JPH0882676A - Synthetic-aperture radar apparatus - Google Patents

Abstract

PURPOSE: To provide a synthetic-aperture radar apparatus, for mounting on a satellite, whose resolution is maintained, in which an antenna size is expanded and whose electric power can be reduced. CONSTITUTION: On the side of a satellite, transmission pulses at continuous frequencies f1 , f2 are generated by a transmitter 123, they are radiated by an antenna part 11, their reflected waves are captured by the antenna part 11, the reflected waves are passed through BPFs(band-pass filters) 125, 126 whose band-pass regions are at the f1 , the f2 , the reflected waves are detected by receivers 127, 128 by means of respective high-frequency signals in a transmitting operation, and video signals are obtained. The video signals are digitized by A/D converters 132, 133, and digital signals are multiplexed by a multiplexer 134 so as to be sent out to a ground station through a communication-system antenna 14. In the ground station, a video multiplexed signal, from the satellite, which is received by a communication-system antenna 15 is separated into two video signals by a separator 16, the video signals are signal-processed by synthetic-aperture processing parts 171, 172, the signals are incoherent-added by an addition processing part 18, and their added result is image-displayed on a radar display device 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic aperture radar device mounted on, for example, an artificial satellite to observe the ground and the like.

[0002]

2. Description of the Related Art As is well known, a synthetic aperture radar device is mounted on an aircraft, transmits a pulse from the aircraft to the ground, receives a reflected signal of the pulse, and analyzes the frequency spectrum and the like of the terrain. And image processing such as resource exploration. Recently, it is considered that the synthetic aperture radar device is mounted on an orbiting satellite to perform a wider range of imaging processing.

However, when the synthetic aperture radar device is mounted on a satellite, various restrictions can be considered in principle because the traveling speed of the mounted satellite is extremely higher than that of an aircraft.
The largest of these is the trade-off between resolution and swath width, and if the resolution is improved for detailed observation, the swath width, which is the observation width, is extremely fatal.

That is, if the width of the antenna is LA, the light velocity is C, the satellite velocity is V, and the number of looks is N, the resolution δ
And the swath width W is expressed by the following equation. δ ≧ (LA / 2) · N (1) W ≦ (LA / 2) · (C / 2V) (2) Therefore, as long as the satellite velocity V is uniquely determined by the orbit, the number of looks N Is determined from the system requirements, the resolution and swath width are uniquely determined by the antenna size, which causes a problem that there is no degree of freedom in design. In other words, if the antenna size is increased to reduce the power consumption, the resolution must be sacrificed.

[0005]

As described above, when the synthetic aperture radar device is mounted on a spacecraft moving on the earth, the number of looks is directly related to the antenna size, the resolution and the swath width. Once the number was determined by the system requirements, there was no design freedom and it was not possible to increase the antenna size and reduce power consumption while maintaining resolution.

The present invention has been made in order to solve the above-mentioned problems, and for mounting on a spacecraft, the number of looks required by the system can be realized regardless of the antenna size, resolution and swath width. An object of the present invention is to provide a synthetic aperture radar device capable of enlarging an antenna size and reducing power consumption while maintaining resolution.

[0007]

To achieve the above object, a synthetic aperture radar apparatus according to the present invention comprises (1) a transmission system for continuously transmitting a plurality of transmission pulses having different frequencies, and A plurality of reception systems that individually receive reflected signals for the transmission pulses, and a signal processing unit that performs incoherent addition by performing synthetic aperture processing independently for each reception signal of the plurality of reception systems, (2) In particular, the transmission system and the plurality of reception systems are mounted on a spacecraft that moves on the earth, the signal processing unit is arranged in a ground station, and each reception signal of the plurality of reception systems is transmitted through a communication line. It is characterized in that it is transferred from the spacecraft to a ground station and input to the signal processing unit.

Alternatively, (3) a transmission system for converting a linear frequency modulation signal into a pulse and transmitting it, a reception system for receiving a reflection signal for the transmission pulse, and a reception signal of this reception system are separated into a plurality of frequency bands, And (4) In particular, the transmission system and the reception system are mounted on a spacecraft that moves on earth, and the signal processing unit performs the synthetic aperture processing independently and performs incoherent addition. The processing unit is arranged in the ground station, and each received signal of the plurality of receiving systems is transferred from the spacecraft to the ground station through a communication line and input to the signal processing unit.

