JP5561013B2 - SAR equipment - Google Patents

Description

  The present invention relates to a SAR device.

  In the field of remote sensing using a flying object such as an artificial satellite or an aircraft, a four-polarization synthetic aperture radar (Full Polarimetry SAR; hereinafter referred to as Full Polarimetry SAR) that uses a microwave band as a sensor for imaging the surface condition. Is used).

  A related full polarimetry SAR technique is described in Patent Document 1. In the full polarimetry SAR described in Patent Literature 1, normally, transmission pulses of H polarization (horizontal polarization) and transmission pulses of V polarization (vertical polarization) are alternately transmitted. Then, the H-polarized ground reflected wave and the V-polarized ground reflected wave are simultaneously received by the two antennas and the receiving system corresponding to each polarized wave.

  FIG. 7 shows the components of the received wave when the transmission pulse of H polarization (horizontal polarization) and the transmission pulse of V polarization (vertical polarization) are alternately transmitted. In the transmission, a transmission pulse of H polarization (horizontal polarization) and V polarization (vertical polarization) are transmitted to the observation target for each pulse. The reflected wave reflected from the observation target is received by the first receiver that receives the H polarization (horizontal polarization) and the second receiver that receives the V polarization (vertical polarization).

JP 2010-085169A (paragraphs “0043” to “0044”, FIG. 4)

  However, since the full polarimetry SAR transmits H polarization and V polarization alternately, it is necessary to set a higher pulse repetition frequency (hereinafter referred to as PRF) than SAR that performs single polarization transmission. . When the PRF is set high, there is a problem that the observation width in the range direction and the off-nadir angle are restricted, making it impossible to observe a wide observation width. In addition, there is a problem in that the range ambiguity increases because the overlapping of received signals increases.

  The object of the present invention is that the observation width in the range direction and the off-nadir angle are limited, making it impossible to observe a wide observation width, and the problem that the range ambiguity increases because the overlap of received signals increases. A SAR device that solves the problem is provided.

  The SAR device of the present invention generates a frequency-modulated pulse signal and outputs a pulse signal, and switches the phase of the input pulse signal every 180 degrees every time the pulse signal is input, and outputs it. Transmitting the pulse signal output from the transmitter or the phase shifter with H polarization, receiving the reception signal with H polarization, and receiving the received signal with H polarization as the first reception The H-polarized antenna that is output to the transmitter and the pulse signal that is output from the transmitter or phase shifter are transmitted using V-polarized light, and the received signal is received using V-polarized light. V polarization antenna that outputs to the second receiver, first receiver that receives the V polarization, second receiver that receives the V polarization, and a polarization plane of +45 degrees with respect to the H polarization. Or reception of H polarized wave reception and V polarized wave reception with respect to a reflected wave of -45 degrees tilted transmission wave The first polarization component (HH polarization component or HV polarization component) for H polarization transmission and the second polarization component (VH polarization component or VV polarization component) for V polarization, respectively. In addition, a total of four types of polarization components (HH, HV, VH, VV) are separated, and the phase of the first or second polarization component data is alternately set to 0 degree and 180 degrees for each transmission pulse. A separation processing unit having a correction phase shifter for inverting.

  According to the SAR device of the present invention, the observation width in the range direction and the off-nadir angle are restricted, and a wide observation width cannot be observed, and the overlapping of received signals increases, so that range ambiguity increases. Can be solved.

It is a block diagram which shows the structure of the SAR apparatus of 1st embodiment by this invention. It is a figure which shows the component of the transmission polarization of 1st embodiment by this invention, and a reception polarization. It is a figure which shows the component of the received polarization | polarized-light processed by the polarization separation process of 1st embodiment by this invention. It is a flowchart which shows operation | movement of the SAR apparatus of 1st embodiment by this invention. (A) The Doppler spectrum of +45 degree transmission H reception of 1st embodiment by this invention is shown.

(B) The Doppler spectrum of -45 degree transmission H reception of 1st embodiment by this invention is shown.
(A) The Doppler spectrum of H reception data after the polarization separation of 1st embodiment by this invention is shown.

(B) The Doppler spectrum of the V reception data after 0/180 degree phase correction after polarization separation of the first embodiment of the present invention is shown.
It is a figure which shows the component of the transmission polarized wave of a general SAR apparatus, and a received wave.

  Embodiments of the present invention will be described below with reference to the drawings.

