CN113640758A - SAR image scaler placement method and system under urban complex environment - Google Patents

SAR image scaler placement method and system under urban complex environment Download PDF

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CN113640758A
CN113640758A CN202110966953.3A CN202110966953A CN113640758A CN 113640758 A CN113640758 A CN 113640758A CN 202110966953 A CN202110966953 A CN 202110966953A CN 113640758 A CN113640758 A CN 113640758A
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corner reflector
angle
azimuth
setting
corner
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CN113640758B (en
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张波
姜文
温晓阳
孙春玲
许璐
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Aerospace Information Research Institute of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/904—SAR modes
    • G01S13/9076—Polarimetric features in SAR
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/40—Means for monitoring or calibrating

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Abstract

The invention provides a method and a system for placing an SAR image scaler in a complex urban environment. Wherein the method comprises: selecting the position of the corner reflector and setting the posture of the corner reflector; the method of selection of the corner reflector position comprises: according to a beam visual angle phi of the SAR sensor, calculating a front overlapping area and a rear shadow area of ground objects around a place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in a building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector; the method for setting the posture of the corner reflector comprises the following steps: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment. The azimuth setting and the angle of the SAR image are stabilized, and the quality of the SAR image is improved.

Description

SAR image scaler placement method and system under urban complex environment
Technical Field
The invention relates to the technical field of intelligent document classification and classification, in particular to a method and a system for placing an SAR image scaler in a complex urban environment.
Background
Synthetic Aperture Radars (SAR) can be mounted on a satellite platform or an airborne platform, emit coherent electromagnetic waves with different polarization modes laterally on a flight path, irradiate the ground, receive and record the intensity and phase of the electromagnetic waves reflected back to a receiving antenna, and generate an SAR image after imaging processing. The SAR image contains three types of information including intensity, polarization and phase. After calibration, generating qualified SAR image product
At present, a scaler is placed on the ground to calibrate the measurement quantities such as the SAR image intensity, the phase, the polarization and the like so as to correct the system error of the SAR sensor. Commonly used scalers are a dihedral angle scaler and a dihedral angle scaler. The dihedral angle calibrator is commonly used for calibrating scattering intensity errors of the SAR image, and the dihedral angle is used for calibrating polarization errors in the SAR image, including polarization crosstalk, polarization imbalance and polarization phase difference. The placement of the scaler is usually selected in an open place, buildings, trees and the like do not exist in the area, and the ground is relatively flat. Therefore, airport areas and field farmlands are generally preferred locations. The regions can be used for completing the arrangement of the corner reflector by utilizing a geological compass, an inclinometer and the like. With the resolution of the SAR image being improved to a sub-meter level, the independent trees and small vehicles have become the target of interest in the SAR image. The application of SAR images also comes to the quantification phase. The method is an important direction for future market development by utilizing manned, unmanned and satellite-borne SAR to image a small area range and acquiring a quantitative SAR image of an attention target. In these small areas, there is often no large open space for the placement of the dihedral corner reflectors. In a complex scene such as a city, the geological compass may cause interference to the normal operation of the compass due to surrounding magnetic equipment, power transmission lines, power generation devices, voltage transformation equipment and the like, and how to select the placement position of the corner reflector in a complex environment by using equipment such as a portable GPS and a goniometer and realize the high-precision placement of the corner reflector is a problem to be solved by the patent.
The prior art is as follows:
1) open field placing corner reflector
The existing corner reflectors are mostly placed in open places such as airport open lands, farmlands, lawns and the like. There is not much restriction on the place where the corner reflectors are placed, since there are no buildings, trees, etc. around the field. The angular reflections are kept as far apart as possible in order not to influence each other. There is a lack of distance and orientation quantification requirements for interference between corner reflectors.
2) The azimuth measurement is carried out based on the compass, the angle difference between the magnetic north direction and the geographical north direction of the corner reflector is called magnetic declination, the magnetic declination of each place is different, and the local magnetic declination can be obtained by looking up the table. The angle taking the magnetic north direction as the initial direction can be conveniently obtained by utilizing the geological compass, and the azimuth acquisition taking the geographical north direction as the calculation angle can be realized by introducing the correction quantity of the local magnetic declination. The azimuth measurement and lofting can be realized by utilizing the geological compass in an open area without interference of communication equipment and power equipment.
