|
|
Earth Imaging Glossary
A,
B,
C,
D,
E,
F,
G,
H,
I,
J,
K,
L,
M,
N,
O,
P,
Q,
R,
S,
T,
U,
V,
W,
X,
Y,
Z
" D "
DACS--Data Acquisition and Control Subsystems
NOAA's header quality information file.
DANGLING ARC
An arc having the same polygon on both its left and right sides and having at least one node
that does not connect to any other arc. See dangling node.
DANGLING NODE
The dangling endpoint of a dangling arc. Often identifies that a polygon does not close
properly (e.g., undershoot), that arcs do not connect properly, or that an arc was digitized past
its intersection with another arc (e.g., overshoot). In many cases, a dangling node may be
acceptable. For example, in a street centerline map, cul-de-sacs are often represented by
dangling arcs.
DATUM
In surveying, a reference system for computing or correlating the results of surveys. There
are two principal types of datums: vertical and horizontal. A vertical datum is a level surface
to which heights are referred. In the United States, the generally adopted vertical datum for
leveling operations is the national geodetic vertical datums of 1929 (differing slightly from
mean sea level). The horizontal datum, used as a reference for position, is defined by: the
latitude and longitude of an initial point, the direction of a line between this point and a
specified second point, and two dimensions which define the spheroid. In the United States,
the initial point for the horizontal datum is located at Meades Ranch in Kansas.
DBMS--Data Base Management System
A DBMS is software that supports processes germane to organizing, cataloging, locating,
storing, retrieving, and maintaining data (i.e., information) in a data base.
DCRsi--Digital Cassette Recording system incremental
The DCRsi rack mount and modular ruggedized systems are one-inch, transverse scan, rotary
digital recorders capable of recording and reproducing at any user data rate from 0 to 13.4
Mbytes/seconds (0-107 Mbits/seconds). DCRsi is a user friendly mass storage data peripheral
with a total storage capacity of 48 gigabytes.
DDR--Data Descriptor Record
A DDR is a file containing image information which may include: (1) number of lines,
number of samples, number of bands, data type, and the system on which the data was
created; (2) corner coordinates of the image and related projection information; (3) the
minimum and maximum values for each band of an image; (4) information describing how
and when each band of the image was acquired; and (5) miscellaneous information (e.g., the
last date and time modifications were made to an image).
DELAYED NEUTRON ACTIVATION ANALYSIS
This non-destructive analytical technique is used to determine concentrations of specific
chemical elements. The procedure is based on artificially induced neutron capture and the
radioactive decay constants of unstable radionuclides that are produced.
DEM--Digital Elevation Models
The U.S. Geological Survey produces five primary types of digital elevation model data.
They are:
7.5-minute DEM (30- x 30-m data spacing, cast on Universal Transverse Mercator (UTM)
projection or 1- x 1-arc-second data spacing). Provides coverage in 7.5- x 7.5-minute blocks.
Each product provides the same coverage as a standard USGS 7.5-minute map series
quadrangle. Coverage: Contiguous United States, Hawaii, and Puerto Rico.
1-degree DEM (3- x 3-arc-second data spacing). Provides coverage in 1- x 1-degree blocks.
Two products (three in some regions of Alaska) provide the same coverage as a standard
USGS 1-x 2-degree map series quadrangle. The basic elevation model is produced by or for
the Defense Mapping Agency (DMA), but is distributed by USGS in the DEM data record
format. Coverage: United States.
30-minute DEM (2- x 2-arc-second data spacing). Consists of four 15- x 15-minute DEM
blocks. Two 30-minute DEMs provide the same coverage as a standard USGS 30- x 60-
minute map series quadrangle. Saleable units will be 30- x 30-minute blocks, that is, four 15-
x 15-minute DEMs representing one half of a 1:100,000-scale map. Coverage: Contiguous
United States, Hawaii.
15-minute Alaska DEM (2- x 3-arc-second data spacing, latitude by longitude). Provides
coverage similar to a 15-minute DEM, except that the longitudinal cell limits vary from 20
minutes at the southernmost latitude of Alaska to 36 minutes at the northern most latitude
limits of Alaska. Coverage of one DEM will generally correspond to a 1:63,360-scale
quadrangle.
7.5-minute Alaska DEM (1- x 2-arc-second data spacing, latitude by longitude). Provides
coverage similar to a 7.5-minute DEM, except that the longitudinal cell limits vary from 10
minutes at the southernmost latitude of Alaska to 18 minutes at the northernmost latitude
limits of Alaska.
DEMODULATION
The process of recovering a signal from a modulated (varied frequency) carrier wave.
