JP3760243B2 - GPS type ocean wave measurement method - Google Patents

Description

  The present invention relates to a GPS-type ocean wave measuring method for measuring a period of ocean waves, in particular, using a GPS system.

  When marine lifeboats land on the sea for rescue, etc., it is important that the wave height, period, wavelength and direction of the ocean waves are within a range that allows the marine lifeboat to land. It is a big factor. However, the current state of ocean waves relies on empirical and intuitive analysis of pilots from aircraft. In general, the wavelength of ocean waves is analyzed based on an image taken over the sea from the sky.

As an example of a method for measuring the period of ocean waves using a GPS system, there is a measurement using a differential GPS method (see Patent Document 1). In this measurement method, a wave observation device including a GPS receiver and a transponder slave station is mounted on a floating target for each wave observation sea area, a transponder master station and a wave data processing device are installed on land, and a transponder slave station is installed. Transmits the latitude, longitude, altitude data and measurement time data of the floating target measured by the GPS receiver to the transponder master station. The transponder master station receives the received data of the floating target received from the transponder slave station as wave data. The wave data processing apparatus supplies the data to the processing apparatus, and performs wave analysis based on the wave observation data for each supplied wave observation sea area.
Japanese Patent Laid-Open No. 2001-27665 ([0013] to [0019], FIGS. 1 and 2)

  In conventional wave observation using GPS, a receiver that receives radio waves from a GPS satellite is placed on a ground station whose position is accurately known, and error information (differential data) such as time error of the GPS signal is placed. The UHF band radio wave is transmitted, and the floating target receives differential data simultaneously with the radio wave from the GPS satellite and corrects the data obtained from the GPS satellite to improve the positioning accuracy. However, it is necessary to provide a ground station facility for transmitting the differential data, and in order to receive the differential data, it is necessary to install a dedicated receiver, which causes problems such as complicated system and high cost. Contains.

  The present inventors have previously described a GPS-type wave height / flow direction flow velocity measuring device and a GPS wave height / flow direction flow velocity measuring apparatus that can accurately measure the wave height and the flow direction flow velocity at an arbitrary position on the ocean or lake using GPS. (Japanese Patent Application No. 2002-103593) has been proposed. Since the high-pass filter and smoothing processing are performed on the GPS signal received by one GPS receiver provided on a floating body floating on the ocean or lake, errors contained in the GPS signal are removed. This makes it possible to accurately measure the wave height and flow direction flow velocity.

  The present inventors have proposed a GPS type wave direction measuring method having a wave direction analysis algorithm based on GPS positioning data (Japanese Patent Application No. 2002-362806). In this proposal, one period of wave is extracted by altitude data that is time series data (time domain data) in the Z-axis direction by GPS positioning, and the maximum peak of the data extracted in that period The wave direction is estimated from the lateral displacement at several points before and after the point.

  Therefore, based on the GPS signal received by the single GPS receiver mounted on the buoy, without depending on other signals such as differential data, the period of the ocean wave from the buoy movement, and the period thus obtained There is a problem to be solved in terms of obtaining the wavelength and wave velocity of ocean waves based on this.

  The object of the present invention is to provide a low-cost, ocean wave cycle based on GPS signals received by a single GPS receiver mounted on a buoy, without relying on signals from other systems such as differential data. Is to provide a GPS type ocean wave measuring method capable of obtaining the wavelength and wave velocity based on the period obtained in this way.

To solve the above problems, GPS offshore wave measuring method according to the invention, against the GPS signals received by the single GPS receiver mounted on the buoy, corrected vertical removal of the jump based on the change in the number of GPS satellites Generating movement data, and then performing high-pass filtering on the modified vertical movement data to generate vertical movement data of the buoy when the buoy is swayed by ocean waves, and then generating the vertical movement data It consists of obtaining the period of the ocean wave by performing frequency spectrum analysis.

  According to this GPS type ocean wave measurement method, based on the GPS signal received by a single GPS receiver mounted on the buoy, the buoy's vertical motion data when the buoy is shaken by the ocean wave is generated, and the vertical motion By performing spectral analysis on the data, the period of ocean waves in which the buoy floats is determined. According to the spectrum analysis of the vertical motion data, the characteristics distributed in the frequency domain can be obtained. For example, the period corresponding to the frequency to which the peak value of the distribution is applied can be set as the period of the ocean wave. In the frequency domain, the peak is not limited to a single peak, and may have a plurality of peaks (maximum values).

