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Lessons and Modules

Introduction to Clouds

From Satellite Data to Images of Clouds

The Satellite Imaging Process

The previous page illustrated that the data produced by the satellite is a number for each location in a grid. A portion of one such grid is shown below.

Sample Gridded Data
Satellite Data: Cloud Optical Thickness for Storm 14 (April 10-14), 1988
11 47.3 47.3 41.3 41.3 19.1 19.1 1.7 1.7 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 1.2 1.2 0.0 0.0 0.0 9.9 9.9
10 60.4 60.4 9.9 9.9 2.1 2.1 1.0 1.0 0.0 0.0 4.5 4.5 3.2 3.2 2.4 2.4 2.1 2.1 0.9 0.9 5.2 10.8 10.8
9 66.9 26.1 26.1 2.8 2.8 1.2 1.2 5.5 5.5 9.4 6.3 6.3 2.4 2.4 3.6 3.6 1.0 1.0 1.2 2.5 2.5 10.6 10.6
8 33.2 9.2 6.8 6.8 1.4 1.4 12.2 22.2 22.2 13.3 13.3 12.4 12.4 14.0 3.9 3.9 3.4 3.4 1.3 4.8 4.8 8.0 8.0
7 4.1 4.1 9.7 2.0 2.0 3.0 21.8 21.8 12.0 12.0 8.0 4.0 4.0 23.1 14.5 14.5 4.6 4.6 2.2 1.0 1.0 3.1 10.4
6 1.0 0.3 8.3 8.3 0.8 4.0 4.0 11.2 11.2 4.1 5.7 5.7 1.8 17.4 17.4 29.6 9.5 9.5 4.9 4.2 4.2 3.6 4.0
5 1.0 1.0 1.3 0.8 0.8 1.2 0.8 0.8 0.8 1.5 3.3 3.3 1.0 34.7 34.7 36.5 13.8 13.8 3.4 5.5 5.5 5.5 3.3
4 0.5 0.5 0.4 0.6 0.3 0.3 1.0 0.6 0.7 0.7 0.8 0.8 0.8 17.1 44.8 27.2 27.2 10.2 3.8 3.8 1.1 4.0 2.2
3 3.0 0.0 0.0 0.5 0.5 0.2 0.2 0.2 0.3 0.5 0.5 3.0 26.6 72.0 72.0 18.7 8.9 4.6 4.6 2.2 0.7 0.2 0.2
2 0.4 0.0 0.7 0.7 0.7 1.0 1.6 1.6 1.2 2.0 4.7 25.5 25.5 66.9 12.4 12.0 12.0 5.2 1.3 5.7 1.8 1.8 2.1
1 1.1 0.5 1.4 0.2 0.2 0.3 0.8 0.8 2.2 2.2 3.6 37.4 48.7 31.7 31.7 26.6 7.9 2.4 0.9 0.9 1.1 2.1 1.8
0 4.9 2.6 1.5 0.8 1.0 1.0 1.3 1.7 3.3 7.2 62.4 62.4 39.3 40.3 20.9 4.7 2.6 2.6 0.8 1.7 2.0 3.5 1.8
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

With digitized data a scientist can mathematically manipulate or "view" the data using a variety of imaging software. Any color scheme can be used for data visualization. When the table above is interpreted with imaging software, different numerical values are assigned different colors. The resultant plot shows the pixels of various colors. In the image below, each color indicates an average value of cloud thickness over a specific geographical area (grid box). This image gives detailed, quantified information about changes in cloud thickness, which can help to classify a cloud.

Cloud optical thickness, Storm 14, 1988

Cloud optical thickness for Storm 14 (April 10-14), 1988.

Which color corresponds to the most optically thick clouds? What does the color purple indicate in the image? Can you locate these thickest clouds in the data table above? What are the actual values of their optical thicknesses?

The image below was created with the same data, but using a grayscale color scheme. The numbers in the data are assigned different shades of gray, giving the most optically thick clouds a white appearance. This image displays less information about detailed cloud characteristics, but looks more like the standard television weather image.

Cloud optical thickness, Storm 14, 1988

Grayscale image of cloud optical thickness for Storm 14 (April 10-14), 1988

If you note the appearance of this small dataset you can make out the (typical) shape of the storm. A common practice is to then superimpose a map over the image of the entire dataset. It then becomes apparent that these clouds are part of a storm system that may cover almost one quarter of the continental United States. A sample satellite picture is shown below illustrating the similar shape of the storm clouds such as in the above dataset.

Infrared satellite image, North America

Infrared satellite image of North America from the Geostationary
Operational Environmental Satellite (GOES)-East, February 4, 1997.

The form below allows you to retrieve similar satellite images of clouds. For example, you might want to see how the clouds appear over the United States today. Remember how the image was produced.

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Now that you know how clouds researchers obtain some of their data, you are ready to proceed to the Data Analysis section, where you will begin to work with some of this data.