Wx Watch: GOES-Next, Now

Those of us who check The Weather Channel and daily news programs for satellite imagery (and who doesn't?) probably can't tell that a major upgrade has taken place in orbit some 23,300 miles overhead. However, the newest versions of the Geostationary Operational Environmental Satellite (GOES) have much better image resolution than earlier GOES models, can detect more subtle differences in temperature, can send more images, and can even pick up certain emergency locator transmitter signals, to name just a few of their new features.

The changes are all part of the National Weather Service's modernization program. The new GOES vehicles, dubbed "GOES-Next," are critical elements in the NWS' plan to revolutionize the way we process and disseminate weather data. Together with the United States' network of automated surface observation stations (ASOS) and our new web of Nexrad Doppler radars, GOES-Next's heap of atmospheric data will be tossed into ever more sophisticated computer forecasting models. It will also make its way into the meteorological workstations of the future, called AWIPS — advanced weather interactive processing stations. From the AWIPS, weathermen will be able to call up an unprecedented amount of highly detailed information and manipulate it more quickly than ever before. The result, we're guaranteed, will be more accurate analyses and forecasts.

How do the GOES-Next satellites differ from their predecessors? "In terms of viewing small-scale features, low-level moisture, and the clarity of the signal sent by the satellite, the improvement is by a magnitude of three or better," says Dr. James Purdom, the chief of NOAA's National Environmental, Satellite, Data, and Information Service's regional and mesoscale meteorology branch. "GOES now gives us a view of weather and clouds that we never had before. We can see fog and stratus clouds at night, for example. There's also good evidence that we can detect supercooled clouds — at least at the higher levels — and our severe storm analysis is also much, much better."

These and other advances come via some new equipment and methodologies. Older GOES satellites were spin-stabilized in their orbits. This means that they constantly rotated about their vertical axes. The spinning action was essential because it stabilized the satellite's attitude in orbit, operating much the same way as a spinning top.

Unfortunately, this also meant that older GOES imagers (they take the pictures) and sounders (they sense temperature and moisture) rotated, too. On each revolution, lenses and sensors caught only a brief look at the weather below. In fact, some 95 percent of the older GOES satellites' time was spent looking into space. When the earth went by in the remaining five percent, the imagers would build a picture, rastering a line at a time. Since the imager and sounder shared the same viewing port, you had a choice of either taking pictures or making soundings. After 30 minutes, you had a satellite picture or sounding. Due to the rotation's effect on signal propagation, you also had a fair amount of radio noise that could contaminate incoming data.

The newest GOES satellites don't spin. They are stabilized in a fixed attitude, so they continuously "stare" at the earth below. No more rastering and no more electrical interference. Images can be created in half the time; and when severe weather threatens, the imager can give an exploded view of a suspect area, building images in as little as one-minute intervals. When pressed, older satellites could make a zoomed-in picture at five-minute intervals.

New imagers also have better detail, thanks to their 10-bit resolution, compared to six bits for previous satellites. In the visible channel, the new satellites can show up to 1,024 shades of gray; earlier versions could see only 64 shades. This heightened sensitivity allows meteorologists to better see cloud edges and thus infer motions of water vapor and winds aloft. The imager can see better under low-light conditions, too. This gives us the first timely views of fog formation at night.

The one-minute viewing interval can be a real eye-opener. One demonstration showed a sped-up video loop comprised of 10 one- minute images linked together. The subject was a large complex of severe thunderstorms. Cloud tops looked like boiling water, and you could see how the storm complex split the upper-level winds, diverting them around the cells. Shock waves created by the storm's updrafts and pressure changes pulsated, spread outward across the cloud complex, and affected the clouds around the periphery of the main cloud shield. All of this detail would not have been observable on older GOES imagery.

The new sounder is no slouch, either. It too gives full-time coverage to the viewing area below. This is possible because the sounder and imager are separate units in GOES-Next satellites. Another important benefit of separate units is the ability to better synchronize weather observations.

The sounder creates a temperature profile of the atmosphere from the ground up, at 40 different pressure levels. Vertical moisture profiles are another product. Together, these two observations provide a hemisphere-wide study of atmospheric stability. An ozone detection feature is also built into the new sounders, as are sensors designed to sample the earth's magnetic field and the sun's output of electromagnetic and X-ray emissions.

As pilots, we should know that the sounder is tasked with determining cloud heights above 12,000 feet. It's no coincidence that the soundings start at 12,000 feet, by the way. That's the upper limit of ASOS cloud-base observability, and GOES-Next has been designed to fill in the gap between the 12,000- and 25,000-foot levels.

The search-and-rescue feature of GOES-Next is yet another function of these satellites. It operates in the ultra high frequency (UHF) band and is designed to pick up signals from the newest emergency locator transmitters that use the 406 MHz frequency. Unfortunately, this rules out detection of the 121.5 MHz emergency locator transmitters that are installed in most aircraft. Certain commercial ships use the 406 MHz frequency, however, and so do some aircraft of foreign registry.

The first of this new batch of satellites was built by Space Systems/Loral and launched from the Kennedy Space Center on April 13, 1994. It was called GOES-I until it reached orbit. Then, according to custom, its name was changed — to GOES-8. Right now, it's parked over the equator at 75 degrees west longitude, where it overlooks the Atlantic Ocean and eastern half of the United States. For this reason, the satellite occupying this position is often called "GOES East."

GOES-7, the current "GOES West," is now stationed at 135 degrees west longitude, where it scans the western states and Pacific Ocean. Launched in February 1987, GOES-7 is an old-timer. In general, GOES satellites have lifetimes of just five years.

Not to worry. GOES-J was launched on May 23, and when it's declared GOES-9 and operational, it will probably take over the GOES West responsibility. GOES-J's more precise instruments may prompt officials to put it in the eastern position, where it can better monitor tropical storms and hurricanes. In this case, GOES-8 would be moved to the western slot. In any event, GOES-7 will be put in standby mode and given a well-deserved rest.

GOES-K, -L, and -M — all built by Space Systems/Loral — will eventually fill out the rest of the five-satellite GOES-Next series. Actually, since this group of satellites is already active, we could call them GOES-Now satellites.

Whatever the name, the evolutionary improvements in weather satellite technology continue to give us more and better information about the medium in which we all fly.