CN115902895B - Single-ratio ultra-high precision signal parameter estimation method for inverse synthetic aperture radar - Google Patents
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Abstract
The invention discloses a single-ratio ultra-high precision signal parameter estimation method for an inverse synthetic aperture radar, which effectively improves the parameter estimation precision by quantizing single bits of signals and utilizing the multiple relation between harmonic components and fundamental component phase parameters generated by single-bit quantization.
Description
Technical Field
The invention relates to the technical field of signal processing, in particular to a single-ratio ultra-high precision signal parameter estimation method, a system, a terminal and a computer readable storage medium for an inverse synthetic aperture radar.
Background
Signal parameter estimation plays a vital role in the fields of radar signal processing and the like, for example, a radar system can acquire information such as target azimuth, altitude, speed, rotating speed and the like by analyzing a target echo signal.
Inverse Synthetic-Aperture Radar (ISAR) is an important branch in the development process of the SAR, and the ISAR can image targets in a long distance all the day and all the weather, thereby playing an important role in the military and civil fields such as aerospace exploration, strategic defense, port monitoring and the like. However, the imaging results obtained by ISAR imaging systems are typically range-Doppler planar projection results of the target and do not provide target orientation specific dimensional information. The azimuth calibration technology can realize target rotation speed estimation by analyzing the change rule of the phase parameter of the echo signal of the target scattering point, so that an ISAR imaging result is converted from a distance Doppler plane (unit: m-Hz) to a distance-azimuth plane (unit: m-m), and further target azimuth size information is given. However, the scaling accuracy depends on the echo signal parameter estimation accuracy. The existing parameter estimation method is larger in error or higher in calculation or hardware implementation complexity. For example, a method of using frequency removal to estimate a Linear Frequency Modulated (LFM) signal parameter, however, the estimation accuracy of such a method is related to the search interval and may be limited by the frequency resolution of the fourier transform; for example, the parameter estimation accuracy is improved by using an iterative adaptive method, however, the searching process of the method has higher computational complexity and poorer real-time performance.
The single-bit quantification can remarkably reduce the burden of data acquisition, storage and transmission, realizes miniaturization and cheapness of products, has higher application value, and is a research hotspot in the current signal processing field. However, single bit quantization can produce harmonic and intermodulation interference, resulting in poor imaging quality degradation. At present, researches on how to reduce harmonic and intermodulation effects are mostly conducted in the academic circles, and researches on improving signal parameter estimation accuracy by utilizing harmonic are not reported. For example, a single frequency threshold is designed to inhibit the harmonic wave generated by single bit quantization, so that the purpose of improving the imaging effect is achieved, but the method aims at harmonic wave inhibition and does not utilize harmonic wave information.
Accordingly, the prior art is still in need of improvement and development.
Disclosure of Invention
The invention mainly aims to provide a single-ratio ultra-high precision signal parameter estimation method, a system, a terminal and a computer readable storage medium for an inverse synthetic aperture radar, and aims to solve the problems of large error and high implementation complexity of a parameter estimation algorithm in the prior art.
In order to achieve the above purpose, the present invention provides a single-ratio ultra-high precision signal parameter estimation method for an inverse synthetic aperture radar, which comprises the following steps:
according to the geometrical relationship among the target scattering points, the radar and the rotation center, calculating to obtain the distance between the target scattering points and the radar;
calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time;
Calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point, and obtaining an expression of the echo signal of the target scattering point;
carrying out single-bit quantization processing on the echo signals of the target scattering points;
Acquiring higher harmonic waves generated by the target scattering point echo signals after single-bit quantization processing, and estimating the frequency modulation rate of the higher harmonic waves to obtain the frequency modulation rate of the target scattering point echo signals before quantization;
estimating the frequency modulation rate of echo signals of target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to distance coordinates to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and the azimuth scaling factor according to the slope of the straight line, and carrying out azimuth scaling of the distance Doppler image according to the azimuth scaling factor.
