# Patent

## Title
Use of multi-beam sonar systems to generate point cloud data and models; data registration in underwater metrology applications

## Abstract

Use of sonar systems to collect dimensional and relational data for use in metrology, mapping, object and structure detection, survey and evaluation applications is disclosed. Systems and methods for collecting underwater data sets, using registration targets, for data registration of underwater acoustic data sets, as well as for data registration of underwater acoustic data sets with above-the-waterline data sets (e.g., laser-based data sets) are described.

## Background
CROSS-REFERENCE TO PRIORITY APPLICATION
This application claims priority to U.S. Provisional Patent Application No. 61/583,558, filed Jan. 5, 2012. The priority application is incorporated herein by reference in its entirety.


BACKGROUND
3D laser scanning techniques are commonly used for terrestrial-based 3D mapping and metrology applications. Multiple data sets covering different, generally overlapping areas are collected and then registered and aggregated to form larger data sets. The techniques for collecting and registering laser data, including surface matching of overlapping data sets, take advantage of the high resolution of the data and the availability of distinctive features within the data sets. Co-registration of GPS and LIDAR generated data may improve the accuracy of data sets. Methods for registration of LIDAR data with optical imagery to improve 3D modeling simulations are also known.
Underwater terrain is typically mapped using acoustic bathymetry systems. Multibeam echosounders, which generally incorporate many narrow adjacent beams arranged in a fan-like swath, can provide high angular resolution and accuracy. The echosounders are generally mounted on vessels that steer overlapping swaths over the target terrain to collect mapping data. The beams may update frequently, allowing reasonably fast vessel speed while maintaining full coverage of the seafloor. Attitude sensors mounted on the vessel may provide data for correction of the boat's roll, pitch and yaw on the ocean surface, and a gyrocompass may be provided for accurate heading information. The Global Positioning System (or other Global Navigation Satellite System (GNSS)) may be used to position the soundings with respect to the surface of the earth. Sound speed profiles (speed of sound in water as a function of depth) of the water column may be collected to correct for refraction or “ray-bending” of the sound waves as a result of non-uniform water column characteristics such as temperature, conductivity, and pressure. A computer system may process all or a portion of this data, correcting for the various factors, as well as for the angle of each individual beam. The resulting sounding measurements are then processed manually, semi-automatically or automatically (in limited circumstances) to produce a map of the underwater terrain.
While the acoustic bathymetry systems described above provide adequate resolution for many purposes, higher resolution underwater mapping and metrology has been difficult to achieve. Optical video cameras are well known and have been in use for many years. Underwater optical video cameras generally use analog or digital video transmission techniques and can provide satisfactory resolution and viewing range in illuminated, clear underwater conditions. Underwater conditions are often not conducive to optical cameras, however, because illumination is poor or because the water lacks clarity. Other types of optoelectronic sensors have also been developed, including various types of spectroscopic systems. Sensors that rely on optics, however, such as spectroscopic systems, have limited viewing range in dark, murky or turbid underwater conditions. For this reason, they have limited use in underwater environments and the information they provide can be quite unreliable.
High resolution imaging sonar (i.e., acoustic) systems have been available and are used in many different underwater applications. Sonar imaging systems provide satisfactory resolution and viewing range in many different water conditions, including murky and turbid underwater conditions. Imaging sonar systems designed for visualization and/or object detection generally scan a fan-shaped beam in a given area by rotating the system or translating it along a line, generating data points and forming images in the direction of the beam rotation or translation. In general, the angle through which the beam is moved is relatively small, the fan-shaped beam has a narrow angle, and the transmitted pulse is short.
Multi-beam sonar systems, including frequency-steerable multi-beam sonar systems, are well known and may be used for many types of 2D and 3D imaging applications, as well as bathymetry, object detection, surveillance and other types of applications. Exemplary frequency-steerable multi-beam acoustic systems, and other types of imaging systems, are disclosed in U.S. Pat. Nos. 7,606,114, 7,542,376 and 7,889,600, which are incorporated herein by reference in their entireties. These systems are capable of providing high resolution underwater imagery.
Underwater installations of various types, such as pipelines, cabling, tunnels, support structures, rigs and the like may require precise, high resolution measurement of underwater components and structures for installation, monitoring and repair purposes. Spoolpiece metrology, which is the measurement of the relative separation and angle between flanges where underwater pipe sections are connected, or where pipe sections are connected to fixed structures, is one exemplary underwater metrology application that requires high resolution underwater data collection. This metrology application requires highly accurate and precise data, to ensure that pipe and flange connections match and to accurately determine dimensional flange and pipe fabrication requirements.
