JPH04244989A - Preparing apparatus for simulated synthetic-aperture radar image - Google Patents

Abstract

PURPOSE:To reduce a processing time for calculation of foreshortening deflection. CONSTITUTION:The amount of foreshortening deflection in pixels at four corners of DTM is calculated in a deflection amount calculating part 21, a relational formula of the amount of foreshortening deflection at the four corners of DTM/ altitude is prepared in an approximation formula preparing part 22, the amount of deflection given by the four corners of the DTM is calculated in a deflection addition processing part 33 by using altitude values in all pixels of the DTM and the above-mentioned relational formula of the amount of foreshortening deflection at four corners of DTM/altitude, and linear primary interpolation of the above-mentioned amount of foreshortening deflection is executed on the basis of the positions of the pixels.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a simulated synthetic aperture radar image creation device, and more particularly to a synthetic aperture radar image (hereinafter referred to as "S").
The present invention relates to a method for calculating geometric distortion (hereinafter referred to as "foreshortening distortion") due to topographical undulations peculiar to AR images (hereinafter referred to as "foreshortening distortion").

0002

2. Description of the Related Art A technique for correlating SAR images and topographic maps is generally called geocoding. To perform geocoding, it is necessary to create an image in which foreshortening distortion, which is unique to SAR images, is corrected.

[0003] A method for creating a geocoded SAR image involves a rectangular digital terrain model (hereinafter referred to as "
There is a method using ``DTM''. That is, a simulated synthetic aperture radar image (hereinafter referred to as a "simulated SAR image") to which a foreshortening distortion specific to SAR images is added is created from the DTM, and a ground control point (hereinafter referred to as a "GCP") is created from the SAR image and the simulated SAR image. This is a method of extracting the GCP information and associating the SAR image with the simulated SAR image based on the GCP information. Since the amount of foreshortening distortion is known in the simulated SAR image, it is possible to remove the foreshortening distortion from the SAR image.

Next, a method for determining the amount of foreshortening distortion to be added to the DTM will be explained with reference to FIG. In FIG. 3, (λ1, θ1) is the (latitude, longitude) of the point A directly below the satellite S, (λ2, θ2) is the (latitude, longitude) of the target point B,
RS is the radius of the earth at the point A directly below the satellite, R is the radius of the earth near the target point B, H is the altitude of the satellite S, and L is the altitude of the target point B. Figure 3 shows that when considering a spherical triangle with a point A directly below the satellite and a target position B having a height L as the vertices of the triangle, the geocentric distance between the point A directly below the satellite and the target point B is the same as the angle φ1 and φ2. , indicating that a predetermined amount δ of foreshortening distortion exists between them. The angles φ1 and φ2 are given by the following equations 1 and 2.

[0005]

[Math 1]

[0006]

[Math 2]

That is, the latitude and longitude (λ2, θ
2), extract the information on height L, find the latitude and longitude (λ1, θ1) of the satellite corresponding to target point B, and the distance from the earth to the satellite (H + RS), and substitute them into the above equation. , the angles φ1 and φ2 are found. Then, the amount of distortion δ can be obtained using the following equation 3.

[0008]

[Math 3]

Conventionally, calculations using Equation 3 have been performed for all pixels of a simulated SAR image.

0010

[Problems to be Solved by the Invention] In the conventional method described above, the latitude, longitude,
Find the altitude, satellite position and altitude, and use that information to
There is a problem in that an enormous amount of processing time is required because complex numerical calculations such as Equation 3 are performed on all pixels of the simulated SAR image.

An object of the present invention is to provide a simulated synthetic aperture radar image creation device that can significantly reduce the processing time for calculating the amount of foreshortening distortion.

0012

Means for Solving the Problems In order to achieve the above object, a simulated synthetic aperture radar image creation device of the present invention has the following configuration. That is, the simulated synthetic aperture radar image creation device of the present invention includes: a DTM input section that imports a rectangular digital terrain model (hereinafter referred to as "DTM") into the device; and the DT.
a distortion amount calculation unit that calculates the amount of foreshortening distortion at the pixels at the four corners of M; an approximate expression creation unit that creates a relational expression between the amount of foreshortening distortion at the four corners of the DTM and the altitude; a distortion addition processing unit that calculates a foreshortening distortion amount for all pixels of the DTM using a relational expression;
It is characterized by including.

