TECHNICAL FIELD

The present invention relates to a detection system and method to check the position of a pipeline in a bed of a body of water .

BACKGROUND ART

Generally, an underwater pipeline is laid in the bed of the body of water and buried in the bed of the body of water at a certain depth, in particular at landings and in shallow water to protect the pipeline from external agents. Once the pipeline has been buried, it is necessary to check if the position of the pipeline in the bed of the body of water falls within the design values. Another parameter to check is the trenching height, which by convention is the distance between the upper end of the pipeline and the upper end of the bed of the body of water.

DISCLOSURE OF INVENTION

One object of the present invention is to provide a detection system to check the position of a pipeline in a bed of a body of water that is simple and inexpensive.

According to the present invention, a detection system is provided to check the position of a pipeline in a bed of a body of water and extending along a predetermined route; the system comprising a device configured to be moved in a moving direction and along the predetermined route, and comprising a support, which mainly extends transversely to the moving direction, a number of acoustic wave sources mounted on the support, configured to transmit acoustic waves through the body of water and the bed of the body of water, and a number of acoustic wave receivers located along the support and configured to receive reflected acoustic waves and emit reception signals related to the reflected acoustic waves; and a processing unit comprising an acquisition unit configured to receive, from the outside, at least one datum selected within a group of known or expected data comprising: the known value of the cross-section of the pipeline, an expected value of the trenching height of the pipeline, the known shape of the pipeline, the expected bathymetric profile of the bed of the body of water, and an expected value of the position of the pipeline; the processing unit being configured to calculate a parameter related to the position of the pipeline in the bed of the body of water on the basis of the reception signals and of said at least one datum selected within the group of data.

With the present invention, by using the at least one datum selected within the data group, the processing unit is able to calculate the parameter related to the position of the pipeline in real time due to the reduction in complexity of the calculation. In this way, the detection system checks if the position of the pipeline in the bed of the body of water respects the assigned design values.

According to a preferred embodiment of the present invention, the processing unit comprises an output interface to correct the moving direction on the basis of the parameter calculated in the previous instant.

With the present invention, the system reduces the detection time because it follows the pipeline using the parameter calculated in real time.

According to another embodiment, the processing unit is configured to calculate the path of the acoustic waves reflected by the pipeline through the body of water and the bed of the body of water on the basis of the reception signals; and to calculate the parameter related to the position of the pipeline on the basis of the calculated path of the acoustic waves.

According to another preferred embodiment, the system comprises a mechanism to adjust the immersion depth of the support in the body of water (6), so as to place the support at a given estimated distance from the pipeline.

With the present invention, the system keeps the distance between the pipeline and the support almost constant, in this way optimizing detection of the parameter and extending the surface covered.

According to another preferred embodiment, each source of said number of sources is configured to emit the acoustic wave with a frequency linearly variable with time within a given frequency range, which depends on the desired space resolution and on the desired penetration depth.

In this way, the acoustic beams have a broad range and a large penetration capability.

According to another preferred embodiment of the present invention, the number of sources is equal to or greater than two, in particular the number of sources is equal to three; one of the three sources being located at the centre of the support and the other two sources being located at the ends of the support.

Thanks to the sensors located at the ends of the support, the device covers a broader surface and enables striking the pipeline with acoustic waves coming from different angles. In this way, the system obtains a better estimate of the parameter . According to another preferred embodiment of the present invention, the number of receivers has a transduction gain from the sound to the reception signal that is substantially independent of the direction of provenance of the sound.

With the present invention, the detection device covers a broad surface and, in consequence, requires a smaller numbers of passes over the pipeline.

According to another preferred embodiment of the present invention, the number of receivers is equal to or greater than two; in particular the number of receivers is equal to or greater than three. Furthermore, the receivers are distributed transversely to the moving direction.

With the present invention, the system enables reducing the passes over the pipeline by reducing the time for calculating the position of the pipeline.

With the present invention, the system receives the reflected acoustic waves from different receivers. In this way, the system receives acoustic waves that have taken different paths and calculates the parameter with high precision.

