Rainfall inversion method and device based on spaceborne synthetic aperture radar, and medium

Abstract

The invention relates to a spaceborne synthetic aperture radar-based rainfall inversion method, equipment and medium, and the method comprises the steps: inverting a radar echo end point according to the slope of a radar echo, and correcting the radar echo in a radar echo signal coverage level range according to the inverted radar echo end point; inverting a ground rainfall capacity function and a rainfall end point in a rainfall range by using a double-layer VIE algorithm based on the corrected radar echo; inverting a rainfall starting point by using the ground rainfall capacity function and the rainfall end point, and inverting a rainfall level function by comparing the rainfall starting point with a prior model by using a minimum distance method; and calculating the ground rainfall by using the rainfall level function and the ground rainfall function. The equipment and the medium are used for implementing the method. Compared with the prior art, the method can be widely applied to inversion of various rainfall types.

Description

Technical Field

[0001] The present invention relates to the technical field of meteorological radars, and in particular to a rainfall inversion method, equipment and storage medium based on spaceborne synthetic aperture radar. Background Art

[0002] With the development of technology, the emergence of Synthetic Aperture Radar (SAR) has provided a more convenient way to measure precipitation. The SAR carried on the satellite platform has the "all-day" characteristics, which makes it possible to perform precipitation measurement tasks. Studies have shown that SAR working in the x-band is more sensitive to precipitation than low-frequency SAR. It can be seen that SAR has good utilization value in rainfall measurement.

[0003] Most common rainfall measurement methods using SAR use an inversion algorithm based on the Volterra Integral Equation (VIE) and a rainfall inversion algorithm based on model-oriented statistics (MOS). Although the VIE algorithm has a rigorous derivation, it requires that rainfall must be distributed vertically, and although the MOS algorithm has no specific requirements for rainfall distribution, it requires a large amount of data to train prior parameters. In the prior art, in order to avoid the above problems, a method is proposed to combine the advantages of VIE and MOS, and a model-oriented statistics and Volterra Integration (MOSVI) inversion algorithm is proposed. Although the defects of using VIE and MOS alone are avoided, more complex rainfall cannot be inverted; another method uses a linear scattering attenuation relationship to generalize the single-layer VIE algorithm to a double-layer model with freezing height as the dividing line, but the algorithm still cannot avoid the vertical uniform distribution of rainfall; in summary, the shortcomings of rainfall prediction in the prior art are: only the inversion results for specific types of rainfall are good, and the reproduction effect for other special types of rainfall is poor.

[0004] Therefore, providing an inversion method that can be widely applied to various types of rainfall is a problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a rainfall inversion method, device and storage medium based on spaceborne synthetic aperture radar.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to a first aspect of the present invention, a rainfall inversion method based on spaceborne synthetic aperture radar is provided, the method comprising:

[0008] The radar echo end point is inverted according to the slope of the radar echo, and the radar echo within the horizontal range covered by the radar echo signal is corrected according to the inverted radar echo end point;

[0009] Based on the corrected radar echo, the double-layer VIE algorithm is used to invert the ground rainfall function and rainfall end point within the rainfall range.

[0010] The rainfall starting point is inverted by using the ground rainfall function and the rainfall end point, and the rainfall level function is inverted by comparing with the prior model using the minimum distance method;

[0011] The ground rainfall is calculated using the rainfall level function and the ground rainfall function.

[0012] As a preferred technical solution, the method of inverting the radar echo endpoint according to the slope of the radar echo includes:

[0013] Obtain the apogee and subsatellite point of the spaceborne synthetic aperture radar, move the apogee toward the subsatellite point, and sample the moving trajectory;

[0014] Calculate the first-order derivative of the normalized radar cross section of the two sampling points before and after the target sampling point and use the calculated first-order derivative as the slope of the normalized radar cross section. If the slopes of the normalized radar cross section of the first two sampling points are both 0 and the slopes of the normalized radar cross section of the last two sampling points are not 0, then the target sampling point is the end point of the radar echo;

[0015] Otherwise, the target sampling point is reselected until the end point of the radar echo is obtained.

[0016] As a preferred technical solution, the radar echo within the horizontal range covered by the radar echo signal is corrected according to the inverse radar echo endpoint, including:

[0017] The cloud body is sampled longitudinally and the average rainfall in the sampling interval is calculated. The expression is:

[0018]

[0019] in, represents the average rainfall in the sampling interval, Δh represents the sampling interval, z t represents the height of the top of the snow layer, V(z) represents the vertical rainfall function, and i represents the number of selected sampling intervals;

[0020] Calculate the original radar echo according to the average rainfall in the sampling interval and extract the first intermediate function;

[0021] The radar echo within the horizontal range covered by the radar echo signal is corrected using the first intermediate function. The expression is:

[0022] σ mSARdB (x last -iΔx)=σ 0 dB +f(iΔx)+…+f(Δx),

[0023] Among them, σ mSARdB Indicates the dB form of the corrected radar echo, x last represents the end point of radar echo, f(iΔx) represents the first intermediate function, x r represents the end point of rainfall, H(x) represents the horizontal rainfall function, V(0) represents the maximum surface rainfall, σ 0 dB This is the dB representation of the radar return without the attenuation of snow.