[First embodiment]
FIG. 1 is a block diagram showing a SAR device according to a first embodiment of the present invention. In FIG. 1, a SAR device 1 includes a transmitter 11, a first receiver 12, a second receiver 13, a phase shifter 14, an H polarization antenna 15, a V polarization antenna 16, An H polarization side circulator 17, a V polarization side circulator 18, and a control device 19 are included.

  Further, the SAR image generation device 2 includes a polarization separation processing unit 20 that separates the H polarization reception data from the H polarization component and the VH polarization component, and the V polarization reception data from the HV polarization component and the VV polarization component. The SAR image reproduction processing unit 21 that reproduces the SAR image from the H polarization reception data and the V polarization reception data, and the full polarimetry SAR image generation unit 22 that generates a full polarimetry SAR image from the separated SAR image of each polarization data. Composed.

  The transmitter 11 generates a frequency-modulated transmission pulse signal. An example is a linear pulse modulator that is modulated to a linear frequency. The first receiver 12 receives an H-polarized received signal reflected from the observation target. The second receiver 13 receives a V polarization received signal reflected from the observation target. These receivers are general receivers that receive a received signal.

  The phase shifter 14 switches the phase for each transmission pulse. The H polarization antenna 15 and the V polarization antenna 16 are antennas that transmit pulse signals with H polarization and V polarization and receive reception signals with H polarization and V polarization. The H polarization side circulator 17 and the V polarization side circulator 18 are for switching between a transmission route and a reception route.

  The transmission pulse signal output from the transmitter 11 is branched into two and transmitted to the H polarization antenna 15 and the V polarization antenna 16 through the circulator. The phase shifter 14 between the transmitter 11 and the V-polarized-wave antenna circulator 18 is switched between 0 degree and 180 degrees for each transmission pulse by a PRI (Pulse Repeat Interval) trigger generated by the control device 19. Here, the control device 19 is a device that generates timing signals such as a transmission trigger and a reception gate with an arbitrary PRI, and controls the timing of each unit.

  Accordingly, an H-polarized transmission pulse is transmitted from the H-polarized antenna 15, and the phase of the V-polarized antenna 16 is changed from 0 to 180 degrees for each transmission pulse with respect to the phase of the H-polarized wave + V Polarization and -V polarization transmission pulses are transmitted alternately. Here, the V polarization having a relative phase of 0 degree with respect to the H polarization is referred to as + V polarization, and the V polarization having a relative phase of 180 degrees is referred to as -V polarization.

  That is, as a whole, two types of linearly polarized waves whose polarization planes are inclined to +45 degrees and −45 degrees with respect to the H polarization are alternately observed from the H polarization antenna 15 and the V polarization antenna 16. Sent to a target (for example, the surface of the earth).

  In this embodiment, the phase shifter 14 is connected between the transmitter 11 and the circulator 18 for the V-polarized antenna, but is connected between the transmitter 11 and the circulator 17 for the H-polarized antenna. It may be. In this case, V-polarized wave is transmitted from the V-polarized antenna 16, and + H-polarized wave and -H-polarized wave whose phase is changed between 0 degree and 180 degrees every transmission pulse are alternately transmitted from the H-polarized wave antenna 15. Sent.

  Subsequently, the reflected wave from the observation target is received by the H polarization antenna 15 and the V polarization antenna 16. After reception, the signals are received by the first receiver 12 (H reception) and the second receiver 13 (V reception) via the circulator 17 for the H polarization antenna and the circulator 18 for the V polarization antenna, respectively. The data is output to the polarization separation processing unit 20.

  FIG. 2 shows received wave components when transmission pulses of +45 degrees transmission polarization and transmission pulses of −45 degrees transmission polarization are alternately transmitted. In transmission, since the phase shifter 14 changes for each transmission pulse as described above, transmission pulses of +45 degrees transmission polarization and transmission pulses of −45 degrees transmission polarization are alternately transmitted. The reflected wave reflected from the observation target is received by the first receiver 12 that receives the H polarization (horizontal polarization) and the second receiver 13 that receives the V polarization (vertical polarization). .

  When the first receiver 12 receives a reflected wave with respect to a transmission pulse signal of +45 degrees transmission polarization, the first receiver 12 receives an HH + VH signal component and receives a reflected wave with respect to a transmission pulse signal of −45 degrees transmission polarization. Receives the HH-VH signal component. When the first receiver 12 receives the HH + VH signal component, the HH-VH signal components before and after the HH + VH signal component become virtual image components.

