WO2020022468A1 - Synthetic aperture radar device, synthetic aperture radar signal processing device, synthetic aperture radar signal processing program, and synthetic aperture radar observation method - Google Patents

Synthetic aperture radar device, synthetic aperture radar signal processing device, synthetic aperture radar signal processing program, and synthetic aperture radar observation method Download PDF

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Publication number
WO2020022468A1
WO2020022468A1 PCT/JP2019/029355 JP2019029355W WO2020022468A1 WO 2020022468 A1 WO2020022468 A1 WO 2020022468A1 JP 2019029355 W JP2019029355 W JP 2019029355W WO 2020022468 A1 WO2020022468 A1 WO 2020022468A1
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Prior art keywords
synthetic aperture
aperture radar
chirp pulse
azimuth
reflected
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PCT/JP2019/029355
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French (fr)
Japanese (ja)
Inventor
貴宏 後藤
對馬　肩吾
スマンティヨ、ヨサファット、テトォコ スリ
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国立大学法人千葉大学
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Publication of WO2020022468A1 publication Critical patent/WO2020022468A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/904—SAR modes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques

Definitions

  • the present disclosure relates to a synthetic aperture radar technology that achieves both high signal-to-noise ratio and high resolution.
  • Patent Literatures 1 to 3 and Non-Patent Literature 1 disclose methods for achieving both high signal-to-noise ratio and high resolution in the synthetic aperture radar technology.
  • a chirp pulse is emitted in a random direction to expand the observation range in the spotlight mode.
  • a chirp pulse is scanned in the range direction and the azimuth direction to realize Scan-SAR, TOPS-SAR, and the like.
  • a mechanical or electrical mechanism for controlling the direction of the irradiation beam is required to intentionally change the direction of the irradiation beam, a circuit is required. It becomes complicated and the system becomes expensive.
  • the present disclosure does not require a mechanical or electrical mechanism for controlling the direction of an irradiation beam while achieving both a high signal-to-noise ratio and high resolution in a synthetic aperture radar technology. It is an object of the present invention to simplify the circuit and reduce the cost of the system.
  • the present disclosure relates to a chirp pulse generation unit that generates a chirp pulse for range compression of a synthetic aperture radar, and a mechanical and electronic pointing device for irradiating the chirp pulse generated by the chirp pulse generation unit.
  • An antenna unit that changes the direction of the irradiation beam in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristic without performing control, a reflection signal receiving unit that receives a reflection signal reflected from the target,
  • a synthetic aperture radar apparatus comprising:
  • the present disclosure also provides a chirp pulse generation unit that generates a chirp pulse for range compression of a synthetic aperture radar, and irradiates the chirp pulse generated by the chirp pulse generation unit according to an inherent directional characteristic.
  • a synthetic aperture radar device comprising: an antenna unit that changes a beam direction in an azimuth direction according to a frequency of an irradiation beam; and a reflected signal receiving unit that receives a reflected signal reflected from a target.
  • the present disclosure also provides a chirp pulse generation procedure for generating a chirp pulse for range compression of a synthetic aperture radar, and a chirp pulse generation procedure for irradiating the antenna section according to a directional characteristic originally provided in the antenna section.
  • This is a characteristic synthetic aperture radar observation method.
  • the beam tilt generated by the directional characteristics of the antenna is positively used, so that the observable azimuth time becomes longer at any observation target position. Therefore, even if an attempt is made to increase the antenna gain, that is, to increase the aperture length in order to realize a high signal-to-noise ratio, the azimuth resolution can be prevented from being reduced by the synthetic aperture.
  • the direction of the irradiation beam is changed in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristics without performing the mechanical and electronic pointing control, the circuit is simplified and the system is inexpensive. Can be realized.
  • the chirp pulse generation unit controls the center frequency for each azimuth position to generate a chirp pulse, so that the azimuth direction of the irradiation beam irradiated by the antenna unit is directed to an observation area having a certain azimuth direction. And performing a synthetic aperture radar observation using a spotlight mode.
  • the chirp pulse generation unit generates a chirp pulse having a shape independent of the azimuth position, thereby changing the direction of the irradiation beam in the azimuth direction and not changing the direction of the irradiation beam in the azimuth direction.
  • a synthetic aperture radar apparatus characterized in that a synthetic aperture radar observation is performed using a strip mode in which the observable azimuth time is longer than in the past.
  • the chirp pulse generation unit may generate a chirp pulse having a shape independent of an azimuth position and having a center frequency such that squint in an azimuth direction of an irradiation beam irradiated by the antenna unit occurs. It is now possible to perform synthetic aperture radar observation using the squint mode, in which the observable azimuth time is longer than when the irradiation beam direction is changed in the azimuth direction and the irradiation beam direction is not changed in the azimuth direction. It is a synthetic aperture radar device characterized by the following.
  • the present disclosure is a reflection signal received by the reflection signal receiving unit of the synthetic aperture radar device described above, of the chirp pulse generated by the chirp pulse generation unit, is reflected from the observation target position for each azimuth position
  • a synthetic aperture radar signal processing apparatus characterized by performing a correlation process between a reference signal that selects only a partial section expected to be used.
  • the present disclosure is a reflection signal received by the reflection signal receiving unit of the synthetic aperture radar device described above, of the chirp pulse generated by the chirp pulse generation unit, is reflected from the observation target position for each azimuth position
  • This is a synthetic aperture radar signal processing program for causing a computer to execute a correlation process between a reference signal in which only a partial section expected to be selected is selected.
  • the receivable range time is shorter than in the related art, but the receivable azimuth time is longer, so that the total receivable time does not decrease. Therefore, even if an attempt is made to increase the bandwidth of the chirped pulse in order to realize a higher range resolution, it is possible to prevent the signal-to-noise ratio from being reduced by the beam tilt.
  • the reflection signal reflected from the observation target position, of the chirp pulse generated by the chirp pulse generation unit only a partial section expected to be reflected from the observation target position for each azimuth position And performing a correlation process in a time domain between the reference signal and the selected reference signal.
  • the reflection signal reflected from the observation target position, of the chirp pulse generated by the chirp pulse generation unit only a partial section expected to be reflected from the observation target position for each azimuth position Is a synthetic aperture radar signal processing program for causing a computer to execute a correlation process in a time domain between the selected reference signal and a reference signal.
  • the receivable range time is shorter than in the related art, but the receivable azimuth time is longer, so that the total receivable time does not decrease. Therefore, even if an attempt is made to increase the bandwidth of the chirped pulse in order to realize a higher range resolution, it is possible to prevent the signal-to-noise ratio from being reduced by the beam tilt. Further, although the calculation time is long, the image accuracy is high.
  • the present disclosure eliminates the need for a mechanical or electrical mechanism for controlling the direction of an irradiation beam while achieving a high signal-to-noise ratio and high resolution in a synthetic aperture radar technology, and simplifies the circuit. In addition, the cost of the system can be reduced.
  • FIG. 4 is a diagram illustrating a chirped pulse waveform and antenna directivity according to the present disclosure.
  • FIG. 3 is a diagram illustrating a configuration diagram of a spotlight mode according to the related art.
  • FIG. 3 is a diagram illustrating a strip mode of the present disclosure.
  • FIG. 3 is a diagram illustrating a score mode according to the present disclosure.
  • 1 is a diagram illustrating a configuration of a synthetic aperture radar system according to the present disclosure.
  • FIG. 3 is a diagram illustrating processing of the synthetic aperture radar system according to the present disclosure.
  • FIG. 5 is a diagram illustrating frequency characteristics of antenna directivity according to the present disclosure.
  • FIG. 5 is a diagram illustrating frequency characteristics of antenna directivity according to the present disclosure.
  • FIG. 5 is a diagram illustrating frequency characteristics of antenna directivity according to the present disclosure.
  • FIG. 4 is a diagram illustrating a time change of a chirp frequency according to the present disclosure.
  • FIG. 4 is a diagram illustrating a time change of the antenna directivity according to the present disclosure.
  • FIG. 3 is a diagram illustrating definitions of a direction and a distance of a target according to the present disclosure.
  • FIG. 4 is an explanatory diagram of an azimuth time during which a reflected signal of the present disclosure exists.
  • FIG. 4 is an explanatory diagram of a range time in which a chirp pulse according to the present disclosure is irradiated toward a target.
  • FIG. 4 is a diagram illustrating a reflection signal and a reference signal according to the present disclosure.
  • FIG. 4 is a diagram illustrating a point extension function of the present disclosure versus a distance in a range direction from a target.
  • FIG. 4 is a diagram illustrating a point extension function of the present disclosure versus an azimuth distance from a target.
  • FIG. 1 shows a chirp pulse waveform and antenna directivity according to the present disclosure.
  • beam tilt caused by the directional characteristics of the antenna is positively used. That is, in irradiating the chirp pulse, the direction of the irradiation beam is changed in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristic without performing the mechanical and electronic pointing control.
  • the chirp pulse sweeps the frequency from the minimum frequency f 0 -B W / 2 to the maximum frequency f 0 + B W / 2 via the center frequency f 0 over the range time 0 ⁇ ⁇ ⁇ ⁇ 0. .
  • an array antenna and a slot antenna are applied as the antenna unit A.
  • Each antenna element of the antenna section A is arranged in the azimuth direction x.
  • each antenna element of the antenna section A is excited in phase, and the irradiation beam of the antenna section A is directed in the front direction y.
  • the chirp pulse sweeps the minimum frequency f 0 -B W / 2
  • each antenna element of the antenna section A is not excited in phase, and the irradiation beam of the antenna section A is shifted in the direction ⁇ min shifted from the front direction y. ⁇ 0.
  • the chirp pulse sweeps the maximum frequency f 0 + B W / 2
  • the respective antenna elements of the antenna section A are not excited in phase, and the irradiation beam of the antenna section A has a direction ⁇ max> 0 shifted from the front direction y.
  • the direction ⁇ of the irradiation beam is changed in the azimuth direction x according to the frequency f of the irradiation beam according to the inherent directional characteristic without performing the mechanical and electronic pointing control. Let it.
  • FIG. 2 shows a configuration diagram of the spotlight mode of the prior art.
  • a chirp pulse having a shape not depending on the azimuth position x is generated, and the antenna control unit 13 (connected by a rotary joint or the like) mechanically directs the beam to thereby control the irradiation beam emitted by the antenna unit A.
  • the azimuth direction x is directed to a certain observation area, and the synthetic aperture radar observation is performed using the spotlight mode.
  • a chirp pulse having a shape not depending on the azimuth position x is generated, and the azimuth of the irradiation beam irradiated by the antenna unit A is controlled electronically by the phase shifter and the distributor of the antenna unit A.
  • the synthetic aperture radar observation is performed using the spotlight mode so that the direction x is directed to a certain observation area.
  • FIG. 5 shows a configuration diagram of the spotlight mode of the present disclosure.
  • the azimuth direction of the irradiation beam radiated by the antenna unit A according to the original directional characteristics without performing mechanical and electronic directional control.
  • x is directed to a certain observation area, and the synthetic aperture radar observation is performed using the spotlight mode.
  • FIG. 5 is also applicable to both the strip mode and the squint mode.
  • FIG. 3 shows the strip mode of the present disclosure.
  • the direction of the irradiation beam is changed in the azimuth direction x, and the observable azimuth time is shorter than when the direction of the irradiation beam is not changed in the azimuth direction x.
  • Synthetic aperture radar observation is performed using the strip mode in which is longer.
  • FIG. 3 shows a strip mode when there is no beam tilt according to the related art.
  • the synthetic aperture radar system S is located at the azimuth direction position x st, i and the chirp pulse sweeps the frequency f 0 ⁇ B W / 2 to f 0 + B W / 2, the target T is captured. Is starting to be.
  • the synthetic aperture radar system S is located at the azimuth direction position x st, f and the chirp pulse sweeps the frequency f 0 ⁇ B W / 2 to f 0 + B W / 2
  • the target T is: The capture range is over.
  • the azimuth direction range x st, i to x st, f is shorter than in the case of the present disclosure described later, the observable azimuth time is shorter than in the case of the present disclosure described later, and the azimuth resolution is the same as that of the present disclosure described later. It is lower than the case of disclosure.
  • FIG. 3 shows a strip mode when there is a beam tilt according to the present disclosure.
  • the synthetic aperture radar system S is located at the azimuth direction position x ' st, i and the chirp pulse sweeps the frequency f 0 -B W / 2, the target T has begun to be captured.
  • the azimuth direction position x'st, i is behind the azimuth direction position xst, i
  • the azimuth direction position x'st, f is ahead of the azimuth direction position xst, f . Therefore, since the azimuth direction range x ′ st, i to x ′ st, f is longer than that of the related art, the observable azimuth time is longer than that of the related art, and the azimuth resolution is higher than that of the related art.
  • FIG. 4 shows the scint mode of the present disclosure.
  • the center frequency is changed from f 0 in FIGS. 1 and 3 to f 0 ′ in FIG. 4 (however, in the case of FIG. 4, f 0 ′ ⁇ f 0 ). And shift.
  • the center frequency is changed from f 0 in FIGS. 1 and 3 to f 0 ′ in FIG. 4 (however, in FIG. 4, f 0 ′> f 0 ). And shift.
  • FIG. 4 shows a squint mode when there is no beam tilt according to the related art.
  • the synthetic aperture radar system S is located at the position x sq, i in the azimuth direction and the chirp pulse sweeps the frequencies f 0 ′ ⁇ B W / 2 to f 0 ′ + B W / 2, the target T is , Has begun to be caught.
  • the synthetic aperture radar system S is located at the azimuth position x sq, f and the chirp pulse sweeps the frequency f 0 ′ ⁇ B W / 2 to f 0 ′ + B W / 2, the target T Has been captured.
  • the azimuth direction range x sq, i to x sq, f is shorter than in the case of the present disclosure described later, so that the observable azimuth time is shorter than in the case of the present disclosure described later, and the azimuth resolution is defined in the following description. It is lower than the case of disclosure.
