Preprocessing is an essential aspect for zero- and double-difference GPS software packages. In the first case we have to produce “clean” code and phase observations on the single receiver and single satellite level, in the second case solely double-difference observations have to be checked. The checks usually are performed on the “minimum constellation” level, i.e., the single receiver level for zero-, the single baseline level for double-difference packages. When analyzing the code observations stemming from a permanent array, this step may be performed in a much more efficient and robust way because the known geometry and, if available, the known atmospheric delays may be removed from the original observations. In an array of n receivers observing m satellites this leaves us with n · m observations and n + m - 1 unknowns (the clock parameters relative to a reference clock). The degree of freedom of f = n · m . (n + m - 1) (for, e.g., n = 10 and m = 10, we have f = 81) allows for a very robust detection of outliers and enables generating a satellite clock file based on code measurements (with very much reduced multipath and noise characteristics). A similar step may be performed with the differences of phase observations between subsequent epochs. Using an analogous procedure as in the case of code observations we may generate phase files with all cycle slips flagged or, in the case of “small-area” arrays, even with cycle slips repaired. Both steps, phase and code cleaning, are performed in the same program unit. We discuss this new development and present first results and applications using data from the AGNES (Automated GPS Network Switzerland) and the IGS (International GPS Service) Networks.

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A regional continuous Global Positioning System (GPS) array, consisting of uniform antenna type, has been established by the Geological Survey of Japan (GSJ) mainly around the Kansai district. Geodetic results for 2.5 years data are as follows. In comparison with the solutions obtained from the Geographical Survey Institute (GSI) continuous GPS array which employs different type of antenna from the GSJ's array, itwas found that the agreements between the daily positions were about 10 mm in horizontal and 15 to 20 mm in vertical components. This result indicates that the influence of the antenna type difference is at this level. The GSJ's GPS stations around the Kansai district were found to have a common annual variation in the vertical component, whose amplitude was different from site to site. There were small correlations with in situ measurements of groundwater-level variation, except for the two stations whose annual variations of the GPS vertical component were the largest. The vertical displacements due to elastic deformation by groundwater-pressure changes in the aquifers were estimated using a simple model, but they were too small to account for the observed variations.

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The intention in this paper is to investigate the form and dynamics of large-scale traveling ionospheric disturbances (LS TIDs) of auroral origin. We have devised a technique for determining LS TID parameters using GPS arrays whose elements can be selected from a large set of GPS stations forming part of the international GPS network. The methodwas used to determine LS TID parameters during a strong magnetic storm of September 25, 1998. The North-American sector where many GPS stations are available, and also the time interval 00:00-06:00 UT characterized by a maximum value of the derivative Dst were used in the analysis. The study revealed that this period of time was concurrent with the formation of the main ionospheric trough (MIT) with a conspicuous southward wall in the range of geographic latitudes 50-60° and the front width of no less than 7500 km. The auroral disturbance-induced large-scale solitary wave with a duration of about 1 hour and the front width of at least 3700 km propagated in the equatorward direction to a distance of no less than 2000-3000 km with the mean velocity of about 300 m/s. The wave front behaved as if it ‘curled’ to the west in longitude where the local time was around noon. Going toward the local nighttime, the propagation direction progressively approximated an equatorward direction.

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Fast and high precision relative GPS positioning over distances up to 100 km is mainly limited by errors in the GPS signals due to propagation through the Earth's ionosphere. With permanent GPS arrays, which are present in many countries nowadays, it becomes possible to correct a user's GPS measurements to a certain extent for these ionospheric delays. A way to do so is to interpolate the ionospheric delays which have been estimated from the network of permanent stations. When these ‘interpolated corrections’ are applied to the user's data, the ionospheric delays may be reduced, which may lead to an improved ambiguity resolution for his (long) baseline.

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The availability of real-time tropospheric data is an important question for atmospheric parameters to be ingested in weather prediction models or in monitoring studies. In the frame of the EU funded project CLIMAP we have developed an on-line system that acquires GPS data from a number of IGS stations distributed around Europe providing hourly batches of GPS observables. An off-line system processing data with a one-day delay was run during one year to tune the characterisitics of the present on-line system. The hourly data are processed using GIPSY/OASIS II software, to obtain the Zenith Total Delay in a near-real-time basis. Every hour, the new batch is merged with the observations of the previous 23 hours to allow the system to process enough data to yield robust results. The question of what prediction for orbits to use has also been addressed, designing the system to always use the best orbits available from the Center for Orbit Determination in Europe, using the quality codes for the prediction of the orbits to remove “bad quality” satellites from the solution. To validate the results, the ZTD time series for each station have been compared against the solutions obtained through a Precise Point Positioning using final precise orbits and clock corrections. The estimation processing has been tuned to account for the particularities of a near-real-time scenario such as the satellite clock correction and the day boundary issue.