One standard method of spoolpiece metrology utilizes Long Baseline (LBL) transponders placed in locations near the pipeline or underwater structure of interest and measures ranges between the transponders very accurately. An array of 6-10 transponders is typically deployed on the seabed, on the pipeline, structure and on the flanges. All the inter-transponder ranges are measured and used to compute the relative position and bearing between the flanges. This process, including deployment, range measurement and recovery, generally requires significant vessel time (on the order of 12-18 hours), with vessel costs often ranging between £60,000 and £110,000 per day. This system, while accurate, is a very high cost and time intensive system.
Using a sonar system to collect precise dimensional and relational data could dramatically reduce the amount of vessel time required and, thus, the cost in various underwater metrology applications. Use of a high resolution sonar system may provide more complete, higher resolution data and imaging as well. This type of system would be useful for many types of underwater metrology, object and structure detection, survey and evaluation applications. Techniques for registration of multiple data sets are required for implementation of such high resolution imaging sonar systems in underwater metrology applications.
Registration of underwater acoustic data with terrestrial data collected using laser-based systems is also challenging and, if done accurately, would provide comprehensive survey and mapping information. Because laser-based data is generally collected above the water line, and acoustic data is generally collected below the water line, and because there are few fixed, distinctive features at or near the water-air interface, registration of above the waterline and below the waterline data sets using common data features isn't feasible. Tidal and water level fluctuations, and wave action, eliminate the use of simple waterline-based registration systems for registering above and below the water line data sets, even when adjusted to account for tidal fluctuations. Registration systems that provide accurate registration of above waterline data sets with underwater data sets would also be useful for many types of survey, mapping and metrology applications.
SUMMARY
Registration targets for facilitating registration of underwater acoustic data sets are described and shown herein. In one embodiment, a geometrical registration target has a geometrical framework structure and at least one projection extending from the structure, the projection provided as a shaped structure having a distinctive top to bottom and/or side to side profile and high acoustic visibility. In another embodiment, a registration target comprises a base structure, a shaft extending from the base, and a shaped target mounted on the shaft or an extension from the shaft, wherein the shaped target has a distinctive top to bottom and/or side to side profile and high acoustic visibility. In another embodiment, a registration target comprises a three-dimensional spherical form. In another embodiment, a registration target is configured to extend both above and below the waterline.
In another aspect, methods for registering underwater acoustic data sets are described, comprising: securely placing one or more registration targets having a distinctive profile and high acoustic visibility in an underwater location in proximity to one or more desired target objects; placing one or more underwater acoustic data collection systems in proximity to the registration target(s) and desired target object(s); collecting a plurality of acoustic data sets, each data set incorporating at least a portion of at least one registration target; mapping each acoustic data set into three-dimensional space in a point cloud format; and registering the plurality of data sets by aligning the registration target(s) forming a part of each data set.
In another aspect, methods for modeling underwater target objects in three dimensional data sets are described, comprising: securely and detachably mounting one or more registration targets having two dimensional structural elements and at least one shaped target projection flush against, or on a plane separated a known distance from, a planar face of the underwater target object(s); collecting a plurality of acoustic data sets in a spherical point cloud format, with each data set incorporating at least a portion of at least on registration target; and registering the plurality of data sets by aligning the registration target(s) forming a part of each data set.
According to yet another aspect, methods for registering data sets collected above the waterline using optical data collection systems with data sets collected below the waterline using acoustic data collection systems are described, comprising: securely mounting one or more registration targets configured to extend both above and below the waterline with at least a portion of the optically visible targets positioned above the waterline and at least a portion of the acoustically visible targets positioned below the waterline; collecting a plurality of optical data sets in a above the waterline and a plurality of acoustic data sets below the water line, with each data set incorporating at least a portion of at least on registration target; mapping each acoustic data set into three-dimensional space in a point cloud format; and registering the plurality of data sets by aligning the registration target(s) forming a part of each data set.



