JP2730296B2 - Ground mapping radar signal processing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing method and apparatus in a ground mapping mode of an on-board radar, for example.

[0002]

2. Description of the Related Art DBS (D
oppler Beam Sharpening) The principle of the signal processing method is shown in FIG.
At

[0003]

(Equation 1)

[0004] If the Doppler frequency at the beam center of the main lobe is “Equation 2”,

[0005]

(Equation 2)

[0006]

(Equation 3)

Therefore, "Equation 1" can be decomposed in the angular direction by Fourier transform, and an image can be reproduced. At this time, if the center frequency remains "Equation 2", an accurate image cannot be reproduced by Fourier transform. The phase correction is performed by setting the center frequency to zero. Conventionally, when performing this phase compensation, a calculation using a rectangular coordinate system has been performed as a method of calculating the distance between the radar platform and the target of the main beam center position.

FIG. 3 is a diagram showing a conventional ground mapping radar signal processing apparatus, in which 1 is a phased array antenna that radiates a transmission wave in a space in a specific direction and receives a reflected wave, and 2 is a phase control of an array antenna module. A beam controller for controlling the beam directivity of the phased array antenna 1, an exciter 3 for generating a transmission wave, and a signal 4 for supplying a signal from the transmitter 3 to the phased array antenna 1 and receiving and detecting a received signal. A circulator for supplying to the section, a receiver for converting the received signal from the circulator to a digital video received signal, an inertial platform sensor for detecting the oscillation of the radar platform, and an oscillation from the inertial platform sensor First-order compensation of the phase change of the received signal is performed directly from the data and beam direction. The primary phase compensation data generator for calculating the coordinate system, 8 en Focused SAR (Synthetic Ap
erture Radar),
A secondary phase compensation data generator 9 for calculating a secondary compensation for a phase change of a received signal in a rectangular coordinate system requires the use of the primary phase compensation data generator 7 and the secondary phase compensation data generator 8. A controller 10 for switching according to the resolution to be performed, a phase compensator for correcting the phase of the video reception signal using the phase compensation data from the primary phase compensation data generator or the secondary phase compensation data generator 8, 11 is an FFT for detecting a Doppler frequency corresponding to an azimuth direction in the beam.
(Fast Fourier Transform) calculator, 12 is the FFT
An amplitude detector for detecting the amplitude of a specific frequency from the data output from the arithmetic unit 11; an image data converter 13 for converting the data output from the amplitude detector 12 into image data; It is a display for displaying image data output from the device 13.

The conventional ground mapping radar signal processing apparatus is configured as described above. In FIG. 7, a squart angle "Equation 4" and an elevation angle "
Number 5 "to a transmitting wave from a phased array antenna 1 toward the ground surface of the target P ₀ in the direction, receives reflected waves from the ground surface at phased array antenna 1, by as receiver 5 circulator 4 The primary phase compensation data generator 7 or the secondary phase compensation data generator 8, which is converted into a digital video reception signal and selected by the controller 9 according to the resolution of the display image, outputs the platform fluctuation data from the inertial platform sensor 6. , And the phase compensator 10 performs phase correction on the video reception signal using the phase compensation data calculated by the phase compensation data generator 7 or 8, and
The Doppler frequency corresponding to the azimuth direction in the beam is detected by the FT arithmetic unit 11, and the image data converter 13 determines whether the image is a video or not, and a high-resolution ground map image can be displayed on the display 14.

[0010]

(Equation 4)

[0011]

(Equation 5)

FIGS. 4 and 5 show the calculation method in the phase compensation data generators 7 and 8, and the observation start time (t = 10) is obtained from the platform fluctuation data "number 6" from the inertial platform sensor 6 and the beam pointing direction. The target point P ₀ in the orthogonal coordinate system with the position of the aircraft 0) as the origin.
Is defined as “Equation 7”, and the distance between P ₀ and the aircraft is R ₀ , and the distance R between the radar and the target point at the observation time t is
Is represented by "Equation 8".