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Simultaneous GPS and water vapor radiometer (WVR) observations were carried out at Tsukuba, Japan from May 1 to June 30, 1998. The precise point positioning method of the GIPSY/OASIS-II software package (GIPSY) was used to retrieve precipitable water vapor (GPS_PWV) from GPS data, which was then compared with precipitable water vapor observed by WVR (WVR_PWV). They agreed quite well with the root mean square difference of less than 1.5 mm. However, periodic variations were found in the difference between GPS_PWV and WVR_PWV (dPWV). Itwas also found that semi-diurnal or diurnal components of these variations had a positive correlation with site displacement due to Ocean Tidal Loading (OTL). Two months of dPWV data were decomposed by the period of a component of OTL, and then composite time series data with a period equal to that of the component were made. This process was performed for K₁, O₁, M₂, and S₁ components of OTL. In each component, a periodic variation in dPWV appeared which was similar to those of the simulated GPS_PWV errors from OTL effects calculated with‘GOTIC’ (Sato and Hanada, 1984), a program for the computation of OTL effect. Inclusion of OTL effects into GIPSY analysis reduced dPWV. In the M₂ component, the amplitude of the dPWV was reduced by about 80%. This suggests that the OTL components calculated by the GOTIC succeeded in simulating the actual site displacement by OTL effects in Japan. On the other hand, in K₁ components, the amplitude of dPWV without OTL in GIPSY is 1.5 times larger than the simulated GPS_PWV error, with considerable error remaining even in the case of GIPSY analysis with OTL. The error may be due to multi-path effect, temperature dependency on conversion from Zenith Wet Delay to PWV, or instrument dependency of WVR on temperature. Analysis utilizing much longer data periods than the present two months is required to overcome these difficulties.

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Water vapour is a key variable in atmospheric processes and plays a crucial role in atmospheric motions on a wide range of scales in space and time. The water vapour content is approximately proportional to the zenith wet delay (ZWD) which, in turn, constitutes a crucial parameter in geodetic microwave space techniques (VLBI and GPS). Apart from being determined by measurement techniques, the ZWD can also be derived from numerical weather prediction (NWP) models such as the non-hydrostatic MM5 model and the hydrostatic HIRLAM model. At the station Robledo de Chavela (Madrid) ZWD values were derived from VLBI, GPS, MM5, and HIRLAM for the beginning of December 1996. The results of the different techniques agree to the sub-centimetre level with correlation values of 0.87 (GPS vs. MM5), 0.81 (GPS vs. HIRLAM), and 0.84 (MM5 vs. HIRLAM). The correlation VLBI vs. MM5 of 0.78 is based on a short VLBI time series and should be considered preliminary. Further studies with longer time series are necessary to confirm this value. The bias and RMS difference values are all contained in the margin provided by the internal errors.

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Very Long Baseline Interferometry (VLBI) is collocated with a permanent Global Positioning System (GPS) receiver and a Water Vapor Radiometer (WVR) at the Onsala Space Observatory in Sweden. Both space geodetic techniques are affected by the propagation delay of radiowaves in the atmosphere, while the remote sensing technique is sensitive to the atmospheric emission close to the center of the 22 GHz water vapor emission line. We present a comparison of estimated equivalent zenith wet delay and linear horizontal delay gradients from an independent analysis of simultaneous VLBI, GPS, and WVR observations. Using different constraints for the variability of the delay and the horizontal gradient in the analysis of the VLBI and the GPS data did not have a large influence on the agreement with the WVR estimates. We found that the weighted rms differences between wet delay estimates from the geodetic techniques and the WVR estimates generally increased for an increased variability in the atmosphere.

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New mapping functions based on in situ meteorological parameters have been developed for calculating the radio path length through the atmosphere at elevations down to 3°. The hydrostatic component of the mapping function is related to the geopotential height of the 200 mb isobaric pressure level above the site and provides a factor of two improvement in accuracy and precision over previous hydrostatic mapping functions at mid-latitudes. The wet component of the mapping function is calculated from the vertical profile of wet refractivity at the site but will provide an improvement of only about twenty-five percent. However, since the effect of known errors in the hydrostatic mapping function dominates that from the wet component, except near the equator, implementation of these mapping functions should reduce the contribution of the atmosphere to errors in estimates by VLBI and GPS of both the vertical component of site position and the radio propagation delay due to water vapor in the atmosphere.

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In space to earth geodetic techniques the atmosphere affects the radio wave propagation. In order to estimate the total non-zenith path delay several mapping functions have been proposed to scale the zenith delay to other elevations. For all of them the basic idea is that the ultimate direction of the ray path is exactly that of the vacuum elevation of the radio source, and this is used to estimate the delay. This is true when we consider VLBI observations from a distant radio source but not the case for satellites or other near-earth radio sources. In this case the radio source distance is no longer infinite, and we have to think of a slightly different radio ray direction. This may insert a reasonable error in delay estimation. Thus, for satellite observations, the source elevation angle must be corrected for the ray bending effect before we use it with a mapping function to scale the delay. This means that either we have to estimate this correction of the angle or we have to develop a model that includes the correction. In this report we evaluate the magnitude of the correction and discuss the way we can approach and map it. Another purpose of this report was to study different mapping functions used to predict the hydrostatic delay at low elevation angles. Also a study of models with constant terms shows that such a model optimized for a site or region can give satisfactory results.

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The Global Positioning System (GPS) is used to provide hourly measurements of precipitable water (PW) in Taiwan during the passage of tropical cyclones. Typhoon Zeb, which caused serious damage in the Philippines, Taiwan, and Japan in mid-October 1998, is used as an example in this paper. GPS data are analyzed from the Central Weather Bureau's (CWB's) three weather stations in Taiwan, and from a site in Tsukuba, Japan. Bernese version 4.0 software is utilized to solve GPS signals for total delay due to the neutral atmosphere at the three CWB sites. Wet delay is obtained by subtracting surface pressure derived dry delay from total delay. Wet delay is then converted to PW through a simple calculation. GPS-observed PW time series demonstrate that PW is, in general, high before and during the occurrence of the typhoon, and low after the typhoon. PW increased from about 5 cm on DoY 285 (October 13) to near 8 cm or so on DoY 288 (October 16) when the typhoon was striking Taiwan, and, then, decreased to 2-3 cm after passage of the typhoon. In addition, GPS-observed PW depletion from 8 cm on DoY 288 to about 3 cm on DoY 290 is found to be consistent with radiosonde observations acquired at the Taipei weather station.

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Repeated GEODYSSEA-GPS measurements and additional GPS data from the IGS and APRGP97/98 constrain the motion of SE-Asia within a global reference frame. Sundaland i.e. Indochina as well as the western and central part of Indonesia, together with South-China, constitute an apparently stable tectonic block that is decoupled from Eurasia. In the ITRF97 this block moves to the east about an Euler pole approximating that of Eurasia, but with a velocity that is one third higher than the eastward directed movement of Eurasia. With respect to India and Australia the Sundaland-South China block is moving due south. This suggests that a) Sundaland-South China are moving coherently to the East along the boundaries studied and b) the eastward motion of India is compensated by the eastward motion of Sundaland-South China. The current rather homogeneous kinematic behaviour of Sundaland-South China that differs in rate (no more than 5 mm) rather than direction from the movement of N-China differs from the kinematics proposed by different modelling approaches throughout the literature. The data help to constrain locations and behaviour of the active fault zones and give information on the interplate and intraplate deformation in the area.

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In the framework of the GEODYnamics of South and South-East Asia (GEODYSSEA) project a network of 42 stations was observed by GPS during two field campaigns in 1994 and 1996. BKG and GFZ realized a third observation of the complete network in 1998. The data was analyzed independently by two analysis centers and a precision of the coordinate solutions was found to be 4-7 mm for the horizontal, and 10 mm for the vertical component. Subsequently, these campaign solutions were merged into one unique solution, which was accurately mapped into the International Terrestrial Reference Frame of 1997 (ITRF97). The global accuracy of this solution with respect to ITRF97 is of the order of 10 mm, while the resolution of the relative horizontal velocities is estimated to be at the level of 2-3 mm/yr. Comparison of the new solution with the previously published GEODYSSEA solution indicates, that improved results for the motion of Sundaland, South China and the overall deformation in the area could be found. Improvements are due to the increased time span and due to a better connection to and the advances in the ITRF reference frame. The new set of coordinates and velocities is used as the basis for scientific interpretations, which have been and will be published in separate papers.

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Papua New Guinea is one of the most active tectonic regions in the world. It comprises several microplates and deforming zones trapped in the collision of the Australian and Pacific Plates. GPS observations have been used to estimate plate velocities across a network of sites spanning most of the country. We present new velocites in the northwestern region of New Guinea, and look in detail at the strain accumulation region between the South Bismarck and Pacific Plates in the New Ireland/New Britain region.

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Mark III VLBI observations between August 1979 and December 1998 were analyzed to yield the terrestrial and celestial reference frames (TRF and CRF) and the Earth Orientation Parameters (EOP). Comparisons with ITRF96, RSC (WGRF) 95 R01 and EOP (IERS) 97 C04 are performed. For CRF, the three orientation angles are not significant at the level of precision of 0.1 mas. Though no significant values are found for the three deformation parameters, coordinate drifts up to 0.5 mas are identifiable for some sources in the southern hemisphere. The relative rotation angles and their rates of change for TRF are not significant respectively at the precision level of 0.2 mas and 0.1 mas/yr. Detailed comparisons however show that the differences in the velocity field are obvious for the eastern part of Eurasian plate and Australian plate. About EOP series, the systematic differences and the relative drifts are not significant respectively at the level of 0.4 mas and 0.1 mas/yr.