The prior art has the following defects:
1) the condition that the corner reflector is required to be placed in an open area is difficult to meet with the marketization development of the manned and unmanned SAR and the detection target area of the urban area with dense human inhabitation. Under the complex environment with a limited field area, no solution is provided in the traditional scheme on how to select a proper corner reflector to place the field to avoid the sheltering of trees and buildings around the field and avoid the overlapping area formed by the height of the trees and the buildings. This will be one of the problems that this patent will solve.
2) The azimuth measurement is carried out by utilizing the geological compass, which is influenced by the correction accuracy of the declination in the traditional method and is also influenced by the surrounding electronic transmission lines and communication devices in the complex environment like a city. These influencing factors will cause the azimuth measurement accuracy of the compass to be unstable, and cannot meet the azimuth lofting requirement in the urban environment. For the convenience of carrying, this patent proposes to utilize the measuring method that a single GPS measuring equipment carries out azimuth angle lofting to solve.
Disclosure of Invention
The invention aims to provide a method and a system for placing an SAR image scaler in a complex urban environment, so as to solve the technical problems in the prior art.
The invention provides a method for placing an SAR image scaler in an urban complex environment, which comprises the following steps: selecting the position of the corner reflector and setting the posture of the corner reflector;
the method of selection of the corner reflector position comprises: according to the beam view angle of the SAR sensor, calculating a front overlap area and a rear shadow area of ground objects around the place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in the building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector;
the method for setting the posture of the corner reflector comprises the following steps: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
In some embodiments, specifically, the method for calculating the front overlap region includes:
Figure BDA0003224449650000031
wherein the content of the first and second substances,
Lfindicating the length of the front overlap zone;
h represents the height of the ground object;
θprepresenting the local angle of incidence of the radar.
In some embodiments, specifically, the calculation method of the rear shadow region includes:
Ls＝H·tan(θp)
wherein the content of the first and second substances,
Lsindicating the length of the back shaded area.
In some embodiments, in particular, the method further comprises: the angle reflector and the ground object keep a certain deviation distance in the azimuth direction as follows:
Figure BDA0003224449650000032
wherein the content of the first and second substances,
Figure BDA0003224449650000033
representing the field angle of the radar aperture, the SAR is imaged in the azimuth direction through the synthetic aperture;
l represents the distance between the corner reflector and the ground object.
In some embodiments, in particular, the method of calculating the strong scattering impact region comprises:
decomposing the building structure into three-plane angle scattering and two-plane angle scattering, and estimating the peak value of the scattering intensity;
the spread of the scattering intensity can be estimated according to a sinc function; the scattering intensity will also decrease as the sinc function extends in the azimuth direction and the range direction; when the ratio of the scattering intensity to the intensity of the placed corner reflector is less than-20 db, this region is the safe region for placing the corner reflector.
In some embodiments, in particular, the corner reflector comprises: a dihedral corner reflector, a horizontal dihedral corner reflector, and an inclined dihedral corner reflector; the placing method further comprises the following steps: firstly, determining the track azimuth direction of a radar on the ground, and then determining the pitch angle and the roll angle of a corner reflector; the method for determining the track azimuth direction comprises the following steps: the track azimuth is realized by a single GPS receiver with RTK function; deducing the linear length of lofting through a positioning measurement error and an error propagation law of a GPS, wherein the specific method comprises the following steps:
firstly, selecting a first fixed point on a ground plane to carry out GPS measurement to obtain a geographical projection coordinate of the first fixed point;
secondly, calculating the geographical projection coordinate of another second fixed point which is 5 meters away from the first fixed point according to the obtained azimuth angle;
finally, the positions of the first and second fixing points are marked on the ground, and a straight line between the two points is marked.
In some embodiments, in particular, the method for setting the posture of the dihedral corner reflector includes:
step a 1: adjusting the azimuth angle: the long edge of the bottom surface of the three-sided corner reflector is coincided with the straight line of the lofting mark;
step a 2: adjusting a pitch angle: adjusting the pitch angle of the bottom surface of the dihedral corner reflector by raising the height of the bottom surface;
step a 3: adjusting the rolling angle: adjusting the rolling angle by adjusting the heights of two points of the long side of the bottom surface of the three-surface corner reflector;
step a 4: respectively suspending plumbs at two points of the long side of the bottom surface of the three-sided corner reflector, so that the plumbs pass through the straight line of the lofting mark, and the long side of the bottom surface of the three-sided corner reflector with the pitch angle is superposed with the straight line of the azimuth lofting;
step a 5: repeating the steps a2-a4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
In some embodiments, in particular, the method of setting the attitude of the horizontal dihedral corner reflector is the same as the method of setting the attitude of the dihedral corner reflector.
