Because of weather satellite technology and communications satellite technology, you can find out the weather anywhere in the world any time of the day. There are television stations that carry weather information all day long. Meteorologists use weather satellites for many things, and they rely on images from satellites. Here are a few examples of those uses:

• Radiation measurements from the earth's surface and atmosphere give information on amounts of heat and energy being released from the Earth and the Earth's atmosphere.
• People who fish for a living can find out valuable information about the temperature of the sea from measurements that satellites make.
• Satellites monitor the amount of snow in winter, the movement of ice fields in the Arctic and Antarctic, and the depth of the ocean.
• Infrared sensors on satellites examine crop conditions, areas of deforestation and regions of drought.
• Some satellites have a water vapour sensor that can measure and describe how much water vapour is in different parts of the atmosphere.
• Satellites can detect volcanic eruptions and the motion of ash clouds.
• During the winter, satellites monitor freezing air as it moves south towards Florida and Texas, allowing weather forecasters to warn growers of upcoming low temperatures.
• Satellites receive environmental information from remote data collection platforms on the surface of the Earth. These include transmitters floating in the water called buoys, gauges of river levels and conditions, automatic weather stations, stations that measure earthquake and tidal wave conditions, and ships. This information, sent to the satellite from the ground, is then relayed from the satellite to a central receiving station back on Earth.

There are two basic types of weather satellites: those in geostationary orbit and those in polar orbit. Orbiting very high above the Earth, at an altitude of 35,800 kilometres (the orbital altitude), geostationary satellites orbit the Earth in the same amount of time it takes the Earth to revolve once. From Earth, therefore, the satellite appears to stay still, always above the same area of the Earth. This orbit allows the satellite to monitor the same region all the time. Geostationary satellites usually measure in "real time", meaning they transmit photographs to the receiving system on the ground as soon as the camera takes the picture. A series of photographs from these satellites can be displayed in sequence to produce a movie showing cloud movement. This allows forecasters to watch the progress of large weather systems such as fronts, storms, and hurricanes. Forecasters can also find out the wind direction and speed by monitoring cloud movement.

The other basic type of weather satellite is polar orbiting. This type of satellite orbits in a path that closely follows the Earth's meridian lines, passing over the north and south poles once each revolution. As the Earth rotates to the east beneath the satellite, each pass of the satellite monitors a narrow area running from north to south, to the west of the previous pass. These 'strips' can be pieced together to produce a picture of a larger area. Polar satellites circle at a much lower altitude at about 850 km. This means that polar satellites can photograph clouds from closer than the high altitude geostationary satellites. Polar satellites, therefore, provide more detailed information about violent storms and cloud systems.

To find out more about an example of a weather satellite, Meteosat, click here.