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Amongst various space techniques, GPS-geodesy has proved to be an indispensible tool worldwide for geodynamics and the determination of parameters governing seismotectonics. To study the Indian plate kinematics, an IGS station has been established in September 1995 at NGRI, Hyderabad, India, under the Indo-German collaborative research programme. During the first off-line data transmisssion phase, about one to two days per week of observations were taken. The data analysis has been carried out at the University of Bonn using the Bernese Software version 4.0. The Hyderabad data have been processed together with the data from 8 other selected IGS stations in and around the Indian plate. In our preliminary analysis, which concentrated on the ITRF96 frame-consistent part of the data set, we found the motion of the Indian plate with respect to the Eurasian plate to be significantly smaller than the model rate, i.e. 3.7 cm/y for Hyderabad instead of 4.5 cm/y in the NUVEL-1A plate model. We detected no significant motion between Hyderabad and Bangalore, lying 500 km apart in N-S-direction on the Indian plate.

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The Black Sea occurs within the Anatolian sector of the Alpine-Himalayan orogenic system. In this region northward moving African and Arabian plates collide with Eurasian plate. From this collision the Anatolian block moves westward with a rotation pole located approximately north of Sinai peninsula. Tectonic styles and rates in the circum Black Sea and along the Crimea have been poorly known. A GPS project was initiated in 1995 with the collaboration between Istanbul Technical University, MIT and Joint Institute of Physics of the Earth (Moscow). To carry out the project, two GPS campaigns were performed. Data have been analysed by the well-known GPS processing program, GAMIT which is a comprehensive GPS analysis package, and GLOBK, a Kalman filter. This paper presents the important outputs from the two GPS campaigns and gives suggestions for the future investigations in the region. The important outcome of the project is that the N-S motions along mostly in the Eastern margin of the Black Sea are in a few mm/year, such as SINO, a southern coast site, with a rate of 1.4 ± 1.7 mm/year in NW direction, and GELE, a northern coast site, with a rate of 2.2 ± 2.8 mm/year in SE direction, while the velocities in the Anatolian region are approximately 10-20 ± 3-5 mm/year.

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Two devastating earthquakes occurred in Turkey, one on August 17 and the other on November 12, 1999. The magnitudes were 7.4 and 7.2 respectively. The epicenter of the first earthquake was located near Golcuk, a town near Kocaeli province, 110 km from Istanbul. The epicenter of the second earthquakewas in Duzce, 150 km from Istanbul. The first earthquake occurred after midnight and killed more than 15000 people. This number is obtained from an official report, while the actual deaths are expected to be more than 20, 000. The earthquake was a nightmare for the whole country, and affected almost 10 cities including Istanbul. The second earthquake occurred on November 12 in the early evening, and killed about 1000 people. The affected area from the two earthquakes has a population of about 20 million, which is one third of the whole population of the country, and almost half of the Turkish economical infrastructures is located in this region. This paper gives an overview of the two devastating earthquakes, including geological background of the region, economical impacts and degrees of damages on different aspects.

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Geodetic VLBI observations have been performed with the European geodetic VLBI network since early 1990 on a regular basis. The purpose of these observations is to determine crustal motion in Europe and to establish a stable reference frame for other space geodetic techniques. Over the years the size of the network and the number of participating stations has steadily increased. Today, the network extends from the island of Sicily in the south to the island of Spitsbergen/Svalbard in the north and from the Iberian peninsula in the west to the Crimean peninsula in the east. The area covered by the network is affected by two main geodynamic processes which are post-glacial rebound effects in the northern part, and the evolution of the Alps-Apennines orogenic systems in the southern part. With nearly 10 years of VLBI observations the determination of crustal motion in Europe is carried out with high accuracy. Baseline measurements are achieved with an accuracy of a few parts per billion. We compare the evolution of baseline lengths and topocentric station displacements with geophysical models. Strain rates in Europe on a large scale are determined from the results of the VLBI analysis.

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The objective of this paper is to outline the fundamental concepts underlying the estimation of a global strain rate model. We use a variant of the method first introduced by Haines and Holt (1993) to estimate the strain rate tensor field within all of the Earth's deforming regions. Currently the observables used are -1650 geodetic velocities, seismic moment tensors from the Harvard CMT catalog, and Quaternary fault slip rate data. A model strain rate field and velocity field are obtained in a least-squares fit to both the geodetic velocities and the observed strain rates inferred from fault slip rates. Seismic moment tensors are used to provide a priori constraints on the style and direction (not magnitude) of the model strain rate field for regions where no fault slip rate data are available. The model will soon be expanded to include spreading rates, ocean transform azimuths, and more fault slip rate data. We present a first estimate of the second invariant of the global model strain rate field. We also present Euler poles obtained by fitting geodetic vectors located on defined rigid plates. We find that 17% of the total model moment rate is accommodated in zones of (diffuse) continental deformation.

