NOAA'S GEOSTATIONARY AND POLAR-ORBITING WEATHER SATELLITES | GOES-8 AND GOES-10
POLAR-ORBITING SATELLITES | HOW SATELLITES ARE NAMED

THE BASICS OF WEATHER RADAR

The word "radar," which is an acronym for "radio detection and ranging," is an important tool in detecting precipitation. Radar has been in use detecting precipitation here in the United States since the late 1950s. The U. S. Weather Bureau developed their first network of vacuum tube radars in 1957.. with the individual radar unit referred to as "WSR57".. with the WSR standing for "weather surveillance radar." Weather radars were made more solid state with the advent of the "WSR74" in the mid 1970s. With tremendous strides in technology, the WSR57 and the WSR74 quickly out grew their usefulness and became harder to maintain during the 1980s.

It was in the late 1980s that the National Weather Service, in a tri-agency effort with the U. S. Departments of Defense and Transportation, developed a network of new doppler weather radars (the WSR88D) across the United States. These computer aided radars are far superior to the earlier radars mainly due to the fact that the radar beam itself was about 2 to 3 times as sensitive as the previous radars when considering signal strength and how we were able to view precipitation. In addition, these doppler radars, based on volume scans of the atmosphere, use algorithms to create additional radar products that include storm total rainfall estimates, vertically integrated liquid (to determine the possibility of hail) as well as radial velocity and storm relative motion which is particularly important in detecting the presence of mesocyclones which can contain tornadoes. In all, about 50 different products are produced in each WSR88D volume scan.. which is performed about every six minutes.

So how does radar work? Weather radars transmit a pulse of energy into the atmosphere and if targets are present, then as the signal becomes scattered, a much smaller part of the pulse energy is reflected back to the radar. The resultant reflected signals, which we refer to as return signals, are indicated on radar displays as "reflectivity" echoes and generally show us areas of precipitation (rain, snow, etc). The larger the target, in this case the precipitation element, the stronger the return signal. Accordingly, not only does the location of these color coded echoes indicate where precipitation is occurring (even though, at times, the precipitation may not reach the ground), but the color indicates the intensity of the precipitation.. with blues and greens indicating lighter precipitation while yellows and reds depict precipitation of heavier intensities. It should be noted that very high reflectivities (red colors) can indicate the presence of hail in more violent thunderstorms.

It should be pointed out that how sensitive a radar happens to be is based upon the wavelength of the pulses of energy that it transmits. While shorter wavelength radars (for example, 3-5 centimeter wavelength radars) can detect smaller precipitation elements and, even, cloud droplets, close in to the radar, longer wavelengths are generally preferred in operational weather forecasting. The longer wavelength radars, such as the National Weather Service's WSR88D, operate at 10 centimeter wavelengths, are much better able to detect precipitation at much greater distances and are able to distinguish smaller atmospheric features throughout the sampled atmosphere. It should be added, as well, that the weaker, generally shorter wavelength radars, such as used at some television stations, are much less expensive than the longer wavelength radars that are used by the National Weather Service.

A very important facet of the new National Weather Service doppler weather radars is the ability, through the understanding of the principle of the Doppler Shift, to not only detect the precipitation (what we have referred to as "reflectivity") but to also detect the motion of the precipitation elements toward or away from the radar, something we refer to as "radial velocity." For the first time ever, by color coding the motion of these targets/echoes, we are able to see wind motion within the precipitation field when that motion is toward or away from the radar. When using the radial velocity and storm relative motion products from the doppler weather radar, it is critical that you understand that "cool" colors (green) indicate motion toward the radar, while "hot" colors (red) indicate wind motion away from the radar.

It goes without saying that this information is extremely important when watching for developing straight line thunderstorm winds, downburst winds, mesocyclones as well as tornadoes. There are three important factors to consider when radar detects a precipitation target. Those considerations, that the radar takes into account when looking at a target, are (1) azimuth angle of the echoes from the radar antenna (when considering that north is at 360 degrees, east is at 90 degrees, south is at 180 degrees and west is located at 270 degrees), (2) elevation angle of the echoes from the radar antenna (ranging from near 0 degrees at the horizon to 90 degrees directly overhead) and (3) judging distance (in miles or kilometers) of the echo from the radar antenna.

What about those pesky "false echoes" we sometime see on radar. Sometimes, the radar energy pulses will be intercepted by vegetation and buildings close to the radar (especially if those things are wet) and the return signal will become contaminated and a wide "ground clutter" pattern is noted. In addition, temperature inversions in the atmosphere can return trapped radar energy which will produce false echoes. These false echoes are referred to as anomalous propagation or, for short, "AP." The newer doppler weather radars are not as prone to this "AP" as the earlier National Weather Service radars or the shorter wavelength radars sometimes used, as mentioned earlier, by television stations. It is important to note, however, that there are times, in clear skies, that the National Weather Service will increase the sensitivity of the WSR88D from "Precipitation Mode" to "Clear Air Mode." This supersensitive reflectivity mode can detect wind shifts in clear air (cloud and precipitation free skies!) and by "targeting" insects, migrating birds and even the bats that fly from under the Congress Street bridge that might be caught in wind pattern.

