Undersampling
– a term
applied to the measurements of the gravity or magnetic field at regular space
intervals which are longer than the size of anomalies striking at acute angles
to the traverse survey lines. In case of U., the
interpolation between discrete data points in the direction of a strike of a
short-wavelength anomaly by gridding algorithms will result in appearance of a
trend of small separated circular or elongated contours (bull’s eyes) instead
of more or less continuous trend of this anomaly. [126]. See also Bull’s
Eye Effect.
Universal Gravitational Constant (G)
–
a force of the gravity attraction between two small uniform spheres, each of the
mass equals to 1 gram and placed so that their centers are 1cm apart. The latest
reference [41]
define this value as
G
= (6.67259 ± 0.00085) 10 –8 cm 3 gm –1sec–2
(in cgs units)
or
G
= (6.67259 ± 0.00085) 10 –11 m 3 kg –1 sec
–2 (in SI units)
U.G.C. is also referred to as Newtonian Gravitational Constant and Big G. See
Newton’s Law of Gravitation.
Universal Transverse Mercator (UTM)
– a global coordinate system based on a standard rectangular
map grid. It is used to determine
“x” and “y” coordinates in meters for each specific location in
reference to the Equator (positive “y” values increase toward the North from
the Equator, and negative “y” values increase toward the South from the
Equator), and one of 60 central meridians within 60 meridianal zones, each 6° of longitude wide, covering the Earth’s surface (positive
“x” values increase toward the East from the given central meridian, and
negative “x” values increase toward the West from the given central
meridian). UTM zones are numbered from west to east. Zone 1 has the central
meridian of 177ºW longitude. Zone 31 has the central meridian of 3ºE
longitude. Each central meriduan is
assigned the False
Easting value of 500
000 m. The Equator is assigned the False
Northing value of 0 in
the Northern Hemisphere and 10 000 000 m in the Southern Hemisphere. [223].
See also False Easting
and False Northing.
Upward Continuation
– a
procedure to recompute the potential field data at an elevation higher than that
at which the potential field was observed. In the frequency domain, U.C.
behaves like a
smoothing Low-Pass Filter. Commonly, U.C.
is used to attenuate near-surface noise, tie the aeromagnetic surveys flown at
different altitudes and calculate a residual component of the potential field
(as a difference between the observed field and the upward continued field). The
general formula of U.C.
can be presented as
F(w) =
1/ehw,
where “h” is the level of upward continuation in meters. The property
of attenuating the gravity or magnetic effects of small-scale topographic and
near-surface density or susceptibility variations allows to use U.C.
in designing cascaded filters. [97, 118, 156, 184, 196, 215, 223]. See also Downward
Continuation and Preferential
Continuation.
Upward Continuation Residual
– a
residual gravity or magnetic field obtained after subtracting the upward
continued field from the original field. See
Residual and Upward Continuation.
UTM
– see Universal
Transverse Mercator.
UXO Detection
– unexploded
ordinance detection. A new military technology adapted to the diamond and gold
exploration as well as ultra-detailed mapping of very subtle magnetic property
differences (such as intrusive/ore body zonation/alteration), monitoring buried
pipelines, and other high-precision applications. UXO acquisition system features DGPS
navigation, ultra-high Amplitude
Resolution (0.001 nT),
high-speed summed sampling (up to 20 summed samples per second), multi-sensor
high-sensitivity gradient measurements at randomly distributed or
regular-oriented points of observation using low-flying and slow-moving
helicopters. See DiaMagÔ.