Support of Gulf of Mexico Hydrate Research Consortium: Activities to Support Establishment of a Sea Floor Monitoring Station Project Semiannual Technical Report

The vertical acoustic line array (VLA) and a similar oceanographic line array (OLA) were developed as part of the Gas Hydrates research program. The development of this array technology has evolved and been integrated into a part of a larger Sea Floor Observatory (SFO) to be installed in the Gulf of Mexico. The SFO is intended to provide a long term means to study characteristics of gas hydrate deposits. This report addresses the development of the VLA and OLA, the new technology developed during this process and the integration of this technology into the SFO. The report also discusses other technology testing opportunities that were undertaken during this program and the evolution of the two original stand alone VLAs into the new SFOintegrated VLA and OLA. Introduction The design for the vertical array includes an array of 16 hydrophones spaced 12.5 meters apart and extending approximately 200 meters up from a point just above the sea floor. A data logger was designed for the first version of the VLA which was self timed to record during the arrival of the acoustic signal of interest. Communication to the data logger was via an acoustic modem. Recovery of the array with its battery pack and data logger was accomplished through activation on an acoustic release connecting the array to the anchor. The design was intended to allow several days of data collection using a near-surface towed sound source. The need for longer term deployments, more precise timing between surface-source firing and bottom recording, and the need to recover larger data sets required integration of the VLA into a SFO. This SFO is to be equipped with a real time communications link to the surface ship and a longer term power source. Modifications are required to interface the VLA data recorder to the SFO and to increase deployment durations from weeks to years. Interest within the Gas Hydrates Consortium for measurement of near sea-floor oceanographic parameters led to the conversion of one of the two VLAs into an OLA. Summary New technology developed following the original VLA development was utilized in the design and construction of a new VLA and an OLA. These improvements included cable design, modifications to software programs, addition of a remote real time “T0” timing command, faster data retrieval through a hardwired and fiber optic Ethernet capability and development of a ROV mateable underwater multi-conductor connector system. Software and hardware changes to the Data Acquisition and Telemetry System (DATS) recorders interfaced the DATS of the original VLA design to the SFO data retrieval system. Experience gained in the deployments of the VLAs was applied to the design and deployment techniques of these arrays.