KR102530834B1 - Apparatus and method to estimate a geodetic coordinate of synthetic aperture radar image - Google Patents

Abstract

It relates to a method for estimating the geodetic coordinates of a coordinate estimation point in an SAR image obtained from an imaging radar platform, which includes (a) lookup of relational information between a nadir angle and an inclination distance corresponding to the nadir angle Creating a table; and (b) estimating the geodetic coordinates of the coordinate estimation point, which is a target of geodetic coordinate estimation, using the lookup table.

Description

Apparatus and method for estimating geodetic coordinates of imaging radar images {APPARATUS AND METHOD TO ESTIMATE A GEODETIC COORDINATE OF SYNTHETIC APERTURE RADAR IMAGE}

The present application relates to an apparatus and method for estimating geodetic coordinates of a Sythetic Aperture Radar (SAR) image. In particular, the present application is a coordinate estimation point in the SAR image that can convert coordinates in the SAR image obtained from the SAR platform (ie, coordinates on the radar coordinate system for the coordinate estimation point in the SAR image) into coordinates on the geodetic coordinate system. It relates to a device and method for estimating geodetic coordinates.

In order to acquire images from the Sythetic Aperture Radar (SAR), the SAR platform (satellite, aircraft, UAV, etc.) moves at a higher altitude than the target area at a constant velocity and transmits a preset signal in a side-looking state to the transmitting antenna. It transmits through, collects echo signals reflected from the surface (target area), receives them with a receiving antenna, and processes the collected reflected signals to acquire images. At this time, the coordinate system of the generated (acquired) image (SAR image) is the radar coordinate system (distance direction, azimuth direction). Here, the distance direction means the slope distance between the SAR platform and the target area, and is not a coordinate system formed at regular intervals on the actual ground surface. Therefore, in order to project an image (SAR image) acquired from SAR onto the actual ground surface, coordinates corresponding to the geodetic coordinate system of the acquired image must be estimated.

In the case of a generally provided SAR image, only the coordinates of the four vertexes of the SAR image are provided. On the other hand, in order to develop a SAR system or use SAR images for geometric correction, image matching, and change detection, it is essential to convert the coordinates on the radar coordinate system for the corresponding SAR image into the geodetic coordinate system.

As an example of a method for estimating geodetic coordinates, there is a method using a GCP (Ground Control Point), which is a corresponding point between the radar coordinate system and the geographic coordinate system, and this is a process of setting the GCP corresponding to the geographic coordinates in the image coordinates composed of image pixels. Geometry correction is performed through the coordinate system conversion of GCP and GCP. This method is mainly used in optical radar. It is difficult to distinguish GCPs due to the influence of speckle noise in SAR images, and it is not easy to map images between different satellites in SAR images, thus obtaining high accuracy and reliability. It is very difficult.

Another method of estimating the coordinates of the geodetic coordinate system is to obtain a solution for the geodetic coordinate system by solving three nonlinear simultaneous equations composed of the range-Doppler equation and the earth ellipsoid model with the Doppler center estimation method, which is relatively complex. There are downsides.

Therefore, it is required to develop a technique for estimating an image (SAR image) obtained from SAR with coordinates corresponding to a geodetic coordinate system with a simpler and higher accuracy.

The background technology of the present application is disclosed in Korean Patent Publication No. 10-2013-0004227.

The present invention is to solve the above-mentioned problems of the prior art, and the geodetic coordinates of the coordinate estimation point in the SAR image that can estimate the image (SAR image) obtained from SAR with coordinates corresponding to the geodetic coordinate system more simply and with high accuracy An object of the present invention is to provide an estimation device and method.

However, the technical problem to be achieved by the embodiments of the present application is not limited to the technical problems described above, and other technical problems may exist.

As a technical means for achieving the above technical problem, a method for estimating the geodetic coordinates of coordinate estimation points in a SAR image obtained from a Synthetic Aperture Radar (SAR) platform according to an embodiment of the present invention includes (a) nadir angle generating relationship information between (Nadir angle) and an inclination distance corresponding to the nadir angle as a lookup table; and (b) estimating the geodetic coordinates of the coordinate estimation point, which is a target of geodetic coordinate estimation, using the lookup table.

In addition, the step (a) may include: (a1) receiving input data including the position and speed of the SAR platform and the nadir angle of a point on the ground where the signal transmitted from the SAR platform is reflected; (a2) setting a flight coordinate system of the SAR platform using the input data; (a3) generating a coordinate transformation matrix between the flight coordinate system and an Earth-Centered Earth-Fixed (ECEF) coordinate system; (a4) estimating a view vector that is a visual direction unit vector from the SAR platform to a point on the ground using the coordinate transformation matrix generated in step (a3); and (a5) estimating an inclination distance corresponding to the nadir angle input in step (a1) using the view vector estimated in step (a4).

In addition, in the step (a), the nadir angle is changed at a preset angular interval with respect to the allowable nadir angle range, the changed nadir angle is applied as the input data, and steps (a1) to (a5) are repeated. The lookup table may be generated by performing the above, and the repeated execution may be performed until the changed nadir angle exceeds the maximum value of the nadir angle allowable range.

In addition, the step (b) includes (b1) measurement including the measured position and speed of the SAR platform, and the measured inclination distance measured from the position of the SAR platform to the estimated coordinate point on the ground corresponding to the estimated coordinate point. receiving data input; (b2) based on the measurement data, estimating a nadir angle for the estimated coordinate point on the land surface using the lookup table; (b3) setting a flight coordinate system of the SAR platform and generating a coordinate transformation matrix between the flight coordinate system and an Earth-Centered Earth-Fixed (ECEF) coordinate system using the measurement data; (b4) generating a view vector that is a visual direction unit vector from the SAR platform to the estimated coordinate point on the ground using the coordinate conversion matrix generated in step (b3) and the nadir angle estimated in step (b2) step; and (b5) estimating the geodetic coordinates of the coordinate estimation point using the view vector generated in step (b4).

Also, the coordinate estimation point may be a point corresponding to any one of pixel points other than the central pixel point among all pixel points in the obtained SAR image.

Meanwhile, the device for estimating the geodetic coordinates of the coordinate estimation point in the SAR image obtained from the Sythetic Aperture Radar (SAR) platform according to an embodiment of the present application includes a nadir angle and an inclination distance corresponding to the nadir angle. a generation unit that generates relationship information between the cells as a lookup table; and an estimator for estimating the geodetic coordinates of the coordinate estimation point, which is a target of geodetic coordinate estimation, by using the lookup table.

In addition, the generation unit receives input data including the location and speed of the SAR platform and the nadir angle of a point on the ground where the signal transmitted from the SAR platform is reflected, and uses the input data to control the flight of the SAR platform. A coordinate system is set, a coordinate conversion matrix between the flight coordinate system and an Earth-Centered Earth-Fixed (ECEF) coordinate system is created, and a unit vector in the visual direction from the SAR platform to the point on the ground is generated using the coordinate conversion matrix. An in-view vector may be estimated, and an inclination distance corresponding to an input nadir angle may be estimated using the estimated view vector.

