RU2740297C1 - Method for visualization of current condition of bottom topography during operation of dredger - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to sonar, in particular, for monitoring state of bottom during ship operation of dredge. Invention makes it possible to operate in conditions of water-soil suspension, which inevitably accompanies work at the bottom. To achieve the result of the lateral sighting sonar antenna is installed on the rotary platform below the dredger housing, form and emit narrowly directed direction of rotation and wide in vertical plane sending signal towards bottom, receiving at several phase points reflected from bottom and suspended in the aqueous medium of signals, which are then amplified, digitized and, using Hilbert converters, form an analytical form of the signal, in which the amplitude and phase of each reflected signal is selected, determining direction of its arrival and by time of arrival of signal after sending distance to reflecting non-uniformity, multiple signals obtained thus forms a set of points, then command is sent to antenna rotation unit for next probing cycle, set of points on different angles of rotation of antennae are transmitted to input of spatial filter to exclude points not related to surface of bottom, and further formation of model of bottom surface, which is visualized in unit of display at given moment in time.

EFFECT: high efficiency of real-time monitoring of the current state of the bottom in the working zone of a dredger in the presence of a water-soil mixture both during operation of the dredger and after its stop.

1 cl, 2 dwg

Description

The invention relates to the field of sonar, in particular, for operational monitoring of the state of the bottom in the process of dredging or mining operations of a dredger vessel. The invention makes it possible to work in the conditions of water-soil suspension, which inevitably accompanies any work on the bottom, and allows the user to obtain a clear picture of the depths of the bottom in the area of the dredger operation with the accuracy (units of centimeters) specified for earthwork at the bottom.

Dredgers are vessels of the technical fleet used for underwater development and excavation during dredging and in hydraulic engineering. A feature of any underwater development and excavation is the formation of water-soil suspension, which interferes with the operation of sonars, and during the operation of dredgers, a model method is used to determine the current shape of the bottom, that is, it is believed that where the working tool of the dredger has passed, there is no soil. But this does not take into account the debris of the edges of the pits and stones falling out of the working tool. The ability to measure depths appears only a few days after the end of the work of the dredger, and in the case of abandoned "under-dredges" they have to be corrected, while incurring the costs of rearranging and operating the dredger or fines.

To increase the efficiency of the dredger, it is necessary to monitor the current state of the bottom surface in depth in real time during the operation of the dredger and see left stones, bumps and foreign objects at the bottom. Optical methods in muddy water do not allow seeing at distances of more than half a meter, electromagnetic rangefinders are limited to units of meters, therefore the only physical field suitable for measurements is the hydroacoustic field.

Known 2D survey sonars, for example, Teledyne Blueview M900 series, they allow you to form a flat image displaying the brightness of the reflection from objects located in the water. Such sonars are analogous to side-scan sonar and do not allow depth measurements, since they only measure the distance to a reflecting object.

The known systems for forming 3D images of underwater objects are a software extension of multi-beam echo sounders, and they cannot work in muddy water - they do not have a criterion for distinguishing between the water-turbidity and mud-bottom boundaries.

Known patent RU2510045C2 (publ. 03/20/2014, IPC G01S15 / 00) "A method for determining the depths of the water area with a side-looking phase sonar and a side-looking phase sonar for its implementation." This patent proposes emitting a hydroacoustic signal towards the bottom and receiving reflected signals at two points located vertically at a given distance, measuring the time delay of the arrival of in-phase signals, as a result of which the distance to it and the direction is determined for each reflecting underwater object, that is, the relative coordinates. To build a bottom surface map, it is necessary to fix this phase side-scan sonar on the vessel and ensure the movement of the vessel along the measured water area. The disadvantage of this solution is the lack of a method for determining the depth map of the water area from a stationary vessel and the presence of errors in determining the depths when working in conditions of water-soil suspension.