Optionally, the method for estimating the single-ratio ultra-high precision signal parameter for the inverse synthetic aperture radar, wherein the calculating to obtain the distance between the target scattering point and the radar according to the geometric relationship among the target scattering point, the radar and the rotation center specifically includes:
in ISAR imaging, the motion of a target relative to a radar is decomposed into a translational component along the sight line of the radar and a rotation component rotating around a certain point, and the target is regarded as a turntable target rotating around the certain point after the translational component of the target is compensated through motion compensation;
according to the geometrical relationship among the target scattering point, the radar and the rotation center, the distance between the target scattering point i and the radar is calculated:
Wherein the coordinates of the scattering point i on the target are (x i,yi), the distance from the scattering point i to the rotation center O is R i, the distance from the radar to the rotation center O is R r, and there is R r>>Ri, the distance from the scattering point i to the radar is R i', the included angle between the line connecting the scattering point i and the point O and the y axis is θ 0, the target rotation speed is w 0,tm＝mT0, the slow time is T 0, the pulse repetition period is m=0, 1, k, m-1, m is the number of pulses for imaging.
Optionally, the method for estimating the single-ratio ultra-high precision signal parameter for the inverse synthetic aperture radar, wherein the calculating, according to the change condition of the distance between the target scattering point and the radar with respect to slow time, obtains doppler frequencies corresponding to the target scattering point at different moments, specifically includes:
according to the change condition of the distance between the target scattering point and the radar about slow time, calculating Doppler frequencies corresponding to the target scattering point i at different moments as follows:
Where dR i′(tm)/dtm denotes deriving R i′(tm) from t m, λ is the wavelength of the radar emission signal.
Optionally, in the method for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar, the calculating phase information of the target scattering point echo according to doppler frequencies corresponding to different moments of the target scattering point to obtain an expression of the target scattering point echo signal specifically includes:
According to Doppler frequencies corresponding to different moments of a target scattering point, the phase information of the corresponding echo is obtained as follows:
After the phase information of the echo is obtained, the echo signal from the target scattering point i is modeled as:
Wherein j represents imaginary unit, sigma i represents amplitude, frequency is f i＝2w0xi/lambda, and tuning frequency is The tuning frequency is a linear function with respect to the distance coordinate y i, the slope of the line is
Optionally, the method for estimating the single-bit ultra-high precision signal parameter for the inverse synthetic aperture radar, wherein the performing single-bit quantization on the target scattering point echo signal specifically includes:
simply written as phi i(tm in equation (3) is phi i, then equation (4) is s i(tm)＝σiexp(jφi), and s i(tm) is subjected to single-bit quantization, and the quantized signal is in the form of:
Wherein Σ (·) represents summation, a 0 =1, a k =2 when k is equal to or greater than 1, a k =0 when k is even, a k≠0,Ak represents the magnitude of k signal components when k is odd, sign (·) represents a sign operation, sign (x) =1 when x >0, sign (x) = -1 when x >0, sign (x) = 0 when x=0;
Then s 1(tm) is ultimately expressed as:
wherein k=1 corresponds to a signal fundamental component, and k is larger than or equal to 1 corresponds to a signal k subharmonic component;
After single-bit quantization processing, a multiple relationship exists between the phase parameters of the signal harmonic wave and the fundamental wave.
Optionally, the method for estimating the single-ratio ultra-high precision signal parameter for the inverse synthetic aperture radar includes obtaining a higher harmonic wave generated by the target scattering point echo signal after single-bit quantization processing, estimating a frequency modulation rate of the higher harmonic wave, and obtaining the frequency modulation rate of the target scattering point echo signal before quantization, and specifically includes:
When estimating the frequency of the signal by using a parameter estimation method such as frequency removal and the like, if the frequency searching interval is delta, the maximum estimation error of the frequency of the formula (4) is delta/2;
According to the formula (6), after single-bit quantization processing of the signal, the frequency and the frequency modulation rate of the k harmonic components are k times of that of the original signal;
And (3) obtaining the frequency modulation of the echo signal of the target scattering point before quantization by estimating the frequency modulation of the k harmonic component in the formula (6), wherein the estimation error of the maximum frequency modulation is delta/(2 k).
Optionally, in the method for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar, the estimating frequency modulation rates of echo signals of target scattering points of different distance units, fitting frequency modulation rate estimation results of different distance units with respect to distance coordinates to obtain a straight line with a slope related to a target rotation speed, calculating a straight line slope, obtaining the target rotation speed and a direction scaling factor according to the straight line slope, and performing direction scaling of a distance doppler image according to the direction scaling factor, including:
Obtaining the frequency modulation rate gamma i of the echo signals of the target scattering points of different range units based on the relation between the frequency modulation rate of the signals and the range coordinates of the target scattering points;
Fitting frequency modulation rate estimation results of different distance units with respect to a distance coordinate y to obtain a straight line with a slope related to a target rotating speed, and solving a straight line slope c;
calculating the target rotating speed according to the slope c of the straight line And calculating an azimuth scaling factor delta a＝λ/(2w0 T according to the target rotating speed, wherein T represents imaging accumulation duration;
And carrying out azimuth scaling on the range-Doppler image according to the azimuth scaling factor.
In addition, in order to achieve the above object, the present invention further provides a single-ratio ultra-high precision signal parameter estimation system for an inverse synthetic aperture radar, wherein the single-ratio ultra-high precision signal parameter estimation system for an inverse synthetic aperture radar comprises:
the target distance calculation module is used for calculating the distance between the target scattering point and the radar according to the geometric relationship among the target scattering point, the radar and the rotation center;
The Doppler frequency calculation module is used for calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time;
The echo signal expression module is used for calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point to obtain an expression of the echo signal of the target scattering point;
the single-bit quantization processing module is used for carrying out single-bit quantization processing on the echo signals of the target scattering points;
the frequency modulation calculation module is used for obtaining higher harmonic waves generated by the target scattering point echo signals after single-bit quantization processing, estimating the frequency modulation rate of the higher harmonic waves and obtaining the frequency modulation rate of the target scattering point echo signals before quantization;
the azimuth calibration module is used for estimating the frequency modulation rate of the echo signals of the target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to the distance coordinates to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and an azimuth calibration factor according to the slope of the straight line, and carrying out azimuth calibration on the distance Doppler image according to the azimuth calibration factor.
In addition, to achieve the above object, the present invention also provides a terminal, wherein the terminal includes: the method comprises the steps of a memory, a processor and a single-ratio ultra-high precision signal parameter estimation program which is stored in the memory and can run on the processor and is oriented to the inverse synthetic aperture radar, wherein the single-ratio ultra-high precision signal parameter estimation program is executed by the processor to realize the single-ratio ultra-high precision signal parameter estimation method which is oriented to the inverse synthetic aperture radar and is described above.
In addition, in order to achieve the above object, the present invention also provides a computer readable storage medium, where the computer readable storage medium stores a single-ratio ultra-high precision signal parameter estimation program for an inverse synthetic aperture radar, and the single-ratio ultra-high precision signal parameter estimation program for the inverse synthetic aperture radar implements the steps of the single-ratio ultra-high precision signal parameter estimation method for the inverse synthetic aperture radar described above when the single-ratio ultra-high precision signal parameter estimation program for the inverse synthetic aperture radar is executed by a processor.
According to the geometrical relationship among the target scattering points, the radar and the rotation center, the distance between the target scattering points and the radar is calculated; calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time; calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point, and obtaining an expression of the echo signal of the target scattering point; carrying out single-bit quantization processing on the echo signals of the target scattering points; acquiring higher harmonic waves generated by the target scattering point echo signals after single-bit quantization processing, and estimating the frequency modulation rate of the higher harmonic waves to obtain the frequency modulation rate of the target scattering point echo signals before quantization; estimating the frequency modulation rate of echo signals of target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to distance coordinates to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and the azimuth scaling factor according to the slope of the straight line, and carrying out azimuth scaling of the distance Doppler image according to the azimuth scaling factor. The invention improves the precision of parameter estimation by utilizing harmonic components generated by single-bit quantization, and realizes high-precision parameter estimation with low calculation and hardware realization complexity.
Drawings
FIG. 1 is a flow chart of a preferred embodiment of the method for estimating parameters of a single-ratio ultra-high precision signal for an inverse synthetic aperture radar of the present invention;
FIG. 2 is a schematic diagram of a transfer target model in a preferred embodiment of the method for estimating parameters of a single-ratio ultra-high precision signal for an inverse synthetic aperture radar of the present invention;
FIG. 3 is a schematic diagram of a simulation ship scattering point model in a preferred embodiment of the method for estimating parameters of a single-ratio ultra-high precision signal for an inverse synthetic aperture radar of the present invention;
FIG. 4 is a schematic diagram of the frequency modulation rate distribution and fitting result based on a conventional scaling method;
FIG. 5 is a schematic diagram of a scaling result based on a conventional scaling method;
FIG. 6 is a schematic diagram of frequency modulation distribution and fitting result based on single bit quantization in a preferred embodiment of the method for estimating parameters of single-ratio ultra-high precision signals for inverse synthetic aperture radar according to the present invention;
FIG. 7 is a schematic diagram of a scaling result based on single-bit quantization in a preferred embodiment of the method for estimating parameters of a single-ratio ultra-high precision signal for an inverse synthetic aperture radar of the present invention;
FIG. 8 is a schematic diagram of a preferred embodiment of the single-ratio ultra-high precision signal parameter estimation system of the present invention for an inverse synthetic aperture radar;
FIG. 9 is a schematic diagram of the operating environment of a preferred embodiment of the terminal of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clear and clear, the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The method for estimating the single-ratio ultra-high precision signal parameters of the inverse synthetic aperture radar according to the preferred embodiment of the invention, as shown in fig. 1, comprises the following steps:
and step S10, calculating to obtain the distance between the target scattering point and the radar according to the geometric relationship among the target scattering point, the radar and the rotation center.