  The second receiver 13 receives an HV + VV signal component when receiving a reflected wave with respect to a transmission pulse signal of +45 degrees transmission polarization, and receives a reflected wave with respect to a transmission pulse signal of −45 degrees transmission polarization. Receives the HV-VV signal component. When the second receiver 13 receives the HV + VV signal component, the HV-VV signal component before and after the HV + VV signal component becomes a virtual image component.

  In this embodiment, antennas are shared for transmission and reception, but separate antennas may be configured for transmission and reception. For example, a +45 degree transmission polarization antenna and a -45 degree transmission polarization antenna may be used for transmission, and an H polarization antenna and a V polarization antenna may be used for reception.

  The transmission polarization and the reception polarization may be rearranged such that the transmission polarization is an H polarization and a V polarization, and the reception polarization is a +45 degree reception polarization and a -45 degree reception polarization. . Any configuration may be used as long as it transmits the same polarization as the two types of received polarization within the same pulse and alternately repeats the transmission of the polarization component orthogonal thereto. The antenna configuration may be a configuration using a phased array antenna.

  The polarization separation processing unit 20 includes separation processing units 23 and 24 that separate received data into components, and each has a correction phase shifter that corrects the phase of each transmission pulse to 0 degrees / 180 degrees.

  Here, the received data input to the SAR device 1 alternately transmits two kinds of linearly polarized waves whose polarization planes are inclined to +45 degrees and −45 degrees with respect to the H polarization, and are reflected from the observation target. There are H reception data and V reception data. The H reception data includes H polarization reflected wave data for +45 degrees transmission (+45 degrees transmission H polarization reception data) and H polarization reflection data for −45 degrees transmission (−45 degrees transmission H polarization reception). Data). The V reception data includes V polarization reflected wave data for +45 degrees transmission (+45 degree transmission V polarization reception data) and V polarization reflection data for -45 degrees transmission (-45 degrees transmission V polarization reception). Data).

  FIG. 3 shows received data input to the polarization separation processing unit 10. The H reception data input to the polarization separation processing unit 20 is divided into an HH polarization component and a VH polarization component.

  The separated HH polarization component is output to the SAR image reproduction processing unit 21 as a continuous continuous data. Here, a series of continuous data refers to data obtained by sequentially receiving the received +45 degree transmission H reception data and -45 degree transmission H reception data. The HH polarization component is output to the SAR image reproduction processing unit 21 in time series without separately separating the +45 degree and −45 degree H received data. The SAR image reproduction processing unit 21 reproduces the received data as it is. In this case, as will be described later, the V-polarized wave transmission component is subjected to phase modulation of 0 degree / 180 degrees for each transmission pulse, and thus is separated on the Doppler frequency axis and is not imaged.

  On the other hand, the separated VH polarization component is output to the SAR image reproduction processing unit 21 after being subjected to phase correction of 0 degree / 180 degrees for each transmission pulse in the correction phase shifter. Examples of a method of correcting the phase of 0 degree / 180 degrees for each transmission pulse include a method of adding or subtracting the correction phase amount by software installed in the correction phase shifter.

  In the SAR image reproduction processing unit 21, the VH polarization component is imaged because the phases are aligned, but the HH polarization component is subjected to phase modulation of 0 degrees / 180 degrees and is separated on the Doppler frequency axis. , Not imaged.

  Similarly, the V reception data input to the polarization separation processing unit 20 includes the HV polarization component that is output in time series as it is without dividing the V polarization reception data for each pulse, and the phase for each transmission pulse is 0 degree / It is divided into VV polarization components corrected to 180 degrees.

  By performing the above processing on the H polarization reception data and the V polarization reception data, it is possible to separate into four types of polarization components (HH, HV, VH, VV).

  Next, FIG. 4 shows a flowchart of the operation of the SAR device of this embodiment. First, the transmitter 11 transmits a pulse signal having a phase difference of 180 degrees each time a pulse signal is generated using a frequency-modulated pulse signal (S2).

  Next, the H polarization antenna 15 receives the reception signal of H polarization, and outputs the received H polarization to the first receiver 12 (S3-1). The V polarization antenna 16 receives a V polarization reception signal and outputs the received V polarization to the second receiver 13 (S3-2). The first receiver 12 inputs ± 45 degrees transmission H polarization reception data to the polarization separation processing unit 20 (S4-1). The second receiver 13 inputs ± 45 degree transmission V polarization reception data to the polarization separation processing unit 20 (S4-2).