[0024] As a preferred technical solution, the first intermediate function expression is:

[0025]

[0026] Where Δx represents the sampling interval and Δx = Δh tanθ, θ represents the incident angle of the radar, x r represents the original rainfall end point, H(x) represents the horizontal rainfall function, and V(0) represents the maximum rainfall on the ground.

[0027] As a preferred technical solution, the steps of inverting the ground rainfall function and the rainfall endpoint include:

[0028] Let the rainfall be evenly distributed in the vertical direction, and rewrite the corrected radar echo function into a first radar echo function including the snowfall attenuation coefficient, the rainfall attenuation coefficient, the snowfall radar reflectivity and the rainfall radar reflectivity, which is expressed as follows:

[0029]

[0030] Among them, σ 0 (x) represents the horizontal radar echo not affected by the attenuation of the snow layer, θ represents the radar incident angle, z0 represents the height of the rain and snow boundary layer, k s represents the snowfall attenuation coefficient, k r represents the rainfall attenuation coefficient, δ, X, ξ all represent the intermediate coordinates in the integral path, η s represents the snowfall radar reflectivity, η r represents the rainfall radar reflectivity;

[0031] Extract the second intermediate function, the expression is: Among them, u and m are parameters with no practical significance; the second intermediate function is used to represent the rainfall attenuation coefficient, snow radar reflectivity, rainfall radar reflectivity and precipitation when the vertical distribution of precipitation is uniform, and the expression is:

[0032]

[0033]

[0034] Among them, p x '(x) is the derivative of p(x), R(x) is the rainfall, j r and b r represents the correlation coefficient of rain, j s and b s are the relevant empirical parameters of snow, a r represents the empirical coefficient of rainfall attenuation coefficient, a s The empirical coefficient representing the snowfall attenuation coefficient;

[0035] Based on the second intermediate function representing the rainfall attenuation coefficient, snowfall radar reflectivity, rainfall radar reflectivity and precipitation when the vertical distribution of precipitation is uniform, the second radar echo function is obtained, and the expression is:

[0036]

[0037] Among them, p X ′ (X) is the derivative of p(X), X represents the intermediate coordinates in the integration path, G1 is a parameter and G2 is a parameter and p(x) represents the second intermediate function;

[0038] The second radar echo function is translated along the x-axis according to the top height of the snow layer and the radar incident angle to obtain a third radar echo function, and the intermediate parameters are extracted. The expression of the third radar echo function is:

[0039]

[0040] The expression of the intermediate parameter is:

[0041] h=X-[z t -(Xxz t tanθ)tanθ]tanθ,

[0042] Then dX = cos 2 θdh;

[0043] The fourth radar echo function is obtained by rewriting the third radar echo function according to the intermediate parameters, and its expression is:

[0044]

[0045] Among them, K1(X) means that the parameter has no practical meaning and K2(X) means that the parameter has no practical meaning and X(x,h) means the parameter has no practical meaning and X(x,h)=hcos 2 θ+xsin 2 θ+z t tanθ;

[0046] According to the fourth radar echo function, the second intermediate function is expressed in the form of the second kind of Volta integral, and its expression is:

[0047]

[0048] in, And has no practical meaning, K3(X) is a parameter with no practical meaning and K4(X) indicates that the parameter has no practical meaning and λ1 is a parameter with no practical significance and λ2 is a parameter with no practical significance and

[0049] When the rainfall is 0, the second intermediate function value is 1. After calculating K1(X), K2(X), K3(X), K4(X) and f1(x) of the second intermediate function expressed in the form of the second kind of Volta integral according to the rainfall and the second intermediate function value, the second intermediate function value in the interval of interest is obtained by iterative calculation, and the rainfall end point is inferred;

[0050] The second intermediate function value obtained by iterative calculation is used to obtain the ground rainfall function.

[0051] As a preferred technical solution, the method for inverting the rainfall starting point is:

[0052] Randomly select multiple consecutive radar echo points before the end point of rainfall, and calculate the average value and root mean square of the normalized radar scattering cross section of all radar echo points except the radar echo point farthest from the end point of rainfall;

[0053] The limit value of the radar echo at the starting point of rainfall is calculated according to the average value and the root mean square. If the normalized radar cross section value of the radar echo point farthest from the end point of rainfall is less than the limit value, the radar echo point farthest from the end point of rainfall is the starting point of rainfall.

