PolyU IR Community: Land Surveying and Geo-Informatics

Temperature projection in Hong Kong using remote sensing and dynamic modelling

Sun, 01 Jan 2012 00:00:00 GMT

Title: Temperature projection in Hong Kong using remote sensing and dynamic modelling

Authors: To, Pui Hang

Abstract: Temperature projections for Hong Kong have been carried out by the Hong Kong Observatory (HKO) in recent years. These projections have largely been based on the local climate data collected at the HKO Headquarters, and data obtained from the Intergovernmental Panel on Climate Change (IPCC). These projections have only been able to reflect the expected temperature change at the HKO Headquarters site, but have paid little attention to the effects of global warming and urbanisation at local scale across the whole of Hong Kong. This research has examined temperature changes due to both global warming and urbanisation effects independently and applied them over the whole of Hong Kong. The effect of global warming on temperature was estimated by regressing the IPCC data against the background temperature recorded at the Ta Kwu Ling (TKL) climate station, which is assumed to be free from urbanisation. Results showed that background temperature in Hong Kong will rise between 0.10℃ and 1.29℃ (with an ensemble of 0.67℃) in total in the next three decades depending on the amount of carbon dioxide emissions at regional scale. Long-term temperature data and the measureable urbanisation parameter plot ratio surrounding different auto weather stations were used to model the temperature changes for different degrees of urbanisation. Models representing daytime and nighttime respectively were developed based on these data, and the results suggested a logarithmic relationship between the rate of temperature change and plot ratio (degree of urbanisation). When the effects of global warming and present and future urbanisation are known, the actual rate of temperature increase at different locations across Hong Kong can be calculated. Future temperature maps can therefore be produced by applying the rate of increases to the current temperature maps. The current temperature patterns over the whole of Hong Kong were retrieved from two ASTER thermal images. One of the images was obtained in summer daytime while the other one was obtained at night. By a method of simple addition, the temperatures are projected towards 2039 in 10-year intervals. This research also studied the effects of future projected higher air temperatures on public health using the parameter of thermal comfort. Mortality is expected to rise as heat-related deaths may occur under a continuously hot environment during both day and night. The thermal comfort levels are also expected to decrease in the future because of the predicted hot and humid weather in Hong Kong.

Description: x, 94 p. : ill., col. maps ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577M LSGI 2012 To

Temporarily coherent point SAR interferometry

Sun, 01 Jan 2012 00:00:00 GMT

Title: Temporarily coherent point SAR interferometry

Authors: Zhang, Lei

Abstract: Spaceborne Interferometric Synthetic Aperture Radar (InSAR) has been proven very useful in assessing remotely ground displacements. InSAR measurements have contributed to better understanding of the processes and mechanisms of geohazards such as earthquakes, volcanoes and landslides. There are two major error sources in InSAR measurements, i.e., decorrelation due to temporal and geometric effects and phase errors introduced by spatial and temporal variations of the atmosphere. The error sources can in extreme cases render the InSAR technology useless. To reduce the errors in InSAR measurements, a relatively new technique, multi-temporal (MT) SAR interferometry, was proposed in the late 1990s. The technique has since then evolved into three categories. The first is commonly referred to as Persistent Scatterers InSAR (PSInSAR or PSI) and it deals with a time series of interferograms generated based on a single-master image. The second makes use of multi-master interferograms including the stacking analysis method and the Small BAseline Subset (SBAS) approach. The last category is an integration of the single- and multi-master interferogram analysis methods. Over the past ten years multi-temporal InSAR has been widely applied for monitoring ground deformation in urban and rural areas and for monitoring infrastructures such as dams, buildings, motorways, and pipelines. However one important limitation in current MT-InSAR methods is the difficulty in estimating correctly the phase ambiguities. Besides, the lack of methods to evaluate the accuracy of MTInSAR results when external data (e.g., levelling and GPS observations) are unavailable is also an issue of concern.; A novel InSAR data analysis method termed Temporarily Coherent Point InSAR (TCPInSAR) is proposed in the thesis. The method can estimate deformation parameters reliably by avoiding the process of phase ambiguity estimation. The method arises from the fact that for a set of multi-master interferograms with short baselines, there are usually a sufficient number of arcs on which the double-difference phase components due to topographic errors and atmospheric artifacts are very small and the relative deformation rates between pairs of connected points are low. Therefore, the double-difference phase components of many such arcs are free from phase ambiguities. If only these arcs are taken as observations in estimating DEM errors and deformation rates, the complexity of parameter estimation can be reduced significantly. Included in the method are a series of innovations. To improve the density of TCPs, especially in areas with a small set of SAR images, we have developed a new TCP identification method based on offset statistics in range and azimuth directions. To make sure the selected TCPs can be connected extensively with relatively short arcs we have proposed an efficient point connection strategy that performs Delaunay triangulation locally. To retrieve the deformation rates reliably we have designed a least squares estimator with an outlier detector that can remove the arcs with phase ambiguities efficiently. To better consider the quality of individual interferograms we have improved the method of variance covariance estimation under the framework of least squares. After validating TCPInSAR technique using simulated datasets, we have applied the TCPInSAR method to the Los Angeles basin in southern California where structurally active faults such as Newport-Inglewood fault are believed capable of generating damaging earthquakes. Both the estimated long-term average subsidence and seasonal deformation in the basin are in good agreement with GPS observations from the Southern California Integrated GPS Network (SCIGN), indicating that the TCPInSAR method is effective for the retrieval of ground motions especially in areas where abundant multi-temporal SAR data are available and dense coherent points can be isolated. To demonstrate the performance of TCPInSAR method on changing landscapes where both the persistently and partially coherent points are available, we also applied the method to the southern part of Macau which is undergoing fast redevelopment.