In some embodiments, specifically, the method of setting the attitude of the tilted dihedral corner reflector includes:
step c 1: using a GPS and a deflection angle between the long edge of the bottom surface of the inclined dihedral corner reflector obtained by three-dimensional coordinate rotation calculation and the track azimuth direction, lofting the straight line with the deflection angle corrected on the ground and marking;
step c 2: adjusting the azimuth angle: the long edge of the bottom surface of the angular inclined dihedral corner reflector is coincided with the straight line of the lofting mark;
step c 3: adjusting a pitch angle: adjusting the pitch angle of the bottom surface by raising the height of the bottom surface;
step c 4: adjusting a rolling angle;
step c 5: and repeating the steps c2-c4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
The second aspect of the present invention provides a system for placing SAR image scaler in urban complex environment, comprising: the device comprises a selection module of a position of a corner reflector and a setting module of the attitude of the corner reflector;
the corner reflector position selection module: according to the beam view angle of the SAR sensor, calculating a front overlap area and a rear shadow area of ground objects around the place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in the building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector;
the attitude setting module of the corner reflector comprises: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:
1) and technical support is provided for the quantitative development of the man-machine or unmanned SAR carried by the airplane. The field selection principle provided by the invention can provide support for setting up a calibration scheme for placing the calibrator in the complex area. The method provides a key step for improving the quality of the airborne SAR image in the urban area.
2) The stable and convenient technical scheme is provided for the key azimuth setting and the angle setting which determine success or failure in SAR image calibration by utilizing the manual scaler. The placement of various corner reflectors such as a three-plane corner, a horizontal two-plane corner and an inclined two-plane corner is completed only by using a conventional instrument GPS, an inclinometer and a plumb.
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In the drawings, which are not necessarily drawn to scale, like reference numerals may describe similar components in different views. Like reference numerals having letter suffixes or different letter suffixes may represent different instances of similar components. The drawings illustrate various embodiments generally by way of example and not by way of limitation, and together with the description and claims serve to explain the disclosed embodiments. The same reference numbers will be used throughout the drawings to refer to the same or like parts, where appropriate. Such embodiments are illustrative, and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.
FIG. 1 is a flowchart of a method for placing an SAR image scaler in a complex urban environment according to the present invention;
FIG. 2 is a graph showing the selection of the length and orientation of the overlap and shadow zones for the upper corner reflector used in the present invention;
FIG. 3 is a diagram of the azimuth, pitch, and roll angle settings for the placement of a dihedral corner reflector used in the present invention;
FIG. 4 is a diagram of the azimuth, pitch, and roll angle settings for the placement of a tilted dihedral corner reflector used in the present invention;
FIG. 5 is a table of scattering intensity peaks for each type of dihedral and dihedral angle used in the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, these information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present invention. The word "if" as used herein may be interpreted as "at … …" or "when … …" or "in response to a determination", depending on the context.
Example 1:
the embodiment provides a method for placing an SAR image scaler in a city complex environment, which comprises the following steps: selecting the position of the corner reflector and setting the posture of the corner reflector;
the method for selecting the position of the corner reflector comprises the following steps: according to the beam view angle of the SAR sensor, calculating a front overlap area and a rear shadow area of ground objects around the place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in the building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector;
the method for setting the posture of the corner reflector comprises the following steps: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
In some embodiments, the method for calculating the specific address, front overlap region comprises:
Figure BDA0003224449650000071
wherein the content of the first and second substances,
Lfindicating the length of the front overlap zone;
h represents the height of the ground object;
θprepresenting the local angle of incidence of the radar.
Further, the calculation method of the rear shadow region comprises the following steps:
Ls＝H·tan(θp)
wherein the content of the first and second substances,
Lsindicating the length of the back shaded area.
The angle reflector and the ground object keep a certain deviation distance in the azimuth direction as follows:
Figure BDA0003224449650000081
wherein the content of the first and second substances,
Figure BDA0003224449650000082
representing the field angle of the radar aperture, the SAR is imaged in the azimuth direction through the synthetic aperture;
l represents the distance between the corner reflector and the ground object.
According to the above method, further, the method for calculating the strong scattering influence region includes:
decomposing the building structure into three-plane angle scattering and two-plane angle scattering, and estimating the peak value of the scattering intensity;
the spread of the scattering intensity can be estimated according to a sinc function; the scattering intensity of the sinc function is reduced along with the extension of the azimuth direction and the distance direction; when the ratio of the scattering intensity compared to the intensity of the placed corner reflector is less than-20 db, this area is the safe area for placing the corner reflector.
