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EUREF'05 National Report of Switzerland New Developments in Swiss National Geodetic Surveying

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    EUREF'05: National Report of Switzerland

    New Developments in Swiss National Geodetic Surveying

    1D. Schneider, B. Vogel, A. Wiget, U. Wild, E. Brockmann, U. Marti, A. Schlatter

Abstract

    The efforts to establish a Swiss Combined Geodetic Network (CH-CGN) were continued with priority last year. Interesting results can be reported from a complete re-observation of the 3D reference network (LV95), from a newly developed Swiss geoid model (CHGeo2004) as well as from a gravity-related national height reference frame (LHN95). ?The performance of the permanent AGNES network and the positioning service (swipos) could be further improved by

    replacing the control center and by introducing a new concept of data distribution over the Internet. The integrity of the services is now being continuously monitored by a special device. The equipment is portable and therefore capable of monitoring the performance of the positioning service even in rural areas. The Permanent Network Analysis Center (PNAC) at swisstopo was enlarged and the co-operation with CODE at the Astronomical Institute at the University of Berne (AIUB) was intensified by consequently using synergies from software development and the analysis procedures.

    during the last years. These results confirm the high 1 Introduction quality and stability of the new national reference The implementation of the Swiss permanent GPS net-frame. Besides these quality aspects, investigations of work AGNES and the performance of the Swiss posi-tectonic movements with a magnitude of 1-2 mm/a and ?tioning system swipos were further improved last year. the determination of a kinematic model for the Swiss The existing control center was completely renewed terrestrial reference system CHTRS95 will be obtained ?and established for secure operation. swipos is now from the analysis of these data (project Swiss4D). available over the Internet, which reduces com-

    munication costs significantly when using GPRS. The objective of the European project ECGN is the

    combination of gravity field related measurements with A project was launched for the network optimization of the measurements of spatial geodesy. The fundamental AGNES. Some instable permanent stations will be dis-point Zimmerwald serves as a core station in this pro-placed. Besides the existing extensions towards Ger-ject. There is a national project called CH-CGN with a many (SAPOS) and Austria (APOS) based on data very similar objective. The ellipsoidal heights of the exchange across the border, the connection with a per-GPS reference network LV95, the orthometric heights manent network in northern Italy is planned. In a few of the new height network LHN95 and the geoid un-years a seamless VRS/RTK positioning system will dulations of the new geoid model CHGeo2004 are perhaps be available to the SDI user in Central Europe. combined in such a way that a consistent geodetic

    The data of both the Swiss permanent GPS network system is obtained. A first solution of CH-CGN with

    AGNES as well as of a subset of the European Per-the three data sets mentioned above was released in

    manent Network (EPN) are processed daily by the Per-March 2005. By using CHGeo2004, it is now possible

    manent Network Analysis Center (PNAC). In addition, to combine both levelling and GPS for the height deter-

    another set of data from permanent European stations mination in practice. The software HTRANS for the

     total delay (ZTD) is processed hourly, to derive zenithtransformation between official height system LN02

    estimates for numerical weather prediction in the scope and LHN95 was released. This was an important pre-

    of the European research project TOUGH. The requisite for the application of this technique in cadas-

    usefulness of the ZTD estimates from GPS for weather tral surveying.

    prediction has now been proved. A service level

    agreement was negotiated with the Swiss MetOffice 2 Fundamental Station Zimmerwald (MeteoSwiss) for the purchase of hourly ZTD data. The SLR observations at the geostation Zimmerwald The performance of the PNAC service is very reliable are being continued in close co-operation between the and satisfies the demands of the various users. Astronomical Institute at the University of Bern (AIUB)

    The milestone of Swiss geodetic surveying in 2004 was and the Swiss Federal Office of Topography rdthe 3 measurement of the National Reference Net-(swisstopo). In the worldwide rating of ILRS, Zimmer-

    work LV95 resulting in the new terrestrial reference wald ranks in the top ten stations with respect to the

    amount of collected data. It is the only station which frame CHTRF2004. A comparison of this solution with

    CHTRF95, which was the reference for the official tracks satellites on two wavelengths at a large scale.

    coordinates of the new national GPS network LV95, The multi-purpose telescope was used very intensively

    showed a good fit of less than 1 cm with the exception during the last months, not only for SLR but also for

    of two unstable stations which had to be replaced optical observations during the night using CCD array.

