A method for calculating the dynamic draft of a ship using secondary echo signals

Abstract

The application relates to a ship dynamic draft calculation method using secondary echo signals, which comprises the following steps: obtaining seabed reflected original acoustic data and performing data conversion and storage, and obtaining stored echo energy data; obtaining the position of primary echoes according to the stored echo energy data; obtaining the position range of secondary echoes according to the position of the primary echoes, and obtaining the position of the secondary echoes according to the maximum value in the position range of the secondary echoes, wherein the secondary echoes include ship bottom and sea surface reflected echoes; and calculating the ship dynamic draft value according to the position difference of the ship bottom and sea surface reflected secondary echoes. The application extracts and accurately calculates the dynamic draft of the ship by using the potential effective information in the acoustic echo data, and improves the accuracy of water depth measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ocean exploration, in particular to a ship dynamic draft calculation method using secondary echo signals. BACKGROUND

[0002] Water depth is one of the most basic data of ocean investigation, and the conventional instrument for offshore water depth measurement is an echo sounder. The transducer of such a device is generally installed in an embedded manner on the ship bottom shell. The formula for water depth measurement is H = ct / 2 + D, wherein H is the water depth, c is the speed of sound propagation in water, t is the travel time of sound waves, and D is the ship draft. The result of water depth measurement is composed of two parts, i.e., the distance from the underwater transducer to the seabed (ct / 2) and the ship draft (D), so the accuracy of the ship draft (D) directly affects the precision of offshore water depth measurement.

[0003] There are two known schemes for measuring the ship draft at present: one is to directly measure the ship draft by using a ruler or a rope in a traditional method, and input the fixed value into the measurement software; and the other is to install a pressure sensor near the transducer, and dynamically modify according to the display value of the pressure sensor in real time. The defect of the first scheme is that the variation of the draft caused by the speed of the ship in the navigation process and the heave and sway of the ship cannot be fed back to the real-time measurement data (if an attitude sensor is connected, the influence can be eliminated), resulting in measurement error, and the precision can only reach the decimeter level. In addition, the change of the ship draft caused by the consumption of fuel and fresh water during the operation of the ship is not necessarily linear, and sometimes the ship draft will suddenly change due to the sudden emptying or filling of the ballast tank caused by the sudden addition of water or the adjustment of the ship ballast, and the change of the ship draft caused by the ship entering the sea area with changing density, especially the river mouth position, etc. These uncertain factors cannot be input in real time to correct the software, thereby affecting the accuracy of water depth measurement. The other scheme of installing a pressure sensor near the transducer needs to additionally purchase a pressure sensor or a device capable of measuring the real-time pressure of the transducer, and the installation and use are extremely inconvenient. If the position of the additional device under water changes, it is not easy to be detected, and the risk and cost of ocean investigation are also increased. The dynamic draft of the ship is an important factor affecting the water depth measurement, so how to more accurately master the dynamic draft of the ship is crucial to the ocean water depth measurement. SUMMARY

[0004] The purpose of the present application is to provide a ship dynamic draft calculation method using secondary echo signals, to extract and accurately calculate the dynamic draft of the ship by using the potential effective information in the acoustic echo data, and to improve the precision of water depth measurement.

[0005] To achieve the above purpose, the present application provides the following scheme:

[0006] A method for calculating the dynamic draft of a ship using secondary echo signals includes:

[0007] Acquire raw acoustic data of seabed reflections, convert and store the data, and acquire the stored echo energy data;

[0008] Based on the stored echo energy data, the location of one echo is obtained;

[0009] Based on the position of the first echo, the position range of the second echo is obtained, and the position of the second echo is obtained based on the maximum value within the position range of the second echo. The second echo includes echoes reflected from the bottom of the ship and the sea surface.

[0010] The dynamic draft of the ship is calculated based on the positional difference of the secondary echoes reflected from the ship's bottom and the sea surface.

[0011] Optional data transformation and storage include:

[0012] The raw acoustic data is converted into decimal echo energy data, and each converted echo energy data is stored as a structure array, wherein the structure array includes pulse number, transmission time, longitude, latitude, start depth, end depth and echo intensity.

