Support of Gulf of Mexico Hydrate Research Consortium: Activities to Support Establishment of a Sea Floor Monitoring Station Project Semiannual Technical Report for the 2nd Quarter

A near sea floor, 200 meter vertical acoustic array is being developed as part of a long term sea floor monitoring station to study gas hydrate deposits. This report addresses progress in the development of a vertical seismic array system specifically designed for 3-dimensional mapping of shallow gas hydrate deposits. The time frame covered in this report includes the first half of the second year of development of this vertical array. The report includes progress in the data logger, vertical array and software. The program includes production of 2 additional arrays and refurbishment of the year one array. Introduction The vertical array is comprised of an array of 16 hydrophones spaced 12.5 meters apart and extending approximately 200 meters up from the sea floor. A data logger and a pressure compensated battery pack are mounted at the bottom of the hydrophone array. The array is suspended via glass flotation and anchored with an expendable concrete weight. Recovery of the array with its battery pack and data logger is accomplished through activation of an acoustic release connecting the array to the anchor. The design is intended to allow several days of data collection using a near surface towed sound source, with shots fired and timed in sequence with the data collection regime programmed into the near bottom mounted data logger. An acoustic modem-based communication system allows the surface ship computer to reprogram and direct this data collection regime. This communications link to the sea floor equipment also provides an ability to recover sample data sets to assess and alter the data collection parameters. The system developed during the first year of effort was successfully installed and recovered in 830 meters of water. The second year efforts include improvements and enhancements to the capability as well as construction of 2 additional vertical arrays capable of deployment in deeper depths. The refurbishment of the first year array is included in this effort. Executive Summary Progress during the first part of FY 2003 included further development of the data logger, the vertical array sensors and systems software. • Software and hardware upgrades to the data logger for the prototype vertical array included enhanced programmable gains, faster sampling rates, and improved surface communications. • The vertical array cabling was upgraded to allow installation of positioning