  • FIG. 4 shows a squint mode when there is a beam tilt according to the present disclosure.
  • the synthetic aperture radar system S is located at the azimuth position x ′ sq, i and the chirp pulse sweeps the frequency f 0 ′ ⁇ B W / 2, the target T has begun to be captured.
  • the synthetic aperture radar system S is located at the azimuth position x ′ sq, f and the chirp pulse sweeps the frequency f 0 ′ + B W / 2, the target T has been captured. .
  • the azimuth direction position x ' sq, i is behind the azimuth direction position x sq, i
  • the azimuth direction position x' sq, f is ahead of the azimuth direction position x sq, f . Therefore, since the azimuth direction range x ′ sq, i to x ′ sq, f is longer than that of the related art, the observable azimuth time is longer than that of the related art, and the azimuth resolution is higher than that of the related art.
  • FIG. 5 shows the configuration of the synthetic aperture radar system according to the present disclosure.
  • FIG. 6 shows the processing of the synthetic aperture radar system of the present disclosure.
  • the synthetic aperture radar system S includes a synthetic aperture radar device 1 and a synthetic aperture radar signal processing device 2.
  • the synthetic aperture radar device 1 includes a chirp pulse generating unit 11, an antenna unit A, and a reflected signal receiving unit 12, and is mounted on an artificial satellite or an aircraft.
  • the synthetic aperture radar signal processing device 2 includes a correlation processing execution unit 21, is mounted on an artificial satellite, an aircraft, a ground facility, or the like, and installs a synthetic aperture radar signal processing program shown in the lower section of FIG. 6 in a computer. Is realized by:
  • the synthetic aperture radar device 1 actively uses the beam tilt caused by the directional characteristics of the antenna.
  • the synthetic aperture radar apparatus 1 does not perform the mechanical and electronic pointing control but changes the direction ⁇ of the irradiation beam according to the frequency f of the irradiation beam according to the inherent directional characteristics. It is changed in the azimuth direction x.
  • the chirp pulse generation unit 11 generates a chirp pulse for range compression of the synthetic aperture radar (step S1).
  • the antenna unit A does not perform mechanical and electronic pointing control but changes the direction of the irradiation beam ⁇ according to the inherent directional characteristics. It is changed in the azimuth direction x according to f (step S2).
  • the reflected signal receiving unit 12 receives the reflected signal reflected from the target T by the antenna unit A (Step S3).
  • the synthetic aperture radar device 1 will be described with reference to FIGS. 7 to 10 are applied to the strip mode, but can be applied to both the spotlight and the squint modes by changing the center frequency.
  • the direction ⁇ of the irradiation beam is expressed by Expression 1 with respect to the frequency f of the irradiation beam.
  • the irradiation beam of the antenna unit A is directed in the direction ⁇ ⁇ 0 shifted from the front direction y.
  • the chirp pulse sweeps the frequency f 0 to f 0 + B W / 2
  • the irradiation beam of the antenna unit A is directed in the direction ⁇ > 0 shifted from the front direction y.
  • the irradiation beam half width of the antenna unit A is ⁇
  • the irradiation beam intensity of the antenna unit A is uniform within the irradiation beam width of the antenna unit A.
  • the irradiation beam intensity of the antenna unit A is assumed to be uniform within the irradiation beam width of the antenna unit A for simplicity, it is not uniform within the irradiation beam width of the antenna unit A as is practical. It may be.
  • FIG. 9 shows a time change of the chirp frequency according to the present disclosure.
  • the frequency f of the chirp pulse is expressed as shown in Expression 2 with respect to the range time ⁇ . Note that the time change of the chirp frequency may be rising to the right or falling to the right, and may not necessarily be a linear time change.
  • FIG. 10 shows a time change of the antenna directivity according to the present disclosure.
  • the direction ⁇ of the irradiation beam is expressed by Expression 3 with respect to the range time ⁇ . It should be noted that the time change of the antenna directivity may be rising to the right or falling to the right, and is not necessarily a linear time change.
  • the synthetic aperture radar signal processing device 2 refers to only a partial section of the chirp pulse irradiated toward the observation target position among the entire section of the chirp pulse irradiated at each azimuth time t as a reflected signal. It is taken into account in the correlation processing between the signals.
  • the correlation processing execution unit 21 performs a correlation process between the reflection signal and the reference signal (Step S11).
  • the synthetic aperture radar signal processing device 2 will be described with reference to FIGS. 11 to 14 are applied to the strip mode, but can be applied to both the spotlight and the squint modes by changing the center frequency.
  • the correlation processing execution unit 21 expects that the reflection signal received by the reflection signal reception unit 12 and the chirp pulse generated by the chirp pulse generation unit 11 are reflected from the observation target position for each azimuth position x. And a reference signal for which only a partial section is selected.
  • the correlation processing execution unit 21 is expected to reflect the reflection signal reflected from the observation target position and the chirp pulse generated by the chirp pulse generation unit 11 from the observation target position for each azimuth position x. Then, a correlation process in a time domain between the reference signal and the selected reference signal is performed. That is, in the present embodiment, the correlation processing execution unit 21 executes the correlation processing in the time domain between the reflected signal and the reference signal, so that the calculation time is long but the image accuracy is high.
  • the correlation processing execution unit 21 may execute the correlation processing in the frequency domain between the reflected signal and the reference signal, thereby significantly reducing the calculation time.
  • FIG. 11 shows the definitions of the direction and distance of the target of the present disclosure.
  • the position of the synthetic aperture radar system S is (x (t), 0), and the position of the target T is (X, Y).
  • the position x (t) in the azimuth direction of the synthetic aperture radar system S, the direction ⁇ (t) of the target T viewed from the synthetic aperture radar system S, and the distance R (t) from the synthetic aperture radar system S to the target T are expressed by the following equation (4). It is represented as Here, v is the speed of the synthetic aperture radar system S.
  • FIG. 12 is an explanatory diagram of the azimuth time at which the reflected signal of the present disclosure exists.
  • Equation 6 corresponds to the azimuth time t i in FIG. 14, and the right side of Equation 6 corresponds to the azimuth time t f in FIG.
  • the beam tilt generated by the directional characteristics of the antenna is positively used, so that the observable azimuth time t becomes longer at any observation target position. Therefore, even if an attempt is made to increase the antenna gain, that is, to increase the aperture length in order to realize a high signal-to-noise ratio, the azimuth resolution can be prevented from being reduced by the synthetic aperture. Further, in order to change the direction ⁇ of the irradiation beam in the azimuth direction x according to the frequency f of the irradiation beam according to the inherent directivity characteristic without performing the mechanical and electronic pointing control, the circuit is simplified and the system is changed. Can be realized at a low price.
  • FIG. 13 is an explanatory diagram of a range time in which the chirp pulse according to the present disclosure is irradiated toward the target T.
  • the range time ⁇ during which the target T can be observed at each azimuth time t is represented by Expression 7. That is, the direction ⁇ (t) of the target T viewed from the synthetic aperture radar system S only needs to satisfy the following condition: (1) The irradiation beam of the antenna unit A starts to turn toward the target T in the course of the chirp at the frequency f.
  • the direction ⁇ (t) is the same as the direction ⁇ ( ⁇ i (t)) + ⁇ of the outer edge of the irradiation beam of the antenna unit A, or the direction ⁇ (t) is ⁇ (0) ⁇ (2) the direction of the outer edge of the irradiation beam of the antenna section A when the irradiation beam of the antenna section A ends toward the target T in the course of the chirp of the frequency f ( ⁇ (0) + ⁇ ).
  • the direction ⁇ (t) is the same as compared to ⁇ f (t)) ⁇ ⁇ , or the direction ⁇ (t) is between ⁇ ( ⁇ 0 ) ⁇ and ⁇ ( ⁇ 0 ) + ⁇ .
  • Equation 8 corresponds to the range time ⁇ i (t) in FIGS. 13 and 14, and the right side of Equation 8 corresponds to the range time ⁇ f (t) in FIGS.
  • FIG. 14 shows the reflection signal and the reference signal of the present disclosure.
  • the reflection signal F (t, ⁇ ) reflected from the target T is represented by Expression 9.
  • the reference signal to be subjected to the correlation processing with the reflected signal F (t, ⁇ ) is determined based on the following theoretical formula of the reflected signal F (t, ⁇ ).
  • the value range of the azimuth time t of the reflection signal F (t, ⁇ ) is expressed by Expression 10 based on Expression 6.
  • the value range of the range time ⁇ of the reflected signal F (t, ⁇ ) is expressed by Expression 11 based on Expression 8 and the delay time of electromagnetic wave propagation.
  • the case where there is no beam tilt and the case where there is a beam tilt will be compared.
  • the range time range ⁇ if ⁇ ⁇ ⁇ ⁇ if + ⁇ 0 (where ⁇ if is the electromagnetic wave propagation Delay time) over the entire range time range ⁇ if ⁇ ⁇ ⁇ ⁇ if + ⁇ 0 and is considered in the correlation process between the reflected signal and the reference signal.
  • the synthetic aperture radar system S is closest azimuth time target T t c, Range Time Range ⁇ c ⁇ ⁇ ⁇ ⁇ c + ⁇ 0 ( however, tau c, a delay time of electromagnetic wave propagation.)
  • tau c a delay time of electromagnetic wave propagation.
  • the azimuth time width in which the reflected signal exists when there is no beam tilt and the azimuth time width in which the reflected signal exists when there is the beam tilt are displayed as having the same length.
  • the azimuth time width in which the reflected signal exists when there is no beam tilt is shorter than the azimuth time width in which the reflected signal exists when there is a beam tilt, and the reflection time when represented as shown in FIG.
  • the area of the signal is not larger when there is no beam tilt than when there is no beam tilt and when there is a beam tilt.
  • the synthetic aperture radar system S is closest azimuth time t c to the target T, among the range time range ⁇ c ⁇ ⁇ ⁇ ⁇ c + ⁇ 0, a part of the range time range max ⁇ i (t c) , ⁇ Only c ⁇ ⁇ ⁇ ⁇ min ⁇ ⁇ f (t c ), ⁇ c + ⁇ 0 ⁇ (see FIG. 13 and Equations 8 and 11) are considered in the correlation process between the reflected signal and the reference signal.
  • the azimuth time t f of the illumination beam of the antenna unit A finishes orientation target T, among the range time range ⁇ if ⁇ ⁇ ⁇ ⁇ if + ⁇ 0, a part of the range time range max ⁇ i (t f) , Only ⁇ if ⁇ ⁇ ⁇ ⁇ min ⁇ f (t f ), ⁇ if + ⁇ 0 ⁇ (see FIG. 13 and Equations 8, 11) are considered in the correlation process between the reflected signal and the reference signal.
  • the receivable range time ⁇ is shorter than in the related art, but the receivable azimuth time t is longer, so that the total receivable time is not reduced. Therefore, even if an attempt is made to increase the bandwidth of the chirped pulse in order to realize a higher range resolution, it is possible to prevent the signal-to-noise ratio from being reduced by the beam tilt.
  • a target P a reflection signal reflected from (X, Y) is F (X, Y) (t, ⁇ )
  • a reflection signal reflected from another target P ′ (X ′, Y ′) is F (X ′, Y ′) (t, ⁇ ).
  • the correlation S between the reflection signal F (X, Y) (t, ⁇ ) and the reflection signal F (X ′, Y ′) (t, ⁇ ) is expressed by Expression 12.
  • the correlation S is expected to take a large value if P: (X, Y) and P ′ :( X ′, Y ′) are close, and P: (X, Y) and P ′ :( X ′, If Y ′) is farther away, a smaller value is expected.
  • the reflected signals reflected from a plurality of targets P 1 : (X 1 , Y 1 ), P 2 : (X 2 , Y 2 ),..., P n : (X n , Y n ) are represented by Expression 13.
  • the reference signal expected to be reflected from the observation target position P: (X, Y) is F (X, Y) (t, ⁇ ).
  • the correlation S between the reflection signal R (t, ⁇ ) and the reference signal F (X, Y) (t, ⁇ ) is expressed by Expression 14.
  • Correlation S is, P 1, P 2, ⁇ , if there is a point very close to the P in P n, are expected to take a large value, P 1, P 2, ⁇ , in the P n If there is no point very close to P, it is expected to take a small value. Therefore, in order to image the presence or absence of the target at the observation target position P: (X, Y), the magnitude of the correlation S relating to the observation target position P: (X, Y) is associated with the number of gradations of the image.
  • the resolution evaluation of the synthetic aperture radar system will be described.
  • the correlation S involving P: (X, Y) and P ′ :( X ′, Y ′) is represented by P: (X, Y) and P ′ :( X ′, Y ′). Is assumed to rapidly decrease as the distance increases. Therefore, the degree to which the correlation S rapidly decreases, that is, the resolution of the synthetic aperture radar system S is evaluated.
  • the reflected signal reflected from the target (0, Y) is represented by Expression 15, and the reference signal expected to be reflected from the observation target position ( ⁇ X, Y + ⁇ Y) is represented by Expression 16.
  • the azimuth direction position of the target is set to 0, generality is not lost. Assuming that the position of the target in the azimuth direction is X, the azimuth time t may be shifted by X / v.
  • the correlation S between the reflection signal F (t, ⁇ ) and the reference signal G (t, ⁇ ) is expressed by Expression 17.
  • ⁇ R (t), R (t), and R ′ (t) are expressed as in Expression 18. Note that the correlation S shown in Expression 17 corresponds to the point extension function shown in FIGS.
  • the correlation S between the reflection signal F (t, ⁇ ) and the reference signal G (t, ⁇ ) is calculated as in Expression 19.
  • a (t) and B (t) are represented as in Expressions 20 and 21.
  • the integration range of the azimuth time t in Expression 19 extends over the azimuth time t that satisfies B (t)> A (t).
  • ⁇ (t) and ⁇ ′ (t) are represented by Expression 22.
  • FIG. 15 shows the point extension function of the present disclosure versus the distance in the range direction from the target.
