JP2016161386A - Image radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image radar device capable of performing fluctuation compensation without specifying a parameter of interpolation on observation data.SOLUTION: An upsampling rate calculation part 10b calculates an upsampling rate of observation data within respective determination allowable values of resolution in a range direction, resolution in an azimuth direction and a signal-to-noise power ratio, determining picture quality when the observation data is imaged, from the respective deterioration allowable values and various elements of a radar. An observation data upsampling part 10c upsamples observation data having its phase compensated by a phase compensation part 10a based upon the upsampling rate that the upsampling rate calculation part 10b calculates. A nearest neighbour interpolation part 10d performs nearest neighbour interpolation on the observation data that the observation data upsampling part 10c upsamples based upon a difference based upon the difference between a measured movement track of the radar and a linear track obtained by approximating it to a straight line.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image radar apparatus that is mounted on a movable platform such as an aircraft or an artificial satellite and observes the ground surface and the like, and more particularly to a synthetic aperture radar (hereinafter referred to as SAR).

  An image radar device composed of SAR irradiates the ground surface with radio waves from the platform on which the device is mounted, receives the reflected waves on the platform side, converts the received reflected waves into analog-digital data, and then uses them as observation data. It is recorded. This observation data is imaged by signal processing called image reproduction. However, when all or part of the observation area is reproduced at a time, the movement trajectory of the platform is regarded as a straight line and signal processing is performed.

However, the actual observation orbit is not straight due to the influence of wind on the aircraft or the orbit of the artificial satellite. For this reason, it is necessary to adjust the phase of the observation data and the reception timing so that it can be regarded as data observed from a straight orbit.
This adjustment is called shake compensation. In motion compensation, phase compensation is realized by multiplying observation data by complex numbers. Also, reception timing compensation is realized by resampling of observation data.

In resampling, observation data is interpolated based on the difference in distance between a linear trajectory used for image reproduction and an actual trajectory (see, for example, Non-Patent Document 1).
Further, for interpolation of observation data, interpolation using a sinc function is common (for example, see Non-Patent Document 2).

  There is a relationship in which an interpolation error is determined by an interpolation method or a parameter, and an image quality and an operation time corresponding to the error are obtained. That is, when the interpolation error is increased by the interpolation method or parameter, the image quality such as the image resolution or signal-to-noise power ratio (Signal to Noise power Ratio; hereinafter referred to as SNR) obtained after image reproduction deteriorates. . Further, when the interpolation error is reduced, the amount of calculation increases and a long calculation time is required.

In the conventional technique, the magnitude of the interpolation error is adjusted according to the interpolation parameters, and the result satisfies the required image quality and calculation time.
In the interpolation using the sinc function, a parameter inversely proportional to the interpolation error called kernel length is set from the viewpoint of interpolation error and calculation time. When it is desired to obtain an image with low image quality but a short calculation time, it is necessary to set this parameter small.

A. Moreira, Y. et al. Huang, “Airborne SAR Processing of Highly Squinted Data Using a Chirp Scaling Approach with Integrated Motion Compensation,” IEEE Trans. Geosci. Remote Sens. , Pp. 1029-1040, vol. 32, no. 5, Sep. 1994. I. G. Cumming, F.M. H. Wong, “Digital processing of synthetic aperture radata,” pp. 197 52-58, Arttech house, 2005.

The interpolation error determined by the interpolation parameter in the conventional technique is an error in the amplitude and phase of the reflected wave stored as observation data.
Since the magnitude of this error varies depending on the value of the observation data, it is impossible to estimate how much error will occur. For this reason, the interpolation parameters cannot be associated with the image quality, and the kernel length to be set in order to satisfy the allowable image quality degradation and the computation time cannot be specified.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image radar apparatus that can perform motion compensation without specifying parameters for interpolation of observation data.

The image radar apparatus according to the present invention includes a phase compensation unit, an upsampling rate calculation unit, an observation data upsampling unit, a nearest neighbor interpolation unit, and an image reproduction unit.
The phase compensation unit compensates the phase of the observation data of the radio wave received by the radar based on the difference between the actually measured movement trajectory of the radar and the linear trajectory approximating this.
The up-sampling rate calculation unit calculates the permissible degradation value from the range resolution, the azimuth resolution and the signal-to-noise power ratio degradation tolerance that determine the image quality when the observation data is imaged, and the radar specifications. The upsampling rate of the observation data is calculated so that it falls within
The observation data upsampling unit upsamples the observation data whose phase is compensated by the phase compensation unit based on the upsampling rate calculated by the upsampling rate calculation unit.
The nearest neighbor interpolation unit performs nearest neighbor interpolation on the observation data up-sampled by the observation data up-sampling unit based on the difference between the actually measured movement trajectory of the radar and the linear trajectory approximated to the straight line.
The image reproducing unit images the observation data interpolated by the nearest neighbor by the nearest neighbor interpolation unit.

