AUVs for oceanographic science at IFREMER, project progress and operational feedback

Transcription

1 AUVs for oceanographic science at IFREMER, project progress and operational feedback Jan Opderbecke Jean-Marc Laframboise IFREMER ISE Research Ltd Department for underwater systems 1734 Broadway Street La Seyne sur Mer Port Coquitlam B.C. Canada V3C 2M8 Tel. +33(0) Tel. : (604) Abstract - The coastal AUV project at IFREMER, launched in 2002, has the aim to develop two oceanographic survey AUV as well as several payload modules and operational tools, in order to provide efficient and economically interesting tools for the French oceanographic community. The corresponding AUVs have been developed by ISE Research Ltd Vancouver. This paper presents developments and operational feed-back in the project period I. INTRODUCTION A. Introduction Ifremer is the French Institute for Ocean Research. The Underwater Systems Department expertises, integrates and maintains the operational underwater vehicles and tools required by the scientists in the various fields of oceanography. The two AUV with payloads and exploitation tools, reach in 2007 a level of routine operation serving the scientific community. The underwater vehicles have been developed by ISER Ltd Vancouver, the integration and optimization of payloads and the development of operational tools in key technological fields has been the task of the Underwater Systems Department. B. Project scope The coastal AUV project at IFREMER was launched in 2002 with the aim to develop two oceanographic survey AUV as well as several payload modules and operational tools, in order to provide efficient and economically interesting tools for the French oceanographic community [1]. The requirements for payload instruments, autonomy and vessel support led to the specification of a medium size AUV 800kg/4,5m rated for coastal and margin work down to 3000m depth [2]. Multidisciplinary oceanographic projects require the systems to be easily re-configured with various payloads between consecutive deployments. The corresponding AUV have been developed by ISE Research Ltd Vancouver, as the first and fourth builds of the Explorer-AUV series. The IFREMER team defines and integrates payloads that match their scientific applications, fits the AUV with specific operational tools, and qualifies the systems within the scientific applications. The project will now enter the exploitation phase where one AUV will be routinely run by Ifremer s operating company Genavir. In the present paper we give a brief technical and functional description of the Explorer series AUV with their payloads and further developments. Technological choices and performances feedback will be discussed in key areas like navigation, acoustic communication, decisional architecture etc. We describe security strategies, system supervision and operational considerations, which are the key points to recurrent and reliable use. The Ifremer AUVs so far have accomplished more than 130 days of diving at sea, with dive programs of increasing complexity and depth. We will resume the experience and results of the three years period of operation. figure 1: the two Ifremer AUV The project scope represents the following investments and developments : 2 Explorer type 3000m rated AUV aster X, first of the ISE Explorer series, received in February 2004; AUV2 (not yet named!), received in December 2006; integration of several payload instruments :

2 multibeam echosounder ; subbottom profiler ; 2 ADCP, upward and downward looking ; 2 fishery sonars, upward and downward looking ; development of the mission management software MIMOSA ; development of a versatile payload controller including time base and synchronization features; development of a multi-vessel launch and recovery system CALISTE (underway). II. THE EXPLORER AUV SERIES The requirements elaborated in the initial project phase resume to : the vehicle must have a size and weight allowing it s deployment from small coastal vessels (~25m length), in order to provide a tool compatible with the technical and economical constraints of coastal oceanographic science. This key feature must include rapid mobilization as imposed by event-related operation on short notice. The autonomy is sufficient for 100km dives with one battery charge. The vehicle, even if fitted with a low rate acoustic data link, and USBL acoustic positioning, is fully autonomous and has technically no need of being escorted by a surface vessel during it s dives. The vehicle has the capabilities for limited ocean margin work with a depth rating of 3000m. On the base of Ifremer s requirements and the experience with their Theseus and Arcs AUV, ISER have designed the Explorer AUV series [3]. The successful choice of the vehicle characteristics for scientific purposes have resulted in the demand from other clients 5 Explorer AUV have been built since The Explorer 3000 AUV in the IFREMER configuration is 4.5m long, it has a displacement of 800kg including payloads. It has a single propulsion and 5 (initially 6) steering planes - three rear and two in the front. The rear top rudder plane carries on it s top antennas for DGPS, radio communication, acoustic re-localization etc.. State-of-the-art equipment, commonly chosen by the client, are used for navigation. The IFREMER vehicles are equipped with ixsea-phins INU, RDI Doppler-log WH300. This navigation solution provides as with an AUV trajectory estimation that drifts with only a few meters per hour drift caused by water current in the descent phase (without DVL bottomlock) can be compensated by sending a position update through the acoustic link once the AUV has reached the bottom-lock. Lithium-Ion technology batteries in a variable and extendable number of modules procure 10KWh of energy in the base configuration. The security system of the AUV is highly developed either on the hardware and on the software side. Three levels of hardware control, each controlled by a specific time delay relay (TDR), ensure the global electric functioning of the system. Controller reboot, seafloor parking state and drop weight release are possible responses. The software exception handling tool within ISE s ACE control software is user-configurable and can be adapted to the particular working conditions. Alarm levels and alarm responses are in particular adapted to the diving phase (descent, survey, targeting ) through special commands in the missionplan. An important feature for the user, the Explorer AUV is an open system architecture, allowing the technical evolution on the client side with new sensor integrations, payload integration, adaptation of the vehicle software and behavior. A fundamental requirement for this is a complete technical documentation and a vehicle software that is to a large extent reprogrammable through a graphical component-connection representation. This feature is important in the scientific environment with varying and quickly evolving requirements. As a modular concept, ISE adapts the vehicle characteristics (length of pressure hull, length of vehicle, payload capacity, battery capacity etc) to the clients requirements. figure 2 : AUV aster X on ADCP survey III. DEVELOPMENTS The software MIMOSA represents a major development. The GIS based software (using ArcGis TM ) is a unique tool [4] that aims to achieve maximum efficiency and low risk of operator error in the design of AUV dives by offering : manipulation of a unique and complete dive-plan object, which includes 4D waypoints, all dive parameters and payload commands, finalized by automatic verification of the consistency of the diveplan with respect to vehicle characteristics and environment; at any moment this diveplan can be exported in the vehicle s dive protocol; by offering an open platform for marine charts (S57, BSP, ) as well as geographically referenced user data in form of geo-images (geo-tiff etc.) and ArcView TM

