| dc.description.abstract | Abstract
F
our-dimensional
geo desy
deals
with
in
tegrated
pro cessing
of
geo detic
observ
ations
in
order to analyse the net
w
ork geometry and its v
ariation with time, when these observ
ations
dep end
on
the
gra
vit
y
eld
of
the
earth
and
its
temp oral
v
ariation.
This
consideration
in
tro duces
the
time dimension in
to the
three-dimensional in
tegrated mo del.
The shap e of the earth and consequen
tly its gra
vit
y eld up on whic
h geo detic observ
ables
dep end c
hanges con
tin
uously with time due to dynamic pro cesses taking place within the
earth
and
also
due
to
third
body
attractions,
for
example
the
mo on
and
the
sun.
This
consideration
leads
to
the
requiremen
t
of
four-dimensional
mo dels
in
precise
geo detic
net
w
orks.
In this study
, the mo del of three-dimensional in
tegrated geo desy is extended to
the four-dimensional geo desy b
y considering the temp oral v
ariation of the net
w
ork p oin
ts
b oth in space
and time.
A general deriv
ation of the observ
ation equation for four-dimensional geo desy w
as carried
out.
In this deriv
ation, the time dep enden
t geo detic observ
ations are treated as functions
of
p osition
of
p oin
ts
in
v
olv
ed
in
eac
h
observ
ation
and
the
gra
vit
y
p oten
tial
functionals
ev
aluated
at
those
p oin
ts.
In
the
rst
step
the
p osition
of
a
p oin
t
at
an
y
desired
epoc
h
(time) is decomp osed in
to a pro
visional p osition at the initial ep o c
h, a co ordinate correc-
tion at this initial ep o c
h and a time v
arying displacemen
t.
In the second step the p oten
tial
functional is decomp osed in
to a kno
wn non-temp oral normal p oten
tial and a time v
arying
disturbing
p oten
tial.
The
disturbing
p oten
tial
is
further
decomp osed
in
to
t
w
o
parts:
a
part
at
the
initial
epoc
h
and
another
part
that
v
aries
with
time.
The
gra
vit
y
p oten
tial
functionals
are
in
general
considered
as
non-linear
and
w
ere
therefore
linearised
b
y
ap-
plying the T
a
ylor series appro
ximation to functionals.
In the last step the results of b oth
the
rst
and
the
second
steps
w
ere
com
bined
and
the
resulting
equation
w | en |