BRIEF DESCRIPTION OF THE FIGURES
This application contains at least one drawing executed in color. Copies of this patent with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
FIG. 1A shows a schematic diagram illustrating a (mechanical) scanning multi-beam sonar system mounted on a stationary platform that may be used to produce data in a point cloud format by scanning a thin vertical sonar slice around underwater structures and objects.
FIG. 1B shows an image produced using data collected using a scanning multi-beam sonar system as schematically illustrated in FIG. 1A.
FIG. 2A shows an image depicting sonar data of underwater pipe and flange structures; FIG. 2B shows the pipe and flange structures modeled from the point cloud data collected; and FIG. 2C shows an image from a CAD model generated using the point cloud data collected from the sonar device.
FIG. 3A shows a schematic perspective view of an exemplary geometric registration target of the present invention, and FIG. 3B shows a schematic illustration of exemplary placement of geometrical registration targets in relation to data collection locations and target objects.
FIG. 4A shows a schematic perspective view of an exemplary distributed point registration target of the present invention, and FIG. 4B shows a schematic illustration of exemplary placement of distributed point registration targets in relation to data collection locations and target objects.
FIG. 5A shows an image of an exemplary spherical registration target; FIG. 5B shows an image of a point cloud data representation of a partial target; FIG. 5C shows a reference target modeled from the point cloud data; and FIG. 5D shows a schematic drawing of an exemplary spherical registration target having a ribbed configuration.
FIG. 6 shows a schematic illustration of an exemplary registration target mounted flush against, or at a known distance from, a target object.
FIG. 7 shows a schematic illustration of an exemplary registration target of the present invention configured to extend both above and below a waterline for registration of above the waterline and below the waterline data sets.
FIG. 8 shows a schematic illustration in which several registration targets of the type illustrated in FIG. 6 are mounted on and around a fixed structure, providing fixed reference points both above and below the waterline for data registration.