In some embodiments, the corner reflector comprises: a dihedral corner reflector, a horizontal dihedral corner reflector, and an inclined dihedral corner reflector; the placing method further comprises the following steps: firstly, determining the track azimuth direction of a radar on the ground, and then determining the pitch angle and the roll angle of a corner reflector; the method for determining the track azimuth direction comprises the following steps: the track azimuth is realized by a single GPS receiver with RTK function; deducing the linear length of lofting through a positioning measurement error and an error propagation law of a GPS, wherein the specific method comprises the following steps:
firstly, selecting a first fixed point on a ground plane to carry out GPS measurement to obtain a geographical projection coordinate of the first fixed point;
secondly, calculating the geographical projection coordinate of a second fixed point at another point 5 meters away from the first fixed point according to the obtained azimuth angle;
finally, the positions of the first and second fixing points are marked on the ground, and a straight line between the two points is marked.
In some embodiments, it is preferable that the method for setting the posture of the dihedral corner reflector includes:
step a 1: adjusting the azimuth angle: the long edge of the bottom surface of the three-sided corner reflector is coincided with the straight line of the lofting mark;
step a 2: adjusting a pitch angle: adjusting the pitch angle of the bottom surface of the three-surface corner reflector by increasing the height of the bottom surface;
step a 3: adjusting the rolling angle: adjusting the rolling angle by adjusting the heights of two points of the long side of the bottom surface of the three-surface corner reflector;
step a 4: respectively suspending plumbs at two points of the long side of the bottom surface of the three-sided corner reflector, so that the plumbs pass through the straight line of the lofting mark, and the long side of the bottom surface of the three-sided corner reflector with the pitch angle is superposed with the straight line of the azimuth lofting;
step a 5: repeating the steps a2-a4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
The method of setting the attitude of the horizontal dihedral corner reflector is the same as the method of setting the attitude of the dihedral corner reflector.
According to the above method, specifically, the method of setting the attitude of the oblique dihedral corner reflector includes:
step c 1: using a GPS and a deflection angle between the long edge of the bottom surface of the inclined dihedral corner reflector obtained by three-dimensional coordinate rotation calculation and the track azimuth direction, lofting the straight line with the deflection angle corrected on the ground and marking;
step c 2: adjusting the azimuth angle: the long edge of the bottom surface of the angular inclined dihedral corner reflector is coincided with the straight line of the lofting mark;
step c 3: adjusting a pitch angle: adjusting the pitch angle of the bottom surface by increasing the height of the bottom surface;
step c 4: adjusting a rolling angle;
step c 5: and repeating the steps c2-c4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
Example 2:
according to the method described in embodiment 1, this embodiment applies the scheme described in embodiment 1 according to a specific background and an application scenario, and as shown in fig. 1, specifically provides a method for placing an SAR image scaler in an urban complex environment, including:
selecting the position of the corner reflector and setting the posture of the corner reflector;
the method of selection of the corner reflector position comprises: according to a beam visual angle phi of the SAR sensor, calculating a front overlapping area and a rear shadow area of ground objects around a place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in a building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector;
the method for setting the posture of the corner reflector comprises the following steps: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle phi of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
As shown in fig. 2, the SAR sensor is used for strabismus ranging imaging, so that a shadow area facing the radar irradiation direction and away from the radar irradiation direction appears on the SAR image for a ground object (such as a building, a tree, etc.) with a height H. Imaging length and ground object height H of the areas on the SAR image and local incidence angle theta of the radarpIt is related.
In some embodiments, the method of calculating the front overlap region comprises:
Figure BDA0003224449650000101
wherein the content of the first and second substances,
Lfindicating the length of the front overlap zone;
h represents the height of the ground object;
θprepresenting the local angle of incidence of the radar;
the calculation method of the rear shadow region comprises the following steps:
Ls＝H·tan(θp)
wherein the content of the first and second substances,
Lsindicating the length of the back shaded area.
As shown in fig. 2, if the ground object has an angle H and the distance is L, the corner reflector should be kept at the offset distance L from the ground object in the azimuth direction to avoid the corner reflector from being blocked by the building in the azimuth directionA。
In some embodiments, the offset distance L is maintainedAThe calculating method comprises the following steps: the distance deviation between the corner reflector and the ground object in the azimuth direction is as follows:
Figure BDA0003224449650000111
wherein the content of the first and second substances,
Figure BDA0003224449650000112
representing the field angle of the radar aperture, the SAR is imaged in the azimuth direction through the synthetic aperture;
l represents the distance between the corner reflector and the ground object.