DESCENDING NODE
Direction satellite is traveling relative to the Equator. A descending node would imply a
southbound Equatorial crossing.
DIAPAUSE DORMANCY
The dormant period among grasshopper eggs used to survive long seasonal dry periods.
DIGITAL COUNT
Digital count is the total number of pixels occurring in an image for each possible data value.
DIGITIZATION
Digitization of graphics typically involves recording the location of each point, line, and
polygon on a map, along with their associated labels and attributes.
DLG--Digital Line Graph
A DLG is line map information in digital form. The DLG data files include information
about planimetric base categories, such as transportation, hydrography, and boundaries.
DLG OPTIONAL FORMAT
The USGS digital line graph (DLG-3) optional format, which was designed for data
interchange, allows for the creation of a vector polygon data structure. The topological
linkages are explicitly encoded for node, area, and line elements. The files are composed of
8-bit ASCII characters organized into fixed logical records of 80 bytes. Bytes 1 - 72 contain
the data, bytes 73 - 77 are blank, and bytes 78 - 80 contain a record sequence number. The
detailed description of the DLG-3 optional format is described in Digital Line Graphs from
1:2,000,000-Scale Maps, Data Users Guide 3 (1990).
DLG STANDARD FORMAT
The DLG Standard Format is no longer distributed. Designed to minimize data storage,
the topological linkages of the USGS DLG standard format are only contained in the line
elements. The files are comprised of standard 8-bit ASCII characters organized into fixed
length records of 144 bytes. Nine distinct record types are defined in this format. Coordinates
are expressed as integer mils (one unit = .001") in a Cartesian coordinate system. The origin
is positioned at the center of the DLG cell. The coordinate domain is limited to the range -
32768 and +32767. These values must be transformed using coefficients stored in the header
record of the file to convert to the original Albers Equal-Area coordinates.
DMA--Defense Mapping Agency
The DMA was established in 1972, when mapping, charting, and geodesy functions of the
Defense Community were combined into this joint Department of Defense agency. The
mission of the Agency is to: produce and distribute to the Joint Chiefs of Staff, unified and
specified commands, military departments, and other department of defense users, timely and
uniquely tailored mapping, charting, and geodetic products, services, and training; provide
nautical charts and marine navigational data to worldwide merchant marine and private
vessel operators; and maintain liaison with civil agencies and other national and international
scientific and other organizations engaged in mapping, charting, and geodetic activities.
The above activities were handled by the DMA Combat Support Center until the Center was
disbanded in 1995 and responsibilities were transferred to the National Imagery Mapping
Agency (NIMA)
DODGING
Dodging is a process used to lighten areas of a photographic print during the main exposure
so that the areas which need lightening receive less than the regular exposure. This process,
which generally provides more image detail and reduces scene contrast, is performed by a
skilled technician using their hands or a paddle over the area in need of less exposure.
DOMSAT--Domestic Satellite
A system that utilizes a geosynchronous satellite to re-broadcast satellite data received at a
central reception and preprocessing center.
DOPPLER SYSTEM
The Doppler system is used to correlate total aeromagnetic readings with the position of the
aircraft at the instant readings are taken. The information is then used for mapping
aeromagnetic data. The Doppler system is self contained in the aircraft and emits a pulsed or
continuous microwave which is sent diagonally downward fore and aft. The frequencies are
then compared in order to obtain true ground speed. The heading is obtained from a special
magnetic compass and is maintained by a directional gyro used as an integrating device. The
distance thus determined has a precision better than one part in a thousand, which is
sufficient for most geophysical surveys.
DOS--Disk Operating System
DOS commonly refers to the disk operating system originally developed by MicroSoft, Inc.
for use on personal computers. This operating system also refers to that operating system
which is used on IBM-compatible personal computers.
DOUGLAS - PEUCKER
An algorithm developed by David H. Douglas (University of Ottawa) and Thomas K.
Peucker (Simon Fraser University, British Columbia). This formula was designed to reduce
the number of points required to represent a digitized line from a map.
Reducing the number of points saves storage space and also allows for generalization of lines
that are very complex.
DRAINAGE BASIN
Geographic area or region containing one or more drainage areas that discharge run-off to a
single point.
DTM--Digital Terrain Model
A DTM is a land surface represented in digital form by an elevation grid or lists of three-
dimensional coordinates.
Did we miss something?
Send your submission to imaging@geocomm.com
Glossary Home
Initial content for this Glossary of terms has been graciously supplied by RADARSAT International - www.rsi.ca
|
|
Sponsored by:
For information
regarding
advertising rates
Click Here!
|
