John Elgy

Airborne remote sensing for urban drainage

Abstract Land cover information suitable for urban drainage modelling is acquired by airborne remote sensing. The scanner used is a line scanner that scans continuously while the aircraft flies forward recording 11 bands of the electromagnetic spectrum. This is classified by first segmenting the image into approximately homogeneous polygons using a Marr–Hidreth edge detector. These polygons are then classified into roofs, paved areas and permeable land. Rigorous accuracy tests are applied to the classified imagery, which shows that this method gives better results than any of those currently used. Dawn thermal imagery was not used in this study.

Use of GIS and Remote Sensing in Water Supply: Applications

This Section applies the theory of the preceding Section to the problems of water supply systems. The first section looks at the use of GIS with environmental process models. The second section covers the use of GIS and remote sensing techniques in demand evaluation and forecasting. The third section looks at two current applications of remote sensing for water supplies; the detection of buried objects and leaks, and the assessment of water quality. The last section considers the issues of using GIS and remote sensing in a utilities environment.

Use of Remote Sensing and GIS for Environmental Modelling and Monitoring

Remote Sensing is proposed as a useful technique for monitoring environmental pollution, in particular landfill sites for landfill gas migration. Landfill gas has the potential to migrate from the site boundaries and cause damage either where it emerges into the atmosphere or in the root zones of vegetation It is also spatially and temporally very difficult to monitor and techniques developed for landfill gas can be applied to other sources of pollution such as ducts or pipelines. The presence of landfill gas in the root zone causes signs of stress to be visible within the vegetation. This stress takes the form of either chlorosis or dieback. Airborne thematic map data and low cost video imagery are used to classify the site according to vegetation stress. A comparison between the efficiency and costs of the two sources of imagery is made. It is recommended that remote sensing is used in conjunction with soil and geological maps in a geographical information system to identify areas of high landfill gas concentration and that this is combined with traditional field measurements to gain a better spatial and temporal understanding of gas migration. The future potential of the technique is discussed

Geographical Infomation Systems and Digital Mapping for Water Supply Inventory

Water companies are complex organizations with many spatially distributed assets; pipes, plants, reservoirs and sewers. Furthermore they must communicate and interact effectively with a constantly changing base of hundreds of thousands of customers; industrial, agricultural and domestic. The statutory framework is continually evolving and companies must, more and more, consider such issues as the environment, liaise and report to regulatory bodies and operate in an increasingly competitive market. An efficient and secure information system is essential. More than most businesses, water companies have to manage uncertainty. In the UK in 1995, for example, a drought, followed by a cold snap caused many burst pipes and consequently increased leakage.

Relevant GIS and Remote Sensing Technology: Theoretical Considerations

The Geographical Information System is well suited as a tool for assisting with water supply problems. It not only carries out the inventory functions, as to what lies where, but assists with the manipulation of the data and the extraction of information for modelling and decision making. This section will describe the fundamental features of GIS directly relevant to water supply projects, and the ways that data are stored in a GIS. The Digital Elevation Model (DEM), which is of great importance to hydrology and water supply, will be considered in some detail. In terms of cost for implementing a GIS solution: manpower, data acquisition, software and hardware rank in about that order. Manpower is a very difficult aspect to specify for a project, so it will only be discussed briefly. Manpower depends as much on existing skills, training requirements and workloads for existing staff as on the GIS. The other three aspects are discussed with respect to the current state of the art; however technology is likely to change in the future.