3 projects; this feature allows the scientific user to design dive track lines with respect to their application data sets, and it allows to visualize dive results before designing consecutive dives; by offering complete multiple vehicle tracking functionalities with replay from external and from the vehicles internal data base; MIMOSA is already licensed to Memorial University of Newfoundland and Bremen University, both of whom possess ISE Exporer-series AUV. It s size with respect to the AUV payload capabilities allows to use other small or medium sized payloads simultaneously (ADCP, magnetometer); various scientific cruises have been accomplished; the figure below shows a survey result from the 2006 BIONILE cruis (RV Meteor), where tha asterx AUV has successfully be used in alternation with MARUM s Quest ROV. On the payload integration side, an independent versatile controller has been developed. This software runs on a separate CPU, which hosts also extensive time control and synchronization functionalities, and allows also to remotely run third party software (instruments configuration etc.). Launch and recovery, which remain critical phases in routine sea work, have lead to the design of the multi-platform LARS system CALISTE the cage solution is based on a unique touch and align concept. figure 4: geophysical MBES survey figure 3 : dive design with the MIMOSA software IV. PAYLOADS AND FIELDS OF APPLICATION The initial historic perspective consisted in a given number of pre-assembled payload instrument modules according to the major fields of application. The actual scenario is a modularity at the instrument level, in response to the complex and changing user requirements. Vehicle reconfiguration with different payload instruments between successive dives is a common need at sea. B. Sub-bottom profiler The Echoes 3000 echo-sounder is designed by ixsea to Ifremer specifications, it operates in a frequency band from 1.5 to 6kHz. It s size and weight exclude simultaneous use with the MBES; the instrument is currently in the phase of integration to the vehicle system the first scientific cruise is programmed in February C. Fishery sonar Two EM-60 (Kongsberg-Simrad) at acoustic frequencies of 70 khz and 200kHz can simultaneously be used on the AUV, in various geometric configurations ; both types of transducer heads can be mounted upward and downward looking; several scientific cruises have been accomplished; besides the fish stock monitoring applications that have motivated the development of this payload, the EK-60 have been experienced in geo-physical applications to provide gas seepage detection; The following payload instruments have been integrated : A. Multibeam echosounder The EM-2000 (Kongsberg-Simrad) is one of the most classical tools for geo-physics. The instrument is owned by the french research organism CNRS Geoscience Azur [5].

