1 Positioning

Contribution of CODE to the ITRF

by S. Schaer, D. Dach, M. Meindl, U. Hugentobler and G. Beutler

The global GPS data analysis at CODE is done on the basis of observations from the IGS tracking network. GPS orbits, Earth rotation parameters (ERPs), station coordinates, troposphere delays, and other specific parameters, are estimated daily in the same parameter adjustment process. For a complete documentation, we refer to the annual reports for the years 1999, 2000, 2001 (Hugentobler et al 2000, 2001, 2003). In the following we address coordinate aspects. Orbits and atmosphere issues are addressed in Section 2, ERP’s in Section 5.

The number of stations processed in the global analysis was increased from 100 to 120 in June 2000 and to 150 in July 2002. Care is taken to process a homogeneously distributed set of global stations considering in particular very remote sites. A station once included into the processing scheme is, whenever possible, not replaced by an other one in order to gain uninterrupted coordinate time series. Seven daily solutions are combined using the full covariance information in order to generate a weekly station coordinate and ERP solution. The geodetic datum is defined with respect to approximately 46 IGS core stations by a minimum constraint condition (three rotations). A SINEX file is generated and made available. It contributes to the solutions of the IGS Global Network Associate Analysis Centers (GNAACs) as well as to the weekly IGS combined SINEX solution generated at the IGS Reference Frame Coordination Center (Natural Resources Canada, NRCan) where the IGS reference frame (the IGS realization of the ITRF reference system) is maintained.

In March 2000 CODE submitted its contribution to the ITRF2000 reference frame realization (see Altamimi et al, 2002). The solution was produced using GPS observations spanning a time interval of more than five years and includes coordinates and velocities for 164 stations. Fig 1.1 shows a comparison of the computed velocity vectors (arrows) with the ITRF97-derived vectors (lines) for a solution that is constrained to the ITRF97 reference frame. Finally, CODE is contributing to the IERS SINEX Combination Campaign with weekly SINEX files realigned to IGS00 covering the year 1999 (see Section 5).

Fig. 1.1: Horizontal station velocities derived from five years of GPS data from the IGS tracking network (arrows) and from ITRF97 (lines).

EUREF Activities at CODE

by S. Schaer, M. Meindl and U. Hugentobler

The IAG Subcommission for the European Terrestrial Reference Frame (EUREF) coordinates the operations of currently more than 130 permanent GPS tracking stations. The data is analyzed by currently 16 Analysis Centers. Until July 25, 1999, the individual subnetwork solutions were combined into one unique EUREF SINEX solution by the CODE Analysis Center (at AIUB). In July 1999 the Bundesamt für Kartographie und Geodäsie (BKG, Frankfurt a. M., Germany) took over this responsibility and became the new EUREF combination center. The EUREF combined SINEX solution is sent every week to the IGS for inclusion into the IGS densified network solution. Details may be gathered from Bruyninx et al. (2002).

In September 2001 some of the processing standards were changed within EUREF. The recommended elevation cutoff angle was lowered from 15 to 10 degrees, elevation-dependent observation weighting was applied, and the Niell mapping function was introduced.

CODE is one of the EUREF Analysis Centers. It is responsible for a subnetwork of about 40 EPS stations. Weekly station coordinate results in SINEX format as well as daily sets of troposphere zenith path delay values for the processed stations are delivered to the EUREF. Apart from our official EUREF solution, eight additional test solutions are computed for comparison purposes. These test solutions include solutions for validating new, refined options such as consideration of low-elevation data, estimation of tropospheric gradient parameters, but also solutions to compare rapid and final orbit products from IGS and CODE.

Analysis of Permanent GPS Networks at swisstopo

by E. Brockmann and D. Ineichen

The permanent GPS networks analysed at swisstopo are shown in Table 1.1:

Network	Stations	Analysis interval	Delay
EUREF Subnet	20 (1 AGNES)	daily	21 days
AGNES + subnet EUREF	65 (29 AGNES)	daily	21 days
AGNES + subnet EUREF	63 (29 AGNES)	hourly	0.5 hours

Table 1.1: Routine GPS data analyses at swisstopo

The data of the Automated GPS Network of Switzerland (AGNES) are being monitored since the end of 1998 on a daily basis and since December 2001 on an hourly basis (see section “GPS Meteorology: Contributions of swisstopo to COST-716”). In addition to the 29 AGNES sites, 40 EUREF sites are processed with the Bernese GPS Software Version 4.2 (Hugentobler et al., 2001) using the final IGS orbit products with a time delay of 3 weeks. This monitoring allows the detection of possible site movements. An updated multi-year solution, where the site coordinates and velocities are solved for, is automatically generated having processed an additional week of data. The results are e.g. estimated velocity and repeatability plots. They are available in the survey section of http://www.swisstopo.ch/ . As an example the horizontal velocities relative to Zimmerwald are shown in Fig. 1.2:

Fig. 1.2: AGNES: Horizontal site velocities in ITRF00 (relative to Zimmerwald) for sites with a “history” of more than 0.5 years (time span summer 1998 – end 2002)

National GPS Reference Network LV95

by B. Vogel, E. Brockmann and A. Wiget

Fig. 1.3: GPS reference network LV95 (main points, densification and connections to neighbouring countries) and AGNES stations in 2003

Densification

Several publications have already dealt with the concept and results of the Swiss national reference network LV95 in detail. In the meantime the planned densification covering the entire country has also been carried out (Schneider et al., 2002). This was promoted accordingly to meet the growing demands of various users (large engineering projects, cadastral survey, etc.). The densified network features station intervals of 10-15 km in the Central Plateau and 15-20 km in the Alpine area. In view of the simultaneously developed AGNES permanent network a further densification is not planned.

Today the new complete network consists of the following station categories:

Reference Network	Number of points	Mean distance [km]	RMS [mm] N / E / U
EUREF EUREF (perm.)	5 ^1 2 ^1	150	2 / 2 / 5
AGNES (perm.)	29 ^1	50	2 / 2 / 5
LV95: main points	104 ^1	15 - 25	10 / 10 / 30
LV95: densification	102	10 - 20	10 / 10 / 30
Transformation: fiducial points old LV03 <-> new LV95	~ 250	5 - 20	20 / 20 / -

¹) including Austrian station Pfänder

Table 1.2: National GPS reference networks (EUREF, AGNES, LV95): Number of points, density and corresponding accuracy

Maintenance, re-measurements and kinematic investigations

The GPS network LV95 is maintained on a regular basis. The sites are visited every five years, and a re-measurement is planned every five to ten years. The first re-measurement took place in 1998 (CHTRF98) and showed excellent agreement with the first determination (CHTRF95) (see Table 2). The selection of stations also allows kinematic studies of the earth's upper crust (project Swiss 4D) (Wiget et al., 2003). First investigations of the coordinates, however, have not shown any significant coordinate changes due to horizontal crustal movements. Further investigations based on re-measurements are planned for 2004.

Number of points	Horizontal position	Height	Scale
	RMS [mm]	RMS [mm]	[ppm]
138	3.3	12.7	-0.05

Table 1.3: Repeatability of GPS network LV95: comparison of the reference frames CHTRF95 and CHTRF98

Combining Levelling with GPS Measurements and Geoid Information:
Recent activities for the new national height system (LHN95) of Switzerland

by A. Schlatter, E. Brockmann, U. Marti and D. Schneider

The use of GPS for height determination and for replacing expensive levelling measurements in regions where maximum accuracy is not needed requires a height system in which levelling and GPS in combination with geoid information lead to compatible results. The new national height system of Switzerland, LHN95, is based on geopotential numbers and orthometric heights obtained from a rigorous kinematic adjustment of all available levelling data since 1902 and should fulfill this task (Schlatter and Marti, 2002; Marti et al., 2002a).

But even with this new (orthometric) height system, full consistency between levelling and GPS measurements has not yet been reached. This consistency between orthometric heights, ellipsoidal heights and the geoid can be verified on GPS/levelling stations. Until now, some 150 GPS stations are connected to the national levelling network (see Fig. 1.4). The discrepancies are in the order of several mm up to 2 dm. They are most likely caused by random and systematic errors in all three data sets.

Fig. 1.4: Residuals at GPS/levelling stations (as of January 2003)

Besides regional effects, the residuals show mainly a systematic trend along the north-south axis. The aim is to obtain corrections for the data sets in a combined adjustment. The method of distributing the residuals using the complete covariance matrices for GPS, levelling and the geoid model was first presented in (Marti et al., 2001). The largest part of the discrepancies was assigned to a correction of the geoid. Therefore, swisstopo realized that an improvement of the geoid model would be one of the most important tasks in the next few years. In the scope of a project called CHGeo2003 work has already been undertaken to continue the densification of the GPS/levelling stations (Schneider et al., 2002). This is a further step towards combined geodetic networks as was proposed in EUREF Resolution No.2 in 2002 (Ihde et al., 2002).

The Automated GPS Network for Switzerland (AGNES)

by U. Wild, R. Hug, S. Grünig and E. Brockmann

During the years 2000 and 2001 the pilot configuration of 10 AGNES stations was densified to the final configuration of 29 stations (c.f. fig. 1.5). The mean distance between two stations is about 50-70 km, i.e. the maximum distance to the nearest reference station is about 35 km, which (at least under good conditions) would still allow for RTK positioning. The station heights are between 300 and 3500 meters above sea level.

Fig. 1.5: Automated GPS Network for Switzerland (AGNES)

With respect to their monumentation, the AGNES stations are classified as follows: class A with a solid foundation on bedrock and local ties to markers in bedrock; class B without a direct foundation in bedrock (typically on buildings) but with a local tie to markers in bedrock; and class C with neither a direct foundation nor a local tie to markers in bedrock. The 9 class A AGNES stations are well adapted for geodynamical studies, whereas the class B and C stations are mainly used for surveying, positioning and for GPS meteorology.

The AGNES stations are equipped with different receiver (22 Trimble 4700, 6 Trimble 4000 SSi, 1 Leica SR530) and antenna types (21 Trimble Geodetic with groundplane, 6 choke rings, 1 Trimble Zephyr and 1 Leica AT504) without radomes. The antennas of the AGNES stations were calibrated (relative calibration) on a geodetic test network with known ground truth within the millimeter level.

Each AGNES station is equipped with a station PC, which controls the GPS receiver, stores the GPS data locally and communicates with the central control facility via the Communication Network (KOMBV) of the Swiss Federal Administration. For all post-processing applications the data are retrieved from the AGNES stations as 1hour RINEX files with a delay of several minutes after the full hour. For real-time applications in the Swiss Positioning Services (swipos), the data are sent every second in a binary format to the central control facility and to the communication server for access over GSM (Wild et al., 2001a).

Swiss Positioning Service (swipos)

by U. Wild, P. Kummer and S. Grünig

The Swiss Positioning Services (swipos) offers two different levels of accuracy:

· swipos-NAV:
DGPS service over FM/RDS and GSM with meter accuracy for applications in navigation and GIS data collection with low accuracy requirements

· swipos-GIS/GEO:

RTK service over GSM with centimeter accuracy, based on the Automated GPS Network for Switzerland (AGNES), for applications in cadastral surveying and GIS data collection with high accuracy requirements

The service swipos-NAV became operational in January 2000 with a nationwide coverage over FM/RDS. After the suppression of the Selective Availability (SA) on 1 May, 2000, the service became unnecessary for a wide range of applications (Brockmann et al., 2001c).

Therefore, the focus was mainly on the RTK service swipos-GIS/GEO, which was established during the years 2000 and 2001 according to the increasing number of AGNES stations. swipos-GIS/GEO is based on the concept of Virtual Reference Stations (VRS), i.e. the user sends his approximate position to the central computation center and receives RTCM correction data which are interpolated for his actual position (Wild et al., 2001b).

swipos-GIS/GEO over GSM was operational in Switzerland from the beginning of 2002. By the end of 2002 and the beginning of 2003, the Swiss real-time network and the corresponding networks in Germany (Baden-Württemberg and Bavaria) were combined in order to offer seamless positioning services between Switzerland, Germany and Austria (planned for 2003) (Wild et al., 2003).

Currently an automatic Integrity Monitoring (IM) of the service is being built up and first tests for the dissemination of RTCM data over Internet (see also EUREF-IP) have been carried out (Brockmann and Wild, 2002b).

The Use of Double Difference Information from Network Solutions to generate Observations for a Virtual GPS Reference Receiver

by A. Jaeggi, G. Beutler and U. Hugentobler

In the framework of a project with the Federal Office of Topography the theoretical background for generating artificial observations for a virtual reference receiver in post processing mode was developed. The use of double difference information from network solutions allows to correct zero difference observations in a preprocessing clock estimation process where the observations can be adjusted on the level of a few millimeters. Applying simple ionosphere and troposphere modeling techniques the artificial phase observations can be calculated for any given location within the network.

The developed procedure makes full use of the ambiguity and ionosphere information from double difference network solutions in order to keep full consistency of the artificial phase observations on the double difference level. The benefit of artificial observations is demonstrated with data from the Automated GPS Network in Switzerland GPS (AGNES). Baseline solutions are found to be determined more precisely (e.g. ambiguity resolution) using a virtual receiver at one end of the baseline (Jaeggi 2001).

GPS Augmentations for Airborne Applications

by O. Perrin, A. Waegli and P.-Y. Gilliéron

Airborne applications are based on different navigation sensors. The Global Positioning System (GPS) has a great potential for navigation purposes in civil aviation. The Geodetic Eng. Laboratory of EPFL has developed activities on the integration of additional sensors to increase the precision of positioning by GPS. The vertical component was especially improved by using a digital barometer in differential mode.

EGNOS (European Geostationary Navigation Overlay Service) will be the European space-based augmentation system. This system augments the performance of GPS by broadcasting differential corrections and integrity information to the user. The Geodetic Eng. Laboratory took part in several tests in collaboration with skyguide (air traffic control in Switzerland). During these trials the EGNOS System Test Bed (ESTB), which is a prototype system for the future EGNOS system, was analyzed. The research focused on the evaluation of the corrections provided by the ESTB. As the ionosphere is the main source of errors in GPS, ESTB ionospheric corrections were compared with other models mostly based on dual-frequency GPS measurements (see fig. 1.6).

Fig. 1.6: Comparison of the CODE (Center for Orbit Determination in Europe) and EGNOS System Test Bed (ESTB) ionospheric delay

Direct georeferencing by INS/GPS in the Helicopter Environment

by J. Skaloud and J. Vallet

This research presents a self-contained, light and flexible mapping system that can be quickly deployed into inaccessible areas. Although designed to measure wind-transported snow volumes and the snow avalanche runoff over an experimental site, the system is suitable for any large-scale 3-D terrain mapping.

Airborne Data Collection System

This system is composed of an electronic device loosely linked to a light but rigid sensor block containing a camera, an IMU and a GPS antenna (fig. 1.7). The relatively small size and weight of the sensor block permits manual pointing of the camera (film-based or digital) towards either the mountain face or the bottom of a valley. Such hand-held steering allows mapping of the avalanche release and deposit zones during the same flight and also dampens the engine-induced vibration. The exterior orientation (EO) parameters of the camera are determined directly by GPS/IMU integration. The orientation performance of the navigation solution is improved by integrating the data from a second GPS antenna placed on the helicopter tail.

Fig. 1.7: The sensor block

Navigation Data Processing

In order to obtain the best positioning/attitude performance, the inertial data are integrated with GPS double differential code and carrier-phase measurements in a centralized Kalman filter configuration. It is a well-known fact that updating an inertial system with navigation information of better quality prevents the unbounded growth of position and attitude errors. Usually GPS provides a means of 'in-flight alignment' of the inertial system, eliminating the need for the system carrier to be held stationary due to the 'north-seeking' process prior to flight. The accuracy of the in-flight alignment is strongly affected by the dynamics of the carrier. Since the accelerations induced by helicopter maneuvers are considerably smaller than those of an aircraft, this problem needs to be circumvented by other means. Here, the necessary information is derived from a second GPS antenna placed at the tail. Thanks to a relatively long (5 meter) distance between the GPS antennas, a GPS-derived azimuth is sufficiently accurate and can be used as additional information aiding the IMU. Practical experience showed that this helps in achieving and maintaining alignment accuracy of 0.01-0.02 deg.

GPS Meteorology: Contributions of swisstopo to COST-716

by E. Brockmann and D. Ineichen

Since 1999 the Swiss Federal Office of Topography has been active in the European project COST-716 (exploitation of ground-based GPS for climate and numerical weather prediction application). After a successful benchmarking (van der Marel et al., 2001), swisstopo has been contributing zenith total delay estimates in near real-time (NRT-ZTD) since December 2001. Fig. 1.8 shows the stations used. In addition to the 29 AGNES sites, 20 EUREF sites are processed. Furthermore, about 12 sites from other networks, mainly in France, are being used in order to improve the station distribution in the western part of Europe. This area is important because the dominating weather conditions from the Atlantic Ocean usually pass over France before they reach Switzerland. 95% of the solutions arrive at the data archive of the UK met office within 1 hour and 45 minutes.

MeteoSwiss used the NRT-ZTD estimates in a test study for numerical weather prediction. The numerical forecast models were computed for the different test periods (summer, winter, autumn) in two different ways: A run with assimilated GPS-derived ZTD estimates and a run without assimilated ZTDs were carried out. A comparison of the results showed a positive impact of GPS (Guerova et al., 2002) for summer and a slightly negative impact for winter. A by-product of the hourly processing is the monitoring of the site coordinates. Cumulative solutions averaging 12-24 hourly solutions allow the detection of coordinate changes of the order of 2 cm.

Since January 2003, ZTD values can even be extracted from the real-time positioning software GPSNet 2.0 with accumulation intervals of 1 minute with a negligible time delay. swisstopo will also be active in the follow-up European project TOUGH “Targeting Optimal Use of GPS Humidity Measurements in Meteorology “ (2003-2005).

Fig. 1.8: European permanent GPS stations processed by swisstopo in the COST-716 project

Microwave Water Vapor Radiometry

by B. Bürki, A. Somieski, H.-G. Kahle, P. Sorber and R. Gyger

The Water Vapor Radiometers (WVR) as developed at the Geodesy and Geodynamics Lab (GGL) in col­lab­oration with Captec, Biel, Switzerland, have been deployed in several national and international projects. In addition to other instruments sensing tropospheric water vapor such as radio sondes, GPS, and solar spectrometers (see contribution of Somieski et al.), these instruments incorporate an independent data source. Hence they represent an external validation tool which can be applied e.g. in dedicated GPS networks designed for GPS Met purposes. In order to im­prove the over­all performance, reliability, and high serviceability, the instruments owned and operated by the GGL have been subjected to sub­stantial changes. The hardware as well as the software have been upgraded such that the instru­ments now are cap­able to operate unattended. 
In a first application the new type of WVR has been applied in the frame of the project ESCOMPTE (http://www.ggl.baug.ethz.ch/research/wg55/escompte.html, and 
http://medias.obs-mip.fr:8000/escompte/maquette/projetESCOMPTE.php3). 
Figure 1.9 shows the observed water vapor in terms of integrated Zenith Precipitable Water vapor con­tent (ZPW) observed at the station Vallon Dol, France for the time period from june 13. to 22. 2001. The radio­metric measurements reveal a good coincidence with solar spectrometer, radio sonde, and GPS measure­ments.
 
Fig. 1.9: Integrated Zenith Precipitable Water vapor (ZPW) content as observed with GPS (black), solar spectrometer (red), water vapor radiometer (yellow), and radio sondes (turquoise/blue).
During fall 2002 a common calibration campaign has been carried out at the Geo-fundamental station of Wettzell, Germany. The main goal of this project, which was carried out in collaboration with several Euro­pean partners from Belgium, Germany, and Switzerland, was an intercomparison and –calibration bet­ween different types of instru­ments and methods. 
 