1 swisstopo (Swiss Federal Office of Topography), Geodesy Division, Seftigenstrasse 264, CH-3084 Wabern, Switzerland,

    Phone: ++41 31 963 22 56, Fax: ++41 31 963 24 59, e-mail: dieter.schneider@lt.admin.ch, Web-Site: http://www.swisstopo.ch

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    It is planned to replace the laser system, which has The time-series data will also be used for investigating reached its life span, sometime in the near future. long-term gravity variations. In addition, the Geodesy

    and Geodynamics Laboratory (GGL) at the ETH There are three GNSS receivers which track data con-Zurich installed a permanently running tidal gravimeter tinuously. A Trimble 4700 is operating on the main in Zimmerwald. Relative gravimetric measurements station of the national reference network AGNES. Its between the two sites are performed repeatedly in order antenna is mounted on a stable mast. Besides this, GPS to monitor gravity on both sites. No significant long-and GLONASS satellites are being tracked by an Ash-time gravity variations have been observed until now. tec Z18 and a Javad Legacy receiver, which both pro-The results also fit very well with earlier data collected vide data for the IGS network. in 1997 [Marti and Richard, 2005].

    In March 2005 a levelling line from a stable node of

    the national height network LHN95 in Berne to the

    Zimmerwald site was re-measured after a 10-year time

    interval. No significant relative height changes between

    Bern, the metas facility in Wabern and the geostation

    were found except a few local instabilities of some

    markers in Zimmerwald.

    3 Gravity Field and Geoid

    The establishment of a national gravity network is now

    a basic assignment of national geodetic surveying. This was not the case in Switzerland before, because the

    basic gravity network was traditionally regarded as a Fig. 1: Absolute gravity measurements (FG5) scientific observation network established and main-Absolute gravity measurements have successfully been tained by the Swiss Geodetic Commission. Up to now,

    there was no need for intensive gravity measurements carried out twice on the gravity station in 2004 [Marti

    (except for UELN and EVRS) because the official and Richard, 2004] and in March 2005 in co-operation

    national height network (LN02) was a pure levelling with the Swiss Federal Office of Metrology and Accre-

    network, adjusted without taking into account any ditation (metas) using an FG5 free-fall device. The

    gravimetric corrections. same instrument is being operated almost continuously

    at a stable site of the metas laboratory in Wabern, about

    10km from Zimmerwald (Fig. 1).

    Freiburg

    Wangensibl

    BaselweinPratteln

    ZürichporrKoblachmontTisis

    galgbiel

    menzWabernZimmerwaldChuradrfpayethunInterlakenRingBäzbergEngadinAndermattGuspisbachJungfraujochLausanne

    aquamaloBrigpfynversmnthM.Ceneri

    mend

    Milano

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    Fig. 2: Concept for a new National Gravity Network LSN2004

    large dots: absolute gravity stations (0 order; including connecting stations to neighboring countries); small

    dots: relative stations (1st order)

    In the context of creating a new national height refer-use of this equipment for geodetic surveying in the ence frame LHN95 (Chapter 6), swisstopo has tried to coming years.

    establish gravimetric surveying as a part of its own re-An integral concept for a new countrywide National sponsibility. A small team of surveyors was trained in Gravity Network LSN2004 was established [Marti and the field of gravimetry so that relative measurements Schneider, 2005] at swisstopo. The network (Fig. 2) using gravimeters and software from ETH Zurich could contains existing absolute and relative measurements be performed independently [Schlatter et al., 2005]. which were collected by geodesists from ETH Zurich The Swiss Federal Office of Metrology and Accredita-in the nineties. In order to check old absolute data and tion (metas) gathered valuable know-how in the field to replace instable sites, new absolute as well as rela-of absolute gravity measurements during the last few tive measurements will be gathered within the next few years. It owns and operates an FG5 free-fall device for years. Extensions will also be measured to neighboring metrological purposes. The instrument is compared absolute stations in Germany, Austria and Italy. Finally, regularly in European calibration campaigns and meets a new network adjustment will be performed, all international standards. A service level agreement with stations will be documented and the results will be this federal institute was drawn up which will allow the stored in a data base and made available to the public.