  According to the present invention, since the upsampling rate and the nearest neighbor interpolation of the observation data are performed based on the upsampling rate calculated from the degradation allowable value of the parameter that determines the image quality when the observation data is imaged, the user can Shake compensation can be performed without specifying interpolation parameters for observation data.

It is a block diagram which shows the structure of the image radar apparatus which concerns on Embodiment 1 of this invention. 3 is a flowchart showing an operation of the image radar apparatus according to the first embodiment. FIG. 3 is a diagram showing an outline of radar observation by the image radar apparatus according to the first embodiment. 6 is a diagram illustrating an example of a state of observation data in an intermediate stage of image reproduction by an image reproduction unit according to Embodiment 1. FIG. It is a figure which shows the relationship between the waveform of a sinc function of observation data, and a tangent. It is a block diagram which shows the structure of the image radar apparatus which concerns on Embodiment 2 of this invention. 6 is a flowchart showing the operation of the image radar apparatus according to the second embodiment.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of an image radar apparatus 1 according to Embodiment 1 of the present invention. The image radar apparatus 1 irradiates a target such as the ground surface with a radio wave from a radar mounted on a movable platform such as an aircraft or an artificial satellite, and the radar receives a reflected wave from the target to obtain observation data. Observation data from the radar is converted into an image by image reproduction.
In the following, a case where the image radar apparatus 1 performs phase compensation and interpolation of observation data at a time will be described. However, as in Non-Patent Document 1, rough motion compensation and differential motion compensation (differential) You may comprise so that it may divide into two times (motion compensation).

In FIG. 1, an actual observation trajectory storage unit 2 is a storage unit provided so that data can be read from both the linear trajectory calculation unit 3 and the inter-orbit distance calculation unit 5. Stored together with the radio wave reception time.
Here, the actual observation orbit information is information indicating the position of a point corresponding to a distance of zero for radar observation at each radio reception time of radar observation.
The radio wave reception time of radar observation is the time when the radar mounted on the platform receives the reflected wave of the radio wave irradiated toward the target.
The position of the point corresponding to zero distance of radar observation is the position where the distance from the radar is zero, and corresponds to the phase center position of the transmission / reception antenna that transmits and receives the radio wave and the reflected wave included in the radar. That is, the actual observation orbit information at each radio wave reception time of the radar observation indicates the actually measured radar movement orbit. Hereinafter, the actually measured trajectory of the radar is referred to as “actual observation trajectory”.

The actual observation orbit information is, for example, a global positioning system (GPS), an inertial navigation system (INS), or an inertial measurement unit (IMU) mounted on the platform. It may be obtained from such equipment. It may also be obtained from a radar device that measures the position of the platform.
The actual observation orbit information may be a result of signal processing or information processing on information obtained from these devices.
Furthermore, the coordinate system of the actual observation orbit information may be a geocentric fixed coordinate system, a latitude, a longitude, an altitude, or an original three-dimensional coordinate system. Examples of time expression methods include world standard time and local time.

The linear trajectory calculation unit 3 calculates radar linear trajectory information from the actual observation trajectory information stored in the actual observation trajectory storage unit 2 for each radio wave reception time of radar observation.
The linear trajectory information includes position coordinates obtained by approximating a point corresponding to a distance of zero in radar observation to a straight line, and information on radio wave reception time corresponding to this point. That is, the linear trajectory information at each radio wave reception time of radar observation indicates a linear trajectory approximating the actual observation trajectory to a straight line.
Hereinafter, this approximated trajectory is referred to as a “straight trajectory”. The straight track information calculated by the straight track calculation unit 3 is stored in the straight track storage unit 4.
The linear trajectory storage unit 4 is a storage unit that can be written to by the linear trajectory calculation unit 3 and can read data from the inter-orbit distance calculation unit 5, and stores linear trajectory information.

The interorbital distance calculation unit 5 calculates the distance between the point Pa and the observation point Pt corresponding to the radar observation distance zero on the actual observation orbit at each radio observation time of the radar observation from the actual observation orbit information and the straight orbit information. And the distance difference between the point Pl corresponding to the radar observation distance zero on the linear orbit at the radio wave reception time corresponding to this point Pa and the distance between the observation points Pt.
The inter-orbit distance storage unit 6 is a storage unit that can be written by the inter-orbit distance calculation unit 5 and can read data from the phase compensation unit 10a and the nearest neighbor interpolation unit 10d. The distance difference for each radio wave reception time of radar observation calculated by the distance calculation unit 5 is stored.