The device with a number of receivers greater than or equal to three has the advantage of estimating the parameter more precisely and of having fewer constraints on the minimum distance between the receivers. In fact, the reflected acoustic waves align themselves along a hyperbolic path in the space-time domain and, in consequence, the device with a number of receivers equal to or greater than three can reconstruct the hyperbolic path of the reflected waves thanks to the readings of the three receivers, as a hyperbola is unambiguously defined by three points. In addition, with the present invention, the detection device with a minimum number of three receivers reduces problems of spatial aliasing.

According to another preferred embodiment, the number of sources and the number of receivers are placed so as to form an upside-down V with the concave part facing the bed of the body of water; in particular, the V forming an angle lying within the range having limits of 80° and 100°; preferably, the number of sources is greater than or equal to two, and the number of receivers is greater than or equal to three.

With the present invention, the detection device extends the radius of coverage of the detected surface with a smaller length or a smaller immersion depth for a given detected surface .

According to another preferred embodiment, the processing unit is configured to calculate the speed of sound through the bed of the body of water from the reception signals and so reduces measurement errors regardless of the use of any standard speed tables .

Furthermore, the number of receivers has a transduction gain from the sound to the reception signal that is substantially independent of the direction of provenance of the sound.

With the present invention, the device enables calculating the parameter related to the position of the pipeline without knowing the exact position of the pipeline, but knowing the probable position. Furthermore, the device has a radius of coverage with a wide angle that allows detecting the parameter in just one pass, without the need to perform criss-cross passes over the pipeline. In addition, the processing unit is configured to perform statistical autocorrelation between the reception signals to compensate for directional power losses due to the wide angle of the illumination beam.

In addition, the processing unit is connected to the source to control transmission signals for the emission of the acoustic waves and is configured to calculate the parameter related to the position of the pipeline in the bed of the body of water on the basis of the transmission signals, preferably on the basis of a statistical correlation between the transmission signals and the reception signals. In this way, the device provides the position of the pipeline with high precision.

Another object of the present invention is to provide a method for detecting the position of a pipeline in the bed of a body of water that is simple and inexpensive.

According to the present invention, a detection method is provided to check the position of a pipeline in a bed of a body of water extending along a predetermined route; the method comprising the steps of moving, in a moving direction and along the predetermined route, a number of acoustic wave sources and a number of acoustic wave receivers distributed transversely to the moving direction; transmitting acoustic waves through the body of water and the bed of the body of water; receiving the acoustic waves reflected by the pipeline; acquiring, from the outside, at least one datum selected within a group of known or expected data comprising: the known value of the cross-section of the pipeline, an expected value of the position of the pipeline, the shape of the pipeline, the bathymetric profile of the bed of the body of water, and an expected value of the position of the pipeline; and calculating a parameter related to the position of the pipeline in the bed of the body of water on the basis of the reflected acoustic waves received and on the basis of said at least one datum selected within the group of data.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will become clear from the description that follow of a non-limitative embodying example, with reference to the figures of the accompanying drawings, in which:

- Figure 1 is a rear elevation view, with parts removed for clarity, of a detection system of the position of a pipeline in the bed of a body of water, and with parts in section of the pipeline, of a body of water and of a bed of a body of water;

- Figure 2 is a plan view, with parts removed for clarity, of Figure 1 ;

- Figure 3 is a block diagram of a detection device of the detection system; and

- Figure 4 is a rear elevation view, with parts removed for clarity, of an alternative embodiment of the detection system of Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to Figures 1 and 2, reference numeral 1 indicates, as a whole, a detection system 1 for checking the position of a pipeline 4 in the bed 5 of a body of water 6 and comprising a vessel 2 and a detection device 3. In use, the vessel 2 is configured to proceed in a moving direction D. The device 3 comprises a connection system 7 to connect it to the vessel 2 and be moved in the body of water 6. In particular, the connection system 7 comprises actuators 8 that enable adjusting the immersion depth of the support 9 in the body of water 6 so as to place the support 9 at an estimated distance D2 from the pipeline 4.

