Installed System Redundancy for Wave Measurements Gulf of Alaska

Abstract

The industry-sponsored Gulf of Alaska Wave and Wind Measurement Program is producing useful data by following an uncommon strategy of installed spare producing useful data by following an uncommon strategy of installed spare hardware. The lessons learned during this program have direct application to measurement of these data in other parts of the world. The knowledge gathered on buoy moorings and buoyancy, telemetry, and long-term battery life will be particularly useful. Introduction In recent years, there has been an increasing interest in understanding and quantifying the wave climate of the Gulf of Alaska. Several differing programs have been developed by various organizations and investigators to describe operational criteria acid to predict design waves that may be expected at specific locations. In March 1974 Marathon Oil Co., as administrator, initiated one such program for a participant group of 13 oil companies. Intersea Research Corp., is the prime contractor for the program, with Evans-Hamilton, Inc., acting as project coordinator between Marathon and Intersea. project coordinator between Marathon and Intersea. This industry-sponsored program is known as the Gulf of Alaska Wave and Wind Measurement Program (GAWWMP). The program was designed to acquire ocean-wave data at five locations and wind data at four locations spread across the Alaskan shelf from the Trinity Islands on the west to Yakutat on the east, a distance of about 600 nautical miles (Fig. 1). These systems have been in operation since early Sept. 1974, and the present program calls for continuous observations through the winter program calls for continuous observations through the winter of 1975-76. Project field operations will be concluded by early summer 1976 unless the program is extended. The resulting data will be suitable for studies of the average wave height and average zero-crossing period at all five sites, and the nondirectional wave spectrum at three of the sites. Standard references (such as the Climatological and Oceanographic Atlas for Mariners) indicate gale-force winds (Beaufort Force 8, 37.4 knots) about 10 percent of the time in fall and winter, with seas greater than 8 ft occurring with a similar frequency. Therefore, (GAWWMP has approached the data-collection problem with an "installed-spares" strategy for the vulnerable in-ocean hardware. This strategy for success is supported by contractual requirements for specific, proven off-the-shelf hardware and partial forfeiture of the contractor's fee in the event minimum data are not produced. This paper discusses some of the hardware produced. This paper discusses some of the hardware features of general interest, as well as the experience with the installed-spares strategy. Instrumentation The over-all GAWWMP data gathering system is shown schematically in Fig. 2. Its individual components are described below. Waverider Buoy The wave sensor specified for this program was the Waverider, a spherical surface-following buoy containing a stabilized platform with vertical accelerometer, batteries, double-integration circuits, and a radio transmitter. This instrument was manufactured by Datawell bv. of Haarlem, The Netherlands. The sensor is integrated with a mooring system, radio receiver, and demodulator. JPT p. 482