In this GPS offshore wave measuring method, the period of the ocean waves, the wave height power in the frequency domain obtained by the frequency spectrum analysis, the wave height power can be obtained as the inverse of the frequency to give the maximum peak value.

ここで、Ｔは周期、Ｌは波長、ｈは水深である。
上記関係式は、海洋波の周期と波長、及びその海洋波が水面に存在する海洋の水深を関係づける海洋工学上の式である。水深は、海図又は実測で求めることができる。したがって、求めた海洋波の周期に基づいて、或いはスペクトル別に、関係式を満たすような波長を求めることができる。 In this GPS type ocean wave measurement method, the wavelength of the ocean wave can be estimated for each period of the ocean wave from the following relational expression established between the period and the water depth.

Here, T is the period, L is the wavelength, and h is the water depth.
The above-mentioned relational expression is an expression in ocean engineering that relates the period and wavelength of the ocean wave and the depth of the ocean where the ocean wave exists on the water surface. The water depth can be determined by chart or actual measurement. Therefore, a wavelength that satisfies the relational expression can be obtained based on the obtained ocean wave period or for each spectrum.

  In this GPS type ocean wave measuring method, the wave speed of the ocean wave can be obtained from the cycle of the ocean wave and the wavelength for each cycle of the ocean wave. Specifically, the wave velocity of the ocean wave can be obtained by dividing the wavelength by the period. Since the wavelength shows a different value depending on the period, the wave velocity of the ocean wave is obtained according to each period or for each spectrum.

  In this GPS type ocean wave measurement method, an initial value of the wavelength when the water depth h is infinite on the right side of the relational expression using the period T obtained by the spectrum analysis is obtained, and the period T and the water depth are calculated. In the right side of the relational expression using h, the initial value is substituted for the wavelength L to obtain the updated value of the wavelength, and then the updated value is substituted for the wavelength L to further update the wavelength L The calculation for obtaining the value is repeated, and the updated value determined to have converged can be estimated as the wavelength of the ocean wave having the period T on the ocean at the depth h. Since the above relational expression is a transcendental equation, an analytical analytical solution cannot be generally obtained. However, an equation structure in which the wavelength L is included on the left side and the right side, and the left side is the wavelength L itself. It is possible to apply an iterative calculation method. By such an iterative calculation method, when it is determined that the updated value has converged, the updated value can be made an approximate solution sufficiently approximating the solution of the equation. In addition, as an actual water depth, the water depth calculated | required by the chart or measurement is used.

  The GPS type ocean wave measuring method according to the present invention proposes a method for estimating the period of ocean waves, and further the wavelength and wave speed based on the period. Based on the GPS signal received by the single GPS receiver, the vertical motion data of the swaying motion of the buoy equipped with the single GPS receiver is generated, and the frequency analysis of the vertical motion data is performed to analyze the frequency of the ocean wave. Is identified. Further, the period of the ocean wave is obtained from the frequency, and from the result, the wavelength for each spectrum is calculated using an approximate expression, and the wave speed is also calculated. In the case of maritime rescue, this GPS type ocean wave measurement method can be applied by dropping a drop-type buoy equipped with a single GPS receiver from an aircraft to a marine accident position. The state of the ocean surface at the marine accident location can be immediately grasped with quantitative values, which can be transmitted to the rescue boat pilot or coastal land, improving the success rate of rescue and preventing secondary distress and disasters. Expected to be useful.

  Hereinafter, embodiments of a GPS type ocean wave velocity measuring method according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing an outline of a system to which a GPS type ocean wave measurement method according to the present invention can be applied. A drop type buoy (hereinafter abbreviated as “GPS buoy”) 1 equipped with a single GPS receiver 2 is suspended in the ocean, and the single GPS receiver 2 receives GPS signals from a plurality of GPS satellites 3 orbiting the orbit. Can be received by sequentially switching. Although not shown in the figure, the GPS buoy 1 can communicate with a ship that navigates in the vicinity of the buoy and an aircraft that flies over the sea. The symbol h indicates the water depth from the sea surface to the sea floor 4, and the symbol L indicates the wavelength of the ocean wave 5.

