JP4909800B2 - Synthetic aperture radar equipment - Google Patents

Description

  The present invention relates to a Synthetic Aperture Radar (SAR) device, and more particularly to an endfire (flight path) type synthetic aperture radar device whose target is a target existing in a three-dimensional space.

  Conventionally, a synthetic aperture radar device (hereinafter also abbreviated as “SAR device”) that reveals the undulation and structure of an object by irradiating the object with radio waves while moving and analyzing the reflected wave. It has been known.

  This SAR apparatus is generally used for observing a target (two-dimensional target) existing on the ground side of the flight path. When a target existing in the flight path direction in the air, that is, a target in a three-dimensional space, is observed using this SAR device, since the SAR device is based on a linear array sensor, a cone as shown in FIG. A shaped beam is formed.

Therefore, as shown in the luminance diagram of FIG. 9B, for example, if a target exists in a region surrounded by a broken line, a high-luminance image is obtained in the entire radial direction. I cannot tell if a goal exists.
Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press (2003) pp.176-178 Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press (2003) pp.210-217

  As described above, in a conventional SAR device, when a target in a three-dimensional space is observed, an image in which the position where the target exists cannot be distinguished is obtained, so the center of the target cannot be specified, and tracking cannot be performed. There is a problem.

  The present invention has been made to solve the above-described problems, and its problem is that a synthetic aperture capable of observing and tracking a target existing in a three-dimensional space in the flight path direction with high resolution and high accuracy. It is to provide a radar apparatus.

In order to solve the above problems, a first invention is a synthetic aperture radar device mounted on a flying object, wherein the resolution of the beam formed in a conical shape with respect to the flight path axis of the flying object is in the cross-range direction. And a synthetic aperture radar processing unit that generates an image including the target, and a size of the entire beam formed in the cone shape in which the target included in the image generated by the synthetic aperture radar processing unit is observed is minimized. A flight path center setting unit that sets the flight path center so that the flight path center is set, and a guidance control unit that guides the flying object so that the flight path center set by the flight path center setting unit matches the target center It is characterized by that.

  In the second invention, the flight path center setting unit sets a plurality of flight path centers, and the intensity of the image obtained from the synthetic aperture radar processing unit for each of the set plurality of flight path centers. The guidance control unit recognizes the shape of the target based on the change, and guides the flying object to an arbitrary point of the target shape recognized by the flight path center setting unit.

According to the first invention, the synthetic aperture radar processing unit takes a sufficient synthetic aperture length, increases the resolution in the cross range direction of the beam formed conically with respect to the flight path axis, and generates a target image. Using the fact that the center of the flight path is the same as the center of the target when the size of the entire beam formed in the conical shape where the target is observed is the smallest, no matter where the target exists in the cone , Since the flying object is guided in the center direction of the target, the target existing in the three-dimensional space in the flight path direction can be observed and tracked with high resolution and high accuracy.

  Further, according to the second invention, a plurality of flight path centers are set, a target shape is recognized by a change in image intensity corresponding to each of the set plurality of flight path centers, and the recognized target Since the flying object is guided to an arbitrary point of the shape, not only the center of the target but also an arbitrary point can be tracked.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, the principle of SAR will be described. FIG. 1 shows a model of SAR. This model shows an example in which side monitoring is performed as a general model. Synthetic aperture radar processing (hereinafter referred to as “SAR processing”) by transmitting and receiving radio waves with a SAR device mounted on a flying object. This shows a state where the target is detected by performing.

Now, assuming that the transmission / reception signal is e (t) and the reference signal for AZ (cross range) compression is r (t), the signal s (t) after AZ compression can be calculated by the following equation (Non-Patent Document 1). reference).

here,
e (t); transmission / reception signal E (f); Fourier transform of e (t) r (t); reference signal R (f); Fourier transform of r (t) s (t); SAR image S (f); Fourier transform of s (t) FFT []; Fourier transform FFT ^-1 []; Inverse Fourier transform *; Complex conjugate In SAR processing, correction of the reference signal is required when there is a target flight path or airframe fluctuation. is there. FIG. 2 is a block diagram illustrating a functional configuration of the SAR device according to the first embodiment of the present invention configured to correct the reference signal. As a reference signal correction method, correction using GPS / INS (Global Positioning System / Inertial Navigation System) and correction using autofocus (see Non-Patent Document 2) are used. .

  The SAR device includes a first FFT unit 1, a second FFT unit 2, a multiplication unit 3, an IFFT unit 4, a high luminance extraction unit 5, a GPS / INS unit 6, a correction value processing unit 7, a reference signal processing unit 8, and a flight path center setting. A unit 9 and a guidance control unit 10 are provided. The synthetic aperture radar processing unit of the present invention includes a first FFT unit 1, a second FFT unit 2, a multiplication unit 3, an IFFT unit 4, a high luminance extraction unit 5, a GPS / INS unit 6, a correction value processing unit 7, and a reference signal processing unit. 8 is composed.

