Understanding -

Images obtained by satellites and high- apart and are analogous to - altitude aircraft give engineers and scien- lenths and how closely they are spaced. tists a tool to study landforms, vegetation health patterns, environmental pollution, Other parts of the spectrumCsuch as the and other effects of human activities on invisible near-infrared wavelengthsCcan the ’s surface. be recorded by either electronic sensors or special photographic films sensitive to Satellites and high-altitude aircraft these . These sensors and equipped to record scenes of the use films record the reflected by the both visible and invisible parts of the ground and the ’s spectral energy. The . Near-infrared color-infrared film images referred to in light is invisible to the human , but this fact sheet should not be confused adding it to these images allows with electronic (thermal to “see” the surface of the Earth in other recordings), a process in which long-wave than natural . The result is “color- or “far-infrared” is electronically infrared” . detected and subsequently displayed at visible wavelengths. Near-infrared and The electromagnetic spectrum is the sci- visible wavelengths that are simultaneous- entific term for the collective types of ly recorded combine to provide a unique light and energy emitted from the Sun. view of the Earth’s vegetation and other NASA color-infrared --New Orleans, La The part of the spectrum visible to the features of the planet’s surface. human eye is the normal of col- infrared film. Unhealthy or dormant vege- ors we see every day. Passing This unique aerial view, created by a tation may appear light or a light shining through a prism separates white combination of wavelengths, gives scien- shade of - (), depending on light into individual colors, just as sun- tists a means to better understand what is the plant’s degree of good health. These light through raindrops creates a rainbow. happening on the Earth’s surface. For color distinctions make color-infrared More technically, a prism divides light example, leaves of healthy, growing vege- photographs useful in assessing the health into its component wavelengths. Ripples tation reflect a high level of near-infrared of plants. , on the other hand, on a lake can be close together or far wavelengths and appear red on color- absorbs near-infrared wavelengths and appears in the image. Water with varying amounts of suspended particles appears as shades of blue. Also, near- infrared wavelengths penetrate atmos- pheric haze and result in clear, crisp images. This is an important consideration when collecting satellite images and high- altitude aerial photographs.

Satellite electronic sensors and aerial color-infrared films both record visible and near-infrared wavelengths, but each of these systems requires different labora- tory processes. Here is how they work. Color-Infrared Photographs

Both standard-color and color-infrared films are manufactured to have three dis- tinct layers, or emulsions. Each layer is Color photograph--near Burlington, Vt Color-infrared photograph--same area

US Department of the Interior USGS Fact Sheet 129-01 US Geological Survey December 2001 sensitive to different wavelengths or ener- How to Find More Information gy. Standard-color film emulsions normal- ly record the visible wavelengths as red, For information about ordering color- green, and blue. After the picture has been infrared composites or color-infrared aeri- taken, chemical processing of the film al photographs, please contact any Earth generates cyan, magenta, and dyes Science Informatioon Center, or call proportional to the amount of 1-888-ASK-USGS. given each layer. Color pictures result when the human eye views the varying More information on color-infrared tech- combinations of the three dye layers. nology is available from many libraries. Color-infrared film has a yellow filter over the three emulsion layers to block Among the many books exploring this untraviolet (UV) and blue wavelengths. subject are the following: Processing color-infrared film after expo- M.M. Thompson’s Maps for America, sure produces yellow, magenta, and cyan U.S. Geological Survey (Government dyes. The near-infrared wavelengths and Printing Office, Washington, D.C., 1987), the lack of UV and blue wavelengths and Robert K. Holtz’s The Surveillant Landsat color-infrared composite--San Franscisco, Calif result in a clear, crisp color-infrared Science: of the image. Green, healthy vegetation has a Environment (John Wiley and Sons, high reflection level of near-infrared 1985). For more technical information, wavelengths and appears red on the you could consult the Manual of Remote processed film; red objects with very low Sensing, published by the American near-infrared reflection appear green; Society of Photogrammetry and Remote green objects with very low near-infrared Sensing, 5410 Grosvenor Lane, Bethesda, reflection appear blue; and blue objects MD 20814-2160. with very low near-infrared reflection appear black. For information on other USGS products and services, call 1-888-ASK-USGS, use The Federal Government has color- the Ask.USGS fax service, which is avail- infrared photographic coverage of the able 24 hours a day at 703-648-4888, or entire United States from a high altitude visit the general interest publications Web (40,000 feet) and is obtaining similar cov- site on mapping, geography, and related erage at a lower altitude (20,000 feet) for topics at mac.usgs.gov/mac/isb/pubs/ many States. pubslists/. Color-Infrared Composite Images For additional information, visit the ask.usgs.gov Web site or the USGS home Another type of color-infrared image is page at www.usgs.gov. NASA color-infrared photograph--San Diego, Calif the color-infrared composite of multispec- tral data collected by electronic sensors on satellites such as Landsat. These sen- sors record the light levels of Earth's reflected energy (from blue/green wave- lengths through infrared wavelengths) and transmit these data in digital format to the ground in sets of four or seven wave- length-dependent bands for each typical Landsat scene. On the ground, the data may be converted to hardcopy images similar in appearance to conven- tional color-infrared photographs. Computerized image-recording devices process the bands of green, red, and near- infrared digital data, exposing conven- tional color film or paper with blue, green, and red light, respectively. In the resulting image, growing healthy vegeta- tion appears red, clear water appears black, sediment-laden water appears light Landsat color-infrared composite--Williams, Calif, blue, and urban areas appear blue-gray. quadrangle