Method and device for extracting back scattering energy of observed object based on SAR (Synthetic Aperture Radar) image

Abstract

The invention relates to a method and a device for extracting back scattering energy of an observed object based on an SAR (Synthetic Aperture Radar) image. The method comprises the following steps: extracting a space incidence angle and corresponding scattering energy of a radar beam relative to a known observed object based on a spaceborne SAR image, and constructing a spaceborne SAR image observed object back scattering mapping database according to the space incidence angle, the scattering energy and acquisition parameters of the spaceborne SAR image; based on the mapping database, according to the acquisition parameters of the satellite-borne SAR image and the space incident angle of the radar beam relative to the to-be-measured observed object, the scattering energy of the to-be-measured observed object is obtained; according to the method, the electromagnetic wave incident angle relative to the observed object is obtained in an accurate spatial analysis mode, so that the back scattering energy of the observed object extracted from the SAR image has practical application significance.

Description

Technical Field

[0001] The present invention relates to the field of spaceborne synthetic aperture radar application technology, and more particularly to a method and device for extracting backscattered energy of an observed object based on SAR images. Background Art

[0002] Backscattering describes the ability of an object to scatter incident electromagnetic waves in the direction of incidence, and is an important electromagnetic scattering characteristic of an object. Backscattering energy is represented by pixel values ​​in Synthetic Aperture Radar (SAR) images. The stronger the backscattering energy, the greater the detected scattering intensity, and the corresponding pixel value. Backscattering is usually related to the structure and physical size of the observed object. Therefore, in the field of microwave applications, such as SAR image processing and application, it is a common technical approach to analyze the scattering ability, shape, structure and other scattering characteristics of the observed object based on the detected scattering intensity.

[0003] Since the interaction mechanism between electromagnetic waves and observed objects and the scattering process are extremely complex, it is difficult to describe the backscattering expression of objects with complex structures through analytical expressions. Currently, the backscattering calculation or extraction technology for common objects can be divided into three categories.

[0004] The first category is to model the scattering process based on electromagnetic scattering theory and deduce the analytical expression of backscattering; the second category is to use electromagnetic scattering simulation methods and combine object modeling to simulate and calculate the electromagnetic scattering process to obtain the backscattering energy values ​​of the object at different incident angles; the third category is to conduct simulation experiments on equal-scale or scaled-down objects or object models in laboratories and microwave darkrooms to obtain the backscattering energy at different incident angles.

[0005] Among them, the first type of method is limited by the complex scattering process and can only calculate the backscattered energy of some objects with standard structures at limited angles. The second type of method only has high-precision simulation capabilities for electrically small objects, but for electrically large objects, the simulation accuracy needs to be greatly sacrificed due to computational efficiency. The third type of method is also limited by laboratory conditions and has some restrictions on the size of objects that can be tested.

[0006] At the same time, the above methods are usually only applicable to near-field simulations, and the accuracy for far-field simulations is limited. In addition, the above three technical means are quite different from the conditions for obtaining scattering information of observed objects in actual applications. Therefore, the values ​​obtained by the existing methods are difficult to be directly used in actual applications. Summary of the invention

[0007] In view of this, the present invention provides a method and device for extracting backscattered energy of an observed object based on SAR images, aiming to obtain the incident angle of electromagnetic waves relative to the observed object in a precise spatial resolution manner, so that the backscattered energy of the observed object extracted from the SAR image has practical application significance.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] On the one hand, the present application provides a method for extracting backscattered energy of an observed object based on a SAR image, comprising the following steps:

[0010] S1. Determine the spatial incident angle and corresponding scattering energy of the radar beam relative to a known observation object based on the spaceborne SAR image, and construct a backscattering mapping database of the spaceborne SAR image observation object according to the spatial incident angle and the scattering energy, and acquisition parameters of the spaceborne SAR image;

[0011] The step of determining the incident angle of the radar beam relative to the known observation object based on the spaceborne SAR image includes:

[0012] S11, determining the spatial coordinates of the intersection of the satellite radar beam center and the ground;

[0013] S12, obtaining the spatial coordinates of the known observed object according to the spatial coordinates of the intersection point;

[0014] S13, calculating the incident angle of the radar beam relative to the known spatial coordinates of the observed object;

[0015] S14, obtaining a spatial incident angle of the radar beam relative to the known observed object according to the spatial posture of the known observed object and the incident angle of the radar beam relative to the spatial coordinates of the known observed object;

[0016] S2. Based on the spaceborne SAR image observation object backscatter mapping database, the scattering energy of the object to be measured is obtained according to the acquisition parameters of the spaceborne SAR image and the spatial incident angle of the radar beam relative to the object to be measured.

[0017] Preferably, step S11 includes the following steps:

[0018] S111, establishing a space coordinate system with the satellite sub-satellite point as the origin;

[0019] S112, obtaining the horizontal coordinate of the spatial coordinate of the intersection point according to the satellite altitude and the viewing angle below the beam center;

[0020] S113. Obtain the ordinate of the spatial coordinates of the intersection point according to the satellite altitude, the downward viewing angle of the beam center, and the oblique viewing angle of the beam center.

