shore. This surface buoy is mechanically connected to the seafloor and communicates with instrument packages on the mooring line acoustically or via an electrical or fiber-optic cable. Instruments and observatory devices are either directly connected to the seafloor node of the mooring or communicate via an acoustic communication link. The mooring may or may not supply power to peripheral instruments. This class of observatory system draws heavily on several decades of mooring development and the rapid evolution of satellite communications to provide connectivity from shore to instruments in most ocean regions. In contrast to cabled observatories (discussed below), moored-buoy systems are generally less expensive to install, but the trade-off is a greatly diminished communications bandwidth and reduced power availability.
A wide range of sizes and capabilities can be envisioned for the central mooring. The dominant influences on size are the magnitude of power and communications capabilities needed (Table 3-1). A single mooring design cannot satisfy all science requirements. It is possible, however, to group science requirements into those demanding a large central mooring capable of supplying substantial power (>100 W continuous) or relatively high data rates (>100 Mb/day), and those that can be satisfied with smaller, cheaper moorings, which could be deployed singly or in arrays to provide nested-grid spatial coverage of areas of interest. Smaller moorings are also motivated by a desire to obtain rapid event response (within weeks or months). These relocatable systems might provide a few tens of W of power and support data rates of a few megabytes per day (although not necessarily with continuous data transmission).
Data transfer rate, power consumption, and system stabilization requirements are all interlinked, but it is possible to obtain high data-transfer rates at a relatively modest cost provided compromises are made in power and buoy stability. Some satellite systems, because of the need to use a directional antenna, impose strict stability requirements on the surface buoy (<10 degrees per second in pitch, roll, and yaw). Satellite communications can also consume substantial power. As a result, significant amounts of energy will need to be stored within power sources on the mooring. It is difficult at this stage to make specific recommendations with regard to rapid advancements currently taking place in global digital communications. At present, extremely capable satellite communications systems are under development; however, the success of these ventures is far from certain, as demonstrated by the bankruptcy of the Iridium network.1
Data transfer requirements range from less than 1 kb/s to as high as 100 kb/s. In order to prevent disruption to the time-series datasets being collected at a moored-buoy observatory, a backup communications system should be included in the design. Furthermore, the moored system must be capable of storing data onboard if the communications systems were to fail.
Iridium was the first global satellite network for telecommunications. Its 66 crosslinked Low Earth Orbit (LEO) satellites formed a worldwide grid 780 km (485 miles) above Earth.