JP4916777B2 - Image radar device - Google Patents

Description

  The present invention relates to an image radar apparatus that observes topography.

The phase of the radar reception signal is proportional to the distance from the antenna to the scattering point. An image radar device called interferometric synthetic aperture radar or interferometric synthetic aperture radar uses this principle to acquire two radar images under slightly different radio wave incident angles, and to calculate the phase difference between the two radar images. Based on this, the height of the terrain is measured (see, for example, Patent Document 1). FIG. 8 is a topographic observation geometry, which virtually represents a state in which a topographic observation target region 18 having an inclination angle 20 with respect to a virtual horizontal plane 19 is observed from the radar platform 16. The radar platform 16 moves at a constant linear velocity, and the observation target region 18 is observed by radiating radio waves in a direction orthogonal to the velocity direction by an antenna 17a or 17b mounted on the radar platform 16. The reflected waves from the observation target area 18 are received by the two antennas 17a and 17b, and two radar images relating to the observation target area 18 are obtained from the respective received signals. This is a technique widely known as a synthetic aperture radar. The axis of the radio wave propagation direction of the image is called a range, and the axis of the platform velocity direction is called azimuth.
In the radar apparatus, the above two radar images are observed, and an interferogram obtained at that time, that is, a schematic diagram showing a phase difference between two radar images obtained by observing the same region is shown in FIG. . The horizontal axis is the range, and the vertical axis is the azimuth. The shading represents a phase difference from zero to 2π radians. (A) and (b) are interferograms when the terrain inclination angle is zero, and (c) is an interferogram when the terrain inclination angle is not zero.

  In the case of the radar apparatus disclosed in Patent Document 1, first, the registration means compensates for the difference between the range and the azimuth and the difference in resolution for the two radar images obtained from the received signals of the respective antennas 17a and 17b. Then, adjustment is performed so that the same scattering point appears in the same pixel of the image. Next, the phase difference calculation means calculates the phase difference between the two images that have been adjusted, and outputs as an output the position corresponding to the distance difference from the two antennas 17a and 17b to each scattering point on the observation target region 18. A phase difference, for example, FIG. 9A is obtained. Next, the phase difference is calculated by the plane phase removing means on the assumption that the observation target region 18 is the horizontal plane 19, and this is calculated from the phase difference (FIG. 9A) calculated by the phase difference calculating means. Subtract. Then, since the phase difference according to the height of the topography as shown in FIG. 9B is obtained, it is understood that the topography can be calculated based on this phase difference. However, the phase difference shown in FIG. 9 (b) can only be observed when the phase difference is in the range of zero to 2π radians. Therefore, an unwrap operation is performed by using phase unwrap means to open the fold and connect them together. Various methods are known for this method. Finally, using the phase / height conversion means, the phase difference that has been folded back is converted into a height to obtain a height distribution diagram.

JP 2004-191053 A

  As described above, the conventional radar apparatus calculates the phase difference on the assumption that the observation target region 18 is the horizontal plane 19 in order to obtain a height distribution map of the observation target region 18 in FIG. Is subtracted from the phase difference according to the distance difference to the scattering point to obtain the phase difference according to the height of the topography. For this reason, when the observation target region 18 is inclined, the phase difference corresponding to the height of the topography is, for example, as shown in FIG. In this case, on the left side of FIG. 9C, that is, the slope on the platform side of the convex portion of the terrain, a phenomenon occurs in which the density of equiphase difference lines is higher than that of the slope of FIG. 9B. This phenomenon has a problem that an error occurs in the operation of the phase unwrapping means in a noisy environment, and as a result, an error occurs in the height distribution diagram generated by the phase / height converting means.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain an image radar apparatus that obtains a height distribution map with less error.

The image radar apparatus according to the present invention acquires two radar images under conditions where incident angles of reflected waves from the observation target region are slightly different, and measures the height of the topography based on the phase difference between the two radar images. In the image radar apparatus, registration means for adjusting two input radar images so that the same scattering point appears in the same pixel of the image, and calculating the phase difference between the two adjusted radar images. Calculated by the phase difference calculating means, the terrain data storing means for storing the terrain information of the observation target area in advance, the inclination calculating means for calculating a representative inclination in the observation target area based on the terrain information, and the inclination calculating means is calculated by the observed object and the planar phase calculating means for calculating a plane phase corresponding to the scattering point of the region, the phase difference plane phase calculating means from a phase difference of the two radar images calculated by the calculating means having a slope The phase compensation means for reducing the planar phase, the phase unwrapping means for opening and joining the phase compensated phase difference, and the distribution of the height of the observation area by converting the joined phase difference into the height of the topography Phase / height conversion means for obtaining a figure, and height correction means for adding the inclination of the observation target area calculated by the inclination calculation means to the distribution chart of the calculated height are provided.

