Volume 10, Issue 2

The National Geodetic Survey (NGS) recommends using a hybrid geoid model to derive orthometric heights from ellipsoid heights. The accuracy of GEOID03 and GEOID09 were assessed independently in Connecticut. The present research analyses the spatial behavior of residuals derived from the comparison of differential levelled NAVD 88 orthometric heights and GPS-derived orthometric heights (using GEOID03 & GEOID09) at 72 benchmarks in Connecticut. Both geometrical and geostatistical analyses were performed on the residuals. A planar regression model indicates a weak spatial relation for residuals derived from GEOID03. This weakness was not noted in the analysis of residuals derived from GEOID09. Results of a four-parameter regression model does not indicate any need for a correction surface. A kriging surface was created with a fitted spherical semivariogram model and suggests GEOID09 captures more spatial variability of geoid undulation than GEOID03 in Connecticut.

GPS data in southern Sumatra, Indonesia, indicate crustal deformation associated to subduction zone and inland fault of Great Sumatran Fault (GSF). We analyze these deformation characteristics using campaign and continuous GPS data available in southern Sumatra from 2006–2014. After removing the effect of GSF in southern Sumatra and coseismic displacements of 2007 Bengkulu and 2012 Indian Ocean earthquake, we find that GPS sites experienced northwest-ward direction. These GPS velocities correspond to postseismic deformation of the 2007 Bengkulu earthquake and the 2012 Indian Ocean earthquake. We analyze strain using these velocities, and we find that postseismic strains in southern Sumatra are in the range of 0.8–20 nanostrain.

The 2015 Gorkha Nepal Earthquake sequence started with a magnitude M w 7.8 main shock and continued with several large aftershocks, particularly the second major shock of M w 7.3. Both earthquake events were captured using ALOS-2 ScanSAR images to determine the coseismic surface deformation and the source models. In this paper, the displacement maps were produced and the corresponding modelling results were discussed. The single fault model of the main shock suggests that there was nearly 6 m of right-lateral oblique slip motion with fault struck of 292 ° and dipped gently Northeast at 7 ° , indicating that the main shock was on a thrust fault. Moreover, a single fault model for the M w 7.3 quake with striking of 312 ° and dipping of 11 ° was derived from observed result. Both results showed the fault planes struck generally to South and dipped northeast, which depicted the risks since the main shock occurred.

The investigations on low-cost single frequency GPS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox LEA-6T GPS receivers combined with Trimble Bullet III GPS antennas containing self-constructed L1-optimized choke rings can already obtain an accuracy in the range of millimeters which meets the requirements of geodetic precise monitoring applications (see [27]). However, the quality (accuracy and reliability) of low-cost GPS receiver data, particularly in shadowing environment, should still be improved, since the multipath effects are the major error for the short baselines. For this purpose, several adjoined stations with low-cost GPS receivers and antennas were set up next to the metal wall on the roof of the IIGS building and measured statically for several days. The time series of three-dimensional coordinates of the GPS receivers were analyzed. Spatial correlations between the adjoined stations, possibly caused by multipath effect, will be taken into account. The coordinates of one station can be corrected using the spatial correlations of the adjoined stations, so that the quality of the GPS measurements is improved. The developed algorithms are based on the coordinates and the results will be delivered in near-real-time (in about 30 minutes), so that they are suitable for structural health monitoring applications.

While producing large-scale larger than 1:2000 maps in cities or towns, the obstruction from buildings leads to difficult and heavy tasks of measuring mapping control points. In order to avoid measuring the mapping control points and shorten the time of fieldwork, in this paper, a quick mapping method is proposed. This method adjusts many free blocks of surveys together, and transforms the points from all free blocks of surveys into the same coordinate system. The entire surveying area is divided into many free blocks, and connection points are set on the boundaries between free blocks. An independent coordinate system of every free block is established via completely free station technology, and the coordinates of the connection points, detail points and control points in every free block in the corresponding independent coordinate systems are obtained based on poly-directional open traverses. Error equations are established based on connection points, which are determined together to obtain the transformation parameters. All points are transformed from the independent coordinate systems to a transitional coordinate system via the transformation parameters. Several control points are then measured by GPS in a geodetic coordinate system. All the points can then be transformed from the transitional coordinate system to the geodetic coordinate system. In this paper, the implementation process and mathematical formulas of the new method are presented in detail, and the formula to estimate the precision of surveys is given. An example has demonstrated that the precision of using the new method could meet large-scale mapping needs.