4 figure 5: EK60 gas seepage detection (on flat bottom)? D. Current profiler ADCP of the Workhorse family (WH300/600/1200) are used in various ways; a two instrument upward-downward looking configuration is achieved by using the navigation DVL in alternate ADCP mode; an original scientific application has used a high frequency ADCP for the observation of thin water layers with specific physical characteristics these layers were of interest in tracking of dynophysis algae bloom; figure 6: fine layer observation with RDI ADCP the red layer has a thickness of less than 0.5m (length here ~500m) V. CONDITIONS AND MODES OF USE The AUV are typically operated by a team of four, including acoustic positioning and a payload expert. The AUV, surface station and accessories (deck cradle, acoustic devices, vehicle spares ) are conditioned for transport in a single standard 20 container. Mobilization on a vessel is possible in one work-day. The dive preparation, excluding battery charging and payload configuration changes, is less than two hours. The dive-plan can be adjusted until one hour before deployment it can also be recharged by radio transmission while the AUV is at the surface. The AUV are today deployed by aft A-frame or by crane over the side. This procedure has the inconvenience of requiring for recovery the assistance by a rubber boat. The constraint will be abandoned with Ifremer s new deployment cage CALISTE to be put in service in November The routine AUV dive is escorted by the vessel within reach of the acoustic communication devices. Technically, a fully autonomous dive is possible and has been experienced, but legal responsibility issues and minimum vehicle risk lead us in this first phase of routine operation, to opt for escorted diving. The AUV dive is monitored by use of an acoustic data link (Sercel MATS-200), with a general operating range of 1km horizontally and 3km vertically. Several acoustic commands like mission redirection, mission abort or security stop are possible. The acoustic link is not mandatory, and it is only triggered by operator request. Acoustic positioning (ixsea GAPS or Posidonia) can be an additional security but is not mandatory. In various applications the acoustic positioning is requested by the scientific user in order to dispose of additional high quality geographic position references. These enhance the data set (a) during the dive by updating the vehicle navigation or (b) offline by blending the onboard vehicle navigation with the acoustic positioning series. The AUV can be deployed, according to the vessel size, area characteristics etc. up to 25kts of wind and up to sea state 5. The recovery procedure is the critical point regarding the meteorological limitations. The innovation of the AUV as a scientific tool, even if vehicle escort is today a chosen constraint, signifies costeffective and versatile surveying : - rapid deep water surveys operated from small coastal vessels (25m); - fast mobilization, possibility of event-reactive mobilization, easy transport; - combination with other heavy oceanographic systems like the manned submersible NAUTILE or the ROV VICTOR 6000; Nevertheless, non escorted diving is our medium term goal. There is ongoing development on features like emergency seafloor standby parking, releasable emergency Iridium buoy, dynamic mission recovery etc. VI. OPERATIONAL RESULTS The coastal AUV project is today in a phase of analyzing the achieved track record for scientific work. Approximately 2000km of survey dives have been accomplished. The following table indicates this track record. Most of these cruises have been carried out with AUV aster X, AUV2 has been taken to it s first scientific operation in June 2007.

5 ADCP MBES SBP FS Cruises 3 4 1rst in 4 (science) 2008 Dives table 1 : cruises and dives The initial aim of 60 days of operation resulting in a mean daily rate below has been achieved. Scientific references have been produced in three fields with different payload configurations. Major payload integrations are programmed in the period Table 2 indicates the diving depth during scientific cruises. The numbers correspond to recent tools which have only progressively been used with diving to deeper water. Nevertheless, the numbers show that geophysical oceanography requires frequent deep diving, whereas biological and environmental applications are limited to a few hundred meters of water depth. Water depth ADCP MBES SBP FS [m] < Scientific 6 dives in table 2 : number of dives per payload instrument and per water depth VII. CONCLUSION A. Perspectives Strong demand for AUV in scientific projects ensure at least 60 days of operation at sea per year for both AUV in the coming years. New interest from scientists creates need for new payload integration, especially in the bio-chemistry and bio-physics fields : mass-spectrometer, microscopic particle analysis (cytobuoy TM ), water sampling, optical particle density measurement, natural light intensity measurement The AUV mission handling and software security management system is today that of a static state machine. Intelligent error handling and reactive mission management are topics that will receive increased focus in the near future, in order to prevent our vehicles from aborting a dive for exceptions that might be solved by dynamic mission reorganization. These techniques will bring the AUV operation one step closer to the stage of routine fully non-escorted work. The deployment and recovery by aid of the CALISTE recovery cage is a strong potential for the reduction of risk and resources needed for deployment. CALISTE is programmed to be operational in figure 7 : the CALISTE automatic recovery cage B. Cooperation With an aim of continuously improving the AUV systems and their operational potential, Ifremer will continue to develop cooperation on an international level with scientific partners using AUV : Memorial University Newfoundland - Canada, Alfred Wegener Institut Germany, Bremen University/Marum Germany etc. Sharing cost, resources, and operational feed-back is an essential way to foster scientific use and success of high technology tools. The cooperation includes the industrial partner ISE who is strongly committed to the performance and reliability of the Explorer AUV series. C. Conclusion Medium size AUV like the ISE Explorer series have proven to be powerful and efficient tools for oceanographic science. Even when monitored from a vessel, AUV enable access to high quality scientific data without need for huge vessels and heavy equipment. On large vessels, AUV are an ideal complement On off-shore cruises with larger vessels, the systems are complementary in usage and resources to traditional underwater systems. Strong end-user demand confirms the success of the program. Technical reliability being achieved, dynamic mission management will be the key point for non escorted AUV dives in coastal areas in the future. References [1] V. Rigaud et al, First steps in Ifremer.s autonomous underwater vehicle program - a 3000m depth operational survey AUV for environmental monitoring, ISOPE 2004, proceedings, pp , Toulon-France, May 2004 [2] [3] [4] [5] [6] : Hermes news, Issue 7, page 4, Edition winter 2006/2007