Specifically, in ISAR imaging, the motion of a target relative to a radar is decomposed into a translational component along the line of sight of the radar and a rotational component rotating around a certain point (a certain point), the translational component of the target is compensated by motion compensation, the target is regarded as a turntable target rotating around the certain point, and as shown in fig. 2, the distance between a target scattering point i and the radar is calculated according to the geometrical relationship among the target scattering point, the radar and the rotation center:
Wherein the coordinates of the scattering point i on the target are (x i,yi), the distance from the scattering point i to the rotation center O is R i, the distance from the radar to the rotation center O is R r, and there is R r>>Ri, the distance from the scattering point i to the radar is R 'i (i.e., R' i(tm)), the angle between the line connecting the scattering points i and O and the y axis is θ 0, the target rotation speed is w 0,tm＝mT0 is slow (time related to the pulse repetition period), T 0 is the pulse repetition period, and m=0, 1, k, m-1, m is the number of pulses for imaging.
And step S20, calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time.
Specifically, according to the change condition of the distance between the target scattering point and the radar about slow time, calculating Doppler frequencies corresponding to the target scattering point i at different moments as follows:
Where dR i′(tm)/dtm denotes deriving R i′(tm) from t m, λ is the wavelength of the radar emission signal.
And step S30, calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point, and obtaining an expression of the echo signal of the target scattering point.
Specifically, according to the Doppler frequencies corresponding to different moments of the target scattering point, the phase information of the corresponding echo can be obtained as follows:
After obtaining the phase information of the echo, at this time, the echo signal from the target scattering point i may be modeled as:
from the echo signal expression, the echo signal is LFM (Linear Frequency Modulated, linear frequency modulation) signal, wherein j represents imaginary unit, sigma i represents amplitude, frequency is f i＝2w0xi/lambda, and modulation frequency is The tuning frequency is a linear function with respect to the distance coordinate y i, the slope of the line is
And S40, performing single-bit quantification processing on the echo signals of the target scattering points.
Specifically, phi i(tm) in the formula (3) is abbreviated as phi i, then the formula (4) is expressed as s i(tm)＝σiexp(jφi), and s i(tm) is subjected to single-bit quantization, and the quantized signal is in the form of:
Wherein Σ (·) represents summation, a 0 =1, a k =2 when k is equal to or greater than 1, a k =0 when k is even, a k≠0,Ak represents the magnitude of k signal components when k is odd, sign (·) represents a sign taking operation, sign (x) =1 when x >0, sign (x) = -1 when x >0, and sign (x) = -0 when x=0.
Then, s 1(tm) is finally expressed as:
wherein k=1 corresponds to a signal fundamental component, and k is larger than or equal to 1 corresponds to a signal k subharmonic component;
As can be seen from the formula (6), after single-bit quantization processing, a multiple relationship exists between the phase parameters of the signal harmonic wave and the fundamental wave.
And S50, obtaining higher harmonics generated by the target scattering point echo signals after single-bit quantization processing, and estimating the frequency modulation rate of the higher harmonics to obtain the frequency modulation rate of the target scattering point echo signals before quantization.
Specifically, when estimating the frequency of the signal by using a parameter estimation method such as frequency removal, if the frequency search interval is Δ, the maximum estimation error of the frequency of equation (4) is Δ/2; according to the formula (6), after single-bit quantization processing of the signal, the frequency and the frequency modulation rate of the k harmonic components are k times of that of the original signal; at this time, the frequency modulation rate of the k harmonic component in the formula (6) is estimated, so as to obtain the frequency modulation of the echo signal of the target scattering point before quantization, and the corresponding maximum frequency modulation rate estimation error is Δ/(2 k).