  • FIG. 16 shows the point extension function of the present disclosure versus the azimuth distance from the target.
  • the center frequency f 0 is 9.25 GHz
  • the chirp pulse frequency width B W is 800 MHz
  • the chirp pulse time width ⁇ 0 is 1.0 ⁇ s
  • the beam width 2 ⁇ is 1.5 deg
  • the beam The change speed of the tilt is 1.0 deg / 100 MHz
  • the speed v of the synthetic aperture radar system S is 100 m / s
  • the distance in the range direction of the target T is 15.0 km.
  • the same range resolution is obtained when there is a beam tilt according to the present disclosure than when there is no beam tilt according to the related art. That is, in the case where the beam tilt of the present disclosure is present, the range time ⁇ during which the reflected signal from the target T exists is reduced as compared with the case where the beam tilt of the related art is not provided. However, since the azimuth time t during which the reflected signal from the target T is present increases, the same range resolution can be obtained without reducing the total time during which the reflected signal from the target T exists.
  • a synthetic aperture radar apparatus, a synthetic aperture radar signal processing apparatus, a synthetic aperture radar signal processing program, and a synthetic aperture radar observation method provide a synthetic aperture radar technique that achieves both high signal-to-noise ratio and high resolution in synthetic aperture radar technology.
  • a mechanical or electrical mechanism for controlling the beam direction is not required, and the circuit can be simplified and the cost of the system can be reduced.
  • Synthetic aperture radar system A Antenna unit T: Target 1: Synthetic aperture radar device 2: Synthetic aperture radar signal processing device 11: Chirp pulse generating unit 12: Reflected signal receiving unit 13: Antenna driving unit 21: Correlation processing executing unit

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Abstract

The present disclosure provides a synthetic aperture radar device 1 characterized by comprising: a chirped pulse generation unit 11 which generates a chirped pulse for compressing the range of a synthetic aperture radar; an antenna unit A which, when radiating the chirped pulse generated by the chirped pulse generation unit 11, causes the direction of the radiated beam to be changed in the azimuth direction in correspondence to the frequency of the radiated beam, without performing mechanical or electronic directional control and in accordance with inherent directional characteristics; and a reflection signal reception unit 12 which receives a reflection signal reflected from a target T.

Description

合成開口レーダ装置、合成開口レーダ信号処理装置、合成開口レーダ信号処理プログラム及び合成開口レーダ観測方法Synthetic aperture radar apparatus, synthetic aperture radar signal processing apparatus, synthetic aperture radar signal processing program, and synthetic aperture radar observation method
　本開示は、高信号対雑音比及び高分解能化を両立させる合成開口レーダ技術に関する。 The present disclosure relates to a synthetic aperture radar technology that achieves both high signal-to-noise ratio and high resolution.
　合成開口レーダ技術において、以下のトレードオフの解決が要求されている。第１のトレードオフとして、高信号対雑音比を実現するためには、アンテナの高利得化つまり開口長増大が必要となるが、合成開口によりアジマス分解能が低下してしまう。第２のトレードオフとして、高レンジ分解能化を実現するためには、チャープパルスの広帯域化が必要となるが、アンテナの指向特性の不完全性によって生じるビームチルトにより信号対雑音比が低下してしまう。 In synthetic aperture radar technology, the following trade-off needs to be solved. As a first trade-off, in order to achieve a high signal-to-noise ratio, it is necessary to increase the gain of the antenna, that is, to increase the aperture length. However, the azimuth resolution is reduced by the synthetic aperture. As a second trade-off, in order to achieve a high range resolution, it is necessary to broaden the band of the chirped pulse. However, the signal tilt caused by imperfect directional characteristics of the antenna lowers the signal-to-noise ratio. I will.
特許第６０８０７８３号明細書Patent No. 6080783 特許第６０７２２６２号明細書Patent No. 6072262 特許第３３３２０００号明細書Patent No. 3332000
　合成開口レーダ技術において、高信号対雑音比及び高分解能化を両立させる方法が、特許文献１～３及び非特許文献１に開示されている。特許文献１～３では、ランダムな方向にチャープパルスを照射し、スポットライトモードの観測範囲を広げる。非特許文献１では、レンジ方向及びアジマス方向にチャープパルスを走査し、Ｓｃａｎ－ＳＡＲ及びＴＯＰＳ－ＳＡＲ等を実現する。しかし、特許文献１～３及び非特許文献１では、照射ビームの方向を意図的に変化させるためには、照射ビームの方向を制御する機械的又は電気的な機構が必要であるため、回路が複雑化しシステムが高価格化する。 方法 Patent Literatures 1 to 3 and Non-Patent Literature 1 disclose methods for achieving both high signal-to-noise ratio and high resolution in the synthetic aperture radar technology. In Patent Documents 1 to 3, a chirp pulse is emitted in a random direction to expand the observation range in the spotlight mode. In Non-patent Document 1, a chirp pulse is scanned in the range direction and the azimuth direction to realize Scan-SAR, TOPS-SAR, and the like. However, in Patent Documents 1 to 3 and Non-Patent Document 1, since a mechanical or electrical mechanism for controlling the direction of the irradiation beam is required to intentionally change the direction of the irradiation beam, a circuit is required. It becomes complicated and the system becomes expensive.
　そこで、前記課題を解決するために、本開示は、合成開口レーダ技術において、高信号対雑音比及び高分解能化を両立させつつ、照射ビームの方向を制御する機械的又は電気的な機構を不要とし、回路の簡素化及びシステムの低価格化を実現することを目的とする。 Therefore, in order to solve the above problem, the present disclosure does not require a mechanical or electrical mechanism for controlling the direction of an irradiation beam while achieving both a high signal-to-noise ratio and high resolution in a synthetic aperture radar technology. It is an object of the present invention to simplify the circuit and reduce the cost of the system.
　前記課題を解決するために、アンテナの指向特性によって生じるビームチルトを積極的に利用する。つまり、チャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させる。そして、各アジマス位置において照射されるチャープパルスの全体区間のうち、観測対象位置に向けて照射されるチャープパルスの一部区間のみを、反射信号と参照信号との間の相関処理において考慮する。 解決 In order to solve the above problem, positively use the beam tilt caused by the directional characteristics of the antenna. That is, in irradiating the chirp pulse, the direction of the irradiation beam is changed in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristic without performing the mechanical and electronic pointing control. Then, of the entire section of the chirp pulse irradiated at each azimuth position, only a partial section of the chirp pulse irradiated toward the observation target position is considered in the correlation processing between the reflection signal and the reference signal.
　具体的には、本開示は、合成開口レーダのレンジ圧縮用のチャープパルスを生成するチャープパルス生成部と、前記チャープパルス生成部が生成したチャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させるアンテナ部と、ターゲットから反射された反射信号を受信する反射信号受信部と、を備えることを特徴とする合成開口レーダ装置である。 Specifically, the present disclosure relates to a chirp pulse generation unit that generates a chirp pulse for range compression of a synthetic aperture radar, and a mechanical and electronic pointing device for irradiating the chirp pulse generated by the chirp pulse generation unit. An antenna unit that changes the direction of the irradiation beam in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristic without performing control, a reflection signal receiving unit that receives a reflection signal reflected from the target, A synthetic aperture radar apparatus comprising:
　また、本開示は、合成開口レーダのレンジ圧縮用のチャープパルスを生成するチャープパルス生成部と、前記チャープパルス生成部が生成したチャープパルスを照射するにあたり、元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させるアンテナ部と、ターゲットから反射された反射信号を受信する反射信号受信部と、を備えることを特徴とする合成開口レーダ装置である。 Further, the present disclosure also provides a chirp pulse generation unit that generates a chirp pulse for range compression of a synthetic aperture radar, and irradiates the chirp pulse generated by the chirp pulse generation unit according to an inherent directional characteristic. A synthetic aperture radar device comprising: an antenna unit that changes a beam direction in an azimuth direction according to a frequency of an irradiation beam; and a reflected signal receiving unit that receives a reflected signal reflected from a target.
　また、本開示は、合成開口レーダのレンジ圧縮用のチャープパルスを生成するチャープパルス生成手順と、元来アンテナ部に備わっている指向特性に従って、前記アンテナ部が照射する前記チャープパルス生成手順で生成したチャープパルスの照射ビームの方向を、前記照射ビームの周波数に応じてアジマス方向に変化させる照射ビーム照射手順と、ターゲットから反射された反射信号を受信する反射信号受信手順と、を順に備えることを特徴とする合成開口レーダ観測方法である。 The present disclosure also provides a chirp pulse generation procedure for generating a chirp pulse for range compression of a synthetic aperture radar, and a chirp pulse generation procedure for irradiating the antenna section according to a directional characteristic originally provided in the antenna section. An irradiation beam irradiation procedure for changing the direction of the irradiation beam of the chirped pulse in the azimuth direction according to the frequency of the irradiation beam, and a reflection signal reception procedure for receiving a reflection signal reflected from the target, which are sequentially provided. This is a characteristic synthetic aperture radar observation method.
　これらの構成によれば、チャープパルスを照射するにあたり、アンテナの指向特性によって生じるビームチルトを積極的に利用するため、いずれの観測対象位置についても、観測可能なアジマス時間が長くなる。よって、高信号対雑音比を実現するために、アンテナの高利得化つまり開口長増大を実行しようとしても、合成開口によりアジマス分解能を低下させないことができる。また、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させるため、回路の簡素化及びシステムの低価格化を実現することができる。 According to these configurations, when irradiating the chirp pulse, the beam tilt generated by the directional characteristics of the antenna is positively used, so that the observable azimuth time becomes longer at any observation target position. Therefore, even if an attempt is made to increase the antenna gain, that is, to increase the aperture length in order to realize a high signal-to-noise ratio, the azimuth resolution can be prevented from being reduced by the synthetic aperture. In addition, since the direction of the irradiation beam is changed in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristics without performing the mechanical and electronic pointing control, the circuit is simplified and the system is inexpensive. Can be realized.
　また、本開示は、前記チャープパルス生成部が、アジマス位置ごとに中心周波数を制御してチャープパルスを生成することにより、前記アンテナ部が照射する照射ビームのアジマス方向がある観測領域を指向するようにし、スポットライトモードを用いて合成開口レーダ観測を行うことを特徴とする合成開口レーダ装置である。 In addition, according to the present disclosure, the chirp pulse generation unit controls the center frequency for each azimuth position to generate a chirp pulse, so that the azimuth direction of the irradiation beam irradiated by the antenna unit is directed to an observation area having a certain azimuth direction. And performing a synthetic aperture radar observation using a spotlight mode.
　この構成によれば、観測範囲が限られたスポットライトモードを用いるにあたり、回路の簡素化及びシステムの低価格化を実現することができる。 According to this configuration, when using the spotlight mode in which the observation range is limited, the simplification of the circuit and the cost reduction of the system can be realized.
　また、本開示は、前記チャープパルス生成部が、アジマス位置によらない形状を有するチャープパルスを生成することにより、照射ビームの方向をアジマス方向に変化させ、照射ビームの方向をアジマス方向に変化させないときと比べて、観測可能なアジマス時間が長くなるストリップモードを用いて合成開口レーダ観測を行うことを特徴とする合成開口レーダ装置である。 Further, the present disclosure is that the chirp pulse generation unit generates a chirp pulse having a shape independent of the azimuth position, thereby changing the direction of the irradiation beam in the azimuth direction and not changing the direction of the irradiation beam in the azimuth direction. A synthetic aperture radar apparatus characterized in that a synthetic aperture radar observation is performed using a strip mode in which the observable azimuth time is longer than in the past.
　この構成によれば、観測範囲が広くなるストリップモードを用いるにあたり、高アジマス分解能化、回路の簡素化及びシステムの低価格化を実現することができる。 According to this configuration, it is possible to realize high azimuth resolution, simplify the circuit, and reduce the cost of the system when using the strip mode in which the observation range is widened.
　また、本開示は、前記チャープパルス生成部が、アジマス位置によらない形状を有するとともに、前記アンテナ部が照射する照射ビームのアジマス方向のスクイントが生じるような中心周波数を有するチャープパルスを生成することにより、照射ビームの方向をアジマス方向に変化させ、照射ビームの方向をアジマス方向に変化させないときと比べて、観測可能なアジマス時間が長くなるスクイントモードを用いて合成開口レーダ観測を行うことを特徴とする合成開口レーダ装置である。 In addition, according to the present disclosure, the chirp pulse generation unit may generate a chirp pulse having a shape independent of an azimuth position and having a center frequency such that squint in an azimuth direction of an irradiation beam irradiated by the antenna unit occurs. It is now possible to perform synthetic aperture radar observation using the squint mode, in which the observable azimuth time is longer than when the irradiation beam direction is changed in the azimuth direction and the irradiation beam direction is not changed in the azimuth direction. It is a synthetic aperture radar device characterized by the following.
　この構成によれば、斜め前方又は斜め後方でのスクイントモードを用いるにあたり、高アジマス分解能化、回路の簡素化及びシステムの低価格化を実現することができる。 According to this configuration, it is possible to realize high azimuth resolution, simplification of the circuit, and low cost of the system when using the squint mode in the obliquely forward or obliquely rearward direction.
　また、本開示は、以上に記載の合成開口レーダ装置の前記反射信号受信部が受信した反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の相関処理を実行することを特徴とする合成開口レーダ信号処理装置である。 Further, the present disclosure is a reflection signal received by the reflection signal receiving unit of the synthetic aperture radar device described above, of the chirp pulse generated by the chirp pulse generation unit, is reflected from the observation target position for each azimuth position A synthetic aperture radar signal processing apparatus characterized by performing a correlation process between a reference signal that selects only a partial section expected to be used.
　また、本開示は、以上に記載の合成開口レーダ装置の前記反射信号受信部が受信した反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の相関処理、をコンピュータに実行させるための合成開口レーダ信号処理プログラムである。 Further, the present disclosure is a reflection signal received by the reflection signal receiving unit of the synthetic aperture radar device described above, of the chirp pulse generated by the chirp pulse generation unit, is reflected from the observation target position for each azimuth position This is a synthetic aperture radar signal processing program for causing a computer to execute a correlation process between a reference signal in which only a partial section expected to be selected is selected.