[0021] Preferably, the spatial coordinates of the intersection point are expressed as follows:

[0022]

[0023] Where h is the satellite height in the spaceborne SAR image system parameters, θ l is the viewing angle under the beam center, θ sq is the beam center slant angle.

[0024] Preferably, in S12, the spatial coordinates of the known observed object are (x, y, 0), wherein x is obtained by the following steps, and y is the same as the ordinate in the spatial coordinates of the intersection point;

[0025] S121, extracting the minimum bounding rectangle of a known observed object in the spaceborne SAR image, and taking the central pixel coordinates of the minimum bounding rectangle as the pixel coordinates of the known observed object in the SAR image;

[0026] S122, obtaining a distance pixel difference ΔN between the pixel coordinates of the known observed object in the SAR image and the pixel point coordinates corresponding to the center of the radar beam in the SAR image;

[0027] S123, obtaining the horizontal coordinate in the spatial coordinate of the known observed object according to the distance pixel difference according to the following formula;

[0028] x=x0+δ ra ×(N T -N0)

[0029] Where N0 is the pixel coordinate of the radar beam center in the SAR image, NT is the pixel coordinate of the known object in the SAR image, δ ra is the distance resolution, and x0 is the horizontal coordinate in the intersection space coordinates.

[0030] Preferably, in S13, the incident angle includes an incident azimuth angle With the incident pitch angle θ T , the calculation methods are:

[0031]

[0032]

[0033] Where h represents the altitude of the satellite in the space coordinate system.

[0034] In this embodiment, the spatial distance between the satellite and the observed object is also calculated, and the calculation method is:

[0035]

[0036] Preferably, S14 includes the following steps:

[0037] S141. Establish the central coordinate system of the observed object with the known observed object as the origin;

[0038] S142. When the spatial attitude of the known observed object is known and measurable, the angle between the measured normal direction of the observed object and the satellite when the beam passes through is used as the spatial incidence pitch angle of the radar beam relative to the observed object, and the sum of the incident azimuth angle of the radar beam relative to the known observed object spatial coordinates and the azimuth angle of the known observed object is used as the spatial incidence azimuth angle of the radar beam relative to the observed object; that is,

[0039]

[0040] In the formula, is the azimuth of the known observation object, is the incident azimuth of the radar beam relative to the known spatial coordinates of the observed object.

[0041] S143. When the spatial attitude of the known observed object is unknown and cannot be measured, an actual spatial attitude coordinate system is established according to the spatial attitude of the known observed object, and the spatial incident azimuth and pitch angle of the radar beam relative to the observed object are obtained according to the coordinates of the satellite in the actual spatial attitude coordinate system of the known observed object.

[0042] The specific steps are as follows:

[0043] 1) According to the incident azimuth of the satellite in the coordinate system of the known observation center and the pitch angle θ s , convert the satellite coordinates in the star point coordinate system into the coordinates in the center coordinate system of the known observed object;

[0044] The incident azimuth angle and the pitch angle θ s Obtained by the following formula:

[0045]

[0046] In the formula, is the azimuth of the known observation object, is the incident azimuth of the radar beam relative to the known spatial coordinates of the observed object, θ T is the incident elevation angle of the radar beam relative to the known spatial coordinates of the observed object.

[0047] The satellite coordinate conversion method is:

[0048]

[0049] In the formula, (x s ,y s , z s ) is the satellite coordinate in the known observation center coordinate system; and zs =h;

[0050] 2) Establishing a coordinate system of the actual spatial attitude of the known observed object by rotating the central coordinate system of the known observed object around the x-axis and the y-axis in sequence; and determining the coordinates of the satellite in the coordinate system of the actual spatial attitude of the known observed object;

[0051] Among them, the rotation angle around the x-axis is α, then the rotation matrix R x (α) is:

[0052]

[0053] The rotation angle around the y-axis is β, then the rotation matrix R y (β) is:

[0054]

[0055] ″′

[0056] And the coordinates of the satellite in the actual space attitude coordinate system of the known observation object (x S ,y S , z S ) can be obtained by the following formula:

[0057]

[0058] 3) According to the coordinates of the satellite in the actual spatial attitude coordinate system of the known observed object, the spatial incident azimuth and pitch angle of the radar beam relative to the observed object are obtained.

[0059] The calculation method is as follows:

[0060]

[0061] In the formula, is the spatial incident azimuth of the radar beam relative to the observed object, and θ is the elevation angle.

[0062] Preferably, the scattering energy of the known observed object includes backscattering energy and maximum scattering energy; the acquisition formulas are:

[0063]

[0064] Where E is the backscattered energy of the known object, P is the maximum scattering energy of the known object, I represents the image amplitude value within the minimum bounding rectangle of the known object, and H and W are the height and width of the minimum bounding rectangle.