In addition, the generation unit changes the nadir angle at preset angular intervals within the permissible nadir angle range, applies the changed nadir angle to the input data, inputs input data, sets a flight coordinate system, and generates a coordinate transformation matrix. The lookup table is generated by repeatedly performing the process of estimating the view vector and the process of estimating the inclination distance, and the iterative execution may be performed until the changed nadir angle exceeds the maximum value of the nadir angle allowable range.

In addition, the estimation unit receives measurement data including the measured position and speed of the SAR platform, and the measured inclination distance measured from the position of the SAR platform to the coordinate estimation point on the surface corresponding to the coordinate estimation point, and the measurement Based on the data, the nadir angle for the coordinate estimation point on the ground is estimated using the lookup table, and the flight coordinate system of the SAR platform is set using the measurement data, and the flight coordinate system and ECEF (Earth-Centered Earth- A coordinate transformation matrix between fixed) coordinate systems is generated, and a view that is a unit vector in the visual direction from the SAR platform to the coordinate estimation point on the ground using the generated coordinate transformation matrix and the nadir angle estimated in step (b2). A vector may be generated, and the geodetic coordinates of the coordinate estimation point may be estimated using the generated view vector.

Also, the coordinate estimation point may be a point corresponding to any one of pixel points other than the central pixel point among all pixel points in the obtained SAR image.

The above-described problem solving means are merely exemplary and should not be construed as intended to limit the present disclosure. In addition to the exemplary embodiments described above, additional embodiments may exist in the drawings and detailed description of the invention.

According to the above-described problem solving means of the present application, by providing an apparatus and method for estimating the geodetic coordinates of a coordinate estimation point in an SAR image, compared to the conventional geodetic coordinate estimation technology, the image obtained from the SAR corresponds to the geodetic coordinate system with a simpler and higher accuracy. It can be estimated (calculated) with the coordinates of

However, the effects obtainable herein are not limited to the effects described above, and other effects may exist.

1 is a block diagram showing a schematic configuration of an apparatus for estimating geodetic coordinates of a coordinate estimation point in a SAR image according to an embodiment of the present invention.
2 is a diagram schematically illustrating a geometrical remodeling between an SAR platform and an image point considered in the geodetic coordinate estimation device of a coordinate estimation point in a SAR image according to an embodiment of the present application.
3 is a diagram schematically illustrating a process of generating a lookup table by a generation unit in a geodetic coordinate estimation device of a coordinate estimation point in an SAR image according to an embodiment of the present invention.
4 is a diagram schematically illustrating a process of estimating the geodetic coordinates of a coordinate estimation point by an estimator in a geodetic coordinate estimation device of a coordinate estimation point in a SAR image according to an embodiment of the present invention.
5 is a diagram schematically showing geometrical shapes between a SAR platform, an inclination distance, and a nadir angle considered for generation of a lookup table in a generation unit of a geodetic coordinate estimation device of a coordinate estimation point in an SAR image according to an embodiment of the present invention. .
6 is a diagram for explaining a process of generating a coordinate transformation matrix by a generating unit of a geodetic coordinate estimating device of a coordinate estimation point in a SAR image according to an embodiment of the present invention.
7 is a performance evaluation result of the geodetic coordinate estimation device of the coordinate estimation point in the SAR image according to an embodiment of the present invention. is the drawing shown.
8 is a performance evaluation result of the geodetic coordinate estimation device of the coordinate estimation point in the SAR image according to an embodiment of the present invention, generated by the geodetic coordinate estimation device of the coordinate estimation point in the SAR image according to an embodiment of the present application 11 x 11> shows examples of latitude and longitude values for grid points.
9 is a diagram showing an example of comparison of latitude values of lattice points estimated by SNAP and the proposed method, as a performance evaluation result of a geodetic coordinate estimation device of a coordinate estimation point in a SAR image according to an embodiment of the present application.
10 is a diagram showing latitude value differences between lattice points estimated by SNAP and the proposed method, as a result of performance evaluation of the geodetic coordinate estimation device of a coordinate estimation point in a SAR image according to an embodiment of the present invention.
11 is a diagram showing a comparison example of longitude values of lattice points estimated by SNAP and the proposed method, as a performance evaluation result of a geodetic coordinate estimation device of a coordinate estimation point in a SAR image according to an embodiment of the present invention.
12 is a diagram showing differences in longitude values of lattice points estimated by SNAP and the proposed method, as performance evaluation results of the geodetic coordinate estimating device of a coordinate estimation point in a SAR image according to an embodiment of the present invention.
13 is an operational flowchart for a method for estimating geodetic coordinates of a coordinate estimation point in a SAR image according to an embodiment of the present invention.

Hereinafter, embodiments of the present application will be described in detail so that those skilled in the art can easily practice with reference to the accompanying drawings. However, the present disclosure may be implemented in many different forms and is not limited to the embodiments described herein. And in order to clearly describe the present application in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the present specification, when a part is said to be “connected” to another part, it is not only “directly connected”, but also “electrically connected” or “indirectly connected” with another element in between. "Including cases where

Throughout the present specification, when a member is referred to as being “on,” “above,” “on top of,” “below,” “below,” or “below” another member, this means that a member is located in relation to another member. This includes not only the case of contact but also the case of another member between the two members.

Throughout the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

1 is a block diagram showing a schematic configuration of an apparatus 10 for estimating geodetic coordinates of a coordinate estimation point in a SAR image according to an embodiment of the present invention. FIG. 2 is a diagram schematically illustrating a geometric reorganization between an SAR platform and an image point (target area) considered in the geodetic coordinate estimation device 10 of a coordinate estimation point in an SAR image according to an embodiment of the present application. 3 is a diagram schematically illustrating a process of generating a lookup table by the generator 11 in the geodetic coordinate estimating device 10 of a coordinate estimation point in an SAR image according to an embodiment of the present invention. 4 is a diagram schematically illustrating a process of estimating the geodetic coordinates of a coordinate estimation point by the estimator 11 in the geodetic coordinate estimation device 10 of the coordinate estimation point in the SAR image according to an embodiment of the present invention.

Hereinafter, for convenience of description, the device 10 for estimating the geodetic coordinates of the coordinate estimation point in the SAR image according to an embodiment of the present application will be referred to as the present device 10. In addition, in describing the present device 10, an image point (target area) is a point for which geodetic coordinates are to be estimated in the present device 10, and may mean a coordinate estimation point that is a target of geodetic coordinate estimation.

Referring to FIGS. 1 to 4 , the apparatus 10 may mean a device for estimating the geodetic coordinates of coordinate estimation points in a SAR image obtained from a Synthetic Aperture Radar (SAR) platform. This device 10 may be otherwise referred to as a geodetic coordinate estimating device of a coordinate estimation point in an SAR image obtained from a SAR platform, a geodetic coordinate estimating device of an SAR image, and the like.

That is, the apparatus 10 converts the coordinates of an image (SAR image) obtained from SAR (in particular, the coordinates of a coordinate estimation point, which is a specific point to estimate geodetic coordinates in the SAR image) in a radar coordinate system (distance direction, azimuth direction) ) to coordinates on a geodetic coordinate system expressed in latitude and longitude.

