Image: Pictorial representation of data acquired by satellite systems, such as direct readout images from environmental satellites. An image is not a photograph. An image is composed of two-dimensional grids of individual picture elements (pixels). Each pixel has a numeric value that corresponds to the radiance or temperature of the specific ground area it depicts. See gray scale.

Image resolution: The area represented by each pixel of a satellite image. The smaller the area represented by a pixel, the more accurate and detailed the image. For example, if a U.S. map and a world map are printed on identically sized sheets of paper, one square inch on the U.S. map will represent far less area and provide for more detail than one square inch on the world map. In this example the U.S. map has higher resolution. Landsat satellites have a resolution of 30 meters, AVHRR has a resolution of 1 km and Spot resolution is 10 meters.

Infrared radiation (IR): Infrared is electromagnetic radiation whose wavelength spans the region from about 0.7 to 1000 micrometers (longer than visible radiation, shorter than microwave radiation). Remote sensing instruments work by sensing radiation that is naturally emitted or reflected by the Earth's surface or from the atmosphere, or by sensing signals transmitted from a satellite and reflected back to it. In the visible and near-infrared regions, surface chemical composition, vegetation cover, and biological properties of surface matter can be measured. In the mid-infrared region, geological formations can be detected due to the absorption properties related to the structure of silicates. In the far infrared, emissions from the Earth's atmosphere and surface offer information about atmospheric and surface temperatures and water vapor and other trace constituents in the atmosphere. Since IR data are based on temperatures rather than visible radiation, the data may be obtained day or night.

IR See infrared.

Landsat Land Remote-Sensing Satellite, operated by the U.S. Earth Observation Satellite Company (EOSAT). Commercialized under the Land Remote-Sensing Commercialization Act of 1984, Landsat is a series of satellites (formerly called ERTS) designed to gather data on the Earth's resources in a regular and systematic manner. Objectives of the mission are: land use inventory, geological/mineralogical exploration, crop and forestry assessment, and cartography. Landsat has a spatial resolution of 28.5 meters.

Restructured Federal agency responsibilities for the Landsat program are effective for the acquisition and operation of Landsat 7. New operating policy specifies that NOAA will be responsible for satellites after they are placed in orbit, NASA will be responsible for the development and launch of Landsat 7, and that the U.S. government will provide unenhanced data to users at no cost beyond the cost of fulfilling their data request.

Latitude (AKA the geodetic latitude): The angle between a perpendicular at a location, and the equatorial plane of the Earth.

Light: 1. Form of radiant energy that acts upon the retina of the eye, optic nerve, etc., making sight possible. This energy is transmitted at a velocity of about 186,000 miles per second by wavelike or vibrational motion. 2. A form of radiant energy similar to this, but not acting on the normal retina, such as ultraviolet and infrared radiation.

Interplay between light rays and the atmosphere cause us to see the sky as blue, and can result in such phenomena as glows, halos, arcs, flashes, and streamers.

Longitude: The angular distance from the Greenwich meridian (0 degree), along the equator. This can be measured either east or west to the 180th meridian (180 degrees) or 0 degree to 360 degrees W.

Middle infrared: Electromagnetic radiation between the near infrared and the thermal infrared, about 2-5 micrometers.

MultiSpec: MultiSpec is being developed at Purdue University, West Lafayette, IN, by David Landgrebe and Larry Biehl from the School of Electrical and Computer Engineering and LARS. It results from an on-going multiyear research effort that is intended to define robust and fundamentally based technology for analyzing multispectral and hyperspectral image data. The results of the research are implemented into MultiSpec and made available to the user community via the download pages. (MultiSpec Homepage http://dynamo.ecn.purdue.edu/~biehl/MultiSpec/)