[0013]

[Operation] Next, the operation of the simulated synthetic aperture radar image creation apparatus of the present invention constructed as described above will be explained. In the present invention, the amount of foreshortening distortion at the pixels at the four corners of the DTM is calculated, and a relational expression between the amount of foreshortening distortion at the four corners of the DTM and the altitude is created. And this DTM
Relational expression of foreshortening distortion/elevation at four corners and DT
The amount of distortion given by the four corners of the DTM is calculated using the elevation values of all pixels of M, and linear linear interpolation of the amount of foreshortening distortion is performed from the pixel position.

Thus, according to the present invention, the amount of foreshortening distortion is calculated only for the pixels at the four corners of the DTM, so that the calculation processing time can be significantly reduced.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a simulated synthetic aperture radar image creation device according to an embodiment of the present invention. In FIG. 1, the DTM input section 1 takes in DTM data and outputs it to the distortion amount calculation section 21 of the distortion correction preprocessing section 2 and the rotation processing section 31 of the data conversion section 3. The distortion correction preprocessing section 2 prepares for correction of foreshortening distortion specific to SAR images, and the data conversion section 3 adds pseudo luminance and foreshortening distortion to the DTM to create a simulated SAR image.

The distortion amount calculation unit 21 calculates the foreshortening distortion amount for each pixel at the four corners of the DTM at arbitrary altitude intervals (for example, every 1000 m). Equation 3 above is used to calculate the amount of foreshortening distortion.

The approximation formula creation section 22 calculates 4 based on the information on the altitude and the foreshortening distortion amount from the distortion amount calculation section 21.
For each corner pixel, use the following quadratic formulas (Equations 4 to 7)
) to approximate the relationship between the altitude L and the foreshortening distortion amount δ, and its coefficients an to cn (n=1 to 4) are calculated using the method of least squares.

[0018]

[Math 4]

[0019]

[Math 5]

[0020]

[Math 6]

[0021]

[Math 7]

On the other hand, the rotation processing section 31 rotates the DTM so that it is parallel to the direction of microwave irradiation from the satellite. The brightness calculation processing unit 32 calculates the altitude difference between all pixels of the rotated DTM and provides a pseudo brightness value corresponding to the altitude difference. Then, the distortion addition processing unit 33 uses this pseudo brightness value and the four approximate expressions obtained by the approximation expression generation unit 22 to complete a desired simulated SAR image. This will be explained in detail with reference to FIG.

First, substitute the altitude Li of an arbitrary pixel P into Equations 4 to 7, and calculate the foreshortening distortion amount (δLU, δRU, δLD, δ
RD) is calculated. Next, the position of any pixel P (x
Using the X component xi of i, yi), the distortion amounts δU and δD in PU and PD are calculated by linear interpolation shown in Equations 8 and 9 below. Note that in Equations 8 and 9, m is the number of pixels in the X direction of the DTM.

[0024]

[Math. 8]

[0025]

[Math. 9]

Next, the amount of distortion δU calculated using Equations 8 and 9
and δD, using the Y component yi of DTM, the following formula 1
0 is performed to calculate the distortion amount δP at P. Note that in Equation 10, n is the number of pixels in the Y direction of the DTM.

[0027]

[Math. 10]

Then, by moving the brightness value calculated by the brightness calculation processing section 32 based on this distortion amount δP, a simulated SAR image containing foreshortening distortion is completed. This completed simulated SAR image is sent to the CR from the image output unit 4.
It is output to an output device such as T.

[0029]

As explained above, according to the simulated synthetic aperture radar image creation device of the present invention, the amount of foreshortening distortion is calculated only for the pixels at the four corners of the DTM, so the calculation processing time is reduced. This has the effect of significantly reducing the amount.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of a simulated synthetic aperture radar image creation device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a foreshortening distortion correction procedure according to the present invention.

FIG. 3 is an explanatory diagram of foreshortening distortion amount calculation.

[Explanation of symbols]

1 DTM input section 2 Distortion correction preprocessing section 3 Data conversion section 4 Image output section 21 Distortion amount calculation section 22 Approximate formula creation section 31 Rotation processing section 32 Brightness calculation processing unit 33 Distortion addition processing section

Claims (1)

[Claims] [Claim 1] A simulated synthetic aperture radar image creation device comprising; a DTM input section that imports a rectangular digital terrain model (hereinafter referred to as "DTM") into the device;
a distortion amount calculation unit that calculates the amount of foreshortening distortion at the pixels at the four corners of the TM; an approximate expression creation unit that creates a relational expression between the amount of foreshortening distortion at the four corners of the DTM and the altitude; a distortion addition processing unit that calculates a foreshortening distortion amount for all pixels of the DTM using a relational expression;
A simulated synthetic aperture radar image creation device comprising: