CN114994650A - Improved propeller rotating speed estimation method - Google Patents
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Abstract
The invention provides an improved propeller rotation speed estimation method, which comprises the following steps: step 1: DEMON demodulation spectrum analysis: carrying out DEMON analysis on the received ship radiation noise signal x (n) to obtain a DEMON demodulation spectrum analysis result X (f); step 2: extracting a DEMON modulation line spectrum; and step 3: determining alternative fundamental frequencies; and 4, step 4: extracting line spectrum harmonic sequence; and 5: extracting the energy characteristics of the alternative fundamental frequency line spectrum harmonic sequence and estimating the rotating speed of the propeller.
Description
Technical Field
The invention relates to the technical field of underwater acoustic signal processing, in particular to an improved propeller rotating speed estimation method.
Background
The passive sonar target classification and identification is used as a main function of a sonar system, is a technical field of key development of various countries, and has an important application value, the traditional passive target classification and identification is mainly realized by analyzing target radiation noise and extracting characteristics such as a line spectrum, a continuous spectrum and a demodulation spectrum (DEMON spectrum) representing the target physical attribute based on the target physical attribute and the radiation noise characteristic, and the quality of the characteristic extraction is directly related to the quality of an identification result.
The demodulation spectrum characteristic is one of the most common characteristics in passive target classification and identification, and is also the most important characteristic, and parameter information of the target propeller can be obtained through demodulation spectrum analysis, wherein the parameter information mainly comprises propeller rotating speed, propeller rate, propeller number, shaft number and the like, and the information is an important parameter for representing the physical attribute of the target and is also one of the most effective information for target classification and identification.
The method can effectively extract information such as the rotating speed (fundamental frequency), the blade number and the like of the target radiation noise demodulation spectrum structure under the condition of clear and complete structure, but in the experimental process, the target noise demodulation spectrum structure is often unclear and the harmonic structure is incomplete, such as fundamental frequency loss, blade rate loss, only fundamental frequency and partial harmonic and the like, which brings great trouble to propeller parameter information estimation, the target rotating speed is difficult to accurately estimate, the blade number and the shaft number are more difficult to estimate, the wrong propeller parameter information estimation result can directly cause the identification result to be wrong, and the accuracy of the propeller rotating speed estimation is low.
Disclosure of Invention
The problem to be solved by the present invention is to provide an improved propeller rotation speed estimation method for overcoming the above-mentioned disadvantages in the prior art, which solves the problem of low accuracy of propeller rotation speed estimation in the prior art.
The above object of the present invention is achieved by the following technical solutions: an improved propeller speed estimation method, said estimation method comprising the steps of:
step 1: DEMON demodulation spectrum analysis: carrying out DEMON analysis on the received ship radiation noise signals x (n) to obtain a DEMON demodulation spectrum analysis result X (f);
and 2, step: extracting a DEMON modulation line spectrum;
and 3, step 3: determining alternative fundamental frequencies;
and 4, step 4: extracting line spectrum harmonic sequence;
and 5: extracting the energy characteristics of the harmonic sequence of the alternative fundamental frequency line spectrum and estimating the rotating speed of the propeller.
The invention is further configured to: the step 1 further comprises:
1.1 band-pass filtering: according to the modulation strength change conditions of the target in different frequency bands, a band-pass filter is selected to perform band-pass filtering on a received ship radiation noise signal x (N), so that a band-pass filtering signal xf (N) is obtained, wherein N is 1,2
In the formula (I), the compound is shown in the specification,
representing a convolution operation; h is BP (k 1 ) Is the coefficient of a band-pass filter, k 1 ＝1,2,...,N BP ；N BP Is the order of the band pass filter;
1.2 detection: detecting the band-pass filtered signal by adopting a square law to obtain a detected signal y 1 (n)＝|xf(n)| 2 ,n＝1,2,...,N；
1.3 low-pass filtering: to detection signal y 1 (N), N is 1,2, N, and N is low-pass filtered to obtain a low-pass filtered signal
Wherein the content of the first and second substances,
representing a circular convolution operation; h is a total of LP (k 2 ) Is a low pass filter coefficient, k is 1,2 LP ；N LP Is the order of the low-pass filter;
1.4 downsampling: for low-pass filtered signal y 2 (N, N is 1, 2.. times.N, down-sampling processing is carried out to obtain down-sampled signals
y 3 (i)＝y 2 (1:D:N),i＝1,2,...,N/D
In the formula, D is a down-sampling multiple;
1.5 Power Spectrum analysis: accumulating K batches of data to the NFFT point, NFFT KN/D, and recording as y 4 (i),i＝1,2,..KN/D, and performing power spectrum analysis on the accumulated data,
wherein, X (f) is the DEMON demodulation spectrum analysis result, and K is the accumulation batch.
