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On principles, methods and recent advances in studies towards a GPS-based control system for geodesy and geodynamics

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On principles, methods and recent advances in studies towards a GPS-based control system for geodesy and geodynamics
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  See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/24288325 On principles, methods and recent advances instudies towards a GPS-based control system forgeodesy and geodynamics Book  · March 1989 DOI: 10.13140/2.1.3837.0240 · Source: NTRS CITATIONS 2 READS 42 1 author: Demitris DelikaraoglouNational Technical University of Athens 97   PUBLICATIONS   301   CITATIONS   SEE PROFILE All content following this page was uploaded by Demitris Delikaraoglou on 14 January 2017. The user has requested enhancement of the downloaded file.  ~ ~ ~-~~~ NASA Technical Memorandum 100716 . On Principles, Methods and Recent Advances in Studies Towards a GPS= Based Control System for Geodesy and Geodynamics zy n Demitris Delikaraoglou zyxwv ASAIGoddard Space Flight Center Greenbelt, Maryland ., National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 1989  1 ST zyxw F CONTENTS zyx Preface ............................................................................................................. v Acknowledgements ............................................................................................ ix 1 . THE NEED FOR VLBVSLR VIS-A-VIS GPS ...................................................... 1 ............................. 1 .1 -nts for Geodetic and Ge-c Contrml .......................... 2 1.2.1 Very Long Baseline Interferometry (VLBI) .................................. 2 1.2.3 Global Positioning System (GPS) ................................................. 5 ... ... 1.2 Car>ablllties and mations of Avail&& TechrligUeS 1.2.2 Satellite Laser Ranging (SLR) ....................................................... 4 2 . THE ACCURACY OF GPS RELATIVE POSITIONING ............................................. 7 2.1 mes nd ErroE ................................................................................. 2.1.1 Satellite Orbital Biases ................................................................ 9 2.1.2 Propagation Biases ..................................................................... 11 2.1 -2.1 Ionospheric delay errors .................................................. 12 2.1.2.2 Tropospheric delay errors ............................................. 16 2.3.1 Detection and Removal ........................................................ 21 2.4 Clock Errors ..................................................................................... 2 7 2.2 J &&iDsm ....................................................................... 19 2.3 Cvcle Slips ........................................................................................ 20 3 . ESTIMATION OF GPS ORBITAL PARAMETERS ................................................ 31 3.1 -era1 Co- ........................................................................ 31 3.2 ms f Motipn .............................................................................. 33 3.2.1 The Homogeneous or Two-Body Problem .............................. 34 3.2.2 The Inhomogeneous or Perturbed Problem ........................... 37 3.3 zyxwvutsr jkglv Causes Shams Orbital Frrors ................................................. 39 3.3.1 Effects of Errors in the Initial Conditions ............................ 39 3.3.2 Effect of Unmodelled or Improperly Modelled Forces ........... 3 3.4 Perturbwns to GPS Orbits ................................................................ 44 3.4.1 Disturbing Function of the Gravitational Potential ............... 45 3.4.1.1 Linear perturbations ..................................................... 45 3.4.1.2 Higher order (non-linear) perturbations ................... 51 3.4.2 Resonant Perturbations ......................................................... 53 3.4.3 Lunisolar (Third Body) Perturbations ................................. 57 3.4.4 Solar Radiation Pressure ....................................................... 60 4 . TIME. COORDINATE FRAMES. AND OBSERVABLES .......................................... 66 4.1 Time and GPS ........................................................................................ 6 4.2-e Frames ................................................................................ 69 4.3 mrvables .......................................................................................... 73 5 . STRATEGIES FOR ORBIT DETERMINATION AND BASELINE ESTIMATION ....... 80 5.1.2 The Active Control System ..................................................... 83 84 .2 mdes of for Orbit Determtr@ion and Baselinelstimalgm 5.3 A priori information in the GPS Satellite netwQLbS .......................... 85 5.4 Experimental rem ......................................................................... 91 5.1.1 The Fiducial Network System ................................................ 81 .. .. ... .. iii PREWiPG PAGE BUNK zyxwv OT FPLMEO  6. SUMMARY AND DIRECTIONS FOR FUTURE WORK .......................................... 98 REFERENCES zyxwvuts ............................................................................................ 0 0 z LIST OF FIGURES 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3.1 3.2 3.3 3.4 3.5 4.1 4.2 5.1 5.2 5.3 5.4 5.5 5.6 Differential range geometry ........................................................................ 1 1 Influence of ionospheric refraction on GPS observations ............................ 13 Error in differential ionospheric path delay per 1 m of unmodelled (or improperly modelled) vertical ionospheric delay ....................................... 16 Effect of wet tropospheric refraction modelling errors on GPS translated from VLBl experience based on observation periods of 24 hours ....................................................................................................... 