Enable Ocean Observation
The ocean environment challenges the designs of engineers and the skills of sailors and seafarers. Pressure, temperature and corrosion impact mechanical systems and impede most communications and positioning technologies. Until very recently even vessels afloat were removed from the networked world ashore. This is changing as new technologies, and evolutions of old ones, advance techniques for ocean observation.
Unmanned maritime vehicles (UMVs) have been under development for decades. Since the late 1990s several systems have evolved beyond research labs and become commercial realities. Businesses have bloomed and technical advances thought impossible are proving no match for today’s UMVs. These tools are now in routine use for scientific, commercial and military applications.
With robust vehicles available, connectivity is becoming a key element of UMV operations. All operators deploy UMVs for a purpose. Awareness of progress toward mission goals is a key requirement for risk mitigation. Timeliness of information is also important to survey, inspection and observation activities, even if complete data sets must await a physical return of the UMV. Connectivity and networked operations are key enablers of undersea operations, especially ocean monitoring.
While wireless networks and satellite navigation have revolutionized life ashore, acoustic systems bring similar capabilities to undersea operations. Advances in digital signal processing have seen venerable tones and pings give way to broadband schemes. These systems offer reliable connections between many platforms and can also provide positioning information. Wise application of such technology reduces risk and increases productivity. The predominant approach to subsea connectivity is point to point. Adaptive networks have been demonstrated but are not widely deployed. Technologies are mostly closed with operators dependent on single sources or forced to own potentially redundant equipment. Subsea networked connectivity is having an impact, but it still evolving and penetrating the market.
Wireless undersea networking can be fixed (Figure 1) or mobile. One example of an application for a fixed wireless network comes from an experiment in Monterey Bay. In this project two sensors were deployed on the end of a cabled observatory known as the Monterey Accelerated Research System (MARS). These sensors were connected via acoustic telemetry back to the cabled system. By placing a fixed modem on the end of the cable, new instruments could be employed without complex intervention. The original instruments were Remotely Operated Vehicle (ROV) deployed but the concept of ad hoc network assembly was also demonstrated. During operation it was discovered that one of the nodes, was not communicating well with the hard-wired “hub” some 500 meters away. Strong local noise conditions were suspected to be the root cause. Communications were essentially “faint” and unable to provide reliable connectivity to the main modem. By using another modem, in a self-contained housing (Figure 2) as a repeater, it was possible to restore connectivity and continue the operation of the experiment. A short day trip, enabled by the easy deployment of the modem node, provided a low cost solution to what might have otherwise required an ROV intervention.
The capabilities of acoustic telemetry are diverse and worthy of significant review in their own right. This example is simply offered as a real world case where the flexibility of an acoustic repeater provided a significant operational benefit to an ongoing research project. Combining acoustic telemetry with mobile undersea systems, especially Unmanned Underwater Vehicles (UUVs), yields additional benefits to subsea operations.
Ocean observing has traditionally relied on vessels and moorings, with significant logistic investments required. Today, extended endurance UMVs (Figure 3) and autonomous profiling floats offer broad spatial and temporal coverage, affordably. Using buoyancy engines, these UMVs can remain at sea for months or years and do not demand large infrastructure to support their operations. These systems have demonstrated endurance to cover large distances or loiter in place for extended periods. Some simply drift with the currents for years. Physical oceanography has most commonly been the focus of these platforms, due to available sensors and limited payload energy budgets. However, new biogeochemical sensors are routinely being demonstrated on long endurance platforms.
The most significant demonstration of the economic impact of UMVs on ocean observing is the US Navy Littoral Battlespace Sensing - Glider (LBS-G) program. This program of record is acquiring and deploying 150 gliders to support Navy operational observations, with another 150 planned for the future. While the low capital and operational costs of these tools is a clear benefit to the economics of ocean observation, there is another, subtle, effect of great value. Academic or government programs can, and do, share data collected by these platforms freely and often online. With hundreds of gliders and thousands of floats in routine operation there is a large user base to advance new scientific concepts and challenge technologies. The sharing of data and wide user community make ocean observing UMVs highly leveraged investments. Further leverage can be obtained by interfacing these stand-alone systems with subsea networks.
The National Science Foundation has embarked upon the operational use of gliders with acoustic telemetry for its Ocean Observatories Initiative (OOI). OOI is a multi-scale observatory designed to utilize a network of sensor systems to collect physical, chemical, geological and biological data from the ocean and the seafloor on coastal, regional and global scales. The data will be made available to anyone with an internet connection. This information will increase understanding of climate change, ocean and coastal ecosystems, environmental health and climate, and biodiversity. While both coastal and open ocean OOI elements will make use of gliders, the high latitude Global Arrays of the OOI will make use of gliders employing acoustic telemetry. These gliders will be used to provide connectivity between subsea mooring systems and satellite communications to shore similar to Figure 4.
As a preliminary step towards the OOI installation, a number of tests were conducted 2012 to quantify communications between a Teledyne Webb Research Slocum glider equipped with a Teledyne Benthos acoustic modem and the Scripps CORC IV mooring located off the coast of southern California at an approximate depth of about 5000 meters. Many of the tests were conducted with the glider sitting at the surface processing manual commands sent over Iridium satellite link. Others were conducted with the glider in an autonomous mode diving to a particular depth. The slant range to the mooring varied from about 2500 meters (with the glider at depth) to over 7000 meters. Data transfer rates were tested between 15360 bps PSK (phase-shift keying) and 300 bps MFSK (multiple frequency-shift keying). Since then, two OOI Open Ocean gliders spent 330 days each at Station Papa transferring data from the moorings. Operationally the combination of acoustic telemetry and gliders is proving effective.
Considering a comparison to mobile phones, what might UMV operators look forward to in the future? Today a typical smart phone user can carry their device anywhere in the world and make voice calls, read email, surf the web and navigate maps. They can also draw upon a host of specialized “apps” for advanced tasks such as making hotel reservations or currency calculations. This capability is built upon enabling developments in hardware, especially compact processors and power sources, and accepted standards for connectivity. Such a reality is coming to the undersea realm.
UMVs in coming years will draw upon acoustic telemetry to “network” into ever more productive roles. Drifting and energy harvesting surface platforms will provide overhead coverage for acoustic telemetry and positioning to heterogeneous undersea systems. Integrated networks of undersea wireless technologies will provide low bandwidth but reliable coverage much like first generation cellular networks. Full data sets may reside on local UMV solid state drives but status information and key data identified through onboard analytics will be exchanged across the network, ensuring operators are informed and support assets are deployed for maximum efficiency. It will be possible to create the equivalent of “tweets” between systems and across the undersea domain.
UMVs are currently capable systems offering significant value to marine operations. When viewed through the lens of connectivity the potential value of UMVs is just beginning to be revealed. Just as smartphones changed daily life, networked UMVs will bring more capability to ocean observing. There are challenges to this vision, some are technical and others tied to policy questions. But none are insurmountable. New technology developments can be counted on to appear, probably sooner than anyone expects. To harness those developments the UMV community will need to collaborate effectively to create the networks. Engineers and business leaders will need to see the value in standards, potentially open protocols and interoperability across platform types and businesses. Regulators also will need to understand the technology, appreciating the benefits and rapid pace of technical evolution. A future UMV ecosystem is exciting to consider, the path forward is apparent, if not clear, and the value to ocean observing will be substantial.
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