The device 3 comprises a support 9 that mainly extends along an axis A that, in use, is transversal to the moving direction D. In other words, the support 9 extends mainly along axis A; in particular, the size of the support 9 along the axis A is at least twice the size transversal to the axis A of the support 9. In particular, the size of the support 9 along the axis A is at least ten times its size transversal to the axis A. The device 3 comprises a number of acoustic wave sources 10 distributed along the support 9 and a number of acoustic wave receivers 11 distributed along the support 9.

The system 1 comprises a processing unit 12 in communication with the number of acoustic wave sources 10 and the number of acoustic wave receivers 11.

Each acoustic wave source 10 is configured to transmit an acoustic wave through the body of water 6 and the bed 5 of the body of water 6, and is preferably spaced apart from the adjacent sources 10 so that the acoustic waves emitted by the sources 10 pass through the body of water 6 and the bed 5 of the body of water 6 with mutually different angles. In particular, the number of sources 10 is constituted by three acoustic wave sources 10 spaced apart from each other along the support 9. In greater detail, one of the three acoustic wave sources 10 is located at the centre of the support 9 and the other two acoustic wave sources 10 are located at the ends of the support 9. This configuration enables emitting acoustic waves that pass through the body of water 6 and the bed 5 of the body of water 6 from different angles according to the position of each source 10. Each source 10 comprises a transducer 13 that in turn comprises a number of piezoelectric elements . The piezoelectric elements are aligned along an axis that can be parallel to axis A or perpendicular to axis A and are configured so as to be powered individually or in groups. In one non-limitative embodiment of the present invention, the piezoelectric elements are powered in sequence starting from one of them, for example the central one, and then proceeding symmetrically outwards. In another non-limitative embodiment of the present invention, the piezoelectric elements are all powered together in the same manner, so as to increase the directivity of the emitted acoustic wave. In this way, the piezoelectric elements generate CHIRP type acoustic waves having a broad frequency spectrum that ensures a high penetration capability and wide spatial coverage. In addition, a better signal-to-noise ratio is obtained by using CHIRP acoustic waves. Each source 10 of the three sources 10 is therefore configured so as to be omnidirectional along a hemisphere facing the bed 5 of the body of water 6. In other words, each emitted acoustic wave expands following a hemisphere facing the bed 5 of the body of water 6. In a preferred but non-limitative embodiment of the present invention, each source 10 comprises five piezoelectric elements. The transducer 13 comprises a power supply unit for the five piezoelectric elements that is configured to power just one, three of the five, or all five, starting from the central one and proceeding symmetrically outwards. In greater detail, each acoustic wave source 10 is configured to emit an acoustic wave with a cyclical frequency linearly variable with time, the frequency range depending on the desired space resolution and preferably on the cross-section Dl of the pipeline 4, and on the desired penetration depth in the bed 5 of the body of water 6. By way of example, each source 10 is configured to emit a CHIRP type acoustic wave with a duration of between 2 and 6 ms, preferably 4 ms, and which varies linearly with time in the 1 to 60 kHz frequency range, preferably in the 10 to 50 kHz frequency range. The frequency range is chosen on the basis of the desired resolution and the desired penetration. In a preferred embodiment, the desired resolution is in the order of a centimetre.

In an alternative embodiment of the present invention, each source 10 comprises magnetodynamic or magnetostrictive transducers .

The number of acoustic wave receivers 11 is constituted by a number N of acoustic wave receivers 11 aligned along axis A. The number N is variable, depending on the desired resolution. In one embodiment, the number N is equal to one. In another embodiment, the number N is equal to three. The detection device 3, with a number N of receivers 11 grater or equal to three, has the advantage of estimating the position of the pipeline 4 more precisely and of having fewer constraints on the minimum distance between the receivers 11. In fact, the acoustic waves reflected by the pipeline 4 align along a hyperbolic path in the space-time domain and, in consequence, the detection device 3, by having a number of receivers 11 equal to or greater than three, can properly reconstruct the hyperbolic path of the reflected waves thanks to the readings of the three receivers 11, because a hyperbola is unambiguously defined by three points. In this way, the device 3 reduces problems of spatial aliasing. In yet another embodiment, the number N is in the order of tens of receivers 11. The plurality of receivers 11 is arranged such that there is at least one receiver 11 between two sources 10. Furthermore, when the receivers 11 are in the order of tens, the receivers 11 are uniformly distributed with a constant distribution distance; in particular, the distribution distance is smaller than or equal to 40 cm, preferably smaller than or equal to 20 cm. The plurality of receivers 11 extends along axis A for a given length L ranging from 3 to 5 metres, in particular 4 metres. Preferably, the length L is related to the distance between the support 9 and the pipeline 4.

