Image 1: Earth from space

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1 Image 1: Earth from space Credit: NASA Spacecraft: Apollo 17 Sensor: camera using visible light Image date: December 7, 1972 This image is a photograph of Earth taken by Harrison "Jack" Schmitt, an astronaut aboard Apollo 17, which was headed to the moon. Schmitt used an ordinary camera, the kind a professional photographer would use on Earth. When this picture was taken, the spacecraft was 25,000 miles above Earth, so Schmitt was able to capture an image of the entire planet in one frame. Cameras capture visible light from the Sun as it is reflected off materials and objects in its path. Snow, ice, and clouds all reflect a lot of light, so they appear white in the photograph. When this picture was taken, Antarctica was relatively free of cloud cover. You can see it at the bottom of the picture. This picture, which is very famous, is often called "The Blue Marble." 1

2 Think about It Why is it remarkable that this image of the entire Earth was captured in a single frame? Passenger planes fly about 6.5 miles above Earth when they reach cruising altitude. If you photographed Earth from a plane at this altitude, would you capture more or less of Earth in a single frame? Where was the Sun when this photograph was taken behind Earth, behind Apollo 17, or between Earth and Apollo 17? How do you know? 2

3 Image 2: Outline Map of Antarctica Credit: USGS Satellite: none Sensor: none Image date: 1998 You may have seen this kind of map before. It shows the shape of the continent and the names and locations of geographical features such as ice shelves and the South Pole. To help describe the exact location of these features, the mapmaker has drawn lines of longitude and latitude on the map. These lines can be used to give every point on the map a numerical value that locates it precisely on Earth s surface. Early maps of Antarctica were sometimes inaccurate and incomplete. Satellite technology and modern mapmaking techniques make recent maps much more reliable. Of course, there is always some distortion when a curved surface like Earth is drawn on a flat piece of paper. This is especially true when the map covers a large area like Antarctica. 3

4 Think about It Antarctic Exploration Investigation One Before the development of satellite technology, how was information gathered to make maps such as this one? Is the shape of Antarctica in this image the same as the shape in the other images? What is your explanation for any differences? 4

5 Image 3: Elevation Map of Antarctica Antarctic Exploration Investigation One Credit: Study of Place, TERC Satellite: data from more than one satellite Sensor: different types of sensors Image date: April 2001 This map shows how high places are in Antarctica. The information used to make the map comes from the Antarctic Digital Database, which collects data from many maps and satellite sensors. This kind of map is called a topographic map. Topographic maps are used to show three-dimensional features, like mountains and valleys, on a flat piece of paper. They do this by indicating the height of physical features such as mountaintops and valley floors. Lines called contour lines connect points that are the same height. Using this information, we can learn about elevations in Antarctica where it is flat, where there are mountains, the height of mountains, how steeply the land rises and falls, and so forth. 5

6 Think about It Is the South Pole the highest point in Antarctica? How much higher than the South Pole is the highest point? What color is used to show land? What color is used to show ice shelves? 6

7 Image 4: Wind Speed around Antarctica Antarctic Exploration Investigation One Credit: NASA Satellite: QuikSCAT Sensor: SeaWinds (radar) Image date: 07/21/1999 This radar image shows how fast the wind is moving over the ocean around Antarctica. It is a false-color image; the colors represent different wind speeds, not the color of the ocean itself. The winds are not measured directly. Instead, the satellite sweeps radar beams over the surface of the ocean; windy areas have a lot of waves and currents, and these reflect more of the radar signal than calm waters do. Different methods and instruments would be needed to measure wind speed where there is no water. That s why the image doesn't show wind speed over the continent. The gray areas in the image show areas of snow and ice in Antarctica. The darker 7

8 gray area surrounding the Antarctic continent is frozen salt water called sea ice. The people who made the image decided to show other continents in black. Think about It The legend shows wind speed in m/s. What do you think this means? What is the speed of the wind in areas that are colored red? How do you think information about wind speed might be useful to scientists and explorers? How might you measure wind speed over the continent and sea ice? Can you see South America in black in the upper left corner of the image? 8

9 Image 5: Surface Texture of Antarctica Antarctic Exploration Investigation One Credit: NASA Satellite: RADARSAT Sensor: radar Image dates: 18 days in the Antarctic spring of 1997 This is a radar image that shows surface conditions in and around Antarctica. It is different from an ordinary photograph because areas of light and dark represent different kinds of surfaces, not light and shadow. When radar beams are swept over Earth s surface, some surfaces reflect more of the radar signal than others. Smooth surfaces like ice and snow do not scatter much of the radar signal and therefore appear dark. Rough surfaces like rockslides and broken ice reflect more of the signal, so they appear white in the image. This is a high-resolution image, meaning it can map an area in great detail. Radar is a useful technology for mapping Antarctica because it can be used night or day and can penetrate clouds. Think about It What color did the person who made the image choose to represent the smoothest 9

10 surfaces of Antarctica? What color would these surfaces be if you took a photograph with an ordinary camera? What does this image tell you about Antarctica's coastline and ice shelves? 10

11 Image 6: September Sea Ice a 13 year average Credit: Peter N. Schweitzer Satellite: Nimbus 7 Sensor: SMMR and SSM/I (microwave) Image date: September (monthly averages) This image shows the expanse of sea ice around Antarctica. It was created by averaging 13 years of microwave data for the month of September. Microwaves are a form of energy that is constantly being emitted by Earth s many surfaces. Each type of surface (e.g. ocean, ice, or rock) gives off a different amount of microwave radiation, so satellites equipped with microwave sensors can "picture" what the surface looks like, even from very far away. This is a false-color image. The continent is colored green and the ocean blue to make the sea ice, shown in shades of white, more apparent. Microwave sensors are a useful technology for mapping Antarctica because they can detect microwave radiation day or night and in all kinds of weather. Think about It How do you think the image might look different if it was made from data collected on a single day? What season does this image depict in Antarctica? Why do you think the mapmaker, Peter Schweitzer, decided to color Antarctica green? 11