physical geodesy Flashcards
the study of the physical properties of the gravity field of the Earth,
the geopotential, with a view to their application in geodesy.
Physical Geodesy
first to formulate the fact that
two bodies attract each other.
Sir Isaac Newton (1687)
two bodies attract each other.
Gravitational Force
- The sum of gravitational force and the centrifugal reaction acting on a
body - Since the gravitational force is much stronger than the centrifugal
reaction, gravity causes an object to have weight.
Gravity
1 gal = ?
1 cm/sec2
1000 gals = ?
1 kgal = 1 kilogal
0.001 gals = ?
1 mgal = 1 milligal
0.000001 gals = ?
1 μgal = 1 microga
the angular velocity of a point is dependent on the latitude of the point since the distance P from the spin axis
changes.
Centrifugal Force
Phenomenon of light, radio waves, etc. being deflected in passing obliquely from one medium to another of varying density.
Refraction
The force which pulls down a body towards the center of the earth. The sum of gravitational force and the centrifugal reaction acting on a body. It causes an object to have weight.
Gravity
Magnitude of g at the poles
983.221 gals
Magnitude of g at the equator
978.049 gals
it can be seen that gravity varies in
relation to both _______ and _______ of the point
height and latitude
The first gravity measurement was made using a pendulum in a clock.
In 1672, _____, a French astronomer, noted that a clock that kept perfect time in Paris lost 2.5 minutes a day at the equator. In fact, a shorter pendulum was required at the equator to keep the correct
time.
Richer
_______ developed the theory of pendulum behavior. The
period, T or P, of the oscillation of the pendulum is directly related to
the gravitational acceleration, g.
Huygens
Only one parameter is observed. The other one is kept constant.
Relative Determination
P is measured at two station, and the ratio of these corresponding
values of g are determined.
Relative Determination of Gravity
A compensation factor used in gravitational surveys that takes into
account the decrease in the force of gravity with increasing altitude, assuming only air intervenes between the observer and sea level.
Free-air Correction
Free-air Correction
g ground-level > g high up
Variations in Gravity due to Height
gravity correction:
Cr =-0.3086H (mgal)(if m)
- Computation of positions are taken with respect to an ellipsoid
- Measurements are made on the apparent topographic surface of the earth
- One other surface measurement is involved in geodetic
measurements
Geoid
mathematically defined regular surface with specific
dimensions.
ellipsoid
coincides with that surface to which
oceans would conform over the entire earth if free to adjust to the
combined effect of the earth’s mass attraction and the centrifugal
force of the earth’s rotation
Geoid
the shape of an imaginary global ocean dictated by
gravity in the absence of /des and currents.
Geoid
As a result of uneven distribution of the earth’s mass, the geoidal surface is irregular and, since the ellipsoid is a regular surface, the two will not coincide.
3 Geoid Separation
- Geoid Undulations
- Geoid Heights
- Geoid Separations
Geoid is a surface along which the gravity potential is ______ equal and to which the direction of gravity is always
________.
everywhere - perpendicular
Tidal Datums are observed for
how many years?
19 years - Metonic Cycle
measured from the geoid to the point along the
plumb line
Orthometric Height (H)
measured from the ellipsoid to the point along the normal
Ellipsoidal Height (h)
Difference in elevation between the ellipsoid to the geoid. Measured from ELLIPSOID
Geoid Height/ Separation/ Undulation (N)
Geoid below the ellipsoid
NEGATIVE VALUE
Geoid above the ellipsoid
POSITIVE VALUE
the difference between the observed
acceleration of free fall, or gravity, on a planet’s surface, and the
corresponding value predicted from a model of the planet’s gravity
field
Gravity Anomaly
The angle between the plumb line which is perpendicular to the geoid (vertical) and the and the perpendicular to the ellipsoid (normal)
Deflection of the Vertical