[0065] Preferably, in S1, the information generated by each known observation object sample constitutes an observation object backscatter mapping table, and the spaceborne SAR image observation object backscatter mapping database is composed of a plurality of encoded observation object backscatter mapping tables connected end to end.

[0066] On the other hand, the present invention also provides a device for extracting backscatter energy of an observed object based on a SAR image, comprising:

[0067] A backscatter mapping database construction module is used to determine the incident angle and corresponding scattered energy of the radar beam relative to the known observation object based on the spaceborne SAR image, and to construct a backscatter mapping database of the spaceborne SAR image observation object according to the incident angle and scattered energy, and acquisition parameters of the spaceborne SAR image;

[0068] The step of determining the incident angle of the radar beam relative to the known observation object based on the spaceborne SAR image includes:

[0069] S11, determining the spatial coordinates of the intersection of the satellite radar beam center and the ground;

[0070] S12, obtaining the spatial coordinates of the known observed object according to the spatial coordinates of the intersection point;

[0071] S13, calculating the incident angle of the radar beam relative to the known spatial coordinates of the observed object;

[0072] S14, obtaining an incident angle of the radar beam relative to the known observed object according to the spatial posture of the known observed object and the incident angle of the radar beam relative to the spatial coordinates of the known observed object;

[0073] The module for extracting scattered energy of the object to be measured is used to obtain the scattered energy of the object to be measured based on the backscatter mapping database of the object to be measured in the spaceborne SAR image, according to the acquisition parameters of the spaceborne SAR image and the incident angle of the radar beam relative to the object to be measured.

[0074] It can be seen from the above technical solutions that the present invention discloses a method and device for extracting backscattered energy of an observed object based on SAR images. Compared with the prior art, the present invention has the following advantages:

[0075] 1. The existing massive satellite-borne SAR image data can be directly used to obtain the backscattered energy of the observed object at a specific incident angle. The efficiency and economy of the method are much higher than laboratory simulation measurement, and the conditions for obtaining the backscattered energy are closer to the actual application environment and can directly assist in practical applications. At the same time, compared with the electromagnetic simulation method, the numerical reliability and accuracy of the backscattered energy extracted by the present invention are higher;

[0076] 2. It has high-precision geometric solving capability, and can accurately calculate the relative geometric relationship of the observed object's attitude with respect to the satellite platform, thus improving the reliability and accuracy of backscatter energy extraction and application;

[0077] 3. At the same time, the database of spaceborne SAR image observation object backscatter mapping database designed in this application not only records the backscatter energy extraction results, but also covers parameters such as synthetic aperture length and polarization mode that may affect the scattering energy of the observation object. At the same time, it records the theoretical scattering information of the observation object obtained by existing theoretical research or simulation, which provides a reference for method comparison, error analysis, and numerical correction of measured energy, and provides effective and powerful data support for the research and application of backscattering of observation objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0079] Figure 1 This is a flow chart of a method for extracting backscattered energy of an observed object based on a SAR image according to the present invention;

[0080] Figure 2 It is a schematic diagram of the geometric imaging of the sub-satellite point in the space coordinate system and the satellite motion and synthetic aperture radar;

[0081] Figure 3 Schematic diagram of the spatial coordinate system at the center of the observed object. DETAILED DESCRIPTION

[0082] 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 only 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 are within the scope of protection of the present invention.

[0083] Spaceborne SAR is currently an important means of microwave remote sensing in my country. SAR images are also the main carrier of electromagnetic scattering information of the observed objects in microwave remote sensing. The image value is directly related to the backscattering ability of the observed objects. Compared with electromagnetic simulation and laboratory measurement, SAR images can provide more universal, more realistic, and closer to the actual environment backscattering data. At the same time, with the development and deployment of my country's SAR system, it can provide massive data support, and the data acquisition and experimental costs are lower than those in the laboratory; therefore, the backscattering energy of the observed object extracted from the SAR image has practical application significance.

[0084] However, unlike laboratory conditions, objects observed by spaceborne SAR cannot be placed in a pre-specified posture. In addition, the imaging geometry of spaceborne SAR is complex and the posture calculation of the observed object is complex. Therefore, even if the backscattering intensity of the observed object can be directly read from the SAR image, the incident angle of the electromagnetic wave emitted from the satellite relative to the observed object seriously affects the reference and application value of the obtained backscattering energy of the observed object. Therefore, accurately obtaining the incident angle of the radar beam is crucial to extracting the backscattering energy of the observed object.

[0085] In this regard, an embodiment of the present invention discloses a method and device for extracting backscattered energy of an observed object based on a SAR image. The method obtains the incident angle of an electromagnetic wave relative to the observed object in a precise spatial resolution manner, and then constructs a database based on the scattering energy corresponding to the incident angle. Based on the database and massive satellite-borne SAR images, the present invention can quickly obtain the backscattered energy of the observed object at a specific incident angle.

