An approach to the study of urban degradation through remote sensing: a case study of the eastern sector of metropolitan manila
May Celine T. M. Vicente
A. ProblemManila Observatory and Lates-Cems, Ehess, Paris Tel: 00 632 426 59 59; Fax : 00 632 426 61 41; E-mail: celine@pusit.admu.edu.ph In the Philippines, it is becoming evident that marginalization, environmental degradation and susceptibility to disasters are issues that need to be addressed immediately. There are also serious conflicts of spatial interests and disparate development priorities among concerned sectors. Then, too, there is the inability to localize these and other related problems in the appropriate scales of observation. Neither is there an adequate facility to study and monitor intersectoral development impacts. The above conditions are some principal reasons for the discrepancy between visions and actual evolution of development. For the most part, physical framework development plans are unrealized, as is the case in Metro manila. Urban planning in Southeast Asia, particularly in underdeveloped nations, is generally plagued by this discrepancy between perspectives and the actual pattern of development. This clearly shows ecosystems in diverse milieus (urban, rural, rurban, regional); that is, if sustainable development1 is to succeed systematically and progressively. In particular, there is a need to integrate pre-disaster science into the socio-environmental planning process. Pre-disaster science includes such focal research areas as the upper atmosphere (e.g. ozone depletion), climate change (e.g. sea level rise), crustal deformation (e.g. earthquakes) and the environment (e.g. unclean water) (Communication by Fr. McNAMARA, SJ, Director, Manila Observatory). This approach can be facilitated through symptomatic observations of socio-environmental health of the different ecosystems constituting the milieus. Research and analyses of the complex interactions between the elements: earth, air or wind, water and fire or energy and how these affect human settlements and animal habitats must be undertaken accordingly . This study addresses theoretical and technical issues of the aforementioned observations and approaches, in part, by applying remote sensing techniques in the survey and morphological analysis of urban blight. Urban socio-environmental planning is improved by the integration of this study in a model and wider framework of GIS that consequently facilitates the generation of strategic frameworks as "space plans". The study area is the eastern sector of Metropolitan Manila in the Philippines. For the remote sensing analysis or urban degradation, SPOT multispectral and panchromatic data are used in a process of semi-automated interpretation. Image segmentation uses the spatial reasoning "disjunction-conjunction". Results of the study imply a possible cause-effect relationship between natural and man-made degradation in the area. They indicate, most of all, the usefulness of spatial analysis; image segmentation being the sole method for isolating and associating phenomenon. One can thus propose an assessment of critical urban environments. This is an aspect of pre-disaster science that must be incorporated into the (urban) socio-environmental planning process, particularly as this approach addresses the need for sustainable development of ecosystems. B. The Approach or Methodology Adopted We orient the research towards the extraction of themes by the segmentation of imageries. In accordance with the chosen orientation, one adopts an approach that is referred to as "disjunctive-conjunctive". When one speaks of this approach, one uses its context in the domain of logic referring to two forms of opposed but complementary reasoning. (1) "Disjunctive" reasoning A reasoning is considered "disjunctive" when it goes from the general to particular. In terms of spatial reasoning, the "disjunctive" step leads to the simplification of large thematic groups into their components. "Disjunction" is accomplished in the course of this research up to the level of perception of elements that we recognize to be objects. A major example of an ultimately "disjunctive" operator is the geometric intersection of pixels as represented by the minimum to maximum gray of objects corresponding, in turn, to various (classes of) indices or parameters (of detection). (2) "Conjunctive" reasoning In contrast, a "conjunctive" reasoning permits conclusions based on particular known facts. In this research, once the components of large thematic groups have been extracted, one adopts "conjunctive" reasoning by recombining groups of objects in a significant manner (communication by Mr. THOMOPOULOS, E.). The aim of this phase is to analyze relations between localized objects. One draws conclusions based on these large (recombine) thematic groups. As they have been defined in cartography, spatial relations between objects possess at times hierarchical, associative and ordinal (communication by mile RUAS, IGN) nature. These aspects prove to be very useful when one determines the type of processing that is appropriate in order to realize the "conjunctive" phase of the research. It is also essential to show that the two large families of degradation, that is natural and artificial, are not necessarily dissociated. This aspect justified, in part, the inferences in the "conjunctive" phase of the research. Within its limits, the step of "conjunction" is considered significant. The methodology adopted here applies the fundamental principle of conscientious, systematic and responsible planning as aided by RS-GIS. In terms of the detailed methodology for the application of RS-GIS, one refers to ""Figure 35, Tableau 6, Figures 36-40, Tableau 7 and Planches 12-14 (or Figures 52-54)" (VICENTE, 1998) that are to be presented in the Conference. C. Results of RS-GIS Application Thematically, we speak of the following: (1) Degradation of the natural milieu In total, we have:
One observes 7.26% of the study area occupied by precarious or unregulated habitation of high density. These slum and squatter settlements are widely distributed, but more frequently in the intermediary zone or the region between the observed "dome of pollution" and the zone of urban transition. An incompatible mix between housing, industries and large establishments of consumption is evident (13.93% of the study area). Terrain are also considered to be part of the artificial milieu when they are prone to urbanization. One also notices unregulated or incoherent sites where housing are precarious and industries that are probably polluting are situated along rivers. These zones are elevated or flood-prone. The zone of transition, being a basin, is favorable to inundation. This state is aggravated by land fills that are not controlled. These are linked to or caused by urbanization pressures towards the periphery of the metropolis. We note that the placements of structures are inappropriate when these are in the direction of the wind. With a relative humidity elevated (80%) and weak winds (0-1 m/sec), air pollution provoked by industries of the intermediary zone may stagnate in the basin and the coastal zone in the form of a "dome of pollution". This aspect must be studied more profoundly. On the other hand, in the intermediary zone, which unites three important basins, water is strongly charged with sediments which unites three important basins, water is strongly charged with sediments which resemble polluting substances. An image processing algorithm analyzing this phenomenon at the "sub-pixel" level is suggested to better understand the condition. Based on this analysis, the collect of water samples may be undertaken. Also, currents of water circulating towards the Manila Bay and the Laguna Lake make this site and the zone of transition very fragile. A density of land use outside the norm is linked to housing settlements that are precarious or spontaneous. These are widespread, particularly below the "dome of pollution" and in the intermediary zone. Nevertheless, one prefers to avoid hasty conclusions about the conditions below the atmospheric haze without having systematically verified that parts of the study area. D. Contribution of RS-GIS (1) Types of information Intermediary results show urban degradation of the natural and artificial orders in the eastern sector of Metro-Manila. Although the surface covered by these phenomena do not constitute a sufficient basis to give an idea of their importance or gravity, one utilizes this quantification as a relative indicator of the symptom of deterioration suffered by the study area. One recognizes that degradation of the natural milieu (18.39% of the study area) and artificial milieu (12.70% of the study are) are of comparable importance. In fact, their spatial reparation (atmospheric haze, intermediate zone, zone of urban transition) shows a serious if not significant relation. This leads us to remark that there probably exists a cause-effect relation between degradation of the natural and artificial milieus. (2) Facts demonstrated through analyses Terrain verification aided by descriptive statistics confirm the existence of this observed relation of causes and effects. Nevertheless, one was able to discover that the density of precarious habitations seem to be in diminution, most of all alongside major circulation axes, this despite a growing expansion in zones situated along rivers. This suggests the computer-assisted evaluation of intermediary results. These results were obtained by comparing verified and localized zones of precarious habitations and, therefore too, areas of priority development (APD) in both SPOT P 1987 and SPOT P + XS 1991. One can, thereafter, refine classification, failing that which necessitates the correction of errors or resulting imageries. The clarity of classification, in particular that linked to the natural milieu, proves to be significant. A case in point is that of atmospheric pollution. This shows the soundness of the methodology as well as the parameters used for the study of degradation of the natural milieu. In contrast, it is understandable that confusions appear after extracting the de gradation of the artificial milieu. Firstly, one must note that, for lack of time, it was not possible to refine road networks. These have to be removed from zones of habitations, industries and large establishments. Secondly, one takes into account a margin of ambiguity. Nevertheless, the percentage of ambiguous surfaces remains minimal (0.03 to 0.05). Yet it does not allows us to ignore intermediary results on the degradation of the artificial milieu. This fuzzy area may also comprise zones of thematic transition, that is a sub-class of objects changing from one type to another . Finally, the exactness of classification determines, in part, being one of the parameters, the validity of management or renewal options. The morphological model obtained confirms the theory on the duality of the urban system: capitalist establishments juxtapose with primitive zones (of precarious habitations). The fact that these latter zones coexist with suburban developments that are well regulated (for the middle and upper classes) explains the social and economic crises. If one must adhere strictly to our intersectoral view of the urban system, one must also consider these suburban developments being degraded. These degradation