As shown in fig. 2, the outer shape of the building can be generally regarded as a cubic structure, and the scattering shape and scattering intensity of the building are relatively regular, so that the boundary and area of the overlap and shadow area can be easily predicted. However, in modern city construction, more and more special buildings are pursued, and the external structures of the buildings mostly contain dihedral angle and dihedral angle scattering structures such as an outer corridor and a landscape platform, or the external structures contain metal decoration or neon lamp devices, the top of the buildings is provided with a water tower box, an air conditioner cluster and the like. The special geometric structures and metal materials are easy to generate strong scattering in SAR imaging of buildings, and the strong scattering can generate bright areas or bright lines in the direction and the distance of the SAR image. Because the fine three-dimensional structure model of the building body is difficult to master, whether the position of the strong scattering and the strong scattering range exceed the whole overlapping and shading area of the building is difficult to judge.
If the fine structure model of the building is known, or its particular structure can be measured or estimated in the field. As shown in fig. 5, these structures can be decomposed into three-plane scattering and two-plane scattering, and the peak intervals of the scattering intensities can be estimated. The three-plane scattering specifically includes: right-angled, rectangular, and fan-shaped; the peak value of the scattering intensity of the right-angle shape is 4 pi a4/3λ2The peak value of the scattering intensity of the rectangle is 12 pi a4/3λ2The peak value of the scattering intensity of the sector is 15.6a4/3λ2；
The peak value of the scattering intensity of the dihedral angle scattering is 8 pi wh/lambda2Wherein w and h are the width and length of the dihedral angle respectively.
In some embodiments, the method of calculating the strong scattering influence region includes:
decomposing the building structure into three-plane angle scattering and two-plane angle scattering, and estimating the peak value of the scattering intensity;
the spread of the scattering intensity can be estimated according to a sinc function; the scattering intensity will also decrease as the sinc function extends in the azimuth direction and the range direction; when the ratio of the scattering intensity to the intensity of the placed corner reflector is less than-20 db, this region is the safe region for placing the corner reflector.
To summarize: SAR is a two-dimensional image that can be decomposed into a range direction and an azimuth direction. The strong scattering formed by the formation always reacts as: and the distance direction or the azimuth direction is expanded at the position of the ground object. Therefore, the corner reflectors should be placed to avoid being in the same azimuth area or the same distance area as the odd-shaped building body. As in fig. 2, the corner reflector should be placed azimuthally away from the building LA, except for the overlap and shadow areas that avoid the building. Aiming at odd-shaped buildings, the whole azimuth direction and the distance direction of an imaging body of the odd-shaped buildings are avoided, and the specific avoiding distance is estimated according to the intensity attenuation of the Sinc function.
In some embodiments, the corner reflector comprises: a dihedral corner reflector, a horizontal dihedral corner reflector, and an inclined dihedral corner reflector;
when the corner reflector is placed on the ground, as shown in fig. 3, there are three angles to be adjusted. Comprises the following steps: azimuth angle, pitch angle, roll angle. In fig. 3, a planar rectangular coordinate system is first established, the x-axis points to the geographical north direction, the z-axis points to the zenith direction, and the y-axis and the xz-axis form a right-handed system. The azimuth angle of the three-plane angle and the two-plane angle is the long side A of the bottom surface on the oxy plane1B1The angle between the x-axis. The pitch angles of the three-plane angle and the two-plane angle refer to angular reflection.
The important principle of the arrangement of the corner reflector is to make the main axis direction of the radar wave coincide with the main axis direction of the corner reflector. For a dihedral corner reflector, the major axis makes an angle of 35.26 degrees with the bottom surface. For dihedral angles, the included angle between the principal axis and the bottom surface is 45 degrees, and is perpendicular to the intersection line of the two dihedral angles.