[0086] Embodiment 1

[0087] The method for extracting backscattered energy of an observed object based on a SAR image disclosed in this embodiment is as follows: Figure 1 As shown, including:

[0088] S1. Determine the spatial incident angle and scattering energy of the radar beam relative to the known observation object based on the spaceborne SAR image, and construct a backscatter mapping database of the spaceborne SAR image observation object according to the spatial incident angle and scattering energy, and acquisition parameters of the spaceborne SAR image;

[0089] S2. Based on the spaceborne SAR image observation object backscatter mapping database, the scattering energy of the object to be measured is obtained according to the acquisition parameters of the spaceborne SAR image and the spatial incident angle of the radar beam relative to the object to be measured.

[0090] In this embodiment, before constructing the spaceborne SAR image observation object backscatter mapping database, it is preferred to obtain the spaceborne SAR image system parameters, spaceborne SAR image data, and known observation object information in the image to facilitate the subsequent extraction and calculation of the spatial incident angle and scattering energy.

[0091] The SAR image system parameters include at least: satellite altitude h, radar frequency f, polarization mode, beam center slant angle θ sq , the viewing angle θ under the beam center l , range resolution δ ra , synthetic aperture length L, the imaging algorithm used,

[0092] The SAR image data at least includes: an image in a single-view complex data format or an intensity format that has been geometrically corrected but not geocoded, and the SAR image pixel range coordinates (column coordinates of the image) N0 corresponding to the center of the radar beam,

[0093] The known observation object information in the image includes at least: the observation object category, the observation object name, the corresponding pixel set and pixel coordinates of the observation object in the SAR image.

[0094] The implementation process of step S1 is mainly described below:

[0095] In step S1, the step of determining the incident angle of the radar beam relative to the known observation object based on the spaceborne SAR image includes:

[0096] S11, according to the satellite-borne SAR image system parameters, using the relationship between synthetic aperture radar imaging geometry and satellite motion geometry to determine the spatial geometric coordinates T0 of the intersection of the satellite radar beam center and the ground; the calculation method includes:

[0097] S111, establishing a space coordinate system with the satellite sub-satellite point as the origin;

[0098] According to the satellite-borne SAR image system parameters, a spatial coordinate system is established with the sub-satellite point in the system parameters as the origin, wherein the sub-satellite point O is the origin of the spatial coordinate system, the satellite motion azimuth v in the system parameters is used as the y-axis, the distance direction in the system parameters is used as the x-axis, and the ground plane normal is used as the z-axis. The spatial coordinate system is called the sub-satellite point spatial coordinate system or the sub-satellite point coordinate system. The x, y, and z axes of the sub-satellite point coordinate system satisfy the right-hand rule. The geometric relationship between the sub-satellite point spatial coordinate system and satellite motion and synthetic aperture radar imaging is as follows: Figure 2 As shown;

[0099] exist Figure 2 In the above equation, O represents the origin of the space coordinate system (the point below the satellite); S represents the satellite position, coordinates: (0, 0, h); v represents the direction vector of the satellite motion unit, (0, 1, 0); AB represents the intersection of the beam and the ground, that is, the beam range; T represents the observed object, coordinates: (x, y, 0); ST0 represents the beam center; θ sqrepresents ∠X0-S-T0, which is the oblique angle of the beam center; θ1 represents ∠OS-X0, which is the downward angle of the beam center; T0 represents the intersection of the beam center and the ground; X0 represents the projection point of T0 in the range direction, with the coordinates (xo, 0, 0,); Y represents the projection point of T0 in the azimuth direction, with the coordinates (0.y.0.); X represents the projection point of T in the range direction, with the coordinates (x, 0, 0);

[0100] S112, according to the satellite altitude and the angle of view θ below the beam center l , obtain the horizontal coordinate of the intersection point spatial coordinate; specifically according to the satellite height h and the beam center lower viewing angle θ in the satellite-borne SAR image system parameters l , calculate the distance to the spatial coordinate x0 of the intersection point T0 between the beam center and the ground according to the following formula,

[0101] R1=OX0=x0=h×tan(θ l )

[0102] The symbol OX0 represents the length of the line segment between points O and X0, and the value is represented by R1. Figure 2 From the geometric relationship shown, it can be seen that the value of R1 is the distance of point T0 to the coordinate (abscissa) X0;

[0103] S113, according to the satellite height h and the beam center lower angle θ in the satellite-borne SAR image system parameters l , and the beam center slant angle θ sq , calculate the azimuth spatial coordinates of the intersection of the beam center and the ground.

