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No description available.

The research described in the thesis is concerned with the analysis of imagery obtained from aircraft, rockets, and manned and unmanned spacecraft. The imagery is of two types, one being conventional photographic imagery using the visible and/or the near infrared parts of the spectrum. The other is derived from multispectral scanners carried by Landsat 1 and 2 spacecraft in which information is produced separately for each of the two visible and two infrared spectral bands. The analysis is directed towards the automatic machine classification of the images for different applications and also incorporates a comparison of different methods of classification. One method of analysis is based solely upon the spatial variations of intensity in a single waveband and provides textural information for a scene. This variation has been examined using both one and two-dimensional Fourier analysis to provide a mathematical description of the textural changes. Use of spectral information allows greater variation in the methods of analysis which fall into two principal classes. In the unsupervised method group classification of the images is made according to some similarity measure between the spectral content of each picture element and with no a priori information on their identities. The relative advantages of this method as applied to the imagery considered here have been examined in relation to those possessed by the alternative approach, using the supervised method ofanalysis, which requires a priori information on the type and degree of classification which is required. The supervised method employed here assumes a Gaussian distribution for the spectral intensities of each class and uses a maximum likelihood decision rule for the classification. The extent to which the characteristic spectral signature of each class can be spatially extrapolated and still yield acceptable results has been examined, as has the effort of incorporating a 'threshold' below which classification does not take place.

No description available.

This thesis investigates the use of satellite altimetry techniques for measuring surface elevation changes of ice caps. Two satellite altimeters, Radar Altimeter 2 (RA-2) and Geoscience Laser Altimeter System (GLAS) are used to assess the surface elevation changes of three Arctic ice caps. This is the first time the RA-2 has been used to assess the elevation changes of ice caps - targets much smaller than the ice sheets which are the instrument’s primary land ice targets. Algorithms for the retrieval of elevation change rates over ice caps using data acquired by RA-2 and GLAS are presented. These algorithms form a part of a European Space Agency (ESA) glacier monitoring system GlobGlacier. A comparison of GLAS elevation data to those acquired by the RA-2 shows agreement between the two instruments. Surface elevation change rate estimates based on RA-2 are given for three ice caps: Devon Ice Cap in Arctic Canada (−0.09 ± 0.29 m/a), Flade Isblink in Greenland (0.03 ± 0.03 m/a) and Austfonna on Svalbard (0.33 ± 0.08 m/a). Based on RA-2 and GLAS measurements it is shown that the areas of Flade Isblink below the late summer snow line have been thinning whereas the areas above the late summer snow line have been thickening. Also GLAS observed dynamic thickening rates of more than 3 m/a are presented. On Flade Isblink and Austfonna RA-2 measurements are compared to surface mass balance (SMB) estimates from a regional atmospheric climate model RACMO2. The comparison shows that SMB is the driver of interannual surface elevation changes at Austfonna. In contrast the comparison reveals areas on Flade Isblink where ice dynamics have an important effect on the surface elevation. Furthermore, RACMO2 estimates of surface mass budget at Austfonna before the satellite altimeter era are presented. This thesis shows that both traditional radar and laser satellite altimetry can be used to quantify the response of ice caps to the changing climate. Direct altimeter measurements of surface elevation and, in consequence volume change of ice caps, can be used to improve their mass budget estimates.

Urban ground motion due to natural or man-made geological processes is an issue of major importance for local authorities, property developers, planners and buyers. Increased knowledge of this phenomena would benefit all involved but the measurement techniques in common use have either spatial or temporal inadequacies. A technique known as Persistent Scatterer Interferometry (PSI) has been developed which can map ground motion to high precision over large areas with a temporal scale measured in years. PSI takes advantage of the high number of Synthetic Aperture Radar (SAR) images available to mitigate the atmospheric effects that inhibit standard Interferometric SAR (InSAR) techniques. This however involves assumptions about the nature of atmospheric variability, such as its randomness over time, or its spatial extent. In addition, little is known about the Persistent Scatterers (PS) themselves and PSI is only able to provide results relative to a reference PS. The reference PS point is often arbitrarily chosen and may itself be in an area undergoing ground motion, thus adding a degree of ambiguity to any relatively derived motion. The purpose of this work is to investigate possible solutions to these shortfalls and quantify any improvements made. A corner reflector network is established in the Nottingham area of the UK. A data archive is collated over three years containing Global Positioning System (GPS) data at the corner reflector sites, data from surrounding Continuous GPS (CGPS) sites and levelling data. Due to conflicts with the European Space Agency (ESA) Environmental Satellite (ENVISAT), there were insufficient SAR images to com- pute a fully integrated corner reflector PSI study. Instead, the project focussed on atmospheric correction of PSI results using absolute ZWD estimates. Zenith Wet Delay (ZWD) estimates are derived from a Precise Point Positioning (PPP) GPS processing method which does not rely on a network of ground stations and therefore produces absolute ZWD estimates which are less prone to biases and noise. These are interpolated across a PSI study area and used to mitigate the long wavelength effects of atmopheric water vapour in the PSI differential interferograms. The corrected PSI results are then compared to uncorrected results, GPS derived motion and levelling data. Results between the ZWD corrected PSI study and the uncorrected study show statistical improvements in some areas and reductions in others. Correlation factors between double-differenced levelling observations and double-differenced PSI results improve from 0.67 to 0.81. PSI deformation rates also show improvement when compared to GPS deformation rates, although some results do not satisfy statistical tests.

This research is concerned with the use of aerial photographs for the measurement and recording of urban land use. A suitable land use classification scheme and a methodology for the measurement and recording of land use areas are developed. Use is made of these to obtain data for geographical research and as basic information for town planning. - A land use classification scheme suited to the requirements of geographical research, and compatible with the limitations of the air photograph as a data source, is formulated and tested for interpretational accuracy. Methods for the measurement and recording of land areas are discussed, and as a result grid systems are considered to be most suited to the requirements of the project. Tests are carried out to assess the characteristics of line grids and of dot grids used on maps and on aerial photographs. Experimental evidence indicates that the optimum system, balancing accuracy with practicability and economy, involves the use of orthogonal dot grids as overlays to the aerial photographs. The system is used over a seventy square kilometre area in and around Preston, Lancashire, to produce areal data of land use for the years 1946 and 1973. Computer programs are used to derive tabular data of land use, land use change matrices, and a range of computer maps. The results are used in an analysis of the changes in land use, and the relationship between land use and population over the period. The analysis indicates that, within the limits of the data, relationships exist between rates of change of land use and of population, whereas actual land use and population, at the two dates, appear both to be related to location (within the urban area) rather than to each other. The conclusion drawn from the research is that this method of measurement of changes in urban land use by means of aerial photography produces areal data of an accuracy, and in such a form, as to be suited to the purposes specified.

Three-dimensional data are useful for various applications such as visualization for planning, simulation for training and environmental studies, presentations, decision making and many more. The existing methods of texturing 3-D city models use conventional vertical imagery and libraries of generic textures which are sufficient for some applications of 3-D models like training simulation, gaming, and telecommunication planning. However, the needs for photo-realistic, modelling of the complete details, and geometrically accurate 3-D models are growing rapidly in several fields, especially in engineering and cultural heritage documentation. Photorealism and better details can be achieved through using terrestrial imagery but it is a very time-consuming process particularly in large modelling projects. It is possible to improve efficiency by image capture from a moving ground based vehicle but this requires an extra process in the work flow if the initial modelling has been undertaken by aerial photogrammetric processes. Pictometry imagery has been used for visual inspection especially in life-saving situations due to the fact that the Pictometry aerial imagery contains oblique (angled) images which provide better view and greater detail. The more conventional method of collecting aerial images with for example the UltraCamD, can also provide excellent views of roof tops and some of the building facades when located away from the nadir on the images. This research explored the geometry of the Pictometry images (vertical and oblique) and the possibility of using this imagery in 3-D modelling to produce photo-realistic and accurate models. In addition, merging terrestrial imagery with Pictometry imagery to get more ground level details has been investigated in this research. All work has been carried out using the available software packages at the Institute of Engineering Surveying and Space Geodesy (IESSG) and using data provided by Blom Aerofilms Ltd. The results of the aerial triangulation of different Pictometry blocks showed that high quality image measurements have been achieved for all the image blocks. The use of indirect georeferencing produced good quality coordination of ground points. The use of in-flight control has produced good results with additional parameters which mitigate any effects of systematic errors. Good quality AT results have been achieved using minimum ground control which reduces a lot of field work and hence time and money. Extraction of 3D geometry for all buildings in the study area has been performed using both vertical Pictometry imagery and UltraCamD imagery. The polygons extracted from the UltraCamD images have been used as a bench mark (BM) to check the accuracy of polygons extracted from Pictometry. Planimetric and height comparisons of the extracted features from Pictometry system with the BM results have been performed. The results showed that the Pictometry imagery produced good results especially in plan components taking into consideration the differences in the resolution, GSD, and the flying height between the two camera systems. The results of automatically texturing the models have shown that using the vertical blocks (UltraCamD or Pictometry) produced very good roof textures but on the other hand produced less quality facades. The use of the Pictometry oblique block in texturing has produced very good facades but in some instances not such good quality roof textures. The successful combining of vertical and oblique Pictometry images provided an excellent opportunity to produce an efficient method of high quality urban model texturing. The integration of terrestrial images of building facades (whose texture needs enhancement) with the combined aerial imagery block has been successfully and automatically performed. The results are much better than the results obtained by manual texturing which not only depends upon the experience and skill of the operator but is also time consuming and laborious

Differential interferometric synthetic aperture radar (InSAR) is a well used technique for measuring deformations, but often suffers greatly from effects due to atmospheric differences occurring between different SAR images. Recently a new set of techniques have been developed called Persistent Scatterer techniques, which take advantage of the high number of SAR images available to try and model out the atmospheric effects. To aid this process, all present techniques make use of a Digital Elevation Model (DEM) to remove the interferometric phase due to topography, but as a consequence this contaminates the phase values with an unknown error due to the DEM, which has to be modelled out in the processing chain. In this thesis a new Persistent Scatterer (PS) method is proposed that does not use a DEM to remove the topographic phase component, but rather one of the interferograms used in the study, and hence does not need to calculate topographic height corrections. This is achieved by using the Integer Ambiguity Search (IAS) 3-Pass differential technique. The developed algorithms are then tested and assessed over two test sites in central London, UK. The overall conclusions of the research are summarised below. The IAS 3-pass differential interferometry method gives a differential result that is more consistent with 2-pass results than with traditional 3-pass results. By using the IAS 3-pass method, it is possible to do a PS InSAR analysis without recourse to a DEM or needing to derive any topographic information. The developed IAS PSInSAR algorithms have been tested using simulated data, which has shown that the methods developed can identify small scale target motion over a period of a few years. The IAS PSInSAR algorithms were also tested using real SAR data, the results of which are consistent with GPS results of the test site and previous independent investigations.