For both tests, offshore NW Australia and the Shetlands, an Allseas Schilling Robotics UHD ROV system was used as the instrument carrier. This system has a patented station keeping facility, allowing for steady and automatically controlled guidance along a predefined route section. Standard survey equipment fitted on the ROV in addition to INS Instrument Type Surface positioning Veripos Ultra Vessel heading and motion sensor IXSEA Octans Underwater positioning Kongsberg Dual HiPAP500 Transponders Sonardyne WSM ROV heading and motion sensor IXSEA Octans Multibeam echosounder Dual-head Reson Seabat 7125 Depth sensor Paroscientific Digiquartz Altimeter Kongsberg 1007 Doppler Velocity Log RDI 1200kHz Workhorse Navigator Sound velocity sensor and CTD probe Valeport SVX2 Obstacle avoidance sonar Kongsberg MS1000 Survey software in addition to INS software Package Type Online DGNSS QC Veripos VeriFy QC Online positioning EIVA NaviPac ROV sensor data logging EIVA NaviScan Survey data processing EIVA NaviEdit & NaviModel 3D
IXSEA Kongsberg Sonardyne
2/8
ROV INS hardware & software Manufacturer Hardware – (processing) software PHINS - Delph-INS ROV HAIN - NavLab Lodestar SPRINT – Janus
Table 1.
throughINSTALLATION adding sparse DGNSS or acoustics during positioning systems and their repeatability, which is post processing. Migration of the same technology easily checked by comparing the processed pipeline onto the ROV platform is a challenge and In is not positions for each mounted Two types of installation were trialled. 2009asa bracket was made at thepass. frontAofROV an UHD ROV tomultibeam fit the integrated IMU and DVL. In 2012 the instruments were separated: the INS was mounted on the straightforward as it may seem. is required to generate the high density data survey skid whereas the dedicated DVL and depth sensor were mounted at an offset. necessary to accurately detect the top of the pipeline. The presentation provides the results of various This then allows for an accurate comparison trials conducted by Allseas with INS aided ROV between the pipeline positions derived from the positioning along offshore pipelines. Included various passes. are comparisons between various combinations The required calibrations were performed according to standard procedures. The dedicate DVL of ROV positioning survey sensor calibrated data. Although to align with the heading sensor in the INS. INS For clarity the calibration sequence the table below. trials were performed in both 2009 and 2012, the presentation focusses on the most recent trials with Calibrations prior to ROV INS survey work the Sonardyne SPRINT system in April 2012. The Task experience gained during the 2009 trials provided Local vessel and ROV offsets the basis for the recent tests. Calibration SV and CTD probe METHODOLOGY To analyse the performance of a ROV mounted INS, a methodology was developed to survey the same section of a pipeline on the seabed multiple times and in opposite directions.
DGNSS health check Vessel gyro, pitch, roll calibration ROV gyro, pitch, roll calibration APOS (HiPAP) calibration ROV dual head multibeam calibration DVL alignment to INS Position confirmation checks
Table 2.
A pipeline provides a good bench mark for the RESULTS
196 | Hydro12
2009 Test
In 2009 ROV INS tests were performed for a project in NW Australia. A detection criterion deflection over a 50 m length was defined. Both IXSEA and Kongsberg INS solutions were