By way of example, each receiver 11 is a hydrophone of high sensitivity and having a receiving frequency response that is almost flat from approximately 0.1 to 180 kHz and, in particular, deviations from the mean gain value are negligible up to 15 kHz. Furthermore, by way of example, each receiver 11 has a reception diagram, measured at a frequency of 100 kHz, which develops along a circumference of the plane formed by the axes parallel to axis A and to the moving direction D and along a line, which is inside an annulus having a width of 5- 10 dB, in the plane formed by the axes parallel to the A and Z axes, where Z is an axis perpendicular to axis A, to the moving direction D and transversal to the bed 5. In consequence, each receiver 11 has a reception gain substantially the same from whatever direction in space the sound arrives. In other words, each receiver 11 has a transduction gain from the sound to the reception signal SR that is substantially independent of the direction of provenance of the sound.

Therefore, each acoustic wave receiver 11 is configured to receive acoustic waves reflected at different angles and emit reception signals SR, which are related to the reflected acoustic waves and are transmitted to the processing unit 12.

The receivers 11 identify a detection half-plane that extends from the support 9 towards the bed 5 of the body of water 6 and transversely thereto; in particular, the detection plane is perpendicular to the bed 5 of the body of water 6 and the half-plane comprises axis A and axis Z.

According to an alternative embodiment of the present invention, each transducer 13 is configured to work both as a source 10 and as an acoustic wave receiver. According to this embodiment, the device 3 thus comprises a row of receivers 11 and transducers 13, which are aligned along axis A and distributed with a constant distribution distance and are all configured to generate a reception signal SR. The device 3 adjusts, by means of the actuators 8, the distance D2 of the support 9 from the upper end of the pipeline 4 measured along axis Z. The distance D2 is adjusted so as to be within a given range the limits of which are respectively given by: a) the length L; and b) twice the length L; preferably at an estimated distance D2 equal to the product of 1.5 times the length L. In an alternative embodiment shown in Figure 4, the device 103 comprises an upside-down V shaped support 109. Furthermore, the device 103 comprises a plurality of sources 10 and receivers 11 located along the support 109 so as to form an upside-down V, with the concave part facing the bed 5 of the body of water 6. In particular, the support 109 forms an angle in the range between 80° and 100°. In the embodiment shown, the angle is 90°. With the present embodiment, the device 103 needs a smaller immersion depth for a given length L and can detect the pipeline 4 at a greater distance D2 from the pipeline 4 with respect to device 3.

The processing unit 12 is in communication with the acoustic wave sources 10 to control the transmission signals ST and with the acoustic wave receivers 11 to receive the reception signals SR. In addition, the processing unit 12 knows the positions of the sources 10 and associates a datum related to the position of the respective source 10 with each transmission signal ST. In a similar manner, the processing unit 12 knows the positions of the receivers 11 and associates a datum related to the position of the respective receiver 11 with each reception signal SR. According to an alternative embodiment, the transmission signals ST are generated by the acoustic wave sources 10 or by another device associated with the acoustic wave sources 10 and are also sent to the processing unit 12. The processing unit 12 is configured to check if a parameter related to the position of the pipeline 4 in the bed 5 of the body of water 6 falls within certain ranges. In other words, the pipeline 4 has been buried in the bed 5 of the body of water 6 at a given depth and in a given position that are known from the design values and more or less correspond to the effective data except for important deviations in the execution phase. The processing unit 12 is configured to calculate the position of the pipeline 4 and the parameters related to the burying by using all the information known beforehand so as to check if the burying has been correctly performed.

