JPS6375686A - Spot light mapping radar apparatus - Google Patents

Abstract

PURPOSE:To perform azimuth compression with respect to all of points within the same range gate in an observation object by one reference signal, by adding a reference signal extending quantity calculating means and a reference signal extending means etc. CONSTITUTION:A reference signal generating means 8 determines a synthetic aperture time T on the basis of the position and speed informations of a flight body from an inertial navigation apparatus 9 to generate a reference signal of a range -(t/2)-+(T/2). A reference signal extending quantity calculation means 11 extends the reference signal from an antenna beam width to calculate a band width to be expanded and determines a time U to be extended from the instantaneous Doppler change rate of the reference signal to output the same to reference signal extending means 12. A reference signal extended to -(T-U)/2-+(T+U)/2 is supplied to an azimuth compression means 6 enhancing azimuth resolving power from the means 12. By this method, azimuth compression is performed with respect to all of the points within the same range gate in an observation object by one reference signal without performing a large quantity of calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spotlight mapping radar device that is mounted on a flying object such as an artificial satellite or an aircraft and that obtains an image of the ground or sea surface.

[Conventional technology]

We will briefly explain the configuration and principle of the conventional spotlight mapping radar system for this building. FIG. 4 is a block diagram showing the configuration of a conventional spotlight mapping radar device, and FIGS. 5 to 8 are diagrams for explaining its operating principle.

In the figure, (1) is a transmitter, (2) is a transmitter/receiver switch, (3) is an antenna, (4) is a receiver, (5) is a pulse compression means,
(6) is an azimuth compression means, (7) is a display, (8) is a reference signal generation means, (9) is an inertial navigation device,
QG is the antenna driving means, ((l is the transmission signal, (b)
is the received signal, (C) is the observed logarithm, (2) is the center point of the observation target e →, (E) is the leading edge point of the observation target f-q, (F)
is the trailing edge point of the observation target (c), (g) is the antenna beam, and ff+ is the flying object equipped with the spotlight matuping radar device.

The Spotlight Matuping radar device is a so-called synthetic aperture radar device with an antenna stabilization mechanism added to improve azimuth resolution.The principle of operation is described in Vat, Journal of the Japanese Society of Remote Sensing, 1. A
1 (1981), the contents of the article "Synthetic Aperture Radar" will be summarized and briefly explained.

A transmission pulse signal generated by a transmitter (1) is radiated to an observation target (c) on the ground or sea surface as a transmission signal via a transmission/reception switch (2) and an antenna (3).

The emitted transmission signal is reflected by the observation target, and the received signal ←
) is received again by the antenna (3).

The received signal is input to the receiver (4) via the transmitter/receiver switch. The receiver amplifies and detects the high frequency received signal and converts it into a baseband video signal. This video signal is input to pulse compression means (5) and pulse compressed in order to improve distance resolution. Pulse compression improves resolution in the direction perpendicular to the traveling direction of the flying object (a), that is, in the range (distance) direction. At this time, the range resolution ΔR is.

It is expressed as Cτ (1) (C: speed of light, τ: pulse width after pulse compression). After pulse compression, the video signal is passed through azimuth compression means (6)
Accordingly, processing is performed to improve the resolution in the traveling direction of the flying object, that is, the azimuth direction. Azimuth compression is performed using the Doppler effect caused by the movement of the flying object. Now, suppose that a flying object is moving in a uniform straight line at a speed of V as shown in FIG. 5, and consider a case where a point in the observation target is at a distance R1o at time 1=00. Relative distance i@R(tl is R(t+=JT[
Yotsuki A v2t2(2) , :, RO+RO' is given by. Therefore, the instantaneous Doppler frequency fd(t)
using the transmission wavelength λ.

is given by As is clear from the third equation, the received signal is a chirp signal whose instantaneous Doppler frequency changes with time t. At this time.

This is because λ, Ro, and ■ in the third equation are known parameters or parameters that can be measured by the inertial navigation device (9).

The history of the time change of the Doppler frequency (at the point), that is, the Doppler history, is generated by the reference signal generating means (8 (
It can be calculated by Therefore.

