Lasse Møller-Jensen

Towards a spatial CO2 budget of a metropolitan region based on textural image classification and flux measurements

A project on monitoring urban CO2 budgets has been conducted since the year 2000 focusing on the Metropolitan area of Copenhagen, Denmark. Methodologically, the project combines remote sensing with CO2 fluxes measured by eddy covariance technique from the top of a 40-m mast located in the center of Copenhagen. These data are supplemented by flux measurements from a mobile system on a 10-m mast which is moved between different urban types, including a major entrance road, and residential and industrial areas. By comparing the time series of vertical CO2 exchange and the number of cars on the major entrance roads, it is demonstrated that the traffic intensity has a major impact on the urban carbon budget. The spatial distribution of the CO2 emission rates is examined through texture-based classification of Landsat-TM satellite images. Local traffic intensity and local heating is seen as a function of specific local urban land use and activities, and the corresponding satellite image texture is used as a proxy for the CO2 emission from these components. The urban scene is divided into urban land use classes that constitute homogenous areas in terms of main types of activity and these are linked to specific levels of CO2 emission. For this purpose, a multi-scale approach based on co-occurrence matrices has been developed and applied. The paper outlines how the CO2 exchange from the urban sources and sinks can be estimated from continuous flux measurements in central Copenhagen. It is shown that traffic is the largest single CO2 source in the city. The mobile measurements demonstrate that the emission rates ranges from less than 0.8 g CO2 m−2 h−1 in the residential areas up to a maximum of 16 g CO2 m−2 h−1 along the major entrance roads in the city center. An average annual CO2 exchange rate of 35 g CO2 m−2 day−1 is calculated by assigning fluxes to each land use type and excluding the effect of remote sources (power plants, air and sea traffic). This value can be compared to a carbon budget recently calculated from national statistics showing that the local urban sources (road traffic, industry, service and household) have a comparable net emission rate of 38 g CO2 m−2 day−1. The perspective of having more precise knowledge of the distribution of sources and sinks is finally discussed in relation to changing land use patterns.

Classification of urban land cover based on expert systems, object models and texture

The application of intelligent systems within the field of remote sensing is reviewed with special reference to urban land cover mapping from digital satellite imagery. Urban areas constitute spectrally heterogenous land-cover classes and call for the application of intelligent, texture-based image processing methods. The appearance of an urban land-cover class in a digital image generated by remote sensing is closely related to the spatial resolution of the image, i.e. significant changes occur as a result of increased/decreased spatial resolution. This paper discuss how texture information may be derived automatically from a generic spatial model of a possibly composite urban land cover class describing basic properties of the subordinate object classes and the spatial relations between these. A method based on prediction of cooccurrence matrix values corresponding to an urban land-cover class at a specific spatial resolution is described.

Agent‐based modelling of shifting cultivation field patterns, Vietnam

Shifting cultivation in the Nghe An Province of Vietnams Northern Mountain Region produces a characteristic land‐cover pattern of small and larger fields. The pattern is the result of farmers cultivating either individually or in spatially clustered groups. Using spatially explicit agent‐based modelling, and relying on empirical data from fieldwork and observations for parameterization of variables, the level of clustering in agricultural fields observed around a study village is reproduced. Agents in the model act to maximize labour productivity, which is based on potential yield and labour costs associated with fencing of fields, and are faced with physical constraints. The simulation results are compared with land‐cover data obtained from remote sensing. Comparisons are made on patterns as detected visually and using the mean nearest‐neighbour ratio. Baseline simulation outputs show high degrees of spatial clustering and similarity to the land‐cover data, but also a need for further calibration of model variables and controls.

The End of Urbanization?: Towards a New Urban Concept or Rethinking Urbanization

Urban growth and development have always been associated with specific nodes in an urban system. This association, however, does not make much sense in a world where the functional areas of many large cities have merged to form continuous urban landscapes. When more than 85% of a countrys population is urbanized, the process of urbanization as commonly understood has come to an end, so that traditional means of analysis no longer suffice. Within a Danish context, this paper discusses limits to traditional urban analyses based on individual urban places and an urban rural dichotomy. It argues for the use of an alternative concept related to localization within a larger urban landscape and goes on to demonstrate how the pattern of urban growth in Denmark over the last 25 years may be explained by increasing mobility and improved access to labour markets.

Large-area urban growth observations—a hierarchical kernel approach based on image texture

Abstract Geografisk Tidsskrift, Danish Journal of Geography 105(2):39–47, 2005 A multi-scale classification algorithm based entirely on computation of image texture in moving windows is presented and discussed. The rationale for using kernel-based methods as opposed to segment-based methods for texture-based land cover classification is discussed, as well as, the need for identifying strategies that may limit the effects of the inherent weaknesses of the kernel-based methods. Part of the proposed solution to this problem is to omit the search for an optimum kernel size and rather use different sizes concurrently followed by a weighted summary overlay process based on associated scores. The spatial growth pattern of the city of Accra, Ghana, is assessed over a 17 years period using the algorithm. Land-cover maps showing the extension of the new residential areas on the fringe of Accra are produced from Landsat ETM satellite imagery. These areas constitute the rapidly expanding frontier of urban Accra into its rural surroundings. The classification discriminates between new residential areas that have a distinct urban appearance and areas that are in a transition phase between rural and urban use. Finally, comparisons are made to a previous satellite-based study of land cover changes for the period 1985–1991.

Exploiting available data sources: location/allocation modeling for health service planning in rural Ghana

Abstract The preconditions for applying GIS-based location-allocation analysis for health service planning in rural Ghana are examined in terms of data availability and quality. A population map is established from the latest available census using geo-coding methods and digital topographic sheets. A vector-based transport model of the region is established by merging data from several sources including GPS. It is suggested that a hybrid transport model is required. This model combines the possibilities for all-direction transportation inherent in the raster-based approach with the possibilities for road/path transportation inherent in the vector-based approach. All-direction movements are expected to take place close to the villages in order to reach a suitable linear transport corridor represented by a vector. Several scenarios for improving the accessibility aspects of the health service provision are examined in light of Ghanas current health service policy. Location-allocation modelling tools are used to select optimal locations and provide statistics on average distance to health centres and percentage of population covered.

Measuring accessibility and congestion in Accra

Based on extensive GPS measurements, the article addresses the level of intra-urban accessibility in Accra, Ghana, and provides indications of the level of congestion. Traffic flows within the urban area are analysed with respect to speed, time-of-day, direction, road type, and land cover type. The speed information is extrapolated to cover the total mapped urban road network with time- and direction-specific data. A series of time-distance maps are created using network analysis to illustrate the level of accessibility at different times of the day and from different directions relative to the city centre. The article discusses the methodological potential of and barriers to applying GPS tracklog points for analysing traffic flows within an urban road network. Solutions are suggested for filtering GPS measurements, matching GPS measurements with the relevant transport links, even at intersections, and for providing direction- and time-specific flow analysis.

Suburbanisation, homeownership aspirations and urban housing: Exploring urban expansion in Dar es Salaam

This paper offers an exploration of urban expansion from the point of view of the individual residents buying land, settling and living in new, rapidly growing peripheral settlements of Dar es Salaam, Tanzania. The findings suggest that the demand for affordable housing is the primary motivation for residents moving to the periphery. The demand for self-built, owner-occupier housing is especially significant initially, while the demand for non-ownership housing increases in importance later in the process. Income-related motives, on the other hand, are strikingly absent from settlement considerations. Urban residents settle in the periphery, even though income-generation is often tied to working somewhere else, namely in the central parts of the city. The paper proposes that the processes of urban expansion depicted in this study are usefully conceptualised as suburbanisation processes, though it is a type of suburbanisation that has some peculiarities given the particular context, where expansion happens informally and largely unguided by planners.

Towards a framework for delineating sub-districts for primary health care administration in rural Ghana: A case study using GIS

This paper examines the need to carry out primary health care administration, programming and planning beyond the established 110 districts in Ghana. The framework for delimiting the sub-districts is offered by the availability of digital data such as the district boundary, site location, road network and population. Using the specified travel distance from predetermined sites, network analysis generates approximate polygons around the health centres to create functional areas ? the health sub-districts. Additional sites are proposed based on a set of criteria which includes proximity, centrality, population and existing level of infrastructural development in an attempt to improve coverage and bring the total utilization of health facilities closer to 100% in the study area.

Assessing the Land Cover Change of Accra Using Landsat-TM Data

Lasse Moller-Jensen & Poul Yankson: Assessing the Land Cover Change of Accra Using Landsat-TM data. Geografisk Tidsskrift, Danish Journal of Geography 94:xx–xx. Copenhagen, Dec. 1994. The objective of the current study is to produce a land cover map of Accra, Ghana, showing the recent spatial growth in order to assess the nature of this growth and the current spatial development trends. A second purpose is to test the adequacy of Landsat-TM images for urban change detection studies. Comments are made on the rationale for land cover mapping based on digital satellite images. The applied image processing method includes a texture-based classification method, pixel to vector conversion and post processing in a vector-based geographical information system.