Now that you've grasped the basic of weather radar, let's take a look at a few radar images:
(1) Image in Precipitation Mode (Light Pcpn)
(2) Image in Precipitation Mode (T'Storms - Squall Line)
(3) Image in Velocity Mode (Tornado)
(4) Image in Clear Air Velocity Mode
(5) Image in Storm Total Precipitation Mode

NOAA'S GEOSTATIONARY AND POLAR-ORBITING WEATHER SATELLITES | GOES-8 AND GOES-10
POLAR-ORBITING SATELLITES | HOW SATELLITES ARE NAMED

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THE BASICS OF WEATHER RADAR | GOES-8 AND GOES-10
POLAR-ORBITING SATELLITES | HOW SATELLITES ARE NAMED

NOAA'S GEOSTATIONARY AND POLAR-ORBITING WEATHER SATELLITES

Operating the country's system of environmental ( weather ) satellites is one of the major responsibilities of the National Oceanic and Atmospheric Administration's (NOAA's) National Environmental Satellite, Data, and Information Service (NESDIS). NESDIS operates the satellites and manages the processing and distribution of the millions of bits of data and images theses satellites produce daily. The primary customer is NOAA's National Weather Service, which uses satellite data to create forecasts for the public, television, radio, and weather advisory services. Satellite information is also shared with various Federal agencies, such as the Departments of Agriculture, Interior, Defense, and Transportation; with other countries, such as Japan, India, and Russia, and members of the European Space Agency (ESA) and the United Kingdom Meteorological Office; and with the private sector.

NOAA's operational weather satellite system is composed of two types of satellites: geostationary operational environmental satellites (GOES) for short-range warning and "now-casting" and polar-orbiting satellites for longer-term forecasting. Both kinds of satellite are necessary for providing a complete global weather monitoring system.

A new series of GOES and polar-orbiting satellites has been developed for NOAA by the National Aeronautics and Space Administration (NASA). The new GOES-I through M series provide higher spatial and temporal resolution images and full-time operational soundings. The polar-orbiting meteorological satellites (beginning with NOAA-K in 1998) will provide improved atmospheric temperature and moisture data in all weather situations. This new technology will help provide the National Weather Service the most advanced weather forecast system in the world.

Geostationary Operational Environmental Satellites (GOES) GOES satellites provide the kind of continuous monitoring necessary for intensive data analysis. They circle the Earth in a geosynchronous orbit, which means they orbit the equatorial plane of the Earth at a speed matching the Earth's rotation. This allows them to hover continuously over one position on the surface. The geosynchronous plane is about 35,800 km (22,300 miles) above the Earth, high enough to allow the satellites a full-disc view of the Earth. Because they stay above a fixed spot on the surface, they provide a constant vigil for the atmospheric "triggers" for severe weather conditions such as tornadoes, flash floods, hail storms, and hurricanes. When these conditions develop the GOES satellites are able to monitor storm development and track their movements.

GOES satellite imagery is also used to estimate rainfall during the thunderstorms and hurricanes for flash flood warnings, as well as estimates snowfall accumulations and overall extent of snow cover. Such data help meteorologists issue winter storm warnings and spring snow melt advisories. Satellite sensors also detect ice fields and map the movements of sea and lake ice.

NASA launched the first GOES for NOAA in 1975 and followed it with another in 1977. Currently, the United States is operating GOES-8 and GOES-10, launched in 1997. GOES-9 (which malfunctioned in 1998) is being stored in orbit to replace either GOES-8 or GOES-10, should either fail.

GOES-8 AND GOES-10

The United States normally operates two meteorological satellites in geostationary orbit over the equator. Each satellite views almost a third of the Earth's surface: one monitors North and South America and most of the Atlantic Ocean, the other North America and the Pacific Ocean basin. GOES-8 (or GOES-East) is positioned at 75 W longitude and the equator, while GOES-10 (or GOES-West) is positioned at 135 W longitude and the equator. The two operate together to produce a full-face picture of the Earth, day and night. Coverage extends approximately from 20 W longitude to 165 E longitude. This figure shows the coverage provided by each satellite.

The main mission is carried out by the primary instruments, the Imager and the Sounder. The imager is a multichannel instrument that senses radiant energy and reflected solar energy from the Earth's surface and atmosphere. The Sounder provides data to determine the vertical temperature and moisture profile of the atmosphere, surface and cloud top temperatures, and ozone distribution. Other instruments on board the spacecraft are a Search and Rescue transponder, a data collection and relay system for ground-based data platforms, and a space environment monitor. The latter consists of a magnetometer, an X-ray sensor, a high energy proton and alpha detector, and an energetic particles sensor. All are used for monitoring the near-Earth space environment or solar "weather."