JPS6122274A - Method for data processing of synthetic aperture radar - Google Patents

Abstract

PURPOSE:To obtain a processing method further enhanced in azimuth angle determination accuracy, by forming two synthetic aperture beams so as to have a sharp notch at the time of the imaging processing of an echo signal and determining an azimuth angle by utilizing said notch. CONSTITUTION:The echo signal from an object obtained by synthetic aperture radar is preliminarily received and recorded and imaging processing is performed on the basis of this recording data by a correlation method. At this time, a reference function for forming two main beams (synthetic aperture beams) 2-1, 2-2 forming a sharp notch (null) N is fabricated. The echo signal and a transmission wave are subjected to operation processing on the basis of the reference function while taking correlation to form two main beams 2-1, 2-2 for synthesizing the sharp notch N equivalently. If there is an object in the notch direction, the image of the object is erased from an image and, therefore, the azimuth angle of the object is determined from this phenomenon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a data processing method for improving the accuracy of azimuth determination in a synthetic aperture radar mounted on a flying object such as an artificial satellite.

[Technical background and problems of the invention]

Synthetic aperture radar is a side-looking radar mounted on a flying object such as an artificial satellite or aircraft that emits radio waves to the ground or above on the side of the moving object, and receives and synthesizes the reflected waves while moving. This makes it possible to effectively synthesize a large-aperture antenna with a relatively small-aperture antenna.It is used as a video sensor and can obtain high-resolution images in all weather conditions. .

FIG. 1 is an operational perspective view showing the principle of operation for realizing a synthetic aperture radar using a side-looking radar mounted on a moving flying object. A flying object such as an artificial satellite that moves at a speed of ■ on a specific route or orbit set in advance according to a desired purpose, follows an orbit at an altitude of h above the ground.
The onboard small aperture antenna emits transmission pulses at regular intervals. This transmission pulse has a beam width β spread,
It is radiated in a direction perpendicular to the orbit, and at point A1, for example, it becomes a reflected wave (radar echo) from the area BCDE on the ground and is received by a side-looking radar.

While the flying object is moving at a speed V, this reflected wave is manually transmitted one after another, and while observing the ground between lines # and #' parallel to the trajectory with a width of distance BC, the reflected waves are detected at each point in time. Amplitude information and phase information are recorded as the received signal. For example, the point target P is a point on the trajectory of the flying object. The reception of the transmission pulse begins at point A2, and the reception of the transmission pulse ends at point A2.

The reflected wave from the point target P is received during this time, and the received signal includes distance information as well as phase information corresponding to the constantly changing relative velocity.This received signal is recorded and subjected to batch calculation processing ( By using holographic processing), the same effect as using an antenna with a long aperture can be obtained (synthetic aperture method).

In this way, by recording and synthesizing the received signals acquired at each location one after another, a large aperture antenna several times to tens of thousands of times larger than the antenna actually installed can be used to target the target. This is equivalent to observing an object, and as shown in Figure 2, a synthetic aperture beam (synthetic beam pattern) 2 with a sharp beam width is formed in a direction perpendicular to the traveling direction X of the flying object (broadside direction). , clear images with improved lateral resolution can be obtained. Note that 1 is for each position in the traveling direction X of the flying object. , 8, . . . show the real aperture beam patterns.

Incidentally, during imaging processing of a synthetic aperture radar with such a configuration, the azimuth angle of the target point is usually determined using a synthetic aperture beam formed in one direction. Decisions can be made with high precision. However, there is a need for data processing means that can determine the azimuth angle with even higher precision.

[Purpose of the invention]

The present invention was made in response to a request for a data processing method for determining the azimuth of a conventional synthetic aperture radar.
It is an object of the present invention to provide a data processing method for synthetic aperture radar that further improves the accuracy of azimuth determination in synthetic aperture radar by applying a conventional direction finding method.

[Summary of the invention]

The present invention forms two synthetic aperture beams with sharp notches during imaging processing of echo signals of synthetic aperture radar, and utilizes the notches to enable extremely accurate azimuth determination. It is something to do.

[Embodiments of the invention]

Examples of the present invention will be described below.

First, the direction finding method applied in the present invention will be explained.

BACKGROUND ART Conventionally, a method using an Atcock type antenna or the like has been known as one of direction finding methods. As shown in Fig. 3, this detection method arranges two antenna elements S, S2 with wide beam widths at a relatively narrow interval d, and calculates the difference in their received outputs to detect signals in a specific direction. By forming an actual antenna pattern with a sharp notch (null) N and reading the azimuth angle θ at the point when the signal output from the target (T) disappears or becomes the weakest, the direction of arrival of the radio waves can be determined, that is, direction finding can be performed. It is something to do.

The present invention applies such a direction finding method to a synthetic aperture radar to perform data processing for highly accurate azimuth determination. , it is not formed as an actual antenna pattern, but is formed as two synthetic aperture beams that are combined isometrically.

That is, the hardware configuration uses the same synthetic aperture radar as the conventional one, receives and records the echo signal from the object obtained by the synthetic aperture radar, and uses the recorded data to create an image using a correlation method etc. When performing the conversion process, as shown in Fig. 4, a reference function is created that forms two main beams (synthetic aperture beams) 2-I+ 2-11 with a sharp notch N, and using that reference function, , two combined main beams L, , L are formed by correlating the echo signal and the transmitted wave and performing arithmetic processing.

Specifically, the reference function in forming such a synthetic aperture beam may be selected so that the first side rope has a size approximately equal to that of the main beam in addition to the synthetic aperture main beam that is normally formed. .

When the echo signal is converted into an image by performing the correlation calculation process as described above, in the output image, if there is a target T to be sought in the cutting direction (null direction) between the two synthetic aperture beams, the target T is The statue disappears from the image. Therefore, the "null direction" that appears in the imaging processing calculation at that time becomes the azimuth angle of the target solenoid T.

Since the two beams formed in the present invention are formed by synthetic aperture beams, they have a very narrow beam width. Therefore, the notch (null) formed between these combinations is also extremely sharp, which is even better than the azimuth determination accuracy of the conventional synthetic aperture radar data processing method or the conventional direction finding method. 1
Accuracy as high as ~3 orders of magnitude can be obtained.

Furthermore, the incision width "null width" formed by these two synthetic aperture beams in the present invention can theoretically be made as narrow as desired. Therefore, it becomes possible to determine the azimuth angle with extremely high accuracy.

〔Effect of the invention〕

As described above based on the embodiments, the present invention forms two synthetic aperture beams during imaging processing of synthetic aperture radar, and utilizes the extremely narrow "null width" formed thereby. Since this method determines the azimuth of a predetermined target, the azimuth can be determined with extremely high accuracy compared to conventional synthetic aperture radar image data processing methods.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of a general synthetic aperture radar,
FIG. 2 is a diagram showing a synthetic aperture beam formed by a synthetic aperture radar, FIG. 3 is a diagram explaining a direction finding method using a conventional ADC antenna, and FIG. 4 is a diagram showing a synthetic aperture beam of the present invention. FIG. 3 is a diagram illustrating how a synthetic aperture beam is formed by a direction finding method used in a radar data processing method. In the figure, 1 is a real aperture beam, 2 is a synthetic aperture beam,
2-+ and 2-z indicate synthetic aperture beams formed to form the incision.

Claims (1)

[Claims] In a synthetic aperture radar mounted on a flying object such as an artificial satellite, when processing echo signals into images, two synthetic aperture beams are equivalently formed with a sharp notch, and the direction of the notch is used to locate the target point. A synthetic aperture radar data processing method characterized by determining the azimuth angle of a synthetic aperture radar.