  FIG. 2 is a flowchart showing the overall flow of the GPS type ocean wave measurement method according to the present invention. This GPS type ocean wave measuring method is a method of measuring the period / wavelength and wave velocity of ocean waves using the GPS type buoy 1. According to the overall flow shown in FIG. Based on the GPS signal received by the single GPS receiver 2, the three-dimensional position information of the GPS buoy 1 floating on the ocean (more precisely, the three-dimensional position information of the GPS receiver 2) is acquired ( Step 1, abbreviated as “S1” (hereinafter the same). Based on the three-dimensional position information of the GPS buoy 1 acquired in S1, the altitude direction (Z-axis direction) of the GPS buoy 1, that is, the vertical motion data is generated, and the vertical motion data is spectrally analyzed. Is performed (S2). If the three-dimensional position information is obtained over a sufficient time, the vertical motion data can be analyzed for each frequency. In the spectrum analysis in S2, the wave height power for each wave frequency is calculated (S3). The wave height power calculated in S3 can be graphed in the frequency region, for example, to obtain a frequency distribution of the wave height power. The frequency of the wave corresponding to the peak value of the wave height power is regarded as the typical frequency of the ocean wave, and the period of the ocean wave is obtained as the reciprocal of the typical frequency (S4).

  Based on the relational expression previously known between the wavelength and the period, the wavelength and wave velocity of the ocean wave are obtained using the period obtained in S4 (S5). The relational expression is an expression that defines the relation between the water depth h, the period of the ocean wave and the wavelength L, and will be described later together with an analysis flowchart for obtaining the wavelength. Once the wavelength is determined, the wave velocity can be determined by dividing the wavelength by the period. The information obtained about the ocean wave is transmitted to the aircraft and the coastal base station as ocean wave information (S6). As a transmission means, a packet communication function of extra-small radio or a mobile phone can be used.

  FIG. 3 is a data diagram showing an example of obtaining the wave period from the vertical movement of the GPS buoy, and FIG. 4 is a graph showing an example of how to obtain the frequency by wave height spectrum analysis of the vertical movement data of the GPS buoy. is there. In the data diagram shown in FIG. 3, (A) is a continuous data diagram showing the change in the number of GPS satellites 3 received by the single GPS receiver 2 mounted on the GPS buoy 1 shown in FIG. A raw data (raw vertical motion data) diagram showing a change in the height (Z direction) of the GPS buoy 1 obtained from the GPS signal, (C) is the number of GPS satellites 3 from the continuous data diagram shown in (B). FIG. 4D is a continuously corrected data (corrected vertical motion data) diagram showing a change in the height of the GPS buoy 1 when a jump based on the change in the distance is removed. FIG. 4D is a filter process for the continuously corrected data shown in FIG. It is a filter processing data figure which shows the change of the height of the GPS type buoy 1 when it gave.

As can be seen from FIG. 3A, in this example, the number of GPS satellites 3 received in the vicinity of time 264 seconds has decreased from 8 to 7. As can be seen from the raw vertical motion data of the GPS buoy 1 obtained from the GPS signal shown in FIG. 3 (B), the GPS buoy 1 is constantly moving up and down due to ocean waves. It can be seen that the level of fluctuation of the height of the GPS buoy 1 changes (jump phenomenon) in response to the number changing. Fig. 3 (C) shows the corrected vertical motion data after removing such discontinuous changes in the fluctuation level. The data shown in Fig. 3 (C) is subjected to filtering (such as an ultra-long period swell). 3 ), the vertical motion data after the filter processing as shown in FIG. 3D is obtained, and one wave period can be measured from this data. . As a definition of the period T, in general, a so-called zero-up cross method is used in which the time taken from passing through the neutral point of the vertical movement from the bottom to the top and then from the bottom to the top again is applied. However, it is obtained here by applying the following spectral analysis method.

  By performing spectrum analysis on the vertical motion data (wave height data) after the filter processing, a distribution of the wave height power in the frequency domain can be obtained. That is, as shown in FIG. 4, by distributing the frequency on the horizontal axis and the crest power on the vertical axis, a distribution of the crest power according to the frequency can be obtained. In the example shown in FIG. 4, the highest first peak (period 4.5 seconds) appears near 0.22 Hz, the second highest peak (period 5.8 seconds) near 0.17 Hz, and 0 It can be seen that the third highest peak (period 8.4 seconds) appears in the vicinity of .12 Hz. In this case, it is determined as an ocean wave represented by a wave having a period of 4.5 seconds with the highest wave power.

