Tests of Long-Range Ocean Data Telemetry Using Frequency-Agile HF Packet-switching Protocols

Abstract

Experiences with two prototype telemetry systems developed for potential use with moored or drifting ocean instruments are described. The systems transfer data and commands between remote and base stations using direct high-frequency (HF) ionospheric radio propagation (shortwave radio) without intervening relay stations or satellites. The strategy exploits recent developments in digital packet-switching technology, which is readily available and can be inexpensively applied to oceanic problems. The potential advantages of packet methods over satellite methods include low cost, autonomy, two-way exchanges with the remote stations, and typical data rates of 1?10 bit s?1 averaged over several days. Coverage is effectively global but intermittent. Disadvantages mostly result from the interference and skip zones that characterize HF propagation. The tests described here took place near the time of a sunspot minimum; the utility of HF packet telemetry will be greatly increased when the sunspot cycle is near its maximum.