For example, the third harmonic component of the signal in equation (6) is in the form of:
the frequency of the third harmonic component is gamma i-3＝3γi, when the frequency searching interval is delta, the maximum estimation error corresponding to gamma i-3 is delta/2, and at the moment, the maximum estimation error corresponding to gamma i is delta/6. From this, it can be seen that the k harmonic components generated by single bit quantization can effectively improve the gamma i estimation accuracy. In the formula (6), the amplitude a k gradually decreases with the increase of k, so that the amplitude of k harmonic components gradually decreases, and therefore, when the parameter estimation accuracy is improved by using single-bit quantization, an excessive harmonic is not suitable, and a more ideal estimation accuracy can be obtained by using a third harmonic generally.
And S60, estimating the frequency modulation rate of the echo signals of the target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to the distance coordinate to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and the azimuth calibration factor according to the slope of the straight line, and calibrating the azimuth of the distance Doppler image according to the azimuth calibration factor.
Specifically, as can be seen from the formula (4), the tuning frequency of the signal is related to the distance-wise coordinate of the scattering point of the target, and thus the azimuth scaling process is: estimating the frequency modulation rate gamma i of the echo signals of the target scattering points of the different range units by a parameter estimation method based on the process (the frequency modulation rate of the signals is related to the range coordinates, so that the frequency modulation rate under the different range coordinates needs to be calculated to obtain the straight line of the frequency modulation rate relative to the range coordinates); fitting frequency modulation rate estimation results of different distance units with respect to a distance coordinate y to obtain a straight line with a slope related to a target rotating speed, and solving a straight line slope c; calculating the target rotating speed according to the slope c of the straight lineAnd calculating an azimuth scaling factor delta a＝λ/(2w0 T according to the target rotating speed, wherein T represents imaging accumulation duration; and carrying out azimuth scaling on the range-Doppler image according to the azimuth scaling factor.
The effect of the invention can be further illustrated by experimental results, and the software used in the experiment is MATLAB.
The experimental conditions are as follows: the target azimuth dimension of the simulated ship is 25.5m, the target rotating speed is 0.01rad/s, the signal to noise ratio is 10dB, and the frequency modulation rate searching interval is delta=0.01 s -2 as shown in fig. 3.
Fig. 4 shows experimental results corresponding to a conventional calibration method, namely experimental results obtained by directly performing parameter estimation on echo signals of target scattering points of different distance units, fig. 4 shows distribution conditions of frequencies corresponding to the echo signals of different distance units, and the estimated result of the target rotating speed is 0.0116rad/s according to the slope of a fitted straight line. Fig. 5 is a calibration result obtained from the target rotational speed estimation result, and the target azimuth dimension is 21.98m.
FIG. 6 shows the result of frequency modulation distribution obtained by parameter estimation of the third harmonic signal after single bit quantization, wherein the target rotation speed estimation result is 0.0098rad/s by fitting the linear slope. Fig. 7 is a scaling result based on single bit quantization, and the target azimuth dimension is 26.02m.
According to the rotation speed estimation result and the calibration result, the single-bit quantization is utilized to improve the estimation precision of the echo signal parameters, so that higher azimuth calibration precision is obtained, and the experimental result proves the effectiveness of the invention.
Furthermore, the advantages of the present invention can be also illustrated from the distribution of the frequency modulation rate estimation results in the vicinity of the fitted straight line in fig. 4 and 6. According to the formula (4), the relationship between the frequency of the signal and the distance direction is linear, i.e. the estimated frequency result should be strictly distributed on the fitting straight line. From the distribution of the frequency modulation rate estimation results in the vicinity of the fitted straight line in the two graphs, it can be seen that the linear distribution of the frequency modulation rate is poor in fig. 4 due to the large parameter estimation error. In fig. 6, the frequency modulation rate estimation result is more closely distributed near the fitting straight line, so that the parameter estimation accuracy can be effectively improved based on single-bit quantization.
The beneficial effects are that:
(1) The single-bit quantization is applied to signal parameter estimation, so that the parameter estimation precision can be effectively improved.
(2) The implementation process is simple, and the single-bit quantization process only needs to perform symbol bit taking operation on the data.
(3) The data processing operation after single-bit quantization is performed in a binary form and can be realized through logic operation, so that the method has lower computational complexity and can greatly reduce hardware complexity and cost.
(4) The invention takes ISAR azimuth calibration as an example to describe how to realize high-precision signal parameter estimation by single-bit quantization, and the invention can be applied to other situations requiring parameter estimation.