DETAILED DESCRIPTION
Several systems and methods for collecting underwater data sets, and for data registration of underwater acoustic data sets, as well as for data registration of underwater acoustic data sets with above-the-waterline data sets (e.g., laser-based data sets) are described below.
Data Collection and Modeling
Multi-beam sonar systems may be scanned to collect data in a point cloud format. FIG. 1A shows a schematic diagram illustrating a (mechanical) scanning multi-beam sonar system mounted on a stationary platform (e.g., a tripod) that may be used to produce data in a point cloud format by scanning a thin vertical sonar slice around underwater structures and objects. Each profile slice is mapped into 3D space to create a point cloud from which range and angle measurements between objects can be determined. An image generated using point cloud data collected using a scanning multi-beam sonar system mounted and positioned as shown in FIG. 1A is illustrated in FIG. 1B.
Data collected or assembled in a point cloud format as described above may also be used to create accurate models using existing tools, such as computer-aided-design programs, e.g., CAD software. FIGS. 2A-2C show the progression of 3D sonar data as collected (FIG. 2A), the mapping of the sonar data into 3D space in a point cloud format showing objects (pipes and flanges) in a 3D representation (FIG. 2B), and a CAD model of one of the pipe/flange combinations generated based on the point cloud data. Based on CAD and other models, flanges and pipes (and other structures) may be fabricated to match the existing underwater structures, and then interfaced and fastened with the existing underwater structures in a convenient and expedient manner. High resolution imaging sonar systems, as described herein, provide accurate dimensional information and may be processed to provide the information in a variety of formats for use in fabrication, assembly, and the like.
Acoustic Data to Acoustic Data Registration
Methods and systems of the present invention introduce “artificial” registration targets in underwater areas where little to no structure is present, and position one or more registration targets between overlapping scan data sets to enable accurate registration of data sets. These targets facilitate the alignment of overlapping data sets by providing reference points allowing multiple data sets to be “snapped” together.
Artificial underwater registration targets may take a variety of forms. In one embodiment, the artificial registration target is provided as a three-dimensional geometrical structure having acoustically opaque elements and/or surfaces. FIG. 3A shows an exemplary 3D geometrical registration target, and FIG. 3B shows exemplary placement of artificial registration targets vis a vis scan locations and objects.
Geometric registration target 10, illustrated in FIG. 3A, has a three-dimensional rectangular structure with a plurality of connected elements 10A, 10B, etc., illustrated as linear bars, providing a rectangular framework that is acoustically dense and distinguishable from the underwater surroundings, the objects being investigated, and the ocean floor. Suitable materials are well known and include various types of metals, plastics, and the like. The framework structure is generally “open,” permitting at least limited water penetration and flow, and the structure is heavy enough to be positioned in a stable and stationary position on the sea floor or an underwater platform or structure. The registration framework may be weighted to facilitate placement in a desired orientation, or weights may be attached to the framework structure, prior to or following placement, to facilitate stable positioning of the structure.
While registration target 10 is illustrated as a rectangular structure, other geometrical shapes may be provided—e.g. triangular, trapezoidal, etc. Similarly, while the framework bars are illustrated as linear structures, it will be appreciated that curved or more complex linear structures may be provided, and that different framework bars may have different structures—e.g., profiles, sizes, patterns, etc.—that provide differentiated structures for data registration. The framework bars may be perforated, or marked, with distinctive shapes and patterns of perforations, markings, and the like, to provide additional distinctive points of reference for data registration.
Geometrical registration targets 10 additionally have one or more associated projections 12A, 12B, etc., extending from the geometrical framework. Projections 12A, 12B, etc., are preferably provided as shaped structures having a variable top to bottom and/or side to side profiles. One suitable shape is an hourglass or double inverted cone shape, as shown. Other types of shaped structures, including conical shapes, triangular shapes, and the like, are suitable. These types of shaped structures are distinctive in collected data sets and provide good registration accuracy. Projections may be provided at one or more corners of a registration target framework, as illustrated in FIG. 3A, and they may alternatively or additionally be provided elsewhere on the target framework structure. In some embodiments, projections having different shapes and three-dimensional profiles are provided at different locations on the registration target, again providing differentiated structures and distinctive points of reference for data registration.
FIG. 3B shows exemplary placement of geometrical registration targets 10 in relation to scan locations 15, 16, 17 and objects 18, 19. Objects 18 and 19 are illustrated as spoolpieces, or pipeline sections, that need to be joined to one another, or to other pipeline or well structures, or to other underwater structures. Methods of the present invention may involve placement of one or more geometrical registration targets 10 in proximity to, and generally between, one or more metrology target(s), such as pipeline or underwater objects or structures. The registration targets are securely placed on the sea floor or on an underwater structure and anchored, if necessary, to provide stable and stationary positioning of the registration targets. Underwater acoustic data collection systems (e.g., multibeam sonar systems) are placed, or maneuvered in proximity to the registration target(s) and metrology (object) target(s). Multiple data collection systems may be provided and used simultaneously, or a single data collection system may be positioned, sequentially, at multiple scan sites for data collection.