[0104] That is, first calculate the intermediate variables R2 and R3:

[0105]

[0106] Then, the spatial coordinates (x0, y) of the intersection of the beam center and the ground are calculated based on the intermediate variables R2 and R3;

[0107]

[0108] S12, obtaining the spatial coordinates of the known observation object according to the spatial coordinates of the intersection point; in this embodiment, the spatial coordinates of the known observation object are (x, y, 0), wherein x is obtained by the following steps, and y is the same as the ordinate in the spatial coordinates of the intersection point;

[0109] S121. Extract the minimum bounding rectangle of the known object in the spaceborne SAR image. The four corner points of the rectangle are represented by row and column numbers corresponding to the image pixel positions. The coordinates represented by the pixel row and column numbers are called pixel coordinates, where the row coordinate corresponds to the azimuth direction and has a value range from 1 to the image height H. The column coordinate N corresponds to the distance direction and has a value range from 1 to the image width W. The central pixel coordinates of the minimum bounding rectangle are used as the pixel coordinates of the known object in the SAR image. N is used as the pixel coordinates of the known object in the SAR image. T express;

[0110] S122, obtaining the SAR image pixel coordinates corresponding to the beam center according to the satellite-borne SAR image system parameters, and calculating the range pixel difference ΔN between the known observed object pixel coordinates and the beam center pixel coordinates. If the system parameters do not clearly give the corresponding pixel coordinates, the midpoint of the image range direction is used as the SAR image pixel coordinates corresponding to the beam center:

[0111] ΔN=N T -N0

[0112] Where N0 is the range coordinate of the SAR image pixel corresponding to the center of the radar beam, N T is the distance pixel coordinate of the known observed object in the SAR image.

[0113] S123, according to the range resolution δ in the spaceborne SAR image system parameters ra Calculate the distance between the spatial position of the known observation object and the intersection of the beam center and the ground to obtain the spatial coordinates of the known observation object space. The calculation method is as follows:

[0114] x=x0+δ ra ×ΔN

[0115] The final observed object space coordinates are (x, y, 0).

[0116] S13, calculate the spatial incident angle and slant distance R of the radar beam relative to the spatial point where the known observation object is located according to the satellite spatial coordinates (0, 0, h) and the spatial coordinates (x, y) of the known observation object point T (the spatial distance between the satellite and the observed object), wherein the incident angle includes the incident azimuth With the incident pitch angle θ T ;

[0117] In this embodiment, refer to Figure 2 , incident azimuth Refers to ∠YTO, due to With the line segment on the X axis Therefore, the angle is equal to ∠TOX in value, that is, ∠YTO can be obtained by calculating ∠TOX. Figure 2 In the triangle TOX in the XOY plane, according to the trigonometric relationship and the spatial coordinates of the observation point, the tangent value of ∠TOX is the opposite side The length x and the adjacent edge The ratio of the length y of , so the incident azimuth can be calculated by the inverse tangent function

[0118]

[0119] According to the Pythagorean theorem, Figure 2 Calculate the hypotenuse of the triangle TOX on the XOY plane The hypotenuse is also the base of the inclined triangle TSX, and its length is represented by R4:

[0120]

[0121] Incident pitch angle θ T refers to The angle between the normal direction of the observation point and the line segment on the z coordinate axis The parallel relationship shows that this angle is numerically equal to the angle ∠TSO, and the tangent of ∠TSO can be calculated in triangle TSX, and its tangent is equal to the opposite side The length R4 and the adjacent edge The ratio of the length h, so θ T It can be calculated using the inverse tangent function:

[0122]

[0123] Further in triangle TSX, calculate the hypotenuse according to the Pythagorean theorem The length of the satellite is the distance from the observation point, that is, the slant distance R T :

[0124]

[0125] Where R4 is an intermediate variable.

[0126] S14, obtaining a spatial incident angle of the radar beam relative to the known observed object according to the spatial posture of the known observed object and the incident angle of the radar beam relative to the spatial coordinates of the known observed object;

[0127] The specific steps include:

[0128] S141. Establish an observation object center coordinate system with the known observation object as the origin. In this embodiment, a right-handed spatial coordinate system is established with the known observation object in the image as the origin, the observation object orientation obtained by field measurement as the positive direction of the x-axis, and the ground normal as the positive direction of the z-axis. This is called the observation object center spatial coordinate system or the observation object center coordinate system. The observation object center coordinate system is as follows: Figure 3 As shown;

[0129] Figure 3 In the equation, x represents the x-axis, which is in the same direction as the object being observed; n represents the normal direction of the object being observed; yz 、n xz 、n xy are the projection points of the normal n on the planes yTZ, xTz, and xTy, respectively; b represents the beam direction vector, which is parallel to the ST line; ∠OT-Xs, which represents the beam azimuth in the spherical coordinate system; θ s Lz-TS represents the beam pitch angle of the spherical coordinate system; Xs represents the x-axis projection of the sub-satellite point, and the coordinates are (xs, 0, 0,); Ys represents the y-axis projection of the sub-satellite point, and the coordinates are (0, ys, 0,);

[0130] Then, the attitude of the observed object is measured, and the spatial incident angle of the radar beam relative to the observed object is calculated in the coordinate system of the center of the observed object;

[0131] In this embodiment, according to whether the normal angle of the satellite relative to the observed object when the beam passes through the observed object can be directly measured by the instrument, two calculation strategies are adopted, which are as follows:

[0132] S142. When the relative position relationship between the observed object and the satellite is known and the normal angle of the satellite relative to the observed object can be directly measured, the angle between the normal of the observed object and the satellite when the beam passes by is directly measured using an angle measuring instrument to obtain the spatial incident pitch angle θ of the radar beam relative to the observed object. When using an instrument for measurement, taking a protractor as an example, a protractor is arranged at the location of the observed object, its posture is adjusted to be consistent with the posture of the observed object, and one side of the scale is aligned with the position of the satellite when the beam passes by, and the pitch angle θ is recorded by reading the scale;

[0133] According to the direction of the observed object D and the incident azimuth φ in the subsatellite coordinate system T Calculate the spatial incident azimuth φ of the radar beam relative to the observed object. The calculation method is as follows:

[0134]

[0135] Among them, the azimuth of the observed object It indicates the angle between the direction of the observed object and the direction of the satellite. When the direction of the observed object is perpendicular to the direction of the satellite and points to one side of the satellite, is 0 if the object rotates clockwise For positive and counterclockwise rotation is negative, The value range is from -π to +π.

[0136] S143. When the relative position relationship between the observed object and the satellite is unknown and the normal angle of the satellite relative to the observed object cannot be directly measured, a coordinate system of the actual spatial attitude of the known observed object is established, and the spatial incident azimuth and pitch angle of the radar beam relative to the observed object are obtained based on the coordinates of the satellite in the actual spatial attitude coordinate system of the known observed object.

[0137] The specific steps are as follows:

[0138] 1. According to the incident azimuth of the satellite in the coordinate system of the center of the known observation object and the pitch angle θ s , convert the satellite coordinates in the star point coordinate system into the coordinates in the center coordinate system of the known observed object;

[0139] 1.1 Where, according to the direction of the observed object φ D and the incident azimuth φ in the subsatellite coordinate system T Calculate the satellite's azimuth φ in the coordinate system of the observation center s With the pitch angle θ s , the calculation method is as follows:

[0140]

[0141] Among them, the azimuth angle of the observed object φ D It represents the angle between the direction of the observed object and the direction of the satellite. When the direction of the observed object is perpendicular to the direction of the satellite and points to one side of the satellite, φ D is 0, if the object rotates clockwise D For positive and counterclockwise rotation φ D is negative, φ D The value range is from -π to +π, the pitch angle θ s The elevation angle of the satellite relative to the observed object is complementary to that of the sub-satellite coordinate system;

[0142] 1.2 Convert the satellite coordinates (0, 0, h) of the subsatellite point coordinate system into the coordinates (x s ,y s , z s ), the calculation method is as follows:

[0143]

[0144] In the formula, (x s ,y s , z s ) is the satellite coordinate in the known observation center coordinate system; and z s =h;

[0145] 2. Establishing the actual space attitude coordinate system of the known observed object by rotating the center coordinate system of the known observed object around the x-axis and the y-axis in sequence; and determining the coordinates of the satellite in the actual space attitude coordinate system of the known observed object;

[0146] 2.1 The current posture of the object is obtained based on the known information of the object or on-site measurement, and it is assumed that the actual posture of the object is obtained by rotating around the x-axis and y-axis in the origin coordinate system of the object in the direction of the normal of the object perpendicular to the ground plane and the object pointing to the positive direction of the y-axis of the center coordinate system of the object. The initial posture of the target is toward the positive direction of the x-axis and the normal is the positive direction of the z-axis. First, rotate the x-axis as the rotation axis by an angle α, as shown in Figure 3 At this time, the target normal also rotates in the yTz plane, from parallel to the z axis to pointing from the origin to n yz ,Right now Figure 3 ∠zTn yz That is, the rotation angle α, the corresponding rotation matrix R x (α) is:

[0147]

[0148] Then, the target is further rotated around the y-axis with a rotation angle of β, as shown in Figure 3 , the target normal also rotates out of the yTz plane around the y-axis, that is, Rotate around the y axis to n, Figure 3 The corresponding ∠zTn xz That is the rotation angle β, the rotation matrix R y (β) is:

[0149]

[0150] 2.2 According to the actual attitude of the observed object, a new right-handed coordinate system is established with the direction of the observed object as the y-axis and the normal direction of the observed object as the z-axis. In the new coordinate system, the coordinates of the satellite (x S ′,y S ′,z S ′) can be calculated by rotating the coordinates in the original observation center coordinate system:

[0151]

[0152] This formula is equivalent to rotating the newly established coordinate system around the y-axis by -β and then around the x-axis by -α, so that the new coordinate system overlaps with the coordinate system of the center of the observed object. The coordinates of the satellite in the coordinate system of the center of the observed object (x s ,y s , h) is also rotated in the same way, and the coordinates (x S ′,y S ′,z S ′).

[0153] 3. Converting the coordinates into spherical coordinates can obtain the spatial incidence pitch angle and azimuth angle of the satellite relative to the observed object. The calculation method is as follows:

[0154]

[0155] In the formula, is the spatial incident azimuth of the radar beam relative to the observed object, and θ is the elevation angle.

