CN111007493A - Time segmentation fast Fourier transform method for improving ocean current velocity resolution - Google Patents

Time segmentation fast Fourier transform method for improving ocean current velocity resolution Download PDF

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Publication number
CN111007493A
CN111007493A CN201911295067.1A CN201911295067A CN111007493A CN 111007493 A CN111007493 A CN 111007493A CN 201911295067 A CN201911295067 A CN 201911295067A CN 111007493 A CN111007493 A CN 111007493A
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sub
length
fourier transform
signal
fast fourier
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陈章友
魏君杰
刘军益
吴雄斌
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Wuhan University WHU
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Wuhan University WHU
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems

Abstract

The invention relates to a signal processing technology, in particular to a time segmentation fast Fourier transform method for improving ocean current velocity resolution, which comprises the step of converting the length of the time segmentation fast Fourier transform method into the length of the time segmentation fast Fourier transform methodNThe marine radar echo signals are divided into the number ofN i Each sub-section signal having a length ofLAnd number of sub-segment signalsN i Greater than or equal to sub-segment signal lengthL(ii) a For the obtained length ofLEach sub-section signal is respectively subjected to fast Fourier transform to obtain each sub-section signalLA spectral dispersion value; the obtained fast Fourier transform result of each sub-segment signal takes the same frequency spectrum component to arrange according to time sequence to obtain the length ofN i And performing fast fourier transform on the time series signal to obtain the same spectral componentN i And doubling the refined spectrum result. The method has the advantages that the processing architecture is parallelized, the length of sub-segment signals is reduced in multiples, the consumed resources are greatly reduced, and the consumed time is greatly reduced; improvement ofThe ocean echo signal ocean current velocity resolution and the ocean velocity monitoring precision are achieved.

