Transhorizon VHF Telemetry from Ocean Moorings

Abstract

During long deployment periods, it is desirable to communicate remotely with moored or drifting instruments. In addition to providing access to the data set as it is collected, a telemetry capability provides insurance against undetected instrument failure and the associated risk of jeopardized scientific objectives. As part of an ongoing study in the Gulf of Maine, an experimental VHF transhorizon telemetry system was recently deployed with a current meter mooring. The refractive properties of the marine boundary layer made it possible to transmit data with about 70% reliability over a 100 km distance, or about ten times the optical-horizon distance for the antenna heights used. During weather anomalies, large signal-strength enhancements occurred, and these could easily be exploited to increase the data-transfer reliability.