  According to the present invention, the plane phase is subtracted from the phase difference between the two radar images, thereby avoiding a situation where the intervals of the equiphase lines are close as in the interferogram when the terrain is not inclined. Can do. Therefore, the phase unwrapping process can be performed without error, and it is possible to obtain a height distribution map with little error even when the topography of the observation target region is inclined.

Embodiment 1 FIG.
1 is a block diagram showing a functional configuration of an image radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, the registration means 2 adjusts two radar images acquired under conditions where the incident angles of reflected waves from the observation target area are slightly different so that the same scattering point appears in the same pixel of the image. It is. The phase difference calculation means 3 is a means for calculating the phase difference between the two adjusted radar images. The terrain data storage means 11 is a means for previously storing terrain information of the observation target area. The inclination calculation means 10 is a means for calculating a representative inclination in the observation target area based on the terrain information in the terrain data storage means 11. The plane phase calculation unit 9 is a unit that calculates a phase corresponding to a scattering point on the observation target region having the inclination calculated by the inclination calculation unit 10. The phase compensation unit 8 is a unit that subtracts the plane phase calculated by the plane phase calculation unit 9 from the phase difference between the two radar images calculated by the phase difference calculation unit. The phase unwrapping means 5 is means for opening and joining the phase-compensated phase differences. The phase / height conversion means 6 is a means for obtaining a distribution map of the height of the observation target region by converting the connected phase difference into the height of the topography. The height correcting unit 7 is a unit that corrects the calculated distribution of height by adding the inclination calculated by the inclination calculating unit 10. Of the above means, the means 2, 3, 5 and 6 are of the same type as those used in the conventional radar apparatus.

  FIG. 2 is a schematic diagram showing a phase difference between two radar images obtained by observing the same region according to the image radar apparatus of the present invention. 2A shows the phase difference calculated by the phase difference calculation means 3 when the topography is inclined, FIG. 2C shows the phase difference output by the phase compensation means 8, and FIG. 2B shows the planar phase. Each of the phases output by the calculation means 9 is represented. In each interferogram, the horizontal axis is range and the vertical axis is azimuth. The shading represents a phase difference from zero to 2π radians.

Next, the operation will be described.
As shown in FIG. 8, this image radar apparatus irradiates a radio wave in a direction orthogonal to the velocity direction in a state where the antenna 17a or 17b mounted on the radar platform 16 is linearly moving at a constant speed, The reflected waves from the area 18 are received by the two antennas 17a and 17b, respectively, and two radar images relating to the observation target area 18 are obtained from the respective received signals. Note that the previous processing for obtaining the radar image is well known, and is omitted here. The registration unit 2 compensates for the obtained two radar images by compensating for the difference between the range and the azimuth and the difference in resolution so that the same scattering point appears in the same pixel of the image. The phase difference calculating means 3 calculates the phase difference between the two images adjusted by the registration means 2 and outputs the difference in distance from the two antennas 17a and 17b to each scattering point on the observation target region 18. A phase difference corresponding to is obtained. This phase difference is schematically represented as shown in FIG.

但し、ｒ_a はアンテナ１７ａと散乱点２７の距離、ｒ_b はアンテナ１７ｂと散乱点２７の距離、λは電波の波長である。 In the terrain data storage means 11, terrain information of the observation target area 18, for example, a terrain map with rough spatial resolution, or data such as latitude / longitude and altitude of several points is collected and stored in advance. In the slope calculation means 10, for example, a virtual plane is applied to the terrain information in the terrain data storage means 11 by, for example, a least square method, or an average value or mode value of the slope is calculated. And find the height offset value. Next, the plane phase calculation unit 9 calculates a phase difference corresponding to a scattering point on the observation target region having the inclination calculated by the inclination calculation unit 10 (this phase difference is hereinafter referred to as a plane phase). This planar phase is schematically represented as shown in FIG. The planar phase calculation processing operation will be described with reference to FIG. FIG. 3 shows a cross section of the geometry of FIG. 8 in the range direction, where 26 is a virtual plane, and 27 is a scattering point thereon. At this time, the plane phase corresponding to the scattering point 27 can be obtained by the following equation.

However, r _a distance scattering points 27 and antenna 17a, r _b is the antenna 17b and the distance of scattering points 27, lambda is the wavelength of the radio wave.