[0054] Otherwise, multiple radar echo points before the end point of rainfall are reselected until the starting point of rainfall is obtained.

[0055] As a preferred technical solution, the method for inverting the rainfall level function is:

[0056] The minimum distance method is used to calculate the distance difference between the prior level function and the ground rainfall function obtained by inversion under different shape factors, wherein the shape factor is calculated by the rainfall width, and the rainfall width is the difference between the end point of the rainfall and the starting point of the rainfall;

[0057] The shape factor corresponding to the smallest distance difference is selected, and the rainfall level function is inverted based on the shape factor.

[0058] As a preferred technical solution, the method for inverting the ground rainfall is to calculate the ground rainfall based on the rainfall level function and the ground rainfall function obtained by inversion, and its expression is:

[0059]

[0060] Among them, V(0) is the surface rainfall obtained by inversion, x r is the end point of rainfall, z t is the height of the top of the snow layer, θ is the radar incident angle, R(x,0) is the inverted surface rainfall function, and H(x) is the inverted rainfall level function.

[0061] According to a second aspect of the present invention, there is provided a rainfall inversion device based on a spaceborne synthetic aperture radar, comprising a memory and a processor, wherein a computer program is stored in the memory, and the method described is implemented when the processor executes the program.

[0062] According to a third aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, wherein the program implements the method described above when executed by a processor.

[0063] Compared with the prior art, the present invention effectively combines the double-layer IVE algorithm and the MOS algorithm, reduces the use of prior parameters, and does not need to use a huge database to train the parameters required for rainfall inversion. It is suitable for areas with fewer observation samples. Compared with traditional rainfall inversion methods, the present invention can accurately invert rainfall of various distribution types and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a schematic diagram of the two-dimensional precipitation and radar echo model before correction of the present invention;

[0065] Figure 2 is a flow chart of the method of the present invention;

[0066] Figure 3 It is a schematic diagram of the corrected two-dimensional precipitation and radar echo model of the present invention;

[0067] Figure 4 A comparison diagram of the normalized radar cross section before and after correction under the rectangular distribution rainfall condition of the present invention;

[0068] Figure 5 A comparison diagram of the results of using normalized radar cross section to invert ground rainfall before and after correction in the case of rectangular distribution rainfall of the present invention;

[0069] Figure 6 The precipitation distribution map obtained by inversion under the rectangular distribution rainfall condition of the present invention;

[0070] Figure 7 It is an absolute error diagram of precipitation distribution obtained by inversion under the rectangular distribution rainfall condition of the present invention;

[0071] Figure 8 A comparison diagram of normalized radar cross sections before and after correction under the trapezoidal distribution rainfall condition of the present invention;

[0072] Fig. 9 A comparison diagram of the results of using normalized radar cross section to invert ground rainfall before and after correction in the case of trapezoidal distribution rainfall of the present invention;

[0073] Fig.10 The precipitation distribution diagram obtained by inversion under the trapezoidal distribution rainfall condition of the present invention;

[0074] Fig.11 It is a precipitation distribution absolute error diagram obtained by inversion under the trapezoidal distribution rainfall condition of the present invention;

[0075] Fig.12 A comparison diagram of the normalized radar cross section before and after correction under the triangular distribution rainfall condition of the present invention;

[0076] Fig.13 A comparison diagram of the results of using normalized radar cross section to invert ground rainfall before and after correction in the case of triangular distribution rainfall of the present invention;

[0077] Fig.14 The precipitation distribution map obtained by inversion under the triangular distribution rainfall condition of the present invention;

[0078] Fig.15 This is the absolute error diagram of precipitation distribution obtained by inverting under the triangular distribution rainfall condition of the present invention. DETAILED DESCRIPTION

[0079] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0080] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantitative limitation, and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" involved in this application refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there may be three relationships, for example, "A and / or B" can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the objects before and after are in an "or" relationship. The terms "first", "second", "third", etc. involved in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

[0081] Embodiment 1:

[0082] When performing rainfall inversion in a certain area, the rainfall in the area is first simplified into a two-dimensional model that is unrelated in the horizontal and vertical directions, and functions are established in the horizontal and vertical directions respectively, such as Figure 1 As shown in the figure, the x-axis is the cross-track direction; the z-axis is the height direction; the l-axis is the plane wave incident direction; the t-axis is perpendicular to the l-axis; t is the height of the top of the snow layer, in km; z0 is the height of the rain-snow boundary layer, in km; θ is the radar incident angle; δ is the x-axis coordinate of the ground scattering echo attenuation; ξ is the x-axis coordinate of the volume scattering echo attenuation; the microwave pulse emitted by the radar is simplified to a plane wave, and its width is r R ;x l is the starting point of rainfall, x r is the end point of rainfall; x last It is the end point of the radar echo.

