|Remote sensing basics||Aerial photography|
|Manned-space photography||Landsat satellite imagery|
These techniques are based on sensing electromagnetic energy emitted or reflected from the Earth's surface and detected at some altitude above the ground. The electromagnetic spectrum is, thus, the starting point for understanding remote sensing. Passive remote sensing is based on detecting available (background) electromagnetic energy from natural sources, such as sunlight. Active remote sensing, in contrast, depends on an artificial "light" source, such as radar, to illuminate the scene.
Taken from U.S Geological Survey EROS Data Center--see EDC.
The spectral sensitivity of photography ranges from about 0.3 µm (near-ultraviolet) to 0.9 µm (near infrared). Different parts of the spectrum may be photographed by using various combinations of films and filters. Photographs are routinely taken in b/w panchromatic, b/w infrared, color-visible, color-infrared, and multiband types. For example, color-infrared film is exposed to green, red, and near-infrared wavelengths, which are depicted as blue, green and red in the photograph. This shifting of bands to visible colors is called false-color.
|Color photograph in visible light. Cottonwood River at Cottonwood Falls, Kansas. Note normal appearance of vegetation, water, and other objects in the view. Photo date 5/98; © J.S. Aber.|
|Color-infrared photograph of Cottonwood River at Cottonwood Falls, Kansas. Active vegetation appears red and pink. Photo date 5/98; © J.S. Aber.|
|Basic cameras and film.|
Glossary of photographic terms.
|Examples of aerial photographs.|
|Low-Height Unmanned Aerial Platforms|
|South Island of New Zealand.||Chicago and Lake Michigan, Illinois.|
Film selection for space-shuttle photography is relatively conservative. Most photographs are exposed on color-visible films of various types. Color-infrared film is used occasionally, and other special film types are employed rarely. Most photographs have been digitized and converted to video format. "Digitization, rectification, multi-layering (GIS), classification, and mensuration of these digitized analog images is now fairly routine ..." (Lulla et al. 1993).
|Florida, Gulf of Mexico, and Atlantic Ocean.||Smoke from forest fires in Queensland, Australia.|
|Color-infrared view of Bangkok, Thailand.||Color-infrared view, Mt. St. Helens, Washington.|
The presence of human photographers in space provides some important capabilities: to observe and respond quickly to unusual ground events, to preselect and acquire scientifically useful images, and to photograph phenomena from different look angles. "These qualities demonstrate the value of a human observer in orbit in adding to understanding of our planet Earth, and interacting with ground scientists in real time to acquire data and confirm or deny events." (Lulla and Helfert 1991)
NASA Johnson Space Center--Imagery services.
NASA Johnson Space Center--Earth from space.
The following examples show the Missouri River valley and adjacent terrain at Leavenworth,
Kansas. The scene covers approximately nine by 12 miles (14 x 20 km). Each image is derived
from the same dataset, acquired on 28 Sept. 1994 by the Landsat 5 satellite. Autumn imagery
is particularly good for general display of the landscape, as there are many variations in
vegetation and water bodies, and the lower sun position creates some shadowing of the terrain.
The different appearances of these examples reflect the spectral bands and color coding used
to create the composite images. Both natural-color and false-color composites are utilized
throughout the atlas. Click on the small images below to see full-sized versions (app. 125 kb
|Natural-color composite. Image consists of blue, green, and red visible light portrayed in a natural manner. Active vegetation appears green, bare soil and fallow fields are brown, and urban structures are white. Clean water bodies appear black, whereas the Missouri River displays a muddy brown color. Landsat TM bands 1, 2, 3; image processing by J.S. Aber ©.|
|Standard false-color composite. Image consists of green, red, and near-infrared light portrayed in a false-color manner. Active vegetation appears red-pink, bare soil and fallow fields are green, and urban structures are bluish-white. Clean water bodies appear black, whereas the Missouri River displays a green-brown color. Landsat TM bands 2, 3, 4; image processing by J.S. Aber ©.|
|Special-color composite. Image consists of red, near-infrared and mid-infrared light portrayed in a false-color manner. Active vegetation appears green, bare soil and fallow fields are red-brown, and urban structures are purple. Most water bodies are black, and the Missouri River appears dark blue. Landsat TM bands 3, 4, 5; image processing by J.S. Aber ©.|
|Special-color composite. Image consists of green, near-infrared and mid-infrared light portrayed in a false-color manner. Active vegetation appears green, bare soil and fallow fields are red-brown, and urban structures are purple. Most water bodies are black, and the Missouri River appears dark blue. Landsat TM bands 2, 4, 7; image processing by J.S. Aber ©.|
|Vegetation image based on red and near-infrared bands. Active vegetation is green; dormant or dry plants are yellow; plowed fields, pavement, and bare ground are brown. All water bodies appear black. Landsat TM bands 3 and 4 utilized to create the normalized difference vegetation index--see NDVI. Image processing by J.S. Aber ©.|
Landsat program overview.
USGS Landsat program.
Return to Lewis and Clark bicentennial space-age atlas.
Last update Feb. 2005.