When a satellite takes an image from space, the value of each pixel is changed into a radio signal and sent to Earth. Here on Earth the radio signal is changed back into an image. A satellite image is comprised of thousands of pixels.

Satellites typically transmit pixels with assigned values of 0 to 255, with 0 representing pure black and 255 pure white. Intermediate values are represented by varying shades of gray which may be translated to colors ("false colored") by a computer to make the image easier to understand.

Create a satellite image of colored pixels to detect subtle detail in your "transmitted" imagery.

1. To introduce the idea of how pixels combine to produce a recognizable image, look at the image on a computer monitor with a magnifying lens.
2. Newspaper photographs and television images are also made up of pixels. To illustrate use a photocopier to enlarge a newspaper photograph to several times its normal size.
3. Assign a block of values, such as
Pixel Value Number Color
0-45 0 Black
46-90 1 Dark Blue
91-135 2 Light Blue
136-180 3 Orange
181-225 4 Yellow
226-255 5 White
1. Have students create a vertical scale of colors and numbers to place next to their graph paper.
2. Pair up students. Have one student create a picture on graph paper by shading in certain boxes using the colors above. Each square on the graph paper represents one pixel or picture element.
3. Have the second student try to recreate the image as follows:

The artist ("satellite") scans the picture from the left beginning with the first square in row 1. The artist proceeds this way square by square across the row to the last square in row 1, and then scans each row in the same way down the page.

The second student ("the receiving station") records the scan on his/her graph paper. When the "satellite" reads ("transmits") a number, the "receiving station" refers to the block of values to find the corresponding color and "records" that color in the square (i.e., if 54 is read, the color that fills in that square is dark blue).

1. After the students have completed reading and recording all the rows, the students compare the images.

Are the images the same, or was the message garbled?

What depth of detail were students able to achieve?

1. Repeat the activity but reverse the students' roles.

Check out an example that we came up with.

Divining detail

Compare color and black-and-white photos from a newspaper. Which provide more detail?

Shoot black-and-white and color photos of the same image, for example, the classroom bulletin board or Portland Head Light and compare.

Have students draw a picture in pencil and then in color.

Remote sensors help us recognize and record changes to our Earth and our environment. Make a photographic tour of your school's neighborhood, taking pictures of sights students point out. Ask them to predict and record what changes may occur over the next few weeks. Return in 14 days (the length of time it takes a polar satellite to pass over the same spot on Earth again) to the same sights and shoot another roll of film. Compare the two sets of photos. Have students predict how their neighborhood may change in a year, then several years.

How has the neighborhood changed?

Interview long-time residents of the community to find out how the area has changed. Ask if they would share old photographs of community landmarks (manmade and natural). Do they still exist?

Locate an old map of your community at the local historical society or library. Does your town still have the same name its founders gave it?

Discuss the features and facts recorded on the historic map(s) (some show the locations of buildings and mark the dates of great fires and plagues).

Compare an old map to a modern map of your area (town, state, region). Discuss what is listed on these maps. Note map features such as: scale, symbols, legend or key, compass direction showing North, as well as roads, rivers, highway intersections and schools. What does this tell you about the importance of various features then and now?

Predict how the community may change in the future. What changes would make your community better? Make a map of what your community may look like 100 years from now.