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  • 1
    Electronic Resource
    Electronic Resource
    Geoid undulation modelling and interpretation at Ladak, NW Himalaya using GPS and levelling data (1999)
    Springer
    Journal of geodesy 73 (1999), S. 79-86 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Geoid ; GPS ; Himalaya ; Tectonics ; Suture zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Fast and accurate relative positioning for baselines less than 20 km in length is possible using dual-frequency Global Positioning System (GPS) receivers. By measuring orthometric heights of a few GPS stations by differential levelling techniques, the geoid undulation can be modelled, which enables GPS to be used for orthometric height determination in a much faster and more economical way than terrestrial methods. The geoid undulation anomaly can be very useful for studying tectonic structure. GPS, levelling and gravity measurements were carried out along a 200-km-long highly undulating profile, at an average elevation of 4000 m, in the Ladak region of NW Himalaya, India. The geoid undulation and gravity anomaly were measured at 28 common GPS-levelling and 67 GPS-gravity stations. A regional geoid low of nearly −4 m coincident with a steep negative gravity gradient is compatible with very recent findings from other geophysical studies of a low-velocity layer 20–30 km thick to the north of the India–Tibet plate boundary, within the Tibetan plate. Topographic, gravity and geoid data possibly indicate that the actual plate boundary is situated further north of what is geologically known as the Indus Tsangpo Suture Zone, the traditionally supposed location of the plate boundary. Comparison of the measured geoid with that computed from OSU91 and EGM96 gravity models indicates that GPS alone can be used for orthometric height determination over the Higher Himalaya with 1–2 m accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050221
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  • 2
    Electronic Resource
    Electronic Resource
    The GEOID96 high-resolution geoid height model for the United States (1999)
    Springer
    Journal of geodesy 73 (1999), S. 219-236 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Geoid ; GPS ; Datums ; Reference systems ; Gravity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. The 2 arc-minute × 2 arc-minute geoid model (GEOID96) for the United States supports the conversion between North American Datum 1983 (NAD 83) ellipsoid heights and North American Vertical Datum 1988 (NAVD 88) Helmert heights. GEOID96 includes information from global positioning system (GPS) height measurements at optically leveled benchmarks. A separate geocentric gravimetric geoid, G96SSS, was first calculated, then datum transformations and least-squares collocation were used to convert from G96SSS to GEOID96. Fits of 2951 GPS/level (ITRF94/NAVD 88) benchmarks to G96SSS show a 15.1-cm root mean square (RMS) around a tilted plane (0.06 ppm, 178∘ azimuth), with a mean value of −31.4 cm (15.6-cm RMS without plane). This mean represents a bias in NAVD 88 from global mean sea level, remaining nearly constant when computed from subsets of benchmarks. Fits of 2951 GPS/level (NAD 83/NAVD 88) benchmarks to GEOID96 show a 5.5-cm RMS (no tilts, zero average), due primarily to GPS error. The correlated error was 2.5 cm, decorrelating at 40 km, and is due to gravity, geoid and GPS errors. Differences between GEOID96 and GEOID93 range from −122 to +374 cm due primarily to the non-geocentricity of NAD 83.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050239
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  • 3
    Electronic Resource
    Electronic Resource
    An approach to GLONASS ambiguity resolution (2000)
    Springer
    Journal of geodesy 74 (2000), S. 421-430 
    Details
    ISSN: 1432-1394
    Keywords: Key words: GLONASS ; GPS ; Ambiguity resolution ; Satellite geodesy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract.  When processing global navigation satellite system (GLONASS) carrier phases, the standard double-differencing (DD) procedure cannot cancel receiver clock terms in the DD phase measurement equations due to the multiple frequencies of the carrier phases. Consequently, a receiver clock parameter has to be set up in the measurement equations in addition to baseline components and DD ambiguities. The resulting normal matrix unfortunately becomes singular. Methods to deal with this problem have been proposed in the literature. However, these methods rely on the use of pseudo-ranges. As pseudo-ranges are contaminated by multi-path and hardware delays, biases in these pseudo-ranges are significant, which may result in unreliable ambiguity resolution. A new approach is addressed that is not sensitive to the biases in the pseudo-ranges. The proposed approach includes such steps as converting the carrier phases to their distances to cancel the receiver clock errors, and searching for the most likely single-differenced (SD) ambiguity. Based on the results from the theoretical investigation, a practical procedure for GLONASS ambiguity resolution is presented. The initial experimental results demonstrate that the proposed approach is useable in cases of GLONASS and combined global positioning system (GPS) and GLONASS positioning.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900000096
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  • 4
    Electronic Resource
    Electronic Resource
    On-line detection of abrupt changes in the carrier-phase measurements of GPS (1997)
    Springer
    Journal of geodesy 71 (1997), S. 469-482 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Quality control ; Cusum test ; GPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract The detection of cycle slips in carrier-phase data, outliers in phase rate or in code ranges, or any other type of disorder in the measurements of the GPS system, is one of the major quality-control problems that needs to be addressed, especially where GPS is used for real-time applications or for those applications that require continuous and reliable positioning results. This study is concerned with designing algorithms to detect failures or changes of small magnitude, in order to monitor and control the quality of GPS measurements for critical real-time and/or deformation applications. In this regard, the statistical technique known as the cumulative-sum test is described for the detection of abrupt changes in the GPS carrier-phase measurements. Real GPS data have been used to test and evaluate the algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050115
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  • 5
    Electronic Resource
    Electronic Resource
    Preliminary evaluation of the Russian GLONASS system as a potential geodetic tool (1998)
    Springer
    Journal of geodesy 72 (1998), S. 356-363 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Satellite geodesy ; Navigation ; GLONASS ; GPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. By the beginning of 1996 the Russian Global Navigation Satellite System (GLONASS) constellation was completely deployed, although several satellites have already been decommissioned since then. With 17 satellites in operation (status as of 21 December 1997, although two of them are unusable and one is a non-operative spare), GLONASS is now an alternative and a complement to GPS. We present an evaluation of the current status of the GLONASS system, paying particular attention to its possible geodetic applications. Data from several receivers were used for this evaluation, including data from GPS receivers in order to allow for a comparison between GLONASS and GPS. We tested the quality of the geodetic observables, the consistency of the broadcast orbits, the single-point positioning results, and we also looked at multipath errors and cycle slips in our GLONASS data. In general the GLONASS performance has been found to be very satisfactory, even better than GPS in aspects such as single-receiver positioning or in the quality of the second-frequency pseudo-ranges due to the degradation of the GPS measurement quality under selective availability and anti-spoofing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050175
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  • 6
    Electronic Resource
    Electronic Resource
    The CARIB97 high-resolution geoid height model for the Caribbean Sea (1999)
    Springer
    Journal of geodesy 73 (1999), S. 1-9 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Geoid ; Mean sea level ; Ocean dynamic topography ; GPS ; Reference systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. A 2×2 arc-minute resolution geoid model, CARIB97, has been computed covering the Caribbean Sea. The geoid undulations refer to the GRS-80 ellipsoid, centered at the ITRF94 (1996.0) origin. The geoid level is defined by adopting the gravity potential on the geoid as W 0=62 636 856.88 m2/s2 and a gravity-mass constant of GM=3.986 004 418×1014 m3/s2. The geoid model was computed by applying high-frequency corrections to the Earth Gravity Model 1996 global geopotential model in a remove-compute-restore procedure. The permanent tide system of CARIB97 is non-tidal. Comparison of CARIB97 geoid heights to 31 GPS/tidal (ITRF94/local) benchmarks shows an average offset (h–H–N) of 51 cm, with an Root Mean Square (RMS) of 62 cm about the average. This represents an improvement over the use of a global geoid model for the region. However, because the measured orthometric heights (H) refer to many differing tidal datums, these comparisons are biased by localized permanent ocean dynamic topography (PODT). Therefore, we interpret the 51 cm as partially an estimate of the average PODT in the vicinity of the 31 island benchmarks. On an island-by-island basis, CARIB97 now offers the ability to analyze local datum problems which were previously unrecognized due to a lack of high-resolution geoid information in the area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050212
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  • 7
    Electronic Resource
    Electronic Resource
    Unification of vertical datums by GPS and gravimetric geoid models with application to Fennoscandia (1998)
