matrix form, and ensure the uniformity of the coordinate axis scale to facilitate subsequent data processing.

[0083] For steps S2-S3 of the present embodiment, first, the conventional parabolic radar metal ball calibration formula needs to be explained:

[0084] According to the point target radar equation, when the distance between the target and the radar is R, the power received by the radar can be represented as:

[0085]

[0086] where Pt and Pr represent the radar transmit power and the radar receive power respectively, G represents the gain of the antenna (here it is assumed that the transmit gain and the receive gain are the same), λ represents the wavelength, and σ represents the radar scattering cross section area of the target. If the target is not a point target but a distributed target, and the antenna radiation intensity is not uniform, assuming that the antenna beam is Gaussian, the radar receive power can be represented as:

[0087]

[0088] where and represent the horizontal and vertical beam widths of the antenna respectively, c represents the speed of light, and τ represents the pulse width. The reflectivity factor of the meteorological target can be calculated by the above formula. This formula has been widely used in meteorological detection. Taking the RCS equivalent to the geometric cross-sectional area as an approximate method still has certain error. Especially for the high-precision measurement required by weather radar, any error may lead to the decline of calibration accuracy, thereby affecting the QPE accuracy. Therefore, a more accurate formula needs to be used to calculate the RCS of the metal ball, and the radar scattering cross section area σ of the metal ball is obtained by the following formula:

[0089]

[0090]

[0091]

[0092]

[0093] where λ is the wavelength; r is the radius of the metal ball, and k is the wave number; is the first kind of spherical Bessel function, is the second kind of spherical Bessel function. The theoretical RCS of the metal ball obtained by formula (3) is more accurate than the approximation using the geometric cross-sectional area.

[0094] In meteorological practice, it is found that when the Z of the target in the detection area is the same, the precipitation may be significantly different due to the difference in the size of the raindrops. Z can be understood as an equivalent measure of the overall RCS of the raindrop group in nature, so there will be a large raindrop whose Z is equal to that of a small raindrop group. Inspired by this, a metal ball can be equivalent to a large raindrop, so that its reflectivity factor can be directly calculated. Based on formula (1) and formula (2), the calculation formula of the theoretical reflectivity factor of the metal ball calibration can be obtained:

[0095]

[0096] Formula (4) is the traditional parabolic radar metal ball calibration formula. However, the above formula is based on the premise that the antenna pattern is Gaussian. When the pattern is non-Gaussian, there will be a large error. As shown in formula (5), the main lobe of the Gaussian antenna pattern can be approximated by an exponential Gaussian function, and the 3dB beam width is usually directly calculated and substituted into the formula for calculation. Figure 3

[0097] Therefore, the following specific embodiments are proposed for the calculation formula of the theoretical value of the metal ball calibration suitable for any pattern:

[0098] Starting from the radar equation of the volume scattering target, the received power P r is related to the reflectivity factor Z as follows:

[0099]

[0100] where G t represents the transmit gain, G r represents the receive gain, represents the sum of the radar scattering cross sections per unit volume. represents the normalized transmit antenna pattern function, represents the normalized receive antenna pattern function.

[0101] Under the Rayleigh scattering assumption (suitable for small particles such as raindrops), which can be expressed as:

[0102]

[0103] where D i is the diameter of the i-th particle. Usually, the radar reflectivity factor Z is defined as the sum of the sixth powers of all particle diameters in the resolution volume:

[0104]

[0105] Step S2 calculates the combined beam main lobe real solid angle according to the following formula:

[0106] ​

[0107] wherein, is a normalized transmit antenna pattern function; is a normalized receive antenna pattern function; is an azimuth beamwidth; is an elevation beamwidth; Ω is a solid angle integration region;

[0108] Substituting equation (5) gives the relationship between the received power and the reflectivity factor under the Rayleigh scattering assumption when the transmit and receive antenna patterns are not identical:

[0109]

[0110] The integral term of the antenna pattern in the above equation is defined as the real solid angle of the combined beam main lobe for transmission and reception. In a parabolic radar, since the beamwidths of transmission and reception are usually the same, the real solid angle of the combined beam main lobe in the above equation can be simplified to:

[0111]

[0112] Under the condition of a non-Gaussian antenna, the real solid angle of the combined beam main lobe can only be calculated by integration.

[0113] To maintain the form of the theoretical value calculation of the metal ball calibration of the traditional parabolic weather radar, the equivalent beamwidth product is defined as:

[0114]

[0115] wherein, is the equivalent beamwidth product.