  When the H polarization received data is input to the polarization separation processing unit 20, the separation processing unit 23 separates the HH polarization component and the VH polarization component, and the HH polarization component is not divided for each pulse. Output in time series (S5-1). Further, the phase of each VH polarization component is phase-modulated to 0 degree / 180 degrees (S5-2). Similarly, when V polarized wave reception data is input, the separation processing unit 24 separates the HV polarized wave component and the VV polarized wave component, and outputs the HV polarized wave component as it is in time series without being divided for each pulse ( S5-3). The VV polarization component modulates the phase of each pulse to 0 degree / 180 degrees (S5-4). Next, each separated polarization data is converted into a SAR image (S6). Finally, a full polarimetry SAR image is generated (S7).

  Next, the polarization separation according to this embodiment will be described in more detail. 5 and 6 show the Doppler spectrum of each received data.

  FIG. 5A shows a Doppler spectrum of +45 degree transmission H reception data. The +45 degree transmission H received data Doppler spectrum includes signals of the HH polarization component and the VH polarization component, and both components have a spectrum centered on 0 Hz. The thick solid line is the HH polarization component, and the thin solid line is the VH polarization component.

  Here, since the +45 degree transmission H reception data is alternately received for each transmission pulse, both the HH polarization component and the VH polarization component are centered on a frequency that is an integral multiple of PRF / 2. Yes. The thick wavy line is the return of the HH polarization component, and the thin wavy line is the return of the VH polarization component.

  On the other hand, FIG. 5B similarly shows the Doppler spectrum of the −45 degree transmission H reception data, and shows the spectrum of the HH polarization component and the −VH polarization component. Here, the H polarization reception data is not divided into +45 degrees transmission H reception data and -45 degrees transmission H reception data for each transmission pulse, but is handled as a continuous continuous data. The Doppler spectrum at this time is as shown in FIG. Since the HH polarization component is continuous data, aliasing occurs only at an integer multiple of the PRF. On the other hand, the spectrum of the VH polarization component appears at a position centered on the frequency of (PRF / 2 + PRF × integer multiple) because the phases are alternately inverted by 0 degrees and 180 degrees. Therefore, it can be seen that the HH polarization component and the VH polarization component are separated on the Doppler frequency axis. Therefore, in the SAR image reproduction processing unit, by performing the synthetic aperture processing, the VH polarization component is almost removed, and the SAR image using only the signal of the HH polarization component can be obtained.

  Here, the synthetic aperture processing is processing for performing phase synthesis / integration within the synthetic aperture bandwidth in order to increase the resolution in the traveling direction (azimuth direction) in SAR image reproduction, and is part of the SAR image reproduction processing. This is a general synthetic aperture process that constitutes. Data within the synthetic aperture bandwidth on the Doppler frequency axis is extracted, and phase synthesis and integration are performed. When performing the synthetic aperture of the HH polarization component, the HH polarization component is within the synthetic aperture bandwidth on the Doppler frequency axis, and the VH polarization component is outside the synthetic aperture bandwidth on the Doppler frequency axis. By performing processing (integration within the synthetic aperture band), the VH polarization component existing outside the synthetic aperture bandwidth is removed.

  The synthetic aperture bandwidth is only the shaded range in FIG. For this reason, by performing the synthetic aperture processing in the SAR image reproduction processing unit, the VH polarization component is almost removed, and a SAR image using only the signal of the HH polarization component can be obtained. Here, the method of removing the VH polarization separated from the HH polarization component on the Doppler frequency axis by the synthetic aperture processing of the SAR image reproduction processing is shown. However, before the SAR image reproduction processing, Fourier transform or the like is performed to perform Doppler. A method of including processing for removing the VH polarization component on the frequency axis and processing for removing the VH polarization component by a frequency band filter may be used.

  On the other hand, when phase correction of 0 degrees and 180 degrees is performed for each transmission pulse, the positions of the HH polarization and the VH polarization on the Doppler spectrum are switched as shown in FIG. By performing the synthetic aperture processing in the SAR image reproduction processing unit, the HH polarization component is almost removed, and a SAR image using only the signal of the VH polarization component can be obtained. The same applies to the V polarized wave reception data, and it is possible to separate the HV polarized wave component and the VV polarized wave component. Thus, each polarization component can be extracted by shifting the frequency by PRF / 2. In this embodiment, the VH polarization component is extracted by phase correction of 0 degrees and 180 degrees. However, a method such as extracting by shifting the PRF / 2 on the frequency axis by performing Fourier transform may be used. Is also possible.

  The synthetic aperture bandwidth is only the shaded range of FIGS. 6 (a) and 6 (b). Therefore, by performing the synthetic aperture processing in the SAR image reproduction processing unit, the HV polarization component is almost removed, and a SAR image using only the signal of the HH polarization component can be obtained.

