Observatories and Research Facilities for EUropean Seismology
Volume 4, no 1 May 2002 Orfeus Newsletter


GEOSTAR, the European prototype-node of incoming seafloor networks

Paolo Favali and Laura Beranzoli

Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via di Vigna Murata 605, 00143 Roma, Italy

Introduction - GEOSTAR observatory - Data acquired during the missions - The future - Conclusions - Acknowledgements - References

Introduction

In the last decade the European scientific community has acquired a vast experience in deep sea monitoring, thanks to the Marine Science and Technology programs (MAST) of the European Commission (EC). In the framework of MAST, projects were addressed both to feasibility studies of benthic laboratories, like ABEL (Thiel et al., 1994; Berta et al., 1995) and DESIBEL (DESIBEL, 1997) and to developments of new deployment tools and procedures like LOMOS inside the DESIBEL project. These projects led to the realisation of new systems for marine environment investigation as complementary tools to the Remote Operating Vehicles (ROVs), at times considered too expensive for research mission purposes or failing to meet some technological requirements. The new systems can integrate the traditional and simpler observation systems (i.e. moorings) and have significantly increased the range of parameters that can be measured in deep sea and the sea depth range of operations.
The GEOSTAR 1 and 2 projects (GEophysical and Oceanographic STation for Abyssal Research) funded by the EC, in two phases (1995-1998, 1999-2001) have significantly contributed to enhance European capabilities in operating also in abyssal depths. The outcome of these projects was the result of the scientific and technological synergy between research institutes and companies from Italy, France, and Germany under the co-ordination of Istituto Nazionale di Geofisica e Vulcanologia of Italy (INGV). Overviews of the worldwide efforts in the "Seafloor Observatory Science" are reported in: Multidisciplinary Observatories on the deep seafloor (Montagner and Lancelot, 1995), Illuminating the hidden Planet. The future of seafloor observatory science (NRC, 2000) and in Science-Technology Synergy for Research in Marine Environment: Challenges for the XXI century (Beranzoli, Favali and Smriglio, 2002).

GEOSTAR observatory

The GEOSTAR projects have made available a prototype of deep-sea observatory, called GEOSTAR as well (Figure 1), which is able to acquire oceanographic, geophysical and environmental data down to 4000 m water depth with power autonomy up to 1 year. The GEOSTAR prototype successfully operated in two missions. Firstly a short-term demonstration mission carried out in the Adriatic Sea in 1998 in shallow waters (about 40 m; Beranzoli et al., 2000). The second mission was performed in the Tyrrhenian Sea, close to Ustica island (Western Sicily), at a depth around 2000 m, from September 2000 to March 2001. The observatory was recovered in April 2001. In both missions GEOSTAR observatory was deployed and recovered by the R/V Urania, managed by the Italian Consiglio Nazionale delle Ricerche, equipped, during the long-term mission, with an optic-electro-mechanical cable and winch properly designed and realised for the purpose. The cable also ensures the primary communication link with the Bottom Station during the deployments. During the mission geophysical measurements (seismometric, gravimetric, magnetometric), oceanographic measurements (current velocity and direction in the water column up to 500 m above the observatory site), and environmental measurements (water temperature, salinity, light transmission, and water sampling for on-shore laboratory analyses) were acquired with a single reference time provided by a high precision clock.


Figure 1. The GEOSTAR Bottom Station latched to the MODUS on the deck of R/V Urania before the second mission deployment (top); underwater image of the observatory during the descent (bottom).

The GEOSTAR observatory includes three main subsystems: the Bottom Station, the Mobile Docker for Underwater Science (MODUS), and the Communication systems. The most innovative aspects of GEOSTAR observatory concern the deployment procedure. The Bottom Station is driven from the sea surface by means of the MODUS, a vehicle especially realised in the projects, the communication systems, and the sensor package management.
MODUS (0.7 kN in water) is a simplified version of a ROV equipped with thrusters for horizontal movements, altimeter to measure the distance from the seafloor, sonar for the localisation of the Bottom Station in the recovery phase and a standard compass revealing the orientation. In addition, video-cameras allow a visual inspection helping a safe recovery of the Bottom Station. MODUS is also able to carry heavy payload up to 10 kN and is operated from a console on board the ship through the deployment/recovery cable. The Bottom Station (18.7 m3, 1.3 kN in water) is the actual deep-sea observatory and hosts the sensor set, the Data Acquisition and Control System (DACS) and the communication systems. The station frame is made of anti-corrosion aluminium alloy and includes titanium vessels for the electronics and batteries in order to avoid perturbation to the magnetic measurements. The installation requirements, usually fulfilled on land, of particular sensors like the seismometer and the magnetometer were taken into account in order to maintain the data quality usually obtained by sensors operating on land. The DACS manages the whole observatory according to a mission configuration plan. Typical tasks of the DACS are the check of the sensor package functioning, the data storage on hard disks (2 Gbyte x 2), and the check of the status sensors (water intrusion, anomalous increase of internal temperature, etc.). The communications consist of acoustic/satellite system and of data capsules (MESSENGERS). The acoustic/satellite link is based on a surface buoy able to keep in touch with the Bottom Station during the mission and to transfer data and commands to and from an on-land computer station. The MESSENGERS are both automatically released by the Bottom Station (E-type, 32 kbyte capacity each) and upon acoustic command (S-type, 40 Mbyte capacity each). Once at the sea surface, they transmit via ARGOS satellite the position and the data stored. A detailed description of the system is given by Clauss and Hoog (2002), Favali et al. (2002), Gasparoni et al. (2002) and Marvaldi et al. (2002).