  The phase compensation unit 8 subtracts the plane phase obtained by the plane phase calculation unit 9 from the phase difference between the two radar images calculated by the phase difference calculation unit 3. This process is to subtract FIG. 2 (b) from FIG. 2 (a) to obtain FIG. 2 (c). Therefore, the output of the phase compensation means 8 (FIG. 2C) is equivalent to the interferogram when there is no phase difference corresponding to the inclination of the terrain and the terrain shown in FIG. 9B is not inclined. Result can be obtained. Therefore, it is possible to avoid a situation where the intervals of the equiphase lines are close, so that the phase unwrapping means 5 can open the folds of the phase difference compensated by the phase compensating means 8 and connect them without error. The phase / height conversion means 6 converts the phase difference connected by the phase unwrapping means 5 into a height, and obtains a height distribution map of the observation target region as an output. However, this result does not reflect the slope of the terrain and needs to be corrected. Therefore, the height correction means 7 adds the inclination of the observation target area calculated by the inclination calculation means 10 to the height distribution map of the observation target area calculated by the phase / height conversion means 6.

As described above, according to the first embodiment, the plane phase is subtracted from the phase difference between the two radar images, so that the interval between the equiphase lines is equal to the interferogram when the topography is not inclined. Therefore, it is possible to connect the phase differences without error in the phase unwrapping process. Therefore, even if the topography of the observation target area is inclined, a distribution map of height with less error can be obtained.
In the above description, the slope of the terrain is treated as a plane, but it is clear that the same effect can be obtained even with a curved surface. It is of course possible to divide the image and handle it as a large number of planes. The same applies to the following embodiments.

Embodiment 2. FIG.
4 is a block diagram showing a functional configuration of an image radar apparatus according to Embodiment 2 of the present invention. In the figure, portions corresponding to those in FIG. 1 of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted in principle. The second embodiment has a configuration in which an inclination estimation means 14 is provided instead of the topographic data storage means 11 and the inclination calculation means 10 of the first embodiment.
As can be seen from FIG. 2A, in the case of terrain where the undulation is local, it is possible to estimate the phase difference caused by the inclination of the terrain from the interferogram. Therefore, the inclination estimation means 14 estimates the inclination of the topography of the observation target area based on the phase difference between the two radar images calculated by the phase difference calculation means 3. For example, an interferogram of a part of the image is extracted, converted into a terrain slope, and applied to the entire region. Alternatively, the phase of the interferogram may be differentiated in the range direction, the average or mode value may be obtained, and converted to a slope.

  As described above, according to the second embodiment, the plane phase calculation unit 9 calculates the plane phase used by the phase compensation unit 8 using the gradient of the observation target region estimated by the gradient estimation unit 14, and the high Since the height correction means 7 corrects the height of the terrain, it does not require terrain data that requires labor to collect as in the first embodiment, and the distribution of heights with less errors as in the first embodiment. A figure can be obtained.

Embodiment 3 FIG.
FIG. 5 is a block diagram showing a functional configuration of an image radar apparatus according to Embodiment 3 of the present invention. In the figure, the same reference numerals are given to the portions corresponding to FIG. 1 of the first embodiment, and the description thereof will be omitted in principle. In the third embodiment, a radar scattering intensity database 29 for storing data related to the backscattering coefficient is provided instead of the topographic data storage means 11 of the first embodiment, and the inclination estimation means 142 is provided instead of the inclination calculation means 10. It has a configuration with.
The reflectance of radio waves varies depending on the state (covering) and frequency of the ground surface, and the incident angle. For these representative values, the observed or theoretical values are published. Conversely, when the covering and frequency are known, the incident angle can be estimated based on the reflectivity of the radio wave. Therefore, in the third embodiment, the radar scattering intensity database 29 stores in advance the land cover, frequency, and radio wave reflectance for each incident angle, that is, the backscattering coefficient. The inclination estimation unit 142 converts the intensity of the radar image obtained from the registration unit 2 into a backscattering coefficient with reference to the radar scattering intensity database 29, and estimates the incident angle based on the calculated backscattering coefficient. Further, the inclination of the observation target area is calculated from the estimated incident angle. At that time, the intensity of the image may be obtained based on the amplitude and power of one radar image, or may be obtained from two radar images.

  As described above, according to the third embodiment, the plane phase calculation unit 9 calculates the plane phase used by the phase compensation unit 8 using the inclination of the observation target area estimated based on the intensity of the radar image. In addition, since the height correction means 7 corrects the height of the terrain, the terrain data that requires time and labor for collection is not required as in the first embodiment, and the height with little error is the same as in the first embodiment. Can be obtained.