Data is preferably collected in a spherical point cloud format, with each data set incorporating at least a portion of at least one registration target. Registration of the data sets may then be accomplished by aligning reference points, and areas, of the geometrical registration targets forming a part of each data set. Because the objects and the registration targets are stationary, it is not essential that the acoustic data collection systems be maintained in a stationary condition. Data sets incorporating at least a portion of one or more registration targets may be collected from movable, or moving, acoustic systems and registered, accurately, using methods and systems of the present invention.
An alternative type of registration target is illustrated in FIG. 4A; exemplary placement of this type of target vis a vis scan locations and objects targeted for investigation is shown in FIG. 4B.
Registration target 20 illustrated in FIG. 4A is referred to as a distributed point target. Each distributed point target 20 comprises a base 21 providing solid footing for stable placement of the structure; a shaft 22 for elevating the registration target with respect to the base and the sea floor or structure, and a shaped projection 23 to facilitate data registration. Base 21 is generally large enough and heavy enough to be positioned in a stable and stationary position on the sea floor or on an underwater platform or structure. Other types of base structures may be used, depending on the nature of the sea floor, undersea conditions, and the like. The registration target may additionally incorporate a handle 24 or a similar structure to facilitate transport and positioning of the registration target.
Shaped projection 23 is preferably provided as a shaped structure having a variable top to bottom and/or side to side profile. One suitable shape is an hourglass or double inverted cone shape, as shown. Other types of shaped targets, including conical targets, triangular targets, and the like, are suitable. These types of shaped targets are distinctive in collected data sets and provide good registration accuracy. In alternative embodiments, multiple shaped targets may be provided on multiple shafts extending from a base structure, or on one or more limbs projecting from a common shaft. In some embodiments, a tripod-like structure may be substituted for the base and shaft elements. In other embodiments, an inverted tripod structure may project from the base to support multiple shaped targets. In some embodiments, targets having different shapes and three-dimensional profiles are provided at different locations on the registration target, again providing differentiated structures for data registration. These types of shaped structures provide good registration accuracy.
FIG. 4B shows exemplary placement of registration targets 20 in relation to scan locations 25, 26, 27 and objects 28, 29. Objects 28 and 29 are spoolpieces, or pipeline sections, that need to be accurately positioned and joined to one another, or to other pipeline or well structures, or to other underwater structures. Methods of the present invention may involve placement of one or more registration targets 20 in proximity to, and generally between, one or more metrology target(s), such as pipeline or underwater objects or structures. The registration targets 20 are securely placed on the sea floor or on an underwater structure and anchored, if necessary, to provide stable and stationary positioning of the targets. Underwater acoustic data collection systems (e.g., multibeam sonar systems) are placed, or maneuvered in proximity to the registration target(s) and metrology target(s). Multiple data collection systems may be provided and used simultaneously, or a single data collection system may be positioned, sequentially, at multiple scan sites for data collection.
Data is preferably collected in a spherical point cloud format, with each data set incorporating at least a portion of at least one registration target. Registration of the data sets may then be accomplished by aligning reference points, and areas, of the geometrical registration targets forming a part of each data set. Because the objects and the registration targets are stationary, it is not essential that the acoustic data collection systems be maintained in a stationary condition. Data sets incorporating at least a portion of one or more registration targets may be collected from movable, or moving, acoustic systems and registered, accurately, using methods and systems of the present invention.
FIG. 5A shows another embodiment of a registration target of the present invention having a generally spherical configuration. Target 30 may comprise a three-dimensional, generally spherical form 31 having a solid or hollow construction. For applications in which data is collected at the sea floor or near a structure, spherical form 31 may be mounted on a stabilizing platform or base 32 suitable for supporting the target on an underlying surface. Target 30 may additionally incorporate or be associated with a hook or eye 33, or one or more similar structures, that may be used to move the target (using, e.g., a cable or hook) and position it for various data collection applications.
A plurality of spherical targets is generally placed within a pre-determined distance from the sonar device, within the field of data collection. When data is collected in a spherical point cloud format, it is preferred that at least three targets are placed within the data collection range of each sonar device, and that at least three targets are visible from each location within the data collection range to provide definitive points for registration of the point clouds.
FIG. 5B shows point cloud data representing a reference target of the type illustrated in FIG. 5A collected by mechanically scanning a multi-beam sonar system mounted on a fixed platform. FIG. 5C shows a model of the reference target generated from point cloud data using CAD software. Using the center of the model sphere as a reference point, multiple sonar scans including the area (and objects) surrounding the reference target can be registered.
