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Weather Data
This page allows users to obtain weather forecasts and other
weather information using a web interface.
 When weather information is requested, the text data that is needed is obtained
from the National Weather Service (NWS) and the Interactive Weather Information Network
(IWIN).
The raw data is then parsed, cleaned up and presented to the user on a web page. Just like
the example to the right, a live radar image of South Eastern America.
Weather Satellite History and
Usage
Weather satellites were first launched in 1960 in the United States.
Since then, an increasing number of satellites have been launched on a regular basis.
Despite the steady progress and greater coverage of weather information, the format has
not changed much. The rest of the world has adopted almost the exact same standards as
those used in the early 1960s.
The first satellite launched was a polar orbiting type – usually known as NOAA
(National Oceanographic and Atmospheric Administration), orbiting at a height of 860 km
above the earth.
The circular orbits of polar satellites take
them almost directly over the North and South poles. As the satellite moves above the
earth’s surface, a line of about 3,000 km is scanned about twice per second. Ss the
earth rotates, a different strip is imaged. Since it scans constantly, the satellite never
sends complete image, but rather, a continuous never-ending strip.
These satellites use VHF radio to transmit information, using frequencies just above 137
MHz, meaning the satellite image is receivable when it comes over the horizon – as
far as 3,000 km away – and is not available 24 hours a day.
In the late 1970s, it became obvious
that a satellite transmitting 24 hours a day would be a major improvement.
A satellite 40,000 kilometers away will orbit the earth once every 24 hours, which is
exactly the same rate that the earth rotates. Therefore, from a point on the earth, the
satellite appears stationary.
Since the geostationary satellite is much further away from the earth than the polar
orbiting type, the resolution is not as good.
However, because geostationary satellites appear fixed, they can send images of exactly
the same locations as frequently as every 30 minutes. A single geostationary satellite can
also capture approximately 40 percent of the earth’s surface.
The images can be animated by software to show the movement of weather formations for past
time periods.
This gives valuable information on the type, direction and magnitude of the formations,
which improves the ability of weather services to provide more accurate forecasts.
The locations of the weather satellites are as follows:
1. Meteosat 7
over Europe
2. GOES 8 over Eastern America
3. GOES 10 over Western America
4. GMS over Australia / Japan
5. INSAT / Meteosats over Russia / India
Meteosat and GOES re-transmit images from
other geostationary satellites so that if you are in America, for example, you can see the
weather for Australia.
Geostationary satellite transmission on 1691 MHz is called WEFAX, and is fairly standard,
although there are small differences between actual satellites.
Such transmissions require a small 3-foot (90 cm) dish. PDUS is the high-resolution system
from Meteosat that requires a big 6-foot (1.8m) dish. |