9. The invention is further configured to: the step 2 further comprises:
2.1, analyzing the DEMON demodulation spectrum analysis result X (f), if the frequency point f j The spectral line is determined as a line spectrum when the spectral line meets the following two constraint conditions:
①f j at a spectral line energy of maximum in the neighborhood, i.e. X (f) j )>X(f j -1) and X (f) j )>X(f j +1) while
X(f j )>X(f j -2) and X (f) j )>X(f j +2)；
②f j The energy of the spectral line is β dB above the background of the spectral line, i.e.,
in the formula, M B The sliding window is long for the background; XC (f) is the calculation result of the background of the demodulation spectrum;
2.2, zeroing the spectral line positions which do not meet the constraint conditions, reserving the spectral line positions which meet the conditions, and traversing all frequency points to obtain a DEMON modulation line spectrum extraction result P L (f) That is to say that,
the invention is further configured to: and the beta is 6-10 dB.
The invention is further configured to: the step 3 further comprises:
3.1 Co-extraction to M L The root line spectrum and the corresponding frequency point position are k i ,i＝1,2,...,M L Respectively calculate the frequency difference between two line spectraObtaining the difference frequency calculation result delta f i I 1,2, M is the difference frequency number, i.e. M is the number of the difference frequencies
3.2 setting the percentage of frequency error δ, then [. DELTA.f i -δ△f i ,△f i +δ△f i ]Considering the difference frequency in the range as the same difference frequency, counting the occurrence times of each difference frequency, and selecting the line spectrum and the difference frequency in the preset frequency range as alternative fundamental frequencies sf i I ═ 1, 2., P are the number of candidate base frequencies.
The invention is further configured to: the preset frequency range is greater than 0.5Hz and less than 40 Hz.
The invention is further configured to: the step 4 further comprises: for alternative fundamental frequencies sf i And i is 1,2, P, analyzing the relation between the extracted line spectrum and the alternative fundamental frequency, setting a frequency error threshold delta, and if the value of | f is satisfied i -round(f i /sf i )×sf i When | < delta, the line spectrum is regarded as the frequency multiplication harmonic wave of the current alternative fundamental frequency, and so on, the frequency multiplication harmonic wave corresponding to all alternative fundamental frequencies is obtained, and for the alternative fundamental frequency sf i The set of line spectrum harmonic wave sequences is expressed as
ZX i ＝{f j ||f j -round(f j /sf i )×sf i |≤△}，
In the formula (f) j E F, F is the set of extracted line spectra, i 1, 2.
The invention is further configured to: the step 5 further comprises:
5.1 calculating the energy values of all line spectrum harmonic sequence respectively, wherein the set of the line spectrum harmonic sequence energy values is expressed as
E i ＝∑ j {X(f j )||f j -round(f j /sf i )×sf i |≤△}，
In the formula, X (f) j ) Representing f in DEMON demodulation spectrum j Corresponding amplitude, f j Belongs to F, and F is an extracted line spectrum setI ═ 1,2, ·, N;
5.2 selecting the line spectrum sequence with the maximum energy and the harmonic number not less than the preset value, wherein the corresponding fundamental frequency is the propeller fundamental frequency f shaft The estimated result of the rotating speed of the propeller is rn ═ f shaft X 60 rpm.
In conclusion, the beneficial technical effects of the invention are as follows:
(1) the improved propeller rotating speed estimation method is provided for solving the problem that propeller rotating speed estimation is inaccurate under the conditions of fundamental frequency missing or incomplete demodulation spectrum structure and the like in practice, and can effectively realize rotating speed estimation under the conditions of fundamental frequency missing or incomplete demodulation spectrum structure.