  The first FFT unit 1 performs Fourier transform on a transmission / reception signal e (t) input from a receiver (not shown) according to the equation (1), and sends the result to the multiplication unit 3 as a signal E (f). The second FFT unit 2 performs Fourier transform on the reference signal r (t) sent from the reference signal processing unit 8 according to the equation (2), and sends it to the multiplication unit 3 as a signal R (f).

  The multiplication unit 3 multiplies the signal E (f) sent from the first FFT unit 1 and the signal R (f) sent from the second FFT unit 2 according to the equation (3) to obtain a signal S (f) To the IFFT unit 4. The IFFT unit 4 performs inverse Fourier transform on the signal S (f) sent from the multiplication unit 3 in accordance with Expression (4). The signal s (t) obtained by performing the inverse Fourier transform in the IFFT unit 4 is sent to the high luminance extraction unit 5 and the flight path center setting unit 9 as a SAR image. This SAR image corresponds to the “image” of the present invention.

  The high luminance extraction unit 5 extracts a high luminance part from the SAR image indicated by the signal s (t) sent from the IFFT unit 4. The signal representing the high luminance portion extracted by the high luminance extraction unit 5 is sent to the correction value processing unit 7. The GPS / INS unit 6 combines GPS satellite navigation and inertial navigation system, and continuously generates highly accurate position, velocity, attitude information, and the like. Information generated by the GPS / INS unit 6 is sent to the correction value processing unit.

  The correction value processing unit 7 generates a correction value for correcting the reference signal based on the signal representing the high luminance part sent from the high luminance extraction unit 5 and the information sent from the GPS / INS unit 6. And sent to the reference signal processing unit 8. By correcting the reference signal based on the correction value generated by the correction value processing unit 7, a corrected SAR image having a large amplitude and sharpness can be obtained. The reference signal processing unit 8 corrects the reference signal according to the correction value sent from the correction value processing unit 7 and sends it to the second FFT unit 2 as a new reference signal r (t).

  The flight path center setting unit 9 sets the flight path center so that the target included in the SAR image indicated by the signal s (t) sent from the IFFT unit 4 is minimized. The flight path center set by the flight path center setting unit 9 is sent to the guidance control unit 10. The guidance control unit 10 guides the flying object so as to face the flight path center set by the flight path center setting unit 9.

  Next, the operation of the synthetic aperture radar apparatus according to Embodiment 1 of the present invention will be described. Here, a case will be described in which SAR processing centering on the endfire (flight path) direction as shown in FIG. 9 is performed.

  In the endfire direction, a high-resolution beam can be formed conically around the flight path axis. When observing a target with this beam, as shown in comparison with FIGS. 3 and 4, the size of the SAR image observed with a conical beam is determined by the degree of coincidence between the center of the target and the center of the flight path. When the (radial spread) is different and the center of the flight path coincides with the center of the target, the SAR image becomes the smallest.

  For example, as shown in FIG. 3A surrounded by a broken line, when the target exists at a position deviated from the center of the flight path, the center portion has low luminance as shown in the luminance diagram of FIG. , A SAR image with a high brightness as a whole is obtained. In this case, as shown in the intensity distribution diagram of FIG. 3C, the radial spread of the SAR image becomes large (wide).

  On the other hand, when the target exists in the vicinity of the center of the flight path as shown by the broken line in FIG. 4A, the central portion and its surroundings are entirely shown in the luminance diagram of FIG. 4B. SAR images with high brightness and low brightness at the outer periphery are obtained. In this case, as shown in the intensity distribution diagram of FIG. 4C, the radial extent of the SAR image is small (narrow). Therefore, if the point where the size of the SAR image becomes the smallest is found by changing the flight path center, the center of the target can be determined.

  FIG. 5 is a diagram for explaining a method of changing the flight path center performed in the flight path center setting unit 9. As shown in FIG. 5A, the SAR image obtained from the IFFT unit 4 is assigned to a two-dimensional space in which the X axis and the Y axis are orthogonal. At this time, the center of the target exists at a position away from the center of the flight path.

  In this state, as shown in FIG. 5B, the center of the flight path is moved in the X-axis direction, and the position in the X-axis direction is determined by searching for the position where the SAR image becomes the smallest. After that, as shown in FIG. 5C, the flight path center is moved in the Y-axis direction, and the position in the Y-axis direction is determined by searching for the position where the SAR image becomes the smallest. The point where the SAR images in the X-axis and Y-axis directions determined in this way are the smallest is determined as the center of the target, and the center of the target is set as the flight path center.