Further, as shown in fig. 8, based on the above method for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar, the present invention further provides a system for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar, where the system for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar includes:
A target distance calculating module 51, configured to calculate a distance between the target scattering point and the radar according to a geometric relationship among the target scattering point, the radar and the rotation center;
The doppler frequency calculation module 52 is configured to calculate, according to a change condition of a distance between the target scattering point and the radar with respect to slow time, doppler frequencies corresponding to different times of the target scattering point;
the echo signal expression module 53 is configured to calculate phase information of an echo of the target scattering point according to doppler frequencies corresponding to different moments of the target scattering point, so as to obtain an expression of an echo signal of the target scattering point;
The single-bit quantization processing module 54 is configured to perform single-bit quantization processing on the target scattering point echo signal;
the frequency modulation rate calculation module 55 is configured to obtain a higher harmonic wave generated by the target scattering point echo signal after single bit quantization processing, estimate a frequency modulation rate of the higher harmonic wave, and obtain a frequency modulation rate of the target scattering point echo signal before quantization;
The azimuth calibration module 56 is configured to estimate frequency modulation rates of echo signals of target scattering points of different distance units, fit frequency modulation rate estimation results of different distance units with respect to distance coordinates to obtain a line with a slope related to a target rotation speed, calculate a slope of the line, obtain the target rotation speed and an azimuth calibration factor according to the slope of the line, and perform azimuth calibration of the distance doppler image according to the azimuth calibration factor.
Further, as shown in fig. 9, based on the method and the system for estimating the single-ratio ultra-high precision signal parameters facing the inverse synthetic aperture radar, the invention also correspondingly provides a terminal, which comprises a processor 10, a memory 20 and a display 30. Fig. 9 shows only some of the components of the terminal, but it should be understood that not all of the illustrated components are required to be implemented and that more or fewer components may alternatively be implemented.
The memory 20 may in some embodiments be an internal storage unit of the terminal, such as a hard disk or a memory of the terminal. The memory 20 may in other embodiments also be an external storage device of the terminal, such as a plug-in hard disk provided on the terminal, a smart memory card (SMART MEDIA CARD, SMC), a Secure Digital (SD) card, a flash memory card (FLASH CARD), etc. Further, the memory 20 may also include both an internal storage unit and an external storage device of the terminal. The memory 20 is used for storing application software installed in the terminal and various data, such as program codes of the installation terminal. The memory 20 may also be used to temporarily store data that has been output or is to be output. In an embodiment, the memory 20 stores a single-ratio ultra-high precision signal parameter estimation program 40 facing the inverse synthetic aperture radar, and the single-ratio ultra-high precision signal parameter estimation program 40 facing the inverse synthetic aperture radar can be executed by the processor 10, so as to implement the single-ratio ultra-high precision signal parameter estimation method facing the inverse synthetic aperture radar in the present application.
The processor 10 may in some embodiments be a central processing unit (Central Processing Unit, CPU), microprocessor or other data processing chip for running the program code or processing data stored in the memory 20, for example performing the inverse synthetic aperture radar oriented single-ratio ultra-high precision signal parameter estimation method, etc.
The display 30 may be an LED display, a liquid crystal display, a touch-sensitive liquid crystal display, an OLED (Organic Light-Emitting Diode) touch, or the like in some embodiments. The display 30 is used for displaying information at the terminal and for displaying a visual user interface. The components 10-30 of the terminal communicate with each other via a system bus.
In an embodiment, the steps of the method for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar described above are implemented when the processor 10 executes the single-ratio ultra-high precision signal parameter estimation program 40 for inverse synthetic aperture radar in the memory 20.
The invention also provides a computer readable storage medium, wherein the computer readable storage medium stores a single-ratio ultra-high precision signal parameter estimation program facing the inverse synthetic aperture radar, and the single-ratio ultra-high precision signal parameter estimation program facing the inverse synthetic aperture radar realizes the steps of the single-ratio ultra-high precision signal parameter estimation method facing the inverse synthetic aperture radar when being executed by a processor.