The observation data storage unit 7 is a storage unit provided so that data can be read from the range compression unit 9. In the observation data storage unit 7, data obtained by converting the analog signal of the reflected wave received by radar observation into a digital signal is stored as observation data.
Note that the observation data may be data in the form of the phase and amplitude of the reflected wave, or data in the form of a real part and an imaginary part.

  The radar specification storage unit 8 is a storage unit provided so as to be able to read data from the range compression unit 9, the phase compensation unit 10 a, the upsampling rate calculation unit 10 b, and the image reproduction unit 12. Original information is stored. The radar specification information includes, for example, the wavelength, bandwidth, center frequency, and pulse width of the transmission wave transmitted by the transmission / reception antenna, and includes the reception gate width, antenna beam width, etc. for receiving the reflected wave.

The range compression unit 9 performs range compression on the observation data stored in the observation data storage unit 7 for each transmission / reception pulse based on the radar specification information read from the radar specification storage unit 8.
The range compression processing is also called pulse compression, and is signal processing for increasing the resolution of observation data in the range direction by using a method of convolving and integrating observation data and transmission pulses in the time domain or frequency domain.
The range direction is a platform moving direction, that is, a direction orthogonal to the radar moving direction (distance direction to the radar).

The motion compensation unit 10 is a component that performs motion compensation of observation data, and includes a phase compensation unit 10a, an upsampling rate calculation unit 10b, an observation data upsampling unit 10c, and a nearest neighbor interpolation unit 10d.
The phase compensation unit 10a compensates the phase of the observation data of the radio wave received by the radar based on the difference in distance between the actually measured actual trajectory of the radar and the linear trajectory approximated to a straight line.
For example, the phase compensation unit 10a calculates a phase difference corresponding to the distance difference between the orbits from the radar item information read from the radar item storage unit 8 and the distance difference between the tracks read from the inter-orbit distance storage unit 6. The phase difference is removed from the observation data calculated and range compressed by the range compression unit 9.

The image quality deterioration tolerance storage unit 11 is a storage unit provided so that data can be read from the upsampling rate calculation unit 10b, and stores the image quality deterioration tolerance specified by the user.
The allowable image quality deterioration value is an allowable value for deterioration in the resolution in the range direction, an allowable value for deterioration in the resolution in the azimuth direction, and an allowable value for deterioration in the SNR, which determine the image quality when the observation data is imaged.
In the following, the allowable resolution degradation value in the range direction is referred to as “range resolution degradation tolerance”, the azimuth resolution degradation tolerance is referred to as “azimuth resolution degradation tolerance”, and the SNR degradation tolerance is “SNR degradation tolerance”. Called “value”.
The up-sampling rate calculation unit 10b observes the image quality degradation tolerance value based on the image quality degradation tolerance value read from the image quality degradation tolerance value storage unit 11 and the radar specification information read from the radar specification storage unit 8 so as to be within the image quality degradation tolerance value. Calculate the data upsampling rate.

  The observation data upsampling unit 10c upsamples the observation data phase-compensated by the phase compensation unit 10a based on the upsampling rate calculated by the upsampling rate calculation unit 10b. The nearest neighbor interpolation unit 10d obtains the observation data up-sampled by the observation data up-sampling unit 10c based on the distance difference between the actual observation orbit read from the inter-orbit distance storage unit 6 and the linear orbit approximated to a straight line. Interpolate by nearest neighbor method.

The image reproduction unit 12 images the observation data subjected to the nearest neighbor interpolation by the nearest neighbor interpolation unit 10d. For example, the image reproduction unit 12 reproduces an image of observation data subjected to nearest neighbor interpolation based on the linear trajectory information read from the linear trajectory storage unit 4 and the radar specification information read from the radar specification storage unit 8. .
The image storage unit 13 is a storage unit provided so that data can be written by the image reproduction unit 12, and stores an image reproduced by the image reproduction unit 12.

An image obtained by image reproduction may be an image in a general format such as JPEG (Joint Photographic Experts Group), or may be in a unique format unique to the image radar apparatus 1.
The pixel value of the image may be a real number having only an amplitude value or a power value, but may be a complex number having an amplitude and a phase.

