An INMARSAT-C GOES, and EIA485 hybrid communication system for global experiment control

The Atmospheric Radiation Measurement (ARM) program is constructing cloud and radiation monitoring instrumentation that will be deployed at several island sites in the tropical western Pacific Ocean. The atmospheric radiation and cloud systems (ARCS) must operate with minimal maintenance for decades, producing and storing many megabytes of data per day. A reliable global communication system is an essential element of the ARCS design. It must provide immediate direct access to the equipment. High availability and reasonably low cost are essential for this very long-term deployment. Providing executive management and control, the communication system incorporates several special technologies, to meet its requirements: (a) INMARSAT-C provides a simple two-way messaging capability (b) Built-in GPS in the INMARSAT-C radio provides an accurate time standard. (c) The NOAA GOES satellite provides a one-way link for hourly health and basic measurement data. (d) An EIA485 local area network provides a digital link throughout the installation. (e) Node units located conveniently throughout the AFCS and linked by the EIA485 network allow an almost unlimited flexibility and expandability. (f) A robust packet protocol ensures message security and accuracy. The complete communication, control, and data acquisition system is described in detail. The ability of the system to adapt to other physical configurations (telephone, UHF, telnet) is discussed.