In summary, the present invention provides a method, a system, a terminal and a computer readable storage medium for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar, where the method includes: according to the geometrical relationship among the target scattering points, the radar and the rotation center, calculating to obtain the distance between the target scattering points and the radar; calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time; calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point, and obtaining an expression of the echo signal of the target scattering point; carrying out single-bit quantization processing on the echo signals of the target scattering points; acquiring higher harmonic waves generated by the target scattering point echo signals after single-bit quantization processing, and estimating the frequency modulation rate of the higher harmonic waves to obtain the frequency modulation rate of the target scattering point echo signals before quantization; estimating the frequency modulation rate of echo signals of target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to distance coordinates to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and the azimuth scaling factor according to the slope of the straight line, and carrying out azimuth scaling of the distance Doppler image according to the azimuth scaling factor. The invention improves the precision of parameter estimation by utilizing harmonic components generated by single-bit quantization, and realizes high-precision parameter estimation with low calculation and hardware realization complexity.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or terminal that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or terminal. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or terminal that comprises the element.
Of course, those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by a computer program for instructing relevant hardware (e.g., processor, controller, etc.), the program may be stored on a computer readable storage medium, and the program may include the above described methods when executed. The computer readable storage medium may be a memory, a magnetic disk, an optical disk, etc.
It is to be understood that the invention is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims.
Claims (6)
1. The single-ratio ultra-high precision signal parameter estimation method for the inverse synthetic aperture radar is characterized by comprising the following steps of:
according to the geometrical relationship among the target scattering points, the radar and the rotation center, calculating to obtain the distance between the target scattering points and the radar;
calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time;
Calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point, and obtaining an expression of the echo signal of the target scattering point;
carrying out single-bit quantization processing on the echo signals of the target scattering points;
Acquiring higher harmonic waves generated by the target scattering point echo signals after single-bit quantization processing, and estimating the frequency modulation rate of the higher harmonic waves to obtain the frequency modulation rate of the target scattering point echo signals before quantization;
estimating the frequency modulation rate of echo signals of target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to distance coordinates to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and an azimuth calibration factor according to the slope of the straight line, and carrying out azimuth calibration of a distance Doppler image according to the azimuth calibration factor;
The calculating to obtain the distance between the target scattering point and the radar according to the geometric relation among the target scattering point, the radar and the rotation center specifically comprises the following steps:
in ISAR imaging, the motion of a target relative to a radar is decomposed into a translational component along the sight line of the radar and a rotation component rotating around a certain point, and the target is regarded as a turntable target rotating around the certain point after the translational component of the target is compensated through motion compensation;
according to the geometrical relationship among the target scattering point, the radar and the rotation center, the distance between the target scattering point i and the radar is calculated:
Wherein the coordinates of a scattering point i on the target are (x i,yi), the distance from the scattering point i to the rotation center O of the target is R i, the distance from the radar to the rotation center O of the target is R r, R r>>Ri exists, the distance from the scattering point i to the radar is R' i, the included angle between the connecting line of the scattering point i and the O point of the target and the y axis is theta 0, the target rotating speed is w 0,tm＝mT0, the slow time is T 0, the pulse repetition period is m=0, 1, & gt, and M-1, M are the number of pulses for imaging;
according to the change condition of the distance between the target scattering point and the radar about slow time, calculating Doppler frequencies corresponding to the target scattering point at different moments, wherein the Doppler frequencies specifically comprise:
according to the change condition of the distance between the target scattering point and the radar about slow time, calculating Doppler frequencies corresponding to the target scattering point i at different moments as follows:
Where dR 'i(tm)/dtm denotes deriving R' i(tm) about t m, λ being the wavelength of the radar emission signal;
calculating the phase information of the echo of the target scattering point according to the Doppler frequencies corresponding to different moments of the target scattering point to obtain an expression of the echo signal of the target scattering point, wherein the expression specifically comprises the following steps:
According to Doppler frequencies corresponding to different moments of a target scattering point, the phase information of the corresponding echo is obtained as follows:
After the phase information of the echo is obtained, the echo signal from the target scattering point i is modeled as:
Wherein j represents imaginary unit, sigma i represents amplitude, frequency is f i＝2w0xi/lambda, and tuning frequency is The tuning frequency is a linear function with respect to the distance coordinate y i, the slope of the line is
The single-bit quantization processing for the target scattering point echo signal specifically includes:
simply written as phi i(tm in equation (3) is phi i, then equation (4) is s i(tm)＝σiexp(jφi), and s i(tm) is subjected to single-bit quantization, and the quantized signal is in the form of:
Wherein Σ (·) represents summation, a 0 =1, a k =2 when k is equal to or greater than 1, a k =0 when k is even, a k≠0,Ak represents the magnitude of k signal components when k is odd, sign (·) represents a sign operation, sign (x) =1 when x >0, sign (x) = -1 when x >0, sign (x) = 0 when x=0;
Then s 1(tm) is ultimately expressed as:
wherein k=1 corresponds to a signal fundamental component, and k is larger than or equal to 1 corresponds to a signal k subharmonic component;
After single-bit quantization processing, a multiple relationship exists between the phase parameters of the signal harmonic wave and the fundamental wave.