Note that the linear trajectory calculation unit 3, the inter-orbit distance calculation unit 5, the fluctuation compensation unit 10, and the image reproduction unit 12 are realized, for example, by a processor executing a program stored in a memory. A plurality of processors and a plurality of memories may execute the above functions in conjunction with each other.
The actual observation trajectory storage unit 2, the linear trajectory storage unit 4, the inter-orbit distance storage unit 6, the observation data storage unit 7, the radar specification storage unit 8, the image quality degradation allowable value storage unit 11 and the image storage unit 13 are the image radar apparatus. 1 is built in a storage device such as a hard disk device. The storage device may be an SD card, a USB memory, or the like, or an external storage device that can read and write data by communication.

Next, the operation will be described.
FIG. 2 is a flowchart showing the operation of the image radar apparatus 1 according to the first embodiment and shows the processing until the observation data is reproduced.
In step ST1, the linear trajectory calculation unit 3 calculates a linear trajectory by fitting the spatial coordinates of the position indicated by the actual observation trajectory information read from the actual observation trajectory storage unit 2 with a straight line.
As a method for calculating the linear trajectory, for example, fitting by the least square method is used.

Here, FIG. 3 is a diagram showing an outline of radar observation by the image radar apparatus 1, and is orthogonal to the traveling direction of the platform, and is a point Pa (t) on the actual observation trajectory and a point Pl (t) on the straight trajectory. The plane containing is shown. The range r is the distance between the radar and the observation point in FIG. 3, the distance between the point Pl (t) on the linear trajectory and the observation point Pt (t, r), and the point Pa (t) on the actual observation trajectory. This corresponds to the distance to the observation point Pt (t, r).
Next, the interorbital distance calculation unit 5 performs actual observation with the observation point Pt (t, r) shown in FIG. 3 according to the following equation (1) for each pulse transmission / reception time t and range r of radio waves transmitted and received by the radar. A distance difference d (r, t) between the point Pa (t) on the trajectory and the point Pl (t) on the straight trajectory is calculated (step ST2). However, Pt (t, r), Pa (t), and Pl (t) are vectors.
d (r, t) = | Pa (t) −Pt (t, r) | −r (1)

FIG. 3 shows an example of a geometrical arrangement of radar trajectories and observation points. Therefore, the observation point Pt (t, r) is included in the plane shown in FIG. 3, and the height difference from the point Pl (t) on the straight orbit (observation point Pt (t, r) and Is the point where the distance from the point Pl (t) on the linear trajectory is in the range r = | Pl (t) −Pt (t, r) |.
In addition, the observation point Pt (t, r) may be determined on a plane including the point Pa (t) on the actual observation orbit and the point Pl (t) on the straight orbit and including the beam direction of the transmission / reception antenna.

Next, the range compression unit 9 performs range compression on the observation data stored in the observation data storage unit 7 based on the radar specification information read from the radar specification storage unit 8 (step ST3).
Range compression is realized, for example, by convolving and integrating observation data and a transmission wave.
The transmitted wave may be a pulse replica that records the waveform of the actually transmitted radio wave, or a reference function calculated based on radar specifications such as pulse width and transmission bandwidth may be used. Good. Convolution integration can be performed in both the time domain and the frequency domain.
The waveform after the range compression is a sinc function, that is, a superposition of sin (x) / x.

Subsequently, the phase compensation unit 10a performs phase compensation by subtracting the phase corresponding to the distance difference d (r, t) from the range-compressed observation data (step ST4).
For example, if the distance (range) between the radar and the observation point is r, and the observation data after the range compression at the pulse transmission / reception time t is E (r, t), the phase-compensated observation data E ′ (r, t) Can be obtained from the following equation (2). Here, j is an imaginary unit, and λ is the carrier wavelength of the transmission wave.
E ′ (r, t) = E (r, t) exp {−j4πd (r, t) / λ} (2)

Next, the upsampling rate calculation unit 10b is set to fall within the allowable image quality deterioration value based on the allowable image quality deterioration value read from the allowable image quality deterioration value storage unit 11 and the radar specification information read from the radar data storage unit 8. The upsampling rate of the observation data is calculated (step ST5).
Here, the relationship between the image quality degradation allowable value and the image quality in the shake compensation of the present invention will be described.
The present invention is characterized in that the re-sampling of observation data is realized by up-sampling and nearest neighbor interpolation, so that the image quality can be associated with the allowable image degradation value.