In particular, the processing unit 12 calculates the position of the pipeline 4 and the parameters related to the burying of the pipeline 4 in the bed 5 of the body of water 6 on the basis of the reception signals SR. In an alternative embodiment of the present invention, the processing unit 12 calculates the position of the pipeline 4 in the bed 5 of the body of water 6 on the basis of the reception signals SR and the transmission signals ST.

In addition, the processing unit 12 is configured to calculate four other parameters based on the calculated position of the pipeline 4: a first parameter, a second parameter, a third parameter and a fourth parameter.

The first parameter is the value of the trenching height H of the upper end of the pipeline 4 in the bed 5 of the body of water 6. In other words, the "trenching height H" means the distance between the surface of the bed 5 of the body of water 6 and the upper end of the pipeline 4. By way of example, the desired value of the first parameter, namely the trenching height H, is within a first range between 2.5 and 3 metres.

The second parameter is the value of the straightness of the pipeline 4 along axis Z, in other words the maximum vertical excursion of the pipeline 4 along a predetermined length. By way of example, the desired value of the second parameter is an excursion smaller than 20 cm along axis Z over a length of 25 metres of pipeline 4.

The third parameter is related to the shape of the trench in which the pipeline 4 is laid.

The fourth parameter is the value of the thickness of the covering of the pipeline 4, i.e. the amount of covering material on top of the pipeline 4.

In addition, the processing unit 12 comprises an acquisition unit 14 configured to receive, from the outside, for example from an operator or from another device connected to device 3, a value of the speed of sound in the body of water 6 and set this value in the processing unit 12. According to an alternative embodiment of the present invention, the processing unit 12 calculates the speed of sound in the body of water 6 from the reception signals, in particular the processing unit 12 detects the speed of sound in the bed 5 of the body of water 6 from reception signals originated by acoustic waves that propagate directly from the transmitter 10 to the receiver 11 without being reflected. The acquisition unit 14 is also configured to receive, from the outside, a value of the cross-section Dl of the pipeline 4 to look for and to set this value in the processing unit 12.

The acquisition unit 14 is also configured to receive, from the outside, a value related to a probable trenching height H of the pipeline 4 to look for and to set this value in the processing unit 12.

In a preferred but non-limitative embodiment of the present invention, the acquisition unit 14 receives the coordinates of the direction of navigation followed.

In addition, the acquisition unit 14 is configured to store the bathymetric profile of the bed 5 of the body of water 6. In greater detail, the bed 5 of the body of water 6 is analysed along the laying path of the pipeline 4 by a bathometer 16 and the collected data is stored in the acquisition unit 14. The acquisition unit 14 transfers this data to the processing unit 12. According to an alternative embodiment of the present invention, the acquisition unit 14 receives the bathymetric profile in real time from a multibeam sonar. According to an alternative embodiment of the present invention, the processing unit 12 calculates the bathymetric profile from the reception signals SR; in particular, the processing unit 12 calculates the bathymetric profile on the basis of the acoustic waves reflected by the bed 5 of the body of water 6.

The processing unit 12 is configured to detect the parameters of a cylindrical pipeline 4. In other words, the processing unit 12 is configured with a model that describes the pipeline 4 as cylindrical and takes into account the effects of the reflection of the acoustic waves on a cylindrical pipeline 4. In this way, the shape of the pipeline 4 to look for is not an unknown, but defines known values and, in consequence, reduces the computational complexity of the system to be solved.

The acquisition unit 14 is configured to receive, from the outside, a value or a range of values that indicate the expected position of the pipeline 4. In other words, after the laying of the pipeline 4, a range of position values can be defined within which the pipeline 4 will be present.

The processing unit 12 uses the above-identified data to calculate the position P of the pipeline 4; in particular, the processing unit 12 calculates the position P of the upper end of the pipeline 4.

