Ocean wave analysis device and ocean wave analysis program

Abstract

To dispense with the current ocean wave prediction without causing approximately one scan delay display when extracting target echoes without extracting ocean wave clutter as false target echoes using a radar provided on a marine vessel or the like.SOLUTION: An ocean wave analysis device 2 comprises: a scan data analysis unit 21 that analyzes wavelengths and wave directions of past ocean waves on the basis of past scan data; a sweep data wavelength calculation unit 22 that calculates an apparent wavelength of the current ocean wave in a certain direction on the basis of the wavelengths and wave directions of the past ocean wave for current sweep data; and a sweep data phase analysis unit 24 that performs fitting with a sine function and / or a cosine function having the apparent wavelength of the current ocean wave in the certain direction for the current sweep data and analyzes an apparent phase of the current ocean wave in the certain direction.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a technology for removing wave clutter using a radar installed on a ship or the like. [Background technology]

[0002] A technology for removing wave clutter using a radar installed on a ship or the like is disclosed in Patent Document 1, etc. According to Patent Document 1, STC (Sensitivity Time Control), which removes trends from sweep data (radar data acquired when the radar irradiation direction is in a certain direction), can be performed to extract target echoes.

[0003] The problem to be solved by the conventional STC processing is shown in Figure 1. In sweep data, periodic echo fluctuations of ocean clutter may be superimposed on the trend and target echo.

[0004] In the upper part of Figure 1, a weak STC is performed on the sweep data to remove trends without considering the periodic echo fluctuations of ocean clutter. This allows target echoes to be extracted from the sweep data, but ocean clutter may also be extracted as false target echoes.

[0005] In the lower part of Figure 1, strong STC is performed to remove trends from the sweep data, so that periodic echo fluctuations of ocean clutter are also removed. This prevents ocean clutter from being extracted as false target echoes in the sweep data, but also removes target echoes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-066630 [Non-patent literature]

[0007] [Non-Patent Document 1] V. Zinchenko, L. Vasilyev, SOHalstensen, and Y. Liu, “Short-time deterministic prediction of individual waves based on space-time X-band Marine radar measurements,” Journal of Engineering for the Maritime Environment, 2020. Summary of the Invention [Problem to be solved by the invention]

[0008] A technology for analyzing ocean waves based on scan data (radar data acquired when the radar irradiation direction is rotated by a predetermined angle) is disclosed in Patent Document 2, etc. By using Patent Document 2, the results of the ocean wave analysis can be subtracted from the scan data to remove ocean wave clutter.

[0009] The problems to be solved by conventional wave analysis processing are shown in Figures 2 and 3. In the scan data shown by the PPI (Plan Position Indicator) image, periodic echo fluctuations of wave clutter can be superimposed on the trend and target echo.

[0010] In Figure 2, the current waves are analyzed based on the current scan data, and the current wave analysis results are subtracted from the current scan data. This allows target echoes to be extracted from the current scan data, but results in a delayed display of about one scan.

[0011] In Figure 3, past waves are analyzed based on past scan data, current waves are predicted based on the past waves, and the current wave prediction result is subtracted from the current scan data. This allows target echoes to be extracted from the current scan data, but the amount of calculation required for current wave prediction increases, and the current wave prediction result cannot be said to be optimal.

[0012] Therefore, in order to solve the above problems, the present disclosure aims to use a radar equipped on a ship or the like to not extract wave clutter as false target echoes, to extract target echoes without causing a delayed display of about one scan, and to eliminate the need for current wave prediction. [Means for solving the problem]

[0013] To solve the above problem, we focused on the fact that the "wavelength and wave direction" of waves are "stable" in the short term as the wave front moves. Therefore, we analyze the "wavelength and wave direction" of "past" waves based on "past" "scan" data. This means that we analyze the "wavelength and wave direction" of "current" waves, eliminating the need for computationally intensive, suboptimal wave predictions.

[0014] On the other hand, we noticed that the "phase" of waves "fluctuates" even in the short term as the wave front moves. Therefore, the "current" "sweep" data is fitted with a sine wave function and / or cosine wave function with the "wavelength" of the "current" waves to analyze the "phase" of the "current" waves. This avoids delay analysis of the order of "one scan" and only generates delay analysis of the order of "one sweep," eliminating the need for computationally intensive and suboptimal wave predictions.