FIG. 5D illustrates another embodiment of a spherical registration target 35 of the present invention. Registration target 35 has a plurality of ribs 36 forming an “open” spherical structure. In this embodiment, ribs 36 are oriented similarly to latitude and longitude lines, but it will be appreciated that many different types of open spherical frameworks could be constructed as registration targets. Registration target 35 additionally comprises a base 37 and a hook or eye 38, or one or more similar structures, that may be used to move the target (using, e.g., a cable or hook) and position it for various data collection applications.
Object Registration
Because acoustic based underwater scanning systems are generally less accurate than laser-based systems and they can experience relatively large beam spreading in range, it can be difficult to precisely define edges and surfaces that are typically used to accurately model objects (pipes, flanges, etc.) in three dimensional data sets. Methods and systems of the present invention are directed to improving the position and orientation accuracy of modeling specific objects from underwater acoustic point cloud data.
Methods of the present invention deploy targets on and around an object that help define and position specific physical details such as corners and surfaces in 3D space. The targets used are specifically designed to provide and delineate point and surface features in the data relative to the object of interest. These targets can also improve angle measurements of surfaces by effectively presenting a larger surface area for measurement and data collection.
FIG. 6 shows an exemplary registration target 40 comprising two dimensional structural elements, such as two or more bars 42 that intersect, and at least one shaped target 43 positioned at a distance from the intersection of bars 42. Registration target 40 is mounted flush against, or at a known distance from, a structural element of registration object 45, such as on a flange face 46 mounted on a pipeline section 47 having multiple legs 48. In some embodiments, the two dimensional registration target 40 is aligned on substantially the same plane as the plane of the face of flange 46. Various other types of two- and three-dimensional structures may be provided as registration targets. Additional bars may be provided, for example, in a spoke-like arrangement, and alternative geometrical framework structures may be used.
Shaped target 43 is preferably provided as a shaped structure having a variable top to bottom and/or side to side profile. One suitable shape is an hourglass or double inverted cone shape, as shown. Other types of shaped targets, including conical targets, triangular targets, and the like, are suitable. These types of shaped targets are distinctive in collected data sets and provide good registration accuracy. Additional shaped targets having the same or different configurations may be provided at different locations along the bars to provide additional points for registration of data sets.
Placement of the registration target relative to the object facilitates accurate modeling of the target. One embodiment, in which a cross-shaped target structure is mounted flush to or a known distance from a flange face is illustrated in FIG. 6. The registration target is detachably and stably mounted on the object during data collection and is removed following data collection. Mechanical, magnetic, clip-based and other types of mounting systems may be used for detachably mounting one or more registration targets to the object. By placing the shaped registration point targets in the same plane as the flange face, but offset at some distance outside of the face, the modeler can more accurately define the center and orientation of the flange face.
Terrestrial (e.g., Laser) Data to Underwater (e.g., Acoustic) Data Registration
Comprehensive mapping and metrology may be performed when terrestrial data, such as laser scan data, is combined with underwater data, such as acoustic scan data. The main challenge with this task is registration of the terrestrial laser scan data with the underwater acoustic data, because neither the laser nor the acoustic data penetrates the water line, eliminating the possibility of using common data features for registration. Changing water levels due to tidal fluctuations and wave action generally exclude the use of a simple water line based registration point that would change position over time.
Registration targets that are configured to extend both above and below the water line in all anticipated tidal and wave conditions are provided herein. FIG. 7 illustrates one embodiment of a registration target 50 of the present invention comprising a rod 51 having a plurality of shaped targets 52 distributed with known spacing along its length. Shaped targets 52 are illustrated as intersecting planar semi-circular structures, which present distinctive top to bottom and/or side to side profiles. Other suitable shapes include hourglass or double inverted cone shapes, conical targets, triangular targets, and the like, are suitable. These types of shaped targets are distinctive in collected data sets and provide good registration accuracy, both in above waterline and below waterline environments. Additional shaped targets having the same or different configurations may be provided at different locations along the rod(s) to provide additional points for registration of data sets.
Targets 52, in addition to having a shaped structure that is distinctive and easily identified in underwater acoustic data sets, also have distinctive optical properties that are easily distinguishable and identifiable using optical methodologies, such as laser-based data collection systems. Targets 52 are thus provided with optically reflective coatings, or have distinctive colors, refractive patterns, or the like. Different patterns and types of coatings, colors, and the like may be used on different locations along the rod(s) to provide additional points for registration of data sets.
Registration targets 52 are spaced and positioned such that the distance between the uppermost registration target and the lowermost registration target is greater than the sum of the difference between exceptional high and low tides and normal wave height. Multiple registration targets are mounted to a stationary or permanent structure in the scan area, so that registration targets are located both above and below the waterline regardless of the tide and wave activity.
