JPH0587919A - Polarimetric synthetic aperture radar apparatus - Google Patents

Abstract

PURPOSE:To make the apparatus compact and to make calibration easy by switching a transmission signal to two antenna systems for every two transmission triggers, and switching and taking out signals from the two antennas for every transmission trigger, thereby to form a receiving means of one system. CONSTITUTION:A control part 8 outputs a control signal 8a to make a switching part 2 switch for every two transmission trigger signals. At the same time, the control part 8 generates a control signal 8b to control a switching part 9 to switch for every transmission trigger signal. As a result, at every transmitting time, the signals received by an antenna AH for horizontally polarized waves and an antenna AV for vertically polarized waves are input to a terminal of the switching part 9 via circulators 4b, 4a, respectively. Each polarized wave receiving signal is input to a receiving part 5 by the switching operation of the switching part 9. Accordingly, four kinds of data H-H, H-V, V-H, V-V are obtained by one receiving system. It becomes possible to obtain an SAR image to an optional polarized wave through calculations of the data.

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 using a flying object such as an artificial satellite or an aircraft as a platform, and particularly to SAR for arbitrary polarization from data acquired by a combination of horizontal / vertical polarizations. The present invention relates to a polarimetric synthetic aperture radar device that forms an image.

[0002]

2. Description of the Related Art A synthetic aperture radar is a device for emitting two-dimensional data for reproducing an image on the ground by emitting radio waves from a mobile platform such as an artificial satellite to the ground on the side of the traveling direction. In this synthetic aperture radar, pulse compression technology is used to improve range resolution, and synthetic aperture technology is used to improve azimuth resolution. The synthetic aperture technology is a technology that effectively uses the movement of the on-board platform to effectively obtain a high resolution equivalent to that of an antenna with an extremely large diameter.

The synthetic aperture radar is a kind of image radar, and its image (SAR image) is a two-dimensional mapping of the scattered power from an object on the ground surface. The scattered power is affected by the roughness of the object, the complex permittivity, the shape, the frequency of the transmission signal, the polarization, the incident angle, and the like. That is, more information can be obtained from the target object by changing the frequency, polarization, and incident angle.

The polarimetric synthetic aperture radar device is a device intended to obtain as much information as possible on a target object by paying attention to polarization and changing polarization. Conventionally, this polarimetric synthetic aperture radar device has a transmission unit 1, a switching unit 2, an antenna unit 3, a circulator 4a, the same unit 4b, a reception unit 5a, and the same unit 5b as shown in FIG. And a signal processing unit 6, and a control means for controlling each unit such as the transmission unit 1 and the switching unit 2 to control the whole is provided outside the drawing. The antenna unit includes a horizontal polarization antenna A _H and a vertical polarization antenna A _V.

The transmitting unit 1 transmits a transmission trigger signal (see FIG. 4).
In response to (a), a linear-frequency-modulated transmission signal (called a chirp signal) is generated and output to the switching unit 2. The switching unit 2 alternately selects the switching terminals S1 and S2 for each transmission trigger signal, switches the output transmission signal of the transmission unit 1 and sends it to the antenna unit 3 via the circulators (4a, 4b).

For example, as shown in FIG. 4, when the transmission trigger signals occur at times t _i , t _{i + 1} , t _{i + 2} , and t _{i + 3} (FIG. 4 (a)), The switching unit 2 selects the switching terminal S1 at the times t _i and t _{i + 2} , and selects the switching terminal S2 at the times t _{i + 1} and t _{i + 3.} As a result, the horizontal polarization antenna A _H is transmitted at times t _i and t _{i + 2} (FIG. 4 (b)), and is transmitted from the vertically polarized antenna A _V at times t _{i + 1} and t _{i + 3} (FIG. 4). As in (c), horizontal polarization transmission and vertical polarization transmission are alternately performed for each transmission trigger signal.

Then, with respect to the transmission at each time, the scattered wave from the object 7 on the ground surface includes a vertical polarization component and a horizontal polarization component, which are received by two antennas at the same time,
The signal received by the horizontal polarization antenna A _H is received and processed by the reception unit 5 b via the circulator 4 b and input to the signal processing unit 6. The signal received by the vertical polarization antenna A _V is transmitted by the circulator 4 a. The signal is processed by the receiving unit 5a via the signal and input to the signal processing unit 6.

As described above, in the polarimetric synthetic aperture radar device, four types of objects, HH (horizontal polarized wave transmission-horizontal polarized wave reception), HV, VH, and VV are always used for the object. Data is obtained (Fig. 4 (d)), the data is calculated, and SA for arbitrary polarization (combination of polarizations shifted by 90 °)
It is a synthetic aperture radar device that obtains an R image, and is characterized in that information about a target object can be dramatically increased.

[0009]

As described above, the conventional polarimetric synthetic aperture radar system has a problem that the system becomes large and the calibration becomes complicated because two receiving systems are required. .

An object of the present invention is to provide a polarimetric synthetic aperture radar device which can be downsized and facilitated for calibration.

