Optical Clocks for Gravity Field Observation and Geodetic Applications
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Hu
Wu
,
Jürgen Müller,
Annike Knabe
Institut
für Erdmessung (IfE), Hannover
EGU
Generally
Assembly
May
4-8
,
2020
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1
2
Space-to-ground
clock
comparison
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3
One-month
GRACE
satellite
A
orbit
(January
2006)
@
~475
km
sampling rate: 5 s
Degree-error
RMS
in
geoid
height
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k
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4
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Space-to-space
clock
comparison
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2
5
One-month
GRACE
satellite
A
&
B
orbit
(January
2006)
@
~475
km
sampling rate: 5 s
Degree-error
RMS
in
geoid
height
C
l
o
c
k
e
r
r
o
r
o
n
l
y
M
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Clocks
can
detect
the
mass
loss
in
some
areas.
Being
complementary
to
GRACE,
clocks
provide:
•
point-wise
and
•
high
-frequency
sampling
obs.
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s
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t
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o
n
7
Clocks
are
powerful
in
obtaining
height
differences
between
distant
points.
This
makes
them
a
ppropriate
for
height
system unification,
by
identifying:
•
discrepancies (offsets)
between
different
height
datums;
•
systematic
distortions
of
national/regional
levelling
networks.
S
p
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c
e
g
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o
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8
Gravity potential at different altitudes
Gravity
field
above
the
equator
at
different
altitudes
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9
Clocks
in higher orbits
support
realiz
ing
a
global
gravity
or
height
reference
system
,
which
is
:
•
stable/robust
over
time;
•
easy to maintain.
For
gravity
field
determination,
clocks:
•
deliver
the
gravity
potential (difference),
which
is
a
scalar
quantity
and
robust
to
attitude
errors;
•
are assumed for space gravimetric obsevations in two
scenarios, and show the highest sensitivity
to
low-degree
gravity fiel
d
signals.
S
u
m
m
a
r
y
10
As
further
geodetic
applications,
clocks
can:
•
unify
local
height
systems;
•
monitor
mass
changes
like
in
Greenland;
•
realize
a
global
gravity/height
reference
system.
Optical clocks play a crucial role in observing gravity fields and have various geodetic applications. From comparing space-to-ground and space-to-space clocks to detecting mass loss in Greenland, these clocks offer high-frequency sampling data for precise measurements. They also aid in unifying height systems and establishing a global gravity reference frame with stable maintenance over time.
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Presentation Transcript
Optical clocks for gravity field observation and further geodetic applications Hu Wu, J rgen M ller, Annike Knabe Institut f r Erdmessung (IfE), Hannover EGU Generally Assembly May 4-8, 2020
Clocks for space gravimetry / Scenario 1 Space-to-ground clock comparison Potential value ? Reference clock LEO satellite Clock 2
Clocks for space gravimetry / Scenario 1 Degree-error RMS in geoid height Clock error only One-month GRACE satellite A orbit (January 2006) @ ~475 km sampling rate: 5 s 3
Clocks for space gravimetry / Scenario 2 Space-to-space clock comparison Potential difference ?? LEO satellite clocks 4
Clocks for space gravimetry / Scenario 2 Degree-error RMS in geoid height Clock error only One-month GRACE satellite A & B orbit (January 2006) @ ~475 km sampling rate: 5 s 5
Mass loss in Greenland B A A A Clock uncertainty: 10-18 B Clocks can detect the mass loss in some areas. Being complementary to GRACE, clocks provide: point-wise and high-frequency sampling obs. 6
Height system unification Clocks are powerful in obtaining height differences between distant points. This makes them appropriate for height system unification, by identifying: discrepancies (offsets) between different height datums; systematic distortions of national/regional levelling networks. 7
Space geodetic reference frame Gravity potential at different altitudes Gravity field above the equator at different altitudes Potential: [m2/s2] 8
Space geodetic reference frame Clocks in higher orbits support realizing a global gravity or height reference system, which is: stable/robust over time; easy to maintain. 9
Summary For gravity field determination, clocks: deliver the gravity potential (difference), which is a scalar quantity and robust to attitude errors; are assumed for space gravimetric obsevations in two scenarios, and show the highest sensitivity to low-degree gravity field signals. As further geodetic applications, clocks can: unify local height systems; monitor mass changes like in Greenland; realize a global gravity/height reference system. 10