　これらの構成によれば、各アジマス位置において照射されるチャープパルスの全体区間のうち、観測対象位置に向けて照射されるチャープパルスの一部区間のみを、反射信号と参照信号との間の時間領域又は周波数領域の相関処理において考慮する。そして、ある観測対象位置から反射された反射信号について、本開示では従来技術より、受信可能なレンジ時間は短くなるものの、受信可能なアジマス時間は長くなるため、受信可能な総時間は減少しない。よって、高レンジ分解能化を実現するために、チャープパルスの広帯域化を実行しようとしても、ビームチルトにより信号対雑音比を低下させないことができる。 According to these configurations, of the entire section of the chirp pulse irradiated at each azimuth position, only a part of the chirp pulse irradiated toward the observation target position is determined by the time between the reflected signal and the reference signal. It is taken into account in the domain or frequency domain correlation processing. In the present disclosure, for the reflected signal reflected from a certain observation target position, the receivable range time is shorter than in the related art, but the receivable azimuth time is longer, so that the total receivable time does not decrease. Therefore, even if an attempt is made to increase the bandwidth of the chirped pulse in order to realize a higher range resolution, it is possible to prevent the signal-to-noise ratio from being reduced by the beam tilt.
　また、本開示は、前記観測対象位置から反射された反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに前記観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の時間領域における相関処理を実行することを特徴とする合成開口レーダ信号処理装置である。 Further, the present disclosure, the reflection signal reflected from the observation target position, of the chirp pulse generated by the chirp pulse generation unit, only a partial section expected to be reflected from the observation target position for each azimuth position And performing a correlation process in a time domain between the reference signal and the selected reference signal.
　また、本開示は、前記観測対象位置から反射された反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに前記観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の時間領域における相関処理、をコンピュータに実行させるための合成開口レーダ信号処理プログラムである。 Further, the present disclosure, the reflection signal reflected from the observation target position, of the chirp pulse generated by the chirp pulse generation unit, only a partial section expected to be reflected from the observation target position for each azimuth position Is a synthetic aperture radar signal processing program for causing a computer to execute a correlation process in a time domain between the selected reference signal and a reference signal.
　これらの構成によれば、各アジマス位置において照射されるチャープパルスの全体区間のうち、観測対象位置に向けて照射されるチャープパルスの一部区間のみを、反射信号と参照信号との間の時間領域の相関処理において考慮する。そして、ある観測対象位置から反射された反射信号について、本開示では従来技術より、受信可能なレンジ時間は短くなるものの、受信可能なアジマス時間は長くなるため、受信可能な総時間は減少しない。よって、高レンジ分解能化を実現するために、チャープパルスの広帯域化を実行しようとしても、ビームチルトにより信号対雑音比を低下させないことができる。また、計算時間は長いが画像精度は高くなる。 According to these configurations, of the entire section of the chirp pulse irradiated at each azimuth position, only a part of the chirp pulse irradiated toward the observation target position is determined by the time between the reflected signal and the reference signal. This is taken into account in the area correlation processing. In the present disclosure, for the reflected signal reflected from a certain observation target position, the receivable range time is shorter than in the related art, but the receivable azimuth time is longer, so that the total receivable time does not decrease. Therefore, even if an attempt is made to increase the bandwidth of the chirped pulse in order to realize a higher range resolution, it is possible to prevent the signal-to-noise ratio from being reduced by the beam tilt. Further, although the calculation time is long, the image accuracy is high.
　このように、本開示は、合成開口レーダ技術において、高信号対雑音比及び高分解能化を両立させつつ、照射ビームの方向を制御する機械的又は電気的な機構を不要とし、回路の簡素化及びシステムの低価格化を実現することができる。 As described above, the present disclosure eliminates the need for a mechanical or electrical mechanism for controlling the direction of an irradiation beam while achieving a high signal-to-noise ratio and high resolution in a synthetic aperture radar technology, and simplifies the circuit. In addition, the cost of the system can be reduced.
本開示のチャープパルス波形及びアンテナ指向性を示す図である。FIG. 4 is a diagram illustrating a chirped pulse waveform and antenna directivity according to the present disclosure. 従来技術のスポットライトモードの構成図を示す図である。FIG. 3 is a diagram illustrating a configuration diagram of a spotlight mode according to the related art. 本開示のストリップモードを示す図である。FIG. 3 is a diagram illustrating a strip mode of the present disclosure. 本開示のスクイントモードを示す図である。FIG. 3 is a diagram illustrating a score mode according to the present disclosure. 本開示の合成開口レーダシステムの構成を示す図である。1 is a diagram illustrating a configuration of a synthetic aperture radar system according to the present disclosure. 本開示の合成開口レーダシステムの処理を示す図である。FIG. 3 is a diagram illustrating processing of the synthetic aperture radar system according to the present disclosure. 本開示のアンテナ指向性の周波数特性を示す図である。FIG. 5 is a diagram illustrating frequency characteristics of antenna directivity according to the present disclosure. 本開示のアンテナ指向性の周波数特性を示す図である。FIG. 5 is a diagram illustrating frequency characteristics of antenna directivity according to the present disclosure. 本開示のチャープ周波数の時間変化を示す図である。FIG. 4 is a diagram illustrating a time change of a chirp frequency according to the present disclosure. 本開示のアンテナ指向性の時間変化を示す図である。FIG. 4 is a diagram illustrating a time change of the antenna directivity according to the present disclosure. 本開示のターゲットの方向及び距離の定義を示す図である。FIG. 3 is a diagram illustrating definitions of a direction and a distance of a target according to the present disclosure. 本開示の反射信号が存在するアジマス時間の説明図である。FIG. 4 is an explanatory diagram of an azimuth time during which a reflected signal of the present disclosure exists. 本開示のチャープパルスがターゲットに向けて照射されるレンジ時間の説明図である。FIG. 4 is an explanatory diagram of a range time in which a chirp pulse according to the present disclosure is irradiated toward a target. 本開示の反射信号及び参照信号を示す図である。FIG. 4 is a diagram illustrating a reflection signal and a reference signal according to the present disclosure. 本開示の点拡張関数対ターゲットからのレンジ方向距離を示す図である。FIG. 4 is a diagram illustrating a point extension function of the present disclosure versus a distance in a range direction from a target. 本開示の点拡張関数対ターゲットからのアジマス方向距離を示す図である。FIG. 4 is a diagram illustrating a point extension function of the present disclosure versus an azimuth distance from a target.
　添付の図面を参照して本開示の実施形態を説明する。以下に説明する実施形態は本開示の実施の例であり、本開示は以下の実施形態に制限されるものではない。 An embodiment of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of the present disclosure, and the present disclosure is not limited to the following embodiments.
（本開示の合成開口レーダシステムの基本原理）
　本開示のチャープパルス波形及びアンテナ指向性を図１に示す。本開示では、アンテナの指向特性によって生じるビームチルトを積極的に利用する。つまり、チャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させる。図１の上段では、チャープパルスは、レンジ時間０≦τ≦τ０にわたり、最小周波数ｆ０－ＢＷ／２から中心周波数ｆ０を経て最大周波数ｆ０＋ＢＷ／２へと周波数を掃引する。 (Basic principle of the synthetic aperture radar system of the present disclosure)
FIG. 1 shows a chirp pulse waveform and antenna directivity according to the present disclosure. In the present disclosure, beam tilt caused by the directional characteristics of the antenna is positively used. That is, in irradiating the chirp pulse, the direction of the irradiation beam is changed in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristic without performing the mechanical and electronic pointing control. In the upper part of FIG. 1, the chirp pulse sweeps the frequency from the minimum frequency f 0 -B W / 2 to the maximum frequency f 0 + B W / 2 via the center frequency f 0 over the range time 0 ≦ τ ≦ τ 0. .
　図１の中段及び図１の下段では、アンテナ部Ａとして、アレイアンテナ及びスロットアンテナを適用する。アンテナ部Ａの各アンテナ素子は、アジマス方向ｘに配列される。 In the middle part of FIG. 1 and the lower part of FIG. 1, an array antenna and a slot antenna are applied as the antenna unit A. Each antenna element of the antenna section A is arranged in the azimuth direction x.
　チャープパルスが、中心周波数ｆ０を掃引するときには、アンテナ部Ａの各アンテナ素子は、同相で励振され、アンテナ部Ａの照射ビームは、正面方向ｙを指向する。チャープパルスが、最小周波数ｆ０－ＢＷ／２を掃引するときには、アンテナ部Ａの各アンテナ素子は、同相で励振されず、アンテナ部Ａの照射ビームは、正面方向ｙからずれた方向φｍｉｎ＜０を指向する。チャープパルスが、最大周波数ｆ０＋ＢＷ／２を掃引するときには、アンテナ部Ａの各アンテナ素子は、同相で励振されず、アンテナ部Ａの照射ビームは、正面方向ｙからずれた方向φｍａｘ＞０を指向する。このように、チャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向φを照射ビームの周波数ｆに応じてアジマス方向ｘに変化させる。 When the chirp pulse sweeps the center frequency f 0 , each antenna element of the antenna section A is excited in phase, and the irradiation beam of the antenna section A is directed in the front direction y. When the chirp pulse sweeps the minimum frequency f 0 -B W / 2, each antenna element of the antenna section A is not excited in phase, and the irradiation beam of the antenna section A is shifted in the direction φ min shifted from the front direction y. <0. When the chirp pulse sweeps the maximum frequency f 0 + B W / 2, the respective antenna elements of the antenna section A are not excited in phase, and the irradiation beam of the antenna section A has a direction φmax> 0 shifted from the front direction y. To be oriented. As described above, in irradiating the chirp pulse, the direction φ of the irradiation beam is changed in the azimuth direction x according to the frequency f of the irradiation beam according to the inherent directional characteristic without performing the mechanical and electronic pointing control. Let it.
　従来技術のスポットライトモードの構成図を図２に示す。上段では、アジマス位置ｘによらない形状を有するチャープパルスを生成したうえで、アンテナ駆動部１３（回転接手等で接続）によって機械的に指向制御することにより、アンテナ部Ａが照射する照射ビームのアジマス方向ｘがある観測領域を指向するようにし、スポットライトモードを用いて合成開口レーダ観測を行う。下段では、アジマス位置ｘによらない形状を有するチャープパルスを生成したうえで、アンテナ部Ａの移相器及び分配器によって電子的に指向制御することにより、アンテナ部Ａが照射する照射ビームのアジマス方向ｘがある観測領域を指向するようにし、スポットライトモードを用いて合成開口レーダ観測を行う。 FIG. 2 shows a configuration diagram of the spotlight mode of the prior art. In the upper stage, a chirp pulse having a shape not depending on the azimuth position x is generated, and the antenna control unit 13 (connected by a rotary joint or the like) mechanically directs the beam to thereby control the irradiation beam emitted by the antenna unit A. The azimuth direction x is directed to a certain observation area, and the synthetic aperture radar observation is performed using the spotlight mode. In the lower stage, a chirp pulse having a shape not depending on the azimuth position x is generated, and the azimuth of the irradiation beam irradiated by the antenna unit A is controlled electronically by the phase shifter and the distributor of the antenna unit A. The synthetic aperture radar observation is performed using the spotlight mode so that the direction x is directed to a certain observation area.
　本開示のスポットライトモードの構成図を図５に示す。アジマス位置ｘごとに中心周波数を制御してチャープパルスを生成することにより、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、アンテナ部Ａが照射する照射ビームのアジマス方向ｘがある観測領域を指向するようにし、スポットライトモードを用いて合成開口レーダ観測を行う。なお、図５はストリップ及びスクイントの両モードにも適用可能である。 FIG. 5 shows a configuration diagram of the spotlight mode of the present disclosure. By generating a chirp pulse by controlling the center frequency for each azimuth position x, the azimuth direction of the irradiation beam radiated by the antenna unit A according to the original directional characteristics without performing mechanical and electronic directional control. x is directed to a certain observation area, and the synthetic aperture radar observation is performed using the spotlight mode. FIG. 5 is also applicable to both the strip mode and the squint mode.
　このように、観測範囲が限られたスポットライトモードを用いるにあたり、回路の簡素化及びシステムの低価格化を実現することができる。 Thus, in using the spotlight mode in which the observation range is limited, the simplification of the circuit and the cost reduction of the system can be realized.
　本開示のストリップモードを図３に示す。アジマス位置ｘによらない形状を有するチャープパルスを生成することにより、照射ビームの方向をアジマス方向ｘに変化させ、照射ビームの方向をアジマス方向ｘに変化させないときと比べて、観測可能なアジマス時間が長くなるストリップモードを用いて合成開口レーダ観測を行う。 FIG. 3 shows the strip mode of the present disclosure. By generating a chirp pulse having a shape independent of the azimuth position x, the direction of the irradiation beam is changed in the azimuth direction x, and the observable azimuth time is shorter than when the direction of the irradiation beam is not changed in the azimuth direction x. Synthetic aperture radar observation is performed using the strip mode in which is longer.
