impact of temporal gravity field parameters determined ... · sośnica et al.: impact of temporal...
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Astronomical Institute University of Bern
(1) Astronomical Institute, University of Bern, Switzerland (2) Bundesamt für Kartographie und Geodäsie, Frankfurt am Main, Germany
IGS Workshop 2014 – Celebrating 20 Years of Service June 23-27 2014, Pasadena, California, USA
Impact of temporal gravity field parameters determined from GNSS satellites on the
estimated Earth rotation parameters
Krzysztof Sośnica (1), Adrian Jäggi (1),
Rolf Dach (1), Daniela Thaller (2)
source: http://boris.unibe.ch/57686/ | downloaded: 13.3.2017
Slide 2 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
Table of contents
Introduction: Motivation GNSS sensitivity to low-degree Earth’s gravity field coefficients Solution set-up Temporal Earth’s gravity field from GNSS C20 and correlation with dynamical orbit parameters Other low-degree coefficients
Earth Rotation Parameters (ERPs) & Geocenter Pole coordinates Pole rates Geocenter coordinates Conclusions
Slide 3 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
Three pillars of satellite geodesy
Current status: IGS provides products related to Geometry and Rotation, but not to temporal variations in the Earth’s Gravity field.
Geometry Rotation
Geometry
Gravity Rotation
This solution: Parameters related to all three pillars are simultaneously estimated, because they are strongly dependent on each other.
Are GNSS satellites sufficiently sensitive to variations of gravity?
Slide 4 Astronomical Institute University of Bern
0.0E+00
5.0E-12
1.0E-11
1.5E-11
2.0E-11
2.5E-11
3.0E-11
3.5E-11C2
0C2
1S2
1C2
2S2
2C3
0C3
1S3
1C3
2S3
2C3
3S3
3C4
0C4
1S4
1C4
2S4
2C4
3S4
3C4
4S4
4
Mean a posteriori errors – monthly solutions
GRACE
multi-SLR
CHAMP
GPS+GLONASS
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
Sensitivity of GNSS solutions to low-degree gravity coeff.
GNSS satellites are very sensitive to gravity field coefficients of degree 2. For coefficients above degree 3, GNSS are typically very sensitive only to resonant gravity field coefficients.
R R R R R R
R: resonant coefficients causing “secular drifts” of GPS semi-major axes
Slide 5 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
List of estimated parameters & solution set-up
We processed 10 years of GPS and GLONASS data using the standard orbit modeling as from CODE with two major exceptions: 7-day solutions are generated
instead of the 3-day long-arc solutions as for the IGS.
The Earth's gravity field coefficients up to degree/order 4/4 and geocenter coordinates are simultaneously estimated along with other parameters.
Estimated parameters
GNSS solutions up to 32 GPS and
24 GLONASS satellites
Orb
its
Osculating elements
a, e, i, Ω, ω, u0 (1 set per 3 days)
Dynamical parameters
D0, Y0, X0, XS, XC – unconstrained DS, DC, YS, YC – constrained at 10-12
(1 set per 3 days)
Pseudo-stochastic pulses
R, S, W (constrained, estimated every 12h)
Earth rotation
parameters XP, YP, UT1-UTC
(Piecewise linear, 1 set per day) Geocenter coordinates 1 set per 7 days
Earth gravity field
Estimated up to d/o 4/4 (1 set per 7 days)
Station coordinates 1 set per 7 days Other parameters
Troposphere ZD (2h),
gradients (24h) and ZTD biases
Slide 6 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
C20 from GPS+GLONASS Offset between SLR and GNSS↓
Semiannual signal is not recovered ↓
GNSS dynamic orbit parameters : D0, Y0, X0, XS, XC
Orbit parameters in the X direction are correlated with C20
GNSS dynamic orbit parameters : D0, Y0, X0, XS, XC
Offset is reduced ↓
Semiannual signal is recovered↓
Slide 7 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
C21, S21, C30 from GPS+GLONASS GNSS-derived gravity field parameters agree quite well with the CSR RL05 results (median difference of 8.2.10-11), but: GNSS-derived
parameters show both: the seasonal signals as well as draconitic periods,
C20 is correlated with orbit parameters in the X direction.
Gravity coefficients benefit from the contribution of GLONASS (after 2008, when the station coverage improves).
↓ Annual signal
↓ 2nd harmonic
↓ 3rd harmonic
Slide 8 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
Question:
How much affected are the GNSS-derived parameters by neglecting the temporal gravity field variations, since GNSS satellites are sufficiently sensitive to
recover the temporal variations of Earth’s low-degree gravity field ?
Slide 9 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
X- pole coordinate
↓ Annual signal
↓ 7th harmonic
Semiannual signal ↓
Differences w.r.t. IERS-08-C04
For the X pole coordinate: • the amplitude of the 7th harmonic is reduced from 15.9 to 12.2 µas, • the amplitude of the annual signal is reduced from 12.8 to 6.9 µas, • the mean offset w.r.t. IERS-08-C04 is reduced from -10.5 to -9.9 µas, for the solutions without and with estimating gravity field parameters, respectively.
Slide 10 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
X- pole rate
For the X pole rate: • the amplitude of the 7th harmonic is reduced from 3.5 to 1.8 µas/day, • the mean offset w.r.t. IERS-08-C04 is reduced from 2.2 to 2.0 µas/day,
for the solutions without and with estimating gravity field parameters, respectively.
Differences w.r.t. IERS-08-C04
↓ 7th harmonic
↓ 3/7 of draconitic year ↓ 6/7 of draconitic year
Slide 11 Astronomical Institute University of Bern
Sośn
ica
et a
l.: I
mpa
ct o
f tem
pora
l gra
vity
fiel
d pa
ram
eter
s de
term
ined
fro
m G
NSS
sat
ellit
es
on th
e GN
SS-d
eriv
ed E
arth
rot
atio
n pa
ram
eter
s. IG
S W
orks
hop
2014
, Pas
aden
a, C
A, U
SA
Z component of geocenter coordinates (C10)
When estimating the gravity field coefficients and heavily constraining once-per-revolution orbit parameters in the X direction, the Z geocenter coordinate from GNSS solutions (C10): • is by far less affected by solar radiation pressure modeling, • is closer to the SLR results as compared to GNSS solutions without estimating gravity field.
↓ 3rd harmonic ↓ 5th harmonic
Values shifted by +/-20 mm
Slide 12 Astronomical Institute University of Bern
Summary The GNSS satellites are sufficiently sensitive to low-degree gravity field
parameters, to recover the temporal gravity field variations.
The simultaneous estimation of gravity field parameters along with ERPs, station coordinates, troposphere, and other GNSS parameters is feasible.
The empirical orbit parameters in the X direction are correlated with C20, and thus, the X-parameters partly absorb the C20 variations. However, not all the gravity variations are
absorbed by empirical parameters.
Unabsorbed gravity variations may contaminate the ERP estimates by introducing spurious peaks of seasonal and draconitic signals in the GNSS
solutions when not estimating gravity field parameters.
Spurious seasonal and draconitic signals can be reduced by estimating the gravity field along with other GNSS parameters.
Astronomical Institute University of Bern
(1) Astronomical Institute, University of Bern, Switzerland (2) Bundesamt für Kartographie und Geodäsie, Frankfurt am Main, Germany
IGS Workshop 2014 – Celebrating 20 Years of Service June 23-27 2014, Pasadena, California, USA
Thank you for your attention