Mon Oct 13, F. Flechtner
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Kloko\vcn\'ık, J., Wagner, C. A., Kostelecký, J., and Bezd\vek, A., 2015. Ground track density considerations on the resolvability of gravity field harmonics in a repeat orbit. Advances in Space Research, 56(6):1146–1160, doi:10.1016/j.asr.2015.06.020.
• from the NASA Astrophysics Data System • by the DOI System •
@ARTICLE{2015AdSpR..56.1146K,
author = {{Kloko{\v{c}}n{\'\i}k}, J. and {Wagner}, C.~A. and {Kosteleck{\'y}}, J. and {Bezd{\v{e}}k}, A.},
title = "{Ground track density considerations on the resolvability of gravity field harmonics in a repeat orbit}",
journal = {Advances in Space Research},
keywords = {Gravity field of the Earth, Resonant/repeat orbit missions, Ground track density, Resolvability, Maximum degree/order limit},
year = 2015,
month = sep,
volume = {56},
number = {6},
pages = {1146-1160},
abstract = "{One of the limiting factors in the determination of global gravity field
parameters is the spatial sampling, namely during phases when
the satellite is in an orbit with few revolutions for each
repeat cycle. This often happens when it is freely passing
(drifting) through the atmosphere and encountering a fair number
of such deficient repeat orbits. This research was triggered in
2004 by the significant but only temporary, 2-3 months long,
decrease of the accuracy of monthly solutions for the gravity
field variations derived from GRACE. The reason for the dip was
the 61/4 resonance in the GRACE orbits in autumn 2004. At this
resonance, the ground track density dramatically decreased and
large (mainly longitude) gaps appeared in the data-coverage of
the globe. The problem of spatial sampling has been studied
repeatedly (Wagner et al., 2006; Kloko{\v{c}}n{\'\i}k et al.,
2008; Weigelt et al., 2009) and simple rules have been derived
to limit the maximum order for unconstrained solutions
(inversions) for the gravity field parameters or their
variations from observations of a single satellite. Here we work
with the latest rule from Weigelt et al. (2013) which
distinguishes the maximum attainable order according to the
parity of the two parameters defining the repeat orbit or
orbital resonance, {\ensuremath{\beta}} the number of nodal
satellite's revolutions in {\ensuremath{\alpha}} nodal days
({\ensuremath{\alpha}}, {\ensuremath{\beta}} co-prime integers,
the ratio {\ensuremath{\beta}}/{\ensuremath{\alpha}}
irreducible). This rule, that the resolvable order (in a repeat
near polar orbit) should be {\ensuremath{\beta}} for odd parity
({\ensuremath{\beta}} - {\ensuremath{\alpha}}) and
{\ensuremath{\beta}}/2 for even parity ({\ensuremath{\beta}} -
{\ensuremath{\alpha}}) orbits, arose from the discovery that the
number of distinct and equally spaced equatorial crossings
(ascending and descending passes) for odd parity
({\ensuremath{\beta}} - {\ensuremath{\alpha}}) is
2{\ensuremath{\beta}} while for even parity orbits it is only
{\ensuremath{\beta}}. We extend this insight over all achievable
latitudes and assess the ground track density (or coverage) by
way of the maximum distances between subsatellite points at
arbitrary latitude, specifically for the nearly polar (drifting)
orbits of CHAMP, GRACE, and the repeat tuned GOCE. We
demonstrate clearly how latitude (and also the orbital
inclination) is important and affects the choice of an order
resolution limit. A new rule, compromising between
{\ensuremath{\beta}} and {\ensuremath{\beta}}/2 for each
specific repeat orbit, is proposed, based on the average maximum
distance between subsatellite points over the achievable
latitudes. Although these findings allow an initial estimate of
recoverability based solely on the global spatial sampling of
the ground track, a more refined analysis involving the
inversion of specific observations is still outstanding.}",
doi = {10.1016/j.asr.2015.06.020},
adsurl = {https://ui.adsabs.harvard.edu/abs/2015AdSpR..56.1146K},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
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