　図３の上段では、従来技術のビームチルトがないときのストリップモードを示す。まず、合成開口レーダシステムＳが、アジマス方向位置ｘｓｔ、ｉに位置するとともに、チャープパルスが、周波数ｆ０－ＢＷ／２～ｆ０＋ＢＷ／２を掃引するときには、ターゲットＴは、捕捉され始めている。次に、合成開口レーダシステムＳが、アジマス方向位置ｘｓｔ、ｆに位置するとともに、チャープパルスが、周波数ｆ０－ＢＷ／２～ｆ０＋ＢＷ／２を掃引するときには、ターゲットＴは、捕捉範囲され終わっている。ここで、アジマス方向範囲ｘｓｔ、ｉ～ｘｓｔ、ｆは、後述の本開示の場合より短いため、観測可能なアジマス時間は、後述の本開示の場合より短く、アジマス分解能は、後述の本開示の場合より低い。 The upper part of FIG. 3 shows a strip mode when there is no beam tilt according to the related art. First, when the synthetic aperture radar system S is located at the azimuth direction position x st, i and the chirp pulse sweeps the frequency f 0 −B W / 2 to f 0 + B W / 2, the target T is captured. Is starting to be. Next, when the synthetic aperture radar system S is located at the azimuth direction position x st, f and the chirp pulse sweeps the frequency f 0 −B W / 2 to f 0 + B W / 2, the target T is: The capture range is over. Here, since the azimuth direction range x st, i to x st, f is shorter than in the case of the present disclosure described later, the observable azimuth time is shorter than in the case of the present disclosure described later, and the azimuth resolution is the same as that of the present disclosure described later. It is lower than the case of disclosure.
　図３の下段では、本開示のビームチルトがあるときのストリップモードを示す。まず、合成開口レーダシステムＳが、アジマス方向位置ｘ’ｓｔ、ｉに位置するとともに、チャープパルスが、周波数ｆ０－ＢＷ／２を掃引するときには、ターゲットＴは、捕捉され始めている。次に、合成開口レーダシステムＳが、アジマス方向位置ｘ’ｓｔ、ｆに位置するとともに、チャープパルスが、周波数ｆ０＋ＢＷ／２を掃引するときには、ターゲットＴは、捕捉範囲され終わっている。ここで、アジマス方向位置ｘ’ｓｔ、ｉは、アジマス方向位置ｘｓｔ、ｉより後方にあり、アジマス方向位置ｘ’ｓｔ、ｆは、アジマス方向位置ｘｓｔ、ｆより前方にある。よって、アジマス方向範囲ｘ’ｓｔ、ｉ～ｘ’ｓｔ、ｆは、従来技術より長いため、観測可能なアジマス時間は、従来技術より長く、アジマス分解能は、従来技術より高い。 The lower part of FIG. 3 shows a strip mode when there is a beam tilt according to the present disclosure. First, when the synthetic aperture radar system S is located at the azimuth direction position x ' st, i and the chirp pulse sweeps the frequency f 0 -B W / 2, the target T has begun to be captured. Next, a synthetic aperture radar system S, the azimuth direction position x 'st, with located in f, chirped pulses, when sweeping the frequency f 0 + B W / 2, the target T has finished the capture range. Here, the azimuth direction position x'st, i is behind the azimuth direction position xst, i , and the azimuth direction position x'st, f is ahead of the azimuth direction position xst, f . Therefore, since the azimuth direction range x ′ st, i to x ′ st, f is longer than that of the related art, the observable azimuth time is longer than that of the related art, and the azimuth resolution is higher than that of the related art.
　このように、観測範囲が広くなるストリップモードを用いるにあたり、高アジマス分解能化、回路の簡素化及びシステムの低価格化を実現することができる。 Thus, when using the strip mode in which the observation range is widened, it is possible to realize a high azimuth resolution, a simple circuit, and a low cost system.
　本開示のスクイントモードを図４に示す。アジマス位置ｘによらない形状を有するとともに、アンテナ部Ａが照射する照射ビームのアジマス方向ｘのスクイントが生じるような中心周波数を有するチャープパルスを生成することにより、照射ビームの方向をアジマス方向ｘに変化させ、照射ビームの方向をアジマス方向ｘに変化させないときと比べて、観測可能なアジマス時間が長くなるスクイントモードを用いて合成開口レーダ観測を行う。 ス ク FIG. 4 shows the scint mode of the present disclosure. By generating a chirp pulse having a shape independent of the azimuth position x and having a center frequency such that a squint in the azimuth direction x of the irradiation beam irradiated by the antenna unit A is generated, the direction of the irradiation beam is changed in the azimuth direction x. The synthetic aperture radar observation is performed using a squint mode in which the observable azimuth time is longer than when the irradiation beam direction is not changed in the azimuth direction x.
　ここで、斜め前方でのスクイントモードを用いるときには、中心周波数を図１、３でのｆ０から図４でのｆ０’（ただし、図４の場合では、ｆ０’＜ｆ０）へとシフトさせる。一方で、斜め後方でのスクイントモードを用いるときには、中心周波数を図１、３でのｆ０から図４でのｆ０’（ただし、図４の場合では、ｆ０’＞ｆ０）へとシフトさせる。 Here, when the obliquely forward squint mode is used, the center frequency is changed from f 0 in FIGS. 1 and 3 to f 0 ′ in FIG. 4 (however, in the case of FIG. 4, f 0 ′ <f 0 ). And shift. On the other hand, when using the squint mode obliquely rearward, the center frequency is changed from f 0 in FIGS. 1 and 3 to f 0 ′ in FIG. 4 (however, in FIG. 4, f 0 ′> f 0 ). And shift.
　図４の上段では、従来技術のビームチルトがないときのスクイントモードを示す。まず、合成開口レーダシステムＳが、アジマス方向位置ｘｓｑ、ｉに位置するとともに、チャープパルスが、周波数ｆ０’－ＢＷ／２～ｆ０’＋ＢＷ／２を掃引するときには、ターゲットＴは、捕捉され始めている。次に、合成開口レーダシステムＳが、アジマス方向位置ｘｓｑ、ｆに位置するとともに、チャープパルスが、周波数ｆ０’－ＢＷ／２～ｆ０’＋ＢＷ／２を掃引するときには、ターゲットＴは、捕捉範囲され終わっている。ここで、アジマス方向範囲ｘｓｑ、ｉ～ｘｓｑ、ｆは、後述の本開示の場合より短いため、観測可能なアジマス時間は、後述の本開示の場合より短く、アジマス分解能は、後述の本開示の場合より低い。 The upper part of FIG. 4 shows a squint mode when there is no beam tilt according to the related art. First, when the synthetic aperture radar system S is located at the position x sq, i in the azimuth direction and the chirp pulse sweeps the frequencies f 0 ′ −B W / 2 to f 0 ′ + B W / 2, the target T is , Has begun to be caught. Next, when the synthetic aperture radar system S is located at the azimuth position x sq, f and the chirp pulse sweeps the frequency f 0 ′ −B W / 2 to f 0 ′ + B W / 2, the target T Has been captured. Here, the azimuth direction range x sq, i to x sq, f is shorter than in the case of the present disclosure described later, so that the observable azimuth time is shorter than in the case of the present disclosure described later, and the azimuth resolution is defined in the following description. It is lower than the case of disclosure.
　図４の下段では、本開示のビームチルトがあるときのスクイントモードを示す。まず、合成開口レーダシステムＳが、アジマス方向位置ｘ’ｓｑ、ｉに位置するとともに、チャープパルスが、周波数ｆ０’－ＢＷ／２を掃引するときには、ターゲットＴは、捕捉され始めている。次に、合成開口レーダシステムＳが、アジマス方向位置ｘ’ｓｑ、ｆに位置するとともに、チャープパルスが、周波数ｆ０’＋ＢＷ／２を掃引するときには、ターゲットＴは、捕捉範囲され終わっている。ここで、アジマス方向位置ｘ’ｓｑ、ｉは、アジマス方向位置ｘｓｑ、ｉより後方にあり、アジマス方向位置ｘ’ｓｑ、ｆは、アジマス方向位置ｘｓｑ、ｆより前方にある。よって、アジマス方向範囲ｘ’ｓｑ、ｉ～ｘ’ｓｑ、ｆは、従来技術より長いため、観測可能なアジマス時間は、従来技術より長く、アジマス分解能は、従来技術より高い。 The lower part of FIG. 4 shows a squint mode when there is a beam tilt according to the present disclosure. First, when the synthetic aperture radar system S is located at the azimuth position x ′ sq, i and the chirp pulse sweeps the frequency f 0 ′ −B W / 2, the target T has begun to be captured. Next, when the synthetic aperture radar system S is located at the azimuth position x ′ sq, f and the chirp pulse sweeps the frequency f 0 ′ + B W / 2, the target T has been captured. . Here, the azimuth direction position x ' sq, i is behind the azimuth direction position x sq, i , and the azimuth direction position x' sq, f is ahead of the azimuth direction position x sq, f . Therefore, since the azimuth direction range x ′ sq, i to x ′ sq, f is longer than that of the related art, the observable azimuth time is longer than that of the related art, and the azimuth resolution is higher than that of the related art.
　このように、斜め前方又は斜め後方でのスクイントモードを用いるにあたり、高アジマス分解能化、回路の簡素化及びシステムの低価格化を実現することができる。 As described above, when the obliquely forward or obliquely backward squint mode is used, a high azimuth resolution, a simplified circuit, and a low-cost system can be realized.
（本開示の合成開口レーダシステムの構成及び処理）
　本開示の合成開口レーダシステムの構成を図５に示す。本開示の合成開口レーダシステムの処理を図６に示す。合成開口レーダシステムＳは、合成開口レーダ装置１及び合成開口レーダ信号処理装置２から構成される。合成開口レーダ装置１は、チャープパルス生成部１１、アンテナ部Ａ及び反射信号受信部１２から構成され、人工衛星又は航空機等に搭載される。合成開口レーダ信号処理装置２は、相関処理実行部２１から構成され、人工衛星、航空機又は地上設備等に搭載され、図６の下欄に示した合成開口レーダ信号処理プログラムをコンピュータにインストールすることにより実現される。 (Configuration and processing of the synthetic aperture radar system of the present disclosure)
FIG. 5 shows the configuration of the synthetic aperture radar system according to the present disclosure. FIG. 6 shows the processing of the synthetic aperture radar system of the present disclosure. The synthetic aperture radar system S includes a synthetic aperture radar device 1 and a synthetic aperture radar signal processing device 2. The synthetic aperture radar device 1 includes a chirp pulse generating unit 11, an antenna unit A, and a reflected signal receiving unit 12, and is mounted on an artificial satellite or an aircraft. The synthetic aperture radar signal processing device 2 includes a correlation processing execution unit 21, is mounted on an artificial satellite, an aircraft, a ground facility, or the like, and installs a synthetic aperture radar signal processing program shown in the lower section of FIG. 6 in a computer. Is realized by:
　まず、合成開口レーダ装置１は、アンテナの指向特性によって生じるビームチルトを積極的に利用する。つまり、合成開口レーダ装置１は、チャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向φを照射ビームの周波数ｆに応じてアジマス方向ｘに変化させる。 First, the synthetic aperture radar device 1 actively uses the beam tilt caused by the directional characteristics of the antenna. In other words, when irradiating the chirp pulse, the synthetic aperture radar apparatus 1 does not perform the mechanical and electronic pointing control but changes the direction φ of the irradiation beam according to the frequency f of the irradiation beam according to the inherent directional characteristics. It is changed in the azimuth direction x.
　チャープパルス生成部１１は、合成開口レーダのレンジ圧縮用のチャープパルスを生成する（ステップＳ１）。アンテナ部Ａは、合成開口レーダのレンジ圧縮用のチャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向φを照射ビームの周波数ｆに応じてアジマス方向ｘに変化させる（ステップＳ２）。反射信号受信部１２は、ターゲットＴから反射された反射信号をアンテナ部Ａにより受信する（ステップＳ３）。図７～１０を用いて、合成開口レーダ装置１について説明する。図７～１０は、ストリップモードについて適用されるが、中心周波数を変更すれば、スポットライト及びスクイントの両モードについて適用可能である。 The chirp pulse generation unit 11 generates a chirp pulse for range compression of the synthetic aperture radar (step S1). When irradiating a chirp pulse for range compression of the synthetic aperture radar, the antenna unit A does not perform mechanical and electronic pointing control but changes the direction of the irradiation beam φ according to the inherent directional characteristics. It is changed in the azimuth direction x according to f (step S2). The reflected signal receiving unit 12 receives the reflected signal reflected from the target T by the antenna unit A (Step S3). The synthetic aperture radar device 1 will be described with reference to FIGS. 7 to 10 are applied to the strip mode, but can be applied to both the spotlight and the squint modes by changing the center frequency.
　本開示のアンテナ指向性の周波数特性を図７、８に示す。照射ビームの方向φは、照射ビームの周波数ｆに対して、数式１のように表される。ただし、ａ＞０である。なお、ａ＜０であってもよく、アンテナ指向性の周波数特性は、必ずしも原点（ｆ－ｆ０＝０、φ＝０）を通らなくてもよく、必ずしも直線的な周波数特性でなくてもよい。
Figure JPOXMLDOC01-appb-M000001
 7 and 8 show frequency characteristics of the antenna directivity of the present disclosure. The direction φ of the irradiation beam is expressed by Expression 1 with respect to the frequency f of the irradiation beam. However, a> 0. Note that a <0 may be satisfied, and the frequency characteristics of the antenna directivity do not necessarily have to pass through the origin (ff- 0 = 0, φ = 0), and need not necessarily be linear frequency characteristics. Good.
Figure JPOXMLDOC01-appb-M000001
　チャープパルスが、周波数ｆ０－ＢＷ／２～ｆ０を掃引するときには、アンテナ部Ａの照射ビームは、正面方向ｙからずれた方向φ＜０を指向する。チャープパルスが、周波数ｆ０～ｆ０＋ＢＷ／２を掃引するときには、アンテナ部Ａの照射ビームは、正面方向ｙからずれた方向φ＞０を指向する。アンテナ部Ａの照射ビーム半幅は、ηであるとし、アンテナ部Ａの照射ビーム強度は、アンテナ部Ａの照射ビーム幅内で一様であるとする。なお、アンテナ部Ａの照射ビーム強度は、簡単のために、アンテナ部Ａの照射ビーム幅内で一様であるとしているが、実際のように、アンテナ部Ａの照射ビーム幅内で一様でないとしてもよい。 When the chirp pulse sweeps the frequency f 0 −B W / 2 to f 0 , the irradiation beam of the antenna unit A is directed in the direction φ <0 shifted from the front direction y. When the chirp pulse sweeps the frequency f 0 to f 0 + B W / 2, the irradiation beam of the antenna unit A is directed in the direction φ> 0 shifted from the front direction y. It is assumed that the irradiation beam half width of the antenna unit A is η, and that the irradiation beam intensity of the antenna unit A is uniform within the irradiation beam width of the antenna unit A. Although the irradiation beam intensity of the antenna unit A is assumed to be uniform within the irradiation beam width of the antenna unit A for simplicity, it is not uniform within the irradiation beam width of the antenna unit A as is practical. It may be.
