Strategies to mitigate aliasing of loading signals while estimating GPS frame parameters

The existence of intra-plate deformation of the Sundaland platelet along its eastern edge in North Borneo, South-East Asia, makes it an interesting area that still is relatively understudied. In addition, the motion of the coastal area of North-West Borneo is directed toward a frontal foldand-thrust belt and has been fueling a long debate on the possible geophysical sources behind it. At present this foldand-thrust belt is not generating significant seismic activity and may also not be entirely active due to a decreasing shelfal extension from south to north. Two sets of Global Positioning System (GPS) data have been used in this study; the first covering a time period from 1999 until 2004 (ending just before the Giant Sumatra-Andaman earthquake) to determine the continuous Sundaland tectonic plate motion, and the second from 2009 until 2011 to investigate the current deformations of North Borneo. Both absolute and relative positioning Moreover, station velocities and rotation rate tensors on the northern part of North Borneo suggest a clockwise (microblock) rotation. The first analysis of vertical displacements recorded by GPS in North-West Borneo points to low subsidence rates along the western coastal regions of Sabah and inconsistent trends between the Crocker and Trusmadi mountain ranges. These results have not been able to either confirm or reject the hypothesis that gravity sliding is the main driving force behind the local motions in North Borneo. The ongoing Sundaland-Philippine Sea plate convergence may also still play an active role in the present-day deformation (crustal shortening) in North Borneo and the possible clockwise rotation of the northern part of North Borneo as a micro-block. However, more observations need to be collected to determine if the northern part of North Borneo indeed is (slowly) moving independently.

Section: Gps Datamentioning

confidence: 99%

Quantifying deformation in North Borneo with GPS

Mustafar

Simons

Tongkul

et al. 2017

“…(4). We would do this because, for stations with fairly short time series in particular, not estimating annual oscillations (as part of the trajectory model) can cause them to alias to 'leak into' geodetic estimates of station velocity (Dong et al 2002;Collilieux et al 2012). Adding cycles to all our station trajectory models improves the geometrical consistency of our velocity estimates, but may slightly degrade our post-alignment fits with the predictions of ITRF.…”

Section: Contrasting General Station Trajectory Models With Those Empmentioning

confidence: 99%

Trajectory models and reference frames for crustal motion geodesy

Bevis

Brown

2014

191

169

We sketch the evolution of station trajectory models used in crustal motion geodesy over the last several decades, and describe some recent generalizations of these models that allow geodesists and geophysicists to parameterize accelerating patterns of displacement in general, and postseismic transient deformation in particular. Modern trajectory models are composed of three sub-models that represent secular trends, annual oscillations, and instantaneous jumps in coordinate time series. Traditionally the trend model invoked constant station velocity. This can be generalized by assuming that position is a polynomial function of time. The trajectory model can also be augmented as needed, by including one or more logarithmic transients in order to account for typical multi-year patterns of postseismic transient motion. Many geodetic and geophysical research groups are using general classes of trajectory model to characterize their crustal displacement time series, but few if any of them are using these trajectory models to define and realize the terrestrial reference frames (RFs) in which their time series are expressed. We describe a global GPS reanalysis program in which we use two general classes of trajectory model, tuned on a station by station basis. We define the network trajectory model as the set of station trajectory models encompassing every station in the network. We use the network trajectory model from the each global analysis to assign prior position estimates for the next round of GPS data processing. We allow our daily orbital solutions to relax so as to maintain their consistency with the network polyhedron. After several iterations we produce GPS time series expressed in a RF similar to, but not identical with ITRF2008.M. Bevis (B) · A. Brown Division of Geodetic Sciences, School of Earth Sciences, Ohio State University, Columbus, OH, USA e-mail: mbevis@osu.edu We find that each iteration produces an improvement in the daily repeatability of our global time series and in the predictive power of our trajectory models.

“…Since we are interested in the non-linear coordinate variations, the secular reference frame of the long-term coordinates is arbitrarily defined by means of internal constraints (Altamimi et al 2007). Then, the transformation parameters (translation and rotations) are estimated between each weekly solution and the estimated secular coordinates of the epoch using a subset of well distributed stations in order to minimize aliasing errors (Collilieux et al 2012). Finally, we estimate the coordinate residuals about the long-term trend by additionally removing the transformation parameters.…”

Section: Observed Height Time Seriesmentioning

confidence: 99%

Nontidal ocean loading: amplitudes and potential effects in GPS height time series

Dam

Collilieux

Wuite

et al. 2012

107

Ocean bottom pressure (OBP) changes are caused by a redistribution of the ocean's internal mass that are driven by atmospheric circulation, a change in the mass entering or leaving the ocean, and/or a change in the integrated atmospheric mass over the ocean areas. The only previous global analysis investigating the magnitude of OBP surface displacements used older OBP data sets (van Dam et al. in J Geophys Res 129:507-517, 1997). Since then significant improvements in meteorological forcing models used to predict OBP have been made, augmented by observations from satellite altimetry and expendable bathythermograph profiles. Using more recent OBP estimates from the Estimating the Circulation and Climate of the Ocean (ECCO) project, we reassess the amplitude of the predicted effect of OBP on the height coordinate time series from a global distribution of GPS stations. OBP-predicted loading effects display an RMS scatter in the height of between 0.2 and 3.7 mm, larger than previously reported but still much smaller (by a factor of 2) than the scatter observed due to atmospheric pressure loading. Given the improvement in GPS hardware and data analysis techniques, the OBP signal is similar to the precision of weekly GPS height coordinates. We estimate the effect of OBP on GPS height coordinate time series using the MIT reprocessed solution, mi1. When we compare the predicted OBP height time series with mi1, we find that the scatter is reduced over all stations by 0.1 mm on average with reductions as high as 0.7 mm at some stations. More importantly we are able to reduce the scatter on 65 % of the stations investigated. The annual component of the OBP signal is responsible for 80 % of the reduction in scatter on average. We find that stations located close to semi-enclosed bays or seas are affected by OBP loading to a greater extent than other stations.