JPH06148321A - Device for making up foreshortening distortion compensation table - Google Patents

Abstract

PURPOSE:To reduce time required for making up and processing a foreshortening distortion compensation table used for compensating the foreshortening distortion of an SAR (synthesis aperture radar) image greatly. CONSTITUTION:A DTM input part 1 inputs a DTM (rectangular numerical topography model) with a pixel spacing which is two times larger than that of the SAR image to be processed and a rotary processing part 2 rotates it and then aligns it. A part 3 for calculating the amount of distortion calculates the amount of foreshortening distortion for each pixel of the DTM. A table make-up/processing part 4 make up a geocoding SAR image address/SAR image address correspondence table which becomes the entity of the foreshortening distortion compensation table for the SAR image with the same pixel spacing as that of DTM based on the calculated result of the part 3 for calculating the amount of distortion and then performs enlargement processing. The geocoding SAR image address/SAR image address correspondence table which becomes the entity of the foreshortening distortion compensation table for the SAR image to be processed is make up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for creating a foreshortening distortion correction table used for removing foreshortening distortion due to topographical relief from a SAR (synthetic aperture radar) image.

[0002]

2. Description of the Related Art The SAR image obtained when the SAR is mounted on a flying body such as a satellite and a microwave radar beam is irradiated obliquely downward at a right angle to the flight direction to observe the surface of the earth is the characteristic of the SAR. In addition, the higher the altitude of the object, the more geometrical distortion that is caused by the terrain ups and downs, such that the object leans toward the aircraft. Such distortion is generally called foreshortening distortion, and an image obtained by correcting foreshortening distortion from a SAR image is called a geocoded SAR image.

A method of creating a geo-coded SAR image includes a rectangular numerical terrain model created from a topographic map (hereinafter,
There is the following method using DTM).

First, a SAR simulation image to which a distortion called a foreshortening distortion peculiar to the SAR image, which is caused by topographical relief, is added is created from the DTM. Next, the SAR simulation image and the SAR image are matched and the same ground reference point is extracted. That is, S
The AR image and the SAR simulation image are associated with each other. Then, the foreshortening distortion correction of the SAR image is performed using the foreshortening distortion correction table to obtain a geocoded SAR image.

Here, the foreshortening distortion correction table means the SAR image and the geocoded SAR.
It is an address correspondence table with an image, and is conventionally created as follows.

First, a DTM having the same pixel spacing (pixel size) as the SAR image to be processed is prepared, and DT
The DTM is rotated so that the line direction, which is the unit of M processing, and the microwave irradiation direction from the satellite are parallel to each other.

Next, the foreshortening distortion amount is calculated for each pixel of the DTM from the altitude data and the orbit information (position, altitude, etc.) of the satellite, the foreshortening distortion position of each pixel of the DTM is calculated, and the position is also determined. Then, the DTM transfer destination address is obtained.

For example, 28 pixels on one line of DTM (assuming that the size of one pixel is, for example, 5 m, and consecutive addresses 1 to 28 starting from 1 are given)
Assuming that each elevation is indicated by a black circle in FIG. 7, the foreshortening distortion position of each pixel based on the elevation and the foreshortening distortion amount calculated from the orbit information of the satellite is, for example, the one indicated by a white circle in FIG. 7, The destination address of each pixel is as shown in FIG.

Next, from the destination address table shown in the upper part of FIG. 9 in which the portion of the foreshortening distortion amount is removed from FIG. 8, the structure of the foreshortening distortion correction table shown in FIG. A geocoded SAR image address / SAR image address correspondence table that is an element is created.

The SAR image address value corresponding to the geocoded SAR image address 1 is the DTM destination address value corresponding to the DTM address 1, and this DTM destination address value is the initial value of the judgment reference value.

The SAR image address value corresponding to the geo-coded SAR image address n is determined by comparing the DTM destination address value corresponding to the DTM address n with the determination reference value and giving the larger value. At this time, if the determination reference value is smaller than the current DTM move destination address value, the current D
The TM move destination address value is used as a new judgment reference value.

[0012]

As described above, conventionally, the foreshortening distortion correction table is created by using the DTM having the same pixel spacing as the SAR image to be processed. That is, when the pixel spacing of the SAR image to be processed is 5 m, the DTM of pixel spacing 5 m is used, and when the pixel spacing of the SAR image to be processed is 10 m, the DTM of pixel spacing 10 m is used. There is.

Here, since the processing for every pixel is required to create the foreshortening distortion correction table, for example, when the pixel spacing is halved,
The number of pixels is quadrupled, which requires about quadrupled creation time.

The present invention has been made in view of such circumstances, and an object thereof is D having a larger pixel spacing, that is, a smaller number of pixels than the SAR image to be processed.
The TM is used to create a foreshortening distortion correction table that can be used for distortion correction of the SAR image, thereby significantly shortening the time for creating the foreshortening distortion correction table.