　本開示のチャープ周波数の時間変化を図９に示す。チャープパルスの周波数ｆは、レンジ時間τに対して、数式２のように表される。なお、チャープ周波数の時間変化は、右肩上がりでもよく右肩下がりでもよく、必ずしも直線的な時間変化でなくてもよい。
Figure JPOXMLDOC01-appb-M000002
 FIG. 9 shows a time change of the chirp frequency according to the present disclosure. The frequency f of the chirp pulse is expressed as shown in Expression 2 with respect to the range time τ. Note that the time change of the chirp frequency may be rising to the right or falling to the right, and may not necessarily be a linear time change.
Figure JPOXMLDOC01-appb-M000002
　本開示のアンテナ指向性の時間変化を図１０に示す。照射ビームの方向φは、レンジ時間τに対して、数式３のように表される。なお、アンテナ指向性の時間変化は、右肩上がりでもよく右肩下がりでもよく、必ずしも直線的な時間変化でなくてもよい。
Figure JPOXMLDOC01-appb-M000003
 FIG. 10 shows a time change of the antenna directivity according to the present disclosure. The direction φ of the irradiation beam is expressed by Expression 3 with respect to the range time τ. It should be noted that the time change of the antenna directivity may be rising to the right or falling to the right, and is not necessarily a linear time change.
Figure JPOXMLDOC01-appb-M000003
　次に、合成開口レーダ信号処理装置２は、各アジマス時間ｔにおいて照射されるチャープパルスの全体区間のうち、観測対象位置に向けて照射されるチャープパルスの一部区間のみを、反射信号と参照信号との間の相関処理において考慮する。 Next, the synthetic aperture radar signal processing device 2 refers to only a partial section of the chirp pulse irradiated toward the observation target position among the entire section of the chirp pulse irradiated at each azimuth time t as a reflected signal. It is taken into account in the correlation processing between the signals.
　相関処理実行部２１は、反射信号と参照信号との間の相関処理を実行する（ステップＳ１１）。図１１～１４を用いて、合成開口レーダ信号処理装置２について説明する。図１１～１４は、ストリップモードについて適用されるが、中心周波数を変更すれば、スポットライト及びスクイントの両モードについて適用可能である。 The correlation processing execution unit 21 performs a correlation process between the reflection signal and the reference signal (Step S11). The synthetic aperture radar signal processing device 2 will be described with reference to FIGS. 11 to 14 are applied to the strip mode, but can be applied to both the spotlight and the squint modes by changing the center frequency.
　具体的には、相関処理実行部２１は、反射信号受信部１２が受信した反射信号と、チャープパルス生成部１１が生成したチャープパルスのうち、アジマス位置ｘごとに観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の相関処理を実行する。 Specifically, the correlation processing execution unit 21 expects that the reflection signal received by the reflection signal reception unit 12 and the chirp pulse generated by the chirp pulse generation unit 11 are reflected from the observation target position for each azimuth position x. And a reference signal for which only a partial section is selected.
　本実施形態では、相関処理実行部２１は、観測対象位置から反射された反射信号と、チャープパルス生成部１１が生成したチャープパルスのうち、アジマス位置ｘごとに観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の時間領域における相関処理を実行する。つまり、本実施形態では、相関処理実行部２１が、反射信号と参照信号との間の時間領域の相関処理を実行することにより、計算時間は長いが画像精度は高くなる。ここで、変形例として、相関処理実行部２１が、反射信号と参照信号との間の周波数領域の相関処理を実行することにより、計算時間を大幅に短縮してもよい。 In the present embodiment, the correlation processing execution unit 21 is expected to reflect the reflection signal reflected from the observation target position and the chirp pulse generated by the chirp pulse generation unit 11 from the observation target position for each azimuth position x. Then, a correlation process in a time domain between the reference signal and the selected reference signal is performed. That is, in the present embodiment, the correlation processing execution unit 21 executes the correlation processing in the time domain between the reflected signal and the reference signal, so that the calculation time is long but the image accuracy is high. Here, as a modified example, the correlation processing execution unit 21 may execute the correlation processing in the frequency domain between the reflected signal and the reference signal, thereby significantly reducing the calculation time.
　本開示のターゲットの方向及び距離の定義を図１１に示す。合成開口レーダシステムＳの位置を（ｘ（ｔ）、０）とし、ターゲットＴの位置を（Ｘ、Ｙ）とする。合成開口レーダシステムＳのアジマス方向位置ｘ（ｔ）、合成開口レーダシステムＳから見たターゲットＴの方向θ（ｔ）及び合成開口レーダシステムＳからターゲットＴまでの距離Ｒ（ｔ）は、数式４のように表される。ただし、ｖは、合成開口レーダシステムＳの速度である。
Figure JPOXMLDOC01-appb-M000004
 FIG. 11 shows the definitions of the direction and distance of the target of the present disclosure. The position of the synthetic aperture radar system S is (x (t), 0), and the position of the target T is (X, Y). The position x (t) in the azimuth direction of the synthetic aperture radar system S, the direction θ (t) of the target T viewed from the synthetic aperture radar system S, and the distance R (t) from the synthetic aperture radar system S to the target T are expressed by the following equation (4). It is represented as Here, v is the speed of the synthetic aperture radar system S.
Figure JPOXMLDOC01-appb-M000004
　本開示の反射信号が存在するアジマス時間の説明図を図１２に示す。各アジマス時間ｔで観測可能なターゲットＴの存在範囲は、数式５のように表される。
Figure JPOXMLDOC01-appb-M000005
 つまり、合成開口レーダシステムＳから見たターゲットＴの方向θ（ｔ）が、以下の条件を満たせばよい：（１）アンテナ部Ａの照射ビームが方向φｍｉｎ＝－ａＢＷ／２を指向するときの、アンテナ部Ａの照射ビームの外縁の方向φ＝φｍｉｎ－η＝－ａＢＷ／２－ηと比べて、方向θ（ｔ）がレンジ方向ｙ寄りであること、（２）アンテナ部Ａの照射ビームが方向φｍａｘ＝＋ａＢＷ／２を指向するときの、アンテナ部Ａの照射ビームの外縁の方向φ＝φｍａｘ＋η＝＋ａＢＷ／２＋ηと比べて、方向θ（ｔ）がレンジ方向ｙ寄りであること。 FIG. 12 is an explanatory diagram of the azimuth time at which the reflected signal of the present disclosure exists. The existence range of the target T that can be observed at each azimuth time t is represented by Expression 5.
Figure JPOXMLDOC01-appb-M000005
 That is, the direction θ (t) of the target T viewed from the synthetic aperture radar system S only needs to satisfy the following conditions: (1) The irradiation beam of the antenna unit A is directed in the direction φ min = −aB W / 2. The direction θ (t) is closer to the range direction y than the direction φ = φ min −η = −aB W / 2−η of the outer edge of the irradiation beam of the antenna unit A at the time. When the irradiation beam of A is directed in the direction φmax = + aB W / 2, the direction θ (t) is closer to the range direction y than the direction φ = φmax + η = + aB W / 2 + η of the outer edge of the irradiation beam of the antenna unit A. That.
　数式５に数式４の第２式を代入すると、ターゲットＴからの反射信号が存在するアジマス時間ｔは、数式６のように表される。ここで、数式６の左辺は、図１４のアジマス時間ｔｉに対応し、数式６の右辺は、図１４のアジマス時間ｔｆに対応する。
Figure JPOXMLDOC01-appb-M000006
 When the second expression of Expression 4 is substituted into Expression 5, the azimuth time t during which the reflected signal from the target T exists is expressed as Expression 6. Here, the left side of Equation 6 corresponds to the azimuth time t i in FIG. 14, and the right side of Equation 6 corresponds to the azimuth time t f in FIG.
Figure JPOXMLDOC01-appb-M000006
　このように、チャープパルスを照射するにあたり、アンテナの指向特性によって生じるビームチルトを積極的に利用するため、いずれの観測対象位置についても、観測可能なアジマス時間ｔが長くなる。よって、高信号対雑音比を実現するために、アンテナの高利得化つまり開口長増大を実行しようとしても、合成開口によりアジマス分解能を低下させないことができる。また、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向φを照射ビームの周波数ｆに応じてアジマス方向ｘに変化させるため、回路の簡素化及びシステムの低価格化を実現することができる。 In this way, in irradiating the chirp pulse, the beam tilt generated by the directional characteristics of the antenna is positively used, so that the observable azimuth time t becomes longer at any observation target position. Therefore, even if an attempt is made to increase the antenna gain, that is, to increase the aperture length in order to realize a high signal-to-noise ratio, the azimuth resolution can be prevented from being reduced by the synthetic aperture. Further, in order to change the direction φ of the irradiation beam in the azimuth direction x according to the frequency f of the irradiation beam according to the inherent directivity characteristic without performing the mechanical and electronic pointing control, the circuit is simplified and the system is changed. Can be realized at a low price.
　本開示のチャープパルスがターゲットＴに向けて照射されるレンジ時間の説明図を図１３に示す。各アジマス時間ｔでターゲットＴを観測可能なレンジ時間τは、数式７のように表される。
Figure JPOXMLDOC01-appb-M000007
 つまり、合成開口レーダシステムＳから見たターゲットＴの方向θ（ｔ）が、以下の条件を満たせばよい：（１）アンテナ部Ａの照射ビームが周波数ｆのチャープの過程でターゲットＴに向き始めるときの、アンテナ部Ａの照射ビームの外縁の方向φ（τｉ（ｔ））＋ηと比べて、方向θ（ｔ）が同じである、又は、方向θ（ｔ）がφ（０）－ηとφ（０）＋ηとの間にあること、（２）アンテナ部Ａの照射ビームが周波数ｆのチャープの過程でターゲットＴに向き終わるときの、アンテナ部Ａの照射ビームの外縁の方向φ（τｆ（ｔ））－ηと比べて、方向θ（ｔ）が同じである、又は、方向θ（ｔ）がφ（τ０）－ηとφ（τ０）＋ηとの間にあること。 FIG. 13 is an explanatory diagram of a range time in which the chirp pulse according to the present disclosure is irradiated toward the target T. The range time τ during which the target T can be observed at each azimuth time t is represented by Expression 7.
Figure JPOXMLDOC01-appb-M000007
 That is, the direction θ (t) of the target T viewed from the synthetic aperture radar system S only needs to satisfy the following condition: (1) The irradiation beam of the antenna unit A starts to turn toward the target T in the course of the chirp at the frequency f. The direction θ (t) is the same as the direction φ (τ i (t)) + η of the outer edge of the irradiation beam of the antenna unit A, or the direction θ (t) is φ (0) −η (2) the direction of the outer edge of the irradiation beam of the antenna section A when the irradiation beam of the antenna section A ends toward the target T in the course of the chirp of the frequency f (φ (0) + η). the direction θ (t) is the same as compared to τ f (t)) − η, or the direction θ (t) is between φ (τ 0 ) −η and φ (τ 0 ) + η .
　数式７に数式３を代入すると、ターゲットＴからの反射信号が存在するレンジ時間τは、数式８のように表される。ここで、数式８の左辺は、図１３、１４のレンジ時間τｉ（ｔ）に対応し、数式８の右辺は、図１３、１４のレンジ時間τｆ（ｔ）に対応する。
Figure JPOXMLDOC01-appb-M000008
 When Expression 3 is substituted into Expression 7, the range time τ during which the reflected signal from the target T exists is expressed as Expression 8. Here, the left side of Equation 8 corresponds to the range time τ i (t) in FIGS. 13 and 14, and the right side of Equation 8 corresponds to the range time τ f (t) in FIGS.
Figure JPOXMLDOC01-appb-M000008
　本開示の反射信号及び参照信号を図１４に示す。ターゲットＴから反射された反射信号Ｆ（ｔ、τ）は、数式９のように表される。そして、反射信号Ｆ（ｔ、τ）との相関処理を実行される参照信号は、反射信号Ｆ（ｔ、τ）の下記理論式に基づいて定められる。
Figure JPOXMLDOC01-appb-M000009
 FIG. 14 shows the reflection signal and the reference signal of the present disclosure. The reflection signal F (t, τ) reflected from the target T is represented by Expression 9. The reference signal to be subjected to the correlation processing with the reflected signal F (t, τ) is determined based on the following theoretical formula of the reflected signal F (t, τ).
Figure JPOXMLDOC01-appb-M000009
　ただし、反射信号Ｆ（ｔ、τ）のアジマス時間ｔの値域は、数式６に基づいて、数式１０のように表される。そして、反射信号Ｆ（ｔ、τ）のレンジ時間τの値域は、数式８及び電磁波伝搬の遅延時間に基づいて、数式１１のように表される。
Figure JPOXMLDOC01-appb-M000010
Figure JPOXMLDOC01-appb-M000011
 ここで、ビームチルトがない場合とビームチルトがある場合とを比較する。 However, the value range of the azimuth time t of the reflection signal F (t, τ) is expressed by Expression 10 based on Expression 6. Then, the value range of the range time τ of the reflected signal F (t, τ) is expressed by Expression 11 based on Expression 8 and the delay time of electromagnetic wave propagation.
Figure JPOXMLDOC01-appb-M000010
Figure JPOXMLDOC01-appb-M000011
 Here, the case where there is no beam tilt and the case where there is a beam tilt will be compared.
　まず、ビームチルトがない場合では、各アジマス時間ｔにおいて照射されるチャープパルスの全体区間のうち、ターゲットＴに向けて照射されるチャープパルスの全体区間にわたり、反射信号と参照信号との間の相関処理において考慮する。 First, when there is no beam tilt, the correlation between the reflected signal and the reference signal over the entire section of the chirp pulse irradiated toward the target T among the entire section of the chirp pulse irradiated at each azimuth time t. Take into account in processing.