FIG. 8 shows an exemplary application in which several registration targets of the type illustrated in FIG. 6 are mounted on and around a bridge structure, with some of the targets above and some of targets below the water line. In alternative embodiments, registration targets having distinctive patterns or configurations of shaped targets may be provided and placed in predetermined locations to provide distinctive, fixed reference points for above the waterline and below the water line data registration.
EXAMPLE
The effectiveness of underwater sonar scanning technology using a BlueView Technologies BV5000-1350 3D mechanical scanning multi-beam frequency steered sonar system was tested. BlueView Technologies, Inc., 2151 N. Northlake Way, Suite 214, Seattle, Wash. 98103, www.blueview.com. The BV5000-1350 system operates at a frequency of 1.35 MHz and has 256 beams with a 1° beam width and a 0.18° beam spacing. The sonar field of view of 45×1°, with a sector/spherical scan area of 45-360°, and an update rate of up to 40 Hz. Data output formats include .son, .off and .xyz files. The system was operated with an integral pan & tilt mechanism and mechanical scanning system. BlueView ProScan software provided real-time scan control, monitoring and post processing, with export in point cloud formats.
A MeshLab point cloud viewer was used to view point cloud data collections and extract point-to-point measurements. Leica Geosystems' Cyclone-REGISTER 3D data registration and imaging software was used to clean 3D underwater data collected from the BlueView BV5000-1350 sonar system and combine and register multiple scans. Leica Geosystems' Cyclone-MODEL modeling software was used to model standard components and export them to a CAD file.
The BV5000-1350 3D mechanical scanning sonar system used for this demonstration consisted of an MB1350 sonar head calibrated in-house using an element spacing of 0.000587 m, a pan and tilt unit, and a tripod (about one meter high) for deployment. The following software was used during collection of sonar data: BlueView ProScan V3.3—Build 5401—BlueView's sonar data interface for sonar setup, collection and point cloud generation; and Meshlab v1.2.1, a 3D point cloud viewer that generates fully rotational 3D imagery and includes point-to-point measurement functions.
Four pipes with flanges were placed on supporting structures and arranged, in different orientations, in the dry-dock at distances of up to 30 m from the sonar head. Spherical reference targets having a configuration similar to that illustrated in FIG. 5A and a diameter of 0.386 m were placed in a triangular pattern within a 5-10 m distance from the sonar head. The reference targets were constructed from concrete, mounted to a polygonal base, and each had a metal eye protruding opposite the base for convenient handling. In general, at least 3 registration targets were visible from each location to provide definitive points for registration of point clouds.
A terrestrial laser scanning survey of the pipes, flanges and spherical references targets was conducted prior to flooding the dry-dock and used as a baseline for comparing the 3D sonar scans. All laser scanning data was collected using a Leica HDS C10 time of flight scanner. HDS blue and white targets were placed around the perimeter of the dry dock and in the cry dock itself prior to commencing laser scanning. A minimum of three control targets were observed at the start and end of each scan. All control targets were assigned unique reference numbers to facilitate data processing. During scanning, all items of interest were scanned on a nominal 3 mm grid. To register the C10 data, the station files were imported into Cyclone and individually registered using the unique control targets. Auto-add cloud constraints were run on the point cloud data to tighten the registration.
The scanning multi-beam sonar system was calibrated, in the dry dock, by performing a scan where a flat surface of the dry dock was visible. An XYZ file was imported into point cloud software, the flatness of the surface was assessed, and it was determined that a 3.5° tilt addition would be used for subsequent scans. The dry-dock was then filled with water and all pipes were referenced to marks on the dry-dock floor to confirm that there was no indication of shifting of any of the test pieces. The sound speed in water was measured as 1476 m/s and that value was entered into the Proscan software to provide proper scaling of the point cloud data.
Point cloud data sets were collected using the scanning multi-beam sonar system scanned at 360° with scan speeds of 0.5°/sec and 1°/sec. The scanning locations were chosen to produce significant point cloud detail of the pipes and flanges. To register the 1° data, the xyz files were imported into Cyclone, the spherical targets were modeled, and the center of each sphere was given a unique reference number. Model spheres were fit to all the sonar point cloud elements created by the spherical reference targets. Alternate targets, e.g., cross-shaped targets, were used to supplement the areas of the dry dock where three spherical targets were not visible.
Multiple sonar scans were registered together to generate a composite point cloud of the entire surveyed area. Pipe and flange CAD models were created from the point cloud data, and ranges and angles between flanges were determined using CAD models. The average distance uncertainty compared to the laser measurements for flanges spaced at a distance of 30 m was 6 cm, and the average angle uncertainty compared to the laser measurements for flanges spaced at a distance of 30 m was 0.8°. The average distance uncertainty compared to the laser measurements for flanges spaced at a distance of 40 m was 7 cm, and the average angle uncertainty compared to the laser measurements for flanges spaced at a distance of 30 m was 0.9°. The multi-beam sonar system satisfied the accuracies generally required for spool piece metrology and demonstrated reduced setup complexity and reduced time for measurement. The sonar system produced data similar to that produced by laser scanning techniques and was generated using existing software, procedures and know-how.
It will be understood that the foregoing descriptions of various embodiments of methods and systems of the present invention are merely illustrative of the invention and its varied embodiments. Modifications to various aspects of the methods and systems of the present invention will be apparent to those skilled in the art and are intended to fall within the scope and purview of this disclosure and the following claims.

