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"Everyday Engineering"

"Everyday Engineering" was a technical column posted regularly on the VACETS forum. The Chair of of this column is Dr. Hoang Viet-Dung. For more publications produced by other VACETS  members, please visit the VACETS Member Publications page or Technical Columns page.

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Weather Satellite Systems

Several months ago, I published an article on Global Positioning System (GPS). I am following it up with this article on weather satellite systems. Neither the GPS or these weather satellite systems are communication systems per se, but they are interesting milestones of the satellite industry.

During the soccer season, I become much interested in weather forecasts: I just want to know whether I will get my practices and games in for that week. Trying to catch the 5 minutes forecast on the daily news on television is not very satisfying. Well, for a spare $20,000 I can have my very own weather station in my home.

Weather satellites come in two basic forms: geostationary and polar orbiting. Geostationary Operational Environmental Satellites (GOES) orbit the Earth at a distance of some 19,337 nautical miles. These satellites can view a sector of the Earth approximately + 600 in latitude and + 600 in longitude. Pictures from these satellites are often seen on TV weather reports. Large and precisely-aimed antennas are required to insure reliable reception of GOES weather pictures.

Television and Infrared Observation Satellites (TIROS), on the other hand, orbit the Earth at an altitude of only 450 nautical miles. TIROS are Low Earth Orbit (LEO) satellites. While GOES station on the equator, TIROS are set up to circle the poles. With two active satellites in orbit, every point on the surface of the Earth is scanned four times each day. Transmission from TIROS are made on a number of radio frequencies. These signals, which only have to traverse a few hundred miles to reach the Earth from orbit, can be received with simple, non-directional antennas that are much more practical for use on boats or on mobile vehicles. Equipment required to receive and process the satellite information costs $900 to $1,000, plus the cost of the computer and its display/printer and power supply. A complete system can be assembled for less than $2,500, the salary of the meteorologist not included

One of the latest weather-related product to hit the market is 'Weather for Windows' from Canada's Global Meteorological Technologies Ltd (GMT). The product uses a 486 PC connected to an INMARSAT-C terminal. Information is sent via INMARSAT's Fleetnet service. The display is a near real- time graphical weather map of the world that can be zoomed to show local areas. Weather ships and buoys can be highlighted to display the weather information for that specific station. Maps can be configured to display ice formation or possible fish shoal locations. A complete system (INMARSAT-C terminal, 486 PC, Weatherwise software and access to Fleetnet) will cost Canadian $20,000. An additional $16.40 will be charged for the use of the service per voyage day. GMT receives the original weather data from NOAA (TIROS/GOES), constructs the graphical data and broadcasts to the ships via Fleetnet.

For around 100,000 French Francs (approximately US $20,000), yachtsmen and fishermen can procure a 'Sea Mac' system (INMARSAT-C terminal, Apple Macintosh computer, and software) from the French firm Informatique et Mer, that will display a range of weather data (wind speed and direction, wave height, barometric pressure, water temperature etc.) in a graphical format. The system allows zooming into a specific area of the globe for detailed weather information. The system will also provide a five days forecast in an animated weather map.

Viet-Dung Hoang, Ph.D.

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