(2) According to the method, the extracted DEMON modulation line spectrum and line spectrum difference frequency are used as alternative fundamental frequencies, and propeller rotating speed estimation is carried out through a harmonic search and energy comparison method, so that the problem of propeller rotating speed estimation under the condition that the modulation fundamental frequencies are absent can be effectively solved, and the problem of propeller rotating speed estimation under the condition that the fundamental frequencies are clear but the harmonic structures are incomplete can be effectively solved.
(3) Simulation and actual data analysis results show that: the method provided by the invention effectively realizes the rotating speed estimation under the condition of unclear or incomplete DEMON modulation line spectrum structure.
Drawings
FIG. 1 is a flow chart of an improved propeller speed estimation method of the present invention;
FIG. 2 is a diagram of the result of the estimation of the rotational speed of the propeller under the condition of complete harmonic structure of the simulation data according to the present invention;
FIG. 3 is a diagram of the result of the estimation of the rotational speed under the condition of missing fundamental frequency of the propeller according to the simulation data of the present invention;
FIG. 4 is a diagram of the result of the estimation of the rotational speed under the condition of incomplete harmonic structure of the simulation data propeller in the present invention;
FIG. 5 is a diagram of the estimation result of the rotation speed under the condition of missing fundamental frequency of the actual data propeller in the present invention.
Detailed Description
In order to make the technical means, the creation features, the achievement purposes and the functions of the invention clearer and easier to understand, the invention is further explained in the following with the accompanying drawings and the detailed description.
(one) implementation procedure
As shown in fig. 1, the present invention proposes an improved propeller speed estimation method, said estimation method comprising the steps of:
step 1: DEMON demodulation spectrum analysis: DEMON analysis is carried out on the received ship radiation noise signal x (n) to obtain a DEMON demodulation spectrum analysis result X (f).
1.1 band-pass filtering: according to the modulation intensity change conditions of the target in different frequency bands, a band-pass filter is selected to perform band-pass filtering on a received ship radiation noise signal x (N) to obtain a band-pass filtering signal xf (N), wherein N is 1,2
In the formula (I), the compound is shown in the specification,
representing a convolution operation; h is BP (k 1 ) Is the coefficient of a band-pass filter, k 1 ＝1,2,...,N BP ；N BP Is the order of the band-pass filter;
1.2 detection: detecting the band-pass filtering signal by adopting a square law to obtain a detection signal y 1 (n)＝|xf(n)| 2 ,n＝1,2,...,N；
1.3, low-pass filtering: to detection signal y 1 (N), N is 1,2, N, and N is low-pass filtered to obtain a low-pass filtered signal
Wherein the content of the first and second substances,
representing a circular convolution operation; h is LP (k 2 ) Is a low pass filter coefficient, k is 1,2 LP ；N LP Is the order of the low pass filter;
1.4 downsampling: for low-pass filtered signal y 2 (N, N is 1, 2.. times.N, down-sampling processing is carried out to obtain down-sampled signals
y 3 (i)＝y 2 (1:D:N),i＝1,2,...,N/D
In the formula, D is a down-sampling multiple;
1.5 Power Spectrum analysis: accumulating K batches of data to the NFFT point, NFFT KN/D, and recording as y 4 (i) 1,2, KN/D, and performing power spectrum analysis on the accumulated data,
wherein, X (f) is the DEMON demodulation spectrum analysis result, and K is the accumulation batch.
In the step 1, an algorithm for calculating a low-frequency demodulation spectrum by demodulating a received broadband signal is called DEMON analysis in sonar signal processing, a demodulated low-frequency time domain signal is called an envelope signal, a power spectrum of the demodulated low-frequency time domain signal is called a DEMON demodulation spectrum, a DEMON demodulation spectrum analysis result X (f) can be obtained by analyzing and processing the DEMON demodulation spectrum, and ship physical characteristics such as propeller rotation speed and the like can be obtained by the DEMON analysis, so that the method has important value for automatic and intelligent signal processing of underwater equipment.
And 2, step: and extracting the DEMON modulation line spectrum.