Since the SAR image is based on the radar coordinate system, the device 10 converts the coordinates of the coordinate estimation point in the SAR image (ie, the coordinates of the coordinate estimation point for the SAR image on the radar coordinate system) into coordinates on the geodetic coordinate system. We propose a technique that can be estimated by

In this application, the SAR platform may mean a satellite, an aircraft, an unmanned aerial vehicle (UAV), and the like.

The device 10 may include a generating unit 11 and an estimating unit 12 .

The generating unit 11 may generate relationship information between a nadir angle and a slant range corresponding to the nadir angle as a LookUp Table (LUT). A process of generating a lookup table by the generation unit 11 can be more easily understood with reference to FIG. 3, and a more detailed description thereof will be described later.

The estimator 12 may estimate the geodetic coordinates of coordinate estimation points that are targets of geodetic coordinate estimation using the lookup table generated by the generator 11 . In this case, the coordinate estimation point means a point (specific pixel) in the SAR image, which may mean a coordinate based on a radar coordinate system. This coordinate estimation point may mean a point (pixel point) corresponding to any one of the remaining pixel points excluding the central pixel point among all pixel points in the obtained SAR image, but is not limited thereto, and is a radar of the SAR image. It may mean a point corresponding to any one of the coordinates on the coordinate system.

The process of estimating geodetic coordinates by the estimator 12 can be more easily understood with reference to FIG. 4, and a more detailed description thereof will be described later. Prior to a detailed description, the geometry of the components considered in the apparatus 10 will be described with reference to FIG. 2 as follows.

Referring to Figure 2, S ^e is the location of the SAR platform, P ^e is the position on the ground surface to be estimated (that is, the position on the ground surface of the coordinate estimation point, which means the position on the ECEF coordinate system of the coordinate estimation point), u ^e is P ^e from S ^e Means a unit view vector (line-of-sight vector) up to. The superscript e means the ECEF coordinate system, so S ^e means the coordinates of the satellite (SAR platform) in the ECEF coordinate system. An Earth-Centered Earth-Fixed (ECEF) coordinate system may be referred to as an Earth-Centered Earth-Fixed Coordinate System. r represents the slope distance between S ^e and P ^e . Here, the position S ^e of the SAR platform and the slope distance r are measured values, and the velocity vector v ^e of the SAR platform is also a measured value.

That is, the values for the location and speed (i.e. S ^e , v ^e ) and slope distance (i.e. r ) of the SAR platform considered in the device 10 are measured values (measured values), and are known values. can mean

According to this, the present device 10 is a position P ^e on the ECEF coordinate system of an image point (coordinate estimation point) from known values S ^e , v ^e , r is estimated as in Equation 7 described later, and the estimated P ^e It is possible to estimate the geodetic coordinates of the coordinate estimation point by performing conversion to the geodetic coordinate system (latitude, longitude) as shown in Equation 8 described later.

In order to estimate the geodetic coordinates of the coordinate estimation point, the generation unit 11 of the apparatus 10 may generate a lookup table. This can be more easily understood with reference to FIG. 3 .

Referring to FIG. 3, the generating unit 11 determines the position and speed of the SAR platform and the nadir angle (i.e., a nadir angle for a point on the ground (image point, arbitrary point) where a signal transmitted from the SAR platform is reflected. Arbitrary nadir angle) may be input (S11). Next, the generation unit 11 may set (define) the flight coordinate system of the SAR platform using the received input data (S13).

Next, the generation unit 11 may generate a coordinate conversion matrix between the set (defined) flight coordinate system and the ECEF (Earth-Centered Earth-Fixed) coordinate system (S14). Next, the generation unit 11 may estimate (calculate) a view vector (unit view vector), which is a unit vector in the visual direction from the SAR platform to a point on the ground, using the coordinate conversion matrix generated in step S14 (S15 ).

Next, the generation unit 11 may estimate an inclination distance corresponding to the nadir angle input in step S11 using the view vector estimated in step S14 (S16). At this time, in step S16, the generation unit 11 sets the estimated slope distance and the corresponding nadir angle (ie, the nadir angle input in step S11) as a set based on the estimated slope distance and records them in the lookup table. can

In addition, the generation unit 11 changes the nadir angle at a predetermined angular interval (for example, 1 degree, 0.5 degree, etc.) with respect to the permissible nadir angle range, applies the changed nadir angle as input data of step S11, and applies the changed nadir angle as input data in step S11. A lookup table may be generated by repeatedly performing steps S16 to S16. At this time, iterative execution may be performed until the changed nadir angle exceeds the maximum value of the nadir angle allowable range. Through this repetition, the inclination distance for each nadir angle can be estimated (calculated), and through this, the generation unit 11 can generate a lookup table by recording the inclination distance according to the change in nadir angle.

In other words, when the generator 11 receives the input data in step S11, it can determine whether the nadir angle in the received input data exceeds the maximum value of the nadir angle permissible range (S12). At this time, if the nadir angle in the input data does not exceed the maximum value of the permissible nadir angle range (S12-NO), the generating unit 11 performs steps S13 to S16 based on the nadir angle, and determines the nadir angle. After changing by the preset angle interval, the changed nadir angle may be applied again in step S11. Accordingly, in step S11, the generating unit 11 may receive input data including the changed nadir angle. Thereafter, the generation unit 11 may perform step S12 again based on the changed nadir angle. At this time, as a result of performing step S12 again, if the changed nadir angle does not exceed the maximum value of the permissible nadir angle range, the processes of steps S13 to S16 and S11 described above may be performed again, which means that the changed nadir angle allows the nadir angle to be accepted. It can be repeated until the maximum value of the range is exceeded. If the nadir angle changed in step S11 exceeds the maximum value of the permissible nadir angle range (S12-YES), the generation unit 11 may end the process of generating the lookup table.

Here, the permissible nadir angle range may be designated as a range of general nadir angles used in SAR, but is not limited thereto, and may be variously set or changed by user input.

Describing the process of generating the lookup table again, as shown in FIG. 5 , the generator 11 may generate the lookup table to estimate the relational expression between the nadir angle and the slant range.

5 is a geometrical opening between the SAR platform, inclination distance, and nadir angle considered for generating a lookup table in the generation unit 11 of the geodetic coordinate estimation apparatus 10 of the coordinate estimation point in the SAR image according to an embodiment of the present invention. is a schematic diagram of

Referring to FIGS. 3 and 5 , since it is not possible to know the exact nadir angle of the SAR platform and the image point (target area) in the prior art, a process of estimating the nadir angle from a given inclination distance is required. Accordingly, the generation unit 11 may generate a lookup table (LUT) representing a relationship between an inclination distance and a nadir angle through, for example, the process illustrated in FIG. 3 .

In the apparatus 10, the generation unit 11 may be otherwise referred to as a lookup table generation unit.

The process of generating a lookup table by the generation unit 11 can be referred to as a process of estimating and recording an inclination distance according to an arbitrary nadir angle (arbitrary nadir angle) at a given SAR platform location. To this end, the generation unit 11 generates a general nadir angle range used in SAR (for example, the nadir angle range may be approximately 10 degrees to 50 degrees, and may be different depending on the satellite SAR system and each operation mode). Designate (i.e., set the permissible range of nadir angle), calculate each inclination distance value for the nadir angle at preset intervals (e.g., 1 degree, 0.5 degree, etc.) to create a look-up table can be created (constructed).