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Satellite-based navigation rapidly evolved into an efficient tool extensively used in a wide variety of civilian applications covering numerous modes of transportation, communication, administration, geodesy, agriculture, and many others. The current systems globally available are the US Global Positioning System (GPS) and the conceptually very similar Russian Global Navigation Satellite System (GLONASS). Considering the worldwide applications, GPS clearly predominates over GLONASS. However, GPS and GLONASS are mainly under military control of single nations and, also critical, do not fulfill certain performance requirements of the civil users, especially in terms of safety-critical applications. Thus, augmentations to the current systems and even completely new systems are under investigation. These are usually summarized under the abbreviation Global Navigation Satellite Systems (GNSSs). The various types of GNSS are described where emphasis is put on the future US and European contributions to the second-generation GNSS, i.e., the modernized GPS and the definition of the new European Galileo system. These two systems may be characterized as “compatible competitors”-thus, one might ask for whom the bell tolls.

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Low elevation data may be included in the processing of small scale engineering GPS applications, in order to improve satellite geometry and reduce the required observation time. Careful weighting of the phase observations is needed then, because of increased noise and systematic errors. The measured carrier-to-noise-power-density ratio (C/N0) has proven to be an excellent tool for the estimation of the random errors of the phase observables. In this paper an extended weight model using robust estimation is presented, in particular the Danish Method. This model combines the information inherent in C/N0 and the residuals of the double differenced phase observations in order to model random errors and signal distortion effects.

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The key requirement of centimeter-level real-time kinematic (RTK) positioning using the Global Positioning System (GPS) relies on the ability to fast and accurately determine the ambiguities of carrier-phase observations to their inherent integer values. In addition, the identification must be completed on the fly since the remote receiver is constantly in motion. The Kalman filter-based algorithm described in this paper uses an ionospheric information filter to perform on-the-fly phase ambiguity resolution for high precision RTK applications. Experiments based on 16 independent test baselines ranging from 10-50 km in length indicate that the algorithm can reliably achieve centimeter-level positioning accuracy, provided that a small enough threshold value for ambiguity identification is pre-defined and that sufficient geometry change in the GPS constellation is observed. Experimental results also show that the convergence (initialization) time for ambiguity resolution is linearly proportional to instantaneous baseline length, and the slope of the regression line increases with tighter ambiguity identification criteria.

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This paper deals with the problem of properly weighting satellite observations which are non-uniform in quality. The technique, the variance component estimation method developed by Helmert, was first applied to the 1987 LAGEOS I SLR data by Sahin et al. (1992). This paper investigates the performance of the globally distributed SLR stations using the Helmert type variance component estimation. As well as LAGEOS I data, LAGEOS II data were analysed, in order to compare with the previously analysed 1987 LAGEOS I data. The LAGEOS I and II data used in this research were obtained from the NASA Crustal Dynamics Data Information System (CDDIS), which archives data acquired from stations operated by NASA and by other U.S. and international organizations. The data covers the years 1994, 1995 and 1996. The analysis is based on “full-rate” laser observations, which consist of hundreds to thousands of ranges per satellite pass. The software used is based on the SATAN package (SATellite ANalysis) developed at the Royal Greenwich Observatory in the UK.

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Continuously operating GPS networks have been used for many years in support of: (a) geodetic goals such as the determination of crustal motion on a variety of spatial scales, and (b) to provide pseudo-range corrections for Wide Area DGPS (WADGPS) implementations. Recently, regional-scale GPS permanent networks have been developed for multi-functional uses, including to support centimetre-accuracy, medium-range, carrier phase-based GPS positioning for surveying or precise navigation applications. In such an implementation the generation of carrier phase correction messages in a manner analogous to WADGPS requires that the integer ambiguities between GPS reference stations be fixed in real-time. Although the ambiguities could be resolved at the beginning of operation the challenge remains: how to recover an integer ambiguity if a cycle slip or data gap occurs, or if a new satellite rises? In this paper, the linear data combination algorithm that has been used is described, and the issue of “ambiguity recovery” techniques for data correction generation purposes is addressed. Three strategies are suggested: (1) using an “ambiguity recovery” technique if the data gap is shorter than a minute or so; (2) re-determining the integer ambiguities using an ionospheric correction derived from the tracking to other satellites when a new satellite rises, or after a long period of data loss, and; (3) re-determining the integer ambiguities with the aid of data corrections generated on previous days. Several 7-day continuous data sets were used for algorithm testing. The corrections can be generated from multiple reference stations in the post-processing mode and then used for comparison purposes with the simulated real-time processing mode using the proposed algorithm. Results confirm that the proposed algorithm can provide reliable carrier phase data corrections for centimetre-accuracy, real-time GPS positioning.