    Springer
    Journal of geodesy 72 (1998), S. 64-70 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Vertical datums ; Unification ; GPS ; Geoid ; Fennoscandia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. The second Baltic Sea Level (BSL) GPS campaign was run for one week in June 1993. Data from 35 tide gauge sites and five fiducial stations were analysed, for three fiducial stations (Onsala, Metsähovi and Wettzell) fixed at the ITRF93 system. On a time-scale of 5 days, precision was several parts in 109 for the horizontal and vertical components. Accuracies were about 1 cm in comparison with the International GPS Geodynamical Service (IGS) coordinates in three directions. To connect the Swedish and the Finnish height systems, our numerical application utilises three approaches: a rigorous approach, a bias fit and a three-parameter fit. The results between the Swedish RH70 and the Finnish N 60 systems are estimated to −19.3 ± 6.5, −17 ± 6 and −15 ± 6 cm, respectively, by the three approaches. The results of the three indirect methods are in an agreement with those of a direct approach from levelling and gravity measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050149
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  • 8
    Electronic Resource
    Electronic Resource
    Geodetic measurement of horizontal strain across the Red River fault near Thac Ba, Vietnam, 1963–1994 (1999)
    Springer
    Journal of geodesy 73 (1999), S. 298-310 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Crustal deformation ; triangulation ; GPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Geodetic measurements from 1963 through 1994 are used to estimate horizontal strain rates across the Red River fault near Thac Ba, Vietnam. Whether or not this fault system is currently active is a subject of some debate. By combining: (1) triangulation from 1963, (2) triangulation in 1983, and (3) Global Positioning System (GPS) observations in 1994, horizontal shear strain rates are estimated without imposing any prior information on fixed stations. The estimated rates of shear strain in ten triangular subnetworks surrounding the fault trace are not significantly different from zero at 95% confidence. The maximum rate of dextral shear is less than 0.3 μrad/year in all but one of the triangles. The estimates help bound the slip rate in a simple elastic dislocation model for a locked, vertical strike-slip fault. By assuming a locking depth of 5–20 km, the most likely values for the deep slip rate are between 1 and 5 mm/year of right-lateral motion. These values delimit the 23% confidence interval. At 95% confidence, the slip rate estimate falls between 7 mm/year of left-lateral motion and 15 mm/year of right-lateral motion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050247
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  • 9
    Electronic Resource
    Electronic Resource
    Gps Ambiguity Resolution as a Classification Problem (1999)
    Springer
    Studia geophysica et geodaetica 43 (1999), S. 61-72 
    Details
    ISSN: 1573-1626
    Keywords: GPS ; ambiguity resolution ; classification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract In this contribution we explore the analogy between GPS ambiguity resolution on the one hand, and the problem of statistical classification, on the other hand. As classification rules we discuss the Bayes-, the MAP-, the ML- and the Minmax-rule. It is shown to what extent ambiguity resolution may be considered a classification problem. It turns out that both problems show many similarities, although some marked differences exist as well. These similarities and differences are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1023310125038
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  • 10
    Electronic Resource
    Electronic Resource
    Repeated Geodetic Measurements in the West Bohemia Seismoactive Region: Period 1993 - 1996 (1997)
    Springer
    Studia geophysica et geodaetica 41 (1997), S. 319-328 
    Details
    ISSN: 1573-1626
    Keywords: earthquake swarms ; surface deformations ; GPS ; precise levelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract The western part of the Bohemian Massif is characterized by repeated occurrences of intraplate earthquake swarms. To study surface deformations of this anomalous region, a network covering about 2000 square kilometres for repeated geodetic measurements was established in 1993 - 1994. The positions of the individual points of the network were carefully picked with respect to local tectonic structure and earthquake foci distribution. GPS and precise levelling measurements were performed 1-2 times a year. The GPS data were processed by Bernese GPS software. No tendency to any displacement - either horizontal or vertical - of geological blocks was derived from the geodetic data for the period 1993 - 96. Only displacements of less than 5 mm/year in average could occur in the whole region in that period; larger displacements would have been revealed by our measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1023355300199
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