To this end, the generation unit 11 sets the flight coordinate system of the SAR platform (S13), generates a coordinate transformation matrix between the flight coordinate system and the ECEF coordinate system (S14), and utilizes the estimated coordinate transformation matrix and the nadir angle for SAR. A unit view vector heading from the platform to the image point (point on the ground) is estimated (S15), and the estimated view vector, the position of the SAR platform, and the slope distance to the image point are utilized using the WGS-84 earth ellipsoid model. The process of estimating and recording (S16) can be performed. A detailed description of each step is as follows.

In step S13, the generation unit 11 may define a flight coordinate system. The flight coordinate system may be defined as shown in FIG. 2 . If the velocity vector of the SAR platform is defined as the X-axis ( X ^b ) of the flight coordinate system and the position vector of the SAR platform is defined as the Z-axis ( Z ^b ) of the flight coordinate system, the Y-axis ( Y ^b ) of the flight coordinate system is as shown in Equation 1 below: determined according to the right-hand rule. That is, the generation unit 11 may define the flight coordinate system of the SAR platform as shown in Equation 1 below using the position and speed of the SAR platform input in step S11.

[Equation 1]

Next, in step S14, the generation unit 11 may generate a coordinate transformation matrix. This can be more easily understood with reference to FIG. 6 .

6 is a diagram for explaining a process (S14) of generating a coordinate transformation matrix by the generation unit 11 of the apparatus 10 for estimating coordinates of a coordinate estimation point in a SAR image according to an embodiment of the present application. In particular, FIG. 6 is a diagram schematically illustrating an example of a flight coordinate system and an ECEF coordinate system.

)을 추정할 수 있으며, 이때 추정된 좌표변환행렬의 전치행렬이 비행좌표계에서 ECEF 좌표계로의 좌표변환 행렬(

)로 정의될 수 있고, 이는 아래 식 2와 같을 수 있다. 즉, 생성부(11)는 비행좌표계에서 ECEF 좌표계로의 좌표변환 행렬을 아래 식 2와 같이 정의할 수 있다. Referring to FIG. 6 , for conversion from the flight coordinate system to the ECEF coordinate system, first, the generation unit 11 may estimate a coordinate conversion matrix from the ECEF coordinate system to the flight coordinate system. In order to estimate the coordinate conversion matrix from the flight coordinate system to the ECEF coordinate system, the generator 11 converts the coordinate conversion matrix from the ECEF coordinate system to the flight coordinate system (

) can be estimated, and at this time, the transposed matrix of the estimated coordinate transformation matrix is the coordinate transformation matrix from the flight coordinate system to the ECEF coordinate system (

), which can be defined as Equation 2 below. That is, the generation unit 11 may define a coordinate transformation matrix from the flight coordinate system to the ECEF coordinate system as shown in Equation 2 below.

The view vector is defined in the flight coordinate system using the nadir angle. In order to calculate the geodetic coordinates of an image point, a view vector must be converted into a vector on the ECEF coordinate system. Therefore, in order to convert the view vector into a vector on the ECEF coordinate system, a coordinate transformation matrix between the ECEF coordinate system and the flight coordinate system must be estimated, and the generator 11 can generate (estimate) the coordinate transformation matrix as shown in Equation 2 below. (S14).

[Equation 2]

일 수 있다.in equation 2

can be

,

은 도6에 도시된 바와 같이 ECEF 좌표계상에서 표현된 SAR 플랫폼의 속도벡터 V ^e 에 대한 방위각과 고도각이다. ECEF 좌표계의 Z축을 기준으로

만큼 회전변환을 가하고, 회전변환된 좌표계의 Y축을 기준으로

만큼 회전변환을 가하면, 비행좌표계의 X축과 ECEF 좌표계의 X축이 일치하게 된다. 이때, 비행좌표계의 Y, Z 축과 회전변환된 좌표계의 Y, Z 축은

만큼 틀어져있게 되며,

는 아래 식 3과 같을 수 있다.here,

,

is the azimuth and elevation angles for the velocity vector V ^e of the SAR platform expressed on the ECEF coordinate system as shown in FIG. Based on the Z axis of the ECEF coordinate system

rotation transformation is applied as much as possible, and based on the Y-axis of the rotation-transformed coordinate system,

If the rotation transformation is applied by the amount, the X-axis of the flight coordinate system and the X-axis of the ECEF coordinate system coincide. At this time, the Y and Z axes of the flight coordinate system and the Y and Z axes of the rotated coordinate system are

It will be as wrong as

may be the same as Equation 3 below.

[Equation 3]

이고,

는 ECEF 좌표계에서의 비행좌표계의 Y축 좌표값을 나타낸다.here,

ego,

represents the Y-axis coordinate value of the flight coordinate system in the ECEF coordinate system.

Next, in step S15, the generating unit 11 may estimate a view vector. The view vector is defined as a unit vector in the visual direction from the SAR platform to the image point, and can be defined as Equation 4 below in the flight coordinate system according to the definition of the nadir angle.

[Equation 4]

를 이용하여 뷰 벡터를 아래 식 5와 같이 계산(추정)할 수 있다. 즉, 생성부(11)가 단계S15에서 추정하는 뷰 벡터는 ECEF 좌표계 상에서 표현되는 값일 수 있으며, 아래 식 5와 같이 정의될 수 있다.A view vector is required for position estimation of an image point on the ECEF coordinate system. Therefore, the view vector must be a value expressed on the ECEF coordinate system, and the generator 11 converts the coordinates to the coordinate transformation matrix generated in step S14.

The view vector can be calculated (estimated) as shown in Equation 5 below. That is, the view vector estimated by the generation unit 11 in step S15 may be a value expressed on the ECEF coordinate system, and may be defined as Equation 5 below.

[Equation 5]

Here, u is the view vector, subscript e is the ECEF coordinate system, and subscript b is the flight coordinate system. In the present application, a view vector may be used interchangeably with a unit view vector.

Next, in step S16, the generation unit 11 may estimate and record the inclination distance.

의 추정은 일예로 아래 식 6과 같이 기 알려진 방법을 이용하여 추정될 수 있다.Specifically, the unit view vector u ^e from the position S ^e of the SAR platform Slope distance to intersection with WGS-84 earth ellipsoid model in direction

Estimation of can be estimated using a known method, for example, as shown in Equation 6 below.

[Equation 6]

일 수 있다.here,

can be

The values of Earth major radius and Earth minor radius utilize the WGS-84 earth ellipsoid model, and in step S16, the generation unit 11 estimates and records the inclination distance for the arbitrary nadir angle (arbitrary nadir angle) input from Equation 6 above. can do.

Through the above process, the generation unit 11 may generate a lookup table.

In the foregoing description, steps S11 to S16 may be further divided into additional steps or combined into fewer steps, depending on the implementation of the present application. Also, some steps may be omitted if necessary, and the order of steps may be changed.