[0013]

(Equation 6)

[0014]

(Equation 7)

[0015]

(Equation 8)

Here,

[0017]

(Equation 9)

[0018]

[0019]

(Equation 10)

Then, R is

[0021]

[Equation 11]

## EQU1 ## Therefore, the change in distance

[0023]

(Equation 12)

Is

[0025]

(Equation 13)

## EQU1 ## Here, compensation using only the first-order term as “Equation 12” is referred to as first-order compensation, and compensation using up to the second-order term is referred to as second-order compensation. In this way, the amount of phase change can be obtained by calculating the distance change amount, and the phase compensation can be performed by multiplying the echo by the radar echo.

[0027]

[Equation 14]

In the actual calculation, the movement amount of the aircraft for each PRI (Pulse Repetition Interval) that is the observation sample interval is calculated.

[0029]

(Equation 15)

Then,

[0031]

(Equation 16)

Is

[0033]

[Equation 17] Becomes Therefore,

[0034]

(Equation 18)

## EQU1 ## Since “Equation 19” is the difference between the distance “Equation 20” at the i-th time and the distance “ Equation 21 ” at the i−1-th time,

[0036]

[Equation 19]

[0037]

(Equation 20)

[0038]

(Equation 21)

The amount of phase compensation is

[0040]

(Equation 22)

## EQU1 ## Thus, at each observation point,
The difference between the slant range at the previous observation point and the slant range at the observation start point are integrated, and the phase change at each observation point is calculated to compensate. It is carried out. When an attempt is made to obtain a resolution equal to or less than the allowable error "equation 26", an approximation error increases in the primary correction. Therefore, the primary correction and the secondary correction are switched depending on the resolution.

[0042]

(Equation 23)

Then, the primary compensation is

[0044]

(Equation 24)

The secondary compensation is as follows:

[0046]

(Equation 25)

Is as follows.

[0048]

The conventional ground mapping radar signal processing apparatus as described above has the following problems. That is, in the calculation using the conventional rectangular coordinate system, the calculation formula is complicated, the calculation error is large, and it is close to real-time processing. Therefore, when high resolution is not required, only the first-order compensation is required. Perform phase compensation,
When high resolution is required within the resolution range defined by the unfocused method, hardware is switched to perform secondary compensation. That is, when a high resolution is desired, many complicated calculations are performed, so that real-time processing is difficult, and the image quality is apt to deteriorate. The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a ground mapping radar signal processing device capable of obtaining an image at higher speed and with higher precision as compared with the related art.

[0049]

(Equation 26)

[0050]

The ground mapping radar signal processing device according to the present invention uses a polar coordinate system for the operation in the phase compensation, uses a simpler operation expression than the conventional one, and has a resolution with an allowable error of "number 26" or less. And a device therefor that can be obtained only by first-order compensation.

[0051]

According to the present invention, a high-quality radar image of the ground surface can be obtained in real time by an approximation calculation method using a polar coordinate system capable of suppressing the approximation error amount at high speed in the phase compensation amount calculation in the phase compensation. Can be obtained.

[0052]

FIG. 1 shows an embodiment of the present invention.
7, squint angle from the radar platform 15 "Number 4", and a transmitting wave from a phased array antenna 1 toward the ground surface of the target P ₀ in elevation "Number 5" direction, the reflected wave from the ground surface Is received by the phased array antenna 1, passed through the circulator 4, converted into a digital video reception signal by the receiver 5, and the phase compensation data generator 7 uses the platform sway data from the inertial platform sensor 6 to perform calculation in the polar coordinate system Calculate the phase compensation data and calculate the phase compensator 1
Reference numeral 0 denotes a phase correction for the video reception signal using the phase compensation data calculated by the phase compensation data generator 7, a FFT calculator 11 detects a Doppler frequency corresponding to the beam, and an image data converter. 13 enables the display 14 to display a high-resolution ground surface map image.

FIG. 2 shows a calculation method in the phase compensation data generator 7, in which the coordinates of the target P ₀ in the polar coordinate system are represented by “Equation 2” with the position of the aircraft at the observation start time (t = 0) as the origin.
7 "

[0054]

[Equation 27]

The relative distance R between the aircraft and the target at the time t is expressed as follows.

[0056]

[Equation 28]

Here,

[0058]

(Equation 29)

If the condition is satisfied, R can be approximated as follows using the binary series expansion.