[0015]

In order to achieve the above object, the present invention provides a foreshortening distortion correction table creation apparatus used for correcting foreshortening distortion of an SAR image, which is a processing target. Based on the foreshortening distortion amount calculated by the distortion amount calculating unit for calculating the foreshortening distortion amount for each pixel of the DTM having a pixel spacing of an integer multiple of After the geocoded SAR image address / SAR image address correspondence table, which is a constituent element of the foreshortening distortion correction table for SAR images having pixel spacing, is created, enlargement processing is performed to make the target S
Geocoded SAR image address / S that is a component of the foreshortening distortion correction table for AR images
And a table creation processing unit for creating an AR image address correspondence table.

[0016]

In the foreshortening distortion correction table creating apparatus of the present invention, the distortion amount calculating unit performs S
DTM with pixel spacing that is an integer multiple of AR image
The foreshortening distortion amount is calculated for each pixel of, and the table creation processing unit first based on the foreshortening distortion amount calculated by the distortion amount calculating unit, first, for the SAR image having the same pixel spacing as the DTM. Foreshortening distortion correction for the SAR image to be processed is created by creating a geocoded SAR image address / SAR image address correspondence table, which is a component of the foreshortening distortion correction table, and then subjecting this table to expansion processing. A geocoded SAR image address / SAR image address correspondence table that is a constituent element of the table is created.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Referring to FIG. 1, one embodiment of the foreshortening distortion correction table creating apparatus of the present invention is a DTM.
An input unit 1, a rotation processing unit 2, a distortion amount calculation unit 3, a table creation processing unit 4, and a table output unit 5 are provided, and the table creation processing unit 4 includes a distortion addition processing unit 41 and an offset calculation processing unit. 42 and a resampling processing unit 43.

The operation of this embodiment and the detailed functions of each part will be described below.

Assuming that the SAR image to be processed has a pixel spacing of 5 m, for example, a DTM having a pixel spacing of 10 m is used in this embodiment.

The DTM input unit 1 inputs a DTM of a pixel spacing of 10 m from a storage device (not shown) or the like.

Next, the rotation processing unit 2 receives this input DT.
The DTM is rotated so that the line direction, which is the unit of M processing, and the microwave irradiation direction from the satellite are parallel to each other.

Next, the distortion amount calculation unit 3 calculates the foreshortening distortion amount for each pixel of the DTM from the altitude data and the satellite orbit information.

Next, the table creation processing unit 4 corrects the foreshortening distortion for the SAR image having the same pixel spacing as the DTM, based on the foreshortening distortion amount of each pixel of the DTM calculated by the distortion amount calculating unit 3. A geocoded SAR image address / SAR image address correspondence table that is a constituent element of the table is created, and then enlarged processing is performed to thereby become a constituent element of the foreshortening distortion correction table for the SAR image to be processed. A SAR image address / SAR image address correspondence table is created to complete the foreshortening distortion correction table.

Finally, the table output section 5 outputs the foreshortening distortion correction table created by the table creation processing section 4 to an electronic disk or the like (not shown).

The function of the table creation processing section 4 will be described in detail below.

The table creation processing section 4 carries out the following processing for each DTM line.

First, the distortion adding processing unit 41 adds a foreshortening distortion to the elevation data for each pixel of the DTM on the line to indicate the moving destination of each pixel of the DTM / DTM address / DTM moving destination address. Create a correspondence table.

That is, the altitude of each 14 pixels on one line of the DTM (assuming that the size of one pixel is 10 m and consecutive addresses 1 to 14 starting from 1 are given) is the black circle in FIG. And the foreshortening distortion amount calculated by the distortion amount calculating unit 3 from the altitude and the orbit information of the satellite is shown in FIG. 3, for example, the foreshortening distortion amount is calculated for each pixel. By adding a value divided by pacing 10 m to the address of the pixel, a DTM destination address as shown in FIG. 3 is obtained, and the upper side of FIG. 4 composed of the DTM address and the DTM destination address in FIG. D as shown in
A TM address / DTM destination address correspondence table is created. The white circles in FIG. 2 indicate the DTM with distortion.

Next, the offset calculation processing section 42
From the DTM address / DTM transfer destination address correspondence table created by the distortion addition processing unit 41 as shown in the upper side of FIG. 4, the following logics (1) and (2) are used, as shown in the lower side of FIG. Geocoded SAR image address / SA
An R image address correspondence table is created.

(1) The SAR image address value corresponding to the geocoded SAR image address 1 is a value obtained by subtracting 1 from the DTM moving destination address value corresponding to the DTM address 1, and this DTM moving destination address value is used as the criterion. Use the initial value.

(2) For the SAR image address value corresponding to the geocoded SAR image address n, the DTM destination address value corresponding to the DTM address n is compared with the determination reference value, and n is subtracted from the larger value. The value. When the determination reference value is smaller than the current DTM destination address value, the current DTM destination address value is set as a new determination reference value.

In other words, the geocoded SAR image and the SAR image are associated with each other not by the absolute address of the SAR image but by the offset (offset) from the geocoded SAR image. This is for facilitating the table expansion process described later.