When the lookup table is generated, the estimator 12 may estimate the geodetic coordinates of coordinate estimation points that are targets of geodetic coordinate estimation using the generated lookup table. The process of estimating geodetic coordinates can be more easily understood with reference to FIG. 4 .

Referring to FIG. 4, the estimator 12 includes the measured position and speed of the SAR platform, and the measured inclination distance from the position of the SAR platform to the coordinate estimation point P ^e on the ground corresponding to the coordinate estimation point. Measurement data may be input (S21).

Next, the estimator 12 determines the nadir angle for the coordinate estimation point on the surface of the earth using the lookup table S22 generated (previously generated) by the generation unit 11 based on the measurement data input in step S21. It can be estimated (S23).

Next, the estimator 12 may set the flight coordinate system of the SAR platform and generate a coordinate conversion matrix between the flight coordinate system and the ECEF (Earth-Centered Earth-Fixed) coordinate system using the measurement data (S24).

Next, the estimator 12 generates (estimates) a view vector that is a unit vector in the visual direction from the SAR platform to the estimated coordinate point on the ground using the coordinate conversion matrix generated in step S24 and the nadir angle estimated in step S23. It can be done (S25).

Next, the estimator 12 may estimate the geodetic coordinates of the coordinate estimation point using the view vector generated (estimated) in step S25 (S26). In particular, in step S26, the estimator 12 may use the view vector generated (estimated) in step S25 to define the position ( P ^e ) of the coordinate estimation point on the ground expressed in the ECEF coordinate system as shown in Equation 7 described later. there is. That is, the estimator 12 may define the position P ^e on the ECEF coordinate system of the coordinate estimation point on the ground as shown in Equation 7 using the generated view vector. Thereafter, in step S26, the estimator 12 converts the position on the ECEF coordinate system of the estimated coordinate point on the surface into a position on the geodetic coordinate system as shown in Equation 8 described below, thereby converting the position on the converted geodetic coordinate system into the geodetic coordinates of the estimated coordinate point. can be presumed to be

Referring again to the process of estimating geodetic coordinates, in step S21, the estimator 12 receives measurement data, and then uses the pre-generated look-up table to estimate the coordinates at a point on the surface of the earth corresponding to the measured inclination distance input in step S21. It is possible to estimate the nadir angle for (S22).

Then, in step S23, the estimator 12 may estimate the nadir angle. Specifically, it can be said that the nadir angle is absolutely necessary to define the view vector from the SAR platform to the image point (coordinate estimation point on the ground) in the flight coordinate system. Since the slope distance between the SAR platform and the image point (coordinate estimation point on the ground) can be known from the SAR image and the attribute information on the SAR image, the estimator 12 determines the corresponding measurement from the slope distance (measurement slope distance). The nadir angle for the slope distance can be estimated (calculated) (S23). In particular, the estimator 12 determines the inclination distance (measured from this inclination distance) using a lookup table (ie, the lookup table previously generated by the generation unit 11) in which a relationship between an arbitrary nadir angle and inclination distance is predefined. The nadir angle for the measured slope distance) may be calculated (estimated) (S23). At this time, the estimator 12 may use Lagrange interpolation, for example, to calculate (estimate) the nadir angle corresponding to the measured inclination distance in step S23, but is not limited thereto, and is known in the art such as Bi-linear. Various interpolation methods that have been developed or developed in the future can be applied.

Next, in step S24, the estimator 12 may perform flight coordinate system definition (setting) and coordinate conversion matrix generation. At this time, the description of the flight coordinate system definition in step S24 can be understood as the same as or similar to the description of the flight coordinate system definition in step S13. Similarly, the description of the coordinate transformation matrix generation in step S24 can be understood as the same or similar to the description of the coordinate transformation matrix generation in step S14 above. Therefore, even if the details are omitted below, the description of steps S13 and S14 can be equally applied to the description of step S24.

Briefly, in step S24 for defining the flight coordinate system, the estimator 12 converts the velocity vector of the SAR platform to the X axis ( X ^b ) of the flight coordinate system and the position vector of the SAR platform to the flight coordinate system as described in step S13. It is defined as the Z axis ( Z ^b ) of and the Y axis ( Y ^b ) of the flight coordinate system can be defined according to the right-hand rule.

In addition, in step S24, the estimator 12 may generate (estimate) the coordinate transformation matrix as described in step S14, and the generation (estimation) of this coordinate transformation matrix is performed at the estimated nadir angle (that is, in step S23). It is necessary to convert the view vector defined in the flight coordinate system from the estimated nadir angle) to the ECEF coordinate system. That is, the coordinate transformation matrix generated in step S24 may be used to transform the view vector from the nadir angle estimated in step S23 into the ECEF coordinate system.

Next, in step S25, the estimator 12 can estimate (generate) a view vector. In step S25, the estimator 12 may generate a unit view vector in the direction of an image point from the SAR platform using the look-side of the SAR system and the coordinate transformation matrix generated in step S24.

The view vector is defined as a unit vector in the line of sight direction from the SAR platform to the image point, and is defined as a unit vector in the flight coordinate system as shown in Equation 4 above by the nadir angle estimated using the look-up table (LUT) from the input inclination distance. It can be.

The view vector is necessary for estimating the position of the image point on the ECEF coordinate system, and as described in step S15, it can be expressed on the ECEF coordinate system using the flight coordinate system and the coordinate transformation matrix on the ECEF coordinate system.

That is, the description of view vector estimation (generation) in step S25 can be understood as the same as or similar to the description of view vector estimation in step S15. Therefore, even if the content is omitted below, the description of step S15 can be equally applied to the description of step S25.

Next, in step S26, the estimator 12 may estimate (calculate) the geodetic coordinates.

To this end, in step S26, the estimator 12 uses the unit view vector generated using the coordinate conversion matrix, the measured slope distance (estimated slope distance), and the measured position of the SAR platform, and uses a point corresponding to the measured slope distance. A position (P ^e ) on the ECEF coordinate system for can be defined.

In other words, if the view vector is estimated in step S25, in step S26, the estimator 12 calculates the position P ^e of the image point on the ECEF coordinate system (ie, the position on the ECEF coordinate system for the coordinate estimation point on the ground) using Equation 7 below. can be defined together.

[Equation 7]

According to this, the estimator 12 calculates the image point from the known value of the position and speed information of the SAR platform and the measured slope distance (ie, the slope distance from the SAR platform position S ^e to the position P ^e on the ground surface to be estimated). The position P ^e on the ECEF coordinate system can be estimated using Equation 7 above. For reference, r is the slope distance measurement value. However, since not all slope distances for each image point location are provided in SAR imaging products, for example, the slope distance measurement value corresponding to a specific image point is based on the provided slope distance (eg, the center point of the image). It can be obtained in the form of estimating the slope distance for the specific image point whose coordinates are to be estimated with . That is, the slope distance measurement value may be a directly measured measurement value or an indirect measurement value provided in the form of estimation based on a directly measured slope distance value such as the center point of an image.

Thereafter, the estimator 12 may estimate the geodetic coordinates of the image point by converting the location of the estimated image point on the ECEF coordinate system into a geodetic coordinate system (latitude, longitude) as shown in Equation 8 below.