The error in resampling of observation data is determined by the upsampling rate U or the range sampling width δ ′ after upsampling that can be calculated from the upsampling rate.
The upsampling rate U and the range sampling width δ ′ after the upsampling have a relationship of the following formula (3). However, δ is a range sampling width of the observation data, and is a value determined by a sampling frequency of an AD converter that converts a received wave into a digital signal.
δ ′ = δ / U (3)

In resampling in the present invention, since nearest neighbor interpolation is used, even if it is desired to obtain the value of the range r ₀ by resampling, r is within the range represented by the following equation (4). Occurs. That is, the range error is caused by resampling by a maximum of δ ′ / 2.
r ₀ −δ ′ / 2 ≦ r ≦ r ₀ + δ ′ / 2 (4)

FIG. 4 is a diagram illustrating an example of the state of observation data in the middle of image reproduction by the image reproduction unit 12 according to the first embodiment. Here, a case where a radar receives a reflected wave from one point scatterer is shown.
As shown in FIG. 4, when there is no range error, reflected waves from point scatterers arranged in a straight line in the same range as the broken line a are received, and the sinc functions are obtained by performing range compression on these observation data. The waveforms are lined up.
On the other hand, since resampling in the present invention causes a maximum range error of δ ′ / 2, the position of the waveform of the sinc function within a range of ± δ ′ / 2 from the range where there is no range error as indicated by the alternate long and short dash line b. It varies.

In image reproduction, an image is generated by convolving and integrating observation data in the transmission / reception time direction.
However, when convolution integration is performed in a state where the waveform of the sinc function varies as indicated by a dashed line b, the integration is performed in a state where the waveform of the sinc function is shifted, so that the range resolution of the image after integration is that of the sinc function. It degrades by δ ′ = δ / U at the maximum from the resolution represented by the half width or the null point interval.

Further, when the observation data of a certain range at each pulse transmission / reception time is considered because the range has an error of δ ′ / 2 at the maximum, the amplitude in the waveform of the sinc function indicating the reception wave according to the pulse transmission / reception time t Fluctuates.
Considering that the absolute value of the maximum slope of the tangent line c with respect to a point having a range of 0.66Δr is 1.37 / Δr, as shown in FIG. 5, r ₀ = 0. A range error δ ′ / 2 occurs at .66Δr.
However, Δr indicates the range resolution represented by the null point interval in the waveform of the sinc function. The amplitude fluctuation at this time is 1.37δ ′ / (2Δr).

Considering that the maximum amplitude of the sinc function is 1 when the amplitude variation described above is 1.37 δ ′ / (2Δr) where the amplitude has decreased most, the amplitude variation rate is A = 1−1.37δ ′. / (2Δr).
When the maximum value of the sinc function is not 1, the amplitude variation changes in proportion to the maximum value of the sinc function. Here, A is regarded as the maximum amplitude fluctuation rate caused by the range error, and is referred to as an amplitude reduction rate. Since the power of the image is reduced due to the decrease in the amplitude, the SNR of the image is deteriorated. SNR degradation rate of the image is the largest in ^{A 2.}
The amplitude reduction rate A has a relationship of the following formula (5) with the upsampling rate U.
A = 1-1.37δ ′ / (2ΔrU) (5)

Next, let us consider the deterioration of the azimuth resolution (the resolution in the direction of the axis representing the platform traveling direction) due to the amplitude variation.
The most degraded azimuth resolution is calculated by, for example, the half width or null point interval of the result of Fourier transform of the following equation (6).
1-A + A (1-cos (2πx) / 2) (0 ≦ x ≦ 1) (6)

  Further, the azimuth resolution when there is no range error can be calculated based on the radar specification information. Thus, a value obtained by subtracting the azimuth resolution when there is no range error from the degraded azimuth resolution obtained as described above is the azimuth resolution degradation allowable value. When the upsampling rate U is determined, a range resolution deterioration allowable value, an azimuth resolution deterioration allowable value, and an SNR deterioration allowable value are determined.

In the present invention, the range resolution deterioration allowable value, the azimuth resolution deterioration allowable value, and the SNR deterioration allowable value are designated as parameters, and the upsampling rate U is determined so as to be within these deterioration allowable values. For example, assuming that the range resolution degradation allowable value is Kr and the azimuth resolution degradation allowable value is Ks, the upsampling rate calculation unit 10b calculates an upsampling rate that satisfies both Kr and Ks according to the following equation (7).
U = min (1.37δ / (2Δr (1-√Ks)), Kr) (7)

