Glossary

Popular terms used throughout this website

 


EDM (ELECTRONIC DISTANCE MEASURING DEVICE)

Instruments that measure the phase difference between transmitted and reflected or retransmitted electromagnetic waves of known frequency, or that measure the round-trip transit time of a pulsed signal, from which distance is computed.

ELEVATION

Vertical distance of a point above or below a reference surface or datum.

EPHEMERIS

A list of parameters describing the orbital track of a sensor; used to identify the location of the vehicle and its orbit at any given time.

EROSION

Group of natural processes including weathering, dissolution, abrasion, corrosion, and transportation that remove material from any part of the Earth's surface.

ERRORS

Horizontal accuracy (represented as CE90) is a horizontal measurement on the ground defining the radius of a circle within which an object of known coordinates should be found on an image. The probability of a point in the image meeting the recorded accuracy is 90% for CE90. This parameter is expressed in meters.

Vertical accuracy (represented as LE90) is the accuracy at which elevation of a point in the image can be determined. The probability of a point in the image meeting the recorded accuracy is 90% for LE90. This parameter is expressed in meters.

ESTUARY

That portion of a stream influenced by the tide of the body of water into which it flows; an arm of the sea at a river mouth.

FEATURE EXTRACTION

The systematic process of extracting features from imagery, such as roads, railways and water bodies, that can be displayed on maps or in a Geographic Information System (GIS).

FEATURE SEPARATION

Process of preparing a separate drawing, engraving, or negative for selected types of data in the preparation of a map or chart.

FLOOD PLAIN

Belt of low flat ground bordering a stream channel that is flooded when runoff exceeds the capacity of the stream channel.

FORM LINES

Lines, resembling contour lines, drawn to present a conception of the shape of the terrain without regard to a true datum or regular spacing.

FORMAT

Our image data is offered in different formats depending upon what kind of image application software requirements you have. The formats available for each sensor are included on each product page. Examples of formats are:

Format

Description

BIL

Band Interleaved by Line

BIP

Band Interleaved by Pixel

CEOS

The archive header file used by the EDC Data Center is a Committee on Earth Observing Satellites (CEOS) Inventory Exchange Format (IEF) data exchange file. CEOS provides a three character abbreviation for all participating archive centers and receiving stations.

Fast Format

Band sequential format with simplified single header file structure. Used with Landsat and IRS data.

GeoTIFF

TIFF with geographic coordinates included in file header.

LAN

a multiband continuous image file (name is derived from Landsat).

LTWG/LGSOWG

Band sequential format with complicated file 'superstructure'. The format is seldom used but the multiple headers, leaders, descriptors and supplemental files have specialized information, including ephemeris and attitude data, useful for the orthorectification of Landsat data.

SS-BSQ

Band sequential format with complicated file 'superstructure"; includes ephemeris and attitude data, useful for the orthorectification of data.

TIFF

Tag Image File Format. The most common image file format used by commercial GIS software

TIFF World (TFW)

ASCII file containing information for geocoding image data.

GEO-LOCATIONAL ACCURACY

The degree to which the coordinates of points determined from a geospatially referenced image or dataset agree with the coordinates determined by ground survey or other independent, higher-accuracy means.

GEODESY

Science concerned with the measurement and mathematical description of the size and shape of the earth and its gravitational fields. Geodesy also includes the large-scale, extended surveys for determining positions and elevations of points, in which the size and shape of the earth must be taken into account. 

GEOGRAPHIC DATA

The locations and descriptions of geographic features. The composite of spatial data and descriptive data.

GEOGRAPHIC DATA SET

One of the seven geographic data types supported by ARC/INFO. Geographic data sets in ARC/INFO include coverage, grids, DBMS tables, tins, images, Lattices and CAD drawings.