 
Development of Geodetic MObile Solar Spectrometer GEMOSS I

by A. Somieski, B. Bürki, H.-G. Kahle and P. Sorber

The water vapor in earth troposphere causes refraction of transatmospheric microwave signals and limits the accuracy of high precision GPS positioning and satellite radar altimetry. For remote-sensing of tropospheric water vapor a new Geodetic MObile Solar Spectrometer (GEMOSS I) has been developed at the Intitute of Geodesy and Photogrammetry (IGP, Group of Prof. H.-G. Kahle) and the Institute of Spectrochemistry and Applied Spectroscopy (ISAS) in Berlin. GEMOSS I is based on an improved optical construction, which is permanently adjusted with high accuracy by 5 computer-controlled step motors. Within a single GEMOSS spectrum appr. 1900 water vapor absorption lines of sun radiation are measured in the large range between 730 nm and 910 nm simultaneously. Furthermore the optimized light sensitivity of the GEMOSS I allows its deployment under low-level radiation conditions and thus increases the time period of data acquisition. In the framework of the EU-project GAVDOS first successful measurements were carried out on the island of Crete (Greece) to calibrate the JASON altimeter satellite. Figure 1.10 shows the zenith wet path delay (ZWPD) measured by GEMOSS I at the January 11th 2003, when the JASON satellite crossed over Crete. Since the retrieval of ZWPD is based on the analysis of more 40 different water vapor absorption lines an accuracy of appr. 0.5 cm could be achieved. 

Fig. 1.10: Zenith wet path delay during the overflight of JASON satellite as observed near the ground track at Crete (Greece) by means of the Geodetic Mobile Solar Spectrometer GEMOSS I:

Determination of the 3 Dimensional Refractivity Field: GPS Tomography

by M. Troller, B. Bürki, A. Geiger and H.-G. Kahle

It is commonly accepted that GPS meteorology can be successfully used to model the refraction effect on radiowave signals traversing the troposphere. We developed a method to estimate and model the spatial distribution of the tropospheric water vapor. A tomographic software package called AWATOS has been realized. It is based on the assimilation of GPS double difference observations. These are allocated to a voxel model, which is defined according to the distribution of the GPS stations. Performing a least-squares adjustment, the refractivity of each voxel is determined. Tests of the software were performed, based on simulated and real data. A field campaign was initiated on the Big Island of Hawaii, which is ideal for test purposes because of an already installed dense GPS permanent network (c.f. fig. 1.11), associated with large height differences between the stations. The tomographic profiles of the real data sets were compared with 18 radiosondes launched during the campaign. The results obtained for continuous atmospheric conditions fit well (c.f. Fig. 1.12). The statistical evaluation revealed an accuracy of around 5-20 ppm for the wet refractivity. However, the special conditions on the Hawaiian Island have to be kept in mind. The distribution of stations from sea level to a height of over 4000 m is exceptional.

Our group participated in the joint meteorological project ESCOMPTE (Field experiment to constrain models of atmospheric pollution and emissions transport). Together with six French research groups on GPS meteorology, we operated a GPS network in the project area of Marseille. In this project, the height distribution of stations from sea level to only 600 m is very unfavourable. For comparison, a set of instruments for remote sensing of water vapor was also used. The data analysis of this project is in progress [Bock et al., 2002a, 2002b].

Fig. 1.11: Core of the tomographic voxel model for the Hawaiian campaign. The model consists of 16 layers of 3 x 3 core voxels. Blue boxes show the location of the GPS stations.

Fig. 1.12: Sample of a wet refractivity profile at station Volcano Village.

For further details see the project page on: http://www.ggl.baug.ethz.ch/research/wg56/

Modelling of GPS estimated path delays

by M. Troller, E. Brockmann, A. Geiger

High-precision GPS measurements require the modelling of the tropospheric refractivity field in order to correct for atmospheric refraction effects. Nowadays, the potential of the increasing number of GPS permanent stations can be utilized. Usually, the network is automatically processed, and GPS estimated path delays are available. We developed a software package COITROPA (Collocation and Interpolation of Path Delays) to model the GPS estimated path delays based on least-square collocation.

The AGNES network, which covers the whole Swiss territory, represents an optimal GPS network for our approach. Calculations were done during several years. Time series of various stations demonstrate that the accuracy is increasing continuously with a rising number of permanent stations. The success of this method was verified with statistical analysis. Hence, an accuracy of less than one centimeter was achieved (c.f. fig. 1.13).

For details see the project page on: http://www.ggl.baug.ethz.ch/research/wg60/

Fig. 1.13: Zenith total delay on station Zimmerwald (ZIMM) aquired with the COITROPA software package. For comparison, the GPS estimated path delay obtained with BERNESE GPS processing is plotted.

4 Dimensional Meteorological Modelling of Pathdelays (COMEDIE)

by M. Troller, A. Geiger, B. Bürki and H.-G. Kahle

Tropospheric path delays represent a main error source in GPS precise positioning. We developed a software package COMEDIE to model the meteorological parameters pressure, temperature and water vapor pressure in 4 dimensions (space and time). The path delays are influenced by these parameters. COMEDIE allows to integrate the path delay along an arbitrary ray. An accurate modelling requires a dense network of meteorological measurements. The ANETZ network of MeteoSchweiz contains 72 stations, distributed over the entire Swiss territory. However, the height distribution of the network is not optimal. To obtain reliable values for the refractivity field in the upper layers of the atmosphere, radiosonde data are mandatory. So far, we used this method mainly in Switzerland. GPS estimated path delays of IGS stations (station Zimmerwald), the AGNES network and the MAGIC project (Meteorological Applications of GPS Integrated Column Water Vapor Measurements in the Western Mediterranean, station Zimmerwald) are used for comparisons and statistical analysis. The evaluations show a good agreement of the COMEDIE data with the GPS estimated values (see fig. 1.14). A RMS of around 1 cm was achieved.

For details see the project page: http://www.ggl.baug.ethz.ch/research/wg37/

Fig. 1.14: Total zenithal delay on stations Zimmerwald (ZIMM) aquired with COMEDIE and the GPS estimated processing of IGS (2 hours mean) and MAGIC (15 minutes mean).