[0116] Thus, the formula for calculating the calibration theoretical reflectivity factor of the metal ball in step S3 is:

[0117]

[0118] wherein, Z is the reflectivity factor; λ is the wavelength; σ is the radar scattering cross section of the metal ball; is the equivalent beamwidth product; c is the speed of light; τ is the pulse width; K is the dielectric constant; R is the round trip distance between the radar and the metal ball.

[0119] In one embodiment, for a one-dimensional phased array radar, since the azimuth beamwidths of its transmission and reception are the same, its azimuth beamwidth is always The equivalent elevation beamwidth can be calculated by the equivalent beamwidth product Thus, after calculating the equivalent beamwidth product, it also includes:

[0120] For a one-dimensional phased array radar, the fixed azimuth beam width is obtained ;

[0121] The equivalent elevation beam width is calculated according to the following formula:

[0122]

[0123] wherein, is the equivalent elevation beam width; is the equivalent beam width product.

[0124] Thus, the formula for calculating the calibration theoretical reflectivity factor of the metal ball in step S3 is:

[0125]

[0126] wherein, Z is the reflectivity factor; λ is the wavelength; σ is the radar scattering cross section of the metal ball; c is the speed of light; τ is the pulse width; K is the dielectric constant; and R is the echo distance between the radar and the metal ball.

[0127] As Figure 4~5 shown, the non-Gaussian two-dimensional antenna pattern is quite different from the Gaussian type, and it cannot be approximated by an exponential Gaussian function, otherwise a large error will be caused in the calculation result. The two-dimensional antenna pattern should be integrated by the generalized metal ball calibration theory in the above embodiment, and then the equivalent beam width is calculated to obtain the accurate phased array metal ball calibration theory value.

[0128] In one embodiment, step S4 specifically includes:

[0129] controlling the metal ball to hover at a preset position and perform a serpentine scan to determine the position of the metal ball relative to the radar;

[0130] adjusting the mechanical elevation angle of the phased array radar to align the normal of the transmitting beam with the metal ball, and performing multiple sets of RHI scans to obtain normal alignment data;

[0131] adjusting the mechanical elevation angle of the radar to deviate the normal of the transmitting beam from the metal ball, and performing multiple sets of RHI scans to obtain normal deviation data;

[0132] based on the normal alignment data and / or the normal deviation data, extracting the radar detection parameters at the position of the metal ball, and calculating the actual reflectivity factor.

[0133] A metal ball calibration process suitable for one-dimensional phased array weather radar is given below. The specific steps are as follows:

[0134] Preparation steps before calibration: choose a sunny day with small wind speed; select an area with less multipath effect according to the surrounding terrain of the radar location, and calculate the approximate location of the UAV; calculate the required rope length for calibration to ensure that the UAV echo has less effect on the metal ball.

[0135] Device preparation steps: specific devices include: one UAV equipped with high-precision RTK and laser ranging camera, UAV remote control, UAV battery array, one metal ball, one set of suspension rope, one pair of gloves, and one notebook computer.

[0136] Snake-shaped scanning to find the ball step: after the UAV takes off, it hovers at the appropriate position, at which time the laser ranging camera is used to obtain the approximate position of the metal ball, and a certain range of snake-shaped scanning is carried out with the position as the center. Let the azimuth angle and the pitch angle of the metal ball relative to the radar be and , then the range of the snake-shaped scanning is [ -4, +4] and [ -4, +12], which ensures that the radar can find the UAV and the metal ball. After obtaining the data, more accurate metal ball positions are obtained according to the actual radar base data.

[0137] Normal alignment test step: adjust the mechanical elevation angle of the radar to , so that the normal of the radar beam aligns with the metal ball, and then multiple RHI scans are carried out.

[0138] Normal deviation test step: according to the predetermined normal deviation angle , the mechanical elevation angle is adjusted to based on the mechanical elevation angle of (4), and then multiple RHI scans are carried out.

[0139] Data processing step: after collecting all the data, classify them according to the running mode and the normal, and for the same type of data, record the reflectivity factor, differential reflectivity, correlation coefficient and differential phase shift at the accurate position of the metal ball. Combine multiple sets of data into time series and calculate the mean and standard deviation.

[0140] As shown in Figure 6 , there is a 1dB difference between the theoretical value calculated using the generalized metal ball calibration theory and the theoretical value calculated using the traditional formula. According to the reflectivity factor of the measured metal ball echo, under the traditional metal ball calibration theory framework, the performance of the radar meets the standard; but under the generalized metal ball calibration theory framework, the reflectivity factor of the radar is low, which does not meet the standard. This comparison result proves that the traditional theory cannot accurately reflect the true performance of the phased array radar in the non-Gaussian mode, while the method of the present application can more accurately reveal the deviation of the radar detection accuracy.

