Quantifying deformation in North Borneo with GPS

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 fold-and-thrust belt and has been fueling a long debate on the possible geophysical sources behind it. At present this fold-and-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 methods were carried out to investigate horizontal and vertical displacements. Analysis of the GPS results indicates a clear trend of extension along coastal regions of Sarawak and Brunei in North Borneo. On the contrary strain rate tensors in Sabah reveal that only insignificant and inconsistent extension and compression occurs throughout North-West Borneo. Moreover, station velocities and rotation rate tensors on the northern part of North Borneo suggest a clockwise (micro-block) 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

Wavelet packets based denoising method for measurement domain repeat-time multipath filtering in GPS static high-precision positioning

Repeatable satellite orbits can be used for multipath mitigation in GPS-based deformation monitoring and other high-precision GPS applications that involve continuous observation with static antennas. Multipath signals at a static station repeat when the GPS constellation repeats given the same site environment. Repeat-time multipath filtering techniques need noise reduction methods to remove the white noise in carrier phase measurement residuals in order to retrieve the carrier phase multipath corrections for the next day. We propose a generic and robust three-level wavelet packets based denoising method for repeat-time-based carrier phase multipath filtering in relative positioning; the method does not need tuning to work with different data sets. The proposed denoising method is tested rigorously and compared with two other denoising methods. Three rooftop data sets collected at the University of Nottingham Ningbo China and two data sets collected at three Southern California Integrated GPS Network high-rate stations are used in the performance assessment. Test results of the wavelet packets denoising method are compared with the results of the resistor–capacitor (RC) low-pass filter and the single-level discrete wavelet transform (DWT) denoising method. Multipath mitigation efficiency in carrier phase measurement domain is shown by spectrum analysis of two selected satellites in two data sets. The positioning performance of the repeat-time-based multipath filtering techniques is assessed. The results show that the performance of the three noise reduction techniques is about 1–46 % improvement on positioning accuracy when compared with no multipath filtering. The statistical results show that the wavelet packets based denoising method is always better than the RC filter by 2–4 %, and better than the DWT method by 6–15 %. These results suggest that the proposed wavelet packets based denoising method is better than both the DWT method and the relatively simple RC low-pass filter for noise reduction in multipath filtering. However, the wavelet packets based denoising method is not significantly better than the RC filter

Flight test results and analysis of SBAS-like algorithm from the implementation of the Asia-Pacific GNSS test bed

AbstractThe Asia-Pacific GNSS Test Bed is a regional collaborative programme that brings together aviation practitioners in the field of satellite navigation within the Asia-Pacific to study the performance of global navigation satellite systems (GNSS) and to develop a regional plan that will lead to a successful implementation of GNSS in the region. The program is a work program under the Asia-Pacific Economic Cooperation GNSS Implementation Team (APEC GIT), a working group under the APEC. The Test Bed has been in operation since August 2006. The system architecture reflects hybrid architecture between a satellite-based augmentation system (SBAS) and a ground-based augmentation system (GBAS). Test reference stations (TRSs), consisted of a dual-frequency GPS receiver, a communication interface, and a data archival hardware, have been installed in the participating economies. GPS data collected at the TRSs will be transmitted to the test master station (TMS) in Bangkok, Thailand. SBAS messages will be generated and the messages will be broadcasted through a test VHF station (TVS). A test user platform (TUP) will receive GPS signal and the SBAS messages broadcast from TVS and then calculate and archive the TUP’s positions.This paper discusses performance analysis and flight test results conducted in Thailand in September 2007. During flight trials, noting that the Test Bed broadcasts SBAS messages through a VHF data link (VDL) similar to that of GBAS, the impacts of VHF broadcast, such as transmitting power, terrain effects, and impacts of different aircraft attitudes and positions are analysed. Preliminary analysis result indicates that, while the GBAS VDL coverage is very good through out the 30nm airport terminal area, during approach, and even during taxi, considerations should be given to levels of transmitting power to eliminate possible intermittent loss of VHF messages received by the aircraft receiver. This intermittent loss of VHF messages results in very strong fluctuation of horizontal protection levels (HPL) and vertical protection levels (VPL) calculated by the TUP. To yield with possible problem, windowing techniques are proposed and analysed.</jats:p

Insight into the 2004 Sumatra–Andaman earthquake from GPS measurements in southeast Asia

Data collected at ,60 Global Positioning System (GPS) sites in southeast Asia show the crustal deformation caused by the 26 December 2004 Sumatra–Andaman earthquake at an unprecedented large scale. Small but significant co-seismic jumps are clearly detected more than 3,000 km from the earthquake epicentre. The nearest sites, still more than 400 km away, show displacements of 10 cm or more. Here we show that the rupture plane for this earthquake must have been at least 1,000 km long and that non-homogeneous slip is required to fit the large displacement gradients revealed by the GPS measurements. Our kinematic analysis of the GPS recordings indicates that the centroid of released deformation islocated at least 200 km north of the seismological epicentre. It also provides evidence that the rupture propagated northward sufficiently fast for stations in northern Thailand to have reached their final positions less than 10 min after the earthquake, hence ruling out the hypothesis of a silent slow aseismic rupture