Remote Sensing

Remote Sensing Images and Instruments

Characteristics of different satellite systems, including their spatial resolution, spectral bands, and polarization features, determine the way their imagery is used and how it is affected by the atmosphere.

On the right is an image of the Winyah Bay area of South Carolina. The dark area to the right is open water; the sandy beaches show up pale and blue-white; and the vegetated areas, mostly salt marsh, are green in this image. This is not a photograph, however, but a false color composite of images from Landsat satellite sensors receiving the reflected energy in several wavelengths.

Data from the Landsat series of earth observation satellites have been available since 1972. The primary source of data from the first three Landsat satellites was the Multispectral Scanner System (MSS). The Thematic Mapper (TM) of Landsats 4 and 5 was a major improvement over MSS in terms of spectral resolution (four wavebands of imagery taken at different parts of the electromagnetic spectrum for MSS, seven narrower wavebands for TM). It also improved spatial resolution (80 meters for MSS, 30 meters for TM).

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False Color Image

The combined images using bands 3, 4, and 5.

The first three TM bands or channels, centered at wavelengths of 503, 594, and 677 nm, are in the visible spectrum and correspond to blue, green,and red. Channels 4 and 5 are near-infrared and channel 7 is a middle-infrared band. Channel 6 is in the thermal region; it has a different spatial resolution (120 m) and different physical properties, and is rarely used in the environmental sciences. TM data have been widely used for resource inventory, environmental monitoring, and a variety of other applications.

Since 1979, the Advanced Very High Resolution Radiometers (AVHRR) onboard the National Oceanic and Atmospheric Administration series of meteorological satellites have been in continuous polar orbit. Despite the name, the spatial resolution of AVHRR is not nearly as fine as that of TM. AVHRR is actually considered a comparatively low-resolution sensor. However, AVHRR data have become extremely important for global studies because they carry multiple bands in the visible, the infrared, and the thermal spectra, and a complete coverage of the earth is available twice daily with 1.1-km resolution at nadir and from two platforms. AVHRR has made possible for the first time the expansion of studies of the earth's surface from the regional scale to the global scale using remote-sensing techniques.

From:   Fast Algorithms for Removing Atmospheric Effects from Satellite Images by Hassan Fallah-Adl, Joseph JaJa, Shunlin Liang, and John Townshend (University of Maryland) and Yoram J. Kaufman (NASA Goddard Space Flight Center) IEEE Computational Science and Engineering: Summer 1996