    55 m

    54 m

    53 m

    52 m

    51 m

    50 m

    49 m

    48 m

    47 m

    46 m

    45 m

    44 m

Fig. 3: Swiss National Geoid Model CHGeo2004

    The new national geoid model CHGeo2004 of Switzer-resulting residuals between the astrogeodetic, the gravi-land (Fig. 3) was released [Marti, 2004, c] in March metric and the GPS/ levelling geoid model. The official 2005. It was determined by combining gravity, vertical geoid model CHGeo2004 which was released to the deflections and GPS/levelling observations. Its accura-surveyor community is primarily based on GPS/level-cy (1 σ) is in the order of 2-3 cm as could be verified ling, since the geoid model is mainly used for GNSS by comparisons with independent data. Besides the height determination with the aim of being consistent standard models (topography and global geopotential with levelling and the orthometric system LHN95. For model), a simple 3D density model of the Earth's crust reasons of comparison and for the data exchange with was introduced for the reduction of the observations. neighboring countries, a quasi-geoid was also deter-The computation method was basically a least-squares mined. Finally, transformation routines HTRANS be-collocation with a slight modification: the parameters tween the national height systems LHN95 and LN02 of the covariance function were chosen to minimize the

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and the European Vertical System (EVS) were de-

veloped and released [Marti, 2003].

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    Austria for APOS [Wild et al., 2003; Wild and Grünig, 4 Permanent GPS Network AGNES and 2005]. ?Positioning Service swipos Some of the AGNES stations do not fulfill all require-The permanent GPS network AGNES has been operat-ments (e.g. distance to immediate neighbors, stability ing since 1997. After a two-year pilot phase with only of the site, undisturbed satellite reception). One station 11 stations, the network was completed between 2000 (JUJO), for example, is located on the Jungfraujoch at and 2002 to nationwide coverage by adding 19 other an altitude of 3580 m, which is suitable for scientific stations. This configuration of a total of 30 stations (in-purposes (atmosphere research) but not as a reference cluding Pfänder, A) has been operating permanently station for a VRS network because of the large height since January 2003. It serves various purposes such as difference to its neighbors. ?real-time positioning (swipos), national surveying, A proposal for optimizing the network constellation monitoring tectonic movements and collecting ZTD within the next two years was decided on. It includes data for atmosphere research and meteorological the establishment of two new stations (Zermatt and prediction. [Wild et al., 2005] Brienz in addition to JUJO, which will no longer be In the meantime, the data flow of 9 selected German used for VRS/RTK) and the displacement of two others. and Austrian stations have been added to the system so The coverage towards the southeast will be extended that a seamless positioning service RTK/VRS can also by accessing the data stream from four additional be provided for the area where these neighboring coun-stations in Lombardia (Istituto di Ricerca per l’Eco-tries meet. In exchange, data from a few Swiss stations logia e l’Economia Applicate alle Aree Alpine are sent to Germany for its SAPOS system and to (IREALP)) [Grünig and Wild, 2005].

Fig. 4: Optimization of the AGNES network (project 2005-06)

    area of coverage (radius of circles: 30 km)

    Besides the mentioned drawbacks of the AGNES net-In fall 2004, the AGNES control center at the Federal work constellation, the operation and maintenance of Office of Informatics and Telecommunication (BIT) the permanent network did not pose any problems last was adapted to the newest technological standards. All ?year. All requirements with respect to the standards of AGNES and swipos servers were moved into a so-integrity and accuracy were fulfilled. The stations were called "demilitarized zone" (DMZ) where they are visited once a year as planned, and there were no better protected against any attacks over the Internet. In damages to be reported. addition, those servers which are indispensable for a ?secure operation of the positioning service swipos

    were installed redundantly (Fig. 5).

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    ?Fig. 5: AGNES/swipos Control Center

    ?The DGPS service swipos-NAV using FM/RDS ; The NTRIP client will have access to a source table broadcasting has been operational since 1996. The with all available data streams in real time together service on FM/RDS was discontinued at the end of with their source ID and additional information such 2004 because the technology had reached its life-time. as approximate position, the system or network and The reference station in Zurich was dismantled at the the data format.

    beginning of 2005. The same positioning service is ?Besides the existing service over GSM, the swipos now available free of charge (except for communi-positioning system has also been available over the cation costs) using GSM and GPRS/NTRIP. Internet since January 2005. The source table is acces-Together with the renewal of the AGNES control sible from: http://www3.swisstopo.ch:8080. Commu-

    center, the required conditions for disseminating GPS nication costs can be reduced significantly by using corrections over the Internet using the NTRIP protocol GPRS since the costs are based on the amount of data were established. The system is based on a 3-phase and no longer on the time required for the transmission architecture (Fig. 6): of the data.