[0141] The various embodiments described in this specification are presented by way of example, and each embodiment is not necessarily composed of all features described with respect to other embodiments. Each embodiment described in this specification can be implemented in conjunction with one or more other embodiments described in this specification without departing from the scope or spirit of the application. In the drawings, the same reference numbers and designations in different drawings indicate embodiments that are the same, functionally similar, comiieet with one or more of the same requirements, or are otherwise functionally related. The various embodiments described in this specification can be implemented in conjunction with computer hardware, computer program products, and / or computer-implemented methods.

[0142] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A calibration method for phased array weather radar based on generalized metallic sphere calibration theory, characterized in that, Includes the following steps: S1: In a microwave anechoic chamber, acquire two-dimensional antenna pattern data of multiple beam directions of a phased array weather radar in at least one operating mode. S2: Perform numerical integration on the two-dimensional antenna pattern data to calculate the real-fixed angle of the main lobe of the combined transmitting and receiving antennas, and calculate the equivalent beamwidth product based on the real-fixed angle of the main lobe of the combined antenna; calculate the real-fixed angle of the main lobe of the combined antenna according to the following formula: in, This is the normalized transmit antenna pattern function; This is the normalized receiver antenna pattern function; This refers to the azimuth beamwidth; Ω represents the elevation beamwidth; Ω represents the solid angle integral region. The equivalent beamwidth product is calculated using the following formula: in, It is the product of the equivalent beamwidth; S3: Calculate the calibration theoretical reflectivity factor of the metal sphere based on the product of its theoretical radar cross-section and equivalent beamwidth; the formula for calculating the calibration theoretical reflectivity factor of the metal sphere is: Where Z is the reflectivity factor; λ is the wavelength; σ is the radar cross-section of the metal sphere; c is the speed of light; τ is the pulse width; K is the dielectric constant; and R is the echo distance between the radar and the metal sphere. S4: Obtain the actual detection echo data of the phased array radar on the metal sphere under different operating modes and beam directions, and calculate the actual reflectivity factor; S5: Compare the actual reflectivity factor with the calibration theoretical reflectivity factor to complete the calibration of the phased array weather radar.

2. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 1, characterized in that, The operating mode mentioned in step S1 includes at least one of narrow transmit and narrow receive mode and wide transmit and narrow receive mode; the beam pointing includes normal alignment pointing and at least one normal deviation pointing.

3. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 1, characterized in that, Step S1 further includes: for the predetermined beam pointing in each mode, controlling the antenna to move along a serpentine scanning path to obtain near-field intensity distribution data, and converting the near-field intensity distribution data into two-dimensional antenna pattern data in azimuth and elevation dimensions in degrees.

4. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 1, characterized in that, After calculating the equivalent beamwidth product, the method further includes: For a one-dimensional phased array radar, obtain its fixed azimuth beamwidth. ; The equivalent pitch beamwidth is calculated using the following formula: in, This is the equivalent pitch beamwidth; It is the product of the equivalent beamwidth.

5. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 4, characterized in that, In step S3, the formula for calculating the calibration theoretical reflectivity factor of the metal sphere is: Where Z is the reflectivity factor; λ is the wavelength; σ is the radar cross-section of the metal sphere; c is the speed of light; τ is the pulse width; K is the dielectric constant; and R is the echo distance between the radar and the metal sphere.

6. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 1, characterized in that, The radar cross-section σ of the metal sphere is calculated using the following formula: Where λ is the wavelength; r is the radius of the metal sphere; and k is the wave number. For a sphere of the first kind, the Bessel function is... It is a Bessel function of the second kind of sphere.

7. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 1, characterized in that, Step S4 specifically includes: The metal ball is controlled to hover at a preset position and perform a serpentine scan to determine its position relative to the radar. Adjust the mechanical elevation angle of the phased array radar to align the normal of the transmitted beam with the metal sphere, and perform multiple RHI scans to obtain normal alignment data; Adjust the radar's mechanical elevation angle to deviate the normal of the transmitted beam from the metal sphere, and perform multiple RHI scans to obtain normal deviation data; Based on the normal alignment data and / or normal deviation data, radar detection parameters at the location of the metal sphere are extracted, and the actual reflectivity factor is calculated.

8. The phased array weather radar calibration method based on the generalized metallic sphere calibration theory according to claim 7, characterized in that, The scanning range of the serpentine scan in step S4 is: Centered on the preset position (θ0, φ0) of the metal ball, the range in the azimuth direction is [θ0-4°, θ0+4°], and the range in the pitch direction is [φ0-4°, φ0+12°].

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