[0015] However, it was noted that the "wavelength" of the "apparent" "current" waves in the "sweep" direction is different from the "wavelength" of the "current" waves based on the "past" "scan" data. Therefore, for the "current" "sweep" data, the "wavelength" of the "apparent" "current" waves in the "sweep" direction is calculated based on the "wavelength and wave direction" of the "past" waves.

[0016] Therefore, the "wavelength, wave direction, and phase" of the "current" waves can be analyzed for the "current" "sweep" data. Then, the "current" wave analysis results can be subtracted from the "current" "sweep" data, and wave clutter can be removed. Then, STC, etc. can be performed on the "current" "sweep" data, and target echoes can be extracted.

[0017] Specifically, the present disclosure is a wave analysis device that uses radar to analyze the wavelength, wave direction, and phase of waves, and is characterized by comprising: a scan data analysis unit that analyzes the wavelength and wave direction of past waves based on past scan data (radar data acquired when the radar irradiation direction is rotated a predetermined angle); a sweep data wavelength calculation unit that calculates the apparent wavelength of the current waves in a certain direction based on the wavelength and wave direction of the past waves for current sweep data (radar data acquired when the radar irradiation direction is in a certain direction); and a sweep data phase analysis unit that fits the current sweep data with a sine wave function and / or cosine wave function having the apparent wavelength of the current waves in the certain direction, and analyzes the apparent phase of the current waves in the certain direction.

[0018] According to this configuration, when analyzing the wavelength, wave direction, and phase of current waves using radar equipped on a ship, etc., delay analysis of about one scan is not performed, but only delay analysis of about one sweep is performed, thereby eliminating the need for computationally intensive and non-optimal wave prediction.

[0019] The present disclosure also provides a wave analysis device further comprising a sweep data wave extraction unit that extracts wave spatial frequency components from the current sweep data and removes lower and / or higher spatial frequency components, and the sweep data phase analysis unit extracts wave spatial frequency components from the current sweep data and then fits them with a sine wave function and / or a cosine wave function having the apparent wavelength of the current wave in the certain direction.

[0020] According to this configuration, by extracting only the spatial frequency components of the waves from the current sweep data, it is possible to perform highly accurate fitting of sine wave functions and / or cosine wave functions, and to analyze the wavelength, wave direction, and phase of the current waves with high accuracy.

[0021] The present disclosure also provides a wave analysis device characterized in that the sweep data phase analysis unit increases amplitude attenuation in the fitting results after fitting to the current sweep data as the distance from the radar increases.

[0022] According to this configuration, by attenuating the fitting results after fitting a sine wave function and / or a cosine wave function to the current sweep data at long distances, it is possible to remove wave clutter from the current sweep data with high accuracy.

[0023] The present disclosure also provides a wave analysis device characterized in that the sweep data phase analysis unit increases amplitude attenuation in the fitting function used when fitting the current sweep data as the distance from the radar increases.

[0024] According to this configuration, the wavelength, wave direction and phase of the current waves can be analyzed with high accuracy by attenuating the fitting function when fitting a sine wave function and / or a cosine wave function to the current sweep data at long distances.

[0025] The present disclosure also provides a wave analysis device further comprising: a wave clutter removal unit that subtracts a fitting result after fitting to the current sweep data from the current sweep data and removes wave clutter; and a target echo extraction unit that extracts target echoes by performing at least one of STC (Sensitivity Time Control) that removes trends from the current sweep data after the wave clutter has been removed, and CFAR (Constant False Alarm Rate) that sets an amplitude threshold.

[0026] According to this configuration, by using a radar equipped on a ship or the like, wave clutter is not extracted as a false target echo, and when extracting a target echo, a delayed display of approximately one scan is not generated, and it is possible to eliminate the need for non-optimal wave prediction that requires a large amount of calculation.

[0027] The present disclosure also provides a wave analysis program for causing a computer to sequentially execute the processing steps executed by the processing units included in the wave analysis device described above.

[0028] According to this configuration, it is possible to provide a program having the above-described effects.