Embodiment 4 FIG.
FIG. 6 is a block diagram showing a functional configuration of an image radar apparatus according to Embodiment 4 of the present invention. In the figure, the same reference numerals are given to the portions corresponding to FIG. 1 of the first embodiment, and the description thereof will be omitted in principle. In the fourth embodiment, the height correcting means 7 of the first embodiment is not used, and instead, the phase correcting means 12 is provided between the phase unwrapping means 5 and the phase / height converting means 6. .
In the phase correction unit 12, the phase difference calculated by the plane phase calculation unit 9 is added to the phase difference that is opened and joined by the phase unwrap unit 5 to correct the phase difference.
In the first embodiment, the inclination is corrected after the height of the terrain is obtained. In the fourth embodiment, the inclination is obtained by adding a plane phase before obtaining the height of the terrain. Is corrected. Also in this case, it is possible to obtain a height distribution diagram with less error equivalent to that in the first embodiment.

Embodiment 5 FIG.
FIG. 7 is a block diagram showing another functional configuration of an image radar apparatus according to Embodiment 5 of the present invention. In the figure, the same reference numerals are given to the portions corresponding to FIG. 6 of the fourth embodiment, and the description thereof will be omitted in principle. The fifth embodiment has a configuration in which a plane phase estimation means 13 is provided in place of the topographic data storage means 11 , the inclination calculation means 10 and the plane phase calculation means 9 of the fourth embodiment.
The plane phase estimation unit 13 estimates the plane phase corresponding to the scattering point on the observation target area having an inclination based on the phase difference between the two radar images calculated by the phase difference calculation unit 3. For example, an interferogram of a part of the region is extracted and applied to the entire region as a phase difference caused by the slope of the terrain. Alternatively, the average or mode value may be obtained by differentiating the phase of the interferogram in the range direction.
As described above, according to the fifth embodiment, the phase compensation unit 8 compensates for the phase difference of the radar image using the plane phase based on the slope of the terrain estimated by the plane phase estimation unit 13, and the phase correction is performed. The means 12 corrects the phase difference connected by the phase unwrapping means 5 so that the terrain data that requires time and effort for collection as in the first and fourth embodiments is not required. Similarly, a height distribution map with less error can be obtained.

It is a block diagram which shows the function structure of the image radar apparatus by Embodiment 1 of this invention. It is a schematic diagram showing the phase difference of the two radar images which observed the same area | region which concerns on the image radar apparatus of this invention. It is sectional drawing of the range direction of the geometry of topographic observation. It is a block diagram which shows the function structure of the image radar apparatus by Embodiment 2 of this invention. It is a block diagram which shows the function structure of the image radar apparatus by Embodiment 3 of this invention. It is a block diagram which shows the other function structure of the image radar apparatus by Embodiment 4 of this invention. It is a block diagram which shows the function structure of the image radar apparatus by Embodiment 5 of this invention. It is explanatory drawing which shows the geometry of the condition of topographic observation. It is a schematic diagram showing the phase difference of the two radar images which observed the same area | region which concerns on the conventional radar apparatus.

Explanation of symbols

  2 registration means, 3 phase difference calculating means, 5 phase unwrapping means, 6 phase / height converting means, 7 height correcting means, 8 phase compensating means, 9 plane phase calculating means, 10 slope calculating means, 11 topography data storage Means, 12 phase correction means, 13 plane phase estimation means, 14, 142 inclination estimation means, 29 radar scattering intensity database.

Claims (5)