[0083] Assuming that the ground surface is flat, the rainfall layer and the snow layer are independent of each other, and the melting layer is ignored, the precipitation can be expressed as: R(x,z)=V(z)H(x), where V(z) is the vertical distribution function of precipitation (in mm / h), H(x) is the horizontal function of precipitation, and x and z are the coordinates on the x-axis and z-axis respectively.

[0084] In the vertical direction, this embodiment uses a double-layer rainfall model to perform analytical approximation on the vertical precipitation distribution data measured by Yuter to obtain the precipitation of each layer in the vertical direction, which is expressed as follows:

[0085]

[0086] Among them, V(0) is the maximum surface rainfall; p r is the liquid particle distribution coefficient (typical value for equatorial convection is 0.62); p s is the distribution coefficient of frozen particles (typical value for equatorial convection is 0.5); z0 and z t They are the height of the top of the rainfall layer and the height of the top of the snow layer, respectively. Both can be determined by the functional relationship between the spatial height and the temperature at the corresponding position.

[0087] For spaceborne radar, the radar echo received from the precipitation unit includes the echo scattered by the ground, i.e., the surface scattering σ srf (x) and the echo scattered by the precipitation unit, namely, the volume scattering σ vol (x), so its expression is:

[0088] σ SAR (x) = σ srf (x)+σ vol (x),

[0089]

[0090]

[0091] Where η(z) is the radar reflectivity, k(z) is the rain cloud attenuation coefficient, z is the integral coordinate of the ground scattering echo along the z axis, z′ is the integral coordinate of the precipitation unit scattering echo along the z axis, σ 0 is the radar echo value from the ground that is not affected by rainfall, z s1 、z s2 is the upper and lower limits of the surface scattered echo attenuation on the z axis, r1 、z r2 is the upper and lower limits of the rainfall resolution unit on the z axis, r3 、z r4 are the upper and lower limits of the rainfall body scattering echo attenuation on the z-axis.

[0092] In radar meteorology, the power form is often used to fit the radar reflectivity, that is:

[0093]

[0094] Where λ is the radar wavelength; |K0| 2 is the complex refractive index, and for the snow layer, |K0| 2 Take 0.19, for the rainfall layer, |K0| 2 Take 0.93; R(x, z) is the rainfall at the (x, z) coordinate; c, j are empirical parameters, and the values ​​of the empirical parameters obtained at different times and locations are quite different. In this embodiment, the empirical parameters for rainfall are: c=300, j=1.35; the empirical parameters for snowfall are: c=182, j=1.60.

[0095] Based on the above conditions, this embodiment provides a rainfall inversion method based on spaceborne synthetic aperture radar. The process of the method is as follows: Figure 2 As shown, the detailed steps include:

[0096] S1. Inversely calculate the radar echo endpoint according to the slope of the radar echo, and correct the radar echo within the horizontal range covered by the radar echo signal according to the inversely calculated radar echo endpoint:

[0097] Radar echo end point x last The inversion of is the starting point of the entire algorithm. <x last When x>x last When the radar echo is no longer affected by the attenuation of the snow layer, that is, σ SAR =σ 0 , the slope is 0, so it can be obtained by σ SAR The slope of the radar echo is used to determine the end point of the radar echo and when the normalized radar cross section σ of a certain point SAR When the slope is 0, this point is the end point of the radar echo.

[0098] To prevent random noise from affecting the reliability of inversion, the inversion steps of the radar echo endpoint are as follows:

[0099] S11. Obtain the apogee and subsatellite point of the satellite-borne synthetic aperture radar, move the apogee toward the subsatellite point, and sample the moving trajectory.

[0100] S12. Calculate the first-order derivatives of the normalized radar cross sections of the two sampling points x+Δx and x+2Δx before the target sampling point x and the two sampling points x-Δx and x-2Δx after the target sampling point x, and use the calculated first-order derivatives as the slope of the normalized radar cross section. If the slopes of the normalized radar cross sections of the sampling points x-Δx and x-2Δx are both 0 and the slopes of the normalized radar cross sections of the sampling points x+Δx and x+2Δx are not 0, then the target sampling point is the end point of the radar echo, where Δx is the sampling interval.

[0101] S13. Otherwise, reselect the target sampling point and repeat step S12 until the radar echo end point is obtained.

[0102] The steps to correct the radar echo according to the inverted radar echo end point are as follows:

[0103] When x is greater than the rainfall end point x r When , the radar echo only has surface scattering, so: σ SARdB =σ srfdB , where σ SARdB The dB form of radar scattering echo, σ srfdB It expresses the radar surface scattered echo in dB.

