A 4000-meter-rated deepwater cabled ocean observing system: Lessons learned from two years of operation

In recent years, there have been several major initiatives to install fiber-optic cabled ocean observatories in the United States, Canada, Japan, and Europe. Lighthouse has operated a fiber-optic cabled ocean observing system off the northern coast of the Sultanate of Oman for seven years: the Lighthouse Ocean Research Initiative (LORI) I. In early 2010, a second cabled system was installed farther to the south, LORI II. LORI II is comprised of three, 2500-m-long moored arrays each equipped with eight Doppler current profilers and additional environmental sensors. The moorings sit along the 3000 m bathymetric line, so the uppermost current Doppler profiler uses a low frequency (75 kHz) to capture velocities and acoustic backscatter for the uppermost 500 m of the water column. Lighthouse had significant experience operating a cabled array in shallower water (<;1350 m) and had deployed and recovered autonomous arrays from the same locations as the cabled LORI II instruments several times in the past and thus confidence was high the system would operate as installed. After deployment, the quality of the raw data was very good with nearly all of the installed sensors reporting; but by year two, communication with two of the moorings had been lost. The cause of the problem has been tentatively identified. Herein, we discuss the research, development, installation, and operation of LORI II over the past two and a half years, scientific results from LORI II data, and the lessons learned from seven years of successful operation of the LORI I cabled system, all of which will be incorporated in a new-and-improved, science-driven, cabled LORI II design.