Next, by the resampling processing unit 43,
The geocoded SAR image address / SAR image address correspondence table shown on the lower side of FIG. 4 is enlarged in accordance with the pixel spacing of the SAR image to be processed. In this case, the pixel spacing of the SAR image to be processed is 5 m, and the pixel spacing of the DTM used is 10 m, so the table size is enlarged to double the SAR image of 5 m pixel spacing. Create a suitable geo-coded SAR image address / SAR image address correspondence table.

That is, the geocoded SA on the lower side of FIG.
R image address / SAR image address correspondence table, which is the SAR image address 3 at the beginning of the table, is set to 6 as the SAR image address corresponding to the geocoded SAR image addresses 1 and 2, and the next SAR image address 2.5 is set. By continuing to the last SAR image address, the operation of setting the doubled 5 as the SAR image address corresponding to the geocoded SAR image SAR addresses 3 and 4, the geocode with 28 addresses as shown in FIG. A table for correspondence between the dead SAR image address and the SAR image address is created.

With the above, the processing for one line of DTM is completed, and the table creation processing unit 4
By repeating the same process for all lines of
Geocord SAR image address / SAR image address correspondence tables as shown in FIG. 5 are created for the number of lines. As a result, the foreshortening distortion correction table for the SAR image having the pixel spacing of 5 m to be processed is completed. Since the number of lines of the DTM is half the number of lines of the SAR image to be processed, at the time of actual correction, the geocoded SAR image address / SAR image address correspondence table created as shown in FIG. 5 is used to process the SAR image to be processed. It may be applied to two adjacent lines. Of course, two lines may be created in the foreshortening distortion correction table in advance.

FIG. 6 shows how the distortion of the SAR image is removed according to the contents of the geocoded SAR image address / SAR image address correspondence table of FIG.
Is a SAR image for one line, 12 is a geo-coded SAR image for one line, 31 and 32 are pixels, and an arrow indicates a destination.

[0038]

As described above, according to the present invention, a DTM having a pixel spacing that is an integral multiple of the SAR image to be processed is used. First, for a SAR image having the same pixel spacing as the DTM. Geocoded S that is a component of the Foreshortening distortion correction table
By creating an AR image address / SAR image address correspondence table and then enlarging it, a geocoded SAR image address / SAR image address that is a constituent element of the foreshortening distortion correction table for the SAR image to be processed A correspondence table is created, and a geocoded SAR image that is a component of a foreshortening distortion correction table for a SAR image having the same pixel spacing from a DTM having a pixel spacing that is an integral multiple of the SAR image to be processed The processing time for creating the address / SAR image address correspondence table is the geocoded SAR which is a component of the foreshortening distortion correction table for the SAR image from the DTM having the same pixel spacing as the SAR image to be processed. Picture Address / SAR image address correspondence table can remarkably shortened compared with the case of creating directly, while since the expansion of the table can be done by a simple process, it is possible to greatly reduce the overall processing time.

The foreshortening distortion correction table created by the present invention is slightly less accurate than the foreshortening distortion correction table created directly from the DTM having the same pixel spacing as the SAR image to be processed, As described above, the processing time can be greatly shortened, and the practical effect is sufficiently large.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a relational diagram between a DTM and a DTM with distortion.

FIG. 3 is a relational diagram of a DTM address, a distortion amount, and a DTM destination address.

FIG. 4 DTM address / DTM destination address correspondence table and geocoded SAR image address / SAR
It is a block diagram of an image address correspondence table.

FIG. 5 is a configuration diagram of a geocoded SAR image address / SAR image address correspondence table after enlargement.

FIG. 6 is an explanatory diagram of a foreshortening distortion removal method for a SAR image.

FIG. 7 is a diagram showing a relationship between a DTM used for explaining a conventional example and a DTM with distortion.

FIG. 8 is a relational diagram of a DTM address, a distortion amount, and a DTM destination address used for explaining a conventional example.

FIG. 9 is a DTM address / DT used for explaining a conventional example.
M destination address correspondence table and geocoded SA
It is a block diagram of an R image address / SAR image address correspondence table.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... DTM input part 2 ... Rotation processing part 3 ... Distortion amount calculation part 4 ... Table creation processing part 41 ... Distortion addition processing part 42 ... Offset calculation processing part 43 ... Resampling processing part 5 ... Table output part

Claims (1)

[Claims] 1. A device for creating a foreshortening distortion correction table used for correcting foreshortening distortion of a SAR image, wherein each pixel of a numerical terrain model having a pixel spacing that is an integral multiple of the SAR image to be processed. On the other hand, a distortion amount calculation unit for calculating a foreshortening distortion amount, and a foreshortening distortion for a SAR image having the same pixel spacing as the numerical terrain model based on the foreshortening distortion amount calculated by the distortion amount calculation unit. After the geocoded SAR image address / SAR image address correspondence table, which is a constituent element of the correction table, is created, enlargement processing is performed so that the S
Geocoded SAR image address / S that is a component of the foreshortening distortion correction table for AR images
A foreshortening distortion correction table creation device, comprising: a table creation processing unit that creates an AR image address correspondence table.