Testing and Integration of a Cabled Ocean Observatory: Complexity is Greater than the Sum of the Off-the-Shelf Parts

Selection and integration of instruments for cabled seafloor observatories present challenges which can differ significantly from traditional autonomous, short-term deployments of individual devices. Both NEPTUNE Canada and instrument providers have learned a great deal from the experiences of specifying, procuring, testing, integrating and deploying complex combinations of seafloor instruments on its observatory in the Northeast Pacific. The current NEPTUNE Canada science suite (i.e., exclusive of the network infrastructure) consists of 130 instruments (and many more sensors), 170 cables of various types, 12 Junction Boxes and 636 connectors. Science proposals from researchers typically specified exact instrument manufacturers and models. Procurement requirements, however, meant that, in most cases, a competitive process had to be followed in which functional requirements (science needs) were specified. In addition, however, there were other requirements which had to be met related to the overall network infrastructure characteristics; e. g., power options, communications protocols, grounding issues, etc. As a result two documents were prepared by the NEPTUNE Canada Engineering staff, "Instrument Requirements" and "Instrument Quality Requirements", which accompanied orders for instruments. In most instances these requirements required relatively minor changes in the COTS instruments; e. g., changes in power supplies, removal of grounding through housings to sea water. In a few cases, especially with high-frequency active acoustic sensors, there were more substantial issues discovered which had to be addressed. While from an electronic and data perspective most instrument issues were relatively easily addressed, it was quickly learned that significant problems are common on many instruments related to corrosion; these include the use of dissimilar metals as well as insufficient, or inappropriate use of, sacrificial anodes. NEPTUNE Canada is in discussion with some of these manufacturers to address these matters in order to improve the longevity of their instruments on the seafloor. Considerable emphasis by NEPTUNE Canada was placed on Quality Assurance and testing, fundamental to a successful deployment of subsea instrumentation and of the network infrastructure itself. This began with dialog among the network architect, vendors and suppliers and the end users in the science community. It was essential that all parties were clear on the standards and tests that wereto be applied and the criteria for acceptable construction and performance. The NEPTUNE Canada test program includes incoming inspection and functional testing according to clearly defined procedures which relate directly to the published criteria. Component level testing of instruments and cable assemblies, followed by saltwater testing of fully integrated platform instrumentation suites, werecarried out to maximize success rates going into the ocean for long-term deployment. NEPTUNE also focussed significant effort on developing instrument platform designs which would be versatile, rugged, resistant to corrosion, able to be installed in different seafloor terrains and able to be deployed and recovered by an ROV in an efficient, safe manner. For versatility and ease of deployment, a relatively few platform designs were developed which could meet the many different science requirements. Instruments can be mounted in a stationary position on a platform, on mechanized mounts positioned away from the platform, or on the seafloor completely remote from the platform (several tens to hundreds of meters) with dedicated mounting stands. The final mounting configurations are normally determined by the instruments themselves, and the science requirements of the principal investigators. They must be capable of withstanding the stress of deployment and recovery from the ship, and sometimes being relocated by ROV manipulators once on the ocean floor. A solid understanding of the abilities of the ship and the ROV used to deploy and recover the equipment is required to minimize ship time. Detailed plans of equipment deployment and/or recovery for each platform must be thoroughly prepared and agreed upon with the ship's crew and the ROV personnel prior to installation. NEPTUNE Canada views the learning experiences of the past several years to be of great benefit not only with respect to meeting its own objectives in terms of establishing a reliable, multi-disciplinary seafloor observatory, but also in assisting other developing observatories worldwide, as well as instrument manufacturers, to understand better the specific requirements of the rapidly expanding ocean observatory market.