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Successful integer estimation of carrier phase ambiguities of Global Navigation Satellite Systems (GNSS) is the key to many high precision positioning applications. In order to describe the quality of the positioning results rigorously, one needs to know the probabilistic properties of both the integer and noninteger parameters in the GNSS model. In this contribution these probability distributions are presented and discussed. The probability mass function of the integer ambiguities is needed to evaluate the ambiguity success rate and the distribution of the GNSS baseline is needed to evaluate the relevant confidence regions for positioning.

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An Optimal Method for Estimating GPS Ambiguities (OMEGA) that enables very high performance and computational efficiency has been developed and demonstrated. This method employs two search space reduction processes-a scaling and a screening process-that are related to the search space transformation and the ambiguity candidate filtering in multi-search levels. To obtain the highest efficiency, an optimization procedure, which determines the parameters to minimize the number of candidates under given conditions, is implemented in closedform before the search-verification step. The method is essentially based on the least-squares-approach originally proposed by Hatch but uses a modified and more efficient process. Two improved algorithms are introduced in this paper. First, an alternative algorithm for the spectral decomposition, which reduces the dimension of the residuals vector to its degrees of freedom, is given in closed form. This algorithm is implemented in the computational step of the quadratic form of the residuals in order to increase computational efficiency. Second, an efficient error model for the threshold of the filter equation that is used to derive the search space scaling process is given. This error model shows two advantages: 1) it bounds noise signals of the filter equation; 2) it gives efficient thresholds so that the scaling effects for the search space can be increased.

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In GPS and GLONASS satellite-based positioning, the correct determination of the integer carrier phase ambiguities is the key to achieve precise positioning results. The process of determining the ambiguities, called ambiguity resolution, is usually separated into three steps: (a) estimating the float or real-valued ambiguities, (b) searching the best integer ambiguity set, (c) validating the best ambiguity set. Whilst the theory and methodology for ambiguity estimation and search are well documented, the ambiguity validation issue is still under investigation. Existing ambiguity validation procedures are based on various statistical assumptions and therefore, may have different performances in practical applications. In this paper, the major ambiguity validation procedures are analysed and their performances in both GPS and GLONASS ambiguity resolution are numerically compared. It is concluded that both the probability of estimating ambiguities correctly and confidence levels of the ambiguity discrimination tests are both important indicators of the reliability of ambiguity resolution.

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Precise, long-range, airborne GPS kinematic positioning requires the use of carrier phase measurements, the data processing of which suffers from the technical challenges of “on-the-fly” ambiguity resolution and cycle slip repair. In this paper the authors describe how the combination of an ‘ambiguity recovery’ technique and a ‘linear bias correction’ method has been used to support oceanographic mapping in Australian waters, together with the augmentation from the Laser Airborne Depth Sounder (LADS) system. Two experiments, carried out on the 4th December 1997 in the Torres Strait between Papua New Guinea and Australia, and on the 20 May 1998 at Lake Argyle in Australia, were analysed. The results indicate that the topography of the water surface can be obtained with sub-decimetre accuracy, with a spatial resolution of a few metres. The main errors are attributable to multipath interference of the GPS signals at the antennas from the aircraft surface.

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The benefits of combined use of the GLONASS and GPS navigation satellite constellations have become obvious for applications such as open-cast mining operations and highly dynamic vehicles such as spaceplanes. Moreover, using GLONASS satellites in addition to GPS is useful for long baseline applications since it increases the numbers of satellites in common view. Japan's National Aerospace Laboratory (NAL) has been conducting feasibility studies using combined GPS/GLONASS positioning for spaceplane landing systems and the precise navigation of stratospheric airships. This paper presents the results of the first Japanese kinematic GPS/GLONASS flight test. In the test, the difference in estimated position between dual frequency GPS and single frequency GPS/GLONASS systemswas found to be within a fewcentimeters, indicating thatGLONASS carrier phase ambiguities were correctly resolved. To demonstrate the benefits of combining GLONASS with GPS navigation, an on-the-fly (OTF) test of instantaneous ambiguity resolution with a 30 degree cutoff angle was performed. The OTF performance of the combined GPS/GLONASS system was found to be similar to that of a GPS system with a cutoff angle of 10 degrees, showing that augmentation of GPS with GLONASS will be useful for highly dynamic vehicle applications.

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A concept of precise kinematic positioning and flight-state monitoring of an airborne remote sensing system is presented here, based on practical experiences from the EU project AGMASCO. Within the project about two months of kinematic GPS flight data and static reference data have been collected in Europe over four campaigns during the past three years. An independently developed GPS software package as well as several commercial GPS software packages have been used for data processing. In this paper, the methods of creating the tropospheric model for the aircraft trajectory and the use of static ambiguity results as conditions in the kinematic positioning are discussed. These concepts are implemented in the kinematic GPS software KSGSoft, and have demonstrated excellent performance.