The method for setting the posture of the corner reflector further comprises the following steps: firstly, determining the track azimuth direction of a radar on the ground, and then determining the pitch angle and the roll angle of a corner reflector; the method for determining the track azimuth direction comprises the following steps: the plane positioning precision of the GPS receiver with the RTK function can reach +/-2 cm, and the elevation direction is +/-5 cm. The track azimuth can be realized by a single GPS receiver with RTK function, so that the labor cost and the material resource cost in field measurement are saved. And the determined direction directly takes the geographical north direction (oy axis) as a starting direction, so that declination correction in lofting measurement according to a compass and the influence of electric equipment and magnetic equipment are avoided. According to the calculation of the error propagation rate in the measurement, when the lofting distance between two points is more than 5 meters, the reverse calculation error of the azimuth angle of the GPS equipment with the positioning measurement error of 0.2 cm can be controlled within 0.1 degree. When the course azimuth lofting is carried out, the method can be carried out according to the following steps:
first, a fixed point P is selected on the ground level1Carrying out GPS measurement to obtain a geographical projection coordinate of the GPS; secondly, calculating the distance P through the obtained azimuth angle1Another point P other than 5 m2The geographical projection coordinates of (a); finally, in the ground plane P1And P2And marks a straight line between the two points.
As shown in fig. 3, the three-sided corner reflector is mounted with its orientation set primarily based on the lofted line P1P2, and its roll and pitch angles set primarily based on the inclinometer.
In some embodiments, the method for setting the attitude of the dihedral corner reflector includes:
step a 1: adjusting the azimuth angle: the long edge of the bottom surface of the three-sided corner reflector is coincided with the straight line of the lofting mark; i.e. the long side A of the bottom surface of the corner reflector1B1And P1P2Overlapping;
step a 2: adjusting a pitch angle: adjusting the pitch angle of the bottom surface of the trihedral corner reflector by raising the height of said bottom surface, i.e. by raising A1B1Or C1And adjusting the pitch angle of the bottom surface. Specifically, the inclinometer can be placed on the bottom surface and connected with the edge A1B1Are perpendicular to each other. When the inclinometer has a reading of E1＝90°-θp-35.26°＝54.74°-θpWhen it is stopped, lifting A1B1Or C1The height of (d);
step a 3: adjusting the rolling angle: the roll angle is adjusted by adjusting the height of two points on the long side of the bottom surface of the three-sided corner reflector, i.e. the inclinometer is placed on the bottom surface and connected with the edge A1B1Are parallel. By adjusting A1Or B1Such that the inclinometer reads 0;
step a 4: respectively suspending the plumb at two points of the long side of the bottom surface of the three-sided corner reflector to enable the plumb to pass through the straight line of the lofting mark, and realizing the superposition of the long side of the bottom surface of the three-sided corner reflector with the pitch angle and the straight line of the azimuth lofting, namely at A1And B1Separately hanging the plumb hammers at the positions so that the plumb hammers pass through P1P2A wire. To achieve having pitchLong side A of the bottom plate of the corner1B1And the direction P1P2Overlapping;
step a 5: repeating the steps a2-a4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
As shown in fig. 3, in performing polarization scaling of the SAR image, a horizontal dihedral angle and a rotational dihedral angle are commonly used scalers. For the setting of the horizontal dihedral angle, the procedure is the same as that of the setting of the dihedral angle. However, in the second step of pitch adjustment, the reading of the tilt instrument should be E2＝90°-θp-45°＝54-θp。
The oblique dihedral angle means that the dihedral angle in fig. 4 is rotated by η degrees around the principal axis of the dihedral angle. The dihedral angle at 45 degrees η is commonly used to scale the cross-polarization path in polarized SAR images.
When the dihedral angle is actually placed, since the inclined reference axis is the major line of sight (LOS) of the dihedral angle, the long side a of the bottom surface is rotated1B1The angle to the x-axis no longer coincides with the heading orientation. It is necessary to first determine the long side A of the bottom surface after rotation1B1The included angle between the inclined dihedral angle bottom plate and the flight path direction also needs to be determined1C1The pitch angle alpha relative to the horizontal plane, and finally the bottom edge A of the inclined dihedral angle1B1Or C1D1Angle of rotation beta with respect to the ground plane (plane oxz). When these three angles are determined, the oblique dihedral angles can be manipulated in the actual layout.
Firstly, a local coordinate system of an inclined dihedral angle is established
Figure BDA0003224449650000141
Wherein
Figure BDA0003224449650000142
The axis is in line with the track direction, the z-axis points to the zenith direction, the y-axis is in line with
Figure BDA0003224449650000143
The shaft constitutes a right-hand system. In that
Figure BDA0003224449650000144
The following three angles can be calculated in the coordinate system by using a three-axis rotation method so as to directly aim at the ground mark line by using a plumb bob and directly measure the inclination angle by using an inclinometer: (1) dihedral corner bottom plate middle edge A1B1Relative to heading azimuth
Figure BDA0003224449650000145
Angle of declination ω. (2) Pitch angle alpha when inclined dihedral angle is finally settled (dihedral angle bottom plate middle edge B1C1Relative to the horizontal plane
Figure BDA0003224449650000146
The clamping foot of (3) a rolling angle beta (a middle edge A of a dihedral angle bottom plate)1B1Or C1D1For the horizontal plane
Figure BDA0003224449650000147
The included angle of (d).