[0060]

[Equation 30]

Accordingly, the distance variation “Equation 12” is

[0062]

(Equation 31)

Is obtained. Here, the phase compensation amount calculated by only the first-order term relating to time t is equal to or less than １ ／ of the transmission wavelength, which is an allowable error, below the synthetic aperture length for obtaining the resolution defined by the unfocused method. Therefore, the second and higher-order terms related to the time t can be ignored. Using this, the phase compensation amount “Equation 14” can be obtained, and the resolution within the resolution range defined by the unfocused method can be obtained only by the first-order compensation. The amount of aircraft movement for each PRI, which is the observation sample interval, is expressed as
Assuming 5 ”, the difference between each observation point and the slant range from the previous observation point is

[0064]

(Equation 32)

Is obtained. Therefore, the difference between the observation start point and the slant range from the observation point is

[0066]

[Equation 33]

Is obtained. In this case, if the phase compensation is performed using Equation 34, a phase compensation amount with sufficient accuracy can be obtained.

[0068]

(Equation 34)

[0069]

As described above, the present invention employs an arithmetic method using a polar coordinate system for the arithmetic processing for calculating the amount of phase compensation when performing phase compensation. Moreover, since the phase compensation amount with sufficient accuracy can be obtained only by the primary compensation without switching the apparatus, there is an effect that a high-quality image can be obtained in real time.

[Brief description of the drawings]

FIG. 1 is a ground mapping radar signal processing device according to an embodiment of the present invention.

FIG. 2 is a diagram of a phase compensation calculation processing method in a polar coordinate system.

FIG. 3 is a conventional ground mapping radar signal processing device.

FIG. 4 is a diagram showing a first-order compensation calculation processing method in a rectangular coordinate system.

FIG. 5 is a diagram showing a secondary compensation calculation processing method in a rectangular coordinate system.

FIG. 6 shows a DBS (Doppler) for an airborne radar.
FIG. 2 is a diagram illustrating the principle of signal processing.

FIG. 7 is a diagram illustrating a geometric relationship between a radar platform and a target surface to be mapped.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 phased array antenna 2 beam controller 3 exciter 4 circulator 5 receiver 6 inertial platform sensor 7 primary phase compensation data generator 8 secondary phase compensation data generator 9 controller 10 phase compensator 11 FFT (Fast Fourier Transform) Arithmetic unit 12 Amplitude detector 13 Image data converter 14 Display unit 15 Radar platform

Claims (2)

(57) [Claims] 1. An orthogonal coordinate system of a radar platform obtained by irradiating a radar beam from above to a target ground surface in the direction of a squint angle, receiving a reflected wave from a main lobe of an antenna, and obtaining an inertial platform sensor.
Real-time processing as a method of calculating the amount of change in the distance between the radar and the target at the center position of the main beam from the fluctuation information at
To minimize the error amount to below the allowable value.
Performance using only the first order term of the binary series expansion in the coordinate system
The phase compensation amount is calculated by using the formula, the phase compensation is performed on the echo signal of the main lobe, and the Doppler frequency in the azimuth direction is detected by Fourier transform processing, thereby obtaining an azimuth direction radar image in real time. A ground mapping radar signal processing method characterized in that: 2. An antenna that radiates a transmission wave from the sky to a space in a specific direction and receives a reflected wave, a beam controller that controls the beam directivity of the antenna, an exciter that generates a transmission wave, A receiver that converts the received signal of the antenna into a digital video received signal, an inertial platform sensor that detects the motion of the radar platform and outputs the motion data in a rectangular coordinate system, and a beam data and beam pointing from the inertial platform sensor When calculating the amount of phase change of the received signal from the direction, in order to keep all the processing within real time and to suppress the error amount to an allowable value or less,
A phase compensation data generator that calculates an amount of phase compensation in a polar coordinate system using an operation using only the first order term of a binomial series expansion, and a phase of a received signal using phase compensation data from the phase compensation data generator Compensator for correcting the azimuth, and FF for detecting the Doppler frequency corresponding to the azimuthal direction in the beam
T (Fast Fourier Transform)
An arithmetic unit, an image data converter for converting data output from the FFT arithmetic unit into image data, and a display for displaying image data output from the image data converter. Ground mapping radar signal processor.