Subsequently, the upsampling rate calculation unit 10b calculates the amplitude reduction rate A by substituting the upsampling rate U obtained by the above equation (7) into the above equation (5). Then, using this amplitude reduction rate A, the azimuth resolution is calculated from the above equation (6).
The upsampling rate calculation unit 10b obtains the true azimuth resolution Δa from the calculated azimuth resolution and radar specification information, and when Δa satisfies the relationship of the following equation (8), the upsampling rate U at this time is calculated. As a calculation result, the process of step ST5 is terminated.
Δa + Ka ≧ Δa ′ (8)

When the relationship of the above equation (8) is not satisfied, the upsampling rate calculation unit 10b increases the upsampling rate U and obtains the amplitude reduction rate A by the above equation (5). To calculate the azimuth resolution using the above equation (6).
Then, as described above, the upsampling rate U is repeatedly increased until an upsampling rate U that satisfies the relationship of the above equation (8) is found.
The upsampling rate U is increased by adding or multiplying a constant value, for example. However, the upsampling rate U is a real number of 1 or more.

  The relationship between the image quality allowance and the upsampling rate may be calculated every time the image quality allowance is changed. In addition, a result calculated in advance or a result calculated in the past may be stored, and the upsampling rate may be determined with reference to a result stored every time the image quality deterioration allowable value is changed.

Returning to the description of FIG.
Next, the observation data upsampling unit 10c upsamples the observation data phase-compensated by the phase compensation unit 10a based on the upsampling rate U calculated in step ST5 (step ST6). As an up-sampling method, for example, a zero padding method in which 0 value is added to data obtained by Fourier transform of observation data in the range direction and inverse Fourier transform is used.

Next, the nearest neighbor interpolation unit 10d, based on the distance difference between the actual observation trajectory read from the inter-orbit distance storage unit 6 and the linear trajectory approximating this to the straight line, the observation data upsampled in step ST6. Is interpolated by the nearest neighbor method (step ST7).
Specifically, the nearest neighbor interpolation unit 10d replaces the observation data in the range r with the observation data closest to rd (r, t) in the upsampled observation data.
Note that a series of processing from step ST2 to step ST7 is performed at each pulse transmission / reception time.

The image reproducing unit 12 reproduces the observation data subjected to nearest neighbor interpolation in step ST7 using the linear trajectory information and the radar specification information (step ST8).
For the image reproduction, for example, a range Doppler method, a chirp scaling method, a ω-k method, or the like is used.

As described above, the image radar apparatus 1 according to the first embodiment includes the phase compensation unit 10a, the upsampling rate calculation unit 10b, the observation data upsampling unit 10c, the nearest neighbor interpolation unit 10d, and the image reproduction unit 12.
In particular, the up-sampling rate calculation unit 10b determines from the resolution in the range direction that determines the image quality when the observation data is imaged, the resolution in the azimuth direction, the allowable image quality deterioration value that is each allowable deterioration value of SNR, and the specifications of the radar. The upsampling rate U of the observation data is calculated so as to be within the image quality degradation allowable value.
The observation data upsampling unit 10c upsamples the observation data whose phase is compensated by the phase compensation unit 10a according to the upsampling rate U.
The nearest neighbor interpolation unit 10d performs nearest neighbor interpolation on the observation data up-sampled by the observation data up-sampling unit 10c based on the difference between the actually measured radar movement trajectory and the linear trajectory approximated to the straight line.
Since the upsampling rate of the observation data and nearest neighbor interpolation are performed based on the upsampling rate U calculated from the image quality degradation allowable value in this way, the user can perform the motion compensation without specifying the parameters for the interpolation of the observation data. It can be carried out.
Furthermore, since the user designates not the interpolation parameter but the image quality degradation allowable value as the parameter, the parameter can be changed according to the user's required image quality.

Further, the upsampling rate calculation unit 10b according to the first embodiment is a relational expression between the absolute value of the maximum value of the tangent slope with respect to the waveform obtained by processing the observation data with a function for increasing the resolution in the range direction and the upsampling rate U. Is used to calculate the upsampling rate U of the observation data so that it falls within each allowable degradation value. In the first embodiment, the function for increasing the resolution of observation data in the range direction is a sinc function, and the absolute value of the maximum value of the tangent slope is 1.37.
In this way, the upsampling rate U of the observation data can be calculated so as to be within the image quality degradation allowable value.
In addition, although the case where the waveform after range compression was expressed by the sinc function was shown, it can also be expressed by other functions. However, the processing using the sinc function can estimate the upsampling rate U with a smaller amount of calculation as described above.

Embodiment 2. FIG.
In the first embodiment, the case where the upsampling rate is calculated so as to be within the allowable image degradation value has been shown. However, in the second embodiment, in addition to the allowable image degradation value, a reference value for the processing time of the shake compensation is also considered. A configuration for calculating the upsampling rate will be described.