In some embodiments, the method of setting the attitude of the tilted dihedral corner reflector includes:
step c 1: using GPS and the deflection angle between the long edge of the bottom surface of the inclined dihedral corner reflector and the track azimuth obtained by three-dimensional coordinate rotation calculation to the ground, lofting the straight line with the deflection angle corrected on the ground and marking, namely using GPS and the deflection angle omega obtained by three-dimensional coordinate rotation calculation, lofting P on the ground1P2Marking;
step c 2: adjusting the azimuth angle: the long edge of the bottom surface of the angular inclined dihedral corner reflector is coincided with the straight line of the lofting mark, namely the long edge A of the bottom surface of the dihedral corner reflector is coincided by a plumb bob1B1And P1P2Overlapping;
step c 3: adjusting a pitch angle: by raising the height of said bottom surface, the pitch angle of the bottom surface is adjusted, i.e. by raising or lowering A1B1And adjusting the pitch angle of the bottom surface. Specifically, the inclinometer can be placed on the edge A1B1Or A1D1When the inclinometer is aboveWhen the reading is alpha, stopping lifting A1B1The height of (d);
step c 4: adjusting the rolling angle: particularly, the inclinometer is arranged at E1F1By adjusting the edge A1D1Such that the inclinometer reads beta;
step c 5: and repeating the steps c2-c4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
Example 3:
according to the scheme, the invention also provides a system for placing the SAR image scaler in the urban complex environment,
the method comprises the following steps: the device comprises a selection module of a position of a corner reflector and a setting module of the attitude of the corner reflector.
The corner reflector position selection module: according to a beam visual angle phi of the SAR sensor, calculating a front overlapping area and a rear shadow area of ground objects around a place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in a building outline structure; and avoiding the influence areas, and selecting the placement position of the corner reflector.
The attitude setting module of the corner reflector comprises: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle phi of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
Moreover, although exemplary embodiments have been described herein, the scope thereof includes any and all embodiments based on the present application with equivalent elements, modifications, omissions, combinations (e.g., of various embodiments across), adaptations or alterations. The elements of the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. It is intended, therefore, that the specification and examples be considered as exemplary only, with a true scope and spirit being indicated by the following claims and their full scope of equivalents.
The above description is intended to be illustrative and not restrictive. For example, the above-described examples (or one or more versions thereof) may be used in combination with each other. For example, other embodiments may be used by those of ordinary skill in the art upon reading the above description. In addition, in the above detailed description, various features may be grouped together to streamline the application. This should not be interpreted as an intention that a disclosed feature not claimed is essential to any claim. Rather, subject matter of the present application can lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that these embodiments may be combined with each other in various combinations or permutations. The scope of the application should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
The above embodiments are only exemplary embodiments of the present application, and are not intended to limit the present application, and the protection scope of the present application is defined by the claims. Various modifications and equivalents may be made by those skilled in the art within the spirit and scope of the present application and such modifications and equivalents should also be considered to be within the scope of the present application.

Claims (10)

1. A SAR image scaler placement method under a complex urban environment is characterized by comprising the following steps: selecting the position of the corner reflector and setting the posture of the corner reflector;
the method of selection of the corner reflector position comprises: according to the beam view angle of the SAR sensor, calculating a front overlap area and a rear shadow area of ground objects around the place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in the building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector;
the method for setting the posture of the corner reflector comprises the following steps: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
2. The SAR image scaler placement method under the urban complex environment of claim 1, wherein said front overlap area calculation method comprises:
Figure FDA0003224449640000011
wherein the content of the first and second substances,
Lfindicating the length of the front overlap zone;
h represents the height of the ground object;
θprepresenting the local angle of incidence of the radar.
3. The SAR image scaler placement method under the urban complex environment according to claim 2, wherein said method for calculating the back shadow comprises:
Ls＝H·tan(θp)
wherein the content of the first and second substances,
Lsindicating the length of the back shaded area.