  In order to completely separate the PRF, it is necessary to set the PRF higher. However, the PRF may be relatively low by narrowing the synthetic aperture bandwidth as compared with the single polarization observation.

  As described above, the SAR device of this embodiment can separate four types of polarization components (HH, HV, VH, VV). Therefore, the PRF for each polarization component is the same as the actual operation PRF, and the PRF can be set lower than that of the SAR device described in Patent Document 1. This has the effect of enabling off-nadir angle observation. Further, in the SAR device described in Patent Document 1, the ambiguity between the azimuth and the range is deteriorated because the PRF for each polarization is half of the actual operation PRF. Then, it becomes possible to set PRF low, and there is an effect that this restriction can be reduced.

  In this embodiment, polarization separation is performed by phase correction. However, the present invention is not limited to this, and extraction may be performed by performing a Fourier transform and shifting by PRF / 2 on the frequency axis. May be.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above description, and various modifications can be made without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 SAR apparatus 2 SAR image reproduction | regeneration analysis apparatus 11 Transmitter 12 1st receiver 13 2nd receiver 14 Phase shifter 15 H polarization antenna 16 V polarization antenna 17, 18 Circulator 19 Control apparatus 20 Polarization separation processing Unit 21 SAR image reproduction processing unit 22 Full polarimetry SAR image generation unit 23, 24 Separation processing unit

Claims (6)

A transmitter that generates a frequency-modulated pulse signal and outputs the pulse signal;
A phase shifter that switches and outputs the phase of the input pulse signal every 180 degrees each time the pulse signal is input;
The pulse signal output from the transmitter or the phase shifter is transmitted with H polarization, and the reception signal with H polarization is received. The received reception signal with H polarization is sent to the first receiver. An H polarization antenna that outputs;
The pulse signal output from the transmitter or the phase shifter is transmitted with V-polarization, and a V-polarized received signal is received, and the received V-polarized received signal is sent to the second receiver. An output V polarization antenna;
A first receiver for receiving the H polarization;
A second receiver for receiving the V polarization;
The received data of H-polarized wave reception and V-polarized wave reception with respect to the reflected wave of the transmitted wave whose polarization plane is inclined +45 degrees or −45 degrees with respect to the H polarized wave, respectively, A total of four types of polarization components (HH, HV, VH, VV) for the second polarization component (VH polarization component or VV polarization component) with respect to V polarization, and HH polarization component or HV polarization component) A separation processing unit having a correction phase shifter that alternately reverses the phase of the first or second polarization component data to 0 degrees and 180 degrees for each transmission pulse;
A SAR device comprising:   The SAR apparatus according to claim 1, further comprising a process of removing unnecessary polarization components separated on a Doppler frequency axis from the data of the four types of polarization components that have undergone phase correction. A SAR image reproduction processing unit for reproducing the data of the four types of polarization components that have undergone the phase correction into SAR images;
The SAR device according to claim 1, further comprising: The received data of H-polarization reception and V-polarization reception with respect to the reflected wave of the transmission wave whose polarization plane is inclined +45 degrees or -45 degrees with respect to the H polarization, respectively, is the first polarization component (HH A total of four types of polarization components (HH, HV, VH, VV) for the polarization component or HV polarization component) and the second polarization component (VH polarization component or VV polarization component) for the V polarization Separating the data as
Inverting the phase of the data of the first or second polarization component alternately between 0 degrees and 180 degrees for each transmission pulse;
Generating a frequency-modulated pulse signal and outputting the pulse signal;
The pulse signal is transmitted from the H polarization antenna with H polarization,
Each time the pulse signal is generated, transmitting a pulse signal having a phase difference of 180 degrees in the V polarization from the V polarization antenna;
Receiving a received signal with H polarization, and outputting the received received signal with H polarization to the H polarization receiver;
Receiving a received signal with V polarization and outputting the received received signal with V polarization to the V polarization receiver;
SAR apparatus receiving method including: The method further includes the step of removing unnecessary polarization components separated on the Doppler frequency axis from the data of the first or second polarization component in which the phase is alternately inverted at 0 degree and 180 degrees for each transmission pulse. The reception method of the SAR device according to claim 4. The method further includes a step of reproducing the data of the first or second polarization component in which the phase is alternately inverted at 0 degrees and 180 degrees for each transmission pulse , respectively, into the SAR image. SAR apparatus receiving method.

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