The closest prototype is "A method for determining depths in real time when examining the bottom topography with a side-scan sonar followed by its restoration" (RU2521127C2, publ. 06/27/2014, IPC G01S 15/89), including measuring the delay time of the in-phase signals of the bottom reverberation , received by two antennas, vertically spaced by several wavelengths of elastic vibrations, and resolution of measurement ambiguity, calculation of depths. Then, at each phase coincidence of the interfering signals, the instantaneous value of the signal frequency in the lower channel is recorded, the delay time of the appearance of the signal in the upper channel with the same instantaneous frequency is measured, the measured value of the delay time is multiplied by the value of the operating frequency of the interferometer, the ordinal numbering of a number of measurements of the arrival delay of in-phase signals during each sounding in real time. The depths are calculated corresponding to each interference fringe, and during the subsequent restoration of the bottom topography from the measured depths, the representativeness (significance) of critical topography points is assessed by representing a smooth continuous bottom topography surface with a Kronrod-Riba tree.

The advantage of the prototype over analogues is the ability to form a smooth continuous surface of the bottom relief.

The disadvantage of the prototype is the lack of filtration of the suspension density jumps and, as a consequence, the presence of errors in determining the depths when working in conditions of water-soil suspension created by a working dredger.

The technical result of the invention is to improve the efficiency of operational monitoring of the current state of the bottom in the working area of the dredger in the presence of a water-soil mixture both during the operation of the dredger and after it has stopped. This is achieved by installing a side-scan interference sonar antenna on a rotating platform below the dredger body in order to obtain a set of bottom cross-sectional profiles under the dredger with different azimuth, after which spatial filtering of the received echo signals to separate reflections from the bottom and from irregularities in the aquatic environment (water-soil suspension) and building a smooth bottom surface.

It is known that the amplitude of the signal reflected from medium inhomogeneities has the form [1]:

(1)

(one)

Where

p (t) - pressure at the receiver,

p ₀ (t) - pressure on the radiator,

r - distance to the location object,

m _v - specific coefficient of back reflection, depending on the reflecting volume, particle size and radiation frequency,

R _A is the directivity characteristic of the transceiver,

c is the speed of sound in water,

τ is the time delay relative to the message,

R _Э - equivalent radius of the reflecting object,

β is the absorption coefficient of the medium.

In order to receive the signal reflected from the bottom it is necessary:

- that the reflecting object was much greater than the half wavelength of the probe signal (R _E >> c / f);

- so that the medium conducting the signal is as less absorbing as possible (parameter β is as small as possible).

In this case, the frequency of the sounding signal is limited from below by the location accuracy (the ability to detect small objects at the bottom), and from above by the absorbing capacity of the water-soil mixture. When the particle size of the mixture is less than 1 mm, the frequency of the probing signal should be 100 ... 300 kHz at a location of 20 ... 75 meters from the dredger. It should be borne in mind that the range of the location is also limited by the depth of the reservoir and cannot be more than 5..7 depths. The higher the frequency, the higher the location accuracy, but the shorter the operating range, the lower the frequency - on the contrary, the longer the sonar range, but the lower the accuracy.

The signal reflected from the unevenness of the bottom hits the receiving antennas so that the signal arriving from different directions arrives with different signal time delays. For this, the receiving antennas are positioned at a certain vertical distance, as shown in FIG. 2.

Thus, we receive two signals [2]:

,

,

That is, the signals differ only in the signal arrival delay, which depends on the distance between the receiving elements, the direction of arrival and the speed of sound in water.

When using a probe tone (when a time-limited sinusoidal signal is sent), the signal arrival delay can be expressed in terms of the phase difference of the two received signals:

.

...

Measuring the phase difference of two signals is a typical operation in digital processing and analytical presentation of signals (for example, after the Hilbert transform):

.

...

Hence the requirement for the location of receiving antennas - they should be located at a distance of no more than half the wavelength of the received signal. If this requirement is violated, direction finding ambiguity appears - several directions appear, the phase difference of the received signals from which has the same value.