4. The SAR image scaler placement method under urban complex environment according to claim 2, characterized in that said method further comprises: the angle reflector and the ground object keep a certain deviation distance in the azimuth direction as follows:
Figure FDA0003224449640000021
wherein the content of the first and second substances,
theta represents the field angle of the radar aperture, and SAR images through the synthetic aperture in the azimuth direction;
l represents the distance between the corner reflector and the ground object.
5. The SAR image scaler placement method under urban complex environment of claim 1, wherein the calculation method of the strong scattering impact area comprises:
decomposing the building structure into three-plane angle scattering and two-plane angle scattering, and estimating the peak value of the scattering intensity;
the spread of the scattering intensity can be estimated according to a sinc function; the scattering intensity will also decrease as the sinc function extends in the azimuth direction and the range direction; when the ratio of the scattering intensity to the intensity of the placed corner reflector is less than-20 db, this region is the safe region for placing the corner reflector.
6. The SAR image scaler placement method under urban complex environment according to claim 1, wherein said corner reflector comprises: a dihedral corner reflector, a horizontal dihedral corner reflector, and an inclined dihedral corner reflector; the placing method further comprises the following steps: firstly, determining the track azimuth direction of a radar on the ground, and then determining the pitch angle and the roll angle of a corner reflector; the method for determining the track azimuth direction comprises the following steps: the track azimuth is realized by a single GPS receiver with RTK function; deducing the linear length of lofting through a positioning measurement error and an error propagation law of a GPS, wherein the specific method comprises the following steps:
firstly, selecting a first fixed point on a ground plane to carry out GPS measurement to obtain a geographical projection coordinate of the first fixed point;
secondly, calculating the geographical projection coordinate of a second fixed point at another point 5 meters away from the first fixed point according to the obtained azimuth angle;
finally, the positions of the first and second fixing points are marked on the ground, and a straight line between the two points is marked.
7. The SAR image scaler placement method under urban complex environment of claim 6, wherein the method for setting the pose of the dihedral corner reflector comprises:
step a 1: adjusting the azimuth angle: the long edge of the bottom surface of the three-sided corner reflector is coincided with the straight line of the lofting mark;
step a 2: adjusting a pitch angle: adjusting the pitch angle of the bottom surface of the dihedral corner reflector by raising the height of the bottom surface;
step a 3: adjusting the rolling angle: adjusting the rolling angle by adjusting the heights of two points of the long side of the bottom surface of the three-surface corner reflector;
step a 4: respectively suspending plumbs at two points of the long side of the bottom surface of the three-sided corner reflector, so that the plumbs pass through the straight line of the lofting mark, and the long side of the bottom surface of the three-sided corner reflector with the pitch angle is superposed with the straight line of the azimuth lofting;
step a 5: repeating the steps a2-a4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
8. The SAR image scaler placement method under urban complex environment of claim 7, wherein the setting method of the pose of the horizontal dihedral corner reflector is the same as the setting method of the pose of the trihedral corner reflector.
9. The SAR image scaler placement method under urban complex environment of claim 8, wherein the method for setting the pose of the tilted dihedral corner reflector comprises:
step c 1: using a GPS and a deflection angle between the long edge of the bottom surface of the inclined dihedral corner reflector obtained by three-dimensional coordinate rotation calculation and the track azimuth direction, lofting the straight line with the deflection angle corrected on the ground and marking;
step c 2: adjusting the azimuth angle: the long edge of the bottom surface of the angular inclined dihedral corner reflector is coincided with the straight line of the lofting mark;
step c 3: adjusting a pitch angle: adjusting the pitch angle of the bottom surface by raising the height of the bottom surface;
step c 4: adjusting a rolling angle;
step c 5: and repeating the steps c2-c4 to gradually refine the azimuth angle, the pitch angle and the roll angle to preset angles.
10. A SAR image scaler placement system under urban complex environment, characterized in that, the system comprises: the device comprises a selection module of a position of a corner reflector and a setting module of the attitude of the corner reflector;
the corner reflector position selection module: according to the beam view angle of the SAR sensor, calculating a front overlap area and a rear shadow area of ground objects around the place where the corner reflector is to be placed, and a strong scattering influence area caused by a similar angle reflection part in the building outline structure; avoiding the influence areas, and selecting the placing position of the corner reflector;
the attitude setting module of the corner reflector comprises: and calculating azimuth angles, pitch angles and rolling angles of different types of corner reflectors according to the track azimuth direction of the sensor platform and the beam viewing angle of the SAR sensor, and setting the postures of the corner reflectors according to an inclinometer and single-station GPS measuring equipment.
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