The processing unit 12 uses the calculated position P of the pipeline 4 to calculate the first parameter, i.e. the value of the trenching height H. The processing unit 12 uses the calculated position P of the pipeline 4 to calculate the second, third and fourth parameters . In a preferred but non-limitative embodiment of the present invention, the processing unit 12 calculates the second, third and the fourth parameter on the basis of the values of the first parameter. In greater detail, the processing unit 12 receives the reception signals SR and calculates the path that the acoustic waves have taken when moving in the body of water 6 and in the bed 5 of the body of water 6 on the basis of ray tracing theory and one or more of the following data items: the set or calculated speed of sound in the body of water 6, the profile of the bed 5 of the body of water 6, an expected value for the position of the pipeline 4, the set shape of the pipeline 4, the known value of the cross-section Dl of the pipeline 4, the position of the sources 10 and of the receivers 11 along the support 9, an expected value for the trenching height H, and the coordinates of the direction of navigation followed. From this analysis, the processing unit 12 calculates path curves that represent the paths taken by the acoustic waves reflected by the pipeline 4 and by the bed 5 of the body of water 6.

The processing unit 12 calculates the speed of sound in the bed 5 of the body of water 6 from the reception signals SR and calculates the position P of the pipeline 4 on the basis of the calculated speed of sound in the bed 5 of the body of water 6 and the calculated path curves. In greater detail, the processing unit 12 calculates the values related to the position of the upper end of the pipeline 4, in particular to the position along axis A and axis Z of the upper end of the pipeline 4, and the speed of sound in the bed 5 of the body of water 6 by means of a semblance functional averaged over the number of the plurality of receivers 11. The semblance functional is an integral in phase in Gaussian windows of the reception signals SR along the calculated path curves. The processing unit 12 calculates the mean statistical value and standard deviation of the results of the semblance functional averaged over the number of receivers 11, and defines the position P of the pipeline 4 and the speed of sound in the bed 5 of the body of water 6. In addition, the processing unit 12 calculates the first parameter, i.e. the trenching height H, on the basis of the position P of the pipeline 4.

Thanks to the reception signals SR deriving from different sources 10 that originated reflected acoustic waves from mutually different angles, it is possible to determine the speed of sound in the bed 5 of the body of water 6 using ray theory.

According to an alternative embodiment of the present invention, the processing unit 12 calculates the speed of sound in the bed 5 of the body of water 6 with a statistical autocorrelation or a convolution integral of the reception signals SR coming from the various receivers 11 that detect the acoustic waves striking the pipeline 4 with different angles. The processing unit 12 then calculates the position P of the pipeline 4 on the basis of the calculated speed of sound in the bed 5 of the body of water 6 and the calculated path curves.

According to a preferred but non-limitative embodiment of the present invention, the processing unit 12 is connected to the sources 10 to control the transmission signals ST that define the transmitted acoustic waves. The processing unit 12 uses the transmission signals ST as trigger signals to acquire the reception signals SR. Furthermore, in an alternative embodiment of the present invention, the processing unit 12 integrates the above-described process by using a statistical correlation between the transmission signals ST and the reception signals SR so as to increase measurement resolution and lower the uncertainties.

The processing unit 12 comprises an output interface 15 configured to define the moving direction D on the basis of the presumed dislocation of the pipeline 4. The output interface 15 is configured to correct the moving direction D on the basis of the position P of the pipeline 4 calculated in the previous instant by the processing unit 12.

In one embodiment of the present invention, the processing unit 12 calculates the propagation speed of the acoustic waves in the body of water 6 on the basis of the reception signals related to the unreflected acoustic waves; calculates the bathymetric profile of the bed 5 of the body of water 6 from the reception signals SR or receives said bathymetric profile from the outside by means of the acquisition device 14; calculates the propagation speed of the acoustic waves in the bed 5 of the body of water 6 from the reception signals SR related to the reflected acoustic waves; calculates the position P of the pipeline 4; checks if the position P of the pipeline 4 falls within the assigned design values; and calculates the corrections for the moving direction D on the basis of the detected position P.

Finally, it is evident that variants can be introduced regarding the present invention with respect to the described embodiments without departing from the scope of the appended claims .

It is also evident that the system and the method forming the subject of the present invention are suitable for calculating the position of a pipeline lying in an uncovered trench. In this case, the trenching height H is defined as the distance between the surface of the bed 5 of the body of water 6 at the edges of the trench and the upper end of the pipeline 4.