Journal of Surveying Engineering

At the beginning of the 21st century, a significant technological change took place in geodetic astronomy. In Zurich and Hannover, digital zenith camera systems were developed based on digital imaging sensors (charge-coupled device) that strongly improved the degree of automation, efficiency, and accuracy of the observation of the direction of the plumb line and its vertical deflection. This paper describes the instrumental design of the new digital zenith camera systems and gives an overview of the data processing with focus on the models used for astrometric data reduction and tilt correction. Results of frequently repeated observations of vertical deflections and comparison measurements show an accuracy of vertical deflection measurements of better than 0.1 arc sec. Application examples for vertical deflection data from zenith camera observations, such as the high-precision local gravity field determination in engineering projects and gravity field validation are summarized.

The integration of globe navigation satellite system (GNSS) with inertial navigation system (INS) is being heavily investigated as it can deliver more robust and reliable systems than either of the individual systems. In order to ensure the integrity of navigation solutions, it is necessary to incorporate an effective quality control scheme which uses redundant information provided by both the measurement and dynamic models. As the GNSS receiver autonomous integrity monitoring (RAIM) algorithms are well developed, here they are adapted to integrated GNSS/INS systems referred as extended RAIM $\left(e\text{RAIM}\right)$ , which are derived from the least-squares estimators of the state parameters in a Kalman filter, to assess GNSS/INS performance for a tightly coupled scenario. In addition to the RAIM capabilities, $e\text{RAIM}$ procedures are able to detect faults in the dynamic model and isolate them from the measurement model. The analysis includes outlier detection and identification capabilities, reliability and separability measures of integrated GNSS/INS systems. The performance of the system is also investigated with respect to diminishing satellite visibility conditions.

An eigenparameter analysis plays an important role in varied fields where a symmetric tensor is involved. This technique allows one to investigate the principal behaviors (i.e., magnitudes and orientations) of a physical phenomenon that can be represented as a rank-two symmetric tensor. In this study, an analytical approach that enables rotation- and translation-free estimations of the eigenparameters from a symmetric tensor is developed, with a goal to remove the errors associated with a neglect and/or miscalculation of reference frame variations during a dynamical process. Two numerical examples, one with simulated data and the other with real light detection and ranging (LIDAR) surveying data, have been carried out to demonstrate the capability of the proposed approach in estimating the principal strains from a symmetric strain tensor. The results reveal that the proposed approach is capable of giving a direct estimate for the strain tensor without being affected by the rotation and translation of the reference frame and thus produces a principal strain estimate of a higher quality.

The third Nanjing Yangtze River Bridge is a steel pylon cable stayed bridge. Such a structure is new in China and therefore brings new challenges to the work of control surveys. This paper describes the survey methods used for building and erecting the steel pylons and for construction of the steel tower. The survey methods adopted have proven successful and can be used as reference for similar projects in the future.

The performance of the new EGM2008 global geopotential model (GGM), over the northern Nile valley and delta in Egypt, has been evaluated. Over 305 global positioning system (GPS)/levelling stations, the standard deviation of the undulation differences has been estimated to be 0.23 m. Thus, it can be concluded that the EGM2008 is superior to earlier GGMs over the northern area of Egypt by a factor of 1.6. Moreover, four mathematical models have been investigated in order to incorporate local data sets with the EGM2008, leading to the conclusion that the first-order polynomial is the optimum one. An improvement of about 26% has been obtained after applying that regression model, and the standard deviation has been decreased to 0.17 m. As a result, the EGM2008 produces a crucial influence on integrated GPS surveys where the orthometric heights can be obtained without any additional costs. Such a practice presents a suitable alternative, from an economical point of view, to substitute the expensive traditional levelling technique particularly for topographic mapping.

This study selected five indexes to determine the relationship between data quality and positioning precision. These indexes are multipath on L1, multipath on L2, observations by cycle slips, clock offset, and clock stability. To reduce the number of common errors, six types of global positioning system (GPS) receivers are selected and set up in an Ultra-Short Distance Network at the National Measurement Laboratory, Taiwan, for 3 days. The first three indicators are calculated with the Teqc software, and the last two indicators are computed using the Bernese software. Moreover, the observations from three GPS tracking stations, namely, short baseline (about 25 km), middle baseline (about 150 km), and long baseline (around 2000 km), were downloaded from the Internet and processed using Bernese software. Analytical results indicate that clock stability and observations divided by cycle slips are found to be very important positioning factors. Clock offset and multipath effects do not significantly affect the GPS results.