Case Study • INFOMAR – Deployment of Moving Vessel Profiler • AML Oceanographic Logo

Case Study • INFOMAR – Deployment of Moving Vessel Profiler (MVP) • AML Oceanographic

Snapshot
Service
Deployment of Moving Vessel Profiler (MVP) for INFOMAR
Role
Service Provider ● Equipment Provider
Client
INFOMAR
Year
2017
Location
Celtic Sea, Ireland
Environment
Offshore
Region
Europe
Details

Background

The Integrated Mapping for the Sustainable Development of Ireland's Marine Resource programme, INFOMAR, is Ireland's national marine mapping programme. It is the successor to the Irish National Seabed Survey (INSS), and is a joint venture of the Geological Survey of Ireland (GSI) and the Marine Institute (MI), funded by the Department of Communications, Climate Action and Environment.

The overarching objective of the INFOMAR programme is to create a range of integrated seabed mapping products for the entirety of Ireland's offshore waters. In order to achieve this, INFOMAR deploys a range of survey vessels, from small craft operating in the near shore areas to ocean going research vessels such as the RV Celtic Explorer and RV Celtic Voyager.

The use of the MVP allowed vessel speed to be maintained, reduced the number of line turns required during the survey, and is estimated to have increased the survey coverage and efficiency by 12%.

Thomas Furey
INFOMAR Joint Programme Manager, Marine Institute of Ireland


The Celtic Sea

During the last two years, INFOMAR offshore mapping focused on the SE Celtic Sea, an area of importance for shipping, and of significant economic value for fisheries having been designated in 2003 as a Biologically Sensitive Area by the European Commission.

The Celtic Sea is a complex area from an oceanographic perspective with a transition from stratified to mixed water occurring in the eastern extent towards the entrance to the Irish Sea. It tends to be more stable and stratified however with uniform thermocline development and regular seasonal and tidal variability in the central area.


Objectives

During 2017 survey planning, to better control sound velocity variability in the water column in this challenging area and to improve multibeam data integrity, it was decided to recommission the MVP200 system, which had not been utilised for several years. The specific objectives were to:

  • Increase survey efficiency
  • Allow better sound velocity controls on the echo sounders and improve overall data quality
  • Add value to the data set for research collaboration in an important fisheries ground. More specifically, to investigate the nature of internal waves and variability of the thermocline.

With advance instrumentation calibrations and lab support on planning and engineering requirements to recommission the MVP200 provided by AML engineers, followed up by onsite support during mobilisation, the MVP200 was fully operational prior to vessel departure for survey.

The hydrographic survey took place between the 21st of July and the 5th of August, with the core Irish scientific team augmented by two international research groups, as part of Ireland's Atlantic Ocean Research Alliance endeavour on collaboration. Prof. John E. Hughes Clarke led a team from the Centre for Coastal and Ocean Mapping (University of New Hampshire), and students joined from the BEAMS programme in the University of Charleston.

A specific focus of the research led by Prof. Clarke is to define methodologies to image and automatically extract the thermocline variability from the underway acoustic imagery (EK60 or Multibeam Water Column (WC) data). The use of the MVP was critical in supporting this research in order to directly measure the location of the top and bottom of the thermocline for comparison with its acoustically imaged depth at the various operational EK60 frequencies. Related research activity also focused on multispectral backscatter analysis, and use of the onboard ADCP to define tidal current regimes.


Equipment

To facilitate the extent of research undertaken in parallel with the core mapping activities, a complex instrumentation array were configured and synchronised in order to avoid acoustic interferences. In summary the following acoustic array was used:

  • Multibeam Echosounders: EM1002 (95 kHz), EM302 (30 KHz) + WC, EM2040 (200 KHz) + WC

  • Singlebeam Echosounder: EK60 (18, 38 and 120 kHz)

  • ADCP: Ocean Surveyor (75 kHz)

  • Sub-Bottom Profiler: ECHOES3500 Chirp (1 to 10 KHz)


Survey Results

The MVP was deployed off the starboard aft side of the vessel using a boom to keep it as far away as possible from the magnetometer cable. The MVP sensor was deployed almost continuously at survey speed of 7.5 to 8 knots. The recovery messenger was deliberately located so that the sensor would sit at ~4.5 to 5.5m at normal tow speed. This matches the depth of the EM302 array. The MVP was routinely launched to ~10m off the bottom every ~half an hour. As the survey consisted of ~2 hour lines, this typically provided 4 to 5 profiles during each survey line.

In total, over 4000 km of survey line acoustic data were acquired and over 500 MVP casts were taken in 14 days. The use of the MVP allowed vessel speed to be maintained, reduced the number of line turns required during the survey, and is estimated to have increased the survey coverage and efficiency by 12%.

The frequency at which MVPs were taken meant that the sound velocity control for the echo sounders was greatly enhanced.

The preliminary results on thermocline studies indicate a strong correlation between the EK60 data, Multibeam WC data, and the MVP data. With hydrographic effort and accuracy requirements anticipated to rise in the future, an increasing need to better understand oceanographic variability to underpin ecosystem and climate studies, and finally with technology scale down, multi-sensor MVP data acquisition will likely become routine in future ocean mapping initiatives.

 
Related Case Studies
Fugro Germany Marine mobilised the Moving Vessel Profiler System (MVP200) as part of the survey equipment aboard the Survey Vessel Fugro Discovery in order to meet the client's requirement to perform a sound velocity cast at least every two hours. Working on behalf of the Norwegian Hydrographic Service on the MAREANO 2017 Project, the Fugro Discovery ... Moresurveyed an area of 3,220 km² in the Barents Sea. During 16 operational days, 130 of 150 Conductivity, Temperature and Depth (CTD) Profiles were automatically taken using the Moving Vessel Profiler (MVP) system in water depths up to 400 m.

The MVP System proved itself to be very reliable, robust and relatively easy to operate. The capability to perform CTD cast while the vessel is underway not only saves a lot of time and labour but contributes to increased Multibeam data quality and significantly increases daily and overall production.

Paul Rybinski – Party Chief
MV Fugro Discovery Fugro Germany Marine GmbH
The CTD Profiles were verified and applied instantly to the EM712 Multibeam Echosounder acquisition software (Kongsberg SIS). With an average survey speed of 9 knots, the MVP towfish equipped with an AML Micro CTD was constantly towed behind the vessel; casts were performed with a vessel speed between 4 and 8 knots (depending on the desired profile depth). The MVP System proved itself to be very reliable, robust and relatively easy to operate. The capability to perform CTD cast while the vessel is underway not only saves a lot of time and labour but contributes to increased Multibeam data quality and significantly increases daily and overall production. CTD casts are performed regularly or as soon as the environmental conditions change due to fluctuation of surface sound velocity for example; The CTD profiles are applied immediately without the need to stop data acquisition.

During the MAREANO survey campaign, the Fugro Discovery worked in areas where drift ice was present. When surveying in vicinity to isolated ice bergs or drift ice, the sound velocity in the upper water column was changing rapidly and the MVP system was used advantageously to ensure that the Multibeam Echosounder (MBES) was frequently updated with the correct sound velocity and absorption coefficients while the vessel was under­way constantly acquiring bathymetric data.
Keywords
Acoustic Doppler Current ProfilerADCPCeltic SeaInstrumentationMoving Vessel ProfilerMVPMultibeam EchosounderMBESOceanographyOffshoreResearch VesselSinglebeam EchosounderSBESSub-Bottom ProfilerSBPSurvey
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