Precise Determination of Offshore Sea Level

by A. Geiger and M. Cocard

New buoys have been designed based on previous experiences. The newly developed buoys have a displacement of 10 kg which is a significant weight reduction compared to the predecessor. With its 40 cm diameter it can easily be handled. The dimension of the buoy, weight of battery, receiver, and antenna have optimally been chosen and designed in order to reach the exact floating balance. No ballast is needed to stabilize the buoy or to reach the foreseen floating line in the middle of the spherical buoy. The shell is fabricated from polycarbonate, which is transparent for the microwaves also. Therefore, the whole buoy can be waterproofed sealed containing the battery, receiver and antenna (fig. 1.15). The buoy is designed to accommodate Novatel DL-4 receiver. The new pinwheel antenna is used. The operation autonomy reaches about 20 hours. For the experiment the measurement rate will be set to 0.5 sec sampling interval, producing about 5 MB data per hour. First tests where successfully completed. The data is processed by own kinematic software which is able to calculate long baselines in kinematic mode.

Fig. 1.15: Light weight buoy for sea level surface flow determination in a friendly sea

Sensor Attitude Determination Using GPS Antenna Array and INS

by E. Favey, A. Geiger and M. Cocard

Many airborne laser scanning systems acquire the sensor's attitude relying on a very accurate, yet expensive inertial system in conjunction with a single GPS receiver for trajectory recovery. For any type of airborne imaging sensor or laser scanning system, correct attitude measurements are crucial to the production of accurate data. We have developed an approach to acquire the sensor attitude using a combination of an array of single frequency GPS antennas together with an Inertial Measuring Unit (IMU) measuring at a sampling rate of 100 Hz. The drift of the IMU is stabilized by a 4 Hz attitude update acquired by GPS. The attitude of the two independent methods are compared with each other. The information is further merged to process airborne laser scanning data, which in turn serves to estimate the attitude quality by comparing the height of the resulting digital surface model with known ground information. The laser employed was ScaLars II owned by the Institute of Navigation, Univ. of Stuttgart. This laser also provides intensity images, which allows to verify the horizontal position of the laser footprint with known ground truth. The results from a variety of real flight data were used to estimate the total system's accuracy. Sensor dependent issues like IMU drift, GPS ambiguity resolution, and merging GPS with IMU data are also assessed. An overall accuracy of about 17 cm seems to be feasible.

Fig. 1.16: DTM of Unteraarglacier measured by airborne Laserscanning without any passpoints. This measurement can be compared to future survey in order to determine the glacial retreat.

Monitoring Three-Dimensional Movement, Oscillations, Rotations in Structural Engineering

by A. Geiger and M. Kistler

The monitoring of the three-dimensional movement inclusive the rotations of built structures is sometimes difficult. In different cases GPS can ease the task. We developed a tool to determine the complete three-dimensional movement of a structure by GPS. It is based on multiple antennae arrays. As an example of application we mention here the determination of the exact position of the path of a cabin of a ropeway. This curve is not visualised by a cable or a rope, it is so to say a virtual curve. The determination of the path by classical methods is very time consuming and often impossible. In many cases the path can satisfactorily be calculated by approved mathematical models. However, in cases where the curve should exactly be known positioning by GPS can help. A very important aspect considers the oscillations of the vehicle. The determination of oscillations is of major interest for the safety assessment of an installation. Passing at the towers, wind loading and emergency stops are operations possibly causing unfavourable oscillations of the cabin. The complete oscillatory movement can be monitored by using at least three GPS receivers on the cabin. In this paper it is shown that it is possible to determine relevant physical and geometrical parameters of a ropeway installation as well as the oscillatory or attitude part of its movement. Real measurements confirm the efficiency of the method and reveal the high resolution for the determination of the complete 3-D movement (translations and rotations) of the ropeway. The frequency and the amplitude of different oscillating modes induced by an emergency stop can clearly be determined.

Performance Analysis of Cellular Positioning Methods for LBS and Navigation

by A. Geiger, Ph. Kehl and St. Ziegler

The analysis aims at three main points: Quantitative estimation precision without knowledge of exact antenna sites, a priori analysis in regions where antennas are not yet installed and extract general characteristics of a network in view of navigation.

For these investigations we first developed and implemented algorithms which are based on continuous antenna-distribution rather than on discrete position of the antennae (see section 4). In a first step the density of base stations is defined. The density is calculated by division of the number of antennae within a defined area. Instead of fixing the value of the area we fix the number of antennae, which shall be included in a minimum circle around the point under consideration. The maximum radius of the circle is 35 km corresponding to the maximum range of operation for the GSM technique. If no antenna is found within such a circle, the density will be set to zero. The bigger the number is chosen, the smoother the density function will appear. Numbers of 4, 7, 10 have been analysed.

The algorithms for calculation of the precision of formal variances of the positioning correspond to the classical (over-determined) least square solution. However, the discrete positions of the antennas are replaced by distribution functions (or densities) and sums are converted to integrals. The fundamentals of this method have been developed for qualitative analysis in satellite geodesy and for error assessment.

The equations are modified for Cell-Identification (CID), angle of arrival (AOA), observed time difference (TDOA), and for combinations of these measurement methods. The corresponding density is calculated by setting the number of antennas within the minimum circle to 4. From densities the precision can be calculated and represented. As an example the precision (in m) of AOA is shown in figure 1.17. The area of the canton of Zurich is depicted. The precision of Cell-ID is directly correlated to the density of antenna, whereas AOA and TDOA are susceptible to the geometric distribution of the antennae. Typical error curves can be recognized for the AOA method especially when antennas are aligned along e.g. an autobahn (see red ellipse in fig. 1.17).

Fig. 1.17: Precision of Positioning by using angle of arrival technique (AOA) in [m]. Typical error figures can be recognized especially when antennas are aligned along e.g. motorways (indicated as autobahn).

This new method allows to deduce general statements on the performance of existing and planned networks. Antennae density can be predicted by a functional algorithm, which takes population, number of work places etc. into account. The predicted densities can directly be introduced in navigational performance analysis. The analysed data showed that the TDOA is not very sensitive to density whereas CID depends strongly on density. This may lead to the statement that CID is well suited for business centres; rural areas however, will be poorly covered by good precision from CID. The following table may sum up these findings in terms of suitability (+++ good, ---bad):

Environment	TDOA	AOA	CID
Centres	++	+++	+++
Urban	++	+	-
Rural	++	--	---

Determination of Thermal Stratification and Turbulence of the Atmospheric Surface Layer over Various Types

by A. I. Wejss and P. Flach

Refraction is a detrimental problem in terrestrial optical measurements and can be regarded as major source of systematic errors in the precise determination of distances and directions. In general, refraction is a function of the density inhomogeneities of the propagation medium. As the "classical" method of temperature-gradient determination does not meet the requirement of a representative integral determination of the refractive index gradient field, several methods to determine and correct the refraction influence have been developed further during the last few years at the Institute of Geodesy and Photogrammetry of the ETH Zürich.

