6. Cooperative Programs
Evaluation of Arctic Meteorological Buoys
GERALD F. APPELL
The United States Interagency Arctic Buoy Program (USIABP) was formed in 1991 to establish and maintain a network of drifting meteorological buoys in the Arctic. The USIABP is a collaborative program funded by nine government agencies/programs and managed by the National Ice Center in Suitland, Maryland. USIABP supports the International Arctic Buoy Program (IABP) which consists of many countries participating in the collection of meteorological data from Arctic drifting buoys.
The buoys are strategically deployed to define the surface synoptic scale atmospheric pressure, air temperature, and sea ice drift fields. The data are available in real time, via ARGOS satellite transmissions, to operational weather forecasting centers. Data are also used for research into climate change. At the inception of the program, 25 buoys were gathering temperature and pressure data in the Arctic with 72% reporting on the Global Telecommunications System (GTS). In early 1994, 47 buoys were in operation with 96% reporting on the GTS.
The IABP uses many different buoys with different sensors, configurations, and sampling schemes. Many of the temperature measurements reported by the buoys were suspect when compared with atmospheric model predictions. In 1993 it was decided by the USIABP to halt deployment of new buoys until the sources of temperature measurement errors were investigated. A program was established to evaluate the available "off-the-shelf" Arctic buoy systems being used by the IABP. As part of this evaluation, a long-term test site was established at the CMDL facility in Barrow, Alaska (BRW).
In 1995 the USIABP resumed procurement and deployment of buoys based on a
buoy design derived from tests at BRW.
In August 1993, a Coastal Climate buoy and a DSI-TAD buoy were placed at BRW. A data acquisition system was placed at the site consisting of a Telonics ARGOS uplink receiver and a Compaq notebook computer. Buoy transmissions are received and logged on the computer. Weekly interrogations of the computer are done from Silver Spring, Maryland, and data files are downloaded. In December 1993 a Canadian MetOcean CALIB buoy was added to the array, and in March 1994 a Norwegian ICEX buoy was placed at the site.
In August 1994 a meteorological station was placed at the buoy array site. This site collects temperature data from aspirated sensors at the 1 m and 2 m levels. It also collects solar radiation, barometric pressure, and wind data. The purpose of this system is to explore the horizontal and vertical temperature distribution compared with the CMDL sensors (20 m horizontal separation, CMDL sensors at 2 m and 15 m levels). Data are collected from the station via GOES satellite or dial-up phone link.
A fifth buoy was added to the site in August 1994. This buoy is a Canadian MetOcean buoy similar in design to the Coastal Climate buoy.
In May 1995 the sixth and last buoy was added to the site. This buoy was specified,
designed, and built based on the experience and knowledge gained from the BRW
tests. This buoy was manufactured by Coastal Climate and was based on the successful
design of their original ice buoy. All of the air deployable buoys were removed
from the site in 1995 with sufficient data acquired. At the close of 1995 three
buoys remained at BRW, the two Coastal Climate buoys and the one MetOcean buoy.
All buoys in the test program undergo a temperature sensor calibration at the National Weather Service Test Facility in Sterling, Virginia, before shipment to Barrow, Alaska.
Each buoy has its own measurement scheme, sampling interval, data format, and data transmission interval. Data collected in Silver Spring, Maryland, is processed and reduced into a standard 1-hour averaged data format. CMDL meteorological data are sent monthly on a computer diskette for comparison with buoy data. An INTERNET link was established with BRW in 1994 for retrieval of ice buoy data. Compressed files from the buoy data acquisition system are placed on the laboratory computer for retrieval via FTP. This has saved the expense of downloading data via telephone.
Measurements are analyzed and compared with the meteorological station and CMDL standards. Temperature differences between sensors and/or standards are analyzed to learn the effects of sensor height differences, solar radiation, and wind. Results show significant differences are attributed to the measurement height of the sensors above the surface and to solar radiation effects.
In 1994, based on BRW test results, a specification was developed to procure new ice buoys. A contract was awarded to Coastal Climate Company for five new systems. The performance of the original Coastal Climate buoy placed at BRW has been superior to the others regarding accurate temperature measurements. This new specification required an improved sampling and ARGOS reporting scheme for the buoys. The ICEX, DSI-TAD, and MetOcean CALIB buoys were removed from the site in early 1995 after conclusion of tests. These buoys were deemed unacceptable based on proximity of sensors to the ground and susceptibility to blowing snow coverage.
Analysis of data acquired in 1995 showed that the new Coastal Climate buoy
performed as expected. The quality of temperature data obtained from the three
remaining buoys is comparable. These buoys all measure temperature at a fixed
height of 2 m above the surface and provide sufficient shielding of solar radiation.
In August 1996, the original Coastal Climate buoy will have operated continuously
in Barrow for 3 years, meeting its design life.
It is planned to discontinue the buoy test program in Barrow in August 1996.
Sufficient information on buoy performance has been acquired to assure that
improved sensors will be available to the USIABP.