17 Geometry of multipath effect on GPS signals ............................................... 19 Cycle slips and outlier observations can be readily seen in the rate of change-of-phase observable ................................................................... 22 Cycle slip removal residuals following simple polynomial fits to the phase observable ................................................................................... 22 The satellite orbit geometry as projected onto a unit sphere; the geometry of the orbital ellipse ............................................................... 35 Perturbation effects on the GPS satellite orbits due to the second zonal harmonic of the geopotential ....................................................................... 50 Perturbation effects on GPS orbits due to higher degree and order terms of the geopotential excluding Cz0 ....................................................... 52 Schematic representation of the earth's ellipticity causing resonant effects on the GPS orbits ............................................................................. 53 Solar radiation pressure geometry .............................................................. 62 Precession and Nutation angles ..................................................................... 71 Schematic representation of carrier beat phase observable generation ..... 75 Schematic representation of the Canadian GPS-based Active Control System station operation ............................................................................ 82 Site locations for the Spring '85 and Summer '86 GPS Experiments ......... 91 Orbit precision with 6-day multi-arc solutions using TI-4100 data from the Spring '85 Experiment ................................................................. 93 GPS vs. VLBl at Owens Valley (non-fiducial station) illustrating the effect of variation of the arc length .............................................................. 94 Day-to-day baseline repeatability at Owens-Mojave (245 km) and Owens-Hat Creek (484 km); 6-day orbits held fixed in daily solutions ... 95 Baseline repeatability using the "free" network approach with single- pass, short-arcs for satellites 6, 8, 9 and 11 ............................................ 97 . iv  PREFACE zyxwv . In the past decade or so, there has been considerable interest and progress in the development and utilization of space techniques for precise measurements of geodetic baselines, earth orientation, and various geodynamic studies, especially for measuring large-scale distortions within plates and determining the rates of interplate motion. These methods rely heavily on extra-terrestrial reference sources such as the distant quasars or other compact extragalactic objects used in zyx ery Long Baseline Interferometry (VLBI), or the moon used for Lunar Laser Ranging (LLR) and the low- earth satellites such as LAGEOS and STARLETTE used in Satellite Laser Ranging (SLR). Notably, VLBl and SLR have achieved significant superiority over other conventional approaches for measuring vector baselines very precisely. As currently applied, VLBl and SLR have reached a level of maturity that to date can be used to measure routinely baseline vectors with lengths up to intercontinental distances with repeatabilities of 0.01 parts per million or better in both length and orientation. In both techniques a number of fixed stations are used to determine the variations of the earth’s angular orientation in space, to measure plate tectonic motions through monitoring of the locations of the fixed stations with respect to each other, and to contribute to the maintenance of a reference frame with respect to which the motion of additional points of interest can be determined by means of mobile VLBl and SLR equipment. However, in addition to the high cost of instrumentation and operation, such mobile systems can still be somewhat limited in their ability to occupy sites which are not easily accessible, thus limiting their use for many regional geodetic and geodynamic applications where more measurements of this type are needed, at more frequent intervals in time and space. Operational costs are particularly high for SLR due to the system’s susceptibility to weather. Typically, zyxw   to 30 days for fixed (and up to 60 days for mobile) site occupations are required if the length of intersite baselines up to intercontinental distances were to be determined to a precision of 3-5 m. By contrast, for the most basic IRIS network of fixed VLBl sites (i.e. the POLARIS and Wettzell observatories) the time typically required to achieve sub-decimeter accuracies in the determination of baselines of similar lengths corresponds to observation intervals of the order of 24 hours. Mobile VLBl systems are less sensitive to adverse weather, but involve considerable operations since the smaller-diameter antennas yield less- sensitive interferometers than normally achievable with the larger fixed antennas which, in turn, impose severe limitations in the observing schedules (often restricting observations to the stronger sources) and tend to distort the experimental geometry and observing strategies. This decrease in sensitivity can, in principle, be compensated for by high-gain antennas, low-noise receivers and multi-observing sessions but not without the expense of all the attendant complexities and increased cost of operations. Although these technologies are becoming an increasingly important tool for geodynamic studies, the future role of mobile VLBl and SLR may well be fulfilled by using alternative techniques such as those utilizing the signals from the Global Positioning System (GPS) which, already without the full implementation of the system, offers a favorable combination of cost and accuracy and has consistently demonstrated the capability to provide high-precision densification control in the regional and local areas of the VLBl and SLR networks. Although GPS itself is still technically in its testing phase and is not expected to become fully operational until the early 1990’s with the V
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