Volume 5, Issue 3-4

This paper presents algebraic transformations of cadastral topological data. The traditional notation of data in attribute tables has been transformed into a matrix. The new approach supports algebraic transformations and has produced new descriptive forms for cadastral structures. In the second part of the paper, new topological data were transformed to a quantum metric to generate new descriptions of the neighborhood of sets of geometric elements relating to cadastral data. The resulting descriptions can be used in analytical processes such as neighborhood analyses and aggregation of areas.

Data snooping is one of the best established methods of gross error detection in geodetic data analysis. Since it is based on hypothesis testing, it requires the choice of levels of error probability. This choice is often, to some degree, arbitrary. If the levels chosen are too high, we run the risk of losing many good measurements that are not actually contaminated by gross errors. If the levels chosen are too low, we run the risk of leaving gross errors undetected. We propose to choose levels of error probability such that the desired parameters are best estimated in some sense. This can be done using the Monte Carlo method. We applied this procedure to a geodetic precision network from construction of a diversion tunnel. Depending on the stochastic model of the measurement process, we observed a gain of such an optimal choice of a few percent of the mean point standard deviation. This comes at a price of considerable computer time consumption. Even on a fast computer, a typical computation of a medium-sized geodetic network may take several minutes.

The dedicated satellite gravity missions CHAllenging Minisatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), and Gravity field and steady-state Ocean Circulation Explorer (GOCE) and their recent and expected Global Geopotential Models (GGMs) present new opportunities for the determination of gravity-related heights. Global Positioning System (GPS), the recent GGMs, and reference value W 0 are used to study the construction of different height systems and verify high-degree global geopotential models. This approach matches well with all theoretical basics of height systems. The presented numerical strategy is independent of height anomaly and geoid undulation computation. Using the International Terrestrial Reference Frame (ITRF) coordinates at 47 GPS stations of the Turkish National Vertical Control Network (TNVCN), the gravity potential values are computed based on new-generation GGMs. The computed gravity potentials are converted into different height systems. A global mean sea level represented by a geoid potential has been taken as reference for the heights. The GGM-derived geopotential numbers, Helmert orthometric, and Molodensky normal heights at the GPS stations are compared against the results from precise leveling. The numerical application demonstrates that three types of gravity-related heights can be determined with a similar accuracy level (12 cm). When long-term deformations such as tectonic activity and possible land subsidence/uplift effects on the heights of benchmarks of the TNVCN are taken into account, the obtained results are significant, and also, under the light of the dedicated satellite gravity missions, high-resolution GGMs such as EGM2008 have an important potential for the realization of a unified height system. The experimental study shows a datum bias of 38 2 cm between the TNVCN datum and the global datum.

Global Navigation Satellite System (GNSS) receivers provide diverse measurements, namely the code and carrier phase measurements. The measurements' rates between successive epochs are similar in both observables, but the change in carrier phase can be determined on one order of magnitude higher than the change in code. This diversity of measurements is used in the measurements domain to improve position accuracy. The code measurements are contaminated with diverse errors that fall in different frequency bands (i.e., multipath error, falls in a high to medium frequency band 0.1 to 0.003 Hz, whereas the ionospheric error is in the lower frequency band 0 to 1.2e4 Hz). As these errors have different frequency components, the methodology is presented whereby the multipath error can be mitigated through frequency domain processing. In this article, an innovative codesmoothing technique is used, namely multiresolution real-time (MRRT) code-smoothing technique. This technique is used in real-time scenarios to mitigate multipath error (medium to high frequency) and noise (high frequency) and to retain the ionospheric error (low frequency) untouched in the mitigation procedure. The proposed MRRT technique is superior to those in the literature in the way that it can effectively remove the multipath and noise in real-time scenario and retain the smoothed code unbiased with low variance.

This article deals with the approach to determining the geopotential numbers from Global Positioning System (GPS) satellite surveying and disturbing potential at a point on the Earth's surface. The disturbing potential was solved by the Brovar-type solution of Molodenskii's boundary value problem but in the context of the fixed problem. The solution is compatible with the techniques for smoothing of external field: removerestore techniques, residual terrain model, and use of high-resolution global geopotential models. This method provides an absolute geopotential numbers related to the so-called world height system. As an example, we calculate the disturbing potential model in Southern Brazil. The general condition of the sparse and absent gravity values is the main point to be solved. The absolute and relative accuracies of the quasigeoid model were tested vs. GPS/leveling data. Based on 99 GPS/leveling points, the mean value of fitting for the quasigeoid model was estimated near 0.032 m in the absolute view and 0.2 ppm in the relative view.

The wet delay is one of the most difficult sources of error to quantify in global navigation satellite systems (GNSS) due to its spatial and temporal variability. However, its estimation is vital in some applications, such as in Precise Point Positioning (PPP), network real-time kinematic and weather forecast. Such estimation is usually carried out for its projected component along the zenith, defined as the zenith wet delay (ZWD). Prediction of the ZWD is important if there is a break in its estimation, and in providing initial values for future processing. In this paper, prediction modeling for the ZWD is investigated. An autocorrelation study was first performed on ZWD data over three different days at the international GNSS service station ONSALA to provide an insight into the temporal correlations among ZWDs. The choice of this station was based on the availability of reliable ZWD data measured by water vapor radiometers, which provide a reference for assessment of the accuracy of predicted values. Results have shown that successive ZWD estimates are significantly correlated for up to 1.7 hours. Different trend and smoothing prediction models were then investigated. Since prediction of ZWD requires continuous data sequence, interpolation methods of possible missing ZWD values are discussed. The use of linear interpolation or a cubic Hermite polynomial was found to be sufficient for interpolation of ZWD. Test results of prediction models show that the single-exponential smoothing model was the best performer where ZWD estimates were forecasted with a root mean square error of less than 1 cm for up to two hours.

This study calibrates the footprint positions of 8.5 million Chang'E-1 and 8.8 million SELENE laser altimetry measurements against accurately known lunar laser reflector locations. The resulting datasets are used to estimate triaxial, biaxial and spherical models of the lunar figure based on the two datasets individually. The equatorial semi-major, minor and polar axes of the Chang'E-1 and SELENE solutions differ by 143 m, 3 m and 49 m respectively. The differences between their geometric centers and the lunar center of mass along the three axes are 186 m, 3 m, and 52 m. The complete laser altimetry datasets from the two missions reveal a lunar figure that is more spherical than previously thought. Furthermore, the Chang'E-1 and SELENE solutions are in better agreement with each other than either is with the ULCN 2005 lunar figure.