THE USE OF MEDIUM TO HIGH RESOLUTION SATELLITE IMAGERY FOR URBAN MAPPING APPLICATIONS

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1 THE USE OF MEDIUM TO HIGH RESOLUTION SATELLITE IMAGERY FOR URBAN MAPPING APPLICATIONS Pillay, D.L. Council for Scientific and Industrial Research (CSIR), Satellite Applications Center (SAC), P O Box 395 Pretoria, dlpillay@csir.co.za ABSTRACT Cities in Africa are being subjected to high levels of exploration and development. The existing spatial data for these cities are not only outdated but also exists in an analogue form. Traditional land surveying methods of map updating using field surveys and aerial photography is both costly and time consuming. This paper focuses on the potential use of high-resolution satellite imagery for various urban mapping and feature delineation applications. The CSIR Satellite Application Centre has expanded its current portfolio of earth observation sensors to the precision high-resolution domain. Included in this range are the SPOT 5 (2.5 m panchromatic and 10m multi-spectral), EROS (I.8 m panchromatic) and IKONOS (1 m panchromatic). The use and limitations of medium resolution satellite imagery is related to the comparative advantages of high-resolution satellite imagery. Several applications focusing on the potential use of high-resolution satellite imagery within an urban context is documented. These applications describe the use of high-resolution satellite imagery for mapping urban structures, street map updates, and the use of imagery in disaster management and access control. The future role of high-resolution satellite imagery in urban development studies is explained. The results of these evaluative projects clearly demonstrates the advantages of using high resolution for precision and detail mapping exercises. 1. INTRODUCTION Most cities in Africa are being open to exploration and development, generating a growing demand for up-to-date maps of land topography, land use and other spatial information products. These maps are important for activities ranging from managing land use development, to natural resource management and engineering applications. In Africa most city maps are outdated, and largely exist in analogue form. Traditional land surveying methods of map updating using field surveys and aerial photography is both costly and time consuming. This paper articulates through various applications involving both medium and high-resolution satellite imagery with the intent of highlighting the advantages of high-resolution satellite imagery. 2. THE NEED FOR BETTER SPATIAL INFORMATION The earth observation satellite industry is experiencing a rapid technological change with the launch of a new generation of high-resolution (up to 0.6m) commercial earth imaging satellites. Mapping applications within urban environments are dependant on multi-source remote sensing techniques capable of providing high-resolution data sets over wide geographical areas. The focus of mapping applications within urban environments is on utilizing the latest and least time-consuming methods to ensure the best product quality at a lower cost. The synoptic advantages and large area coverage of medium resolution satellite imagery has been useful in different mapping exercises (5). These applications have, however, been limited to large area mapping with a high degree of generalization. The emergence of high-resolution satellite sensors have introduced a new level of advantages by providing higher spatial resolution for mapping applications, increased geometric capabilities and more frequent revisitation periods (4). The higher spatial resolution has positive implications for urban development applications such as street map updating, feature identification, topographical updates and settlement classification. Proceedings of the 21 st International Cartographic Conference (ICC) Durban, South Africa, August 2003 Cartographic Renaissance Hosted by The International Cartographic Association (ICA) ISBN: Produced by: Document Transformation Technologies

2 F % 75% ? DETECTION RECOGNITION IDENTIFICATION 100% 75% 50% 50% 25% 25% metres 0,5 0,3 Figure 1. The above 2x2 matrix diagram shows the increase in spatial resolution over time, which is in turn related to the level of information that can be derived about an object. 3. SATELLITE IMAGE RECEPTION The CSIR Satellite Applications Center (CSIR), situated at Hartebeeshoek, South Africa has recently expanded its current portfolio of earth observation sensors to the precision high-resolution domain. The Satellite Applications Center has different sectors within its operations catering for the reception, ingestion and value addition of satellite imagery. The center has expanded its ability to acquire high-resolution satellite imagery such as SPOT 5 (2,5 m panchromatic and 10 m multispectral), EROS (1.8m panchromatic), IKONOS (1m) and Quickbird (0.6 m). Figure 2. The satellite coverage area of the Satellite Applications Center.

3 4. SENSOR COVERAGE COMPARISONS Area Coverage Comparison Landsat 180km SPOT Eros (20km squares) Figure 3. Comparison of Landsat, Spot and Eros coverages. 5. TRANSITION FROM RAW DATA TO KNOWLEDGE Satellite imagery for mapping exercises is acquired according to specific parameters including date, time, extent of cloud cover and the actual area of interest coverage needed. The input to this process is machine-orientated scenes the outcome of which is a matrix of digitally referenced numbers. The images are thereafter geo-referenced which involves the collection of GCP (ground control points) of clearly visible ground points that correctly aligns the raw satellite image to a correct ground reference. Included also at this stage is the referencing of digital ancillary data layers such as conservation areas, geology layers, political boundaries and hydrological features. Figure 4. The Process of Data Preparation.