[0011]

In order to achieve the above object, the polarimetric synthetic aperture radar device of the present invention has the following configuration. That is, the polarimetric synthetic aperture radar device of the present invention is a synthetic aperture radar device mounted on a flying body such as an artificial satellite or an aircraft, in which a transmission signal linearly frequency-modulated is horizontally polarized and vertically polarized. Polarimetric Synthetic Aperture Radar Device for Obtaining SAR Image Regarding Arbitrary Polarization from Data Acquired by Combination of Horizontal / Vertical Polarization Signals from Object Received by Both Antennas A means for switching and outputting the transmission signals to the two antenna systems for each two transmission triggers; a means for switching and extracting the reception signals of the two antennas for each transmission trigger; the switching and extracting 2 One receiving means for performing reception processing on a system reception signal;

[0012]

Next, the operation of the polarimetric synthetic aperture radar system of the present invention constructed as described above will be described. In the present invention, the transmission signals alternately transmitted from the two antennas are switched for each two transmission triggers, while the reception signals of the two antennas are switched for each transmission trigger and extracted. As a result, only one system is required as the receiving means, and the device can be downsized and the calibration can be facilitated.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a polarimetric synthetic aperture radar device according to an embodiment of the present invention. In FIG. 1, the same reference numerals are given to the same components as those of the conventional device, but in the present invention, as shown in the figure, two conventional receiving units (5a, 5a,
Instead of b), one receiving unit 5 is added, and a switching unit 9 is added to the input stage of this receiving unit 5 so that received signals from two antennas are input via the switching unit 9, and the control unit 8 Some functions have been added. Hereinafter, the part relating to the present invention will be mainly described.

The control unit 8 outputs to the switching unit 2 a control signal 8a for performing a switching operation for every two transmission trigger signals, while an additional switching unit 9 performs a switching operation for each transmission trigger signal. A control signal 8b that causes the operation is output.

As a result, for example, as shown in FIG. 2, the transmission trigger signals are time t _i , t _{i + 1} , t _{i + 2} , t _{i + 3,} ...
2 (a), the switching unit 2 determines that the time t _i
The switching terminal S1 is selected at the same time t _{i + 1} , and the switching terminal S2 is selected at the time t _{i + 2} and the same time t _{i + 3} . Then, from the antenna A _H for horizontally polarized waves are transmitted at time t _i the same t _{i + 1} (FIG. 2 (b)), the time from the antenna A _V for vertically polarized waves t _{i + 2} at the same t _{i + 2} is transmitted (as shown in FIG. 2C, horizontal polarization transmission and vertical polarization transmission are alternately performed for every two transmission trigger signals.

As described above, for each transmission, the scattered wave from the object 7 on the ground surface includes a vertically polarized component and a horizontally polarized component, which are received by two antennas at the same time. To be done. Therefore, the horizontal polarization antenna A _H and the vertical polarization antenna A _V are different from the conventional ones in t _i , t _{i + 1} , t.
_{i + 2, t i + 3} ...... corresponding polarized signal is received at each time of (FIG. 2 (d)), switching unit signal received with horizontal polarization antenna A _H through the circulator 4b The signal input to one of the switching terminals of 9 and received by the vertically polarized antenna A _V is input to the other switching terminal of the switching unit 9 via the circulator 4a.

Next, the switching section 9 performs a switching operation for each transmission trigger signal, so that the receiving section 5 is shown in FIG.
As shown in (H−H) → (H−V) → (V−
Each polarized wave reception signal is input in the order of (H) → (V-V).

Thus, according to the present invention, in one receiving system, four H-H, H-V, V-H, and V-V are used as in the conventional case.
Obtain the data of the kind, calculate it,
It is possible to obtain a SAR image for a combination of polarizations that are offset by 0 °.

In addition, in the present invention, as compared with the conventional method,
It takes twice as long to get a set of data,
If the cycle of the transmission trigger signal is set to double, no problem will occur.

[0020]

As described above, according to the polarimetric synthetic aperture radar device of the present invention, the transmission signals alternately transmitted from the two antennas are switched for every two transmission triggers, while the two antennas of the two antennas are switched. Since the reception signal is switched and extracted for each transmission trigger, only one system of receiving means is required, and there is an effect that the device can be downsized and calibration can be facilitated.

[Brief description of drawings]

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

FIG. 2 is an operation time chart of the polarimetric synthetic aperture radar device shown in FIG.

FIG. 3 is a configuration block diagram of a conventional polarimetric synthetic aperture radar device.

FIG. 4 is an operation time chart of the polarimetric synthetic aperture radar device shown in FIG.

[Explanation of symbols]

1 transmitter 2 switching unit 3 antenna unit 4a circulator 4b circulator 5 receiving unit 6 signal processing unit 7 target 8 control unit 9 switching unit _AV vertical polarization antenna A _H horizontal polarization antenna

Claims (1)

[Claims] 1. A synthetic aperture radar device mounted on a flying object such as an artificial satellite or an aircraft, wherein a linear frequency modulated transmission signal is alternately transmitted from a horizontal polarization antenna and a vertical polarization antenna, In a polarimetric synthetic aperture radar device for acquiring a SAR image of an arbitrary polarization from data acquired by combining horizontal / vertical polarization signals from an object received by both antennas; Means for switching and outputting to the antenna system every two transmission triggers; Means for retrieving the reception signals of the two antennas for each transmission trigger; and Receiving processing for the two reception signals switched and retrieved. A polarimetric synthetic aperture radar device comprising: one receiving means;