subsea metrology

Sonardyne’s 6G Wideband 2 acoustic technology has, and continues to be, the  primary tool used for the subsea metrology measurement phase. Now, the company  has expanded its offering to include acoustic-inertial capability and a complete software  solution for all stages of the metrology process. Reporting for Sonardyne, Edd Moller,  Global Business Manager – Construction and Survey, and Malik Chibah, Subsea INS  Manager, take a look into Sonardyne’s metrology toolbox. 

Subsea Metrology requires accurate, precise and  robust measurements which are critical for  successful fabrication and installation of  spools and jumpers. Since its introduction,  Sonardyne’s Wideband 2 signal  technology has increased the speed,  robustness and simplicity of acoustic  measurements. Now, with the development  of a dedicated software tool called Connect,  complementary 6G inertial techniques and instruments, the scenarios  in which Sonardyne can assist clients with their metrology campaigns  have greatly expanded. 



Connect software for subsea metrology projects

Connect is Sonardyne’s new metrology software, designed to assist  the user with all phases of a metrology campaign. The software eases  operator burden and complexity by introducing ‘expert’ settings,  automated data collection scripts and robust reduction of measurement  from planning to report delivery. Tailored customer reports are generated  containing the final results with supporting data and QC, improving the  speed and integrity of data processing for acoustic, inertial and implied  metrology techniques. 

Guiding the user through the key stages of metrology including  planning, data collection, quality control, processing and reporting,  both traditional and horizontal metrologies are supported.  Measurements can be directly collected from the metrology instruments,  including Sonardyne’s own 6G transceiver and transponders, depth  sensors and gyrocompasses whilst the  software can also provide results for points on the  structures that are not directly measured by using implied methods. 

All collected data is displayed for checking before proceeding to  processing and reporting; this includes any intermediate processing  stages and users are able to easily select which data they wish to include  or exclude. The final metrology report contains summaries of calculations  to support the results including hub-to-hub horizontal distances, slant  range, depth differences, attitudes and more. 


SPRINT inertial metrology

ROVs equipped with our SPRINT (Subsea Precision Reference Inertial  Technology) technology can now perform hub-to-hub metrology using  the acoustic inertial SLAM (simultaneous location and mapping)  technique. Uniquely, ROV operators can seamlessly switch from  construction and survey operations to metrology without recovering to  mobilise specialist metrology equipment. This solution combines  Sonardyne’s trusted 6G acoustic technology, the field-proven SPRINT  INS platform and Janus post-processing software. 

Metrology-ready ROVs combined with streamlined data collection  and processing offer significant time savings compared to existing  techniques, without compromising integrity and quality of data or  increasing risk. The 6G hardware platform provides a uniquely reliable  set of measurements rich in QC, speeding up traditional acoustic  metrology and lending itself to inertial integration, resulting in SPRINT  acoustic-inertial metrology.


SPRINT ROV positioning for subsea metrology inspection

How does it work?

The SPRINT-equipped ROV is used to place 6G transponders in each  metrology hub and then manoeuvres around the hubs to collect acoustic  ranges between each one. If there is direct line of sight between the  transponders, an acoustic baseline will be collected and used as an  independent QC measurement – in this scenario, no additional seabed  transponders are required. The attitude of each hub can be measured  using a GyroCompatt or a Compatt 6 transponder with an  inclinometer endcap.

All data is logged in real time by the SPRINT surface software with ROV  backup available. The unique architecture of Sonardyne INS provides  real time performance monitoring, detecting systematic errors in the  data. Once collected, Janus post-processing software is used to  determine the position of one transponder relative to the other using the  afore-mentioned SLAM technique. In combination with the hub  orientation measurements, the transponder positions determined from  the SLAM can then be used to provide hub-to-hub horizontal and depth  difference along with the relative bearing between the hubs. 


Real world results

An example of performance is given by a recent metrology campaign where SPRINT metrology has been compared to traditional techniques as a reference:

  • SLAM computed horizontal transponder difference compared to acoustic baseline: 0.02m
  • SLAM computed vertical difference compared to conventional depth loop: 0.01m
  • Significant time savings were realised during mobilisation and data collection referenced to alternative techniques
  • Quality checks and post processing of results were completed onboard using Janus software


GyroCompatt 6

The GyroCompatt 6 integrates Sonardyne’s Wideband  acoustic positioning and Lodestar Attitude and Heading Reference  technology in one small, highly versatile and robust instrument. This  provides high update rate wireless attitude, heading, heave, surge, sway,  pressure, sound velocity and acoustic positioning of any subsea object. 

Compatible with USBL and LBL positioning systems, the GyroCompatt 6  product family provides real time motion data for structure deployment  via the integrated high speed acoustic modem. It is small and light  enough to be ROV installed and a mechanical stab enables precision  alignment to any structure. Position and orientation can be accurately  determined during lowering, set-down and as-built surveys. Using the GyroCompatt 6 for metrology delivers the measurements  required for pipe-end coupling while autonomous logging negates the  need for a vessel and ROV to be on standby for taking measurements. 



15 hours saved

Using GyroCompatts, a leading offshore survey company  recently completed an acoustic metrology project 15 hours quicker than  anticipated. Taking place in the Gulf of Mexico, acoustic metrology  was performed on four proposed jumpers, measuring from the manifold  pressure caps to the wellhead casings. 

Typically, the time taken for one measurement is approximately  12 hours, resulting in a total operational time for this project anticipated  at 48 hours. However, using Sonardyne’s 6G® GyroCompatt  technology, all metrologies were completed in just 33 hours with  accurate results.