[0013] Optionally, obtaining the location of an echo includes: filtering the stored echo energy data, and obtaining the location of the echo based on the location corresponding to the maximum energy value of the filtered data.

[0014] Optionally, filtering the stored echo energy data includes: searching downwards from the Nth data point of the received echo energy data and deleting echo energy data outside a preset intensity range.

[0015] Optionally, the position range of the secondary echo is: [2X-2d, 2X+2d], where X is the position of the primary echo and d is the design draft of the ship.

[0016] Optionally, obtaining the location of the secondary echo includes: using an extremum function to obtain two maxima within the location range of the secondary echo, and using them as the location of the secondary echo.

[0017] Optionally, calculating the dynamic draft of a ship includes: obtaining the positions of several sets of secondary echoes, obtaining several differences, and averaging the several differences to obtain the dynamic draft of the ship.

[0018] The beneficial effects of this invention are as follows: without increasing additional equipment and other costs, this invention obtains accurate ship dynamic draft by interpreting, analyzing and extracting acoustic secondary echo data, which has the advantages of economy and convenience. It can also be used to retrieve information on other interface layers in the inversion detection profile, such as the thermohaline layer, biosphere and fog layer caused by seabed sediments in the ocean. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart illustrating a method for calculating dynamic draft of a ship using secondary echo signals, according to an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of primary and secondary reflections in a sound wave according to an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the dynamic draft of a ship extracted using secondary echo data according to an embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the acoustic data profile after dynamic draft correction according to an embodiment of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The principle of an echo sounder is that sound waves are emitted from a transducer and propagate towards the seabed. Upon hitting the seabed, they are reflected back and received by the transducer. The transducer calculates the distance by recording the time difference between the emitted and received sound waves. However, only a portion of the reflected sound waves is received by the transducer; most continue to propagate in the water. Some of these reflected sound waves hit the hull of a ship and are reflected again, then hit the seabed once more and are received by the transducer – this is the secondary echo. The hull of the ship reflects some sound waves, and the sea surface, as a large interface layer, also reflects some. Because the hull and the sea surface are located at different positions as reflecting surfaces, the travel time of the received secondary echoes is also different, appearing as two non-overlapping time points on the acoustic image. The difference between them is due to the ship's draft. The presence of two strong, non-overlapping secondary echo signals in the original data's echo curve provides the basis and possibility for the implementation of this method. Because ships are affected by ocean dynamics such as wind and waves, they are constantly swaying and rolling. This causes the dynamic draft value recorded by the secondary echo to fluctuate around the true value, requiring further processing to extract the true dynamic draft value of the ship.

[0027] like Figure 1 As shown in the figure, this embodiment proposes a method for calculating the dynamic draft of a ship using secondary echo signals, including:

[0028] Acquire raw acoustic data of seabed reflections, convert and store the data, and acquire the stored echo energy data;

[0029] Based on the stored echo energy data, obtain the location of one echo;

[0030] Based on the location of the first echo, the location range of the second echo is obtained. Within the location range of the second echo, the location of the second echo is obtained based on the maximum value. The second echo includes echoes reflected from the bottom of the ship and the sea surface.

[0031] The dynamic draft of the ship is calculated based on the difference in position between the secondary echoes reflected from the bottom of the ship and the sea surface.

[0032] Further data transformation and storage include:

[0033] The raw acoustic data is converted into decimal echo energy data, and each converted echo energy data is stored as a structure array, which includes pulse number, transmission time, longitude, latitude, start depth, end depth and echo intensity.

[0034] Specifically, the transformation of raw acoustic data includes:

[0035] The raw data from a depth sounder contains a large amount of acoustic signals. Because these data are not in a universal format, they can only be opened by specific acquisition software, and are therefore generally ignored. The raw data can be decoded by analyzing the data protocol and format definitions in the instruction manual. Using Matlab programming, raw data with the *.raw extension can be converted into decimal echo energy data (Power) for easier subsequent processing.

