Lesson Objectives

• Describe types of satellite images and the information that each provides.
• Explain how a Global Positioning System (GPS) works.
• Explain how computers can be used to make maps.

Vocabulary

• Geographic Information System (GIS)
• geostationary orbit
• Global Positioning System (GPS)
• polar orbit
• satellite

Introduction

Modern technology is very useful for Earth scientists. Satellites give researchers a global perspective and can be used to monitor changes. Computers are used for making maps.

Satellite Data

A satellite is a small object that orbits a larger object. Satellites orbit Earth to get a large view of the planet’s surface and for hauling many different types of instruments to monitor all types of conditions (Figure below). Satellite views are important for visualizing global change; for example, the amount of sea ice that is present in the Arctic from winter to winter.

Satellites travel in different orbits:

• In a geostationary orbit (illustrated in Figure below), the satellite orbits at a distance of 36,000 km. Since it takes 24 hours to complete one orbit, which is the same amount of time it takes Earth to complete one rotation, the satellite hangs in the sky over the same spot. What is the value of a satellite in this type of orbit? From this orbit, weather satellites can observe changing weather conditions and communications satellites can relay signals.

• In a polar orbit, seen in Figure below, the satellite orbits at a distance of several hundred kilometers. It makes one complete orbit around the Earth from the North Pole to the South Pole about every 90 minutes. Earth rotates only slightly underneath the satellite, so the satellite can see the entire surface of the Earth in less than a day. What would be the value of this type of orbit? Weather satellites can get a picture of how the weather is changing globally. Some satellites that observe the lands and oceans use a polar orbit.

The National Aeronautics and Space Administration (NASA) has launched a fleet of satellites to study Earth. The satellites are operated by several government agencies, including NASA, the National Oceanographic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS).

Using different types of scientific instruments, satellites measure many things, including the temperatures of the land and oceans, amounts of gases such as water vapor and carbon dioxide in the atmosphere, the ability of the surface to reflect various colors of light, which indicates plant life, and even the height of the ocean’s surface.

You can have lots of fun with satellite maps by playing around with Google maps: http://maps.google.com/. Try searching for these interesting features: Goosenecks State Park, Utah; Mt. Whitney, Lone Pine, California; Empire State Building, New York; or your home. Note that you can zoom in and out to see features in more detail or to see how they fit into the area.

Global Positioning System

Satellites help people locate their position on Earth’s surface. By 1993, the United States military had launched 24 satellites to help soldiers locate their positions on battlefields. This system of satellites was called the Global Positioning System (GPS). Later, the United States government allowed the public to use this system. GPS receivers, like the one pictured in image A of Figure below, are now common.

The GPS receiver detects radio signals from at least four nearby GPS satellites. There are precise clocks on each satellite and in the receiver. The receiver measures the time for radio signals from the satellite to reach it and then calculates the distance between the receiver and the satellite using the time and the speed of radio signals. The receiver triangulates by calculating distances from each of the four satellites. It then determines the location of the GPS receiver, as illustrated in image B of Figure above.

Computer-Generated Maps

Computers have improved how maps are made and have increased the amount of information that can be displayed. Map makers use satellite images and computers to draw maps. Computers break apart the fine details of a satellite image, store the pieces of information, and put them back together in a 2D or 3D image (Figure below).

Geographic Information Systems (GIS) use exact geographic locations from GPS receivers along with any type of spatial information to create maps and images (Figure below). The information might be of people living in an area, types of plants or soil, locations of groundwater, or levels of rainfall. Geologists use GIS to make maps of natural resource distributions.

Lesson Summary

• Satellites give a larger view of the Earth’s surface and make many types of measurements that are of interest to Earth scientists.
• A group of specialized satellites called Global Positioning Satellites help people to pinpoint their location.
• Location information, satellite views, and other information are linked together in Geographical Information Systems (GIS).
• GIS are powerful tools that Earth scientists and others can use to study Earth and its resources.

Review Questions

1. Which type of satellite can be used to pinpoint your location on Earth?
   1. weather satellite
   2. communications satellite
   3. global positioning satellite
   4. climate satellite
2. Explain the difference between geostationary orbits and polar orbits.
3. Describe how GPS satellites can find a location in which there is a transmitter on Earth.
4. What is a Geographical Information System (GIS)?
5. To map the entire Earth’s surface from orbit, which type of orbit would you use? Explain why this would be your best choice.
6. Explain how weather satellites can track a tropical storm from its beginnings.

Further Reading / Supplemental Links

• “Isaac’s Storm”: http://www.randomhouse.com/features/isaacsstorm/.
• About Geographic Information Systems: http://erg.usgs.gov/isb/pubs/gis_poster/.
• Wonderful satellite images of Earth are found at: http://earthobservatory.nasa.gov/.
• How NOAA uses satellites: http://www.noaa.gov/satellites.html.

Points to Consider

• Imagine tracking a hurricane across the Atlantic Ocean. What information would you need to follow its path? What satellite images might be most useful? Research how the National Weather Service tracks and monitors hurricanes.
• What information and type of map would be most useful for understanding the distribution of natural resources for a particular state?
• What are some ways that people use Global Positioning Systems? What problems are easier to solve using GPS?