The sent signal propagates from the emitting antenna at the speed of sound in the water, and the wave front moves through the water-soil suspension towards the bottom and along it. Any inhomogeneity both in the aquatic environment and at the bottom forms a reflected signal that propagates in all directions, including towards the receiving antennas. Thus, the sum of a large number of signals reflected from different points in space comes to the receiving antennas. The amplitudes of the signals, as it was said, depend on the size of the inhomogeneity (the larger the inhomogeneity, the stronger the signal), contrast (the more the density and speed of sound between the materials of the bunch or the water-bottom boundary differ, the stronger the reflection). Therefore, we can assume that each discrete value of the received signal, perceived as a critical point, determines the distance in delay after sending and the direction of arrival from the phase difference between the receiving elements of the antenna, from which the depth of the location and the offset from the antenna can be calculated.

Since the values of the distance and direction of arrival of critical points do not allow judging which of them are more representative, related to the bottom surface, and which are not, with the exception of only the points with the highest value of the minimum and maximum amplitude. To determine the significance of the critical point of the surface as a suitable basis, we will use the concept of "topographic prominence" widely used in foreign cartography [5].

Topographic significance is the height difference between a summit and the highest saddle point that separates that summit from any higher summit. But the direct use of this concept for our purposes is impossible, since it considers only the points of local maxima and saddle points, but does not include the points of local minima of the relief, and it does not rely on mathematical concepts, which does not guarantee the absence of logical and algorithmic errors. The latter is manifested, for example, in the fact that the determination of topographic significance does not allow making an unambiguous choice of the saddle point relative to which the height of the top is measured.

The methods proposed in the prototype (Morse surface, Kronrod-Riba tree) in the presence of water-soil suspension are inapplicable, since they do not allow one to filter out “representative” critical points from clots of water-soil mixture, which have a sufficiently large amplitude of the reflected signal containing saddle points but not showing the current state of the bottom. Therefore, it is necessary to use additional spatial filtering to filter out critical points that are not related to the bottom surface and objects on the bottom.

Kalman filtration is such a filtration that provides a physically justified separation into points related to the bottom surface and noise [3]. But the “ordinary” Kalman filter (CKF) works well only in exceptional - so-called well-conditioned - problems and diverges in most practical problems. A robust and numerically efficient spatial filtering algorithm is required.

The phenomenon of divergence of the theoretical CKF algorithm gave rise to the search for alternatives that are algebraically equivalent to CKF, but much more stable in calculations.

It is well known that the main computational load in the Kalman filter falls on iterations of the Riccati equation [4]. To reduce the amount of computation, Martin Morph and Thomas Kailat [4] proposed to combine the stages of extrapolation and processing of filter measurements in one orthogonalized computation scheme, which made the algorithm stable. At present, the possibility of using parallel computations has appeared, as a result of which this algorithm has been rewritten to be presented in a block form, convenient for parallel computations.

In the proposed method, the antenna is rotated by a predetermined angle after each sounding cycle, the received signal at each cycle contains a sequence of critical points with a coordinate and depth. The program processes the obtained set of critical points in the described way. The calculation results for each block are joined in the form of boundary conditions, after which the calculations are repeated. The number of iterations in this approach turns out to be significantly less than in the classical method of calculations, and the result algebraically coincides.

Thus, it is possible to construct a smooth model of the bottom surface in the area of operation of the dredger with a given accuracy, even in conditions of water-soil suspension from a stationary or slow-moving dredger. This ensures operational monitoring of the seabed condition during dredging or mining operations.

The implementation of the proposed method is shown in the drawings:

FIG. 1 is a block diagram of the sequence of operations when implementing the method;

FIG. 2 is an example of the location of the antennas in relation to the dredger.

The method of visualizing the current state of the bottom relief during operation of the dredger is carried out using (Fig. 1) a probe pulse generator 1, a power amplifier 2, a piezoacoustic emitter 3, which can be combined with a receiver, a set of piezoacoustic receivers 4, amplifiers 5, analog-to-digital converters 6 , a Hilbert transducer 7, a unit for separating the amplitude and phase of the signal 8, a unit for determining the distance and direction of arrival of the signal 9, a spatial filtering unit 10 and a display unit 11. Unit 12 provides antenna rotation control.

The method works as follows.