[0036] After converting the raw data, we obtain freely viewable decimal data. To facilitate further data processing using Matlab programming, the converted data is stored in a custom structure array format. The process of a depth sounder emitting a sound wave and receiving its echo is called a ping. Each ping's data is defined as a structure array, containing seven cells: ping number (Ping_No.), emission time (Date_Time), longitude (Longitude), latitude (latitude), starting depth (Depth_Strating), ending depth (Depth_End), and echo intensity (Data_Values). The echo intensity cell stores the echo data of the current ping in double-precision type.

[0037] Furthermore, obtaining the location of an echo includes: filtering the stored echo energy data, and obtaining the location of an echo based on the location corresponding to the maximum energy value of the filtered data.

[0038] Furthermore, filtering the stored echo energy data includes: searching downwards from the Nth data point of the received echo energy data and deleting echo energy data outside the preset intensity range.

[0039] Specifically, the location of a single echo on the seabed can be determined by analyzing echo energy data. Based on the characteristics of sound wave propagation in water, the propagation energy gradually decreases with increasing propagation time and distance. When the sound wave reaches the seabed, it is reflected. Because the reflection at this solid-liquid interface is much greater than the acoustic scattering signal in the water, the echo energy suddenly increases to its maximum when the seabed echo signal is received. This is represented by a peak in the data image. The maximum echo value received during this sound pulse is the location of the single echo (X), which is the reflection on the seabed. Analysis of a large amount of data revealed that near the ship's bottom, due to reverberation and other noise signals, the echo energy generally exceeds 10dB, which affects the determination of the single echo location. Therefore, limiting conditions were added to the program: First, the determination range avoids the reverberation area near the ship's bottom, searching downwards from the 20th data point of the received echo data; second, the maximum echo energy value searched is limited to between -40dB and 0dB. Data exceeding this range is considered invalid. By overcoming the technical limitations mentioned above, the location (X) of a single echo can be accurately identified. X corresponds to the depth of the single echo location, and the echo intensity at X is P(X). Formula (1) is used for this determination:

[0040] [P(X),X]=max(Data_Values)…………………………………………(1);

[0041] Where max is the built-in maxima function in Matlab, P(X)∈[-40dB,0dB].

[0042] Furthermore, the location range of the secondary echo is: [2X-2d, 2X+2d], where X is the location of the primary echo and d is the design draft of the ship.

[0043] Furthermore, obtaining the location of the secondary echo involves using an extremum function to obtain two maxima within the location range of the secondary echo, which are then used as the location of the secondary echo.

[0044] Specifically, the theoretical location of the secondary echo should be twice the distance of the primary echo. However, due to variations in ship draft and undulation, there is a deviation from this twice-primary-echo location. Using the initially detected primary echo location (X) and the ship's design draft (d) as constraints can improve the efficiency and accuracy of determining the secondary echo location. The range of the secondary echo location is [2X-2d, 2X+2d]. To reduce interference from noise and other factors, the initially estimated secondary echo location is used as the range constraint. Then, the extreme value function (findpeaks) in Matlab is used to find the two maximum locations (y1, y2) within the detection range. These two maximum values ​​are the locations of the secondary echoes at the ship's bottom and the sea surface.

[0045] Figure 2 The image displayed is approximately 130 minutes of continuous acoustic interpretation, measuring a water depth of about 80 meters. Figure 2 A distinct high-intensity reflection line can be seen near a water depth of 80 meters, i.e. Figure 2 The Chinese characters mark the first reflection on the seabed, which is the location of the seabed determined from the acoustic data, also known as the first reflection location. Strong reflection signals also appeared at a water depth of 160 meters. These strong reflection signals consist of two lines: the upper line is the secondary reflection from the bottom of the ship, and the lower line is the secondary reflection from the sea surface. The reason why these two lines do not overlap is due to the difference in position between the bottom of the ship and the sea surface, which reflects the ship's draft.