are due, in part, to marginalization of the poor in contrast to capitalist structures that are strategically favored with respect to the ecosystem. (3) Precision of the measure and quality of localization With respect to confusions between degradation of the natural and artificial milieus, one considers that which are in the interior of the zone below the atmospheric haze as being significant. For lack of complete information, one considers that results of interpretation in the zone with precaution. The evident mix of information in the intermediary zone and zone of transition is in relation to terrain prone to urbanization. The latter enter as a sub-class of the natural and artificial milieus. There exist naturally artifacts and unclassified areas. For example, surface between limits of sub-classes (ex. Water experiencing sedimentation or pollution of medium or high intensity) must be reexamined. As mentioned above, these zones may comprise space in transition between sub-classes of an object to another. There are several techniques to improve these intermediary results. These exercises form part, however, of the rigorous domain of cartography. This may be handled in the future to operationalize the schema of planning, where a GIS integrates RS, in particular for the production of "space plans". E. Limitations (1) For a given theme, levels of measure A critical aspect to the grouping of information is the determination of variables in the form of layers and their levels of representations. In consideration of urban regional observation, this exercise leads us to take note of the necessity to interface the modes "vector" and "raster". It is by these two types of infography that themes and variables of the study are decomposed and aggregated. A certain scale is, therefore, inherent that depends on the resolution and synoptic properties of satellite scenes that, in turn, form the foundations of databases. Given that these databases are , by choice, based on satellite imageries, we see the need for the metrical enhance and permit topological operations. These operations are implicated when generalization of information and their contextulization prove necessary to arrive at alternative perspectives and ultimately realize sustainable development. For the study, the resolution and spatial unit chosen was 10 m x 10 m. This corresponds to the spatial resolution of SPOT P (Panchromatic). To combine these imageries with those that are Multispectral, one had to resample the latter that were otherwise of 20 m x 20 m resolution. In terms of synoptic observation, one chose to work at the scale of 1:93,000. This scale permitted generalization until 1:46,000, which represents a maximum limit for a local scale. It is, therefore, evident that SPOT P + XS imageries are relevant tools for socio-environmental planning. (2) Detection and quantification of qualitative properties Having established the scale and spatial unit for the research, we proceeded to detect and quantify the themes, including their roots and ramifications, in accordance with their properties. The definition of these properties of variables aided us in verifying and optimizing the tools of RS-GIS. In terms of RS, we were able to elaborate parameters and criteria of recognition of themes, sub-themes and objects, for which logical operators of ex traction function in the metrical form. One proposes the application of the mode "vector" to digitize and integrate administrative filters or plans and policies of intervention, including those concerning road networks. One was able to identify in which instances GIS or RS or both should interface with each other. This precision is facilitated by linking information groups. In a addition, their aggregations or desegregations permit us to remark that information of the higher or advanced level of planning demand RS-GIS interfacing. This means that one needs powerful operators allowing logical transformation in the "vector", "raster" or both modes in interface. (3) At small scales, threshold of spatial resolution of small objects Because of the complexity of the ecosystem, visual interpretation plays an important role in the ultimate application of RS-GIS for planning. For this interpretation knowledge of terrain is indispensable. For the research, the use of the scale 1:93,000 until 1:46,500 permitted us to move from one level of generalization to another. This sweep is essential to regional and local planning. It involves the optimization of RS complementary with GIS. In effect, RS-GIS integration demonstrates the exhaustiveness of tools in relation to the analyses of complex spatial systems. Visual interpretation of real structural morphology, which may be symbolic, is facilitated not only through the relation vision-spatial resolution. Moreover, the interpretation is assisted by digital processing (e.g. local statistics, indices). The linkage of logical transformations permits us to operate from one scale of observation to another. The thresholds or limits of spatial resolution determine, in turn, the exhaustiveness of spatial and thematic information. This exhaustiveness is, in part, associated with possible graphic enhancements, thereby surpassing conventional cartography. This advantage confirms the interest for urban planning and development of "space maps" and "space plants". A dictionary may be elaborated relating themes, sub-themes and objects to scales and forms of graphic representation (including legends or symbols, forms, colors). Graphic enhancements permit better spatial reference, analyses and representation of optional development strategies that correspond to localized problems in the milieu under investigation. References:
|