If a period is calculated | required, a wavelength can be calculated | required from the relational expression which relates a wavelength, a period, and water depth. That is, when the water depth is sufficiently deep and the wave phenomenon can be assumed to be a micro-amplitude surface wave, between the wavelength L (shown in FIG. 1), the period T, and the water depth h, g is the gravitational acceleration and the equation (1) There exists a relational expression shown as

Although equation (1) is a transcendental equation and cannot be solved analytically, it can be considered to be solved numerically by the following iterative calculation according to the present invention. In the formula (1), the wavelength L is included in both the right side and the left side, and in particular, the left side is the wavelength L itself. Therefore, when the wavelength L is rewritten as an unknown number x, the equation (1) is a simultaneous equation represented by the following equation (2) consisting of (2-1) and (2-2), that is, one straight line. And the problem of finding the intersection of one curve.

  FIG. 5 is an analysis flowchart showing a numerical analysis method used in the GPS type ocean wave measurement method according to the present invention, and FIG. 6 is a diagram showing the convergence of iterative calculations executed by the analysis flowchart shown in FIG. In the analysis flowchart shown in FIG. 5, when the calculation is started (step 11, abbreviated as “S11”, the same applies hereinafter), first, the water depth h is obtained by a chart or actual measurement (S12). The obtained water depth h is given to equation (2-2) (S13). The period is calculated by obtaining the reciprocal of the vibration frequency obtained by the above-described wave height spectrum analysis (S14). The calculated period T is given to equation (2-2) (S15). By calculating the equation (2-2), the initial value x0 of the wavelength L is calculated (S16). The initial value x (0) is substituted into the right side of the lower expression of expression (2-2), and the obtained y is set as the wavelength update value x (1) (S17). The difference (error) between the previously obtained wavelength (initially, the initial value x (0)) and the updated value obtained this time (in the first case, the updated value x (1)) is evaluated (S18). When the error is equal to or larger than the predetermined value, the process returns to S17, and the update value x (1) is again substituted into the right side of the lower expression of the expression (2-2), and the obtained y is further updated the wavelength. x (2), and an error between the update value x (1) and the update value x (2) is evaluated in S18. Thereafter, the same update value calculation and error evaluation calculation are repeated, and when the difference between x (n + 1) and x (n) becomes sufficiently small, the calculation for obtaining the wavelength L is terminated as converged (S19).

Generally, in the GPS buoy, the measurable period T is 3 to 16 seconds. FIG. 6 shows, as an example, how the solution of the transcendental equation converges when T = 16 and T = 8. Three lines are shown for each period T, and each line corresponds to when the water depth h is changed to 50, 100, and 500 m, respectively. In FIG. 6, it is assumed that the actual water depth h is 50 m from the actual measurement or the chart, and the period T of the ocean wave is 16 seconds. As the initial value x (0) of the wavelength L, the intersection of each equation when h = ∞ is used. That is, x (0) is obtained as L = gT ² / (2π) by setting h = ∞ in the equation (2-2). In FIG. 6, when h = 500 is a sufficiently deep water depth and the period T is 16 seconds, the x coordinate of the intersection (A) between the straight line (y = x) and the curve when h = 500 m is obtained. (X (0) = 400 m). When the water depth h is 50 m, by substituting the initial value x (0) (= 400 m) into the equation (2-2), y (1) (= 260 m) is obtained as the y coordinate of the intersection (B). It is done. According to Expression (2-1), y (1) is set as an updated value x (1) of x (0) (intersection (C)). The difference | x (1) −x (0) | (= 140 m) between the updated value x (1) and the original x (0) is evaluated. If it is determined that the water has not converged sufficiently, when the water depth h is 50 m, by substituting the update value x (1) (= 260 m) into the equation (2-2), the y coordinate of the intersection (D) As a result, y (2) (= 330 m) is obtained. According to Expression (2-1), y (2) is set as an updated value x (2) of x (1) (intersection (E)). The difference | x (2) −x (1) | (= 70 m) between the update value x (2) and the value x (1) before the update is evaluated. Thereafter, the calculation is repeated in the same manner, and when the error between the update value x (n + 1) and the value before update x (n) becomes smaller than a preset value, the wavelength calculation has converged. The updated value at that time is approximated to the wavelength L. In the example of FIG. 6, the calculation was repeatedly started from the initial wavelength value x (0) = 400 m, and converged within an error of 1% at the eighth time.

