by James Careless
Accurate weather forecasting: in the United States, a country fraught with tornadoes, hurricanes, and floods, it is a matter of life and death. This is why the National Weather Service (NWS) relies on satellite transmission to get the latest weather data nationwide, every second of every day.
Specifically, the NWS relies on satellite to deliver three separate weather information systems: Advanced Weather Interactive Processing System (AWIPS), National Oceanic and Atmospheric Administration Weather Wire Service (NWWS) and National Oceanic and Atmospheric Administration (NOAAPort Lite). All three travel along satellite networks managed for NWS by Dyncorp Systems and Solutions of Reston, VA.
"We've created a niche for ourselves, transmitting vital weather data via satellite," notes Richard Warren, Dyncorp's manager of advanced technology engineering. According to the company in fact, two-thirds of all U.S. government civilian weather data travels over Dyncorp-managed satellite networks. That is a statistic that speaks volumes about the NWS' regard for satellites and Dyncorp alike.
Now the details:
AWIPS
AWIPS collects data from the NWS' GOES (Geostationary Orbiting Environmental Satellites)--including images and weather modelling data--and sends it via the SES Americom AMC 4 satellite to the NWS' National Centers, Regional Headquarters and Weather Forecast Offices/River Forecast Offices. (Positioned at 101 degrees W --which puts it over the Southwest United States--AMC 4 provides C-band coverage across North America and Ku-band coverage over North and most of South America.) In turn, these 132 offices analyze the AWIPS data to create forecasts--including weather watches and warnings--for all 50 U.S. states and Puerto Rico.
Functionally, the AWIPS data travels from NWS Headquarters in Silver Spring, MD, over four T-1 lines to Dyncorp's Master Ground Station (MGS) at Ft. Meade, MD. At the MGS site, Dyncorp uplinks the four carriers over a 12-meter antenna to AMC 4. From here the AWIPS carriers travel back to Earth over C-band, where they are received using either 2.4-meter or 3.8-meter C-band antennas. AWIPS' data rate is impressive: over 5 Mbs, with better than 99.9 percent signal availability.
Initially, AWIPS was a Ku-band service. The kind of weather extremes, however, in which its need most usually involve rain, and raindrops attenuate Ku-band signals. The result was that "you could lose the signal at the most important times," Warren says. "This is why we subsequently migrated AWIPS to C-band."
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