Data acquired during the missions

The GEOSTAR observatory performed two scientific missions, a short shallow water demonstration in the 1998 and the first long-term deep sea in the 2000-2001. The first mission took place in the Adriatic Sea and, although mainly dedicated to test the complete functionality of the whole system, produced 439 hours of geophysical and oceanographic data representing the 97,8% of the whole mission period (20 days). The long-term mission was performed in the Tyrrhenian Sea, south-west Ustica island, and produced 4159 hours of geophysical and oceanographic data representing the 99,6% of the whole period duration mission (174 days). The data loss amounts to 16h24m. A detailed description of the acquired data during the first mission can be found in Beranzoli et al. (2000), while the analysis of the second mission data is presently in progress. Examples of seismological data acquired in the demonstration and long-term missions are shown in Figure 2.


Figure 2. Seismological recordings during the missions: top) event in Central Italy (August 15, 1998, 05:18, mb=4.8, 232 km far from the mission site) recorded by Guralp CMG-3T; bottom) events in New Ireland Region (November 16, 2001, 04:54, MW= 8.0 and 07:42, MW=7.8) recorded by the gravity meter prototype of GEOSTAR (Iafolla and Nozzoli, 2002).

The future

Other deep-sea observatories derived from GEOSTAR are going to be realised in the framework of Italian research projects. The Gruppo Nazionale di Difesa dai Terremoti (GNDT), mainly addressed to seismological researches, has recently approved a three-year project, coordinated by INGV, for the deployment and the long-term operation (6-8 months) of a deep-sea observatory offshore the eastern coast of Sicily. The Bottom Station of the observatory, presently in the building phase, will be smaller than the GEOSTAR one and will host, besides status sensors, a three-component broad-band seismometer, a hydrophone, a gravity meter, a single point three-axis current meter and a CT (Conductivity and Temperature) sensor. The observatory will be equipped with an interface for the connection to a submarine electro-optical cable already settled on the sea bottom from the Sicilian coasts provided by Istituto Nazionale di Fisica Nucleare. The observatory will be powered through this cable, which will also assure commands and real-time data exchange. The data will be managed through the web. The deployment of the observatory is scheduled during 2003.
In the framework of the research activities of the Italian Piano Nazionale di Ricerche in Antartide (PNRA) a multidisciplinary benthic station is going to be realised, and it will be used in scientific projects in the Antarctic waters in co-operation with the Alfred Wegener Institut (Germany).
The ORION (GEOSTAR-3) project, recently approved by the EC, represents the evolution of GEOSTAR 1 and 2. The know-how acquired during the previous projects is going to be applied for the realisation of a deep-sea network with a main node, GEOSTAR, and two satellite nodes communicating via acoustics and exchanging commands and data with the main node. A surface buoy, with satellite/acoustic links, will allow the network to be accessed remotely.

Conclusions

The GEOSTAR observatory is a complex system due to the multidisciplinary sensor equipment with very different management requirements and deployment/recovery procedures. This prototype opened a new perspective for the deep-sea monitoring, successfully experimenting innovative technological devices and procedures applicable to different systems. The philosophy we followed approaching the scientific and technical aspects of GEOSTAR was to design, realise and experiment a complex system able to implement the needed actions for long-term missions in deep waters. Having demonstrated the feasibility and reliability of such a system, the derivation of simpler modules dedicated to particular applications, eventually including a reduced set of instruments, also at shallower depths, will be easier. Our further efforts will contribute to go steps behind towards the realisation of permanent seafloor networks, bearing in mind that scientific approaches to extreme environments, like deep oceanic seafloors, has to be intimately linked to high-level technology. This goal is the next important worldwide challenge of the "Seafloor Observatory Science", a young branch of the Earth Sciences. We strongly believe that in the future the global monitoring can benefit of these incoming seafloor networks only by integration with the existing land-based observation networks and research facilities, such as ORFEUS.

Acknowledgements

The GEOSTAR 1 and 2 projects were funded by the EC in the framework of MAST-3 Programme. ORION-GEOSTAR 3 project has been approved by the EC in the framework of the Environment Programme. Thanks are due to all the partners of these projects through the Local Project Managers: F. Gasparoni ( Tecnomare SpA, Italy), M. Marani and F. Gamberi (Istituto per la Geologia Marina-CNR, Italy), J. Marvaldi (IFREMER, France), J.-M. Coudeville and G. Ayela (ORCA Instrumentation, France), J.-P. Montagner (Institut de Physique du Globe de Paris, France), C. Millot (Laboratoire de Océanographie et de Biogeochimie, France), H. Gerber (Technische Fachhochschule, Germany), G. Clauss and S. Hoog (Technische Unversität Berlin, Germany), E. Flueh (GEOMAR, Germany). The authors want to express their gratitude to all the people that have contributed with their work to the success, and particularly to C. Viezzoli, Captain E. Gentile and the crew of the R/V Urania for their skill and careful assistance during the GEOSTAR missions. We are indebted with Prof. Enzo Boschi, President of INGV, for his continuous encouragement. Special thanks are due to Torild Van Eck who invited us to submit the paper. The authors take this occasion to remember their friends and colleagues of the projects recently passed away, Luc Floury from IFREMER and Giuseppe Smriglio from INGV.

References

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