Gravity Changes over Russian River Basins from GRACE - Planetary Exploration and Science: Recent Results and Advances - page 46

The source of these noises is the same polar orbit of the satellites, imperfect
observability of the gravity signals, etc. Scientific teams are developing various
methods of stripe filtering, discussed below.
GRACE data can be used in geophysical, glaciological, oceanographic, and
hydrological studies. Earth rotation research, geodynamics, and climate change
studies also benefit from this mission. A wide range of GRACE science and appli-
cations have been extensively published in journals or presented in international
assemblies.
For the largest country in the world, Russia, not fully covered by meteorological
and hydrological observational networks, GRACE data are especially useful. By
spring 2013 it became clear that Russia has gone through a very snowy winter. Near
Moscow the thickness of snow exceeded up to twice the nominal value and was
more than 70 cm. The questions aroused: can it be detected by GRACE?
In this work the study of regional changes of the gravity field from GRACE
over Russia will be presented. A novel data processing technique - multichannel
singular spectrum analysis (MSSA) - will be applied for the GRACE data filtering
toward improved separation of various signal components, related to hydrological,
seasonal, and climatological changes. Initial data and method will be presented in
the next section, and results of processing will be presented in Sect. 3.3 , followed
by discussions and conclusion.

3.2 Data Processing

3.2.1 Initial Data Preparation

We used JPL Level-2 RL05 GRACE monthly geopotential field data from 01.2003
through 06.2013 with the set of Stokes coefficients complete to degree 60. Release 5
(RL05) of the L2 data product is more accurate than the previous version (RL04)
primarily because of GRACE data and model improvement. Six months of data
(06.03, 01.11, 06.11, 05.12, 10.12, 03.13) were linearly interpolated (overall, N D
126 files were used). Absence of some of these monthly solutions in the recent years
is caused by the difficulties in battery power maintenance on board.
The spherical harmonic decomposition of the gravity field is given by

a
r

n

X

X

n

GM
r

.C nm cosm C S nm sin m/P n .sin '/; (3.1) V.';;r/ D

n D 2 m D 0

here C nm , S nm are normalized Stokes coefficients, representing the exterior geopo-
tential spherical harmonic expansion, n is the degree, m is the order of the spherical
harmonics, P n are the fully normalized associated Legendre polynomials, a is
the mean equatorial radius of the Earth, and the arguments ';;r are latitude,
longitude, and radius, respectively (Panteleev 2000 ).