The probe pulse generator 1 generates a parcel signal, which passes through the power amplifier 2 and the narrow-beam signal is emitted by the antenna 3 into the water under the dredger. The signals reflected from the irregularities at the bottom and in the water column arrive at the receiving elements of the antenna 4, which can be 2 or more for unambiguous direction finding. Signals from the receiving elements are fed to amplifiers 5, ADC 6, digitally converted into an analytical form using Hilbert transducer blocks 7, the analytical signal highlights the amplitude and phase of each signal 8. The direction of arrival is determined from the phase difference between the signals, and the time after transmitting, the distance to the reflective heterogeneity in block 9 is determined. The resulting point cloud, each point with its own distance and direction of arrival, is sent to the spatial filter block 10, where false points (noise) are discarded and a model of the bottom surface is formed, after which the obtained result enters the block 11 to display and visualize the bottom topography. After finishing the processing of one sounding cycle, a command is sent to the antenna rotation unit 12 for the next sounding cycle. The number of cycles is determined by the size of the sector of the angles of the system and the required accuracy of the bottom map.

The use of this invention increases the efficiency of dredging and mining operations on dredgers due to constant monitoring of the quality of the work performed, which makes it possible to do without downtime during the operation of the dredger due to the expectation of suspension sedimentation, subsequent measurements of depths and correction of under-dredging, as well as reduction of excessive deepening of the bottom (dredge stock ). The use of an inexpensive and reliable side-scan interferometric sonar antenna on a turntable provides a more accurate and detailed map of the bottom surface than many times more expensive multibeam echo sounders.

Information sources:

1. Sverdlin G.M. Hydroacoustic transducers and antennas. Textbook for technical schools (Leningrad: Publishing House "Shipbuilding", 1980).

2. Malyshkin G.S. Optimal and adaptive methods for processing hydroacoustic signals. Volume 1. Optimal methods - SPb .: Elektropribor, 2009. - 400 p.

3. Kalman R.E. A New Approach to Linear Filtering and Prediction Problems // ASME Journal of Basic Engineering, 1960, Vol. 82, pp. 34-45.

4. Lange A.A. Optimal Kalman Filtering for Ultra-Reliable Tracking, ESA CD-ROM WPP-237 // Atmospheric Remote Sensing Using Satellite Navigation Systems, Proceedings, Special Symposium of the URSI Joint Working Group FG, 13-15 October 2003, Matera, Italy.

5. Christopherson G.L. Using ARC / GRID to Calculate Topographic Prominence in an Archaeological Landscape. // Arc / INFO User Conference, 2003 .-- 15 pp. Podobnikar T. Method for Determination of the Mountain Peaks // 12th AGILE International Conference on Geographic Information Science, Leibniz Universitat Hannover, Germany, 2009, p. 1-8.

Claims (11)

1. A method of visualizing the current state of the bottom relief during the operation of the dredger, including: placement of the emitting and receiving antennas with the possibility of their rotation under the bottom of the dredger, formation and emission of a signal, which is narrowly directed in the direction of rotation and with a wide directivity characteristic in the vertical plane, towards the bottom, reception of signals reflected from the bottom and suspended matter in the aquatic environment by receiving antennas, which are then amplified, digitized and, using Hilbert transducers, form an analytical form of the signal, and each discrete value of the received signal is perceived as a critical point, isolation, in an analytical form of the signal, the amplitude and phase of each critical point of the reflected signal, determination of the direction of arrival of each critical point of the reflected signal from the phase difference between the receiving elements of the antenna and the distance to the reflective inhomogeneity in the time of arrival after sending, formation of a set of spatial points from all obtained critical points by iteratively performing spatial filtering of critical points for the bottom surface and noise, using the Kalman filter based on the expression of Martin Morph and Thomas Kailat, rotation of the transmitting and receiving antennas for the next sounding cycle, formation of a bottom surface model, in which the sets of spatial points obtained at different positions of the rotary antenna are joined in the form of boundary conditions, and visualization of the generated surface model in the display unit at a given time. 2. The method according to claim 1, in which the frequency of the narrowly directed beam of the sending signal is selected taking into account the particle size of the suspension in the aquatic environment and the accuracy of determining the depths during the operation of the dredger.

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