Maritime’s Single Camera Metrology System (SICAMS) can be used to measure a variety of subsea elements. Images from Parker Maritime.
Some service providers are looking to the past to provide new solutions for subsea metrology operations. Greg App reports.
In an effort to overcome the challenges presented by subsea metrology operations, the oil and gas industry has relied on a number of techniques characterized by a wide range of technical capabilities and limitations. Some methods, such as the use of long baseline acoustics, are technologically advanced but susceptible to underwater noise and time sensitivity. Others, such as the use of a diver taut wire, rely on very basic technology that has remained virtually unchanged for decades. The use of a diver taut wire, while conceptually simple, requires an intervening human element to perform potentially danger- ous work. In order to complete these subsea metrology operations more safely, accurately, and cost effectively, many companies are combining modern technology with a process known as photogrammetry, a concept that dates back to the mid-19th century.
The goal of photogrammetry is to retrieve 3D measurements from a 2D image. If the scale of a photograph is known, the distance between two points that lie on a plane parallel to that of the photographic image can be determined by measuring their distance on that image. Thus, it is possible to construct a dimensionally accurate 3D image of an object given multiple pho- tographs from different angles. While the fundamental idea of photogrammetry is about as old as photography itself, this methodology was not applicable to subsea metrology until the advent of digital camera technol- ogy. Several companies are providing products that fuse this measurement technique with modern technological developments.
One such example is the Savante VOXEL subsea laser system, a laser-aided photogrammetric package capable of generating extremely accurate distance and angle measurements from video and/ or digital images obtained from harsh environments which cause image distortion (such as underwater conditions present in subsea metrology operations).
The VOXEL system, which is designed to operate with an image produced by any subsea digital camera, utilizes 3D triangulation in conjunction with multi-variate camera lens calibrations to translate between the position of various laser illuminated pixels and individual volume elements. These volume elements (dubbed “VOXELS” by Savante) constitute the surface of the object while lasers illuminate it.
Savante’s laser-aided photogrammetry techniques can render dimensionally accurate 3D images in regards to construction, seabed mapping, and damage analysis.
|Laser aided photogrammetry is largely immune to subsea factors that have traditionally hindered subsea metrology operations.|
Parker Maritime’s single camera metrology system (SICAMS), developed in 2007, has been used to measure a variety of subsea elements including shipwrecks, structural dents, caissons, spools, and piping. This system retains its own standardized hardware (including its own camera) to optimize the software’s ability to generate accurate 3D renditions based on obtained 2D images. SICAMS has an enhanced blunder detection and report- ing tool built into the processing soft- ware, which allows for a more accurate 3D rendition of the object being observed. Similar to Savante’s VOXEL technology, SICAMS often relies on laser scanning to optimize results. “We utilize lasers for projecting a point pattern on subsea structures for special applications,” says Rolv Johannessen, Marketing Manager of Parker Maritime. “A set of coordinates can be given for each laser point on the object being observed.”
Due to the complex nature of SICAMS, Parker provides internal training to their engineers in conjunction with external training regarding the related software. “It is mandatory that our engineers have a dimensional control and understand- ing regarding surveying techniques,” Johannessen says.
DimEye Corp.’s patented I-Photogrammetry and video laser scan (VLS) technology can be used to address complex metrology projects, including reverse engineer- ing of in situ components, measurements of defects and anomalies such as pipe dents on flex joints, metrology of closing spools and jumper hub alignment studies.
I-Photogrammetry can be used in conjunction with any digital camera; the user simply needs to capture the necessary photographs before sending them online to DimEye for 3D modeling. However, the photographs need to meet various requirements that enable DimEye to create a digital 3D interpretation.
“In certain situations we are able to provide training classes for other companies to complete basic measurement tasks,” says Arnauld Dumont, Owner, DimEye Corp. “However, we prefer to use our highly trained technicians to complete most measurement applications. In order to ensure accurate results, operators must have a basic understanding of photogrammetry, our data processing software and our VLS software.”
Dimeye’s VLS system combines the benefits of photogrammetry, high- definition video recording and laser technologies. The main advantage of this system is that it does not need stability or ideal environmental conditions (temperature and salinity) to operate effectively. Additionally, the use of video prevents the need to stop multiple times to take photographs at various angles, which in turn reduces the duration of the operation.
|Parker Maritime utilizes lasers for projecting a point pattern on subsea structures.|
DimEye also provides ROV deployed VLS hardware for rental in addition to offshore support services for hardware/ data capture integration.
Even with the addition of modern technological developments, the use of subsea photogrammetry is not without limitations. “The biggest challenge regarding subsea photogrammetry is visibility,” Johannessen says. “The general consensus is that when the ROV can ‘see,’ SICAMS can be used.”
This limitation is directly related to the depth at which SICAMS and other subsea photogrammetry techniques can be used. Johannessen expects that the industry as a whole will respond to this challenge by enhancing their equipment to withstand greater depths, where there is less light and greater pressure (SICAMS is currently limited to 1000m depth). “We expect inertial navigation systems (INS) to play an even bigger role in the future, either as a stand-alone tool or in combination with the current SICAMS hardware and software capabilities.”
The use of INS is relatively new to the subsea and offshore industry. Previously, it had been used primarily for military operations, but it has recently been made more available for civilian use. Rather than rely solely on visual data for obtaining measurements, INS relies on motion to provide dimensional analysis of a given subsea area. This method uses three orthogonal accelerometers located on a subsea vessel (such as an ROV), which measure linear acceleration in the X, Y, and Z direction. Analysis of the results provided by the accelerometers enables an operator to determine position and orientation of the subsea vessel, assuming that the initial values position and velocity are known. The primary advantage of this technology lies in the fact that it can address problems related to line of sight and poor visibility, with the latter being an unavoidable issue at great depths. However, without definite external reference points, this method is prone to small errors regarding acceleration measurements.
|DimEye can provide accurate 3D CAD Models based on images taken from any “off the shelf” camera.|
Dumont sees advancements in optical and processing technology having a significant impact on the future of subsea metrology operations, with his company DimEye playing a role in its development.
“In terms of applications where we can provide relevant analysis, we see these developments in optics providing even more accurate results for metrology applications subsea,” Dumont says. “We are also working to develop real- time processing of our data in the field. We are leveraging the rapidly evolving technology industry that also provides more powerful processing tools at a rapid pace.”
The combination of traditional photogrammetry with modern day technology seems to have provided the industry with an efficient method that excludes the element of human risk while maintaining reliable accuracy in subsea metrology operations. While various limitations remain, current software and hardware developments seem to indicate this could be a viable solution for subsea measurements.