2.1, analyzing the DEMON demodulation spectrum analysis result X (f), if the frequency point f j The spectral line is determined as a line spectrum when the spectral line meets the following two constraint conditions:
①f j at a spectral line energy of maximum in the neighborhood, i.e. X (f) j )>X(f j -1) and X (f) j )>X(f j +1) while
X(f j )>X(f j -2) and X (f) j )>X(f j +2)；
②f j The energy of the spectral line is higher than the background of the spectral line by beta dB, i.e.,
in the formula, M B The sliding window is long for the background; XC (f) is the calculation result of the background of the demodulation spectrum; beta is 6-10 dB;
2.2 zeroing spectral line positions which do not meet the constraint conditions, reserving spectral line positions which meet the constraint conditions, and traversing all frequency points to obtain a DEMON modulation line spectrum extraction result P L (f) That is to say that,
in the step 2, a DEMON modulation line spectrum is extracted through maximum value search and signal-to-noise ratio screening in combination with characteristic representation of the line spectrum, and the DEMON modulation line spectrum can reflect rhythm information of relevant physical attributes of ships, such as propeller rotating speed, propeller blade number and the like.
And step 3: an alternative fundamental frequency is determined.
3.1 Co-extraction to M L The root line spectrum and the corresponding frequency point position are k i ,i＝1,2,...,M L Respectively calculating the frequency difference between every two line spectrums to obtain a difference frequency calculation result delta f i I 1,2, M is the difference frequency number, i.e. M is the number of the difference frequencies
3.2 setting the percentage of frequency error δ, then [. DELTA.f i -δ△f i ,△f i +δ△f i ]Considering the difference frequency in the range as the same difference frequency, counting the occurrence times of each difference frequency, and selecting the line spectrum and the difference frequency in the frequency range of more than 0.5Hz and less than 40Hz as alternative fundamental frequencies sf i I ═ 1, 2., P are the number of candidate base frequencies.
In the step 3, the extracted DEMON modulation line spectrum is comprehensively utilized, and the difference frequency of the DEMON modulation line spectrum and the line spectrum is used as the alternative fundamental frequency, so that the problem of target axial frequency estimation when axial frequency is lost or a DEMON modulation harmonic structure is incomplete is solved.
And 4, step 4: line spectrum harmonic sequence extractionTaking, for alternative fundamental frequencies sf i And i is 1,2, and P, analyzing the relation between the extracted line spectrum and the alternative fundamental frequency, setting a frequency error threshold delta, and if the value of | f is satisfied i -round(f i /sf i )×sf i When | ≦ delta, the line spectrum is considered as the frequency multiplication harmonic of the current alternative fundamental frequency, and so on, the frequency multiplication harmonic corresponding to all alternative fundamental frequencies is obtained, and for the alternative fundamental frequency sf i The set of line spectrum harmonic wave sequences is expressed as
ZX i ＝{f j ||f j -round(f j /sf i )×sf i |≤△}，
In the formula (f) j E F, F is the set of extracted line spectra, i 1, 2.
In the step 4, the harmonic line spectrum of each alternative fundamental frequency is determined by setting a frequency error threshold, so that the harmonic search tolerance can be ensured.
And 5: extracting the energy characteristics of the alternative fundamental frequency line spectrum harmonic sequence and estimating the rotating speed of the propeller.
5.1 calculating the energy values of all line spectrum harmonic sequence respectively, wherein the set of the line spectrum harmonic sequence energy values is expressed as
E i ＝∑ j {X(f j )||f j -round(f j /sf i )×sf i |≤△}，
In the formula, X (f) j ) Indicating f in DEMAN demodulation spectra j Corresponding amplitude, f j E, F is an extracted line spectrum set, i is 1,2, and N;
5.2 selecting the line spectrum sequence with the maximum energy and the harmonic number not less than the preset value, wherein the corresponding fundamental frequency is the propeller fundamental frequency f shaft The estimated result of the rotating speed of the propeller is rn ═ f shaft X 60 rpm.
In the step 5, the propeller shaft frequency is determined by analyzing the energy relationship and the harmonic line spectrum number of each alternative fundamental frequency line spectrum harmonic group, so that the reliability of propeller shaft frequency estimation is improved.
According to the improved propeller rotating speed estimation method, the extracted DEMON modulation line spectrum and line spectrum difference frequency are used as alternative fundamental frequencies, and propeller rotating speed estimation is carried out through a harmonic search and energy comparison method, so that the problem of propeller rotating speed estimation under the condition that the modulation fundamental frequencies are absent can be effectively solved, and the problem of propeller rotating speed estimation under the condition that the fundamental frequencies are clear but the harmonic structures are incomplete can be effectively solved.
