Katarzyna Stepniak

Field Tests of L1 Phase Centre Variation Models of Surveying-Grade GPS Antennas

GNSS antenna electrical phase center variability is a source of errors in precise geodetic measurements, particularly in reference frame maintenance, satellite precise levelling, deformation monitoring, the establishment of geodetic control networks, geodynamic research, etc. It has a considerable influence on the precision and accuracy of the resulting coordinates. Previous research shows that changing the antenna on the monitored point often results in a considerable bias in the derived height coordinate component. In theory, if electrical phase center is sufficiently modeled, antenna changes should have negligible effect on coordinates. We present the analysis of the influence of the GPS antenna models on the resulting marker position. Numerical tests are based on field measurements. The GPS data collected at the test baseline were processed using Bernese GPS Software Version 5.0. The research shows that the IGS and NGS phase center variation models for some types of the surveying (rover) antennas are still imperfect and are contaminated by constant errors, which may exceed even ± 5 mm for horizontal coordinates components and ± 25 mm for vertical ones.

Determining normal heights with the use of Precise Point Positioning

In this paper, the authors analysed the Precise Point Positioning (PPP) performance in determination of normal heights using observations from a test network consisting of ten sites. One-week observation interval was processed using standard PPP approach and Multi-Station PPP (MS-PPP) with ambiguity resolution using the NAvigation Package for Earth Observation Satellites v. 3.3.1 software. In post-processing corrections like the Earth rotation parameters, ocean loadings, antenna phase centre offsets and variations etc. needed to obtain the most accurate position were utilised. By processing the various lengths observing sessions (1 hour, 30 minutes, 15 minutes) the authors examined the degradation of the position determination precision with shortening the observation time. In the study both high-end receivers used most often at CORS, as well as commercial two-frequency receivers were utilised. Normal heights were obtained using PL–geoid–2011 model. The results of the research show that PPP is a viable alternative for Relative GNSS Positioning in the case of GNSS levelling.

Application of the Undifferenced GNSS Precise Positioning in Determining Coordinates in National Reference Frames

Abstract In high-accuracy positioning using GNSS, the most common solution is still relative positioning using double-difference observations of dual-frequency measurements. An increasingly popular alternative to relative positioning are undifferenced approaches, which are designed to make full use of modern satellite systems and signals. Positions referenced to global International Terrestrial Reference Frame (ITRF2008) obtained from Precise Point Positioning (PPP) or Undifferenced (UD) network solutions have to be transformed to national (regional) reference frame, which introduces additional bases related to the transformation process. In this paper, satellite observations from two test networks using different observation time series were processed. The first test concerns the positioning accuracy from processing one year of dual-frequency GPS observations from 14 EUREF Permanent Network (EPN) stations using NAPEOS 3.3.1 software. The results were transformed into a national reference frame (PL-ETRF2000) and compared to positions from an EPN cumulative solution, which was adopted as the true coordinates. Daily observations were processed using PPP and UD multi-station solutions to determine the final accuracy resulting from satellite positioning, the transformation to national coordinate systems and Eurasian intraplate plate velocities. The second numerical test involved similar processing strategies of post-processing carried out using different observation time series (30 min., 1 hour, 2 hours, daily) and different classes of GNSS receivers. The centimeter accuracy of results presented in the national coordinate system satisfies the requirements of many surveying and engineering applications.

Validation of regional geoid models for Poland: Lower Silesia case study

Nowadays, the high accuracy of the horizontal coordinates obtained from GNSS measurements is easily achievable. On the other hand, the precision of GNSS-derived heights is clearly lower. Nevertheless, state of the art measurement technique, field surveying equipment, data processing software and algorithms allow achieving millimeter-level accuracy for ellipsoidal heights. However, in order to obtain the normal heights from GNSS measurements, the application of precise quasigeoid model is necessary. Nowadays, there are several available guasiqeoid models covering the area of Poland, e.g. PL-geoid-2011; EGM2008; “leveling geoid 2001”; European Gravimetric Quasigeoid model EGG2008. In addition, a high-accuracy regional quasigeoid model for the Lower Silesia region was developed in 2015. In this paper, we investigate performance of the application of the selected quasigeoid models to satellite leveling on the basis of test precise leveling network established at the area of Lower Silesia in Poland. In this region, simultaneous precise geometric and satellite leveling measurements were carried out on over 1000 km of leveling lines and over 100 GNSS sites. The results show that the current relative accuracy of the most accurate geoid models is better than