That is, in step S26, the estimator 12 may perform conversion from the position of the image point (estimated coordinate point on the ground) on the ECEF coordinate system to the position on the geodetic coordinate system as shown in Equation 8 below. That is, the estimator 12 can estimate the position on the geodetic coordinate system (ie, the position on the geodetic coordinate system for the coordinate estimation point on the surface) where the transform obtained based on Equation 8 below is the geodetic coordinate of the coordinate estimation point. there is.

[Equation 8]

일 수 있다.here,

can be

As such, the estimator 12 may estimate the geodetic coordinates of the coordinate estimation point based on Equation 8.

In other words, the present device 10 has problems with conventional geodetic coordinate estimation technology (for example, in the case of SAR images, it is difficult to distinguish GCPs due to the influence of speckle noise and it is not easy to map images between different satellites to obtain high accuracy and reliability. It is proposed to solve problems that are very difficult to solve, problems that are complicated to obtain a solution to the geodetic coordinate system when using a system of equations, etc.).

To this end, the device 10 receives the position and speed of the SAR platform and the inclination distance to the image point to be obtained (a coordinate estimation point, in particular, a coordinate estimation point on the ground corresponding to the coordinate estimation point) (S21) , it is possible to set (define) the flight coordinate system for the SAR platform using this (S24). In addition, the apparatus 10 may generate a lookup table using the generation unit 11 before performing step S21 to estimate the geodetic coordinates. At this time, the generation unit 11 determines the slope distance from the measured SAR platform location to the point (image point) from the SAR platform (to be exact, the SAR antenna phase center) according to the nadir angle to the point where the signal transmission direction meets the ground. can be created as a lookup table (LUT).

After the lookup table is generated, the apparatus 10 utilizes (uses) the generated lookup table to measure the slope distance (measured slope distance ), a precise Nadir angle can be estimated (S23).

Thereafter, the present apparatus 10 utilizes (uses) the measured inclination distance (measured inclination distance, that is, the measured inclination distance input in step S21) and the nadir angle estimated in step S23 to determine (defined) the previously set (defined) in step S24. A coordinate conversion matrix between the flight coordinate system and the ECEF (Earth-Centered Earth-Fixed) coordinate system can be created (S24).

Thereafter, the apparatus 10 may generate a unit view vector in the direction of an image point from the SAR platform by utilizing the look-side of the SAR system and the generated coordinate transformation matrix. Thereafter, the present device 10 measures the slope distance (measured slope distance), the generated unit view vector, and the point corresponding to the measured slope distance from the position of the measured SAR platform (coordinates on the ground corresponding to the coordinate estimation point) The coordinates on the geodetic coordinate system for the estimated point) can be estimated (calculated).

In the foregoing description, steps S21 to S26 may be further divided into additional steps or combined into fewer steps, depending on the implementation of the present application. Also, some steps may be omitted if necessary, and the order of steps may be changed.

Hereinafter, performance evaluation results of the device 10 according to an experimental example of the present application will be described.

In one experimental example of the present application, the geodetic coordinate estimation method by the apparatus 10 (hereinafter referred to as 'proposed method' for convenience of description) using the SAR image obtained from the TerraSAR-X satellite is applied to determine the geodetic value of the SAR image. Coordinate estimation was performed.

7 is a performance evaluation result of the geodetic coordinate estimation device 10 of a coordinate estimation point in a SAR image according to an embodiment of the present invention, and the slope distance calculated while changing the nadir angle from 0° to 60° It is a diagram showing the result generated by the LookUp Table.

Referring to FIG. 7 , a nadir angle corresponding to a measured inclination distance (measured inclination distance) may be estimated using a Lagrange interpolation method or the like from a corresponding lookup table (LUT). That is, the estimator 12 may estimate the nadir angle corresponding to the measured inclination distance using the lookup table, and various interpolation methods may be used when estimating the nadir angle.

To quantitatively evaluate the accuracy of the proposed method, SNAP (SeNtinel's Application Platform) was utilized. SNAP is open software developed by the European Space Agency, and is sophisticated software that can process SAR data acquired from SAR satellites.

8 is a performance evaluation result of the geodetic coordinate estimation device 10 of the coordinate estimation point in the SAR image according to an embodiment of the present application. The geodetic coordinate estimation device 10 of the coordinate estimation point in the SAR image according to an embodiment of the present application ) shows an example of latitude and longitude values for <11 x 11> lattice points generated by

Referring to FIG. 8 , SNAP can provide geodesic coordinates for <11 x 11> tie-point grids in latitude and longitude directions as shown in FIG. 8 for an input TerraSAR-X image. In FIG. 8, a yellow circle represents a lattice point, and a blue circle represents a central point of an input SAR image. The purple line connects the corner coordinates of the SAR image provided in the SAR image, and it can be confirmed that the generated lattice points are normally generated. In the performance evaluation experiment according to an embodiment of the present application, the proposed method is applied to the same location as SNAP to estimate the geodetic coordinates for each lattice point and compares them with the results of SNAP.

9 is a diagram showing a comparison example of latitude values of lattice points estimated by SNAP and the proposed method, as a performance evaluation result of the geodetic coordinate estimation apparatus 10 of a coordinate estimation point in a SAR image according to an embodiment of the present application. . 10 is a diagram showing latitude value differences between lattice points estimated by SNAP and the proposed method as performance evaluation results of the geodetic coordinate estimation apparatus 10 of a coordinate estimation point in a SAR image according to an embodiment of the present application.

11 is a diagram showing a comparison example of longitude values of lattice points estimated by SNAP and the proposed method as performance evaluation results of the geodetic coordinate estimation apparatus 10 of a coordinate estimation point in a SAR image according to an embodiment of the present application. . 12 is a diagram showing differences in longitude values of lattice points estimated by SNAP and the proposed method, as performance evaluation results of the geodetic coordinate estimation apparatus 10 of a coordinate estimation point in a SAR image according to an embodiment of the present application.

In other words, FIG. 9 shows the latitude value of the lattice point calculated by SNAP and the latitude value of the lattice point estimated by the proposed method, and FIG. 10 shows the difference between the calculated value of SNAP and the estimated value of the proposed method. Referring to FIGS. 9 and 10 , it can be confirmed that the difference at the lattice points corresponding to the boundary of the image is relatively small, and it can be confirmed that the proposed method and the SNAP calculation value are generally similar.

Figure 11 shows the hardness value of the lattice point calculated by SNAP and the hardness value of the lattice point estimated by the proposed method, and Figure 12 shows the difference between the calculated value of SNAP and the estimated value of the proposed method. Referring to FIGS. 11 and 12, unlike the latitude estimation result, it can be seen that the difference is smaller as it is closer to the center point of the image, and it can be seen that the proposed method and the SNAP calculated value are similar.

On the other hand, to quantitatively evaluate the difference between latitude and longitude estimates for grid points, RMS values were calculated as shown in Equations 9 and 10, and the difference between the estimated values of SNAP and the proposed method was 9.7472e-6 ° and 3.4232 for latitude and longitude, respectively. It can be seen that similar results are obtained with e-5 °.

