System Description

The following information has been taken from:

Brown, W. P. and E. G. Kerut. 1978. Air droppable RAMS (ADRAMS) buoys. AIDJEX Bulletin. 40:21-29.

Thorndike, A. S. and R. Colony. 1980. Arctic Ocean Buoy Program Data Report 19 January 1979 to 31 December 1979. Polar Science Center, University of Washington.

The buoy consists of a 22-inch diameter polycarbonate sphere mounted on a 15-inch diameter, 12-inch high foam crash pad. The electronics, antenna, and battery pack form a single unit inside the sphere and are free to rotate around both vertical and horizontal axes on Teflon bearings. The electronics module contains a pendulous weight so that after deployment, regardless of the final resting position of the sphere, the antenna will be properly oriented for optimum satellite reception.

The system is powered by newly-developed inorganic lithium batteries. These batteries have extremely high energy density on a weight and volumetric basis and allow operation down to the -50 degrees C temperature limit of the system. The battery pack weighs less than nine pounds and provides and expected life of seven to eight months.

A special ruggedized BTT (Buoy Transmit Terminal) was developed to survive the shock of an air drop as well as the low temperature extremes of the Arctic ice pack. The electronics were built in modular form to facilitate expansion and to allow adaptation to other form factors. In addition, a "modified canted turnstile" antenna was developed from a design for the SMS satellite. This antenna provides circular polarization and has a low vertical profile consistent with the buoy's spherical configuration.

In operation the buoy transmits a signal for one second each 62 seconds with a nominal radiated power of 31 dBM. A zero phase reference signal with no modulation is sent for a nominal period of 350 msec. During this period, the receiving satellite acquires phase lock and establishes its phase reference. The next approximately 640 msec of the signal contains the message and is phase modulated +/- 60 degrees at a bit rate of 100 Hz. The first 30 bits of the message contain the bit sync and frame sync followed by the platform identification number. The next two bits are used to provide up to four variations on the 32 bits of data which follow.

For the IABP project, data were received by the TIROS-N and NOAA-A satellites when a satellite was within radio view of the buoy. Satellites had orbital periods of about 102 minutes. Since they were in nearly polar orbits, they saw high latitude buoys on every orbit. A satellite could see a given buoy for between 10 and 20 consecutive minutes. The messages were compared. All were not identical since the actual pressure and temperature usually changed measurably over 20 minutes and there was some noise in the radio link. Typically, several messages were identical. The message from each orbit with the most identical repetitions was selected as the best measurement and the others ignored. In this way, each buoy produced about 14 measurements of pressure and temperature each day early in the year when only one satellite was operating, and somewhat more when both satellites were operating.