  In such repeated calculation, the convergence of the calculation depends on y = x shown in Expression (2-1) in FIG. 6 and the slope on the curve side at the intersection of the curves shown in Expression (2-2). In general, it is known that there is no problem if the slope on the curve side is −1 or more and 0 or less. However, in this problem, the slope of the curve is T even when T = 16 (maximum) and the water depth h is 50 m. Convergence is guaranteed at -0.58. The water depth h is generally considered to be higher than this, and the graph becomes flatter as the water depth h becomes deeper, that is, the slope approaches 0, and the convergence is not lost. In addition, as the period T becomes smaller, the slope in the graph shown in FIG. 6 is further reduced, so convergence is still guaranteed, but the GPS buoy is thrown into a sufficiently deep water area like this time. In view of this, it can be seen that there is no problem with the repetitive calculation by this method.

  An example of wavelength distribution data for each wave number and an example of wave velocity distribution data for each wave number are shown in FIG. 7 and FIG. 8, respectively. 7 and 8, the horizontal axis indicates the wave of one cycle (the time taken from passing through the neutral point from the bottom to the top and then from the bottom to the top again) that can be measured from the vertical movement of the buoy. “Wave number” as an interval, for example, the number present in 10 minutes. In FIGS. 7 and 8, the wavelength or wave speed corresponding to each wave is indicated by a solid line, and the wavelength or wave speed of the wave corresponding to the peak from the first peak to the third peak appearing by spectral analysis is distinguished. It is shown. The significant wavelength is a wavelength calculated from the period when the wave periods are arranged in descending order and an average of one third is taken from the larger one.

It is the schematic which shows an example of the ocean wave measurement system to which the GPS type ocean wave measurement method by this invention is applied. It is a flowchart which shows the whole flow of the GPS type ocean wave measuring method by this invention. It is a data figure which shows an example which calculates | requires the period of a wave from the motion of the up-down direction of a GPS type buoy. It is a graph which shows an example of how to obtain | require the frequency by the wave height spectrum analysis from the signal transmitted from the GPS type buoy. It is an analysis flowchart showing the numerical analysis method used in the GPS type ocean wave measuring method by this invention. It is a figure which shows the convergence of the iterative calculation performed with the analysis flowchart shown by FIG. It is a figure which shows an example of the wavelength distribution data for every wave number. It is a figure which shows an example of the wave velocity distribution data for every wave number.

Explanation of symbols

1 GPS type buoy 2 Single GPS receiver 3 GPS satellite 4 Sea floor 5 Ocean wave T Ocean wave cycle L Ocean wave wavelength h Water depth

Claims (4)

Against the GPS signals equipped with single GPS receiver has received the buoy, to generate a modified vertical motion data obtained by removing the jump based on the change in the number of GPS satellites, then the high pass filtering to the modified vertical movement data And generating the vertical motion data of the buoy when the buoy is swayed by the ocean wave, and then determining the period of the ocean wave by performing frequency spectrum analysis on the vertical motion data. Ocean wave measurement method. 2. The GPS type ocean wave according to claim 1, wherein the period of the ocean wave is obtained as a reciprocal of the frequency at which the peak power has a maximum peak value in a peak power in a frequency domain obtained by the frequency spectrum analysis. Measurement method. The GPS formula according to claim 1 or 2 , wherein the wavelength of the ocean wave is estimated for each cycle of the ocean wave from a convergence value of the following relational expression x (n) established between the cycle and the water depth. Ocean wave measurement method.
x (0) = g × T ² / (2π)
x (n + 1) = g × T ² / (2π) × tanh (2πh / x (n)) (n = 0, 1,...)
Here, T is the period and h is the water depth . The GPS type ocean wave measurement method according to 2 or 3 , wherein the wave velocity of the ocean wave is obtained from the cycle and the wavelength for each cycle of the ocean wave.

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