Description

Time segmentation fast Fourier transform method for improving ocean current velocity resolution
Technical Field
The invention belongs to the technical field of signal processing, and particularly relates to a time-segmented fast Fourier transform method for improving the ocean current velocity resolution.
Background
Fast Fourier Transform (FFT) is used in many fields as a basic tool for signal processing. The existing fast fourier transform also has some drawbacks. One is that if a high spectral resolution is to be achieved, the time series length must be long enough, which results in a large consumption of system resources and requires a large amount of processing time. And secondly, parallel processing cannot be performed. The accuracy requirement of radar detection of the ocean current velocity reaches the magnitude of centimeter per second, the ocean current velocity is not a single value per se and is continuously distributed in a certain velocity range, and therefore the resolution of radar measurement of the ocean current is required to be improved. The defects of the existing fast Fourier transform limit the resolution of the ocean radar for detecting the ocean current velocity.
Disclosure of Invention
The invention aims to provide a method for performing segmented fast Fourier transform processing on an ocean radar echo signal and improving the ocean current velocity resolution.
In order to achieve the purpose, the invention adopts the technical scheme that: a time-segmented fast Fourier transform method for improving the resolution of ocean current velocity comprises the following steps:
step 1, dividing marine radar echo signals with the length of N into N number according to time sequenceiEach sub-section signal has a length of L and the number of sub-section signals is NiGreater than or equal to the sub-segment signal length L;
step 2, performing fast Fourier transform on each sub-segment signal with the length of L obtained in the step 1 to obtain L discrete values of frequency spectrum of each sub-segment signal;
step 3, arranging the same frequency spectrum component of the fast Fourier transform result of each sub-segment signal obtained in the step 2 according to the time sequence to obtain the signal with the length of NiAnd performing fast fourier transform on the time series signal to obtain N of the same spectrum componentiAnd doubling the refined spectrum result.
In the time-segmented fast Fourier transform method for improving the speed resolution of the ocean current, a neutron is in step 1Number of segment signals NiThe value is an exponential power with a base 2, and the sub-segment signal length L is an exponential power with a base 2.
In the time-segmented fast fourier transform method for improving the speed resolution of the ocean current, for the echo time sequence signal of the ocean radar with the length of N, the length L of the sub-segment signal and the number N of the sub-segment signalsiThe product of which is equal to the length N of the marine radar echo time series signal.
In the time segmentation fast Fourier transform method for improving the speed resolution of the ocean current, the number N of sub-segment signals of the ocean radar echo signal continuous in timeiThe value of (a) must be sufficiently large.
The invention has the beneficial effects that: the method of the invention can parallelize the radar echo signal processing architecture; because the length of the sub-segment signals is reduced in multiples, the resources consumed by real-time processing are greatly reduced, and the time consumption is greatly reduced; the frequency spectrum result with very high frequency resolution can be obtained for a continuous time series signal, so that the detection level of the ocean current velocity resolution is greatly improved under the condition that the radar meets the real-time processing condition.
Drawings
FIG. 1 is a flow chart of a time-segmented fast Fourier transform method for improving the ocean current velocity resolution according to embodiment 1 of the present invention;
FIG. 2 is a schematic diagram of the embodiment 1 of the present invention for segmenting a marine radar echo time series signal;
FIG. 3 is a diagram illustrating FFT results of a non-segmented time series signal in embodiment 1 of the present invention;
fig. 4 is a schematic diagram of an FFT result of a sub-segment time series signal according to embodiment 1 of the present invention;
fig. 5 is a schematic diagram of an FFT result of a time sequence signal obtained by rearranging FFT results of sub-segment signals according to the same spectrum component in embodiment 1 of the present invention;
fig. 6 is a schematic flow chart of time-segmented fast fourier transform for improving the ocean current velocity resolution according to embodiment 1 of the present invention;
FIG. 7 is a diagram illustrating fast Fourier transform results of the data of 8192 points with a time duration of 25.6 seconds in embodiment 2 of the present invention;
FIG. 8 is a diagram illustrating fast Fourier transform results of 8 sub-segment data with a duration of 1024 points in 3.2 seconds in embodiment 3 of the present invention;
FIG. 9(a) is a diagram showing the fast Fourier transform result of a time series signal having a subband frequency of 0 in example 3 of the present invention;
FIG. 9(b) is a diagram showing the fast Fourier transform result of the time series signal of the subband frequency of 0.3125 in example 3 of the present invention;
FIG. 9(c) is a diagram showing the fast Fourier transform result of a time series signal having a subband frequency of 0.625 according to example 3 of the present invention;
fig. 10 is a graph comparing the fast fourier transform result of the time-series signal with frequency components of 0, 0.3125, and 0.625 for three sub-segments in example 3 of the present invention with the result of the unsegmented time-series signal.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
According to the method, the signal processing architecture is parallelized by performing segmented fast Fourier transform processing on the marine radar echo signals, and due to the fact that the length of the sub-segment signals is reduced in multiples, resources consumed by real-time processing are greatly reduced, and time consumption is greatly reduced. Under the condition that the radar meets the real-time processing condition, the detection level of the ocean current velocity resolution is greatly improved.
The embodiment is realized by the following technical scheme: as shown in fig. 1, a time-segmented fast fourier transform method for improving the resolution of ocean current velocity includes:
firstly, dividing the marine radar echo signals with the length of N into N in time sequenceiSub-section signals, number N of sub-section signalsiGenerally, the exponential power with 2 as the base can be taken, and other values can also be taken; the length L of the subsegment signals is typically raised to a base 2 exponential power, but may take other values. General number NiIs greater than or equal to the length L to ensure that the segmentation processing result is consistent with the unsegmented result. For the marine radar echo time sequence signal with the length of N, the length L of the sub-segment signal and the number N of the sub-segment signalsiThe product of which is equal to this timeThe sequence signal length N. Number of sub-segment signals N for a temporally continuous sea echo sequenceiThe value of (a) may be sufficiently large.
And secondly, performing fast Fourier transform on each sub-segment signal with the length of L obtained in the first step to obtain L discrete frequency spectrum values of each sub-segment signal.
Thirdly, the same frequency spectrum component is taken from the fast Fourier transform result of each sub-section signal obtained in the second step and is arranged according to the time sequence to obtain a new signal with the length of NiThe time-series signal of (2) is formed for a certain spectral component and has a length of NiPerforming fast Fourier transform on the new time series signal to obtain N related to the frequency spectrum componentiA higher frequency resolution of the multiple refinement results.
And traversing the L discrete values of the frequency spectrum to obtain a frequency spectrum result which is the same as the resolution of the original time series signal directly subjected to Fourier transform. The high-resolution spectrum result of the concerned frequency spectrum component can be obtained by processing only the new time series signal constructed by the concerned frequency spectrum component through fast Fourier transform, and the data processing load can be greatly reduced. Because of the number N of subsegment signals for a continuous time series signaliThe value of (a) can be large enough so that a spectrum result with a very high frequency resolution can be obtained, and correspondingly, the ocean current velocity resolution can be high enough.
Example 1
As shown in fig. 2, in the present embodiment 1, the sequence length N is 16, where x (N) is 1,2, …, and N is the marine radar echo time-series signal. Without loss of generality, as shown in fig. 2, a time-series signal with a length N of 16 is divided into NiA length L of 4 sub-segments is 4 for each sub-segment.
As shown in fig. 3, in this embodiment 1, the result of fast fourier transform spectrum of the marine radar echo time series signal with length N of 16 is obtained. The spectrum sequence is X (n), n is 1,2, …, 16.
As shown in fig. 4, the result of the fast fourier transform spectrum of the 4-segment serial signal in this embodiment 1 is obtained. N thiThe spectrum result of the sub-segment sequence signal is Xm (l),ni) And l is 1,2,3,4, wherein l is the spectrum sequence number of the sub-segment signal.
As shown in fig. 5, the same spectral component l of each sub-segment sequence signal is rearranged in time sequence to obtain a new time-series signal Xm (l, n)i)， n i1,2,3,4, and obtaining a new time series signal with a fast fourier transform spectrum result of x (N), where N is (l-1) x Ni+ni-2. Since the frequency spectrum has periodicity, X (-1) and X (0) in FIG. 5 are X (15) and X (16) in FIG. 3.
Fig. 6 is a schematic flow chart of the processing steps of time-segmented fast fourier transform for improving the ocean current velocity resolution according to embodiment 1. Since the spectrum has periodicity, X (-1), X (0) in FIG. 6 is X (15), X (16) in FIG. 3.
Example 2
An example of a simulation of time-sliced fast fourier transform to improve the ocean current velocity resolution is provided below to illustrate the effect of time-sliced fast fourier transform.
In the simulation example, the working frequency of the radar is assumed to be 4.2 megahertz, three speed values set in the simulation are respectively 1 m/s, 10 m/s and 20 m/s, the signal sampling rate is 320, the sampling time is 25.6 seconds, and the number N of the obtained radar echo data points is 8192.
The frequency result of performing fast fourier transform on 8192 point radar echo data with a duration of 25.6 seconds is shown in fig. 7, and three spectral peaks with frequency components of 0.03906,0.2734 and 0.5469 are seen on a spectrogram, and the obtained speed value is well matched with a set value in consideration of the minimum resolution of 320/8192-0.03906 of a frequency spectrum, corresponding to speeds of 1.395 m/s, 9.766 m/s and 19.53 m/s.
8192 point data with the time length of 25.6 seconds is divided into 8 subsections in time sequence, the time length of each section of data is 3.2 seconds, and the data point is 1024. And respectively performing fast fourier transform on the subsegment sequences with the data points of 1024 points and the time lengths of 8 and the data points of 3.2 seconds to obtain the result shown in fig. 8. It can be seen that the frequency resolution of the result of fig. 8 is 0.3125, which is eight times coarser than the resolution 0.03096 of fig. 7, since the duration of the signal shown in fig. 8 is only one-eighth of the duration of the signal of fig. 7.
Arranging signals with the sub-segment frequency components of 0, 0.3125 and 0.625 in fig. 8 into time series signals with the point number of 8 in time sequence, and then performing fast fourier transform on the signals with the 3 frequency components to obtain the results of fig. 9(a), fig. 9(b) and fig. 9(c), wherein fig. 9(a) is the result of the sub-segment frequency component of 0. It can be seen that fig. 9(a) refines the 0 spectral point of fig. 8 into 8 spectral points, the spectral point spacing is 0.03906, which is one eighth of the spectral point spacing 0.3125 of fig. 8, i.e. the frequency resolution and velocity resolution are improved by 8 times. The sidelobe on the left side of the spectral peak is due to NiIs relatively small. Fig. 9(b) is the result of the frequency component of the sub-segment being 0.3125. It can be seen that fig. 9(b) refines the 0.3125 spectral points of fig. 8 into 8 spectral points with a spectral point spacing of 0.03906, and likewise, the frequency resolution and velocity resolution are improved by a factor of 8. Fig. 9(c) is the result of the frequency component of the subsegment being 0.625. It can be seen that fig. 9(c) refines the 0.625 spectral point of fig. 8 into 8 spectral points with a spectral point spacing of 0.03906, and the frequency resolution and velocity resolution are improved by a factor of 8. The sidelobes on the right side of the spectral peak are due to NiIs relatively small. A comparison of the fast fourier transform results of the time series signals of the subsegment frequency components with the results of fig. 7 for the unsegmented case is shown in fig. 10. As can be seen from fig. 10, the processing result after being divided into subsections is consistent with that of the non-subsection case, thereby proving the correctness of the segmented fast fourier transform processing.
It should be understood that parts of the specification not set forth in detail are well within the prior art.
Although specific embodiments of the present invention have been described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that these are merely illustrative and that various changes or modifications may be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is only limited by the appended claims.

