Bernard Devereux

Flood Detection in Urban Areas Using TerraSAR-X

Flooding is a major hazard in both rural and urban areas worldwide, but it is in urban areas that the impacts are most severe. An investigation of the ability of high-resolution TerraSAR-X synthetic aperture radar (SAR) data to detect flooded regions in urban areas is described. The study uses a TerraSAR-X image of a one-in-150-year flood near Tewkesbury, U.K., in 2007, for which contemporaneous aerial photography exists for validation. The German Aerospace Center (DLR) SAR end-to-end simulator (SETES) was used in conjunction with airborne scanning laser altimetry (LiDAR) data to estimate regions of the image in which water would not be visible due to shadow or layover caused by buildings and taller vegetation. A semiautomatic algorithm for the detection of floodwater in urban areas is described, together with its validation using aerial photographs. Of the urban water pixels that are visible to TerraSAR-X, 76% were correctly detected, with an associated false positive rate of 25%. If all the urban water pixels were considered, including those in shadow and layover regions, these figures fell to 58% and 19%, respectively. The algorithm is aimed at producing urban flood extents with which to calibrate and validate urban flood inundation models, and these findings indicate that TerraSAR-X is capable of providing useful data for this purpose.

State-of-the-Art: DTM Generation Using Airborne LIDAR Data

Digital terrain model (DTM) generation is the fundamental application of airborne Lidar data. In past decades, a large body of studies has been conducted to present and experiment a variety of DTM generation methods. Although great progress has been made, DTM generation, especially DTM generation in specific terrain situations, remains challenging. This research introduces the general principles of DTM generation and reviews diverse mainstream DTM generation methods. In accordance with the filtering strategy, these methods are classified into six categories: surface-based adjustment; morphology-based filtering, triangulated irregular network (TIN)-based refinement, segmentation and classification, statistical analysis and multi-scale comparison. Typical methods for each category are briefly introduced and the merits and limitations of each category are discussed accordingly. Despite different categories of filtering strategies, these DTM generation methods present similar difficulties when implemented in sharply changing terrain, areas with dense non-ground features and complicated landscapes. This paper suggests that the fusion of multi-sources and integration of different methods can be effective ways for improving the performance of DTM generation.

Assessing public aesthetic preferences towards some urban landscape patterns: the case study of two different geographic groups.

Landscape aesthetics is closely linked to people’s daily life, and a large body of studies has been conducted to understand the public’s landscape preferences. These studies commonly focused on comprehensive landscape configuration, yet limited emphasis was placed on the patterns of individual landscape features. This research explored people’s preferences towards the composition and patterns of some specific urban features. Questionnaire-based survey was conducted in two cities: Cambridge, UK and Nanjing, China and more than 180 responses were collected, respectively. Respondents from both sites showed similar preferences towards freely growing trees, individual houses, gable roofs and mixed design of green spaces. On the other hand, respondents from Cambridge and Nanjing have different preferences towards the height of trees, the size of green spaces, and the height diversity of buildings. This survey also proved that the factors of age, education, status and length of living have larger influences on landscape preferences than the factors of gender, and major. Furthermore, strong correlations were found between people’s aesthetic preferences towards comparative landscape patterns, building types, tree shapes and roof structures. The existence of generally shared landscape preferences makes it feasible to conduct international and standardized projects for acquiring comparable and transferable criteria. The methodology and findings of this research provides landscape planners and decision makers with useful reference to compare, evaluate and improve urban landscape configurations to meet people’s needs.

Irrigation Is Forever: A Study of the Post-destruction Movement of Water Across the Ancient Site of Sri Ksetra, Central Burma

Sri Ksetra is a very large urban site created by the Pyu people, ca. fourth century AD, on the southern edge of the Dry Zone of Central Burma. Ancient irrigation works, discovered by Stargardt in 1985–1988 and first published in 1990, were essential to its urban development and, though rarely visible as surface features today, still profoundly affect the post-destruction settlements on the site and their rice harvests. This paper documents the sub-surface and surface movement of moisture across the site after the end of the monsoon season, i.e. in the period from September to February. It is based on the study of combined resources, including spaceborne multi-spectral and multi-temporal satellite imagery, aerial photographs and archaeological maps. It reveals how surface and sub-surface water still flows along the ancient irrigation channels and collection tanks of the site and demonstrates that an ancient system, which has been in an advanced state of sedimentation for over 1,000 years, still functions mainly at a subsurface level, creating differences in soil productivity and drainage today. The study explores the potential value of freely available imagery of medium resolution for archaeological research on other ancient landscapes embedded in modern ones where differences of wetness and vegetation are significant. Finally, these satellite images record the presence of ancient ritual ponds and associated burial terraces in the southern extramural area in a degree of detail that, surprisingly, compares well with the aerial photographs taken over 50 years ago when surface disturbance was at a lower level.