[0009]

In the synthetic aperture radar device having the above configuration (1), n transmission pulses having different frequencies are transmitted,
After each reflection signal is individually received, synthetic aperture processing is performed independently and incoherent addition is performed, so that an equivalent post-processing image can be maintained even if the design look number is 1 / n. .

In the configuration of (2), the signal processing unit is arranged at the ground station to reduce the weight burden on the side of the spacecraft. Further, in the synthetic aperture radar device having the configuration of (3), the linear frequency modulation signal is pulsed and transmitted, and the reflected signal thereof is received, and then separated in n frequency bands. As described above, by performing a transmission / reception process equivalent to the case of transmitting n transmission pulses with different frequencies, and performing incoherent addition by performing synthetic aperture processing on each of the separated reception signals independently, Even if it is 1 / n, the same processed image can be maintained. Here, also in the configuration of (4), by placing the signal processing unit in the ground station, the weight burden on the side of the spacecraft is reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the structure of a synthetic circuit radar device according to the present invention.
1, a transceiver 12, and a signal processor 13. The signal processing unit 13 includes a mode control unit 131, and the mode control unit 131 controls the pointing direction of the antenna unit 11, the transmission pulse repetition period of the transmission / reception unit 12, and the like according to the control data and the phase shifter data.

The transmitter / receiver 12 includes high frequency oscillators 121 and 122 for generating high frequency signals having different frequencies. The high frequency signals (frequency f1, f2) generated by the respective high frequency oscillators 121, 122 are sent to the transmitter 123.
The transmitter 123 converts the two high frequency signals into transmission pulse signals having a predetermined width at a cycle according to the timing signal from the timing control unit 124, and supplies the transmission pulse signal to the antenna unit 11 in a time division manner.

The antenna section 11 radiates a transmission pulse signal input in a designated direction (ground surface) into space,
The reflected wave from the ground surface is captured and transmitted to the transmission / reception unit 12. The transmission / reception unit 12 passes the reflection signals from the antenna unit 11 through band pass filters (BPF) 125 and 126 that pass the bands of the transmission frequencies f1 and f2, respectively, and the receiver 1
Input to 27,128.

Each of the receivers 127 and 128 receives the high frequency signals of the transmission frequency from the high frequency oscillators 121 and 122, respectively, and detects the reflected signals from the band pass filters 125 and 126 with the high frequency signals, whereby the ground surface causes Obtain a video signal that is a shift component. Each video signal is an analog / digital converter (A
/ D) 132, 133, after being converted into digital data, the signal is multiplexed by the multiplexer 134 and transmitted to the ground station through the communication system antenna 14.

In the ground station, the video multiplex signal from the satellite received by the communication antenna 15 is separated into two video signals by the separator 16, and the synthetic aperture processing units 171 and 171, respectively.
After signal processing at 172, addition processing unit 18 performs incoherent addition. The addition result is the radar display 19
The image is displayed by a predetermined analysis process.

The processing operation of the above configuration will be described below. Now, as shown in FIG. 2, it is assumed that the above synthetic aperture radar is mounted on an orbiting satellite A that flies in a satellite orbit at a predetermined altitude from a ground track on the ground surface. The antenna is mounted so that its longitudinal direction is parallel to the satellite orbit. Therefore, the length in the longitudinal direction of the antenna is called the azimuth antenna length, and the length in the width direction is called the elevation antenna length.

The angle formed by the vertical line from the satellite A to the ground surface and the direction of the antenna beam is called the off-nadir angle. The distance from the ground track to the center of the actual beam irradiation range of the antenna is called the ground range.
The range clipped by the beam due to the movement of the satellite A is the observation range, and its width is called the swath width.

Under the above-mentioned usage environment, when transmitting, FIG.
As shown in Figure 2, within the transmission pulse repetition period PRI, two transmission pulses of frequency f1 and f2 (pulse width 50 μm in the figure
s) is radiated continuously in a time division manner.

On the other hand, in the receiving system, FIG.
Two band pass filters 12 having different frequency pass bands (bandwidth 30 MHz) as shown in (b).
5, 126 are used to extract the component within f1 ± 15 MHz and the component within f2 ± 15 MHz from the reflection signal for the transmission pulse. Then, at the receivers 127 and 128, f
By detecting the high-frequency signals 1 and f2, the shift components due to the respective ground surfaces are extracted and converted into video signals.

