Sea Level—In general, the reference elevation of the surface of the sea from which elevations are measured. This term is used as a curtailed form of “mean sea level.”

Shadow—Area produced when a radar beam is blocked from reaching parts of the terrain obscured by other objects. These areas appear in the image as dark or void. Elevation values cannot be determined.

Shoreline—The boundary line between a body of water and the land, in particular, the boundary line between the water and the line marking the extent of high water or mean high water. (Mean high water is a tidal datum computed as the arithmetic mean of the high-water heights observed over a specific 19-year Metonic cycle. For stations with shorter series, a comparison of simultaneous observations is made with a primary control tide station in order to derive the equivalent of the 19-year value.)

Side Lap—The overlap between adjoining swaths of lidar data or adjoining strips of aerial photography.

Slope—The measure of change in elevation over distance, expressed either in degrees or as a percent. For example, a rise of 4 meters over a distance of 100 meters describes a 2.3-degree or 4 percent slope; the maximum rate of change in elevation, either from cell to cell in a gridded surface or of a triangle in a TIN. Every cell in a DEM or triangle in a TIN has a slope value; the lower the slope value, the flatter is the terrain; the higher the slope value, the steeper is the terrain.

Soft Copy Photogrammetry—Stereo photogrammetric procedures that utilize digital imagery in digital stereo photogrammetric workstations (DSPWs)—also called soft copy workstations—that have significant advantages compared to analytical stereoplotters. These advantages include automatic digital image correlation, efficient production of DEMs and digital orthophotos, and superposition of all types of geospatial data over digital imagery. For DEM generation, superimposition means that all elevation mass points, breaklines, and contours can be reviewed in stereo against the actual ground form, and old three-dimensional data can be superimposed on new stereo models to see where DEMs, breaklines, or contours need to be revised.

Spectral Resolution—A description of the way an optical sensor responds to various wavelengths of light. High spectral resolution means that the sensor distinguishes between very narrow bands of wavelength; low spectral resolution means that the sensor records the energy in a wide band of wavelengths as a single measurement.

Standard (1)—An agreed-upon procedure in a particular industry or profession that is to be followed in producing a particular product or result.

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