[0104] S14, vertical sampling of the cloud body, the calculation interval is z t -iΔh <z≤z t -(i-1)Δh average rainfall, the expression is:

[0105]

[0106] in, represents the average rainfall in the sampling interval, Δh represents the sampling interval, z t represents the height of the top of the snow layer, V(z) represents the vertical rainfall function, and i represents the number of selected sampling intervals;

[0107] S15, calculating the original radar echo according to the average rainfall in the sampling interval, and extracting the first intermediate function, wherein the original radar echo function is:

[0108]

[0109] Where f(iΔx) is the first intermediate function, and a represents the empirical parameter of the rainfall or snowfall attenuation coefficient; Δx represents the sampling interval in the horizontal direction and Δx=Δh tan θ.

[0110] Specifically, when iΔh <z t -z0,

[0111]

[0112] Among them, a s An empirical parameter representing the snowfall attenuation coefficient;

[0113] When iΔh≥z t -z0,

[0114]

[0115] Among them, a r An empirical parameter representing the rainfall attenuation coefficient.

[0116] S16, iteratively calculating the first intermediate function value, using the first intermediate function value to correct the radar echo within the horizontal range covered by the radar echo signal, and after correction, Figure 3 As shown, the expression is:

[0117] σ mSARdB (x last -iΔx)=σ 0 dB +f(iΔx)+…+f(Δx),

[0118] Among them, σ mSARdB Indicates the dB form of the corrected radar echo, x last represents the end point of radar echo, f(iΔx) represents the first intermediate function, x r represents the end point of rainfall, H(x) represents the horizontal rainfall function, V(0) represents the maximum surface rainfall, σ 0 dB This is the dB representation of the radar return without the attenuation of snow.

[0119] S2. Based on the corrected radar echo, the double-layer VIE algorithm is used to invert the ground rainfall function and the rainfall end point within the rainfall range.

[0120] S21, making the rainfall evenly distributed in the vertical direction, and rewriting the corrected radar echo function into a first radar echo function including the snowfall attenuation coefficient, the rainfall attenuation coefficient, the snowfall radar reflectivity and the rainfall radar reflectivity, the expression of which is:

[0121]

[0122] Among them, σ 0 (x) represents the horizontal radar echo not affected by the attenuation of the snow layer, θ represents the radar incident angle, z0 represents the height of the rain and snow boundary layer, k s represents the snowfall attenuation coefficient, k r represents the rainfall attenuation coefficient, δ, X, ξ all represent the intermediate coordinates in the integral path, η srepresents the snowfall radar reflectivity, η r Represents rainfall radar reflectivity.

[0123] S22, extract the second intermediate function, the expression is: Among them, u and m are parameters with no practical significance; the second intermediate function is used to represent the rainfall attenuation coefficient, snow radar reflectivity, rainfall radar reflectivity and precipitation when the vertical distribution of precipitation is uniform, and the expression is:

[0124]

[0125] Among them, p x '(x) is the derivative of p(x), R(x) is the rainfall, j r and b r represents the correlation coefficient of rain, j s and b s are the relevant empirical parameters of snow, a r represents the empirical coefficient of rainfall attenuation coefficient, a s An empirical coefficient representing the snowfall attenuation factor.

[0126] S23, based on the second intermediate function representing the rainfall attenuation coefficient, the snowfall radar reflectivity, the rainfall radar reflectivity and the precipitation when the vertical distribution of precipitation is uniform, obtaining a second radar echo function, the expression is:

[0127]

[0128] Among them, p X ′ (X) is the derivative of p(X), X represents the intermediate coordinates in the integration path, G1 is a parameter and G2 is a parameter and p(x) represents the second intermediate function.

[0129] S24, translating the second radar echo function along the x-axis according to the top height of the snowfall layer and the radar incident angle to obtain a third radar echo function, and extracting intermediate parameters, wherein the expression of the third radar echo function is:

[0130] The expression of the intermediate parameter is:

[0131] h=X-[z t -(Xxz t tanθ)tanθ]tanθ,

[0132] Then dX = cos 2 θdh.

[0133] S25, rewrite the third radar echo function according to the intermediate parameters to obtain a fourth radar echo function, which is expressed as

[0134] The formula is:

[0135]

[0136] Among them, K1(X) means that the parameter has no practical meaning and K2(X) means that the parameter has no practical meaning and X(x,h) means the parameter has no practical meaning and X(x,h)=hcos 2 θ+xsin 2 θ+z t tanθ.

[0137] S26. According to the fourth radar echo function, the second intermediate function is expressed in the form of a second-kind Volta integral, and its expression is:

[0138]

[0139] in, And has no practical meaning, K3(X) is a parameter with no practical meaning and K4(X) indicates that the parameter has no practical meaning and λ1 is a parameter with no practical significance and λ2 is a parameter with no practical significance and

[0140] S27, when x ≥ x last When , the rainfall is 0, that is, R(x) = 0, p(x) = 1. After calculating K1(X), K2(X), K3(X), K4(X) and f1(x) of the second intermediate function expressed in the form of the second kind of Volta integral according to the rainfall and the second intermediate function value, the second intermediate function value in the interval of interest is obtained by iterative calculation, and the rainfall end point is inferred.