    ; A random GPS data source (reference station or per-The development of a monitoring device for assessing manent network) is allocated to an NTRIP server. the performance of the real-time positioning service ?The data is forwarded to an NTRIP caster. swipos-GIS/GEO (project VRS monitoring) was com-

    pleted last year. The device is able to automatically log ; All data streams available at the NTRIP caster can

    on to the service and to monitor the VRS/RTK coordi-be accessed from NTRIP clients (users). Users are

    nate solutions by comparing them to a known reference required to authorize themselves with their user

    position. name and password if the data streams are liable to

     costs. In order to provide data simultaneously to a

    number of users, the data streams are multiplexed.

Fig. 6: NTRIP system architecture

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    ?The requested accuracy standard (1 σ) for swipos-2001 in order to contribute to numerical weather pre-GIS/GEO is 2cm (position) and 4cm (height). The diction by providing zenith total delay (ZTD) estimates. system is permanently mounted on the roof of the This activity is embedded in the European project swisstopo building in Wabern. It serves as the perma-TOUGH (Targeting the Optimal Use of GPS ? nent integrity monitoring system of swiposVRS. In Humidity). With time delays of below 1:45 hours, the order to investigate the VRS performance in other local ZTD estimates are delivered to MeteoSwiss and to the areas, the system can be temporarily displaced to UK MetOffice database.

    another location. The main improvements realized during 2004 were

    setting up a parallel operation which sped up the pro-

    cessing time significantly, and introducing ambiguity-

    fixed solutions for all "Swiss" (short) baselines, which

    resulted in an improved quality of estimates (station

    coordinates and ZTDs). Ambiguity resolution enables a

    coordinate repeatability for 1-hour solutions of better

    than 1 cm horizontally and 3 cm vertically. Ambiguity-

    free solutions are worse by a factor of approximately 6

    (horizontally) and 3 (vertically). An improved quality

    of hourly site coordinates is primarily important for the

    detection of station problems. At present the improve-

    ment for the ZTD estimates is small because the station

    coordinates are kept fixed for ZTD retrieval. In the

    future it should be possible to estimate the two para-

    meter types "station coordinates" and "ZTD estimates"

    simultaneously.

    A minor modification was the use of IGS ultra-rapid

     orbits with update rates of 6 hours. Due to these im-

    provements, the delays of our near real-time data pro-Fig. 7: Field test of VRS/RTK using a monitoring cessed with Bernese V4.2 (label "LPT") and real-time device ? using GPSNet (label "LPTR") are data from swipos

    considerably better than the requested standard delays 5 Analysis of Permanent GNSS Data (1:45 h; Fig.8). An example of available data can be Swisstopo has been operating a GNSS permanent net-found under http://www.knmi.nl/samenw/cost716/stat/ work analysis center (PNAC) since 1996. Presently gpsdly_tser.html. swisstopo contributes with LPT and three different network configurations (EUREF-PN, LPTR solutions. Although the LPTR could be de-AGNES and GPS meteo) are being processed (daily livered in less than one hour, the current dataflow is and hourly respectively). Since September 2004, the presently designed for 1-hour delivery only. analysis of the networks has been associated closely The quality of the LPTR solution was considerably im-with the activities at the CODE analysis center of IGS proved with the installation of the newest processing located at the Astronomical Institute at the University version, where the dry Niell mapping for the ZTD of Berne (AIUB). One employee of swisstopo is inte-estimates was implemented. Plots of all different ZTD grated part-time in the CODE group which allows estimates (GPS NRT and GPS real real-time) are synergies to be shared between the two institutes. available under http://www.swisstopo.ch/en/basics/geo/ There is a contribution in this volume which covers this permnetworks/pnac/timeseries.html. The plots are up-field in greater detail [Schaer et al., 2005]. dated every hour. The AGNES network, together with a subset of the

    EUREF permanent network (a total of about 70 sites),

    is being processed on an hourly basis since December

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Fig. 8: Delay for the arrival of 75% of the data

    A special investigation was carried out in the field of GPS tomography [Troller, 2004]. In co-operation with

    the Geodesy and Geodynamics Laboratory GGL at

    ETH Zurich, two weeks of GPS data from October

    2004 were analyzed using the AWATOS software

    package in order to generate tomographic information from GPS [Troller et al., 2004, a]. The results were

    very promising. A continuous generation of tomo-

    graphic information from GPS in near real-time is not yet possible because of non-optimized processing times of the GPS tomography computation. Furthermore,

    near real-time (delay < 1h) meteorological data is not available free of charge. The transition of the opera-tional NRT processing software from Bernese V4.2 to Bernese V5.0 is scheduled from March 2005 until mid-year.