  In the method of changing the flight path center described above, the flight path center is first moved in the X axis direction and then moved in the Y axis direction. However, after the movement in the Y axis direction first, It can also be configured to move between.

  Next, the operation of the synthetic aperture radar apparatus according to Embodiment 1 of the present invention will be described with reference to the flowchart shown in FIG.

  In the flying object guidance process, first, a GPS / INS correction process is performed (step S11). That is, the GPS / INS unit 6 continuously generates highly accurate position, speed, posture information, and the like, and sends them to the correction value processing unit 7. The correction value processing unit 7 generates a correction value for correcting the reference signal based on the information sent from the GPS / INS unit 6 and sends the correction value to the reference signal processing unit 8. The reference signal processing unit 8 corrects the reference signal according to the correction value sent from the correction value processing unit 7 and sends it to the second FFT unit 2 as a new reference signal r (t).

  Next, SAR processing is performed (step S12). That is, the first FFT unit 1 performs Fourier transform on a transmission / reception signal e (t) input from a receiver (not shown) and sends the signal E (f) to the multiplication unit 3. Further, the second FFT unit 2 performs Fourier transform on the reference signal r (t) sent from the reference signal processing unit 8 and sends it to the multiplication unit 3 as a signal R (f). The multiplier 3 multiplies the signal E (f) sent from the first FFT unit 1 and the signal R (f) sent from the second FFT unit 2 and sends the result to the IFFT unit 4 as a signal S (f). The IFFT unit 4 performs an inverse Fourier transform on the signal S (f) sent from the multiplication unit 3 to generate a signal s (t), which is sent to the high luminance extraction unit 5 and the flight path center setting unit 9 as a SAR image. send.

  Next, a high luminance point extraction process is performed (step S13). That is, the high luminance extraction unit 5 extracts a high luminance part of the SAR image indicated by the signal s (t) sent from the IFFT unit 4 and sends it to the correction value processing unit 7.

  Next, an autofocus process is performed (step S14). The correction value processing unit 7 extracts, for example, a peak value (maximum value) from the image sent from the high luminance extraction unit 5, and signals of M cells in a predetermined range in the cross range direction around the extracted peak value. Is subjected to Fourier transform, and a correction value for correcting the reference signal is generated using the signal obtained by the Fourier transform and is sent to the reference signal processing unit 8. The reference signal processing unit 8 corrects the reference signal according to the correction value sent from the correction value processing unit 7 and sends it to the second FFT unit 2 as a new reference signal r (t).

  Next, SAR processing is performed (step S15). That is, in this step S14, the SAR image is generated and sent to the high luminance extraction unit 5 and the flight path center setting unit 9 in the same manner as the processing in step S12 described above.

  Next, it is checked whether or not the SAR image is minimum (step S16). That is, the flight path center setting unit 9 determines whether or not the target included in the SAR image indicated by the signal s (t) sent from the IFFT unit 4 is the minimum in the procedure described with reference to FIG. Investigate. If it is determined in step S16 that the SAR image is not the minimum, then a flight path center setting process is performed (step S17). That is, the flight path center setting unit 9 changes the flight path center according to the procedure described with reference to FIG.

  Next, guidance control processing is performed (step S18). That is, the guidance control unit 10 guides the flying object so as to face the flight path center transmitted from the flight path center setting unit 9. Then, it returns to step S15 and the process mentioned above is repeated until the target contained in a SAR image becomes the minimum. If it is determined in step S16 that the SAR image is not the minimum, the flying object guiding process ends.

  As described above, according to the synthetic aperture radar apparatus according to the first embodiment of the present invention, a sufficient synthetic aperture length is obtained by the synthetic aperture radar process, and the cross range of the beam formed conically with respect to the flight path axis. The target image is generated with the direction resolution increased, and the center of the flight path when the radial size of the image is minimum no matter where the target exists in the conical shape, matches the target center. Since the flying object is guided in the direction of the center of the target, the target existing in the three-dimensional space in the direction of the flight path can be observed and tracked with high resolution and high accuracy.

  The synthetic aperture radar apparatus according to the second embodiment of the present invention recognizes the shape (spread) of a target using the method described in the first embodiment. The configuration of the synthetic aperture radar apparatus according to the second embodiment is the same as that of the synthetic aperture radar apparatus according to the first embodiment shown in FIG. 2 except for the function of the flight path center setting unit 9.

  In addition to the function of determining the center of the target described in the first embodiment, the flight path center setting unit 9 moves the center of the flight path around the determined center of the target and observes the change in the target amplitude. , Recognize the target shape (spread).