  FIG. 6 is a block diagram showing a configuration of an image radar apparatus 1A according to Embodiment 2 of the present invention. As in the first embodiment, the image radar apparatus 1A irradiates a target such as the ground surface with a radio wave from a radar mounted on a movable platform such as an aircraft or an artificial satellite, and the reflected wave from the target is radard. Receive and obtain observation data. Observation data from the radar is converted into an image by image reproduction. In FIG. 6, the same components as those in FIG.

The image radar apparatus 1A includes a fluctuation compensation unit 10A and a processing time upper limit storage unit 14 different from the image radar apparatus 1 of the first embodiment.
The fluctuation compensator 10A includes a time reference upsample rate calculator 10e instead of the upsample rate calculator 10b of FIG.
The time reference upsampling rate calculation unit 10e is a component corresponding to the upsampling rate calculation unit in the present invention, and calculates the upsampling rate U calculated based on the allowable image quality degradation value as the upper limit value of the processing time of the shake compensation. The upsampling rate U is adjusted so as not to exceed.

  The processing time upper limit storage unit 14 is a storage unit provided so that data can be read from the time reference upsampling rate calculation unit 10e. The processing time upper limit storage unit 14 specifies which one of the upper limit value of the shake compensation processing time designated by the user, the image quality allowable value, and the upper limit value of the shake compensation processing time is prioritized. A priority flag is stored.

The linear trajectory calculation unit 3, the inter-orbit distance calculation unit 5, the fluctuation compensation unit 10A, and the image reproduction unit 12 are realized, for example, by a processor executing a program stored in a memory.
A plurality of processors and a plurality of memories may execute the above functions in conjunction with each other.

  Actual observation trajectory storage unit 2, linear trajectory storage unit 4, inter-orbit distance storage unit 6, observation data storage unit 7, radar specification storage unit 8, image quality degradation allowable value storage unit 11, image storage unit 13, and processing time upper limit value The storage unit 14 is constructed in a storage device such as a hard disk device provided in the image radar apparatus 1A. The storage device may be an SD card, a USB memory, or the like, or an external storage device that can read and write data by communication.

Next, the operation will be described.
FIG. 7 is a flowchart showing the operation of the image radar apparatus 1 according to the second embodiment, and shows processing until the observation data is reproduced. Note that the processing from step ST1 to step ST4 and the processing from step ST6 to step ST8 in FIG. 7 are the same as those in FIG.

  In step ST5a, the time reference upsampling rate calculation unit 10e calculates the upsampling rate U so as to be within the image quality degradation allowable value and observes the upper limit value of the processing time of the shake compensation and the observation, as in step ST5 of FIG. The upsampling rate U is adjusted based on the data size of the data. Hereinafter, the adjustment process of the upsampling rate U will be described.

First, the time reference upsampling rate calculation unit 10e refers to the correspondence table between the processing time for shake compensation and the upsampling rate, and the observation data is upsampled at the upsampling rate U calculated based on the allowable image quality degradation value. In this case, the processing time of the shake compensation is specified.
The correspondence table between the fluctuation compensation processing time and the upsampling rate is table data created in advance for each computer performance such as a CPU used in the image radar apparatus 1A of the present invention.
This table data shows the correspondence between the upsampling rate U with respect to the number of sampling points in the range direction of the observation data and the processing time required for shake compensation.

The processing time T ′ at the upsampling rate U calculated based on the allowable image quality deterioration value can be obtained from the following equation (9).
However, the number of sampling points described in the correspondence table is N. Of the upsampling rates described in this correspondence table, the upsampling rate closest to the upsampling rate U is U ′. Further, the processing time corresponding to up-sample rate U 'described above correspondence table T, range direction of the sampling points a n _r of the observation _data, the number of transmit and receive pulses and n _{a.
T '= TUn r n a /} (U'N) ··· (9)

Here, if the processing time T ′ does not exceed the upper limit value Tu of the processing time, or exceeds the upper limit value Tu of the processing time, but the priority flag gives priority to the image quality degradation allowable value, the time reference upsample rate calculation unit 10e outputs the upsampling rate U calculated based on the image quality degradation allowable value as a final calculation result.
On the other hand, when the processing time T ′ exceeds the processing time upper limit Tu and the processing time is prioritized by the priority flag, the time reference upsampling rate calculation unit 10e calculates the following expression (10 ) Is used to calculate the upsampling rate U again, and this upsampling rate U is used as the final calculation result.
_{U = TuU'N / (Tn r n} a) ··· (10)