The improved propeller rotation speed estimation method is provided aiming at the problem that propeller rotation speed estimation is inaccurate under the conditions of fundamental frequency missing or incomplete demodulation spectrum structure and the like in practice, and can effectively realize rotation speed estimation under the conditions of fundamental frequency missing or incomplete demodulation spectrum structure.
(II) simulation and sea test data test results
On the basis of the implementation process, analysis processing is carried out on simulation and actual sea test data to obtain a processing result of the method, the simulation data processing result is shown in figures 2-4, and the actually-recorded target sea test data processing result of a certain commercial ship is shown in figure 5.
Computer simulation: the simulation target fundamental frequency is 4.2Hz, the rotating speed is 252 rpm, 4 blades are adopted, the simulation is divided into 3 cases, the target propeller harmonic structure is complete in the first case, the target propeller fundamental frequency is absent in the second case, and the target fundamental frequency is present in the third case but the harmonic structure is incomplete.
According to the simulation processing result, the target rotating speed can be accurately and effectively extracted and estimated by using the improved propeller rotating speed estimation method under the conditions that the target propeller has complete harmonic structure, missing fundamental frequency, fundamental frequency and incomplete harmonic structure and the like.
Sea test data processing: the actual data is a certain commercial ship target recorded in the sea test, the fundamental frequency is 2.28Hz, the rotating speed is 137 rpm, and the target fundamental frequency in the recorded data is absent.
According to the sea test data processing result, aiming at actual sea test target data, under the condition that a target has a certain DEMON harmonic structure but the fundamental frequency is lost, the rotating speed of the target propeller can be accurately estimated by using the improved propeller rotating speed estimation method.
The simulation analysis and the sea test data processing result show that: by adopting the improved propeller rotating speed estimation method, propeller rotating speed estimation under the conditions of complete propeller harmonic structure, propeller fundamental frequency loss, fundamental frequency existence but incomplete harmonic structure and the like can be accurately and effectively realized, and further characteristic information support is provided for target classification and identification.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.
Claims (8)
1. An improved method of estimating rotor rpm, characterized by: the estimation method comprises the following steps:
step 1: DEMON demodulation spectrum analysis: carrying out DEMON analysis on the received ship radiation noise signals x (n) to obtain a DEMON demodulation spectrum analysis result X (f);
step 2: extracting DEMON modulation line spectrum;
and step 3: determining alternative fundamental frequencies;
and 4, step 4: extracting line spectrum harmonic sequence;
and 5: extracting the energy characteristics of the alternative fundamental frequency line spectrum harmonic sequence and estimating the rotating speed of the propeller.
2. An improved propeller speed estimation method as claimed in claim 1, wherein: the step 1 further comprises:
1.1 band-pass filtering: according to the modulation intensity change conditions of the target in different frequency bands, a band-pass filter is selected to perform band-pass filtering on a received ship radiation noise signal x (N) to obtain a band-pass filtering signal xf (N), wherein N is 1,2
In the formula (I), the compound is shown in the specification,
representing a convolution operation; h is BP (k 1 ) Is the coefficient of a band-pass filter, k 1 ＝1,2,...,N BP ；N BP Is the order of the band-pass filter;
1.2 detection: detecting the band-pass filtering signal by adopting a square law to obtain a detection signal y 1 (n)＝|xf(n)| 2 ,n＝1,2,...,N；
1.3 low-pass filtering: to detection signal y 1 (N), N is 1,2, N, and N is low-pass filtered to obtain a low-pass filtered signal
Wherein the content of the first and second substances,
representing a circular convolution operation; h is LP (k 2 ) Is a low pass filter coefficient, k is 1,2 LP ；N LP Is the order of the low-pass filter;
1.4 downsampling: for low-pass filtered signal y 2 (N, N is 1, 2.. times.N, down-sampling processing is carried out to obtain down-sampled signals
y 3 (i)＝y 2 (1:D:N),i＝1,2,...,N/D
In the formula, D is a down-sampling multiple;
1.5 Power Spectrum analysis: accumulating K batches of data to the NFFT point, NFFT KN/D, and recording as y 4 (i) 1,2, KN/D, and performing power spectrum analysis on the accumulated data,
wherein, X (f) is the DEMON demodulation spectrum analysis result, and K is the accumulation batch.
