The PIs request funding to build, test and deploy an optical telemetry system (OTS) designed for an instrumented seafloor borehole observatory. A series of boreholes drilled on the flanks of the Juan de Fuca ridge in the northeast Pacific have been instrumented as part of the ODP CORK program and are visited on a regular basis for downloading data and for collecting physical samples of subsurface fluids. This installed infrastructure provides a unique opportunity for installing and testing an optical communications node in relatively controlled conditions.
CORK borehole monitoring reveals a very broadband signal from tidal loading and ocean waves to teleseismic activity. Present data rates are limited by several factors but communication rate is the most constraining. Greater sample rates are required to properly sample high frequency signals that include tsunamis and other oceanographic phenomena. Highspeed underwater optical communications will remove this bottle-neck and allow seafloor instruments to collect data at scientifically relevant data rates.
The proposed CORK-OTS would simply plug into the existing underwater connectors on the CORK and would provide additional capability such as data storage and the ability for rapid data retrieval either by periodic visits by a submersible or perhaps more importantly in a remote-mode by using an optical receiver lowered by a cable from the sea surface.
Broader Impacts
The proposed work is an enabling technology that will enhance the infrastructure for research and education in all fields of oceanography. The PIs plan to establish new collaborations with an international partner in Canada, the Pacific Geoscience Center, and with academic colleagues at other universities. In addition, the CORK-OTS may be deployed at other International Ocean Drilling Program sites around the globe. The publication of the results of the proposed work in journals and conferences will enhance science education and technology. The PIs also plan to integrate the proposed research work in their educational activities, which include the hiring of high school students and college undergraduates during the summer periods in their laboratory. The development of the underwater OTS may offer opportunities for commercialization of the technology by government and industry for such use as environmental monitoring and other potential applications.
The primary objective of the CORK Optical Modem development project was to demonstrate the utility of using underwater optical communications in a real-world application of a seafloor observatory. Seafloor observatories are becoming an important avenue of research and of urgent societal relevance as the need for early warning devices for the detection of tsunamis and damaging earthquakes have recently attested (e.g. Japanese 2011 Tohoku earthquake and tsunami and the 2004 Sumatra-Andaman megathrust and tsunami in Aceh). While cabled observatories offer realtime communications and power for seafloor sensors it is not always possible to run ocean floor cables and maintain such infrastructure. Optical communications offers a possible low power but high bandwidth communication strategy for use on distributed seafloor sensors that, while visited periodically, can show the build up of strain and offer an assessment of hazard. We chose a CORK deep seafloor scientific observatory as the demonstration application to showcase how to download data rapidly using optical communication protocols and the feasibility of using vessels of opportunity as well as autonomous robotic vehicles. A CORK is an instrumented borehole drilled several hundred meters into the seafloor. A typical CORK observatory has pressure sensors downhole that measure a wide range of phenomena from oceanographic tidal signals, waves, ocean storms and tsunamis to solid earth pressure waves such as earthquakes and crustal deformation from seafloor spreading events. In a conventional configuration the CORK borehole records the pressure downhole (and at the seafloor) at a rate of once every 10 to 15 minutes. Data must be downloaded by physically plugging an underwater wet mateable connector into the CORK logger using a specialized deep submersible or remotely operated vehicle (ROV). Underwater optical communications offers the opportunity to download data at high data rates (megabits per second) and importantly in a remote fashion without the need for specialized submersible vehicles. During this project we built two portable optical modem systems that were installed at two seafloor boreholes (CORK observatories) located in the northeast Pacific (CORK 857D and CORK 1025C). We carried out demonstration downloads of data at different ranges and data rates. Specifically, we were able to confirm data rates of up to 20 megabits per second at ranges of 100 meters and even 1 megabit/sec at almost 200 m range without any major errors in transmission. As part of the testing regime, our seafloor optical modems provided additional power to the CORK enabling them to sample at a 1 Hertz sample rate. This rate allows phenomena such as earthquakes to be fully captured in the pressure data records without aliasing the data. The 1 Hz data rate also means much more data needs to be transferred on download but this is easily handled by the 1-20 megabit per second download rates provided by optical communications. In fact, these data rates are sufficiently high that it also allows real time video links to be transmitted across ranges from 100 to almost 200 m. We used LED technology as the source for a diffuse (non directional) transmitter with high light intensity, switching speeds and optimal wavelengths for underwater light transmission. We used a photo-multiplier tube (PMT) as a sensitive optical receiver. Important considerations included filtering the wavelengths on the receiver so that the lights from visiting submersible vehicles could be used without interference on the optical communication devices. The diffuse transmitter also means that a cone of optical reception is possible so that precise aiming of the optical receiver is not required. During the five field programs we undertook during this project we successfully demonstrated the use of optical modems on the submersible Alvin, ROV Jason and the autonomous vehicle Sentry. In addition we were able to interrogate the CORK seafloor observatories using an optical modem lowered on a wire from a surface ship obviating the need for specialized submersible vehicles. In one example, we used a ship of opportunity that had no dynamic positioning capability and yet we were able to maintain a watch circle of 100 meters and download megabytes of data from the CORK borehole at 2600 m depth in just a few minutes. High-speed underwater optical communication is an enabling technology that has many potential applications in many different environments from the deep sea to coastal waters. Underwater optical communications is clearly of sufficient interest to allow commercialization of the technology and will enable it to be used in a wide range of environmental, industrial, and defense applications and in that way becomes a benefit to society. One outcome of this project was the creation of the spin-off company Lumasys, which is a partnership with Sonardyne International. Another important outcome was the training and development of young engineers providing opportunities to work on cutting edge technology and to apply that to real world applications.