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The main purpose of this research is to develop a real-time GPS monitoring system with the aid of a Kalman Filter for use in an active tectonic region near Istanbul, and its surrounding region. Currently, an ongoing project exists, funded by the World Bank, that monitors deformation in Istanbul and the Marmara Region. Istanbul is one of the largest cities in the world, and is under possible earthquake threat. In order to set up a powerful control system, a surveying and estimation method was designed and the necessary software, called RT-MODS2 (Real-Time Monitoring Of Dynamic Systems 2), was developed. The software reads real-time input data from GPS receivers and performs deformation analyses with the help of the Kalman Filter. Some studies of filtering and deformation analysis were performed in order to detect failures and outliers, and to increase the reliability of the deformation analysis.

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Anewtsunami observation system has been developed, which employs theRTK-GPS technique to detect a tsunami before it reaches the coast. The system consists of dual-buoys: the Support-buoy, which is sensitive to wind-waves, and the Sensor-buoy, which is of a spar-type and is insensitive to wind-waves. Both buoys are equipped with a GPS antenna. An experiment using this system was carried out for about nine days in March 1999. Observation data were monitored at the onshore base station. The results showed that hourly averaged data is consistent with ocean tides for both buoys. The Sensor-buoy was found not to respond much to wind-waves compared to the Support-buoy. Thus, it may be preferable to use a spar-type buoy for detecting a tsunami efficiently. Furthermore, a simple frequency analysis showed that a tsunami could be easily separated from higher frequency wind waves if a tsunami is superimposed on regular wind waves.

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RTK-GPS is a satellite positioning system which provides instant and accurate positions. The ranging error to the satellite from a user GPS antenna determined by the phase measurement of the carrier waves from the GPS satellites is of the order of mms. Thus an accuracy of a few cm can be easily obtained. The system is easier to operate than a traditional survey system such as the ‘Total Station’. Hence it has been used for many applications in Japan. It is necessary, however, to provide a fast data communication link for the transmission of carrier phase data from a reference station located at a known position, to a user receiver. A radio communication device with low power, is commonly used because it requires no license. However the data transmission area is generally limited to just several hundred meters in radius from the reference station. The authors have investigated RTK-GPS positioning with several different lengths of baseline using data transmission via TV audio-MPX-data broadcast, and evaluated its validity. The carrier phase data is transmitted from the reference receiver at the Tokyo University of Mercantile Marine, to the experimental station of the Asahi National Broadcasting Company, by public phone line with data rate 9, 600 bps. The data, which when multiplexed into TV audio, was then disseminated with the rate of about 8 kbps from the Tokyo Tower. The data transmission delay in this system appeared random between 0.740 and 1.317 s, of which the difference (0.577 s) corresponds to the transmission time of 32 blocks of multiplexed data. Positioning was tried at several fixed points with different lengths of baseline (0-21 km). Tests proved that the accuracy became worse as the length of baselines became longer. The 2drms height are less than the 2.5 cm, and ‘Fix’ solution success rates are more than 98 %, for shorter baselines less than 10 km in length.

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Global Navigation Satellite Systems (GNSS) are commonly used for geodetic and land surveying applications. The stand alone accuracy provided by these GNSS are insufficient for the majority of these operations (GPS, 1995), therefore some form of differential correction method is required. Accordingly, the state survey offices of Germany have installed a differential correction service for geodetic applications. Code- and phase-corrections are broadcast in the VHF-band using the RTCM V2.1 format (RTCM, 1994). One major problem is that the accuracy depends on the distance to a reference station (length of baseline) because of residual orbit and atmospheric biases. To achieve a more precise solution, a number of reference stations are connected together to form a network. Within this network these influences are computed and a set of “area correction parameters” are also transmitted in RTCM message Type 59. Field trials and measurements have confirmed the high accuracy of this service. This paper describes the system itself, investigations of communication methods as well as site planning. In addition measurements from field trials will be presented to demonstrate the high accuracy in a real-time environment.

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The theory and application of statistical quality control is well established in precise positioning, navigation and geodesy. Quality control is made up of several contributing factors, one of which is internal reliability. Internal reliability describes the ability to find biases in observational data and is represented by the Minimal Detectable Bias (MDB). The MDB provides a diagnostic tool to infer the strength with which positioning models can be validated. In this contribution closed-form expressions will be given for the MDBs of GPS code and carrier observations for three different baseline models: the geometry-free model and two variants of the geometry-based model. These expressions apply to any number of carrier frequencies. The expressions take into account the presence of ionospheric disturbances by weighting these effects. As such, they are applicable to baselines of any length.

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Airborne geoid mapping techniques may provide the opportunity to improve the geoid over vast areas of the Earth, such as polar areas, tropical jungles and mountainous areas, and provide an accurate “seam-less” geoid model across most coastal regions. Determination of the geoid by airborne methods relies on the development of airborne gravimetry, which in turn is dependent on developments in kinematic GPS. Routine accuracy of airborne gravimetry are now at the 2 mGal level, which may translate into 5-10 cm geoid accuracy on regional scales. The error behaviour of airborne gravimetry is well-suited for geoid determination, with high-frequency survey and downward continuation noise being offset by the low-pass gravity to geoid filtering operation. In the paper the basic principles of airborne geoid determination are outlined, and examples of results of recent airborne gravity and geoid surveys in the North Sea and Greenland are given.