By correlating a series of received signals for each range with the reference signal generated by the reference signal generating means (8), azimuth compression is possible in the same way as pulse compression. At this time, as shown in FIG. 6, in the case of a synthetic aperture radar whose antenna beam is fixed directly horizontally to the traveling direction of the flying object, the two synthetic aperture times To are limited by the antenna beam width θB. Azimuth resolution Δro is.

For general synthetic aperture radar, it is given by θB or several degrees.

, RθB O〒□ (7) (7) If the following approximate expression is established and the relationship between beam width θB and antenna aperture diameter θB=λ/D is used.

ΔrOki I (8) is established, and the azimuth resolution of the 2 synthetic aperture length is 1/ of the antenna aperture diameter.
Limited to 2.

On the other hand, in a spotlight matuping radar that has an antenna stabilizing mechanism, as shown in FIG. It can be determined by the beam stabilization angle θS independently of the beam width θB. At this time, the two synthetic aperture times T are given by , and the azimuth resolution Δr is given by . By setting O8〉θB, Δr×Δ
It is clear that r O"" 2 αυ holds true, and the spotlight mapping radar device has improved azimuth resolution compared to the synthetic aperture radar device in which the antenna is fixed directly to the side.

Through the above processing, the received signal, which has been further resolved in both the range direction and the azimuth direction, is displayed on the display (7).
Displayed as a dimensional radar image.

[Problem that the invention seeks to solve]

Conventional spotlight matuping radar equipment is configured with two or more spotlights, making it possible to achieve higher resolution than synthetic aperture radar equipment with antennas fixed directly to the side. Since it is necessary to generate a reference signal for each point, there is a problem in that the amount of calculation increases. As shown in Figure 6, when points (), ni), and (he) within the observation target are observed using a synthetic aperture radar device, the Doppler history of each point is as follows.

It can be expressed as (al, (bl, fcl) in FIG. 7a.

Therefore, by correlating with the reference signal having the Doppler history shown in Figure 7b, the dots can be determined according to the respective positions of the two points (E), 2), and (E) as shown in Figure 7C. puller history (al fbl (d) can be transformed perpendicular to the time axis. In other words, azimuth compression is possible with one reference signal. However, in spotlight mapping radar equipment, the second
As shown in the figure, the Doppler history of the two points (E), (N), and (F) for beam stabilization is.

This can be expressed in Figure 8a. As shown in Figure 8a.

The three-point Doppler history is a chirp signal with different Doppler frequencies at the start and end points, so in order to azimuth compress the Doppler history in (a), the reference shown in Figure 8b is used. To azimuthally compress the Doppler history of (cl), we need the signal (α) and (bl (cl).

(b) and (γ) reference signals are required, respectively.

The results of azimuth compression using the reference signals (α), (b), and (r) are shown in FIG. 8C. From FIG. 8C, it can be seen that in the reference signal (d, only the Doppler history (al) is completely compressed, in V?I only Tbl, and in (γ1 (
It can be seen that only cl is completely compressed.

In this way, in the conventional spotlight mapping radar device, while the azimuth resolution is improved.

It is necessary to generate a large number of reference signals.

There was a problem that the amount of calculation increased.

This invention was made to solve the above-mentioned problems, and uses one reference signal to calculate the azimuth pressure m(
The purpose of the present invention is to obtain a spotlight mapping radar device capable of focusing.

[Means for solving problems]

In order to enable focusing on all points within the same range gate within an observation target using one reference signal, the spotlight mapping radar device according to the present invention includes a reference signal extension amount in addition to a conventional reference signal generation means. A reference signal extension means for extending the reference signal based on the calculation means and the amount of extension (time) is added.

[Effect]

In the spotlight mapping radar device of this invention, the maximum and minimum instantaneous Doppler frequencies of all points within the same range gate of the observation target are determined from the distance Ro to the observation target, the velocity V of the flying object, and the antenna beam width θB. Automatically calculate the value.

The reference signal is extended so that one reference signal can cover the range from the minimum value to the maximum value.

