Visible images are available only during daylight hours. The sensors onboard the spacecraft are sensitive to reflected light. The major features seen in these type of images are:

• soil
• vegetation
• water
• clouds
• snow and ice

The lower the reflective value, the darker the image. Reflective values usually are found in three broad categories; lighter reflective values are clouds, darker values being soil and vegetation, and water being the darkest. During the winter months look for snow on the ground. It's quite easy to locate the dendritic pattern of snow.

As land becomes developed, its reflective values increase. This is why developed land is more reflective than forested areas. If you look closely along the Mississippi River, look for the image being lighter in color. This lighter color is indicative of cultivated areas. However cities show up darker or lighter than the surrounding areas. Can you think of a reason for this? Think about what types of materials make up urban areas and then think about the surrounding environments. Are the surrounding areas, forest, desert, grasslands, etc.?

The use of image processing software such as NIH Image can be used to enhance digital imagery. This aspect of earth-space science goes beyond then information being presented here.

Water Vapor Images