When a spacecraft records an image from space, that image, comprised of thousands of pixels (short for picture elements, the dots that make up a picture), is changed into a radio signal and sent to Earth. Here on Earth the radio signal is changed back into a picture. In this exercise, students will experiment with a method similar to that used for producing a satellite-generated image. Students will generate their images on graph paper. Each square on the graph paper represents one pixel or picture element.
Visible satellite images are similar to pictures a photographer might record in that they rely and display reflected light. As long as light is available, land features like mountains, river courses, lakes, silt run-off from rivers into the sea, and coastlines are clearly visible. Clouds appear white to us because they reflect light. Since visible imagery depends on available light, it can only be detected during the day.
Infrared images display gradients of temperature differences. Infrared sensors pick up data both day and night. They show the pattern of heat (infrared radiation) released from the Earth. Heat-producing areas, such as warm water currents or cities (with heat-absorbing concrete and asphalt and heat-producing cars, people, and factories) are bright spots on infrared images. Clouds appear in varying shades of grey, depending on their temperature, which is determined by their height above Earth.
Find out what both visible and infrared satellite images can tell you
- Explain to students that wavelengths of light can be separated into visible and invisible ranges. Show them the range of the electromagnetic spectrum.
- Provide pairs of students with both visible and infrared images of the Atlantic coast. Discuss the differences between infrared and visible satellite images as explained in the introduction to this activity. Then ask students to work together to decide which image is in the visible spectrum and which is infrared.
- Have students use an atlas to find geographic features on the images. Identify Maine, Cape Cod, Cape Hatteras, and Florida. Find other areas of interest. Mark these on your worksheet map of the eastern US.
- Ask students to identify the Gulf Stream in the infrared image. In dark blue pencil, outline and then color the location of the Gulf Stream on the worksheet map. Color the surrounding water lighter blue.
- On the visible image, have students look for clouds and areas where rivers are emptying into the ocean. They may see silt washing into the ocean.
By examining the cloud patterns, can they guess which areas are sunny and which may have rain on this day? Have students lightly shade in the areas that are under cloud cover on their worksheet maps of the eastern US.
What other features can be seen on the visible image that are not detected by infrared sensors?
Place large pieces of construction paper on the ground in full sunlight. Place a thermometer in the center of each. After 10 minutes, compare the thermometer readings. Which are lowest? Highest?
Which color radiates the most infrared radiation (heat) into space? (black)
Which color the least? (white)
- infrared and visible satellite images of the same area or features, including the Atlantic coast of the United States
- worksheet map
- colored pencils
From Joe Cupo's Weatherschool