Artificial satellites revolve around the planets


Most satellites are used for earth observation. Above all, celestial bodies that are used for weather observation are of great importance for life on earth. How can we benefit from observations from space?

Weather satellites are an indispensable source of predicting where and when tropical storms, hurricanes, floods, cyclones, tidal waves and even forest fires will strike. Knowing about these events will help predict and prepare for natural disasters.

The agricultural importance of the weather satellites should not be underestimated either. They support farmers in deciding when the best time is for sowing or harvesting, or when hail and snow threaten. Plants that are sensitive to frost or moisture can be brought to safety in good time with help from space when the weather threatens. Accurate weather forecasts are also important when planning large projects such as the construction of bridges, highways and dams.

The first series of weather satellites to study the earth's cloud cover and demonstrate the value of satellites for meteorological purposes were the Television Infrared Observation Satellites (TIROS). The first of this series was started in 1960 and revealed many new insights into the cloud cover of the earth.

NASA started the Nimbus program in 1964, named after a cloud formation. These satellites, equipped with normal and infrared cameras, were to form the first global meteorological satellite system. Nimbus 7, for example, had an ozone spectrometer on board and played an essential role in studying global ozone distribution and the ozone hole over Antarctica.

The latest weather satellites are part of the GOES (Geostationary Operational Environmental Satellite) program. The last of this series, GOES-I, represents the beginning of a new generation of weather satellites. It is these satellites that provide us with the familiar weather maps on television every day around the world. They take high-resolution images in the visible and infrared range and can also create temperature and moisture profiles of the earth.

Snow cover in the USA © NASA

Countless other satellites with tasks other than weather observation also orbit the earth. So there is the army of GPS satellites, which is used for satellite-based navigation. With their help, the location on earth can be determined exactly to within a few meters. The Global Positioning System (GPS) consists of a network of 24 satellites that orbit the earth on various orbital orbits. Since the orbits of the satellites are between 60 degrees north and 60 degrees south latitude, their signals reach every point on earth. In addition, their function is independent of the weather. Each satellite sends information about the satellite number, position and time to the earth's surface.

To determine the position, the GPS receiver compares the time at which the signal was sent with the time it was received. The distance to the satellite is calculated from the time difference. If the receiver calculates the data from three different celestial bodies, the geographical longitude and latitude, the so-called 2D position, can be determined. Using the data from four or more satellites, a GPS device also calculates the height above the ground.

Theoretically, the location can be determined down to the centimeter with the GPS system. In practice, however, the accuracy is only 20 to 100 meters. This is because the system is a military development and the US Department of Defense artificially degrades the accuracy for civilian users in order to be able to use the greatest possible accuracy alone.

In Germany alone, the GPS system is a valuable aid to around 600,000 drivers in finding the right route in foreign cities. An on-board computer receives the data from the satellites and uses this to calculate the vehicle's location. By comparing it with stored city maps and maps, he can always give the driver the right course, now even with voice output.

Status: March 19, 2001