[0156] Furthermore, in step S1, the scattering energy of the known observed object obtained includes backscattering energy E and maximum scattering energy P; wherein E is the total energy of the image within the minimum bounding rectangle, and P is the maximum energy of the image within the minimum bounding rectangle, and the acquisition formulas are:

[0157]

[0158] Where I represents the image amplitude value within the minimum bounding rectangle of the known observation object, H and W are the height and width of the minimum bounding rectangle, and E and P represent the energy, which is related to the backscattering ability of the observation object.

[0159] In an exemplary embodiment, the present application further constructs a satellite-borne SAR image observation object backscatter mapping database based on the spatial incident angle and scattered energy, and the acquisition parameters of the satellite-borne SAR image; that is, according to the satellite-borne SAR image system parameters, known observation object information, the imaging geometric parameters and SAR image data, establishes the azimuth of the satellite relative to the observation object. The relationship between the pitch angle θ and the total energy E of the minimum circumscribed rectangle of the observed object image constitutes the backscatter mapping database of the spaceborne SAR image observed object.

[0160] In this embodiment, the satellite-borne SAR image observation object backscatter mapping database at least includes: synthetic aperture radar satellite name, imaging mode, radar frequency, polarization mode, synthetic aperture length, imaging algorithm, observation object category, observation object name, observation object image slice, satellite and observation object space distance, beam incident azimuth, beam incident pitch angle, observation object maximum scattering energy, observation object backscattering energy, observation object theoretical backscattering energy. For details, refer to the following table;

[0161]

[0162] In the present invention, the information generated by each observation object sample constitutes an "observation object backscatter mapping table", and a spaceborne SAR image observation object backscatter mapping database is formed by connecting multiple encoded "observation object backscatter mapping tables" end to end.

[0163] The present invention establishes a formatted database, which can provide a technical and data basis for the analysis, research and application of electromagnetic scattering of observed objects.

[0164] Embodiment 2

[0165] This embodiment also provides a device for extracting backscatter energy of an observed object based on a SAR image, comprising:

[0166] A backscatter mapping database construction module is used to determine the incident angle and scattered energy of the radar beam relative to the known observation object based on the spaceborne SAR image, and to construct a backscatter mapping database of the spaceborne SAR image observation object according to the incident angle and scattered energy, and the acquisition parameters of the spaceborne SAR image;

[0167] The step of determining the incident angle of the radar beam relative to the known observation object based on the spaceborne SAR image includes:

[0168] S11, determining the spatial coordinates of the intersection of the satellite radar beam center and the ground;

[0169] S12, obtaining the spatial coordinates of the known observed object according to the spatial coordinates of the intersection point;

[0170] S13, calculating the incident angle of the radar beam relative to the known spatial coordinates of the observed object;

[0171] S14, obtaining an incident angle of the radar beam relative to the known observed object according to the spatial posture of the known observed object and the incident angle of the radar beam relative to the spatial coordinates of the known observed object;

[0172] The module for extracting scattered energy of the object to be measured is used to obtain the scattered energy of the object to be measured based on the backscatter mapping database of the object to be measured in the spaceborne SAR image, according to the acquisition parameters of the spaceborne SAR image and the incident angle of the radar beam relative to the object to be measured.

[0173] Since the implementation principle of the device is consistent with the above method, it will not be repeated here.

[0174] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0175] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for extracting backscattered energy of an observed object based on SAR images, characterized in that: include: S1. Extracting the spatial incident angle and corresponding scattering energy of the radar beam relative to a known observation object based on the spaceborne SAR image, and constructing a backscattering mapping database of the spaceborne SAR image observation object according to the spatial incident angle and the scattering energy, and acquisition parameters of the spaceborne SAR image; The step of determining the spatial incident angle of the radar beam relative to the known observation object based on the spaceborne SAR image includes: S11, determining the spatial coordinates of the intersection of the satellite radar beam center and the ground; S12, obtaining the spatial coordinates of the known observed object according to the spatial coordinates of the intersection point; S13, calculating the incident angle of the radar beam relative to the known spatial coordinates of the observed object; S14, obtaining a spatial incident angle of the radar beam relative to the known observed object according to the spatial posture of the known observed object and the incident angle of the radar beam relative to the spatial coordinates of the known observed object; S2. Based on the spaceborne SAR image observation object backscatter mapping database, the scattering energy of the object to be measured is obtained according to the acquisition parameters of the spaceborne SAR image and the spatial incident angle of the radar beam relative to the object to be measured.

2. The method for extracting backscattered energy of an observed object based on a SAR image according to claim 1, characterized in that: In S11, the step of determining the spatial coordinates of the intersection of the radar beam center and the ground includes: S111, establishing a space coordinate system with the satellite sub-satellite point as the origin; S112, obtaining the horizontal coordinate of the spatial coordinate of the intersection point according to the satellite altitude and the viewing angle below the beam center; S113. Obtain the ordinate of the spatial coordinates of the intersection point according to the satellite altitude, the downward viewing angle of the beam center, and the oblique viewing angle of the beam center.