2. The method for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar according to claim 1, wherein the method for estimating frequency modulation rate of higher harmonics generated by the target scattering point echo signal after the acquisition of single-bit quantization processing, comprises:
When the frequency modulation parameter estimation method is used for estimating the frequency modulation of the signal, the frequency modulation frequency searching interval is delta, and the maximum estimation error of the frequency modulation frequency of the formula (4) is delta/2;
According to the formula (6), after single-bit quantization processing of the signal, the frequency and the frequency modulation rate of the k harmonic components are k times of that of the original signal;
And (3) obtaining the frequency modulation of the echo signal of the target scattering point before quantization by estimating the frequency modulation of the k harmonic component in the formula (6), wherein the estimation error of the maximum frequency modulation is delta/(2 k).
3. The method for estimating single-ratio ultra-high precision signal parameters for inverse synthetic aperture radar according to claim 2, wherein the estimating the frequency modulation rate of the target scattering point echo signals of different distance units, fitting the frequency modulation rate estimation results of different distance units with respect to distance coordinates to obtain a straight line with a slope related to the target rotation speed, calculating a straight line slope, obtaining the target rotation speed and an azimuth scaling factor according to the straight line slope, and performing azimuth scaling of a distance doppler image according to the azimuth scaling factor, specifically comprises:
Obtaining the frequency modulation rate gamma i of the echo signals of the target scattering points of different range units based on the relation between the frequency modulation rate of the signals and the range coordinates of the target scattering points;
Fitting frequency modulation rate estimation results of different distance units with respect to a distance coordinate y to obtain a straight line with a slope related to a target rotating speed, and solving a straight line slope c;
calculating the target rotating speed according to the slope c of the straight line And calculating an azimuth scaling factor delta a＝λ/(2w0 T according to the target rotating speed, wherein T represents imaging accumulation duration;
And carrying out azimuth scaling on the range-Doppler image according to the azimuth scaling factor.
4. A single-ratio ultra-high precision signal parameter estimation system facing an inverse synthetic aperture radar applied to the single-ratio ultra-high precision signal parameter estimation method facing an inverse synthetic aperture radar according to any one of claims 1 to 3, characterized in that the single-ratio ultra-high precision signal parameter estimation system facing an inverse synthetic aperture radar comprises:
the target distance calculation module is used for calculating the distance between the target scattering point and the radar according to the geometric relationship among the target scattering point, the radar and the rotation center;
The Doppler frequency calculation module is used for calculating Doppler frequencies corresponding to the target scattering points at different moments according to the change condition of the distance between the target scattering points and the radar about slow time;
The echo signal expression module is used for calculating the phase information of the echo of the target scattering point according to Doppler frequencies corresponding to different moments of the target scattering point to obtain an expression of the echo signal of the target scattering point;
the single-bit quantization processing module is used for carrying out single-bit quantization processing on the echo signals of the target scattering points;
the frequency modulation calculation module is used for obtaining higher harmonic waves generated by the target scattering point echo signals after single-bit quantization processing, estimating the frequency modulation rate of the higher harmonic waves and obtaining the frequency modulation rate of the target scattering point echo signals before quantization;
the azimuth calibration module is used for estimating the frequency modulation rate of the echo signals of the target scattering points of different distance units, fitting the frequency modulation rate estimation results of the different distance units with respect to the distance coordinates to obtain a straight line with a slope related to the target rotating speed, solving the slope of the straight line, obtaining the target rotating speed and an azimuth calibration factor according to the slope of the straight line, and carrying out azimuth calibration on the distance Doppler image according to the azimuth calibration factor.
5. A terminal, the terminal comprising: the method comprises the steps of realizing the single-ratio ultra-high precision signal parameter estimation method for the inverse synthetic aperture radar according to any one of claims 1-3 when the single-ratio ultra-high precision signal parameter estimation program for the inverse synthetic aperture radar is executed by the processor.
6. A computer-readable storage medium, characterized in that the computer-readable storage medium stores a single-ratio ultra-high precision signal parameter estimation program for an inverse synthetic aperture radar, which when executed by a processor, implements the steps of the single-ratio ultra-high precision signal parameter estimation method for an inverse synthetic aperture radar according to any one of claims 1-3.
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