The approach focuses on the determination of the refractive index gradient in measuring the turbulence of the air by scintillometry using the Scintec SLS20 displaced beam Scintillometer. The turbulent sensible heat flux can be converted by the Monin-Obukov-Similarity into temperature gradients. The advantage of optical scintillation measurements is to derive line-averaged turbulence parameters of the atmospheric surface layer. Up to now this method was said to be restricted to homogeneous surfaces and flat areas. The approach of Alexandra Weiss and Philipp Flach should determine to what extend this method can be applied in inclined areas and inhomogeneous surfaces. Several measurement campaigns – among others the Mesoscale Alpine Program (MAP) – represented the data base of this thesis. All measurements were carried out redundantly in conjunction with other methods such as Sonic, CCD-Cameras, etc.

As a main result it could be demonstrated that the turbulence approach can be extended to areas with inhomogeneous and inclined surfaces. Based on these most encouraging results, the present thesis can be considered as an important milestone in the progress of scientific geodetic and meteorological knowledge and will consequently lead to further research work.

Development of the World's Most Accurate Absolute Electronic Distance Meter (EDM)

by R. Loser

Based on the actual Mekometer principle with polarization modulation, a new EDM for precision tracking of fast moving targets has been developed and tested in a joint project of TU Munich, Leica Geosystems, and IGP/ETH. The key technology to achieve the ambitious specifications of micrometer accuracy was the change from analogue to digital synthesizing procedures and sophisticated real-time data processing. In the mean time, the sub-micrometer accuracy EDM has been successfully implemented into Leica Lasertrackers (fig. 1.18) for industrial metrology and is used in a NASA application.

Fig. 1.18: Functional principle of the EDM

Nanometer Detection Enables Refraction-Free High-Precision Direction Measurement: Development of a Compact Laser Dispersometer

by B. Böckem

The actual limitations in direction and distance measurements are the propagation and distortion of wave fronts in the air. One approach to overcome these limitations is the so-called dispersometer technology based on a two-color method using laser beams with two extremely separated wavelengths of light spectrum. In collaboration with the ETH Laboratory for Solid State Physics we succeeded in generating an adequate laser source by doubling an infrared laser source with a Caliumniobate crystal (see fig. 1.19). For the functionality it was necessary to detect the blue and infrared laser spots in the focal plane of a short focal length geodetic telescope with a resolution of a few nanometers. This has been achieved by the new so-called GAP technology which is based on a special semiconductive effect in differential optical position-sensitive detectors.

Fig. 1.19: The two-color light source of the ETH dispersometer

The effectiveness of this method is demonstrated by the fact that the noise of the refraction-free direction is white. With this method it will be possible to control the trajectory of construction machines with the required accuracy and reliability.

A New Hydrostatic Level System (HLS) for Permanent Height Monitoring of the Neutron Light Source at the

Paul Scherrer Institute (PSI)

by H. Ingensand and E. Meier

A newly designed high-precision Hydrostatic Level System (HLS) has been developed to monitor the vertical position of the quadrupoles at the Paul Scherrer Institute (PSI) with an accuracy of a few microns (c.f. fig. 1.20). This development is the result of a cooperation of Edi Meier and Partners in Winterthur, Stanford Linear Accelerator (USA) and the chair of Geodetic Metrology of the ETH Zürich.

The basic function of the HLS sensor is the determination of the level of a fluid, representing the local reference horizon, by measuring the capacity between the fluid surface and the internal electrode. The circuit of the neutron light source has a length of 560 m and is sectorized into 48 girders carrying the quadrupoles. Each girder is controlled by 4 HLS sensors and can be levelled individually by electric devices. For permanent monitoring a total of 204 sensors send their signals via CAN bus system to a central computer. The HLS has been in operation since November 2000.

Fig: 1.20: HLS mounting and cross section of the sensor

Establishment of an Automatic Multisensor Dam-Monitoring System

by H. Ingensand and R. Stengele

With respect to the Alptransit tunnel construction in the region of dams, a high-resolution optical multisensor monitoring system had to be established. One detrimental effect of tacheometric optical 3-D measurement is the refraction in the area of dams because of the temperature gradients in the shadow of dams. Besides the classical correction technology with single point atmospheric data acquisition, a new approach of local scale correction has been evaluated and implemented to overcome the aforementioned effect. This joint project of Swissphoto/Gruenenfelder and ETH will have a ten year duration period.

The Development of an Alignment System for the Slab Track

by R. Glaus

On new railway lines, a novel construction technique becomes widely accepted in tunnel sections. For the so-called slab track, sleepers are – in contrary to ballast tracks – attached in concrete. The advantage of this method over conventional ballast tracks is the considerably lower maintenance expense. Paving over implicates that corrections to the track alignment are only possible with great efforts. Thus, the alignment of the track has to be carried out extremely accurately. The Institute of Geodesy and Photogrammetry developed an alignment system for staking out the slab track. The system is based on an electronic tacheometer and a track trolley as shown in figure 1.21. The track trolley serves as a platform for inclination sensors, odometers and a track gauge measuring system and was constructed by the HTA Burgdorf in collaboration with terra vermessungen AG, Zurich. The developed track alignment system combines the measurements of the involved sensors and computes correction values of the actual track with respect to the nominal track. These values are used by operators for the alignment. The system is successfully used in the Zurich-Thalwil tunnel by Grunder Ingenieure AG for installing 15 kilometers of slab track. The project is financed by KTI (Kommission für Technologie und Innovation, Bundesamt für Berufsbildung und Technologie).

Fig. 1.21: Alignment of the slab track using the track trolley

High-Precision Alignments with 2-Axes Wire Position Sensors

by H. Dupraz, W. Coosemans, F.Ossart and V. Bourquin

HISTAR (High-Speed Train Aerodynamic Rig) is a project for constructing a highly flexible reduced-scale rig for studying the aerodynamics of high-speed trains operated in a controlled atmosphere. Besides the numerous problems associated with the propulsion and guiding system, the specifications of the facility are characterized by significant constraints of the alignment of the 250-meter track, composed of 40 six-meter steel girders and located in an underground gallery.

According to the expertise acquired at CERN over numerous years, this problem can be better treated by the construction of a "surveying train" that carries a number of sensors (e.g. the inclinometers and electric wire position measure) and performs all necessary measurements. After calculating the appropriate corrections, the adjustment of the aligning components is performed by means of a "Six Strut" support system. The basic idea is simple: the position of a rigid body in space has six degrees of freedom: X, Y, Z, and angular: pitch, roll, and yaw. A support system which uses six orthogonal links, or struts, provides "kinematic" support, that is, just enough support with no additional constraints which could stress and distort the body itself (see fig. 1.22). The struts have ball-jointed end connections, and are arranged orthogonally to simplify position adjustments.