Claims (4)

1. A time segmentation fast Fourier transform method for improving the resolution of ocean current velocity is characterized by comprising the following steps:
step 1, dividing marine radar echo signals with the length of N into N number according to time sequenceiOfSegment signals, each sub-segment signal having a length of L and a number of sub-segment signals of NiGreater than or equal to the sub-segment signal length L;
step 2, performing fast Fourier transform on each sub-segment signal with the length of L obtained in the step 1 to obtain L discrete values of frequency spectrum of each sub-segment signal;
step 3, arranging the same frequency spectrum component of the fast Fourier transform result of each sub-segment signal obtained in the step 2 according to the time sequence to obtain the signal with the length of NiAnd performing fast fourier transform on the time series signal to obtain N of the same spectrum componentiAnd doubling the refined spectrum result.
2. The method of improving ocean current velocity resolution according to claim 1, wherein the number of sub-segment signals N in step 1 is NiThe value is an exponential power with a base 2, and the sub-segment signal length L is an exponential power with a base 2.
3. The method of claim 1, wherein for a length N of the time series signal of the echo of the marine radar, the length L of the sub-section signal and the number N of the sub-section signals are determinediThe product of which is equal to the length N of the marine radar echo time series signal.
4. The method of claim 1, wherein the number of sub-segment signals N is the number of temporally successive ocean radar echo signalsiThe value of (a) must be sufficiently large.
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