[0029] The above-disclosed inventions can be combined as much as possible. [Effects of the Invention]

[0030] In this way, the present disclosure uses radar equipped on ships, etc., to avoid extracting wave clutter as false target echoes, and to extract target echoes without causing a delayed display of approximately one scan, thereby making it possible to eliminate the need for current wave prediction. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram illustrating a problem to be solved in the STC processing of the prior art. [Figure 2] FIG. 1 is a diagram illustrating a problem to be solved in the wave analysis processing of the prior art. [Figure 3] FIG. 1 is a diagram illustrating a problem to be solved in the wave analysis processing of the prior art. [Figure 4] FIG. 1 is a diagram illustrating a configuration of a wave analysis system according to the present disclosure. [Figure 5] FIG. 10 is a diagram showing the procedure of the wave analysis processing of the present disclosure. [Figure 6] FIG. 10 is a diagram showing the contents of a sweep data wavelength calculation process according to the present disclosure. [Figure 7] FIG. 10 is a diagram showing the contents of the sweep data wave extraction process of the present disclosure. [Figure 8] FIG. 10 is a diagram showing the contents of the sweep data phase analysis process of the present disclosure. [Figure 9] FIG. 10 is a diagram illustrating the details of distance attenuation processing of fitting results according to the present disclosure. [Figure 10]FIG. 10 is a diagram illustrating the details of distance attenuation processing of the fitting function of the present disclosure. [Figure 11] 1A and 1B are diagrams illustrating the contents of ocean wave clutter removal processing according to the present disclosure. [Figure 12] FIG. 10 is a diagram showing the target echo extraction result of the STC processing of the prior art. [Figure 13] 10A and 10B are diagrams showing target echo extraction results of the ocean wave analysis processing of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0032]

[0023] The following embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0033] (Overview of the wave analysis system disclosed herein) The configuration of the wave analysis system of the present disclosure is shown in Fig. 4. The procedure for the wave analysis processing of the present disclosure is shown in Fig. 5. The wave analysis system W comprises a radar transceiver 1, a wave analysis device 2, and a radar display device 3. The wave analysis device 2 comprises a scan data analysis unit 21, a sweep data wavelength calculation unit 22, a sweep data wave extraction unit 23, a sweep data phase analysis unit 24, a wave clutter removal unit 25, and a target echo extraction unit 26. The wave analysis device 2 can be realized by installing the wave analysis program shown in Fig. 5 on a computer.

[0034] The wave analysis system W is a radar system installed on a ship or the like. A radar transmitter / receiver 1 emits a radar transmission signal and receives a radar reflection signal. A wave analysis device 2 analyzes waves based on the radar reflection signal, removes wave clutter from the radar reflection signal, and extracts target echoes. A radar display device 3 displays the target echoes from which the wave clutter has been removed.

[0035] In this disclosure, we focus on the fact that the "wavelength and wave direction" of waves are "stable" in the short term as the wave front moves. Therefore, the "wavelength and wave direction" of "past" waves is analyzed based on "past" "scan" data (radar data acquired when the radar irradiation direction is rotated a predetermined angle) (step S1, Figure 6). Therefore, the "wavelength and wave direction" of "current" waves is analyzed, eliminating the need for computationally intensive, suboptimal wave prediction.

[0036] On the other hand, we focused on the fact that the "phase" of waves "fluctuates" even in the short term as the wave front moves. Therefore, the "current" "sweep" data (radar data acquired when the radar irradiation direction is in a certain direction) is fitted with a sine wave function and / or cosine wave function having the "wavelength" of the "current" waves to analyze the "phase" of the "current" waves (steps S4, S5, Figure 8). Therefore, delay analysis of the order of "one scan" is not performed, but only delay analysis of the order of "one sweep", eliminating the need for computationally intensive and suboptimal wave prediction.

[0037] However, the "wavelength" of the "apparent" "present" wave in the "sweep" direction (λ in the right column of Figure 6) S ) is the "wavelength" of the "present" waves based on the "past" "scan" data (λ in the right column of Figure 6). W Therefore, for the "current" "sweep" data, the "wavelength" of the "apparent" "current" waves in the "sweep" direction is calculated based on the "wavelength and wave direction" of the "past" waves (step S2, Figure 6).

[0038] Therefore, the "wavelength, wave direction, and phase" of the "current" waves can be analyzed for the "current" "sweep" data (steps S1, S2, S4, S5, Figures 6 and 8). Then, the analysis results of the "current" waves can be subtracted from the "current" "sweep" data, and wave clutter can be removed (step S6, Figure 11). Then, STC (Sensitivity Time Control) and the like can be executed for the "current" "sweep" data, and target echoes can be extracted (step S7, Figure 11).

[0039] (Contents of the sweep data wavelength calculation process disclosed herein) The details of the sweep data wavelength calculation process of the present disclosure are shown in Fig. 6. The scan data analysis unit 21 analyzes the wavelength and wave direction of past waves based on past scan data (step S1, left and center columns of Fig. 6). Here, the scan data analysis unit 21 performs a two-dimensional Fourier transform on the past scan data to extract the spatial frequency components of the waves, performs a two-dimensional inverse Fourier transform, and outputs and stores images of past wave clutter.