[0141] S28. Obtain a ground rainfall function using the second intermediate function value obtained by iterative calculation.

[0142] S3, using the ground rainfall function and the rainfall end point to invert the rainfall starting point, and using the minimum distance method to compare with the prior model to invert the rainfall level function:

[0143] The steps of retrieving the rainfall starting point include:

[0144] S31. Randomly select six consecutive radar echo points before the end point of rainfall, and calculate the average value and root mean square value of the normalized radar scattering cross section of the five radar echo points before the radar echo point.

[0145] S32. Calculate the limit value of the radar echo at the rainfall starting point based on the said average value and root mean square, and its calculation expression is:

[0146] φ = {AVG5(σ SAR ) - 3RMS5[σ SAR - AVG5(σ SAR )]},

[0147] where AVG5(σ SAR ) represents the average value of the normalized radar cross sections of the five radar echoes closest to the radar echo point; RMS5[σ SAR - AVG5(σ SAR )] represents the root mean square of the normalized radar cross sections of the five radar echoes closest to the radar echo point.

[0148] S33. If the value of the normalized radar cross section of the radar echo point farthest from the rainfall end point is less than the limit value, then the radar echo point farthest from the rainfall end point is the rainfall starting point.

[0149] S34. Otherwise, reselect multiple radar echo points before the rainfall end point, and repeat steps S31 - S33 until the rainfall starting point is obtained.

[0150] The steps for inverting the rainfall horizontal function include:

[0151] S35. Use the minimum distance method to calculate the distance difference between the prior horizontal function and the inverted ground rainfall function under different shape factors;

[0152] The shape factor is calculated from the rainfall width. Specifically: when d = 0, it is a rectangular distribution; when d = W / 2, it is a triangular distribution; when 0 < d < w / 2, it is a trapezoidal distribution; d represents the shape factor, w represents the rainfall width, which is the difference between the rainfall end point and the rainfall starting point.

[0153] S36. Select the shape factor corresponding to the minimum distance difference, and invert the rainfall horizontal function according to this shape factor. The form of the rainfall horizontal function is:

[0154]

[0155] where x r represents the rainfall end point, and x l is the rainfall starting point.

[0156] S4. Calculate the ground rainfall using the said rainfall horizontal function and ground rainfall function:

[0157] S41. Calculate the ground rainfall according to the inverted rainfall horizontal function and ground rainfall function, and its expression is:

[0158]

[0159] Among them, V(0) is the surface rainfall obtained by inversion, x r is the end point of rainfall, z t is the height of the top of the snow layer, θ is the radar incident angle, R(x,0) is the inverted surface rainfall function, and H(x) is the inverted rainfall level function.

[0160] The present embodiment also provides a rainfall inversion device based on a spaceborne synthetic aperture radar, including a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or computer program instructions loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for the operation of the device can also be stored. The CPU, ROM, and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0161] Multiple components in the device are connected to the I / O interface, including: input units, such as keyboards, mice, etc.; output units, such as various types of displays, speakers, etc.; storage units, such as disks, optical disks, etc.; and communication units, such as network cards, modems, wireless communication transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunication networks.

[0162] The processing unit performs the various methods and processes described above, such as methods S1 to S4. For example, in some embodiments, methods S1 to S4 may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into the RAM and executed by the CPU, one or more steps of methods S1 to S4 described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute methods S1 to S4 in any other appropriate manner (e.g., by means of firmware).

[0163] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), complex programmable logic devices (CPLDs), and the like.

[0164] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0165] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0166] Embodiment 2:

[0167] In order to verify the reliability of the method provided in the above embodiment, three types of rainfall distribution are inverted respectively in this embodiment.

[0168] 1) Rectangular distribution rainfall inversion:

[0169] The rainfall width is set to w = 10 km, the maximum ground rainfall is V(0) = 50 mm / h, and the height of the top of the snow layer is z t =13km, the top height of the rainfall layer is z0=4.5km, and the liquid particle distribution coefficient is p r =0.62, the distribution coefficient of frozen particles is p s = 0.5, the radar incident angle is θ = 30°, the radar echo value when the ground is not affected by rainfall is σ0 = -7dB and the shape factor is d = 0km. The inversion results are as follows Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, the inversion data results are V(0) = 50.1 mm / h, x l =22.4km,x r =32.5km, d=0.

