# High School Earth Science/Using Satellites and Computers
## Lesson Objectives

* Describe various 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.

## Satellite Images

If you look at the surface of the Earth from your yard or street, you can only see a short distance. If you climb a tree or go to the top floor of your apartment building, you can see further. If you flew over your neighborhood in a plane, you could see still further. Finally, if you orbited the Earth, you would be able to see a very large area of the Earth. This is the idea behind satellites. To see things on a large scale, you need to get the highest view.
Let's look at an example. One of the deadliest hurricanes in United States history hit Galveston, Texas in 1900. The storm was first spotted at sea on Monday, Aug 27, 1900. It was a tropical storm when it hit Cuba on Sept. 3rd. By Sept. 8th, it had intensified to a hurricane over the Gulf of Mexico. It came ashore at Galveston (Figure 2.34). There was no advanced warning or tracking at the time. Over 8000 people lost their lives.
Today, we have satellites with many different types of instruments that orbit the Earth. With these satellites, we can see hurricanes (Figure 2.35). Weather forecasters can follow hurricanes as they move from far out in the oceans to shore. Weather forecasters can warn people who live along the coasts. Their advanced warning gives people time to prepare for the storm, which helps save lives.
Satellites orbit high above the Earth in several ways. One of the most useful ways is called the geostationary orbit (Figure 2.36).
The satellite orbits at a distance of 36,000 km. It takes 24 hours to complete one orbit. Since the satellite and the Earth both complete one rotation in 24 hours, the satellite appears to "hang" in the sky over the same spot (A). In this orbit, the satellite stays over one area of the Earth's surface. Weather satellites use this type of orbit to observe changing weather conditions. Communications satellites, like satellite TV, also use this type of orbit.
Another useful orbit is the polar orbit (Figure 2.37). 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. In this same amount of time, the Earth rotates slightly underneath the satellite. In less than a day, the satellite can see the entire surface of the Earth. Some weather satellites use a polar orbit to get a picture of how the weather is changing globally. Also 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 the Earth (Figure 2.38). The satellites are operated by several government agencies, including NASA, the National Oceanographic and Atmospheric Administration (NOAA) and the United States Geological Survey (USGS). By using different types of scientific instruments, satellites make many kinds of measurements of the Earth.
* Some satellites measure the temperatures of the land and oceans.
* Some record amounts of gases in the atmosphere such as water vapor and carbon dioxide.
* Some measure their height above the oceans very precisely. From this information, they can get an idea of the sea surface below.
* Some measure the ability of the surface to reflect various colors of light. This information tells us about plant life.
Some examples of the images from these types of satellites are shown in Figure 2.39.
| Ocean surface temperatures. | Water vapor in the atmosphere. |
| Global vegetation. | Water vapor in the atmosphere. |
| Figure 2.39: Various satellite images. ||

## Global Positioning System

Previously, we talked about your position on Earth. In order to locate your position on a map, you must know your latitude and your longitude. But you need several instruments to measure latitude and longitude. What if you could do the same thing with only one instrument? Satellites can also help you locate your position on the Earth's surface (Figure 2.40).
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. Here's how it works.
You must have a GPS receiver to use the system (Figure A 2.41). You can buy many of these in stores. The GPS receiver detects radio signals from nearby GPS satellites. There are precise clocks on each satellite and in the receiver. The receiver measures the time for radio signals from satellite to reach it. The receiver uses the time and the speed of radio signals to calculate the distance between the receiver and the satellite. The receiver does this with at least four different satellites to locate its position on the Earth's surface (Figure B 2.41). GPS receivers are now being built into many items, such as cell phones and cars.

## Computer-Generated Maps

Prior to the late 20th and early 21st centuries, map-makers sent people out in the field to determine the boundaries and locations for various features for maps. State or county borders were used to mark geological features. Today, people in the field use GPS receivers to mark the locations of features. Map-makers also use various satellite images and computers to draw maps. Computers are able to break apart the fine details of a satellite image, store the pieces of information, and put them back together to make a map. In some instances, computers can make 3-D images of the map and even animate them. For example, scientists used computers and satellite images from Mars to create a 3-D image of a large Martian valley called Valles Marineris (Figure 2.42). The image makes you feel as if you are on the surface of Mars and looking into the valley.
When you link any type of information to a geographical location, you can put together incredibly useful maps and images. The information could be numbers of people living in an area, types of plants or soil, locations of groundwater or levels of rainfall for an area. As long as you can link the information to a position with a GPS receiver, you can store it in a computer for later processing and map-making. This type of mapping is called a Geographic Information System (GIS). Geologists can use GIS to make maps of natural resources. City leaders might link these resources to where people live and help plan the growth of cities or communities. Other types of data can be linked by GIS. For example, Figure 2.43 shows a map of the counties where farmers have made insurance claims for crop damage in 2008.
Computers have improved how maps are made. They have also increased the amount of information that can be displayed. During the 21st century, computers will be used more and more in mapping.

## Lesson Summary

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

## Review Questions

* Which type of satellite can be used to pinpoint your location on Earth?
** weather satellite
** communications satellite
** global positioning satellite
** climate satellite
* Explain the difference between geosynchronous orbits and polar orbits.
* Describe how GPS satellites can find your location on Earth.
* If you want to map the entire Earth’s surface from orbit, which type of orbit would you use?
* Explain how weather satellites could track a tropical storm from its beginnings.

## Vocabulary
### Geographic Information System (GIS)

    An information system that links data to a particular location.

### geostationary orbit

    A type of orbit that allows a satellite to stay in above one location on Earth's surface.

### polar orbit

    Orbit that moves over Earth's north and south poles as Earth rotates underneath.

## Points to Consider

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