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Researchers from The University of New South Wales (UNSW), Australia, and from the Geographical Survey Institute (GSI), Japan, have commenced a joint project to develop, deploy and test an innovative hardware/software system design for an automatic, continuously-operated ground deformation monitoring system based on low-cost GPS receiver technology. Conventional continuously-operated GPS (CGPS) networks, such as the one established in Japan by GSI to precisely measure earth surface movement, are very expensive. The high cost being primarily due to the fact that dual-frequency receivers are used. Japan's nationwide GEONET network is the world's largest, numbering nearly 1000 receiver stations, with an average station spacing of the order of 30 km. In order to densify such CGPS networks (important when high spatial resolution for the monitoring of the deformation phenomenon is required), and to promote the use of the CGPS technique in lesser developed countries, a significantly cheaper system architecture is needed. The proposed design is an integrated, dual-mode network consisting of low-cost, single-frequency GPS receivers across the area of interest, surrounded by a sparser network of dual-frequency GPS receivers. Initial tests of data collected at selected stations in the GEONET network have already shown that through enhanced data processing algorithms aCGPSnetwork containing both single-frequency and dual-frequency receivers would be able to deliver better than centimetre level accuracies, at considerably lower cost than present systems based exclusively on dual-frequency instrumentation. This paper reports the results of the first field test of this new CGPS system design, in the Tsukuba area of Japan, in August 1999. The test network consisted of: (a) several stations of the GEONET network surrounding (b) an inner network of four single-frequency Canadian Marconi GPS receivers installed by UNSW researchers. The data from both the GEONET and the UNSW receivers were processed using a specially modified version of the Bernese GPS Software Package. The software first processes the GEONET GPS station data in order to generate empirical corrections which are then applied to the double-differenced data of the GPS baselines located within the test area enclosed by the dual-frequency CGPS stations. These corrections have the effect of improving baseline solution accuracy by up to an order of magnitude, even for baselines ranging up to 100 km in length. The baselines connecting the inner network to the surrounding GEONET stations are processed in a number of modes, including 24 hr files (as is the standard practice for geodynamic applications) and hourly data files (as in volcano deformation monitoring applications). The results indicate that single-frequency-withcorrection processing can achieve accuracies of better than 5 mm in the horizontal components and 3 cm in height, while the dual-frequency results can achieve accuracies better than 2 mm in the horizontal components and 6 mm in height. In the authors' opinion, for certain geodynamic applications there are no significant differences between the single-frequency-with-correction results and the dual-frequency results, especially for the horizontal components.

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A new method of using GPS for monitoring local area deformations such as landslides is presented. Unlike the standard method of using GPS for deformation monitoring where a GPS receiver is required for each point to be monitored, the new method allows multiple points to be monitored with one receiver. A system that implements the concept has been developed. It uses a specially designed electronic component that allows a number of GPS antennas to be linked to a single GPS receiver. The receiver takes data sequentially from each of the antennas attached to the receiver. A distinctive advantage of the approach is that one GPS receiver can be used to monitor more than one point. The cost per monitored point is therefore significantly reduced. The design of the system, as well as the data management and processing strategies will be introduced in detail. Results from some preliminary tests will also be given.

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Throughout late 1998 and early 1999, the International GLONASS Experiment (IGEX) has delivered the first comprehensive inter-continental dual frequencyGLONASS data set. This experiment represents the first opportunity to assess how a second global satellite positioning system could complement existing GPS geodetic infrastructure. Based on analysis of a three station network of IGEX stations from Southern Hemisphere IGEX stations, this paper discusses the internal and external precision of long baseline GPS, GLONASS and combined GPS/GLONASS solutions, and the possible contribution of GLONASS to future regional-scale geodetic work.

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The large near-field displacements before and during an earthquake are invaluable information for earthquake source study and for the detection of slow/silent quakes or pre-seismic crustal deformation events. However due to bandwidth limitations and saturation current seismometers cannot measure many of these displacements directly. In a joint experiment between the University of New SouthWales (UNSW) and the Meteorological Research Institute (MRI), two Trimble MS750 GPS receivers were used in the Real-Time Kinematic (RTK) mode with a fast sampling rate of up to 20 Hz to test the feasibility of a “GPS seismometer” in measuring displacements directly. The GPS antenna, an accelerometer, and a velocimeter were installed on the roof of an earthquake shake-simulator truck. The simulated seismic waveforms resolved from the RTK time series are in very good agreement with the results from the accelerometer and the velocimeter, after integrating twice and once respectively. Moreover, more displacement information are revealed in the GPS RTK results although they are noisier.

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