Over recent years considerable advances have taken place in the field of space geodesy, resulting in a number of highly precise global positioning techniques. The increased resolution of many of the scientific products from the new observational techniques has stimulated the interest of not only geodesists but also geophysicists. Furthermore, their potential to determine the orientation of the earth's axis of rotation (polar motion) and the variations of the rate of rotation of the earth about that axis, was recognised by the scientific community. The result was the establishment of Project MERIT, to intercompare these new observational techniques. Satellite Laser Ranging, a method of measuring the distance from a point on the earth's surface to an artificial satellite by means of timing the flight of a short pulse of laser light, is currently the most accurate available means of tracking near earth satellites. However, in order to reach the accuracy requirements of current geodetic applications dedicated satellites, such as the NASA LAser GEOdynamic Satellite (LAGEOS), must be tracked and specialised processing software must be used. This Thesis describes the basic theory behind the analysis of Satellite Laser Ranging Observations, with a special emphasis on the determination of earth rotation parameters (the polar motion and the variations in the rate of rotation). The development and testing, at Nottingham, of the Satellite Orbit Determination and Analysis Package Of Programs, SODAPOP, for the processing of laser range data, is described. The thesis also presents and discusses the results of the analysis of laser range observations the LAGEOS satellite, from the short and main campaigns of project MERIT.

In the last three decades there have been major changes in how surveying is practiced, and what surveyors have been trained and educated to do with the new expertise that technological advancements offer. Within surveying communities it is generally acknowledged that the changes in the profession have brought about an urgent need for change in educational programmes if they are to have relevance to contemporary practice. The thesis reports on a research study which explored the nature and impact of the educational strategies used in university surveying courses. The study employed a nested case study approach at two levels. Firstly, fifteen initial case studies of university programmes from thirteen countries provided a broad perspective of surveying education across the world. Secondly, two of these programmes were selected for in-depth comparative case studies to provide deeper understandings of the educational systems in two distinct contexts. The inquiry methods for the initial case studies included documentary analysis and interviews of senior academics and representatives of professional surveying bodies. For the two in-depth case studies, the inquiry methods included observations of pedagogical activities, focussed group discussions and interviews of university staff and students as well as professional surveyors. The interviews were recorded and thematically analysed. Some concepts from Bourdieu’s theory of practice were useful in coming to understandings about the interrelationship between the field of surveying education and the field of surveying practice. The study identified tensions and prospects within and between the programmes studied and between them and the profession. The key issues that emerged were: the predominance of highly discipline specific curricula with some indication of a shifting to a more broad-based education; tensions between industry expectations and the academic focus; a high level of interest in the university courses from the profession and uncertainty about the real meaning of geomatics and its relevance to local surveying communities. The findings have critical implications for how surveying/geomatics educational courses are developed in the future. The empirical evidence led to the development of a proposed improved model for contemporary surveying/geomatics education.

A Mobile Laser Scanning System (MLSS) is a kinematic platform combining different sensors, namely: GPS, IMU and laser scanner. These sensors are integrated and synchronised to a common time base providing 3D geo-referenced data. MLSS is used in several areas; such as 3D urban and landscape modelling for visualisation in planning and road design, simulations for environmental management, and to support land use decision-making. The accuracy of 3D geo-referenced points, achieved via Mobile Laser Scanning (MLS) under normal conditions, can reach the level of 3cm. However, this accuracy tends to be degraded in urban areas, because of trajectory errors of the laser scanner (IMU drift due to the limited availability of GPS signal). This, also, can be attributed to the difficulty of matching natural features in the point cloud. Previous researches have tried to overcome the problems in urban laser scanning by focusing on enhancing the performance of the navigation system (NGS). This can be costly and may not achieve the high accuracy level required for some engineering application. When the navigation solution is degraded, the accuracy of the point cloud results will be degraded. Using different data sources is another way to improve accuracy in urban areas. For example using airborne LiDAR, terrestrial imagery, and unmanned aerial vehicle (UAV) but these are very time consuming as well as costly compared to MLS systems. Targets are used in a number of ways in MLS and are often chosen from natural detail points. These can be difficult to define, particularly when high accuracy requirements need to be met, for example, when matching scans together or fitting scans to existing surveys as used in this project, and calibrating the system. The accuracy of MLS in the urban area was tested using three methods, namely ground control points (GCPs), surface to surface comparing, and additional source of data. Also, the effect of range, incidence angle (IA), resolution and brightness on different types of targets (sphere, cone, pyramid and flat target) was studied to explore the optimal target design. Moreover, an algorithm for automatic target detection was developed to detect the optimal target. Then, for each target in the point cloud, the centre/apex was calculated using least squares surface fitting. Tests show that the accuracy of 3D coordinates, obtained from MLS in an urban area is about 2-5 cm. Tests also show that using targets with MLS can improve the quality of results reaching 5 mm levels of accuracy even in the urban area, based on the use of check points to assess the quality and reliability of the outputs Almost all work on this project was carried out using the software packages available at the Nottingham Geospatial Institute (NGI) and MLS data provided by 3D Laser Mapping Ltd. (3DLM). Two terrestrial laser scanners, namely: HDS 3000 and Faro Focus3D have been used for testing the designed targets. The findings of this research will contribute easy, cost effective and improved accuracies in MLS data. This enhances usefulness in applications, such as change detection, deformation monitoring, cultural heritage and the process of 3D modelling, particularly in urban areas.

This thesis is dedicated to the development of two new tropospheric mapping functions for GNSS data processing, based on a high resolution mesoscale numerical weather model (NWM). NWMs have proven to be beneficiary in the processing of GNSS and VLBI data, both for deriving mapping functions and for providing a priori information such as zenith hydrostatic delay (ZHD). The mapping functions derived here make a greater use of the NWM information than the mapping functions currently recommended by the International GNSS Service. In addition to using a single vertical pro¯le at the site in order to derive mapping functions under the assumption of an azimuthally symmetric atmosphere, the NWM was also ray traced every thirty degrees in azimuth. This way, a complete volume of the atmosphere is sensed, and better modelling is expected if the NWM does indeed provide an accurate representation of the atmosphere, by accounting for azimuthal variations. An emphasis was put in this thesis on assessing the mathematical models used to vertically interpolate meteorological information, as they play a key role in computing the refractivities in the ray tracing algorithm. Error sources were identified and quantified. As expected, water vapour is the major source of error. However, the results showed that the model used for the total pressure induced a systematic bias. To derive an azimuth dependent mapping function, the Marini model traditionally used had to be left in favor of a cubic spline interpolation (CSI). This new approach was validated by comparing the performance of the new azimuthally symmetric mapping functions against the updated Vienna mapping functions (VMF1), the best mapping functions currently available. Similar positioning performances were obtained, therefore validating the CSI based approach. The performance of new azimuth dependent mapping functions (AMF) in handling the troposphere asymmetry were compared to those obtained when estimating horizontal tropospheric gradients with an azimuthally symmetric mapping function. Results show a good agreement in the modelling of the asymmetry, and that estimating gradients is justified. The gradient solution performed better overall, although it failed for some sites, and better inter-station consistency was obtained with the AMF. This thesis also investigated the role of the tropospheric modelling in the retrieval of the atmospheric pressure loading (APL) in GNSS data processing, which is now part of the IGS 2008 recommendations. The results show that differential height time series obtained with different tropospheric modelling can correlate with the APL signal to a level up to 0.7. In other words, the choice of tropospheric modelling strategy does greatly influence the retrieval of the APL.

Creating three dimensional digital representations of urban areas, also known as 3D city modelling, is essential in many applications, such as urban planning, radio frequency signal propagation, flight simulation and vehicle navigation, which are of increasing importance in modern society urban centres. The main aim of the thesis is the development of a semi-automated, innovative workflow for creating 3D city models using aerial photographs and LiDAR data collected from various airborne sensors. The complexity of this aim necessitates the development of an efficient and reliable way to progress from manually intensive operations to an increased level of automation. The proposed methodology exploits the combination of different datasets, also known as data fusion, to achieve reliable results in different study areas. Data fusion techniques are used to combine linear features, extracted from aerial photographs, with either LiDAR data or any other source available including Very Dense Digital Surface Models (VDDSMs). The research proposes a method which employs a semi automated technique for 3D city modelling by fusing LiDAR if available or VDDSMs with 3D linear features extracted from stereo pairs of photographs. The building detection and the generation of the building footprint is performed with the use of a plane fitting algorithm on the LiDAR or VDDSMs using conditions based on the slope of the roofs and the minimum size of the buildings. The initial building footprint is subsequently generalized using a simplification algorithm that enhances the orthogonality between the individual linear segments within a defined tolerance. The final refinement of the building outline is performed for each linear segment using the filtered stereo matched points with a least squares estimation. The digital reconstruction of the roof shapes is performed by implementing a least squares-plane fitting algorithm on the classified VDDSMs, which is restricted by the building outlines, the minimum size of the planes and the maximum height tolerance between adjacent 3D points. Subsequently neighbouring planes are merged using Boolean operations for generation of solid features. The results indicate very detailed building models. Various roof details such as dormers and chimneys are successfully reconstructed in most cases.

The advent of the Global Positioning System (GPS) meant that, for the first time, the geodetic and geophysical community has a tool for measurements on a global, continental and national scale. Global GPS networks are already competing with VLBI and SLR for the measurement of inter-continental baselines and earth rotation parameters. The development of the 'high accuracy fiducial GPS technique', as described in this thesis, has produced results comparable with mobile VLBI and SLR systems, but in shorter observational periods and at lower costs. Combined with global GPS networks, which have the potential to provide time-tagged fiducial station coordinates at the observational epochs, coordinates can be determined in a global reference frame. The results in this thesis, from a fiducial GPS campaign to monitor the vertical land movement at tide gauge sites in the UK, demonstrate that millimetric precisions and accuracies can be obtained in all three components over baselines of hundreds of kilometers. The combination of GPS with existing 2-d classical triangulation networks for mapping, engineering surveying and navigation has caused many problems, since the GPS observations are 3-d and of a superior quality. In Europe these problems have been overcome by the establishment of a new high precision reference framework, EUREF, based on fiducial GPS carried out in 1989. This thesis also describes the determination of coordinates for the UK EUREF stations and their application for geodetic control in Great Britain.

Roads are an integral part of today's lifestyle. Indeed, a modern and efficient economy requires a satisfactory road network. The road network in the United Kingdom faces ever-increasing demands with 94% of passenger travel and 92% of freight transport undertaken by road. Maintenance of the network is essential. Prior to the commencement of any maintenance scheme, an accurate highway profile is measured by undertaking a detailed topographic survey of the road surface and the adjacent verges. Traditionally, this is carried out by land surveyors using, for example, a theodolite, EDM and level. Highway surveying by traditional methods is a slow, costly and dangerous process. A photogrammetric technique was devised by Photarc Surveys Ltd of Harrogate, UK to reduce the problems of speed, cost and safety. This helicopter based photographic system can yield topographic data at up to ±5mm rmse through photogrammetric analysis. It is necessary to install ground control points on the hard shoulder for use in the photogrammetric analysis. This research investigates the potential of both conventional aerial triangulation and in-flight GPS assisted aerial triangulation for reducing this ground control requirement. The original photographic system is extended to integrate a GPS positioning system and the performance of this system is assessed through a series of field trials. The results of the research show that the camera can be positioned by the GPS system to within 5 centimetres. The GPS positions can be included in the aerial triangulation to further reduce the requirement for ground control. It is shown that for mapping at the ± 5mm rmse level, there is no potential for height control reduction, even when GPS positions are used. However for mapping at up to ± 20mm, the GPS positions can enable a significant reduction in ground control.

Wide Area Differential GPS (WADGPS) aims at overcoming the main drawback of conventional DGPS, namely the limited range over which the differential corrections are valid, due to the rapid decorrelation of the error sources with increasing distance from the reference station to the user. In the WADGPS approach, error sources are generated for users over a large portion of the earth, such as a communication satellite's entire footprint, by separating and modelling the main sources of error in GPS measurements. This has the effect of eliminating the limit imposed on the validity of the corrections by the geographical or atmospheric environment. A main advantage of WADGPS is the fact that far fewer reference stations are needed to cover the same area, compared to conventional DGPS. Interest in WADGPS has grown during the last few years, the use of WADGPS both for positioning accuracy requirements and the provision of integrity are being explored. Several research establishments have come up with their own WADGPS methodology and algorithms, all sharing a basic principle, namely the requirement that different error sources which affect GPS navigation are dealt with separately, and their spatial and temporal properties are investigated and modelled individually. Research was carried out to develop an advanced method and the corresponding algorithms, which could provide a high precision WADGPS positioning service. The service would be suitable for single or dual frequency users, and could be introduced with very few reference stations. The two main components of the service are a precise, near real-time orbit determination of the GPS satellites, and an accurate estimation and modelling of ionospheric and tropospheric effects. Results from real data indicate that user position accuracy of the order of 2 m and 3 m (RMS) in plan and height components respectively, were achieved over user-reference distances ranging from 2,000 to 3,500 km.

Considerable interest has been show in the development and application of real time On-The-Fly (OTF) kinematic GPS. A major error source and limitation of such a positioning technique is that caused by cycle slips. When these occur, the integer ambiguities must be resolved for, which can take hundreds of epochs to complete depending on satellite availability and geometry. This research has focused on investigating the applications of real time OTF GPS, as well as its limitations and precision, which has been shown in the thesis to be precise to a few millimetres. The limitations of such a system at present include the use of UHF telemetry links, which at best have a line of sight range of -10 km. The research has shown that alternatives are required, and the use of a relay station can prove invaluable. Cycle slips are another major limiting factor when using OTF GPS, as once a cycle slip occurs, it can either be corrected for or the integer ambiguities resolved for. The second option can take hundreds of seconds, depending on the algorithms used and the satellite number and geometry. This research has partly focused on the development of software which will instantaneously detect and correct for cycle slips in high rate GPS data. The applications of real time OTF GPS are numerous. Research has been carried out to investigate its use to monitor and control construction plant as well as monitoring the movement of large structures. As OTF positioning is precise to a few millimetres, it is ideal for the control of construction plant, and has been compared to laser levelling and precise digital levelling. Such a GPS system gives the user a 3-dimensional position for the bulldozer blade, for example. Such information can prove invaluable for quality control as well as developing an automated system, which would be controlled by real time OTF GPS. In addition, real time OTF GPS has been shown in the research to provide instantaneous positioning of large structures in the form of bridges. Such information could provide future systems which would monitor the structure for dangerous movements, resulting in a failure alarm. Carrier phase kinematic GPS has previously been shown to work over baseline lengths of < 20 km. The use of Multiple Reference Stations (MRS) has been shown in this research to enable OTF GPS to be applied over longer baseline lengths, with a precision in the order of 12 cm over 132 km.

Very Long Baseline Radio Interferometry is one of the most recently developed and potentially most useful geodetic measuring techniques. The high accuracy which it can achieve over great distances makes it ideally suited. for studies of many interesting geodetic and geophysical phenomena. The major asset of the system is that, unlike the majority of other accurate techniques, all measurements are independent of the Earth's gravity field. This thesis contains details of the basic theory of the VLBI technique and describes a model which has been developed to analyse data from the system. This is followed by a description of the application of the variation of co-ordinates method to the adjustment of VLBI observations and details the conditions and restrictions to be applied to the adjustment process. The basic procedure and equipment required to make the observations is described and details are given of the Nottingham University Long Baseline Interferometry Programs (NULBIP) which have been developed to perform the data analysis. Data has been obtained and analysed from two independent sets of observations using two different VLBI observing systems. The Canadian system has been used for observations using the three antenna array comprising the Chilbolton Observatory, England, the Algonquin Radio Observatory, Canada, and the Owens Valley Radio Observatory, U. S. A. Observations have also been processed from the Haystack-Goldstone baseline in the U. S. A., observed using the NRAO Mk I VLBI system. The software which has been developed has been tested by comparison with independently derived results on these baselines. The analysis of all the data has shown the VLBI method to be a highly accurate technique capable of measuring intercontinental distances with sub-metre accuracy. The results have indicated the many potential uses of VLBI in geodetic and geophysical research, the major ones of which have been described. The magnitude of systematic scale and orientation errors inherent in the Navy Navigation Satellite System (otherwise known as the TRANSIT system) have been measured by comparing these VLBI results with satellite-Doppler results derived from observations made near the radio telescopes.