In an image radar apparatus that acquires two radar images under conditions where incident angles of reflected waves from the observation target area are slightly different and measures the height of the terrain based on the phase difference between the two radar images,
Registration means for adjusting two input radar images so that the same scattering point appears at the same pixel of the image;
A phase difference calculating means for calculating a phase difference between the two adjusted radar images;
Terrain data storage means for storing terrain information of the observation target area in advance;
An inclination calculating means for calculating a representative inclination in the observation target area based on the terrain information;
A plane phase calculating means for calculating a plane phase corresponding to a scattering point on the observation target region having the inclination calculated by the inclination calculating means;
Phase compensation means for subtracting the plane phase calculated by the plane phase calculation means from the phase difference between the two radar images calculated by the phase difference calculation means;
And phase unwrapping means for joining open return of the phase-compensated phase difference by the phase compensation means,
A phase / height conversion means for converting the connected phase difference into the height of the terrain and obtaining a distribution map of the height of the observation target area;
An image radar apparatus, comprising: a height correction unit that adds the inclination of the observation target region calculated by the inclination calculation unit to the distribution map of the calculated height. In an image radar apparatus that acquires two radar images under conditions where incident angles of reflected waves from the observation target area are slightly different and measures the height of the terrain based on the phase difference between the two radar images,
Registration means for adjusting two input radar images so that the same scattering point appears at the same pixel of the image;
A phase difference calculating means for calculating a phase difference between the two adjusted radar images;
Inclination estimation means for estimating the inclination of the terrain of the observation target area based on the phase difference between the two radar images calculated by the phase difference calculation means ;
A plane phase calculating means for calculating a plane phase corresponding to a scattering point on the observation target area having the inclination estimated by the inclination estimating means ;
Phase compensation means for subtracting the plane phase calculated by the plane phase calculation means from the phase difference between the two radar images calculated by the phase difference calculation means;
Phase unwrapping means for opening and joining the folded phase difference compensated by the phase compensation means;
A phase / height conversion means for converting the connected phase difference into the height of the terrain and obtaining a distribution map of the height of the observation target area;
A distribution diagram of calculated out the height, image radar apparatus characterized by comprising a height correction means for correcting by adding the inclination of the observation target region estimated by the gradient estimation unit. In an image radar apparatus that acquires two radar images under conditions where incident angles of reflected waves from the observation target area are slightly different and measures the height of the terrain based on the phase difference between the two radar images,
Registration means for adjusting two input radar images so that the same scattering point appears at the same pixel of the image;
A phase difference calculating means for calculating a phase difference between the two adjusted radar images;
A radar scatter intensity database for storing data related to the backscatter coefficient;
Based on the radar image intensity obtained from the registration means, the radar scattering intensity database is referred to convert it to a backscattering coefficient, and the incident angle is estimated based on the converted backscattering coefficient. Inclination estimation means for estimating the inclination of the region ;
A plane phase calculating means for calculating a plane phase corresponding to a scattering point on a plane having an inclination estimated by the inclination estimating means;
Phase compensation means for subtracting the plane phase calculated by the plane phase calculation means from the phase difference between the two radar images calculated by the phase difference calculation means;
And phase unwrapping means for joining open return of the phase-compensated phase difference by the phase compensation means,
A phase / height conversion means for converting the connected phase difference into the height of the terrain and obtaining a distribution map of the height of the observation target area;
An image radar comprising: a height correction unit that corrects the distribution of heights calculated by the phase / height conversion unit by adding the inclination of the observation target area estimated by the inclination estimation unit. apparatus. In an image radar apparatus that acquires two radar images under conditions where incident angles of reflected waves from the observation target area are slightly different and measures the height of the terrain based on the phase difference between the two radar images,
Registration means for adjusting two input radar images so that the same scattering point appears in the same pixel of the image; and phase difference calculation means for calculating a phase difference between the two radar images thus adjusted. ,
Terrain data storage means for storing terrain information of the observation target area in advance;
An inclination calculating means for calculating a representative inclination in the observation target area based on the terrain information;
A plane phase calculating means for calculating a plane phase corresponding to a scattering point on the observation target region having the inclination calculated by the inclination calculating means;
Phase compensation means for subtracting the plane phase calculated by the plane phase calculation means from the phase difference between the two radar images calculated by the phase difference calculation means;
And phase unwrapping means for joining open return of the phase-compensated phase difference by the phase compensation means,
Phase correction means for adding the planar phase calculated by the planar phase calculation means to the connected phase difference; and
An image radar apparatus comprising phase / height conversion means for converting the phase difference corrected by the phase correction means into a height of terrain and obtaining a distribution map of the height of the observation target region. In an image radar apparatus that acquires two radar images under conditions where incident angles of reflected waves from the observation target area are slightly different and measures the height of the terrain based on the phase difference between the two radar images,
Registration means for adjusting two input radar images so that the same scattering point appears in the same pixel of the image; and phase difference calculation means for calculating a phase difference between the two radar images thus adjusted. ,
A planar phase estimation means for estimating a plane phase corresponding to the scattering point on a plane having an inclination of the observation target region based on the phase difference of the two radar images calculated by the phase difference calculation hand stage,
A phase compensating means subtracting the estimated plane phase in said plane phase estimation means from the phase difference of the two radar images calculated by the phase difference calculating means,
Phase unwrapping means for opening and joining the phase-compensated phase difference aliasing; and
The phase difference combined connecting with the phase unwrapping means and phase correcting means for correcting by adding the estimated plane phase in said plane phase estimation means,
An image radar apparatus comprising phase / height conversion means for converting the phase difference corrected by the phase correction means into a height of terrain and obtaining a distribution map of the height of the observation target region .

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