[0040] The sweep data wavelength calculation unit 22 calculates the apparent wavelength of the current waves in a certain direction based on the wavelength and wave direction of past waves for the current sweep data (step S2, right column in FIG. 6). Here, the sweep data wavelength calculation unit 22 calculates the apparent wavelength of the current waves in the sweep direction based on Equation 1 (step S2).

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[0041] In this way, when analyzing the wavelength and wave direction of current waves using radar equipped on ships, etc., delay analysis of about one scan is not performed, but only delay analysis of about one sweep is performed, thereby eliminating the need for computationally intensive and suboptimal wave predictions.

[0042] (Contents of the sweep data wave extraction process disclosed herein) The details of the sweep data wave extraction process of the present disclosure are shown in Fig. 7. The sweep data wave extraction unit 23 extracts the spatial frequency components of waves from the current sweep data and removes lower and / or higher spatial frequency components (step S3, Fig. 7).

[0043] Here, the sweep data wave extraction unit 23 performs STC to remove the trend, or performs high-pass filtering to extract the spatial frequency components of the waves and remove the lower spatial frequency components (trend components) (step S3, left and middle columns of Figure 7).

[0044] Then, the sweep data ocean wave extraction unit 23 executes CFAR (Constant False Alarm Rate, which essentially extracts target echoes) to set an amplitude threshold, or executes low-pass filtering to extract the spatial frequency components of the ocean waves and remove higher spatial frequency components (target echoes) (step S3, middle and right columns of Figure 7).

[0045] In this way, by extracting only the spatial frequency components of the waves from the current sweep data, it is possible to perform highly accurate fitting of sine wave functions and / or cosine wave functions, as described below, and analyze the wavelength, wave direction, and phase of the current waves with high accuracy.

[0046] (Contents of the Sweep Data Phase Analysis Process Disclosed Herein) The details of the sweep data phase analysis process of the present disclosure are shown in Fig. 8. The sweep data phase analysis unit 24 extracts the spatial frequency components of waves from the current sweep data (step S3, Fig. 7), fits them with a sine wave function and / or a cosine wave function having the wavelength of the apparent current waves in the certain direction (step S4, Fig. 8), and analyzes the phase of the apparent current waves in the certain direction (step S5, Fig. 8).

[0047] Here, the sweep data phase analysis unit 24 analyzes the apparent current phase of ocean waves in the sweep direction based on Equation 2 (step S5, left to right columns in FIG. 8).

number

[0048] Then, the sweep data phase analysis unit 24 can use canonical correlation analysis to fit the current sweep data with a sine wave function and a cosine wave function having the wavelength of the current waves. Then, the sweep data phase analysis unit 24 can perform fitting in almost real time on the current sweep data, which is one-dimensional data rather than two-dimensional data, with the wavelength of the current waves as known and only the amplitude of the current waves as unknown.

[0049] In this way, when analyzing the wavelength, wave direction, and phase of current waves using radar equipped on ships, etc., delay analysis of about one scan is not performed, but only delay analysis of about one sweep is performed, thereby eliminating the need for computationally intensive and suboptimal wave predictions.

[0050] The details of the distance attenuation process of the fitting "results" of the present disclosure are shown in Figure 9. The sweep data phase analysis unit 24 attenuates the amplitude of the fitting "results" after fitting to the current sweep data more strongly the longer the distance from the radar transceiver 1 (step S4, Figure 9). Here, the sweep data phase analysis unit 24 adjusts the amplitude attenuation of the fitting "results" according to the distance from the radar based on Equation 3.

number

[0051] In this way, by attenuating the fitting "results" of the sine and / or cosine wave functions at long distances for the current sweep data, it is possible to remove wave clutter from the current sweep data with high accuracy, as will be described later.

[0052] The details of the distance attenuation process of the fitting "function" of the present disclosure are shown in Figure 10. The sweep data phase analysis unit 24 increases the amplitude attenuation of the fitting "function" during fitting to the current sweep data as the distance from the radar transceiver 1 increases (step S4, Figure 10). Here, the sweep data phase analysis unit 24 adjusts the amplitude attenuation of the fitting "function" according to the distance from the radar based on Equation 4.

number

[0053] In this way, by attenuating the fitting "function" when fitting a sine wave function and / or cosine wave function to the current sweep data at long distances, the wavelength, wave direction, and phase of the current waves can be analyzed with high accuracy compared to Figure 8.