4 6. SATELLITE IMAGERY FOR URBAN DEVELOPMENT APPLICATIONS 6.1 Mapping areas of change from medium resolution satellite imagery Medium resolution satellite imagery such as Landsat 7 (30 m multi-spectral) can be used to perform large-scale medium resolution spatial queries within urban environments. The wide area coverage (180 x 180km) allows for large areas to be covered with a single scene making it a cost effective assessment tool. In a study using Landsat data (Figure 5), urban planners were able to assess the rate of informal settlement expansion as compared to the rate of new housing settlement development. The synoptic view of satellite imagery allows urban planners and decision makers to visualize the extent and direction of informal settlement expansion in relation to new housing projects being delivered. Figure 5. SPOT Xi imagery used to indicate expansion of informal housing settlements (blue) in comparison to previous years (red). Multi temporal Landsat images overlaid with the ancillary data allows urban planners to assess urban land use trends as well as provide a demand and supply tool for infrastructural development such as housing and roads. The use of relevant ancillary data such as conservation areas allows planners to identify areas of encroachment and environmental sensitivity. The time consuming nature of feature identification due to its spatial resolution and the degree of generalization in performing such a task contributes to the limitations of medium resolution data. Figure 6. New housing development project in the George area. High-resolution imagery provides urban planners with the ability to map infrastructure (red) and monitor environmental sensitive areas (yellow).

5 6.2 Quantifying and mapping extent of change using high-resolution satellite data The emergence of high-resolution satellite imagery has allowed for a higher level of spatial analysis within urban environments. Compensating for the spatial resolution of medium resolution imagery, high-resolution imagery such as EROS 1A provides a spatial resolution of 1.8 m and area coverage of 12 x 12 kilometers. The higher spatial resolution of 1.8 m not only allows for normal spatial updates such as updating topographical map information, but also allows for infrastructure mapping, settlement classification, development of urban green spaces, service provision maps, access control mechanisms and regional planning. Figure 7. High-Resolution imagery used for settlement classification. Informal settlements demarcated on the right (orange) and structured industrial settlements on the left. IKONOS (1m panchromatic) imagery provides the foundation on which powerful tools can be created, including image base map updates, transportation analysis, asset management, environmental planning, crime mapping and analysis, storm water management, public safety and disaster management, and Internet based property information access via GIS. In figure 8 below, access control procedures can be implemented by analyzing the area allocated for public parking in relation to the carrying capacity of the entertainment facility. The green circle indicates the Johannesburg Athletics Stadium. Figure 8. An Example of an IKONOS (1 m) panchromatic imagery over Ellis Park Stadium in Johannesburg.

6 This concept of utilizing high-resolution imagery for developing sound access control procedures can be useful in situations such as the incident that occurred in April of 2001 when 43 fans died when a stampede occurred during a major soccer event. Many issues led to the dreadful incident, such as: lack of discipline of fans to park n ride, booking their tickets earlier, etc. The future planning in the building of sporting facilities can now take into consideration the use of synoptic resources such as high-resolution satellite imagery. 7. THE FUTURE APPLICATIONS OF HIGH RESOLUTION WITHIN URBAN ENVIRONMENTS Various forces such as the rate of population increase, urban sprawl, urban decay and declining service provision challenge the urban environments of different African cities. In reality these forces of change are permanent and force local and provincial authorities to plan in accordance. The need for accurate spatial data is therefore a priority in terms of planning alternatives in order to management of these forces of changes. High-resolution satellite data provides a tool by which these changes can be managed and planned for in the broad expansion of urban environments. The increased spatial accuracy and frequent revisit periods allows planners to construct action scenarios and compile accurate database of spatial environments. The increased capabilities of future satellite systems that would allow for even higher spatial resolution will bring earth observation satellite imagery close to the accuracy specifications of aerial photographs. The advantages, in terms of frequent revisit times, quick processing and the more compatible nature of high resolution satellite imagery data compared to aerial photographs will given the former resource a distinct advantage and preference. 8. REFERENCES [1] Barrett, E. C., Curtis, L.F Introduction to Environmental Remote Sensing, New York: Wiley and Sons. [2] C.P. Lo, Applied Remote Sensing, Longman, Harlow, (1986). [3] L.L.F. Janssen, Principles of Remote Sensing, ITC, Netherlands (2000). [4] P.M. Atkinson and N.J. Tate, Advances in Remote Sensing and GIS Analysis, John Wiley and Sons, New York, (2000). [5] T.M. Lillesand, and R. W. Kiefer, Remote Sensing and Image Interpretation, Wiley and Sons, New York (1994).

7 THE USE OF MEDIUM TO HIGH RESOLUTION SATELLITE IMAGERY FOR URBAN MAPPING APPLICATIONS Pillay, D.L. Council for Scientific and Industrial Research (CSIR), Satellite Applications Center (SAC), P O Box 395 Pretoria, dlpillay@csir.co.za Short Resume Name: Surname: Degree: Institution: Dechlan Liech Pillay Masters in Environment and Development Council For Industrial and Scientific Research (CSIR), Satellite Applications Centre. Pretoria, South Africa. Research interest: GIS, Remote Sensing, Wetlands Current Applications/ Studies: Completing a PhD in land use changes affecting wetlands areas in the Mgeni Catchment. Applications in Subject: The use of high resolution satellite imagery for map updating and feature identification.