Fig. 1.22: View of the support system for alignment

A Mobile Mapping System for Automating Road Data Capture

by P.-Y. Gilliéron, J. Skaloud and H. Gontran

Mobile mapping systems (MMS) currently integrate available navigation techniques, digital 3D photogrammetry, digital mapping and GIS technology. Such complex systems can be very productive when adapted for a complete acquisition of road data; however, their use usually requires a highly qualified team. The concept of the project Photobus is to provide a simple system that is based on standard components and is easy to use.

Photobus is a mobile mapping system for road data base management. Several devices are mounted in a mobile terrestrial vehicle that performs an automated survey of specific road features such as centerline, marks and signs at speeds up to 100 km/h (c.f. fig. 1.23).

These devices include Global Positioning System (GPS) receivers, an Inertial Navigation Unit (IMU), a Charge-Coupled Device (CCD) camera(s) and an optical odometer (wheel sensor). The system is user-friendly and has a fast setup time, which facilitates its portability between different vehicles. Its development is conducted at the Geodetic Eng. Laboratory (TOPO) of the Swiss Federal Institute of Technology Lausanne (EPFL).

Photobus has been used in several trials on precise monitoring of the centerline. The extraction of road geometry using this methodology has proven to work reliably. First results show that the positioning accuracy was always better than 20cm.

Current research strives to achieve a complete automation of the geo-referencing process and a real-time implementation of the feature extraction. In order to improve the positioning of the vehicle, it is planned to integrate DGPS carrier phase correction in real time.

Fig. 1.23 : Architecture of the system Photobus

Athletic Motion Analysis Using Carrier Phase GPS Data

by J. Skaloud, Q. Ladetto and B. Merminod

Coaches constantly ask how and why a racer can perform better any given time. A position-velocity-acceleration (PVA) analysis gives the competitive edge of a point-by-point course performance examination and overall profiles between a racer’s own performances and those of others. In downhill skiing, coaches and others devote long hours to slope recognition, attempting to quantify many factors for choosing an optimal trajectory. A skier’s racecourse time only summarizes many decisions taken, and until now there were no means for separating good decision from bad ones. Applying GPS technology offers the possibility for studying each turn separately and evaluating personal performance as well as that of the equipment.

For useful analysis, a skier’s position must be determined with sub-decimeter accuracy, requiring differential carrier-phase GPS (CDGPS) at 10 Hz frequency or higher. Although ambiguous, the carrier-phase measurement possesses the desired centimetre-level accuracy. The GPS carrier-phase ambiguities are currently determined in-post mission by using state-of-the-art algorithms for high-dynamic application. System evolution calls for inverse Real Time Kinematic (RTK) implementation with the mobile phone used as a data link. Extensive search of the market for suitable instruments revealed considerable performance differences between high-end GPS receivers in terms of signal acquisition and tracking under dynamic and frequent obstructions. The limits of the current technology are also reached quickly once the ergonomic factors are taken into consideration. The development focuses also on trajectory smoothing and modelling that can handle gaps in the GPS data. The trajectories are parameterised in both time and length, and additional parameters like acceleration and curvature are estimated and gate-to-gate performance is presented. An example is shown in figs. 124a and b:

Fig. 1.24a: Speed versus the course terrain.

Fig. 1.24b: Racer’s trajectory when negotiating an S-turn. Each dot represents GPS sampling of the competitor’s position and velocity, although the value of the latter is shown only when passing a gate.

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Marti U., A. Schlatter, E. Brockmann and A. Wiget (2002b): The Way to a Consistent National Height System for Switzerland; IAG Proceedings vol. 125. Vistas for Geodesy in the New Millennium. IAG Symposia vol. 125. Proceedings of the IAG Scientific Assembly, Budapest.

Perrin O. (1999): Intégration de mesures satellitaires et barométriques pour la localisation 3D. Diploma thesis, EPFL, 1999.

Rothacher, M., T. Springer, G. Beutler, R. Dach, U. Hugentobler, D. Ineichen, S. Schaer, U. Wild, A. Wiget, E. Brockmann, C. Boucher, E. Reinhart, H. Habrich (1999): Annual Report 1998 of the CODE Analysis Center of the IGS, IGS Technical Report 1998, K. Gowey et al. (Eds.), IGS Central Bureau, JPL, CA, USA, Nov. 1999.

Sacher M., J. Ihde, U. Marti, A. Schlatter (2002): Status Report of the UELN/EVS Data Base. EUREF Publication No. 12.

Schlatter A., U. Marti, A. Wiget und H.-U. Riesen (2000): AlpTransit Lötschberg Basistunnel: Grundlagenvermessung für die Tunneldurchschläge auf der Basis der Landesvermessung LV95. Beitrag zum XIII. Internationalen Kurs für Ingenieurvermessung in München, 13.-17. März 2000. Ingenieurvermessung 2000, Wittwer, Stuttgart, 2000.

Schlatter A.und U. Marti (2001): Neues Landeshöhennetz der Schweiz. Tagungsband Weiterbildungsveranstaltung 'Neue Referenzrahmen und Koordinatentransformationen in der Geomatik', 10./11. Oktober EPFL.

Schlatter A., E. Brockmann, Th. Signer, A. Wiget und K. Wysser (2001): Konzept- und Machbarkeitsstudie zu HFP2-Netzen im heutigen Umfeld. Vermessung, Photogrammetrie, Kulturtechnik VPK 3/2001.

Schlatter A. und U. Marti (2002): Neues Landeshöhennetz der Schweiz LHN95. Vermessung, Photogrammetrie, Kulturtechnik VPK 1/2002.

Schneider, D. E. Gubler, E. Brockmann, A. Wiget, G. Beutler, M. Rothacher, S. Schaer (1999): "National Report of Switzerland – New Developments in Swiss National Geodetic Surveying", Veröffentlichungen der Bayerischen Kommission für die Internationale Erdmessung, 60, Gubler et al. (Eds.), München, 1999, pp. 211-217.

Schneider D., A. Schlatter, A., Th. Signer und U. Wild (2000a): AlpTransit-Gotthard-Basistunnel: Ergebnisse der kinematischen Analyse des Landesnivellements im Gotthardgebiet und grossräumige Überwachung des Projektgebiets mit Hilfe von Präzisionsnivellements und mit GPS-Permanentnetzen. Beitrag zum XIII. Internationalen Kurs für Ingenieurvermessung in München, 13.-17. März 2000. Ingenieurvermessung 2000, Wittwer, Stuttgart, 2000.

