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.”

NWWS

NWWS is a commercial C-band weather service. Established in 2000, NWWS compiles data from 141 U.S. Weather Centers and sends it out to over 500 commercial and government clients over AMC 4. For a fixed annual fee, subscribers can use as much or as little of the data as they want at 512 kbs. Current customers include radio, television and cable stations; universities; state and federal emergency management services; and many other government agencies.

As with AWIPS, NWWS’ reliability is impressive. Dyncorp provides in excess of 99.9 percent availability for its NWWS C-band signals and routinely delivers 99 percent of all messages within six seconds.

NOAAPort Lite

For those on a tight budget, NOAAPort Lite delivers much of what is found in NWWS, but over Ku-band at 512 kbs. Uplinked from Dyncorp’s 5.6-meter Ku-band antenna at Chantilly, VA, NOAAPort Lite is available 95 percent of the time, or better. “There are a lot of areas where Ku-band is a reliable delivery medium,” Warren explains. “For instance, in the Mojave Desert where it rarely ever rains, we can guarantee service availability 99.95 percent of the time.”

To improve the odds, Dyncorp’s Ku-band transmitter broadcasts “at the highest EIRP allowed by the FCC,” he notes. “We also use the most robust Forward Error Correction possible and nearly 14 dB of uplink power control; we’re pushing the envelope with Ku-band as far as we can.”

But why stick with Ku-band? The answer is money: besides NOAAPort Lite’s lower access fee, “customers prefer to use a smaller, lower cost 1.2-meter Ku-band antenna if it’s at all possible,” Warren says. “After all, even in high rainfall areas such as Southern Florida, we can still deliver 98 percent availability. For some clients, this is more than sufficient for their forecasting needs.”

Standing Up To The Storm

Whatever the service, Dyncorp installs rugged downlinks designed to handle the worst Mother Nature can dish out. “One time, one of our NWS receive sites at Coral Gables, FL, reported problems receiving our signal during a hurricane,” Warren recalls. “As it turned out, there was nothing wrong with the dish: it was still firmly attached to the downlink site’s roof. Trouble was, the roof itself had been blown off by high winds. That’s why the antenna connections were broken.” Dyncorp’s satellite services also kept AWIPS signals reaching into Florida and Louisiana during Hurricane Andrew’s 1992 fury: even when winds reached as high as 177 miles per hour.

To say the least, Dyncorp relies on satellite transmission to get AWIPS where it is needed. Granted, the network does have a terrestrial back-up, but the operative term here is definitely “back-up.” When the weather is turning rough, satellite is the NWS’ and Dyncorp’s preferred venue for getting critical information where it’s needed, and fast.

As for the future? “Dyncorp intends to remain at the forefront of weather data transport via satellite,” Warren says. For instance, Dyncorp is working with AWIPS prime contractor Northrop Grumman to develop an IP/DVB transmission system for this system. The goal is to improve AWIPS’ data throughput and reliability, while reducing overall costs. As well, under contract to NOAA, Dyncorp is studying whether commercial satellites should be used to downlink data from the next generation of GOES satellites (GOES/R). This is because the current GOES fleet uses L-band, which may not accommodate the 35-50 times increase in data rate demand expected of GOES/R.

One thing is certain: wherever there is weather data to be shipped, you will find the NWS, Dyncorp and satellites. Working together, this team helps accurately and reliably answer that time-worn question, “what’s the weather going to be like tomorrow?”

James Careless is the senior contributing editor to Via Satellite.