　具体的には、アンテナ部Ａの照射ビームがターゲットＴに向き始める／終わるアジマス時間ｔｉ／ｔｆでは、レンジ時間範囲τｉｆ≦τ≦τｉｆ＋τ０（ただし、τｉｆは、電磁波伝搬の遅延時間である。）のうち、全てのレンジ時間範囲τｉｆ≦τ≦τｉｆ＋τ０にわたり、反射信号と参照信号との間の相関処理において考慮する。そして、合成開口レーダシステムＳがターゲットＴに最も近づくアジマス時間ｔｃでは、レンジ時間範囲τｃ≦τ≦τｃ＋τ０（ただし、τｃは、電磁波伝搬の遅延時間である。）のうち、全てのレンジ時間範囲τｃ≦τ≦τｃ＋τ０にわたり、反射信号と参照信号との間の相関処理において考慮する。 Specifically, in the azimuth time t i / t f at which the irradiation beam of the antenna unit A starts and ends at the target T, the range time range τ if ≦ τ ≦ τ if + τ 0 (where τ if is the electromagnetic wave propagation Delay time) over the entire range time range τ if ≦ τ ≦ τ if + τ 0 and is considered in the correlation process between the reflected signal and the reference signal. Then, the synthetic aperture radar system S is closest azimuth time target T t c, Range Time Range τ c ≦ τ ≦ τ c + τ 0 ( however, tau c, a delay time of electromagnetic wave propagation.) Of, Over the entire range time range τ c ≦ τ ≦ τ c + τ 0 , is considered in the correlation process between the reflected signal and the reference signal.
　なお、図１４において、ビームチルトがない場合に反射信号が存在するアジマス時間幅と、ビームチルトがある場合に反射信号が存在するアジマス時間幅と、は同じ長さであるように表示しているが、実際には、ビームチルトがない場合に反射信号が存在するアジマス時間幅は、ビームチルトがある場合に反射信号が存在するアジマス時間幅よりも短く、図１４のように表したときの反射信号の面積は、ビームチルトがない場合と、ビームチルトがある場合と、で比較して、ビームチルトがない場合の方が大きいということはない。 In FIG. 14, the azimuth time width in which the reflected signal exists when there is no beam tilt and the azimuth time width in which the reflected signal exists when there is the beam tilt are displayed as having the same length. However, in practice, the azimuth time width in which the reflected signal exists when there is no beam tilt is shorter than the azimuth time width in which the reflected signal exists when there is a beam tilt, and the reflection time when represented as shown in FIG. The area of the signal is not larger when there is no beam tilt than when there is no beam tilt and when there is a beam tilt.
　一方、ビームチルトがある場合では、各アジマス時間ｔにおいて照射されるチャープパルスの全体区間のうち、ターゲットＴに向けて照射されるチャープパルスの一部区間のみを、反射信号と参照信号との間の相関処理において考慮する。 On the other hand, when there is a beam tilt, only a part of the chirp pulse irradiated toward the target T in the entire section of the chirp pulse irradiated at each azimuth time t is set between the reflected signal and the reference signal. In the correlation process of
　具体的には、アンテナ部Ａの照射ビームがターゲットＴに向き始めるアジマス時間ｔｉでは、レンジ時間範囲τｉｆ≦τ≦τｉｆ＋τ０のうち、一部のレンジ時間範囲ｍａｘ｛τｉ（ｔｉ）、τｉｆ｝≦τ≦ｍｉｎ｛τｆ（ｔｉ）、τｉｆ＋τ０｝（図１３及び数式８、１１を参照。）のみを、反射信号と参照信号との間の相関処理において考慮する。そして、合成開口レーダシステムＳがターゲットＴに最も近づくアジマス時間ｔｃでは、レンジ時間範囲τｃ≦τ≦τｃ＋τ０のうち、一部のレンジ時間範囲ｍａｘ｛τｉ（ｔｃ）、τｃ｝≦τ≦ｍｉｎ｛τｆ（ｔｃ）、τｃ＋τ０｝（図１３及び数式８、１１を参照。）のみを、反射信号と参照信号との間の相関処理において考慮する。さらに、アンテナ部Ａの照射ビームがターゲットＴに向き終わるアジマス時間ｔｆでは、レンジ時間範囲τｉｆ≦τ≦τｉｆ＋τ０のうち、一部のレンジ時間範囲ｍａｘ｛τｉ（ｔｆ）、τｉｆ｝≦τ≦ｍｉｎ｛τｆ（ｔｆ）、τｉｆ＋τ０｝（図１３及び数式８、１１を参照。）のみを、反射信号と参照信号との間の相関処理において考慮する。 Specifically, in the azimuth time t i when the irradiation beam of the antenna section A starts to be directed to the target T, a part of the range time range max ｛τ i (t) in the range time range τ if ≦ τ ≦ τ if + τ 0. i ), τ if ｝ ≦ τ ≦ min ｛τ f (t i ), τ if + τ 0 ｝ (see FIG. 13 and Equations 8 and 11) only in the correlation process between the reflected signal and the reference signal. Take into account. Then, the synthetic aperture radar system S is closest azimuth time t c to the target T, among the range time range τ c ≦ τ ≦ τ c + τ 0, a part of the range time range max {τ i (t c) , τ Only c ｝ ≦ τ ≦ min ≦ τ f (t c ), τ c + τ 0 ｝ (see FIG. 13 and Equations 8 and 11) are considered in the correlation process between the reflected signal and the reference signal. Furthermore, the azimuth time t f of the illumination beam of the antenna unit A finishes orientation target T, among the range time range τ if ≦ τ ≦ τ if + τ 0, a part of the range time range max {τ i (t f) , Only τ if ｝ ≦ τ ≦ min ｛τ f (t f ), τ if + τ 0 ｝ (see FIG. 13 and Equations 8, 11) are considered in the correlation process between the reflected signal and the reference signal.
　このように、各アジマス時間ｔにおいて照射されるチャープパルスの全体区間のうち、ターゲットＴに向けて照射されるチャープパルスの一部区間のみを、反射信号と参照信号との間の時間領域又は周波数領域の相関処理において考慮する。そして、ターゲットＴから反射された反射信号について、本開示では従来技術より、受信可能なレンジ時間τは短くなるものの、受信可能なアジマス時間ｔは長くなるため、受信可能な総時間は減少しない。よって、高レンジ分解能化を実現するために、チャープパルスの広帯域化を実行しようとしても、ビームチルトにより信号対雑音比を低下させないことができる。 As described above, of the entire section of the chirp pulse irradiated at each azimuth time t, only a partial section of the chirp pulse irradiated toward the target T is defined as the time domain or frequency between the reflected signal and the reference signal. This is taken into account in the area correlation processing. In the present disclosure, with respect to the reflected signal reflected from the target T, the receivable range time τ is shorter than in the related art, but the receivable azimuth time t is longer, so that the total receivable time is not reduced. Therefore, even if an attempt is made to increase the bandwidth of the chirped pulse in order to realize a higher range resolution, it is possible to prevent the signal-to-noise ratio from being reduced by the beam tilt.
（本開示の合成開口レーダシステムの分解能評価）
　まず、反射信号と参照信号との間の相関処理について説明する。あるターゲットＰ：（Ｘ、Ｙ）から反射された反射信号をＦ（Ｘ、Ｙ）（ｔ、τ）とし、他のターゲットＰ’：（Ｘ’、Ｙ’）から反射された反射信号をＦ（Ｘ’、Ｙ’）（ｔ、τ）とする。反射信号Ｆ（Ｘ、Ｙ）（ｔ、τ）と反射信号Ｆ（Ｘ’、Ｙ’）（ｔ、τ）との間の相関Ｓは、数式１２のように表される。
Figure JPOXMLDOC01-appb-M000012
 相関Ｓは、Ｐ：（Ｘ、Ｙ）とＰ’：（Ｘ’、Ｙ’）とが近ければ、大きな値をとると期待され、Ｐ：（Ｘ、Ｙ）とＰ’：（Ｘ’、Ｙ’）とが遠ければ、小さな値をとると期待される。 (Evaluation of resolution of synthetic aperture radar system of the present disclosure)
First, the correlation process between the reflected signal and the reference signal will be described. A target P: a reflection signal reflected from (X, Y) is F (X, Y) (t, τ), and a reflection signal reflected from another target P ′: (X ′, Y ′) is F (X ′, Y ′) (t, τ). The correlation S between the reflection signal F (X, Y) (t, τ) and the reflection signal F (X ′, Y ′) (t, τ) is expressed by Expression 12.
Figure JPOXMLDOC01-appb-M000012
 The correlation S is expected to take a large value if P: (X, Y) and P ′ :( X ′, Y ′) are close, and P: (X, Y) and P ′ :( X ′, If Y ′) is farther away, a smaller value is expected.
　以上の原理を利用して、反射信号と参照信号との間の相関処理が実行される。複数のターゲットＰ１：（Ｘ１、Ｙ１）、Ｐ２：（Ｘ２、Ｙ２）、・・・、Ｐｎ：（Ｘｎ、Ｙｎ）から反射された反射信号を数式１３のように個々の反射信号の和として表し、観測対象位置Ｐ：（Ｘ、Ｙ）から反射されたと期待される参照信号をＦ（Ｘ、Ｙ）（ｔ、τ）とする。反射信号Ｒ（ｔ、τ）と参照信号Ｆ（Ｘ、Ｙ）（ｔ、τ）との間の相関Ｓは、数式１４のように表される。
Figure JPOXMLDOC01-appb-M000013
Figure JPOXMLDOC01-appb-M000014
 相関Ｓは、Ｐ１、Ｐ２、・・・、Ｐｎの中にＰにごく近い点があれば、大きな値をとると期待され、Ｐ１、Ｐ２、・・・、Ｐｎの中にＰにごく近い点がなければ、小さな値をとると期待される。そこで、観測対象位置Ｐ：（Ｘ、Ｙ）におけるターゲットの有無を画像化するために、観測対象位置Ｐ：（Ｘ、Ｙ）が関わる相関Ｓの大きさを画像の階調数に対応付ける。 Using the above principle, a correlation process between the reflected signal and the reference signal is performed. The reflected signals reflected from a plurality of targets P 1 : (X 1 , Y 1 ), P 2 : (X 2 , Y 2 ),..., P n : (X n , Y n ) are represented by Expression 13. , And the reference signal expected to be reflected from the observation target position P: (X, Y) is F (X, Y) (t, τ). The correlation S between the reflection signal R (t, τ) and the reference signal F (X, Y) (t, τ) is expressed by Expression 14.
Figure JPOXMLDOC01-appb-M000013
Figure JPOXMLDOC01-appb-M000014
 Correlation S is, P 1, P 2, ··· , if there is a point very close to the P in P n, are expected to take a large value, P 1, P 2, ··· , in the P n If there is no point very close to P, it is expected to take a small value. Therefore, in order to image the presence or absence of the target at the observation target position P: (X, Y), the magnitude of the correlation S relating to the observation target position P: (X, Y) is associated with the number of gradations of the image.
　次に、合成開口レーダシステムの分解能評価について説明する。以上の相関処理では、Ｐ：（Ｘ、Ｙ）とＰ’：（Ｘ’、Ｙ’）とが関わる相関Ｓが、Ｐ：（Ｘ、Ｙ）とＰ’：（Ｘ’、Ｙ’）とが離れるに従って、急速に小さくなることを前提としている。そこで、相関Ｓが急速に小さくなる程度、つまり、合成開口レーダシステムＳの分解能を評価する。 Next, the resolution evaluation of the synthetic aperture radar system will be described. In the above correlation processing, the correlation S involving P: (X, Y) and P ′ :( X ′, Y ′) is represented by P: (X, Y) and P ′ :( X ′, Y ′). Is assumed to rapidly decrease as the distance increases. Therefore, the degree to which the correlation S rapidly decreases, that is, the resolution of the synthetic aperture radar system S is evaluated.
　ターゲット（０、Ｙ）から反射された反射信号を数式１５のように表し、観測対象位置（ΔＸ、Ｙ＋ΔＹ）から反射されたと期待される参照信号を数式１６のように表す。
Figure JPOXMLDOC01-appb-M000015
Figure JPOXMLDOC01-appb-M000016
 なお、ターゲットのアジマス方向位置を０としたが、一般性は失われない。ターゲットのアジマス方向位置をＸとすれば、アジマス時間ｔをＸ／ｖだけシフトすればよい。 The reflected signal reflected from the target (0, Y) is represented by Expression 15, and the reference signal expected to be reflected from the observation target position (ΔX, Y + ΔY) is represented by Expression 16.
Figure JPOXMLDOC01-appb-M000015
Figure JPOXMLDOC01-appb-M000016
 Although the azimuth direction position of the target is set to 0, generality is not lost. Assuming that the position of the target in the azimuth direction is X, the azimuth time t may be shifted by X / v.
　反射信号Ｆ（ｔ、τ）と参照信号Ｇ（ｔ、τ）との間の相関Ｓは、数式１７のように表される。ここで、ΔＲ（ｔ）、Ｒ（ｔ）及びＲ’（ｔ）は、数式１８のように表される。なお、数式１７に示した相関Ｓは、図１５、１６に示す点拡張関数に対応する。
Figure JPOXMLDOC01-appb-M000017
Figure JPOXMLDOC01-appb-M000018
 The correlation S between the reflection signal F (t, τ) and the reference signal G (t, τ) is expressed by Expression 17. Here, ΔR (t), R (t), and R ′ (t) are expressed as in Expression 18. Note that the correlation S shown in Expression 17 corresponds to the point extension function shown in FIGS.