As a result, focusing (azimuth compression) is possible at all points within the same range gate of the observation target using one reference signal, so the amount of calculation can be reduced in the spotlight mapping radar device of the present invention.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention is shown in FIG. 1, and its operating situation is shown in FIG. 2, and the drawings will be described in detail. In FIG. 1, ttn and (13 are newly added in this invention. They are reference signal extension amount calculation means and reference signal extension means. Operations of other devices or means (1) to fl[) in the figure is equivalent to the conventional device, so in the following explanation, the azimuth compression of the spotlight mapping radar device according to the present invention will be described, focusing on the operations of the reference signal extension amount calculation means ni+ and the reference signal extension means α. . Now, as shown in Figure 2, the leading edge (ho) of the observation target (c) is determined by the antenna beam @vB.

It is assumed that the reference signal generating means (8) generates a reference signal by using two points as reference points, ie, the center) and the trailing edge.

Based on the position and speed information of the flying object measured by the inertial navigation device (9), the reference signal generating means (8) calculates the distance Ro from the flying object to the reference point.
The velocity of the flying object V and the desired resolution Δr are set, and the 2 composite aperture time T is determined by Equation 11.

The reference signal generating means generates a reference signal within the range of the synthetic aperture time T (-T≦t≦7) shown in FIG. 3b. The reference signal extension amount calculation means αV first calculates the bandwidth A to be extended by extending the reference signal from the antenna beam width θB. Then, the time U to be extended is determined from the oscillation rate (slope) of the instantaneous Doppler frequency of the reference signal, and the extended time U is output to the reference signal extension means az. In the reference signal extension means a3.

As shown in Figure 3b, the reference signal is
/' 2 extended and 2 generation time is -(T+U)/2 to +(T
The reference signal extended to +U)/2 is supplied to the azimuth compression means (6).

In the azimuth compression means (6), the extended reference signal (Fig. 3b) is matched with the input signal No. 3 (Fig. 3a), so that the beam 1 is adjusted as shown in Fig. 3c.
Doppler hist of 3 points 61JG=l (to) in the cave! J
Since the power of (al (bl (d) is concentrated at the time corresponding to each position, the Doppler history of fal (bl (cl) can be simultaneously compressed in azimuth with one reference signal.

〔Effect of the invention〕

As described above, according to the present invention, the reference signal is extended by the reference signal extension amount calculation means and the reference signal extension means so as to cover the entire Doppler frequency band within the antenna beam width. Since the signals can be used to focus all points within the field of view determined by the beam width and within the same range gate, the amount of calculation can be reduced compared to conventional spotlight mapping radars.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a spotlight mapping radar device according to an embodiment of the present invention, and FIG. 2 is a geometry of the spotlight mapping radar device. 3a, 3b, and 3c are explanatory diagrams of the azimuth compression operation of the spotlight mapping radar device according to the present invention, FIG. 4 is a configuration diagram of a conventional spotlight mapping radar device, and FIG. 5 and Fig. 6 shows the geometry of the synthetic aperture radar system - 9 Figs. 7a, 7b and 7c show the geometry of the synthetic aperture radar system [alpha]
Figure 8a. FIGS. 8b and 8c are explanatory diagrams of the azimuth compression operation of the conventional spotlight mapping radar device. In the figure, (1) is a transmitter, and (2) is a transmission/reception switch. (3) is the antenna, (4) is the receiver, and f5+ is the pulse compression means. (6) is an azimuth compression means, (7) is a display, (8) is a reference signal generation means, (9) is an inertial navigation device, a
O is an antenna driving means, ciυ is a reference signal extension amount calculation means, and (Iz is a reference signal extension means. In the figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A spotlight mapping radar device is installed on a flying object such as an artificial satellite or an aircraft, and targets a specific area on the ground or sea surface, and stabilizes the antenna beam toward the observation target. an inertial navigation device that performs measurements; a reference signal generating means that is connected to the inertial device and generates a reference signal from the measurement results; and a reference that calculates the amount by which the reference signal should be extended according to the antenna beam width, that is, the time and band. A reference that is connected to both the signal extension amount calculation means, the reference signal generation means, and the reference signal extension means, and extends the reference signal generated by the reference signal generation means according to the extension amount determined by the reference signal extension amount calculation means. The signal extension means and the azimuth compression means are connected to the reference signal extension means and the pulse compression means and perform azimuth compression by correlating the reference signal after extension with the received signal after pulse compression. A spotlight mapping radar device featuring: