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  • 1.
    Almgren, Kjell
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    A new method for GPS ambiguity resolution on-the-fly at short baselines1998Doctoral thesis, monograph (Other scientific)
  • 2.
    Burman, Helén
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Calibration and orientation of airborne image and laser scanner data using GPS and INS2000Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    GPS and INS measurements provide positions and attitudesthat can be used for direct orientation of airborne sensors.This research improves the final results by performingsimultaneous adjustments of GPS, INS and image or laser scannerdata. The first part of this thesis deals with in-airinitialisation of INS attitude using GPS and INS velocitydifference. This is an improvement over initialisation on theground. Even better results can probably be obtained ifaccelerometer biases are modelled and horizontal accelerationsmade larger.

    The second part of this thesis deals with GPS/INSorientation of aerial images. Theoretical investigations havebeen made to find the expected accuracy of stereo models andorthophotos oriented by GPS/INS. Direct orientation will becompared to block triangulation. Triangulation can to greaterextent model systematic errors in image and GPS-coordinates.Further, the precision in attitude after triangulation isbetter than that found in present INS performance. On the otherhand, direct orientation can provide more effective dataprocessing, since there is no need for finding or measuring tiepoints or ground control points. In strip triangulation, thenumber of ground control points can be reduced, since INSattitude measurements control error propagation through thestrip. Even if consecutive images are strongly correlated indirect orientation, it is advisable to make a relativeorientation to minimise stereo model deformations.

    The third part of this thesis deals with matching laserscanner data. Both elevation and intensity data are used formatching and the differences between overlapping strips aremodelled as exterior orientation errors. Special attention ispaid to determining misalignment between the INS and the laserscanner coordinate systems. We recommend flying in fourdifferent directions over an area with elevation and/orintensity gradients. In this way, misalignment can be foundwithout any ground control. This method can also be used withother imaging sensors,e.g.an aerial camera.

    Keywords:Airborne, Camera, Laser scanner, GPS, INS,Adjustment, Matching.

  • 3.
    Carballo, Gabriel
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Statistically-based multiresolution network flow phase unwrapping for SAR interferometry2000Doctoral thesis, monograph (Other scientific)
  • 4.
    Dunkars, Mats
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Automatic generation of a view to geographical database2001Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    This thesis concerns object oriented modelling and automatic generalisation of geographic information. The focus however is not on traditional paper maps, but on screen maps that are automatically generated from a geographical database. Object oriented modelling is used to design screen maps that are equipped with methods that automatically extracts information from a geographical database, generalises the information and displays it on a screen. The thesis consists of three parts: a theoretical background, an object oriented model that incorporates automatic generalisation of geographic information and a case study where parts of the model have been implemented.

    An object oriented model is an abstraction of reality for a certain purpose. The theoretical background describes different aspects that have impact on how an object oriented model shall be designed for automatic generalisation. The following topics are described: category theory, the human ability to recognise visual patterns, previous work in automatic cartographic generalisation, and object oriented modelling.

    A view is here defined to consist of several static levels, or maps, defined at different resolutions. As the user zooms the level that is appropriate for the particular resolution is shown. An object class belongs to one and only one level and has a certain symbolisation. The automatic creation of new objects in a level is discussed as well as the relation between objects in different levels. To preserve topological relations between objects in a level a network structure is formed between all linear objects in a level and objects that might cause conflicts are modelled using dependencies.

    The model is designed for a set of typical geographical object classes such as road, railroad, lake, river, stream, building, built-up area etc. The model is designed to handle information in a scale-range from 1:10 000 to 1:100 000. The model has been implemented for a subset of these classes and tested for an area covering approximatley 60 km2.

  • 5.
    Ellmann, Artu
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Least squares modification of Stokes formula with application to the Estonian geoid2001Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Many applications in geodesy,geophysics and engineering require physically defined heightsrelated to an equipotential surface of the Earth, thegeoid.

    During the last two decades theincreased need for refined geoid models has been driven by thedemands of users of GPS, who nowadays must transformGPS-derived geodetic heights into orthometric heights, makingthem compatible with the local vertical datum. Therefore, forthe conversion and combination of these fundamentally differentheight systems, the geoid model must be known with an accuracycomparable to the accuracy of GPS and traditional levelling,i.e. a few centimetres.

    Stokes formula enables thedetermination of the geoidal height from the global coverage ofgravity anomalies. In practice, the area of integration islimited, thus implying a truncation error of the estimatedgeoidal height. The modification of Stokes formula allows theuser to compensate the lack of a global coverage of gravitydata by a combination of terrestrial gravity with a globalgeopotential model (here EGM96). The minimization of thetruncation error, the influence of erroneous gravity data andpotential coefficients could be treated using the least squaresmodification of the Stokes formula, proposed by Sjöberg in1984.

    The aim of this thesis is todetermine the Estonian geoid by the biased least squaresmodification of Stokes formula. The significant improvement ofthe data coverage in Baltic Sea region in last few years iscomprised in the research.

    Geoid determination by Stokesformula requires that there are no masses outside the geoid,and the classical approach is to apply a so-calledremove-restore technique.

    As proposed by Sjöberg in1994, corrections related to topography (and atmosphere) couldbe made on the geoid directly. Thus the combined correction oftopographic (and atmospheric) masses, as a sum of direct andindirect effects, can replace the traditional approaches.

    The expressions for the totaltopographic (and atmospheric) effects for the biased leastsquares modification of Stokes formula are derived and appliedin the numerical computations.

    The geoid is calculated bydifferent sets of modification coefficients. The preference isgiven to the geoid model called EST-01 which is calculated bythe following initial conditions: modification degree 360,terrestrial gravity anomaly variance 9mGal2(correlation length 0.1° ), truncationcap radius 2° .

    The model EST-01 is validated by26 high-precision GPS/levelling points.

    The mean bias of -30cmand a small tilt between EST-01 and GPS/levellingpoints were detected, most likely caused by long wavelengtheffects. A root mean square error of 3.0cmfor post-fitting residuals was obtained using afour-parameter fitting.

    The accuracy of the relativeheight determination was evaluated by a set of lower orderGPS/levelling points. For baselines shorter than 12kma root mean square error of 2.3cmwas obtained, which is satisfactory for the mostpractical applications.

    Key words: geoid, Stokes formula, least squaresmodification, total topographic correction, total atmosphericcorrection, GPS/levelling.

  • 6.
    Gajdamowicz, Krzysztof
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Automated processing of georeferenced colour stereo images for road inventory1998Doctoral thesis, comprehensive summary (Other scientific)
  • 7.
    Hagenäs, Per
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Positioning with supported GPS, A simulation study1995Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The satellite based on positioning system GPS has a very high potential in accuracy and general performance. It has also low cost, low weight and low power consumption.

    However, among all good proprieties there exist some bad ones. The most serious disadvantages of GPS are that the satellite signal is often disturbed by other electromagnetic signals and that it is shaded by physical obstacles. This diminishes accuracy and reliability, especially when GPS data is used in real time.

    To decrease this uncertainly, the GPS system should be supported by a complementary sensor. For this supported GPS system the following questions are raised:

    -how should this positioning system look like and what mathematical methods should be used to get most accurate estimate of the navigation parameters?

    -how should the achieved accuracy be estimated?

    -how could erroneous observations be sorted out?

    This report suggests several methods to solve these problems. Some of these are tested with for this purpose developed software called GPSlab. The main idea is that this is an optimization problem that should be common for all types of sensors to be integrated. A realization of the solution of these problems as software, is here called “A Navigation core”

    Suggestions presented in this report are:

    -an optimal estimate of parameters should be carried out on the row data level. This has the advantage to preserve the position information content,

    -with help of a supporting device it is possible to use several epochs to calculate a more accurate point solution,

    -if the ambiguities are solved to a number of satellites, also if the number is less than four, a new adjustment of the coordinates should BE Carried out. In this adjustment the observations with solved ambiguities are given a high weight and the pseud oranges are given a low.

    -a kalman filter could be used on the raw data level. It could detect deviations in the observations such as malfunctions, multipath, cycle slips and other significant errors,

    - a calibration of the supporting device should be performed when the ambiguities to observed satellites are solved.

    -it is proposed that Förstner’s method could be used to estimate the proper weights

    -a method is proposed to detect large errors

    -the accuracy of the solved parameters is estimated with the help of an optimal weighted point solution, with or without the solved ambiguity

    -a method to decrease the search volume of possible solutions for ambiguity is proposed,

    - a method to integrate sensors with different properties is suggested.

     

    The simulations show that with the used positioning method, it seems likely to solve the ambiguities, with the support of an Medium Accuracy Navigation System. It also seems possible to solve the ambiguities with the support of an odometer as the only supporting sensor. In that case, however, there have to be at least six satellites, good satellite geometry, small height variations and small errors in the odometer.

    Furthermore, the azimuth information of the GPS should be used and the observations should be weighted. This system must be initialized with at least five satellites when the receiver is not moving and with at least, probably 7-8 satellites that the receiver moves.    

     

  • 8.
    Horemuž, Milan
    et al.
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Sjöberg, Lars Erik
    KTH, Superseded Departments, Infrastructure.
    Rapid GPS ambiguity resolution for short and long baselines2002In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 76, no 07-jun, 381-391 p.Article in journal (Refereed)
    Abstract [en]

    A method of quick initial carrier cycle ambiguity resolution is described. The method applies to high-quality dual-band global positioning system observations. Code measurements on both frequencies must be available. The rapidity of the method is achieved through smoothing pseudoranges by phase observables and forming linear combinations between the phase observables. Two cases are investigated. Case 1: ionospheric bias is neglected (short distances); and case 2: the bias is taken into account (longer distances, more than, say, 10 km). The method was tested on six baselines, from 1 to 31 km long. In most cases, single-epoch ambiguity resolution was achieved.

  • 9.
    Hunegnaw, Addisu
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Geoid determination over Ethiopia with emphasis on downward continuation of gravity anomailes2001Doctoral thesis, comprehensive summary (Other scientific)
  • 10.
    Jansson, Patric
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Precise kinematic GPS positioning with Kalman filtering and smoothing1998Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The Global Positioning System (GPS) has proven to be auseful tool for the determination of positions of a widevariety of moving platforms to accuracies in the order of a fewcentimetres. One of the critical aspects of precise kinematicGPS positioning at the centimetre level is the determination ofinteger carrier phase cycle ambiguities. The carrier phaseobservable is the most precise measurement available, but onlythe fractional part of the phase can be measured. In thisthesis, a newly developed method at KTH for resolving theunknown integer ambiguities has been implemented and tested onreal data. The results show that the method is very efficientand fast on kinematic GPS data at short baselines. In allcases, the new method was able to resolve the ambiguitieswithin five epochs after that both L1 and L2 observables areavailable from at least five satellites.

    For a land mobile user, however, the satellite signal isoften subject to shadowing by trees, bridges, buildings, orhills. This situation will for the precise user, working withresolved ambiguities, severely degrade the accuracy of theestimated positions until enough of satellites,i.e.at least four, are available again. With respect tothe necessary effort, it should be carefully investigatedwhether the realtime capacity is in fact needed for a giventask. If it is found appropriate for the surveying task topost-process the data, a very cost-effective way to bridge theintervals with data deficiency is to use mathematical means asoptimal smoothing algorithms. In this thesis, three differentsmoothing algorithms have been reviewed, discussed and testedon kinematic GPS data: The Fraser-Mayne smoother, theRauch-Tung-Striebel smoother, and the Bryson-Frazier smoother.During shorter intervals of data deficiency (some tenths ofseconds), it is found that the smoothing algorithms will helpsustainingthe precision and estimates that are close to thetrue ones. In fact, their performances at these occasions arefound to be remarkably good.

    At short baselines, it is common practice only to usestandard models for describing the influence from theatmosphere on the observables. Additionally, multipath is noteasily described in the model and is another disturbing factorinfluencing the measurements that is left unmodelled.Consequently, it is not a wild guess that time correlationsbetween measurements, in some cases, may exist. Aiming ataccuracies at the level of some few centimetres, it is foundthat kinematic GPS measurement sequences should be carefullyinvestigated in terms of existing time correlations.

    In this thesis, a general recursive statistical testingscheme for measurement model errors are reviewed and discussedfor Kalman filter design and error analysis. The adoptedapproximate adaption algorithms were found to be viablealternatives to their more rigorous counterparts. The resultsshow that in practice it is possible to revert the filter tooperate under the null hypothesis after adaption of up to threeslips, which is in contrast to what Teunissen and Salzmann(1989) and Salzmann (1995) found out. However, in this case,the obtained results may be sub-optimal.

    Key words:GPS, Kalman filter, smoothing

  • 11.
    Jansson, Patric
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Underwater Positioning1994Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The project underwater positioning was initiated by the Swedish National Road Administration (SNRA) in 1990. The aim of the project is to study positioning techniques and methods which can be used to position and locate man-made structures and features, especially engineering structures, piles for the foundation*laying of bridge pillars, in shallow water. In many years, SNRA has used a taut wire system, which today cannot meet their accuracy demands. In the very beginning of the project, acoustic, light and inertial techniques were considered to be the alternative techniques, which already would have been able to meet the demands. Or would be able to meet them in the nearest future after some modifications or developments. Therefore, a study of these techniques have been performed by the author in this thesis.

    The behavior and the proprieties of acoustics in water are described. The main phenomena and effects influencing underwater sound transmission, like different kinds of transmission losses and noise, are explained. Long, short and ultrashort baseline method and their different modes, inherent properties and errors sources are described. Among these three different methods, each of the three has distinct advantages and disadvantages. Long baseline and short baseline system have reached an advanced level of maturity and little further development of basic hardware components is anticipated in the future. The design of systems combining two of the three different methods, long and short baseline or long and ultrashort baseline systems, have advanced dramatically in the last years and seem to provide the best of both worlds, convenience, speed and accuracy.    

    An alternative to acoustics for accurate underwater positioning is electromagnetic radiation. This technique applied at frequencies high enough to be useful is highly absorbed in the sea because of the electrical conductivity of seawater. The only useful range is the optical one, but even there, one’s capabilities are limited to approximately 100 meters. Optical properties of the ground water environment are explained and the laser technique and its applications in water are described. In spite of the fact that the working range is not by far as long as for acoustics or electromagnetic radiation.

    After the review of existing techniques, some numerical investigations are carried out in order to estimate the precision of transponder coordinates on or near the seabed when four different parameters or coordinates are changed, i.e. surface positioning technique, network configuration, platform tracking pattern and transponder depths. Although optimization of the tracking pattern and network configuration are not thoroughly investigated, several patterns and configurations are examined in the simulations.

    The results of the numerical investigations show only slight differences between the two different surface positioning techniques. The considered standard deviation of the vertically transferring may be optimistic, which affect the results to a great extent. The lowest precision values of seabed sites are yielded assuming vertically transferred transponder sites and with a total number of four transponders at the seabed. On the contrary, including an additional transponder, from 5 to 6 and 6 to 7 transponders.

    From the results of the concept GPS as the surface positioning technique one can conclude that the surface track pattern should be symmetrically spread over and around the seabed transponder network and be made as dense as possible. Subsequently Kalman filtering and optimum smoothing should be paid attention in this type of analysis.

  • 12.
    Klang, Dan
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Reconstruction of geometric road data using remotely sensed imagery1999Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The objective of this thesis is to find an automatic methodfor accurate and robust reconstruction of geometric road data.Remotely sensed images serve as the main source during thereconstruction process. Rapidly increasing requests foraccurate and actual road data, mainly driven by commercialinterests such as route optimisation, car navigation, andtelecommunication topics, stresses the need for automation ofmapping procedures. As shown in this thesis, two majoradvantages are achieved if the existence of a geographicaldatabase is taken into consideration during the imageinterpretation procedure. First, the geographical updatingprocedure is simplified and automated while using the locationof old already mapped objects as start positions during theroad database reconstruction. Second, semantic information alsoavailable in the database can be used in the image analysis.For example, road width is a useful parameter forobject-related image operations.

    The developed road data reconstruction method is dividedinto four subtopics. First, the ortho-corrected image isprocessed using derivatives of a Gaussian filter to enhancelinear structures. The road width, either extracted from thedatabase or estimated by an operator, steers the filteringprocess. Second, road intersections and dead ends, in thisthesis named node points, are determined. Different matchingalgorithms, all based on existing road data and thepre-processed image, are developed and tested. Third, awell-established method, snakes, is used for determination ofthe road delineation between two node points. Drawbacks such ashigh requests for accurate start values and sensitive parametersettings initiated the idea of a road data reconstructionmethod based on Least Squares image matching. The methoddeveloped and tested in this thesis matches the modelled road,representing the road cross-section, and a remotely sensedimage. Two fundamental similarities between the adopted nodepoint and delineation methods are the formulation of anartificial template image describing the road cross-section andthe required image pre-processing. Smoothing constraints areincluded in the iterative delineation procedure to ensure astable solution. Finally, automation of geographical dataupdating requires accuracy estimates of all data sourcesincluded in the process. The method presented in this thesisallows for calculation of statistical measures, where eachvertex of the road segment is quality estimated, useable asinput in a decision procedure for updating.

    Accuracy evaluations are performed on a test data setincluding results from a manual interpretation and digitisationof SPOT multispectral images. Differential GPS measurementsfrom 27 kilometres of a forestry road network serve asreference data during the comparison between manualinterpretation and the results from the developed roadreconstruction method. The test results from the automated roaddata reconstruction show an improved accuracy compared tomanual interpretation. An analysis of the error componentsindicates a major influence from the image location, 7.5metres, while the contribution from the road reconstructionalgorithm is approximate 4 metres, in this test correspondingto 0.2 pixels.

    Keywords:object-related image processing, node pointdetermination, road delineation, image matching, accuracyestimates, accuracy study.

  • 13.
    López, Carlos
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Quality of geographic data1997Doctoral thesis, comprehensive summary (Other scientific)
  • 14.
    Mahlander, Camilla
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Detection of geographic changes and location of sites supported by fuzzy set theory2000Licentiate thesis, monograph (Other scientific)
  • 15.
    Mårtensson, Stig-Göran
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Height Determination by GPS - a Practical Experiment in Central Sweden2001Doctoral thesis, monograph (Other scientific)
  • 16.
    Nahavandchi, Hossein
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Precise gravimetric-GPS geoid determination with improved topographic corrections applied over Sweden1998Doctoral thesis, comprehensive summary (Other scientific)
  • 17.
    Sjöberg, Lars Erik
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Topographic effects by the Stokes-Helmert method of geoid and quasi-geoid determinations2000In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 74, no 2, 255-268 p.Article in journal (Refereed)
    Abstract [en]

    The topographic potential and the direct topographic effect on the geoid are presented as surface integrals, and the direct gravity effect is derived as a rigorous surface integral on the unit sphere. By Taylor-expanding the integrals at sea level with respect to topographic elevation (H) the power series of the effects is derived to arbitrary orders. This study is primarily limited to terms of order H-2. The limitations of the various effects in the frequently used planar approximations are demonstrated. In contrast, it is shown that the spherical approximation to power H-2 leads to a combined topographic effect on the geoid (direct plus indirect effect) proportional to (H) over tilde(2) (where terms of degrees 0 and 1 are missing) of the order of several metres, while the combined topographic effect on the height anomaly vanishes, implying that current frequent efforts to determine the direct effect to this order are not needed. The last result is in total agreement with Bjerhammar's method in physical geodesy. It is shown that the most frequently applied remove-restore technique of topographic masses in the application of Stokes' formula suffers from significant errors both in the terrain correction C (representing the sum of the direct topographic effect on gravity anomaly and the effect of continuing the anomaly to sea level) and in the term t (mainly representing the indirect effect on the geoidal or quasi-geoidal height).

  • 18.
    Sjöberg, Lars Erik
    et al.
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Hunegnaw, A.
    Some modifications of Stokes' formula that account for truncation and potential coefficient errors2000In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 74, no 2, 232-238 p.Article in journal (Refereed)
    Abstract [en]

    Stokes' formula from 1849 is still the basis for the gravimetric determination of the geoid. The modification of the formula, originating with Molodensky, aims at reducing the truncation error outside a spherical cap of integration. This goal is still prevalent among various rnodifications. In contrast to these approaches, some least-squares types of modification that aim at reducing the truncation error, as well as the error stemming from the potential coefficients,, are demonstrated. The least-squares estimators are provided in the two cases that (1) Stokes' kernel is a priori modified (e.g. according to Molodensky's approach) and (2) Stokes' kernel is optimally modified to minimize the global mean square error. Meissl-type modifications are also studied. In addition, the use of a higher than second-degree reference field versus the original (Pizzetti-type) reference field is discussed, and it is concluded that the former choice of reference field implies increased computer labour to achieve the same result as with the original reference field.

  • 19.
    Sjöberg, Lars Erik
    et al.
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Nahavandchi, H.
    The atmospheric geoid effects in Stokes' formula2000In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 140, no 1, 95-100 p.Article in journal (Refereed)
    Abstract [en]

    The application of Stokes' formula requires that the atmospheric effect on the gravity anomaly is removed. We show that this direct effect reaches about -40 cm over the Himalayas and Antarctica. The restoring of the atmospheric masses yields the indirect atmospheric effect, reaching about -20 cm for the same regions. Consequently, the total atmospheric effect on the geoid is of the order of - 60 cm. However, for most areas close to sea level, the correction is within a few centimetres. Furthermore, the total atmospheric geoid effect is derived for the truncated as well as the modified Stokes formula. It is emphasized that the traditional (IAG) approach to adding a direct atmospheric effect to gravity may lead to a serious geoid bias in the truncated Stokes formula. However, as all the parameters of the bias are known, it can easily be corrected. In contrast, we suggest that the total atmospheric effect on the geoid be determined separately. In this approach the bias is avoided.

  • 20.
    Sjöberg, Lars Erik
    et al.
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Pan, M.
    Asenjo, E.
    Erlingsson, S.
    Glacial rebound near Vatnajokull, Iceland, studied by GPS campaigns in 1992 and 19962000In: Journal of Geodynamics, ISSN 0264-3707, E-ISSN 1879-1670, Vol. 29, no 2-Jan, 63-70 p.Article in journal (Refereed)
    Abstract [en]

    Since about 1920 the Vatnajokull ice cap in Iceland has experienced a significant retreat, corresponding to a volume reduction of more than 180 km(3). With two GPS campaigns in 1992 and 1996 along the southern border of the glacier preliminary results reveal land uplift rates of 1-6 mm/yr, after a one-parameter (bias) fit with recent earth rheology models. The best fit model suggests that the lithosphere in the area is about 30 km thick and the viscosity of the asthenosphere 5 x 10(18) Pa s. The rms fit of uplift rate at all GPS sites is +/-1.4 mm/yr. As the GPS data alone cannot provide the absolute uplift rates, the one-parameter fit to the theoretical modelling implies that the absolute rates were estimated by the matching of the GPS data and model. The resulting uplift rate at station Hofn (1 mm/yr) is not consistent with two independent sources, and we therefore conclude that further GPS epoch and permanent GPS site data are needed to confirm the present geodynamic processes near Vatnajokull.

  • 21.
    Wiman, Håkan
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Area based segmentation and matching of aerial images for geometric description of buildings1997Doctoral thesis, comprehensive summary (Other scientific)
  • 22.
    Ågren, Jonas
    KTH, Superseded Departments, Geodesy and Photogrammetry.
    Processing of the 1992, 1994 and 1997 Campaigns in the Northen GPS Deformation Traverse2001Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The Northern GPS Deformation Traverse was established to detect movements at two major shear zones now active in northern Sweden, namely the NW trending Bothnian-Senja zone and the N trending Bothnian-Seiland zone. So far three GPS campaigns have been observed the processing of these three campaigns, and to investigate and compare different processing and analysis strategies. It should be noticed that the investigations that are of a purely geodetic nature.

    The campaigns were processed in the Bernese software 4.0 using several different methods. In the first part of the work, more or less the standard method for long baselines described in the Bernese manual (Rothacher, 1996) was applied. In this case all situations in a session were first processed together, using the ionosphere-free linear combination L3, zenith tropospheric parameters, and correct modelling of the correlations. After that, the normal equations from the sessions were analyzed for the baselines between adjacent stations along the traverse, it was found that the results were very bad in the vertical component, the results are more promising in the horizontal, but the different solutions are nevertheless quite noisy. In addition, a few large errors were found also in the horizontal.    

    In the second part of the work, the relatively short individual baselines between adjacent stations were processed separately. The main purpose of this type of processing was to evaluate different processing methods, such as processing with and without zenith tropospheric parameters using either L1 or L2 plus an ionosphere model, and to find out what extent errors caused by antenna-mixing and site dependent effects are present in the data. Another aim was to find out if the baseline mode of processing is suitable for the present project in its own rights. The results show that elevation dependent errors, caused by antenna type mixing and/or site-dependent effects like scattering, are responsible to a considerable degree for the height errors found in the first part. As could be expected, because of the higher noise level for L3, the tests further indicate that the short baselines should be processed without the ionosphere-free linear combination, using for instance L1 and an ionosphere model instead. Also in the horizontal components, considerably better results are obtained in this way.

    In the final part, the campaigns were processed as the first part, but with the difference that L1 and an ionosphere model was used for the shortest baselines, while L3 was applied for the longer ones. The results in the horizontal indicate that the mix of frequencies has worked well. The short baselines are comparable to the best results from the processing of individual baselines, while the accuracy over longer distances is more or less independent of baseline length. At this point we also have investigated how large uncertainly we have because of the method that is used to estimate velocities from the final campaign solutions. Two different methods are compared. The first one is to utilize unweighted linear regression separately for each baseline and telocentric component, while the second is to make a simultaneous adjustment in the horizontal components, using the full cofactor matrices from the final campaign solutions for the weighting. In the latter case, all available correlations are modelled correctly. We conclude that we have significant uncertainties because of the method that is used in this step at the present stage, when only three campaigns are available.      

       

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