## Claims

1. A registration target, comprising a geometrical framework and at least one projection extending from the geometrical framework, wherein the geometrical framework is formed as a ribbed open three-dimensional spherical structure from a plurality of connected elements permitting at least limited water flow through the three-dimensional structure and the at least one projection is provided as a shaped structure having a distinctive top to bottom and/or side to side profile and high acoustic visibility wherein the connected elements forming the three-dimensional structure have distinctive markings including patterns of perforations providing additional points of reference for data registration.

2. A method for registering underwater acoustic data sets, comprising:
securely placing one or more registration targets having a distinctive profile and high acoustic visibility in an underwater location;
collecting a plurality of acoustic data sets, each data set incorporating at least a portion of at least one of the one or more registration targets;
mapping each acoustic data set into three-dimensional space in a point cloud format; and
registering the plurality of data sets by aligning at least one of the one or more registration target(s) forming a part of each data set,
wherein securely placing comprises securely positioning the one or more registration targets configured for three-dimensional applications within a field of data collection at the underwater location, wherein the one or more targets are visible from each location within a data collection range.

3. The method of claim 2, wherein at least one of the one or more registration targets comprises a base structure, a shaft extending from the base, and a shaped target mounted on the shaft or an extension from the shaft, wherein the shaped target has a distinctive top to bottom and/or side to side profile and high acoustic visibility.

4. The method of claim 2, wherein at least one of the one or more registration targets comprises a three-dimensional spherical form mounted on a stabilizing platform and having a hook or eye extending from the spherical form.

5. The method of claim 2, wherein at least one of the one or more registration targets comprises a three-dimensional open framework structure.

6. The method of claim 2, additionally comprising importing the point cloud data to a software modeling tool.

7. The method of claim 2, wherein securely positioning the one or more registration targets comprises securely positioning at least three registration targets within the field of data collection at the underwater location, wherein the at least three targets are visible from each location within the data collection range.

8. The method of claim 2, wherein collecting a plurality of acoustic data sets includes mechanically scanning a multi-beam sonar system mounted on a fixed platform.

9. A method for modeling underwater target objects in three dimensional data sets, comprising:
securely and detachably mounting one or more registration targets having two dimensional structural elements and at least one shaped target projection flush against, or on a plane separated a known distance from, a planar face of the underwater target object(s);
collecting a plurality of acoustic data sets in a spherical point cloud format, with each data set incorporating at least a portion of at least one registration target; and
registering the plurality of data sets by aligning the registration target(s) forming a part of each data set.

10. The method of claim 9, wherein securely and detachably mounting one or more registration targets comprises removing the one or more registration targets from the planar face of the underwater target object(s) following the data collecting.

11. A method for registering data sets collected above a waterline using optical data collection systems with data sets collected below the waterline using acoustic data collection systems, comprising:
securely positioning one or more registration targets to extend both above and below the waterline, wherein each registration target comprises at least one optically visible target and at least one acoustically visible target and at least one optically visible target is positioned above the waterline and at least one acoustically visible target is positioned below the waterline;
collecting a plurality of optical data sets above the waterline and a plurality of acoustic data sets below the water line, with each data set incorporating at least a portion of at least one registration target;
mapping each acoustic data set into three-dimensional space in a point cloud format; and
registering the plurality of data sets by aligning the registration target(s) forming a part of each data set.

12. The method of claim 11, wherein at least one of the one or more registration targets is configured to extend both above and below the waterline, and comprises a rod-like structure having a plurality of targets distributed in a predetermined spacing along its length, wherein at least a portion of the targets are configured to extend below the waterline and are acoustically visible and at least a portion of the targets are configured to extend above the waterline and are optically visible.

13. The method of claim 11, wherein at least one registration target comprises a plurality of optically visible targets, wherein different optically visible targets having distinctive optical properties are provided at different locations along a portion of the registration target extending above the waterline.

14. The method of claim 11, wherein each of the registration targets is configured such that a distance between an uppermost optically visible target and a lowermost acoustically visible target is greater than a sum of the difference between exceptional high and low tides and normal wave height.