Introduction to Geomatics Engineering GEODESY « a branch of applied mathematics concerned with the determination of the size and shape of the earth and the exact positions of points on its surface and with the description of variations of its gravity field » 1
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Introduction to Geomatics Engineering
GEODESY « a branch of applied mathematics concerned with the determination of the
size and shape of the earth and the exact positions of points on its surface and
with the description of variations of its gravity field »
1
Three pillars of Geodesy
2
Geodynamical Geodesy Geodetic techniques are used
to study geodynamic processes, such as plate tectonic
motions, postglacial rebound (now called glacial
isostatic adjustment) or variations in Earth rotation and orientation.
Physical Geodesy: the observation and use of gravity
measurements (from ground, air and space) to
determine the figure of the Earth, notably the geoid,
which involves the formulation and solution of boundary-value problems
Geometrical/Mathematical Geodesy: computations,
usually on the reference ellipsoid, to yield accurate
positions from geodetic measurements, including map
projections, which involves aspects from differential
geometry.
Satellite/Space Geodesy: determination of the orbits of
satellites (hence inferring the gravity field) or for
determining positions on or near the Earth’s surface
from ranging measurements to navigation satellites.
Four branches of Geodesy
Geokinematics
3
Global horizontal velocity vectors
4
Station motion: Post glacial rebound
5
Station motion: Solid Earth Tides
6
Station motion: Tidal Ocean Loading
7
International Terrestrial Reference Frame (ITRF)
8
International Celestial Reference Frame (ICRF)
9
Time Systems (Scales)
Siederal Time Scales Atomic Time Scales Dynamical Time Scales
GMST : Greenwich Mean Siederal Time
TAI : Temps Atomique International (Atomic time)
ET : Ephemeris Time
GAST : Greenwich Apparent Siederal Time
UTC : Universal Time Coordinated
TDT : Terrestrial DynamicalTime
LMST : Local MeanSiederal Time
GPST : GPS Time BDT : Barycentric Dynamical Time
LAST : Local Apparent Siederal Time
TCB : Barycentric Coordinate Time
UT1 : Universal Time 1 TCG : Geocentric CoordinateTime
TT : Terrestrial Time
10
Siederal Time Scales
1 mean siederal day = 1 mean solar day – 3m 55.909s
11
Atomic Time Scales
TAI – UT1 = 0s (The epoch of TAI agreed with the epoch of UT1 on 1st of January 1958)TAI – UT1 = 6.1s on 1st of January 1968TAI – UT1 = 16.4s on 1st of January 1978
12
Earth rotation
• Why do we care?– Dynamical equations
expressed in a non-rotating frame (e.g. spacecraft tracking)
– Sensitive to mass transport in the earth (e.g. winds, ocean currents, etc)
– Sensitive to the deep internal structure of the earth