The two video signals thus obtained are multiplexed, sent to the ground station through the communication line, separated again, and incoherently added. That is, since the two video signals are both reflection shift components on the same ground surface, noise components can be suppressed by performing incoherent addition processing on both. Therefore, the azimuth look number in the synthetic aperture radar design is halved.
Even in this case, an image image having an image quality equivalent to the number of looks in the conventional method can be obtained.

In this way, if the azimuth look number in the radar design is halved, it is possible to obtain the same resolution by using an antenna having a azimuth width twice that of the radar designed by the conventional method. At this time, from equations (1) and (2), a swath width of about twice can be obtained under the same resolution, and the design trade-off can be avoided. Table 1 shows the difference in action and effect between the conventional azimuth 2-look 1-pulse system and the azimuth 1-look 2-pulse system of the above embodiment.

[0022]

[Table 1]

As shown in the evaluation column, in the conventional method, since the antenna size is small, it is necessary to cover with the transmission power, and there is a problem that the required power is large. Therefore, the efficiency of the device and the power supply capability are improved. While required,
In the method of the embodiment, the antenna size is large, so that it is necessary to reduce the weight, but the required power is ½. However, it is required to obtain the frequency and reduce the size and weight of the receiving system.

In the above embodiment, the case of two pulses has been described, but the same processing can be performed by transmitting a larger number of pulses, and the image quality of the image image can be further improved. In addition, since a large antenna can be used for power, there is a secondary merit that required transmission power can be reduced.

By the way, in the above embodiment, two transmission pulses having different frequencies are radiated, but one chirp signal (that is, a linear frequency modulation signal) whose frequency continuously changes is pulsed and transmitted, 2 on the receiving side
By separating into two frequency bands and performing incoherent addition, it is possible to obtain the same effect as the above embodiment.
This is realized as a so-called look addition in the range direction. Of course, the number of separations on the receiving side is not limited to 2, and can be changed according to the number of looks. Needless to say, various modifications can be made without departing from the scope of the present invention.

[0026]

As described above, according to the present invention, it is possible to realize the number of looks required by the system for mounting on a spacecraft regardless of the antenna size, the resolution and the swath width, thereby maintaining the resolution. As it is, it is possible to provide a synthetic aperture radar device capable of enlarging the antenna size and reducing power consumption.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a configuration of an embodiment of a synthetic aperture radar device according to the present invention.

FIG. 2 is a diagram for explaining various parameters in an orbiting satellite equipped with the synthetic aperture radar device.

FIG. 3 is a diagram for explaining a transmission pulse waveform and bandpass filter characteristics of the above-described embodiment.

[Explanation of symbols]

11 ... Antenna part, 12 ... Transmitting / receiving part, 121, 122 ...
High frequency oscillator, 123 ... Transmitter, 124 ... Timing control unit, 125, 126 ... Band pass filter (BPF),
127, 128 ... Receiver, 13 ... Signal processing unit, 131 ...
Mode controller, 132, 133 ... Analog / digital converter (A / D), 134 ... Multiplexer, 14 ... Communication antenna, 15 ... Communication antenna, 16 ... Separator, 171, 1
72 ... Synthetic aperture processing unit, 18 ... Addition processing unit, 19 ... Radar display.

Claims (4)

[Claims] 1. A transmission system for continuously transmitting a plurality of transmission pulses having different frequencies, a plurality of reception systems for individually receiving reflected signals corresponding to the plurality of transmission pulses, and respective receptions of the plurality of reception systems. A synthetic aperture radar apparatus comprising: a signal processing unit that performs synthetic aperture processing on signals independently and performs incoherent addition. 2. The transmission system and the plurality of reception systems are mounted on a spacecraft that moves on the earth, the signal processing unit is arranged in a ground station, and each reception signal of the plurality of reception systems is transmitted through a communication line. 2. The signal is transferred from the spacecraft to a ground station and input to the signal processing unit.
The synthetic aperture radar device described. 3. A transmission system for converting a linear frequency modulation signal into a pulse and transmitting the same, a reception system for receiving a reflection signal corresponding to the transmission pulse, and a reception signal of the reception system separated into a plurality of frequency bands, each of which is independent. A synthetic aperture radar device comprising: a signal processing unit that performs synthetic aperture processing and performs incoherent addition. 4. The transmission system and the reception system are mounted on a spacecraft that moves on the earth, the signal processing unit is arranged in a ground station, and each reception signal of the plurality of reception systems is transmitted through a communication line to the space. The synthetic aperture radar device according to claim 3, wherein the synthetic aperture radar device is configured to be transferred from a navigation body to a ground station and input to the signal processing unit.