Tomasz Liwosz

Integrated precipitable water vapour measurements at Polish Polar Station Hornsund from GPS observations verified by aerological techniques

Abstract We present results of the comparison of integrated precipitable water measurements from GPS solution and aerological techniques: CIMEL-318 sun-photometer and radiosoundings (RAOB). Integrated Precipitable Water (IPW) - important meteorological parameter is derived from GPS tropospheric solutions by known procedure for GPS station at Polish Polar Station, Hornsund (Svalbard). The relation between 2 m temperature and the mean temperature of atmosphere above, used to convert from wet part of tropospheric delay (ZWD) to IPW, has been derived using local radiosonde data at Ny Alesund. Sunphotometer data have been provided by AERONET. Quality of dedicated tropospheric solutions has been verified by comparison with EPN tropospheric combined product. Several IPW comparisons and analyses lead to determination of systematic difference between techniques: GPS IPW and sunphotometer data (not present in case of RAOBs). IPW measured by CIMEL is on average 5% bigger (0.5 mm) than IPW from GPS. This bias changes seasonally and is a function of atmospheric temperature what signals some systematic deficiencies in solar photometry as IPW retrieval technique. CIMEL IPW show some temperature dependent bias also in relation to radiosoundings.

Integrated precipitable water from GPS observations and CIMEL sunphotometer measurements at CGO Belsk

Abstract This paper describes results of integrated precipitable water co-located measurements from two techniques: GPS solution and CIMEL-318 sunphotometer. Integrated Precipitable Water (IPW) is an important meteorological parameter and is derived from GPS tropospheric solutions for GPS station at Central Geophysical Observatory (CGO), Polish Academy of Sciences (PAS), Belsk and compared with sunphotometer (CIMEL-318 device by Cimel Electronique) data provided by Aerosol Robotic Network (AERONET). Two dedicated and independent GPS solutions: network solution in the sub-network of European Permanent Network (EPN) and precise point positioning solution have been made to obtain tropospheric delays. The quality of dedicated tropospheric solutions has been verified by comparison with EPN tropospheric combined product. Several IPW comparisons and analyses revealed systematic difference between techniques (difference RMS is over 1 mm). IPW bias changes with season: annual close to 1 mm IPW (and semi-annual term also present). IPW bias is a function of atmospheric temperature. Probable cause of this systematic deficiency in solar photometry as IPW retrieval technique is a change of optical filter characteristics in CIMEL.

Verification of the Polish geodetic reference frame by means of a new solution based on permanent GNSS data from the years 2011-2014

Abstract The new solution for the Polish geodetic primary GNSS network was created to verify the currently used reference frame (PL-ETRF2000). The new solution is based on more GNSS data (more daily observation sessions included, a longer data timespan, GLONASS observations added) which were processed in a newer reference frame (IGb08) according to up-to-date methodology and using the latest version of Bernese GNSS Software. The new long-term solution (spanning 3.7 years) was aligned to the IGb08 reference frame using a minimum constraints approach. We categorized Polish reference stations into two categories according to their data length. We obtained good agreement of the new solution with the PL-ETRF2000: for most stations position differences did not exceed 5 mm in horizontal, and 10 mm in vertical components. However, for 30 stations we observed discontinuities in position time series, mostly due to GNSS equipment changes, which occured after the introduction of PL-ETRF2000. Position changes due to the discontinuities reached 9.1 mm in horizontal components, and 26.9 mm in vertical components. The new solution takes into account position discontinuities, and in addition also includes six new stations which were installed after the introduction of the PL-ETRF2000. Therefore, we propose to update the currently-used reference frame for the Polish geodetic primary network (PL-ETRF2000) with the new solution. The new solution was also accepted by the EUREF Technical Working Group as a class A solution (highest accuracy) according to EUREF standards.

Geodetic and Geodynamic Studies at Department of Geodesy and Geodetic Astronomy Wut

Abstract The article presents current issues and research work conducted in the Department of Geodesy and Geodetic Astronomy at the Faculty of Geodesy and Cartography at Warsaw University of Technology. It contains the most important directions of research in the fields of physical geodesy, satellite measurement techniques, GNSS meteorology, geodynamic studies, electronic measurement techniques and terrain information systems.

Assessment of continental hydrosphere loading using GNSS measurements

Abstract Presented paper is dedicated to problems of deformation of the Earths crust as a response to the surface loading caused by continental waters. The aim of this study was to specify areas particularly vulnerable to studied deformation and to compare calculated and observed displacements. Information of the continental water volume was taken from the WaterGAP Global Hydrological Model. Calculated values of the deformations were verified with the results obtained with programs SPOTL and grat. Vertical deformations were almost 10 times higher than the deformation in the horizontal plane, for which reason later part of the paper focuses on the former. In order to check agreement of the calculated and observed deformation 23 stations of International GNSS Service (IGS) were selected and divided into three groups (inland, near the shoreline and islands). Before comparison outliers and discontinuities were removed from GNSS observations. Modelled and observed signals were centred. The analysed time series of the vertical displacements showed that only for the inland stations it is possible to effectively remove displacements caused by mass transfer in the hydrosphere. For stations located in the coastal regions or islands, it is necessary to consider additional movement effects resulting from indirect ocean tidal loading or atmosphere loading.

EFFECT OF THE GLONASS-SPECIFIC RECEIVER ANTENNA PHASE CENTER CORRECTIONS ON THE RESULTS OF EUROPEAN REGIONAL GNSS NETWORK

ABSTRACT In the paper I investigated the effect of the GLONASS-specific receiver antenna phase center corrections on the results of a regional permanent GNSS network. I made analysis, using Bernese GPS Software 5.0, of GPS-only and GPS-GLONASS (GNSS) observations collected at permanent sites in Europe. Two types of GNSS solutions were computed: with GPS phase center corrections used for observations of both systems, and with the system specific corrections for observations of the respective system. The Bernese software was modified accordingly to use GLONASS specific corrections for GLONASS measurements. The results, i.e., coordinates and tropospheric zenith delays were analyzed and compared between computed solutions. Introducing GLONASS-specific receiver antenna phase center corrections did not improve the repeatability of the GNSS coordinate time series. Differences of coordinates between the two GNSS solutions were highly repeatable but offsets (biases) were observed; maximum bias for horizontal component was 1 mm and 4 mm for up component. Similar biases were observed for stations with the same antenna models. Periodic signal with a period of 1/3-year was found in difference time series between GPS and GNSS solutions for north component with a maximum peak-to-peak amplitude 2.8 mm. The periodic signal was attributed to GLONASS.