[Equation 9]

[Equation 10]

According to the foregoing, the apparatus 10 can more easily convert and estimate the coordinates on the radar coordinate system of the SAR image into the coordinates on the geodetic coordinate system.

In conventionally known geodetic coordinate system estimation techniques, information on the center point of most SAR images is provided (ie, the information on the center point is considered as a value known in advance). Therefore, in the prior art, based on the center point of such an image (SAR image), the delta X and Y values are determined to some extent in the X direction and Y direction of the image, and the known center point information is included. Based on the information, the positions of pixels at different points in the images are calculated.

On the other hand, the device 10 considers where the SAR platform is located in the SAR image (ie, relative SAR platform location information with respect to the SAR image) rather than information about the number of pixels in the image. Assuming that the distance (i.e. slope distance) from the SAR platform to a point on the ground of the SAR image (in particular, a coordinate estimation point on the ground) is known, the corresponding slope distance (i.e. measured slope distance) and a pre-generated lookup table It provides a technology that can more easily calculate (estimate) the position of the geodetic coordinate system for the estimated point on the surface of the SAR image by using the SAR image.

In the prior art, when information on the center point of the SAR image (i.e., the origin of the SAR image) and information on the four boundary corners are provided, the displacement is estimated from this, and the geodetic coordinate system is calculated (estimated) based on the estimated information. )do. Therefore, in order to estimate the geodetic coordinates of points other than the central point (origin) in the SAR image (ie, a specific pixel point) in the SAR image, this conventional technique takes a long time, such as requiring an additional calculation process, and is easy to use immediately. There are problems that cannot be estimated. In addition, in the case of the prior art, as another example, there is a method of obtaining a solution by solving a nonlinear equation, but this is complicated and takes a long time. On the other hand, since the present apparatus 10 creates a lookup table in advance and estimates the geodetic coordinates based on the lookup table, it can solve the problems of the prior art and provide easier estimation of the geodetic coordinates. there is.

In addition, the coordinate transformation matrix considered in the present device 10 (ie, the coordinate transformation matrix generated in steps S14 and S24 described above) is generated with information provided from sensors such as inertial devices existing in the SAR platform Rather, it may be generated based on a newly designated frame based on the velocity vector of the SAR platform (ie, a frame arbitrarily designated by the device 10 in order to generate a lookup table).

In other words, since information necessary to create a coordinate transformation matrix is generally not provided by SAR images or SAR platforms, the apparatus 10 can set coordinates so that a coordinate transformation matrix can be generated. Specifically, in the apparatus 10, it can be confirmed that the frames are set to exist on the YZ plane even when the view vector is generated, and if there is no such setting, the coordinate transformation matrix may not be generated. Therefore, in the apparatus 10, the flight coordinate system setting itself may already be set to create a coordinate transformation matrix.

In the prior art, the flight coordinate system is generally set to X as the direction of travel, Y as the direction perpendicular thereto, and setting the elevation axis as Z without such consideration. In general, SAR transmits (irradiates) a signal (beam) on the YZ plane in a side-looking manner. Since it is not known exactly whether or not it is transmitted, it can be said that the apparatus 10 has created a lookup table to obtain more accurate nadir angle information (estimating an accurate nadir angle).

That is, in the prior art, since only the information of the center point (origin) of the SAR image was provided, only information such as, for example, the nadir angle was 10 degrees from the center of the image, whereas the apparatus 10 generates a lookup table and Based on this, by performing geodetic coordinate estimation, the SAR image is used to estimate not only the center point of the image as in the prior art, but also each vertex of the image or other pixel points (i.e., any one pixel in the image). Coordinates can be calculated (estimated). According to this, when the SAR platform irradiates a signal (beam) toward any one point on the ground, the device 10 can calculate not only the geodetic coordinates of that one point (ie, the center point of the image), but any one Geodetic coordinates for points other than points can also be provided so that they can be calculated.

In the lookup table generated by the apparatus 10, information such as that if the slope distance is the first value, the angle of the direction of the irradiated beam (ie, the angle of the nadir) should be an angle a (ie, the slope distance and Relationship information between nadir angles) may be pre-calculated and recorded/stored.

In the apparatus 10, inclination distance and nadir angle information must be acquired to create a lookup table. In this case, information on nadir angles and inclination distances with respect to the central point of each SAR image, for example, exists in the SAR image product, and may be a given value. That is, the information on the slope distance and nadir angle considered when generating the lookup table may be values given in advance when the SAR platform provides the SAR image. The nadir angle may refer to an angle when a beam is irradiated to the center of the SAR image.

Assume that a first image is generally acquired as a SAR image. At this time, in the prior art, only estimation of geodetic coordinates for the center point of the first image was possible. At this time, if the position is moved exemplarily by 10 pixels to the left from the center of the first image, the inclination distance to the shifted point (position movement point) will have a different value from the inclination distance to the center point.

As such, if the location is changed to a point other than the center point, the slope distance will also change accordingly, and furthermore, it will be seen that the irradiation direction of the signal (beam) irradiated from the SAR platform is also changed. However, in the prior art, simply the first image As only the nadir angle and inclination distance information for the center point is provided, there is a problem in not knowing the nadir angle and inclination distance information for the changed point (ie, the location movement point). If it is desired to know the nadir angle and inclination distance information for a conventionally changed point, a complicated and additional calculation process is required or another SAR image (eg, a second SAR image) with the changed point as the center of the image is additionally required. It can be said that there are problems such as the need to acquire and perform estimation based on additionally acquired images.

Therefore, unlike the prior art in which the nadir angle and inclination distance are provided only for the center point of the SAR image, the device 10 provides the nadir angle and inclination for each pixel (all pixels) in the SAR image at a point corresponding to each pixel. The distance can be calculated in advance and created as a lookup table. Thereafter, when an input requesting estimation of geodetic coordinates for an arbitrary point in the SAR image is made (for example, as in step S21, the present device 10 is the slope distance to the estimated point on the ground corresponding to the estimated coordinate point). When the measured inclination distance is input) (at this time, an arbitrary point may mean a coordinate estimation point), by using a look-up table in which relation information between the nadir angle and inclination distance for each point is stored, the corresponding arbitrary point can be more immediately and easily Geodetic coordinates for points can be estimated accurately and quickly.

Hereinafter, based on the details described above, the operation flow of the present application will be briefly reviewed.

13 is an operational flowchart for a geodetic coordinate estimation method (proposed method) of a coordinate estimation point in a SAR image according to an embodiment of the present invention.

The geodetic coordinate estimation method of the coordinate estimation point in the SAR image shown in FIG. 13 can be performed by the apparatus 10 described above. Therefore, even if the content is omitted below, the description of the device 10 can be equally applied to the description of the method for estimating the geodetic coordinates of the coordinate estimation point in the SAR image.

Referring to FIG. 13 , in step S31, the generation unit may generate relationship information between a nadir angle and an inclination distance corresponding to the nadir angle as a lookup table.

