Comparison of full-repeat and sub-cycle solutions in gravity
recovery simulations of a GRACE-like mission Siavash Iran Pour,
Nico Sneeuw, Matthias Weigelt, Tilo Reubelt EGU General Assembly,
Vienna, Austria, 3 - 8 April 2011 1 Slide 2 2 Sampling the Earth
from orbit Aliasing of high-frequency geophysical signals to lower
frequencies (eventually seen in the recovered gravity eld)
tornado.sfsu.eduwww.ni.com EGU General Assembly, Vienna, Austria, 3
- 8 April 2011 Slide 3 3 Strategies to mitigate the aliasing
problem Satellite conguration design Alternative recovery
strategies (different solutions) How different solutions deal with
the problem? Two different solutions strategies for the gravity eld
recovery: - Repeat period of a repeat orbit scenario - Sub-cycle of
the scenario Investigation of the aliasing behavior of different
solution strategies The possibility of sub-cycle solution for
further processing EGU General Assembly, Vienna, Austria, 3 - 8
April 2011 Slide 4 4 Orbit Design (Choosing the orbital parameters)
Orbit Integration (Integrate the satellite parameters in the
presence of the gravity field) Inversion (SH coefficients
estimation) for different time periods Calculating positions and
velocities of the satellites, as well as range, range rate and
range acceleration EGU General Assembly, Vienna, Austria, 3 - 8
April 2011 Slide 5 5 Orbit design GRACE like configuration Repeat
orbit of 125/8 Near circular, near polar orbit Differential orbital
elements EGU General Assembly, Vienna, Austria, 3 - 8 April 2011
Slide 6 6 Orbit integration Static field egm96 Varying fields: 6
hourly time series of gravity potential spherical harmonic
coefficient series - Atmosphere: ECMWF ERA-40 - Ocean: OMCT -
Hydrology: PCR-GLOBWB driven with ECMWF meteorological data - Ice:
ECMWF - Solid Earth: DEOS University of Luxembourg - Models
reprocessed by Mass Transport Study ESA Contract 20403 January 2005
Up to degree 60 (avoiding spatial aliasing by ) EGU General
Assembly, Vienna, Austria, 3 - 8 April 2011 Slide 7 7 Repeat Period
Check EGU General Assembly, Vienna, Austria, 3 - 8 April 2011 Slide
8 8 Inversion SH coefficients estimation up to degree 60 Comparison
of different solutions through maps, coefficients and degree RMS 24
days Input fieldSolution EGU General Assembly, Vienna, Austria, 3 -
8 April 2011 Slide 9 9 8 days (cycle period) 3 days (sub-cycle)
Input fieldSolution EGU General Assembly, Vienna, Austria, 3 - 8
April 2011 Slide 10 10 Differential SH coefficients Triangle plots
24 days8 days (cycle period)3 days (sub-cycle) EGU General
Assembly, Vienna, Austria, 3 - 8 April 2011 Slide 11 11 24 days8
days (cycle period) 3 days (sub-cycle) Degree RMS EGU General
Assembly, Vienna, Austria, 3 - 8 April 2011 Slide 12 12 Spatial
aliasing of the higher degrees? Remove the static field which may
have the biggest contribution! 3 days 46 revolutions => l max 23
L in = 60, L out = 23L in = 23, L out = 23 EGU General Assembly,
Vienna, Austria, 3 - 8 April 2011 Slide 13 13 Veryfing the
hypothesis Observe the differential potential (V total V static )
at the positions of one of the satellites Estimate the differential
SH coefficients (K lm ) from the differential potential observation
Could be meaningful! Further investigation: Spatial aliasing by the
changing field? L in = 60, L out = 23 EGU General Assembly, Vienna,
Austria, 3 - 8 April 2011 Slide 14 14 Summary Almost similar
results for cycle period (8 days) and the longe time (24 days)
solutions Sub-cycle soltion does not provid good results for the
degrees up to half of the revolutions in the period when the orbit
is integrated by higher degrees The static field may have the
largest contribution for the spatial aliasing effect on the
sub-cycle solution The remaining aliasing effect may come from the
spatial aliasing of the changing field itself (the future work)
Thank you EGU General Assembly, Vienna, Austria, 3 - 8 April
2011