[0054] (Contents of the ocean wave clutter removal process disclosed herein) The details of the wave clutter removal process of the present disclosure are shown in Fig. 11. The wave clutter removal unit 25 subtracts the fitting result after fitting to the current sweep data from the current sweep data to remove wave clutter (step S6, upper left column, upper right column, and lower left column of Fig. 11). However, trend components are superimposed on the target echo.

[0055] The target echo extraction unit 26 removes wave clutter from the current sweep data, and then performs at least one of STC, which removes trends, and CFAR, which sets an amplitude threshold, to extract target echoes (step S7, lower left and lower right columns of FIG. 11).The current sweep data is then stored, and the current scan data is displayed.

[0056] The target echo extraction results of the conventional STC processing are shown in Fig. 12. The first row of Fig. 12 shows the current sweep data received by the radar transceiver 1. The second row of Fig. 12 shows the current sweep data after STC has been executed. It can be seen that when extracting target echoes, there is a high possibility that ocean wave clutter will be extracted as false target echoes.

[0057] The target echo extraction results of the wave analysis processing of the present disclosure are shown in FIG. 13. The first row of FIG. 13 shows the current sweep data received by the radar transceiver 1. The second row of FIG. 13 shows the current sweep data fitted with a sine wave function and a cosine wave function. The third row of FIG. 13 shows the current sweep data from which wave clutter has been removed. The fourth row of FIG. 13 shows the current sweep data from which STC has been executed. It can be seen that when extracting target echoes, there is a low possibility that wave clutter will be extracted as a false target echo.

[0058] In this way, by using radar equipped on ships, etc., it is possible to avoid extracting wave clutter as false target echoes, to extract target echoes without causing a delayed display of about one scan, and to eliminate the need for computationally intensive and suboptimal wave prediction. [Industrial Applicability]

[0059] The wave analysis device and wave analysis program disclosed herein use radar equipped on ships, etc., to avoid extracting wave clutter as false target echoes, and to extract target echoes without causing a delayed display of approximately one scan, thereby eliminating the need for current wave prediction. [Explanation of symbols]

[0060] W: Wave analysis system 1: Radar transmitter and receiver 2: Wave analysis device 3: Radar display device 21: Scan data analysis unit 22: Sweep data wavelength calculation unit 23: Sweep data wave extraction section 24: Sweep data phase analysis section 25: Wave clutter removal section 26: Target echo extraction unit

Claims

1. A wave analysis device that analyzes the wavelength, wave direction, and phase of waves using radar, a scan data analysis unit that analyzes the wavelength and wave direction of past waves based on past scan data (radar data acquired when the radar irradiation direction is rotated by a predetermined angle); a sweep data wavelength calculation unit that calculates the apparent wavelength of the current waves in a certain direction based on the wavelength and wave direction of the past waves for current sweep data (radar data acquired when the radar irradiation direction is in the certain direction); a sweep data phase analysis unit that performs fitting of the current sweep data with a sine wave function and / or a cosine wave function having a wavelength of the apparent current wave in the certain direction, and analyzes the phase of the apparent current wave in the certain direction; A wave analysis device comprising:

2. a sweep data wave extraction unit that extracts wave spatial frequency components from the current sweep data and removes lower and / or higher spatial frequency components; The sweep data phase analysis unit extracts spatial frequency components of waves from the current sweep data and then fits the extracted waves with a sine wave function and / or a cosine wave function having an apparent wavelength of the current waves in the certain direction.

2. The wave analysis device according to claim 1, wherein:

3. The sweep data phase analysis unit increases the attenuation of amplitude as the distance from the radar increases with respect to the fitting result after fitting to the current sweep data.

3. The wave analysis device according to claim 1 or 2.

4. The sweep data phase analysis unit increases the attenuation of amplitude of a fitting function when fitting the current sweep data as the distance from the radar increases.

3. The wave analysis device according to claim 1 or 2.

5. a wave clutter removal unit that subtracts a fitting result after fitting to the current sweep data from the current sweep data to remove wave clutter; a target echo extracting unit that extracts a target echo by performing at least one of STC (Sensitivity Time Control) for removing trends and CFAR (Constant False Alarm Rate) for setting an amplitude threshold on the current sweep data after removing the ocean wave clutter; The wave analysis device according to claim 1 , further comprising:

6. A wave analysis program for causing a computer to sequentially execute the processing steps executed by each processing unit included in the wave analysis device according to claim 1.

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