At this time, step S31 is a step of receiving input data including the location and speed of the SAR platform and the nadir angle of a point on the ground where the signal transmitted from the SAR platform is reflected (step 1), using the input data to Setting the flight coordinate system of the SAR platform (step 2), generating a coordinate conversion matrix between the flight coordinate system and ECEF (Earth-Centered Earth-Fixed) coordinate system (step 3), and using the generated coordinate conversion matrix to generate the SAR A step of estimating a view vector, which is a visual direction unit vector from the platform to a point on the ground (step 4), and a step of estimating an inclination distance corresponding to the nadir angle input in step 1 (step 5) using the estimated view vector. can include

In addition, in step S31, a lookup table may be generated by changing the nadir angle at preset angular intervals within the permissible nadir angle range, applying the changed nadir angle to the input data, and repeatedly performing steps 1 to 5. At this time, iterative execution may be performed until the changed nadir angle exceeds the maximum value of the nadir angle allowable range.

Next, in step S32, the estimator may estimate the geodetic coordinates of the coordinate estimation point, which is a target of geodetic coordinate estimation, using the lookup table generated in step S31.

In addition, step S32 is a step of receiving measurement data including the measured position and speed of the SAR platform and the measured inclination distance measured from the position of the SAR platform to the estimated coordinate point on the ground corresponding to the estimated coordinate point (step 1). ), based on the measurement data, estimating the nadir angle for the coordinate estimation point on the ground using a lookup table (step 2), setting the flight coordinate system of the SAR platform using the measurement data, and setting the flight coordinate system and the ECEF Generation of a coordinate conversion matrix between (Earth-Centered Earth-Fixed) coordinate systems (step 3), line of sight from the SAR platform to the estimated coordinate point on the ground using the created coordinate conversion matrix and the nadir angle estimated in step 2 It may include generating a view vector that is a direction unit vector (step 4), and estimating the geodetic coordinates of the coordinate estimation point using the generated view vector (step 5).

In addition, the coordinate estimation point considered in step S32 may be a point corresponding to any one of pixel points other than the center pixel point among all pixel points in the obtained SAR image.

In the foregoing description, steps S31 and S32 may be further divided into additional steps or combined into fewer steps, depending on an embodiment of the present invention. Also, some steps may be omitted if necessary, and the order of steps may be changed.

A method for estimating geodetic coordinates of a coordinate estimation point in an SAR image according to an embodiment of the present disclosure may be implemented in the form of program instructions that can be executed through various computer means and may be recorded on a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the medium may be those specially designed and configured for the present invention or those known and usable to those skilled in computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic media such as floptical disks. - includes hardware devices specially configured to store and execute program instructions, such as magneto-optical media, and ROM, RAM, flash memory, and the like. Examples of program instructions include high-level language codes that can be executed by a computer using an interpreter, as well as machine language codes such as those produced by a compiler. The hardware devices described above may be configured to act as one or more software modules to perform the operations of the present invention, and vice versa.

In addition, the method for estimating the geodetic coordinates of the coordinate estimation point in the SAR image described above may be implemented in the form of a computer program or application stored in a recording medium and executed by a computer.

The above description of the present application is for illustrative purposes, and those skilled in the art will understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present application. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present application is indicated by the following claims rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts thereof should be construed as being included in the scope of the present application.

Claims (6)

A geodetic coordinate estimation method of a coordinate estimation point in a SAR image obtained from a Sythetic Aperture Radar (SAR) platform,
(a) generating relationship information between a nadir angle and a slope distance corresponding to the nadir angle as a lookup table; and
(b) estimating the geodetic coordinates of the coordinate estimation point, which is a target of geodetic coordinate estimation, using the lookup table;
including,
In step (a),
(a1) receiving input data including the position and speed of the SAR platform and the nadir angle of a point on the ground where a signal transmitted from the SAR platform is reflected;
(a2) setting a flight coordinate system of the SAR platform using the input data;
(a3) generating a coordinate transformation matrix between the flight coordinate system and an Earth-Centered Earth-Fixed (ECEF) coordinate system;
(a4) estimating a view vector that is a visual direction unit vector from the SAR platform to a point on the ground using the coordinate transformation matrix generated in step (a3); and
(a5) estimating an inclination distance corresponding to the nadir angle input in step (a1) using the view vector estimated in step (a4);
In step (a2),
The velocity vector of the SAR platform is defined as the X-axis of the flight coordinate system, the position vector of the SAR platform is defined as the Z-axis of the flight coordinate system, and the Y-axis of the flight coordinate system is defined as the X-axis and the Z-axis according to the right hand rule. It is defined based on the axis,
Characterized in that the view vector is arranged on the YZ plane based on the flight coordinate system, the geodetic coordinate estimation method delete According to claim 1,
In step (a),
Generating the lookup table by changing the nadir angle at preset angular intervals within the permissible nadir angle range, applying the changed nadir angle to the input data, and repeating steps (a1) to (a5);
The iterative execution is performed until the changed nadir angle exceeds a maximum value of the permissible nadir angle range. According to claim 1,
In step (b),
(b1) receiving measurement data including the measured position and speed of the SAR platform, and the measured inclination distance measured from the position of the SAR platform to the estimated coordinate point on the ground corresponding to the estimated coordinate point;
(b2) based on the measurement data, estimating a nadir angle for the estimated coordinate point on the land surface using the lookup table;
(b3) setting a flight coordinate system of the SAR platform and generating a coordinate transformation matrix between the flight coordinate system and an Earth-Centered Earth-Fixed (ECEF) coordinate system using the measurement data;
(b4) generating a view vector that is a visual direction unit vector from the SAR platform to the estimated coordinate point on the ground using the coordinate conversion matrix generated in step (b3) and the nadir angle estimated in step (b2) step; and
(b5) estimating the geodetic coordinates of the coordinate estimation point using the view vector generated in step (b4);
A method for estimating geodetic coordinates including According to claim 1,
The coordinate estimation point is a point corresponding to any one of the remaining pixel points excluding the center pixel point among all pixel points in the obtained SAR image. An apparatus for estimating the geodetic coordinates of coordinate estimation points in the SAR image obtained from the Sythetic Aperture Radar (SAR) platform,
a generation unit that generates relationship information between a nadir angle and an inclination distance corresponding to the nadir angle as a lookup table; and
an estimator for estimating the geodetic coordinates of the coordinate estimation point, which is a target of geodetic coordinate estimation, using the lookup table;
including,
The generator,
Receive input data including the position and speed of the SAR platform and the nadir angle of a point on the ground where a signal transmitted from the SAR platform is reflected, and use the input data to set a flight coordinate system of the SAR platform, A coordinate transformation matrix between the flight coordinate system and an Earth-Centered Earth-Fixed (ECEF) coordinate system is generated, and a view vector, which is a visual direction unit vector from the SAR platform to a point on the ground, is estimated using the coordinate transformation matrix, Estimating an inclination distance corresponding to an input nadir angle using the estimated view vector;
The generator,
The velocity vector of the SAR platform is defined as the X-axis of the flight coordinate system, the position vector of the SAR platform is defined as the Z-axis of the flight coordinate system, and the Y-axis of the flight coordinate system is defined as the X-axis and the Z-axis according to the right hand rule. Define based on axis,
The geodetic coordinate estimation device, characterized in that the view vector is disposed on the YZ plane based on the flight coordinate system.

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