RGB = NRG

Landsat 7 images are color composites, made by assigning the three primary colors to three bands of the Enhanced Thematic Mapper (ETM+) sensor. These images are not color photographs, they are "false color" images (green fields won't necessarily look green in the image).

One common way that primary colors are assigned to bands can be easily remembered using the mnemonic -

RGB = NRG (Red, Green, Blue = Near Infrared, Red, Green, or "energy")

Red = Near IR (ETM+ band 4)

Green = Red (ETM+ band 3)

Blue = Green (ETM+ band 2)

This image uses Landsat ETM+ Bands 4,3,2. The image depicts an area just north of Tokyo, Japan.

This common band combination makes vegetation appear as shades of red, because vegetation reflects a lot of near infrared light. The brighter the red, the healthier the vegetation. Soils with little or no vegetation will range from white (for sand) to greens and browns, depending on moisture and organic matter content. Water will range from blue to black. Clear, deep water is dark, and sediment-laden or shallow water appears lighter. Urban areas look blue-gray. Clouds and snow are both white.

This assignment of colors is only one of many possible combinations. Any combination of bands can be represented by red, green, and blue. In the following activity you will have the opportunity to manipulate the seven bands of Landsat 7. Let's learn more. (continue on to Different Color Composites)