[0046] Calculate the ship's dynamic draft:

[0047] By identifying the location depths (y1, y2) of the two maxima, which represent the secondary reflections (y1) caused by the ship's bottom and (y2) caused by the sea surface, respectively, the true distance (d1) between the two maxima is calculated using formula (2):

[0048] d1=|y1-y2|……………………(2).

[0049] Furthermore, calculating the ship's dynamic draft includes: obtaining the positions of several sets of secondary echoes, obtaining several differences, and averaging these differences to obtain the ship's dynamic draft.

[0050] Specifically, the distance (d1) represents the transducer draft during a single acoustic pulse detection. Averaging multiple data points yields the ship's real-time dynamic draft (D), calculated using the following formula:

[0051] D = (d1 + d2 + d3 + d4 + ... + d...) n ) / n……………………(3);

[0052] Where n is the number of data points.

[0053] The difference between the two echoes is used to obtain Figure 3 The solid line represents the ship's draft calculated from each depth measurement, fluctuating between 5.1 and 6.0 meters. This fluctuation is due to the real-time changes and fluctuations in the distance between the sea surface and the hull caused by the ship's rolling and undulating motion. Ship draft is a relatively stable value over a short period. Its variation is influenced by changes in the ship's own weight and seawater density. Therefore, without significant weight adjustments (adding water, refueling, sewage discharge, ballast adjustments, etc.), the draft is a relatively stable value. Thus, averaging short-term sample data yields the final draft. Figure 3The average value marked by the dashed line is 5.52 meters, which is the real-time draft of the ship identified through secondary echo data during the current period.

[0054] Echo sounders can only record the distance between the transducer surface and the seabed. The proposed method, which uses secondary echoes to extract the ship's dynamic draft, can accurately correct the data. This not only remedies the deficiency of forgetting to record historical ship draft data but also improves the accuracy of ship depth sounding data. For example... Figure 4 As shown, the calculated dynamic draft of the ship completes the entire seawater profile. The upper colored blank area represents the ship's draft, and the location of the strong reflection layer in the middle of the image after dynamic draft correction represents the actual seabed depth.

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for calculating the dynamic draft of a ship using secondary echo signals, characterized in that, include: Acquire raw acoustic data of seabed reflections, convert and store the data, and acquire the stored echo energy data; Based on the stored echo energy data, the location of one echo is obtained; Based on the position of the first echo, the position range of the second echo is obtained, and the position of the second echo is obtained based on the maximum value within the position range of the second echo. The second echo includes echoes reflected from the bottom of the ship and the sea surface. The dynamic draft of the ship is calculated based on the positional difference of the secondary echoes reflected from the ship's bottom and the sea surface.

2. The method for calculating ship dynamic draft using secondary echo signals according to claim 1, characterized in that, Data transformation and storage include: The raw acoustic data is converted into decimal echo energy data, and each converted echo energy data is stored as a structure array, wherein the structure array includes pulse number, transmission time, longitude, latitude, start depth, end depth and echo intensity.

3. The method for calculating ship dynamic draft using secondary echo signals according to claim 1, characterized in that, Obtaining the location of an echo includes: filtering the stored echo energy data, and obtaining the location of the echo based on the location corresponding to the maximum energy value of the filtered data.

4. The method for calculating ship dynamic draft using secondary echo signals according to claim 3, characterized in that, Filtering the stored echo energy data includes: searching downwards from the Nth data point of the received echo energy data and deleting echo energy data outside the preset intensity range.

5. The method for calculating dynamic draft of a ship using secondary echo signals according to claim 1, characterized in that, The location range of the secondary echo is: [2X-2d, 2X+2d], where X is the location of the primary echo and d is the design draft of the ship.

6. The method for calculating dynamic draft of a ship using secondary echo signals according to claim 1, characterized in that, Obtaining the location of the secondary echo involves using an extremum function to obtain two maxima within the location range of the secondary echo, which are then used as the location of the secondary echo.

7. The method for calculating ship dynamic draft using secondary echo signals according to claim 1, characterized in that, Calculating the dynamic draft of a ship includes: obtaining the positions of several sets of secondary echoes, obtaining several differences, and averaging the several differences to obtain the dynamic draft of the ship.

Images