3. An improved propeller speed estimation method as claimed in claim 2, wherein: the step 2 further comprises:
2.1, analyzing the DEMON demodulation spectrum analysis result X (f), if the frequency point f j The spectral line is determined as a line spectrum when the spectral line meets the following two constraint conditions:
①f j at a spectral line energy of maximum in the neighborhood, i.e. X (f) j )>X(f j -1) and X (f) j )>X(f j +1), with X (f) j )>X(f j -2) and X (f) j )>X(f j +2)；
②f j The energy of the spectral line is higher than the background of the spectral line by beta dB, i.e.,
in the formula, M B The sliding window is long for the background; XC (f) is the calculation result of the background of the demodulation spectrum;
2.2, zeroing the spectral line positions which do not meet the constraint conditions, reserving the spectral line positions which meet the conditions, and traversing all frequency points to obtain a DEMON modulation line spectrum extraction result P L (f) That is to say that,
4. an improved propeller speed estimation method as claimed in claim 3, wherein: the beta is 6-10 dB.
5. An improved propeller speed estimation method as claimed in claim 3, wherein: the step 3 further comprises:
3.1 Co-extraction to M L The root line spectrum and the corresponding frequency point position are k i ,i＝1,2,...,M L Respectively calculating the frequency difference between two line spectrums to obtain a difference frequency calculation result delta f i I 1,2, M is the difference frequency number, i.e. M is the number of the difference frequencies
3.2 setting the percentage of frequency error δ, then [. DELTA.f i -δ△f i ,△f i +δ△f i ]Considering the difference frequency in the range as the same difference frequency, counting the occurrence times of each difference frequency, and selecting the line spectrum and the difference frequency in the preset frequency range as alternative fundamental frequencies sf i I 1,2, P is the number of candidate fundamental frequencies.
6. An improved propeller speed estimation method as claimed in claim 5, wherein: the preset frequency range is greater than 0.5Hz and less than 40 Hz.
7. An improved propeller speed estimation method as set forth in claim 5, wherein: the step 4 further comprises: for alternative fundamental frequencies sf i And i is 1,2, and P, analyzing the relation between the extracted line spectrum and the alternative fundamental frequency, setting a frequency error threshold delta, and if the value of | f is satisfied i -round(f i /sf i )×sf i When | < delta, the line spectrum is regarded as the frequency multiplication harmonic wave of the current alternative fundamental frequency, and so on to obtain all alternative fundamental frequencies
Corresponding frequency-multiplied harmonic, for alternative fundamental frequency sf i The set of line spectrum harmonic wave sequences of which are expressed as
ZX i ＝{f j ||f j -round(f j /sf i )×sf i |≤△}，
In the formula (f) j E F, F is the set of extracted line spectra, i 1, 2.
8. An improved propeller speed estimation method as set forth in claim 7, wherein: the step 5 further comprises:
5.1 calculating the energy values of all line spectrum harmonic sequence respectively, wherein the set of the line spectrum harmonic sequence energy values is expressed as
E i ＝∑ j {X(f j )||f j -round(f j /sf i )×sf i |≤△}，
In the formula, X (f) j ) Representing f in DEMON demodulation spectrum j Corresponding amplitude, f j E, F is an extracted line spectrum set, i is 1,2, N;
5.2 selecting the line spectrum sequence with the maximum energy and the harmonic number not less than the preset value, wherein the corresponding fundamental frequency is the propeller fundamental frequency f shaft The estimated result of the rotating speed of the propeller is rn ═ f shaft X60 revolutions per minute.
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| CN116400337A (en) * | 2023-06-08 | 2023-07-07 | 中国人民解放军国防科技大学 | Ship noise modulation line spectrum extraction and axial frequency estimation method based on line segment detection |
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| CN116400337A (en) * | 2023-06-08 | 2023-07-07 | 中国人民解放军国防科技大学 | Ship noise modulation line spectrum extraction and axial frequency estimation method based on line segment detection |
| CN116400337B (en) * | 2023-06-08 | 2023-08-18 | 中国人民解放军国防科技大学 | Ship noise modulation line spectrum extraction and axial frequency estimation method based on line segment detection |
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