The following information has been adapted from Brown, W. P. and E. G. Kerut. 1978. Air droppable RAMS (ADRAMS) buoys. AIDJEX Bulletin 40:21-29.
The ADRAMS buoy was developed to provide remote tracking of drifting sea ice near the Arctic Coast and adapted for use by the International Arctic Buoy Program. Because it can be dropped from aircraft, the ADRAMS buoy costs less to deploy than sensing systems requiring manual installation and allows monitoring of areas and seasons previously inaccessible. ADRAMS buoys contain transmitters and digital encoding that allow data to be received by polar orbiting satellites, such as that collected by the IABP project's pressure and temperature sensors. Deployed by parachute, the buoy is designed to survive and properly orient its antenna on any type of terrain. The 90 pound package contains enough batteries for seven to eight months operation at surface temperatures as low as -50 degrees C.
Document Type: Platform Document
Revision Date: December 1995
Air Droppable RAMS (ADRAMS) Buoy
History of ADRAMS Buoy
In 1975 (prior to International Arctic Buoy Program activation), shipping problems due to drifting ice pack experienced by the Bureau of Land Management and the Arctic Ice Dynamics Joint Experiment (AIDJEX) program indicated a need for a device that would allow remote tracking of Arctic ice pack drifting near shore.
Urgencies required that the buoys be deployed during the all-dark Arctic winter under adverse weather conditions. Previously-developed Arctic data buoys were not suitable because their installations would have required a crew to land on the ice, an operation too hazardous for the dark of winter.
Therefore, the concept for a small buoy which could be deployed from an aircraft via parachute was evolved. For the original project, the tracking scheme selected was the NIMBUS-6 satellite Random Access Measurement System (RAMS) since it was being used successfully in other buoy programs. The buoy was given the acronym ADRAMS (Air droppable RAMS).
For the IABP protocol, the buoys were dropped by parachute from C-130 (Hercules) aircraft at designated latitudes and longitudes. Many of the drops were made in the dark or during cloudy weather, and no attempt was made to select the kind of ice they landed on. It's possible that a buoy may have landed in an open lead or on a high pressure ridge, but the more reasonable assumption is that buoys were situated on sea ice within a meter or so of sea level. During summer, some buoys may have been afloat in shallow melt ponds on the sea ice surface.
However, the buoys were designed with watertight hulls in consideration of the possibilities, and with antennas that would remain vertical regardless of landing attitude. The buoy systems were to withstand ice pack surface temperature extremes of +10 to -50 degrees Celsius, and were structured to withstand landing impacts on either smooth or rough ice.
The NOAA Data Buoy Office was selected to spearhead the original development of the ADRAMS because of its wide experience in developing data buoys for the open ocean as well as for the Arctic. Polar Research Laboratory of Santa Barbara, California, was contracted to perform the ADRAMS design, development, and fabrication.
The International Arctic Buoy Program is funded and managed by its participants. Representing eight countries, participants include operational and research agencies, meteorological and oceanographic institutes, and nongovernmental organizations. Participant contributions include equipment, services, and program coordination, as well as funding.
IABP participants are:
The ADRAMS buoy was developed to provide remote tracking of drifting sea ice near the Arctic coast. The International Arctic Buoy Program (IABP, 19 January 1979 to 31 December 1979) used these buoys to provide measurements of surface atmospheric pressure over the Arctic basin and to define the large scale field of motion of the sea ice.
The original ADRAMS were designed with the following constraints
In addition to these initial design considerations, the IABP requirements called for the incorporation of a precision barometer and internal temperature sensor. The temperature sensor range was +30 to -50 degrees C with better than .1 degree C resolution. The barometer pressure range was 950 to 1050 millibars with .1 millibar resolution. Since the buoy had to be water tight, a special Teflon membrane was used for the pressure port which allowed barometric pressure changes to enter the buoy but kept moisture out.
The buoys were distributed over an area 70 degrees north latitude to 90 degrees north latitude:
In order to maintain the antenna in a vertical position, the entire electronics assembly was designed as a pendulous self-leveling gimbal revolving inside a 22-in diameter sphere. The gimbal approach was found to be much simpler and more reliable than attempting to deploy automatically fixed antennae in upright positions on rough ice surfaces would have been. The gimbal ensured that the antennae would be vertical not only upon landing but also during future wind disturbances, or movement caused by ice surface changes such as melting, or polar bear interference.
The pressure sensor used in the buoy was a quartz beam which oscillates at a resonant frequency dependent primarily on the pressure and to a lesser extent on the temperature. Sensors were selected for long term stability and low power consumption.
The temperature sensor was primarily intended to monitor the temperature of the pressure sensor, and no attempt was made to verify the absolute accuracy of temperature readings. (See temperature and pressure.)
The buoy transmits a one second signal each 62 seconds consisting of its identification code and the measured pressure and temperature. These data were received by the TIROS-N and NOAA-A satellites when a satellite was within radio view of the buoy. The satellites had an orbital period 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 10 to 20 messages received during this period were compared, and the message from each orbit with the most identical repetitions selected as the best measurement. In this way, each buoy produced about 14 temperature and pressure measurements per day early in the year when only one satellite was operating, and somewhat more when both satellites were operating.
The frequency of the radio signal received at the satellite was Doppler shifted because of the relative motion between the satellite and the buoy. Buoy messages were retransmitted by the satellite to earth receiving stations and relayed to Service Argos in Toulouse, France. There, messages were decoded, pressure and temperature readings converted into physical units, and the buoy locations determined. Service Argos distributed data over the Global Telecommunications System with a time lag of about 4 to 5 hours from the time of measurement, and sent a magnetic tape containing all buoy data to the Polar Science Center each month.
The buoy's basic internal components were a radio transmitter, some timing and coding logic, a pressure sensor, a temperature sensor, and a battery power supply. These were contained in a spherical hull of 62 cm radius.
The processed data set consists of estimates of atmospheric pressure, temperature, and ice velocity at a fixed grid of points in space and at three hour intervals. The essential steps in the processing were
The following acronyms and abbreviations are used in this document.
|ADRAMS buoy||Air Droppable Random Access Measurement System Buoy|
|AIDJEX||Arctic Ice Dynamics Joint Experiment|