    6 National Reference Frames Fig. 9: Re-measurement of the Swiss GPS Refer-

    ence Network LV95 (CHTRF2004) A second complete re-measurement of the National

    GPS Reference Network LV95 took place in 2004. The A project for the establishment of a new National campaign was combined with the second re-measure-Height Network (LHN95) has been under development ment of the monitoring network "NEOTEKTONIK since 1996 [Schlatter, 2005]. By March 2005 the final NORDSCHWEIZ", which was installed in 1988 for the kinematic adjustment of this network using levelling investigation of tectonic movements in northern data measured over a time period of more than 100 Switzerland on behalf of the National Cooperative for years, together with gravity, was carried out. Finally, a the Disposal of Radioactive Waste (NAGRA). More combined geodetic network adjustment CH-CGN was than 288 GPS stations were measured within eleven performed by using these orthometric heights together campaigns of one week each (Fig. 9). A total of 5400 with GPS-derived heights and data from the geoid hours of GPS tracking, including the data of the model. AGNES permanent network, were processed in an al-

    The results, which will be presented at this symposium most automatic manner. There is a contribution in this

    [Schlatter et al., 2005, are very promising as far as the volume which covers this work in detail [Brockmann et

    application of GNSS height determination is concerned. al., 2005].

    Discrepancies on the cm level on the Swiss Plateau and

    below 5 cm in the Alps are to be expected (Fig. 10)

    when GPS-derived heights will be compared with

    orthometric heights from LHN95 after applying the

    new geoid model "CHGeo2004".

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    ing authorities of the cantons is now operational. The

    actual tasks which remain are migrating the large 1 cmamount of data and instructing the internal and external full accuracy lower accuracyusers [Wild et al., 2005].

    The project "Swiss4D", with the objective of obtaining

    a kinematic analysis of geodetic observation data for

    investigating crustal deformations, could only be con-

    tinued with very limited resources. A research project

    with the Geodesy and Geodynamics Laboratory GGL

    at the Federal Institute of Technology in Zurich (ETH)

    was completed. The main outcome of this project is

    documented in the final report [Egli, 2004; 2005; Egli

    et al., 2005]. The findings were introduced in the soft-

    ware ALSC-Strain (adaptive least-squares collocation). This tool can be used for the detection of stable or de-Fig. 10: GPS-height residuals of the combined adjust-formed zones from 3D velocity fields which can be ob-

    ment CH-CGN (orthom. heights LHN95, tained from repeated GPS measurements of control net-

    geoid CHGeo2004, GPS heights CHTRF2004) works (LV95), permanent network analysis (AGNES)

    and from kinematic adjustments of levelling networks

    (LHN95). The method and the software ALSC-Strain 7 Geodetic Projects will now be applied to the large data set of the repeated The "Control Point Data Service", which is under de-GPS measurements CHTRF2004, of the NAGRA mon-velopment at swisstopo, will make all geodetic control itoring network "NEOTEKTONIK NORDSCHWEIZ" point data available over the Internet. The graphical and of the time series from AGNES (Fig. 11). user interface for the capture, revision and administra-

    tion of the control points by swisstopo and the survey-

Fig.11: Strain rates (nstrain/a) in northern Switzerland predicted using ALSC-Strain (interpolated in a 5-km

    grid) [preliminary results, courtesy O. Heller (GGL, ETHZ)]

    The joint project for testing differential SAR interfero-levellings are available. The differences of velocity metry in two test areas in Switzerland with the Swiss normalized by a common mean between levelling and GAMMA Remote Sensing Company was concluded INSAR reached values between -0.5 and +0.6 mm/a, [Wegmüller, 2005]. Eleven scenes shot between 1992 which are far larger than the standard deviations of and 2000 in the region of Zurich and Central Switzer-0.1 mm/a for the vertical velocities from levelling. land were analyzed. The results are rather disillusion-They are most likely caused by noise in the INSAR ing. In a focus on the area of Zug, where long-time data.

    series of deformations from repeated terrestrial meas-Various contributions from geodesy towards establish-urements show subsidence rates of a few mm/a, no ing of a National Spatial Data Infrastructure NSDI in significant deformations could be detected from the Switzerland are coordinated in a project GRIPS (Geo-INSAR analysis. In a more extended area, comparisons detic Reference data as Internet Products and Services) with vertical deformations from repeated national [Wiget, 2005].

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