Description: xvii, 107 leaves : ill. (chiefly col.) ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P LSGI 2012 Zhang

Effectiveness of visual, screen and dynamic variables in animated maps

Sun, 01 Jan 2012 00:00:00 GMT

Title: Effectiveness of visual, screen and dynamic variables in animated maps

Authors: Wang, Jue

Abstract: Evaluation of the effectiveness of visual variables for map presentation has been an important research topic in cartography. A number of investigations on this topic have been carried out. However, most of them focused on static maps on paper or screen. Along with the development of computer graphics and Internet technology, animated maps are more and more demanded to represent spatial-temporal data effectively and appropriately. To meet the increasing requirements for dynamic representation and to provide supports for spatial-temporal data visualization, it is necessary to study which and how different variables affect map animation and to evaluate the effectiveness of traditional visual variables and newly included screen and dynamic variables for presentations in animated maps. This study aims to evaluate the effectiveness of these three sets of variables for presentations in animated maps. To evaluate the influence of different variables on human perception on the animated maps, an experimental test was designed and conducted. A set of traffic data were used for generation of animated maps and these maps were evaluated by 732 readers (or subjects in psychology) via Internet. Quantitative approaches were developed and the effectiveness and validity of various variables were compared. Since the most effective variables are faster detected and can arouse more accurate, efficiency and accuracy were considered in each trial of the experiment when a subject (reader) reading animated maps. Efficiency means the time for one to acquire the required information from the animated map, and accuracy means that the correctness of information acquired by map readers (subjects). Results suggest that, in an animated map, (1) for screen variables, "Transparency" and "Blur" are the most effective, "Neon Glow" is effective, and "Resolution" and "Spatter" are not effective; (2) for visual variables, "Color Hue" and "Size" are most effective, "Color Value" and "Color Saturation" are effective, "Shape" is not effective; (3) for the dynamic variable "Rate of Change", "Medium Change" is most effective, "Large Change" is effective, and "Small Change" is not effective. For the dynamic variable "Duration", "7-8 fps" is most effective, and "4-6 fps" and "9-12 fps" are still effective. The empirical results obtained from this study will shed light on understanding how different variables affect human perception on animated maps and give guidance for animated mapping design.

Description: vi, 149 leaves : ill. (some col.) ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577M LSGI 2012 Wang

Selective omission of road networks in multi-scale representation

Sun, 01 Jan 2012 00:00:00 GMT

Title: Selective omission of road networks in multi-scale representation

Authors: Zhou, Qi

Abstract: Spatial data can be represented at different scales, which leads to the issue of multi-scale spatial representation. Multi-scale spatial representation has found wide applications in web mapping and small-format mobile devices. So far, there are still two main limitations with current methodologies. First, continuous transformation of spatial representation to any arbitrary scale is still not available; second, spatial data are represented at different scales for different applications and are updated separately. An ideal solution is to automatically transform the spatial representation at the largest scale to that at any smaller scale. This transformation may involve a series of operations such as collapse, selective omission, simplification, smoothing and displacement. This study focuses on the selective omission in a road network, which is one type of the most important features on a map. More specifically, three issues are addressed, i.e., (1) formation of roads in a network from road segments; (2) selective omission of roads; and (3) determination of the percentage of roads to be selected. A road network in the database is normally stored in the form of intersections and segments. However, recognition is normally performed on roads. Thus it is very desirable to build road segments into long individual roads (called strokes). In stroke building, a total of seventeen strategies with geometric, thematic and hybrid parameters as criteria were investigated. In this investigation, Hong Kong maps at different scales were used, a measure (i.e., accuracy rate) was proposed and statistical tests were carried out to detect any significance differences of performance using these strategies. It was found from experimental results that the differences in performance by most of these strategies are not significant. It was also found that the inclusion of thematic attributes (e.g., road class or road name) may sometimes improve the performance.; For selective omission in a road network, two typical existing approaches (i.e., stroke-based and mesh-based) were first evaluated by both quantitative analysis and visual inspection. It was found that the stroke-based approach performs better in a road network with linear patterns; by contrast, the mesh-based approach only performs better in a road network with areal patterns (e,g., grid-like patterns). This inspired us to develop an integrated approach. In this integrated approach, a hierarchical structure for both meshes and linear roads were first built and these two hierarchies were integrated into a single structure. Experimental results showed that this integrated approach performs much better than the two existing approaches. In addition, there also is a need for determining the percentage of roads for selection. This process involves either some scale-related parameters or empirical models (e.g., the classic 'Radical Law') to express the relationship between a map scale and the number of roads to be selected. However, experimental results showed that these parameters may vary between cases, and these models are not suitable for all possible cases. It is therefore very desirable to adaptively determine the percentage required for a representation at a specific scale. The back propagation neural network was adopted to give such a solution. Experimental results verified the feasibility of using this approach to adaptive selective omission. In summary, in this study, at first experimental tests were carried out to evaluate existing methodologies and new methodologies were developed based on the findings from these tests, including an integrated approach and the new application of back propagation neural network. Statistical tests show that these two methodologies work well. However, automated transformation in scales is a rather complex problem and further development is still needed.

Description: xiv, 142 leaves : ill., maps ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P LSGI 2012 Zhou