[0170] 2) Trapezoidal distribution rainfall inversion:

[0171] The rainfall width is set to w = 10 km, the maximum ground rainfall is V(0) = 50 mm / h, and the height of the top of the snow layer is z t =13km, the top height of the rainfall layer is z0=4.5km, and the liquid particle distribution coefficient is p r =0.62, the distribution coefficient of frozen particles is p s = 0.5, the radar incident angle is θ = 30°, the radar echo value of the ground not affected by rainfall is σ0 = -7dB and the shape factor is d = 3km. The inversion results are as follows Figure 8 , Fig. 9 , Fig.10 and Fig.11 As shown, the inversion data results are V(0) = 50.2 mm / h, x l =23.1km,x r =32.5km, d=3.

[0172] 3) Triangular distribution rainfall inversion:

[0173] The rainfall width is set to w = 10 km, the maximum ground rainfall is V(0) = 50 mm / h, and the height of the top of the snow layer is z t =13km, the top height of the rainfall layer is z0=4.5km, and the liquid particle distribution coefficient is p r =0.62, the distribution coefficient of frozen particles is p s = 0.5, the radar incident angle is θ = 30°, the radar echo value of the ground not affected by rainfall is σ0 = -7dB and the shape factor is d = 5km. The inversion results are as follows Fig.12 , Fig.13 , Fig.14 and Fig.15 As shown, the inversion data results are V(0) = 50.9 mm / h, x l =22.1km,x r =32.4km, d=5.

[0174] 4) Summary and analysis:

[0175] from Figure 4-Figure 15 It can be seen from the inversion result diagram that although there is a certain error in the inversion of the left half of the rainfall, the error is negligible in terms of the overall error. In order to verify that the method provided by the above embodiment is more accurate than the traditional method, the present method, IVE algorithm and MOS algorithm are used to invert the ground rainfall, and the results are shown in Table 1.

[0176] Table 1 Relative errors of surface precipitation inverted by different algorithms under different horizontal distributions

[0177] Horizontal distribution type MOS algorithm IMV algorithm This method Rectangular distribution 8.1％ 8.9％ 7.5％ Trapezoidal distribution 12.2％ 13.4％ 10.4％ Triangular distribution 15.6％ 15.4％ 10.8％

[0178] According to the above table, it can be seen that the method provided by the above embodiment has higher accuracy in inverting rainfall of various types of distributions compared with the traditional method.

[0179] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A rainfall inversion method based on spaceborne synthetic aperture radar, characterized in that: The method includes: The radar echo end point is inverted according to the slope of the radar echo, and the radar echo within the horizontal range covered by the radar echo signal is corrected according to the inverted radar echo end point; Based on the corrected radar echo, the double-layer VIE algorithm is used to invert the ground rainfall function and rainfall end point within the rainfall range. The rainfall starting point is inverted by using the ground rainfall function and the rainfall end point, and the rainfall level function is inverted by comparing with the prior model using the minimum distance method; The ground rainfall is calculated using the rainfall level function and the ground rainfall function.

2. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 1, characterized in that: The method of inverting the radar echo endpoint according to the slope of the radar echo comprises: Obtain the apogee and subsatellite point of the spaceborne synthetic aperture radar, move the apogee toward the subsatellite point, and sample the moving trajectory; Calculate the first-order derivative of the normalized radar cross section of the two sampling points before and after the target sampling point and use the calculated first-order derivative as the slope of the normalized radar cross section. If the slopes of the normalized radar cross section of the first two sampling points are both 0 and the slopes of the normalized radar cross section of the last two sampling points are not 0, then the target sampling point is the end point of the radar echo; Otherwise, the target sampling point is reselected until the end point of the radar echo is obtained.

3. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 2, characterized in that: The method of correcting the radar echo within the horizontal range covered by the radar echo signal according to the inverse radar echo endpoint comprises: The cloud body is sampled longitudinally and the average rainfall in the sampling interval is calculated. The expression is: in, represents the average rainfall in the sampling interval, Δh represents the sampling interval, z t represents the height of the top of the snow layer, V(z) represents the vertical rainfall function, and i represents the number of selected sampling intervals; Calculate the original radar echo according to the average rainfall in the sampling interval and extract the first intermediate function; The radar echo within the horizontal range covered by the radar echo signal is corrected using the first intermediate function. The expression is: σ mSARdB (x last -iΔx)=σ 0 dB +f(iΔx)+…+f(Δx), where σ mSARdB Indicates the dB form of the corrected radar echo, x last represents the end point of radar echo, f(iΔx) represents the first intermediate function, x r represents the end point of rainfall, H(x) represents the horizontal rainfall function, V(0) represents the maximum surface rainfall, σ 0 dB This is the dB representation of the radar return without the attenuation of snow.

4. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 3, characterized in that: The first intermediate function expression is: Where Δx represents the sampling interval and Δx = Δhtanθ, θ represents the incident angle of the radar, x r represents the original rainfall end point, H(x) represents the horizontal rainfall function, and V(0) represents the maximum rainfall on the ground.

5. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 1, characterized in that: The steps of inverting the surface rainfall function and the rainfall endpoint include: Let the rainfall be evenly distributed in the vertical direction, and rewrite the corrected radar echo function into a first radar echo function including the snowfall attenuation coefficient, the rainfall attenuation coefficient, the snowfall radar reflectivity and the rainfall radar reflectivity, which is expressed as follows: Among them, σ 0 (x) represents the horizontal radar echo not affected by the attenuation of the snow layer, θ represents the radar incident angle, z0 represents the height of the rain and snow boundary layer, k s represents the snowfall attenuation coefficient, k r represents the rainfall attenuation coefficient, δ, X, ξ all represent the intermediate coordinates in the integral path, η s represents the snowfall radar reflectivity, η r represents the rainfall radar reflectivity; Extract the second intermediate function, the expression is: Among them, u and m are parameters with no practical significance; the second intermediate function is used to represent the rainfall attenuation coefficient, snow radar reflectivity, rainfall radar reflectivity and precipitation when the vertical distribution of precipitation is uniform, and the expression is: Among them, p x '(x) is the derivative of p(x), R(x) is the rainfall, j r and b r represents the correlation coefficient of rain, j s and b s are the relevant empirical parameters of snow, a r The empirical coefficient representing the rainfall attenuation coefficient, a s The empirical coefficient representing the snowfall attenuation coefficient; Based on the second intermediate function representing the rainfall attenuation coefficient, snowfall radar reflectivity, rainfall radar reflectivity and precipitation when the vertical distribution of precipitation is uniform, the second radar echo function is obtained, and the expression is: Among them, p X ′ (X) is the derivative of p(X), X represents the intermediate coordinates in the integration path, G1 is a parameter and G2 is a parameter and p(x) represents the second intermediate function; The second radar echo function is translated along the x-axis according to the top height of the snow layer and the radar incident angle to obtain a third radar echo function, and the intermediate parameters are extracted. The expression of the third radar echo function is: The expression of the intermediate parameter is: h=X-[z t -(X-x-z t tanθ)tanθ]tanθ, Then dX = cos 2 θdh; The fourth radar echo function is obtained by rewriting the third radar echo function according to the intermediate parameters, and its expression is: Among them, K1(X) means that the parameter has no practical meaning and K2(X) means that the parameter has no practical meaning and X(x,h) means the parameter has no practical meaning and X(x,h)=hcos 2 θ+xsin 2 θ+z t tanθ; According to the fourth radar echo function, the second intermediate function is expressed in the form of the second kind of Volta integral, and its expression is: in, And has no practical meaning, K3(X) is a parameter with no practical meaning and Indicates that the parameter has no practical meaning and λ1 is a parameter with no practical significance and λ2 is a parameter with no practical significance and When the rainfall is 0, the second intermediate function value is 1. After calculating K1(X), K2(X), K3(X), K4(X) and f1(x) of the second intermediate function expressed in the form of the second kind of Volta integral according to the rainfall and the second intermediate function value, the second intermediate function value in the interval of interest is obtained by iterative calculation, and the rainfall end point is inferred; The second intermediate function value obtained by iterative calculation is used to obtain the ground rainfall function.

6. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 1, characterized in that: The method for inverting the rainfall starting point is: Randomly select multiple consecutive radar echo points before the end point of rainfall, and calculate the average value and root mean square of the normalized radar scattering cross section of all radar echo points except the radar echo point farthest from the end point of rainfall; The limit value of the radar echo at the starting point of rainfall is calculated according to the average value and the root mean square. If the normalized radar cross section value of the radar echo point farthest from the end point of rainfall is less than the limit value, the radar echo point farthest from the end point of rainfall is the starting point of rainfall. Otherwise, multiple radar echo points before the end point of rainfall are reselected until the starting point of rainfall is obtained.

7. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 1, characterized in that: The method for inverting the rainfall level function is: The minimum distance method is used to calculate the distance difference between the prior level function and the ground rainfall function obtained by inversion under different shape factors, wherein the shape factor is calculated by the rainfall width, and the rainfall width is the difference between the end point of the rainfall and the starting point of the rainfall; The shape factor corresponding to the smallest distance difference is selected, and the rainfall level function is inverted based on the shape factor.

8. The method for rainfall inversion based on spaceborne synthetic aperture radar according to claim 1, characterized in that: The method for inverting the ground rainfall is to calculate the ground rainfall based on the rainfall level function and the ground rainfall function obtained by inversion, and the expression is: Among them, V(0) is the surface rainfall obtained by inversion, x r is the end point of rainfall, z t is the height of the top of the snow layer, θ is the radar incident angle, R(x,0) is the inverted surface rainfall function, and H(x) is the inverted rainfall level function.

9. A rainfall inversion device based on spaceborne synthetic aperture radar, comprising a memory and a processor, wherein a computer program is stored in the memory, characterized in that: When the processor executes the program, the method according to any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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