3. The method for extracting backscattered energy of an observed object based on SAR images according to claim 1, characterized in that: In S12, the spatial coordinates of the known observed object are (x, y, 0), where x is obtained by the following steps, and y is the same as the ordinate in the spatial coordinates of the intersection point; S121, extracting the minimum bounding rectangle of a known observed object in the spaceborne SAR image, and taking the central pixel coordinates of the minimum bounding rectangle as the pixel coordinates of the known observed object in the SAR image; S122, obtaining the distance pixel difference between the pixel coordinates of the known observed object in the SAR image and the pixel point coordinates corresponding to the center of the radar beam in the SAR image; S123, obtaining the horizontal coordinate in the spatial coordinate of the known observed object according to the distance pixel difference according to the following formula; x=x0+δ ra ×(N T -N0) Where N0 is the pixel coordinate of the radar beam center in the SAR image, NT is the pixel coordinate of the known object in the SAR image, δ ra is the distance resolution, and x0 is the horizontal coordinate in the intersection space coordinates.

4. The method for extracting backscattered energy of an observed object based on SAR images according to claim 3, characterized in that: In S13, the incident angle includes the incident azimuth angle With the incident pitch angle θ T , the calculation methods are: Where h represents the altitude of the satellite in the space coordinate system.

5. The method for extracting backscattered energy of an observed object based on SAR images according to claim 4, characterized in that: In S13, the spatial distance between the satellite and the observed object is also calculated as follows:

6. The method for extracting backscattered energy of an observed object based on SAR images according to claim 1, characterized in that: S14 includes the following steps: S141. Establish the central coordinate system of the observed object with the known observed object as the origin; S142. When the spatial attitude of the known observed object is known and measurable, the angle between the measured normal direction of the observed object and the satellite when the beam passes through is used as the spatial incidence pitch angle of the radar beam relative to the observed object, and the sum of the incident azimuth angle of the radar beam relative to the known observed object spatial coordinates and the known observed object orientation azimuth angle is used as the spatial incidence azimuth angle of the radar beam relative to the observed object; S143. When the spatial attitude of the known observed object is unknown and cannot be measured, an actual spatial attitude coordinate system is established according to the spatial attitude of the known observed object, and the spatial incident azimuth and pitch angle of the radar beam relative to the known observed object are obtained according to the coordinates of the satellite in the actual spatial attitude coordinate system.

7. The method for extracting backscattered energy of an observed object based on SAR images according to claim 6, characterized in that: S143 includes: According to the incident azimuth and elevation angle of the satellite in the known observation center coordinate system, the satellite coordinates in the star point coordinate system are converted into coordinates in the observation center coordinate system; By rotating the center coordinate system of the observed object around the x-axis and the y-axis in sequence, an actual space attitude coordinate system based on the known observed object is established; and the coordinates of the satellite in the actual space attitude coordinate system are determined; According to the coordinates of the satellite in the actual space attitude coordinate system, the spatial incident azimuth and pitch angle of the radar beam relative to the observed object are obtained.

8. The method for extracting backscattered energy of an observed object based on SAR images according to claim 1, characterized in that: It is known that the scattering energy of the observed object includes backscattering energy and maximum scattering energy; the acquisition formulas are: Where E is the backscattering energy of the known observation object, P is the maximum scattering energy of the known observation object, I represents the image amplitude value within the minimum bounding rectangle of the known observation object, and H and W are the height and width of the minimum bounding rectangle.

9. The method for extracting backscattered energy of an observed object based on SAR images according to claim 1, characterized in that: In S1, the information generated by each known observation object sample constitutes an observation object backscatter mapping table, and the spaceborne SAR image observation object backscatter mapping database is composed of multiple encoded observation object backscatter mapping tables connected end to end.

10. A device for extracting backscattered energy of an observed object based on SAR images, characterized in that: A method for extracting backscatter energy of an observed object based on a SAR image according to any one of claims 1 to 9, comprising: A backscatter mapping database construction module is used to determine the spatial incident angle and corresponding scattering energy of the radar beam relative to the known observation object based on the spaceborne SAR image, and to construct a backscatter mapping database of the spaceborne SAR image observation object according to the spatial incident angle and the scattering energy, and acquisition parameters of the spaceborne SAR image; The step of determining the incident angle of the radar beam relative to the known observation object based on the spaceborne SAR image includes: S11, determining the spatial coordinates of the intersection of the satellite radar beam center and the ground; S12, obtaining the spatial coordinates of the known observed object according to the spatial coordinates of the intersection point; S13, calculating the incident angle of the radar beam relative to the known spatial coordinates of the observed object; S14, obtaining a spatial incident angle of the radar beam relative to the known observed object according to the spatial posture of the known observed object and the incident angle of the radar beam relative to the spatial coordinates of the known observed object; The module for extracting scattered energy of the object to be measured is used to obtain the scattered energy of the object to be measured based on the backscatter mapping database of the object to be measured in the spaceborne SAR image, according to the acquisition parameters of the spaceborne SAR image and the spatial incident angle of the radar beam relative to the object to be measured.

Images