  FIG. 7 is a diagram for explaining the principle of recognizing the target shape performed in the flight path center setting unit 9. The flight path center setting unit 9 sets the flight path center to a plurality of other flight path centers as shown in FIG. 7B from the state where the flight path center matches the center of the target as shown in FIG. Set the position and collect the intensity of the SAR image. In this case, if the target is within a predetermined range from the center of the flight path, the strength increases, otherwise the strength decreases. Therefore, by plotting the intensity at the center of a plurality of flight paths, the target shape as shown in FIG. 7C can be recognized.

  Next, the operation of the synthetic aperture radar apparatus according to Embodiment 2 of the present invention will be described with reference to the flowchart shown in FIG. In the following description, the same reference numerals as those used in the first embodiment are assigned to parts that perform the same process as the flying object guidance process in the synthetic aperture radar apparatus according to the first embodiment shown in the flowchart of FIG. The explanation will be simplified.

  In the flying object guidance process, first, a GPS / INS correction process is performed (step S11). Next, SAR processing is performed (step S12). Next, a high luminance point extraction process is performed (step S13). Next, an autofocus process is performed (step S14). Next, SAR processing is performed (step S15). Next, it is checked whether or not the SAR image is minimum (step S16). If it is determined in step S16 that the SAR image is not the minimum, then a flight path center setting process is performed (step S17). Next, guidance control processing is performed (step S18). Then, it returns to step S15 and the process mentioned above is repeated.

  If it is determined in step S16 that the SAR image is not the minimum, a flight path center setting process is performed (step S19). That is, the flight path center setting unit 9 sets a new flight path center around the currently set flight path center.

  Next, strength confirmation and storage are performed (step S20). That is, the flight path center setting unit 9 checks the strength of the SAR image obtained by the flight path center set in step S19, and stores the magnitude of the strength in a memory (not shown).

  Next, it is checked whether or not the flight path center setting has been completed by a predetermined number (step S21). If it is determined in step S21 that the setting of the flight path center has not been completed, the process returns to step S19 and the above-described processing is repeated.

  On the other hand, when it is determined in step S21 that the setting of the flight path center has been completed, shape recognition processing is performed (step S22). That is, the flight path center setting unit 9 recognizes the target shape by plotting the magnitude of the intensity stored in the memory. Thus, the flying object guiding process ends. If the shape of the target can be recognized in this manner, the center of the target or any point other than the center can be tracked although illustration is omitted.

  As described above, according to the synthetic aperture radar apparatus according to the first embodiment of the present invention, a plurality of flight path centers are set, and the image intensity change corresponding to each of the set plurality of flight path centers is set. Therefore, since the target shape is recognized and the flying object is guided to the center of the recognized target shape, not only the center of the target but also any point can be tracked.

  In the first and second embodiments described above, the case of improving the resolution in the cross range direction in the SAR processing has been described. However, in the range direction, the resolution can be improved by using a technique such as pulse compression. Can do.

  The present invention can be used for a synthetic aperture radar apparatus that tracks a target existing in front of a three-dimensional space.

It is a figure which shows the model for demonstrating the principle of SAR performed with the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a block diagram which shows the functional structure of the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the operation principle (the 1) of the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the operation principle (the 2) of the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the method to change a flight path center in the operation | movement of the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a flowchart which shows operation | movement of the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the process which recognizes the shape of a target in operation | movement of the synthetic aperture radar apparatus which concerns on Example 2 of this invention. It is a flowchart which shows operation | movement of the synthetic aperture radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the conventional synthetic aperture radar apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st FFT part 2 2nd FFT part 3 Multiplication part 4 IFFT part 5 High-intensity extraction part 6 GPS / INS part 7 Correction value process part 8 Reference signal process part 9 Flight path center setting part 10 Guidance control part

Claims (2)

A synthetic aperture radar device mounted on a flying object,
A synthetic aperture radar processing unit that generates an image including a target by increasing the resolution in the cross range direction of a beam formed conically with respect to the flight path axis of the flying object;
A flight path center setting unit that sets the flight path center so that the overall size of the cone-shaped beam in which the target included in the image generated by the synthetic aperture radar processing unit is observed is minimized;
A guidance control unit that guides the flying object so that the flight path center set by the flight path center setting unit matches the center of the target;
A synthetic aperture radar apparatus comprising: The flight path center setting unit sets a plurality of flight path centers, and changes the intensity of the image obtained from the synthetic aperture radar processing unit for each of the set plurality of flight path centers to form a target shape Recognize
The synthetic aperture radar apparatus according to claim 1, wherein the guidance control unit guides the flying object to an arbitrary point of the target shape recognized by the flight path center setting unit.

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