Schneider D., E. Brockmann, U. Marti, A. Schlatter and U. Wild (2000b): Introduction of a Precise Swiss Positioning Service "swipos" and Progress in the Swiss National Height Network "LHN95"; Paper presented at the EUREF'2000 Symposium, Tromsö, 21. - 24. 6. 2000. Technischer Bericht 00-20, Bundesamt für Landestopographie, Wabern.

Schneider D., E. Brockmann, U. Marti, A. Schlatter, T. Signer, A. Wiget and U. Wild (2002): National report of Switzerland: New developments in Swiss National Geodetic Surveying. In: Torres, J.A. and H. Hornik (Eds): Subcommission for the European Reference Frame (EUREF). EUREF Publication No. 11.

Sierk, B.[2001]: Solar Spectrometry for Determination of Tropospheric Water Vapor, Geodätisch-geophysikalische Arbeiten in der Schweiz, Volume 62, Schweizerische Geodätische Kommission.

Signer Th. und B. Vogel (2000): Aufbau der neuen Landesvermessung der Schweiz, Teil 8; Gesamtausgleichung des GPS-Landesnetzes mit dem Diagnosenetz der Triangulation 1. und 2. Ordnung 'DIA95'. Berichte aus der L+T, Nr 14, 2000.

Signer Th. (2001): Landesvermessung LV95: Übersicht und Stand des Projektes. Tagungsband Weiterbildungsveranstaltung 'Neue Referenzrahmen und Koordinatentransformationen in der Geomatik', 10./11. Oktober EPFL.

Signer Th. (2002): Landesvermessung LV95: Übersicht und Stand des Projektes. Vermessung, Photogrammetrie, Kulturtechnik VPK 1/2002.

Skaloud J., Q. Ladetto, B. Merminod, M. Vetterli, M. Gyr, A. Marcacci, P. Luthi and Y. Schutz (2001): Athletic Analysis With Racing Heart. GPS World, Oct 2001.

Skaloud J. and J. Vallet (2002): High Accuracy Handheld Mapping System for Fast Helicopter Deployment. Joint International Symposium on Geospatial Theory, Processing and Applications. ISPRS Comm. IV, Ottawa, Canada, July 9-12 2002.

Somieski, A.; Bürki, B.; Kahle, H.-G.; Becker-Ross, H.; Florek, S., Okruss, M. (2003): Geodetic Mobile Solar Spectrometry: Description of the New Spectrometer GEMOSS and First Measurements, Geophys. Res. Abstr., Volume 5, 2003.

Somieski, A.; Bürki, B.; Cocard, M.; Geiger, A.; Kahle, H.-G. (2002): Water Vapor Remote Sensing Techniques - water vapor radiometry and solar spectrometry, Geophys. Res. Abstr., Volume 4, 2002.

Springer, T. (2000): Analysis Activities. In: IGS 1999 Annual Report, IGS Central Bureau, JPL, CA, USA.

Springer, T., J. Kouba, Y. Mireault (2000): 1999 Analysis Coordinator Report. In: IGS 1999 Technical Reports, K. Gowey et al. (Eds.), IGS Central Bureau, JPL, CA, USA, Nov. 2000, pp. 15-55.

Troller M. (2001): Szintillometrie zur Refraktionskorrektur von Tachymetermessungen? VPK 9, pp. 603-607

Troller M., M. Cocard und A. Geiger (2001): Modellierung 4 dimensionaler Refraktionsfelder zur Berechnung von Weglängen-Korrekturen bei Satellitenmessungen. Proc.: Simulation raumbezogener Prozesse: Methoden und Anwendungen, 26.9.2000, Münster , IfGI prints (Nr.9), pp. 21-31, 2000.

Troller M., E. Brockmann, M. Cocard and A. Geiger (2002): GPS-Derived Path delays Versus Four-Dimensional Meteorological Modelling. COST-716 workshop Potsdam, Jan. 28-29 2002.

Vallet J., J.Skaloud, O. Koelbl and B. Merminod (2000): Development of a helicopter-based integrated system for avalanche mapping and hazard. The international archives of the Photogrammetry, Remote Sensing and Spatial Sciences, Amsterdam 2000.

Vallet J. (2002): Saisie de la couverture neigeuse de sites avalancheux par des techniques aéroportées. Ph-D Thesis EPF, Lausanne 2002

Waegli A. (2003): Evaluation de mesures dynamiques pour la navigation aérienne dans le cadre du projet EGNOS. Diploma thesis, EPFL, 2003.

Weber, R., T. Springer (2001): Analysis Activities. In: IGS 2000 Annual Report, IGS Central Bureau, JPL, CA, USA.

Weiss A., M. Hennes and M. Rotach (2000): Derivation of refractive index and temperature gradients from optical scintillometry for the correction of atmospherically induced problems in highly precise geodetic measurements. Paper presented at EGS 2000, Nizza, April 25-29, 2000. In: Kluwer Academic Press, Netherlands.

Weiss A. (2002): Determination of thermal stratification and turbulence of the atmospheric surface layer over various types. Diss. ETH No. 14514, IGP, geomETH, ETH Zürich.

Wiget A., A. Geiger, M. Kistler, E. Brockmann, A. Schlatter and D. Schneider (2003): Modelling the kinematics of the deformation of the Swiss geodetic reference network: Project Swiss-4D. Poster to be presented at the XXIII General Assembly of the International Union of Geodesy and Geophysics in Sapporo, Japan, July 2003.

Wild U., E. Brockmann, R. Hug, Chr. Just, P.Kummer, Th. Signer, A. Wiget (2000): Automatisches GPS-Netz Schweiz (AGNES), Ein multifunktionales Referenznetz für Navigation und Vermessung, VPK 6/2000.

Wild U., R. Hug, S. Grünig, E. Brockmann (2001a): The Automated GPS-Network Switzerland (AGNES): status report and future developments. Proceedings NavSat 2001, 13-15 November 2001, Nice.

Wild U., S. Grünig, R. Hug, P. Kummer, I. Pfammatter und U. Bruderer (2001b): Swipos-GIS/GEO: real-time Positionierung in der ganzen Schweiz mit cm-Genauigkeit. VPK 03/2001.

Wild U., S. Grünig, H. Derenbach, G. Dick, M. Klette, R. Gedon, H. Titz and N. Höggerl (2003): Konzept für die Verbindung der real-time GPS-Netze in D - A - CH. swisstopo Report 02-38, Wabern, Switzerland, 2003.

Wildi Th. and R. Glaus (2002): A Multisensor Platform for Kinematic Track Surveying. 2nd Symposium on Geodesy for Geotechnical and Structural Engineering, May 21-24, 2002, Berlin.