Figure JPOXMLDOC01-appb-M000017
Figure JPOXMLDOC01-appb-M000018
　反射信号Ｆ（ｔ、τ）と参照信号Ｇ（ｔ、τ）との間の相関Ｓは、数式１９のように計算される。ただし、Ａ（ｔ）及びＢ（ｔ）は、数式２０、２１のように表される。そして、数式１９のアジマス時間ｔの積分範囲は、Ｂ（ｔ）＞Ａ（ｔ）を満たすアジマス時間ｔにわたる。さらに、θ（ｔ）及びθ’（ｔ）は、数式２２のように表される。
Figure JPOXMLDOC01-appb-M000019
Figure JPOXMLDOC01-appb-M000020
Figure JPOXMLDOC01-appb-M000021
Figure JPOXMLDOC01-appb-M000022
 The correlation S between the reflection signal F (t, τ) and the reference signal G (t, τ) is calculated as in Expression 19. However, A (t) and B (t) are represented as in Expressions 20 and 21. The integration range of the azimuth time t in Expression 19 extends over the azimuth time t that satisfies B (t)> A (t). Further, θ (t) and θ ′ (t) are represented by Expression 22.
Figure JPOXMLDOC01-appb-M000019
Figure JPOXMLDOC01-appb-M000020
Figure JPOXMLDOC01-appb-M000021
Figure JPOXMLDOC01-appb-M000022
　本開示の点拡張関数対ターゲットからのレンジ方向距離を図１５に示す。本開示の点拡張関数対ターゲットからのアジマス方向距離を図１６に示す。点拡張関数を計算するにあたり、中心周波数ｆ０を９．２５ＧＨｚとし、チャープパルス周波数幅ＢＷを８００ＭＨｚとし、チャープパルス時間幅τ０を１．０μｓとし、ビーム幅２ηを１．５ｄｅｇとし、ビームチルトの変化速度を１．０ｄｅｇ／１００ＭＨｚとし、合成開口レーダシステムＳの速度ｖを１００ｍ／ｓとし、ターゲットＴのレンジ方向距離を１５．０ｋｍとする。 FIG. 15 shows the point extension function of the present disclosure versus the distance in the range direction from the target. FIG. 16 shows the point extension function of the present disclosure versus the azimuth distance from the target. In calculating the point expansion function, the center frequency f 0 is 9.25 GHz, the chirp pulse frequency width B W is 800 MHz, the chirp pulse time width τ 0 is 1.0 μs, the beam width 2η is 1.5 deg, the beam The change speed of the tilt is 1.0 deg / 100 MHz, the speed v of the synthetic aperture radar system S is 100 m / s, and the distance in the range direction of the target T is 15.0 km.
　図１５を参照すると、従来技術のビームチルトがない場合と比べて、本開示のビームチルトがある場合では、同程度のレンジ分解能が得られていることが分かる。つまり、従来技術のビームチルトがない場合と比べて、本開示のビームチルトがある場合では、ターゲットＴからの反射信号が存在するレンジ時間τが減少するため、ターゲットＴからの反射信号の周波数帯域が減少するものの、ターゲットＴからの反射信号が存在するアジマス時間ｔが増加するため、ターゲットＴからの反射信号が存在する総時間が減少することなく、同程度のレンジ分解能が得られる。そして、反射信号と参照信号との間の相関処理において、各アジマス時間ｔにおいて照射されるチャープパルスのうち、チャープパルス時間幅τ０の全部を考慮する場合と比べて、ターゲットＴに向けて照射される一部を考慮する場合では、高信号対雑音比を実現することができる。 Referring to FIG. 15, it can be seen that the same range resolution is obtained when there is a beam tilt according to the present disclosure than when there is no beam tilt according to the related art. That is, in the case where the beam tilt of the present disclosure is present, the range time τ during which the reflected signal from the target T exists is reduced as compared with the case where the beam tilt of the related art is not provided. However, since the azimuth time t during which the reflected signal from the target T is present increases, the same range resolution can be obtained without reducing the total time during which the reflected signal from the target T exists. Then, in the correlation processing between the reflected signal and the reference signal, of the chirp pulses irradiated at each azimuth time t, irradiation toward the target T is performed as compared with the case where the entire chirp pulse time width τ 0 is considered. When considering a part to be performed, a high signal-to-noise ratio can be realized.
　図１６を参照すると、従来技術のビームチルトがない場合と比べて、本開示のビームチルトがある場合では、より高いアジマス分解能が得られていることが分かる。つまり、従来技術のビームチルトがない場合と比べて、本開示のビームチルトがある場合では、チャープパルスを照射するにあたり、アンテナの指向特性によって生じるビームチルトを積極的に利用するため、いずれの観測対象位置についても、観測可能なアジマス時間ｔが長くなる。よって、高信号対雑音比を実現するために、アンテナの高利得化つまり開口長増大を実行しようとしても、合成開口によりアジマス分解能を低下させないことができる。 を Referring to FIG. 16, it can be seen that higher azimuth resolution is obtained when there is a beam tilt of the present disclosure than when there is no beam tilt of the related art. In other words, when there is a beam tilt according to the present disclosure as compared with the case where there is no beam tilt according to the related art, the beam tilt caused by the directional characteristics of the antenna is actively used in irradiating the chirp pulse. Also at the target position, the observable azimuth time t becomes longer. Therefore, even if an attempt is made to increase the antenna gain, that is, to increase the aperture length in order to realize a high signal-to-noise ratio, the azimuth resolution can be prevented from being reduced by the synthetic aperture.
　本開示の合成開口レーダ装置、合成開口レーダ信号処理装置、合成開口レーダ信号処理プログラム及び合成開口レーダ観測方法は、合成開口レーダ技術において、高信号対雑音比及び高分解能化を両立させつつ、照射ビームの方向を制御する機械的又は電気的な機構を不要とし、回路の簡素化及びシステムの低価格化を実現することができる。 A synthetic aperture radar apparatus, a synthetic aperture radar signal processing apparatus, a synthetic aperture radar signal processing program, and a synthetic aperture radar observation method according to the present disclosure provide a synthetic aperture radar technique that achieves both high signal-to-noise ratio and high resolution in synthetic aperture radar technology. A mechanical or electrical mechanism for controlling the beam direction is not required, and the circuit can be simplified and the cost of the system can be reduced.
Ｓ：合成開口レーダシステム
Ａ：アンテナ部
Ｔ：ターゲット
１：合成開口レーダ装置
２：合成開口レーダ信号処理装置
１１：チャープパルス生成部
１２：反射信号受信部
１３：アンテナ駆動部
２１：相関処理実行部 S: Synthetic aperture radar system A: Antenna unit T: Target 1: Synthetic aperture radar device 2: Synthetic aperture radar signal processing device 11: Chirp pulse generating unit 12: Reflected signal receiving unit 13: Antenna driving unit 21: Correlation processing executing unit

Claims (10)

  1. 　合成開口レーダのレンジ圧縮用のチャープパルスを生成するチャープパルス生成部と、
    　前記チャープパルス生成部が生成したチャープパルスを照射するにあたり、機械的及び電子的な指向制御を行なわず元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させるアンテナ部と、
    　ターゲットから反射された反射信号を受信する反射信号受信部と、
    　を備えることを特徴とする合成開口レーダ装置。     A chirp pulse generator for generating a chirp pulse for range compression of the synthetic aperture radar,
    Upon irradiating the chirp pulse generated by the chirp pulse generation unit, the direction of the irradiation beam is changed in the azimuth direction according to the frequency of the irradiation beam according to the inherent directional characteristic without performing mechanical and electronic pointing control. An antenna section to be changed,
    A reflection signal receiving unit that receives a reflection signal reflected from the target,
    A synthetic aperture radar device comprising:
  2. 　合成開口レーダのレンジ圧縮用のチャープパルスを生成するチャープパルス生成部と、
    　前記チャープパルス生成部が生成したチャープパルスを照射するにあたり、元来備わっている指向特性に従って、照射ビームの方向を照射ビームの周波数に応じてアジマス方向に変化させるアンテナ部と、
    　ターゲットから反射された反射信号を受信する反射信号受信部と、
    　を備えることを特徴とする合成開口レーダ装置。     A chirp pulse generator for generating a chirp pulse for range compression of the synthetic aperture radar,
    Upon irradiating the chirp pulse generated by the chirp pulse generation unit, according to the inherent directional characteristics, an antenna unit that changes the direction of the irradiation beam in the azimuth direction according to the frequency of the irradiation beam,
    A reflection signal receiving unit that receives a reflection signal reflected from the target,
    A synthetic aperture radar device comprising:
  3. 　前記チャープパルス生成部が、アジマス位置ごとに中心周波数を制御してチャープパルスを生成することにより、前記アンテナ部が照射する照射ビームのアジマス方向がある観測領域を指向するようにし、スポットライトモードを用いて合成開口レーダ観測を行う
    　ことを特徴とする、請求項１又は２に記載の合成開口レーダ装置。     The chirp pulse generation unit controls the center frequency for each azimuth position to generate a chirp pulse so that the azimuth direction of the irradiation beam irradiated by the antenna unit is directed to a certain observation area, and the spotlight mode is set. The synthetic aperture radar apparatus according to claim 1, wherein synthetic aperture radar observation is performed using the apparatus.
  4. 　前記チャープパルス生成部が、アジマス位置によらない形状を有するチャープパルスを生成することにより、照射ビームの方向をアジマス方向に変化させ、照射ビームの方向をアジマス方向に変化させないときと比べて、観測可能なアジマス時間が長くなるストリップモードを用いて合成開口レーダ観測を行う
    　ことを特徴とする、請求項１から３のいずれかに記載の合成開口レーダ装置。     The chirp pulse generation unit generates a chirp pulse having a shape that does not depend on the azimuth position, thereby changing the direction of the irradiation beam in the azimuth direction and observing compared to the case where the direction of the irradiation beam is not changed in the azimuth direction. The synthetic aperture radar apparatus according to any one of claims 1 to 3, wherein the synthetic aperture radar observation is performed using a strip mode in which a possible azimuth time is long.
  5. 　前記チャープパルス生成部が、アジマス位置によらない形状を有するとともに、前記アンテナ部が照射する照射ビームのアジマス方向のスクイントが生じるような中心周波数を有するチャープパルスを生成することにより、照射ビームの方向をアジマス方向に変化させ、照射ビームの方向をアジマス方向に変化させないときと比べて、観測可能なアジマス時間が長くなるスクイントモードを用いて合成開口レーダ観測を行う
    　ことを特徴とする、請求項１から４のいずれかに記載の合成開口レーダ装置。     The chirp pulse generation unit has a shape that does not depend on the azimuth position, and generates a chirp pulse having a center frequency such that squint in the azimuth direction of the irradiation beam irradiated by the antenna unit is generated. The synthetic aperture radar observation is performed using a squint mode in which the observable azimuth time is longer than when the direction of the irradiation beam is not changed in the azimuth direction. 5. The synthetic aperture radar device according to any one of 1 to 4.
  6. 　請求項１から５のいずれかに記載の合成開口レーダ装置の前記反射信号受信部が受信した反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の相関処理を実行する
    　ことを特徴とする合成開口レーダ信号処理装置。     The reflection signal received by the reflection signal receiving unit of the synthetic aperture radar device according to any one of claims 1 to 5, and a chirp pulse generated by the chirp pulse generation unit reflected from an observation target position for each azimuth position. A synthetic aperture radar signal processing apparatus for performing a correlation process between a reference signal that selects only a partial section expected to be performed.
  7. 　前記観測対象位置から反射された反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに前記観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の時間領域における相関処理を実行する
    　ことを特徴とする、請求項６に記載の合成開口レーダ信号処理装置。     A reflected signal reflected from the observation target position, and a reference signal that selects only a partial section expected to be reflected from the observation target position for each azimuth position among the chirp pulses generated by the chirp pulse generation unit. The synthetic aperture radar signal processing apparatus according to claim 6, wherein correlation processing is performed in a time domain between.
  8. 　請求項１から５のいずれかに記載の合成開口レーダ装置の前記反射信号受信部が受信した反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の相関処理、
    　をコンピュータに実行させるための合成開口レーダ信号処理プログラム。     The reflection signal received by the reflection signal receiving unit of the synthetic aperture radar device according to any one of claims 1 to 5, and a chirp pulse generated by the chirp pulse generation unit reflected from an observation target position for each azimuth position. Correlation processing between a reference signal that has selected only a partial section expected to have been performed,
    Synthetic Aperture Radar signal processing program for causing a computer to execute
  9. 　前記観測対象位置から反射された反射信号と、前記チャープパルス生成部が生成したチャープパルスのうち、アジマス位置ごとに前記観測対象位置から反射されたと期待される一部区間のみを選択した参照信号と、の間の時間領域における相関処理、をコンピュータに実行させる
    　ための、請求項８に記載の合成開口レーダ信号処理プログラム。     A reflected signal reflected from the observation target position, and a reference signal that selects only a partial section expected to be reflected from the observation target position for each azimuth position among the chirp pulses generated by the chirp pulse generation unit. The synthetic aperture radar signal processing program according to claim 8, which causes a computer to execute a correlation process in a time domain between:
  10. 　合成開口レーダのレンジ圧縮用のチャープパルスを生成するチャープパルス生成手順と、
    　元来アンテナ部に備わっている指向特性に従って、前記アンテナ部が照射する前記チャープパルス生成手順で生成したチャープパルスの照射ビームの方向を、前記照射ビームの周波数に応じてアジマス方向に変化させる照射ビーム照射手順と、
    　ターゲットから反射された反射信号を受信する反射信号受信手順と、
    　を順に備えることを特徴とする合成開口レーダ観測方法。     A chirp pulse generation procedure for generating a chirp pulse for range compression of a synthetic aperture radar,
    An irradiation beam that changes the direction of the irradiation beam of the chirp pulse generated in the chirp pulse generation procedure radiated by the antenna unit in the azimuth direction according to the frequency of the irradiation beam according to the directional characteristics originally provided in the antenna unit. Irradiation procedure;
    A reflected signal receiving procedure for receiving a reflected signal reflected from the target,
    A synthetic aperture radar observation method characterized by comprising:
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