An approach to the study of urban degradation through remote sensing: a case study of the eastern sector of metropolitan manila
(2) Degradation of the artificial milieu
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.