As described above, the image radar apparatus 1A according to the second embodiment includes the phase compensation unit 10a, the time reference upsampling rate calculation unit 10e, the observation data upsampling unit 10c, and the nearest neighbor interpolation unit 10d as the motion compensation unit 10A. Is provided.
The time reference upsampling rate calculation unit 10e uses the observation data so as to be within the allowable image quality deterioration value based on the allowable image quality deterioration value including the allowable range resolution deterioration value, the allowable azimuth resolution deterioration value, and the allowable SNR deterioration value and the radar specifications. The upsampling rate U is calculated. Then, the upsampling rate U is adjusted so that the processing time of the shake compensation when the observation data is upsampled at the calculated upsampling rate U does not exceed a predetermined upper limit value.
With this configuration, it is possible for the user to perform motion compensation by designating the allowable image quality degradation value and the upper limit value of the processing time as parameters without designating the parameters for the observation data interpolation.

In addition, the time reference upsampling rate calculation unit 10e according to the second embodiment refers to a priority flag that designates which one of the image quality allowable value and the fluctuation compensation processing time upper limit is to be prioritized, and the priority flag. If priority is given to the image quality allowance, the upper limit value Tu is set to the processing time of the shake compensation when the observation data is upsampled at the upsampling rate U calculated to be within the image quality allowance. Even if it exceeds, the up-sampling rate U is output as a calculation result.
Accordingly, the user can designate which of the image quality deterioration allowable value and the shake compensation processing time upper limit is to be prioritized by flag information based on the priority flag.

  In the present invention, within the scope of the invention, any combination of each embodiment, any component of each embodiment can be modified, or any component can be omitted in each embodiment. .

  1, 1A image radar device, 2 actual observation trajectory storage unit, 3 linear trajectory calculation unit, 4 linear trajectory storage unit, 5 inter-orbit distance calculation unit, 6 inter-orbit distance storage unit, 7 observation data storage unit, 8 radar specifications Storage unit, 9 range compression unit, 10, 10A oscillation compensation unit, 10a phase compensation unit, 10b upsample rate calculation unit, 10c observation data upsampling unit, 10d nearest neighbor interpolation unit, 10e time reference upsampling rate calculation unit, 11 Image quality deterioration tolerance storage unit, 12 image reproduction unit, 13 image storage unit, 14 processing time upper limit storage unit.

Claims (6)

A phase compensator for compensating the phase of the observation data of the radio wave received by the radar, based on the difference between the actually measured movement trajectory of the radar and a linear trajectory approximating the straight line;
From the resolution in the range direction that determines the image quality when the observation data is imaged, the resolution in the azimuth direction, the permissible degradation value of the signal-to-noise power ratio, and the specifications of the radar, the observation data is within the permissible degradation value. An upsampling rate calculator for calculating the upsampling rate of
Based on the upsampling rate calculated by the upsampling rate calculation unit, an observation data upsampling unit that upsamples observation data whose phase has been compensated by the phase compensation unit;
Based on the difference between the measured radar movement trajectory and the linear trajectory approximating this to a straight line, the nearest neighbor interpolation unit that performs nearest neighbor interpolation on the observation data upsampled by the observation data upsampling unit,
An image radar apparatus comprising: an image reproducing unit configured to image observation data subjected to nearest neighbor interpolation by the nearest neighbor interpolation unit.   The upsampling rate calculating unit adjusts the upsampling rate so that the processing time of shake compensation when the observation data is upsampled at the calculated upsampling rate does not exceed a predetermined upper limit value. The image radar device according to claim 1.   The upsampling rate calculation unit refers to flag information in which priority is given to each of the deterioration allowable values and the upper limit value of the processing time of the shake compensation, and the deterioration allowable values are specified in the flag information. If the observation data is upsampled at an upsampling rate calculated so as to be within the above allowable deterioration values, even if the processing time of shake compensation exceeds the upper limit value, The image radar apparatus according to claim 2, wherein the sample rate is output as a calculation result.   The upsampling rate calculation unit uses the relational expression between the absolute value of the maximum value of the tangent slope and the upsampling rate with respect to the waveform obtained by signal processing with a function for increasing the resolution of the observation data in the range direction. The image radar apparatus according to claim 1, wherein an upsampling rate of observation data is calculated so as to be within an allowable value.   The image radar apparatus according to claim 4, wherein the function for increasing the resolution of the observation data in the range direction is a sinc function.   6. The image radar apparatus according to claim 5, wherein an absolute value of a maximum value of the tangent slope is 1.37.

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