Abstract
The distribution of vegetation within an urban area plays a major role in providing a satisfactory environmental condition within the urban area for its inhabitants. In most cities however, these vegetation areas are threatened by alternate urban land use due to pressure on land. In this study social parameters of an urban area are related with the density of urban vegetation in the respective planning units of the city using a vegetation cover map. By this, areas having a poor environmental condition could be easily recognised and the environmental condition of the city as a whole could be assessed. Further, it is shown how satellite data could be related with social parameters and the density of urban vegetation so that these relations could be used for continuous environmental monitoring of the urban are. To achieve this, the authors have used a proposed index UI, computed by using Landsat TM band 7 and 4 and the modified Soil adjusted Vegetation index (MSAVI). As a case study the City of Colombo in Sri Lanka is used.
1.0 Introduction
In recent times the importance of urban vegetation in preventing he deterioration the deterioration of the urban environment as been rcognised. Vegetation in urban areas strongly controls the hermal environment, it helps in the retention of rainfall runoff and reduces the level of suspended particles in the atmosphere. Hence the quantity and quality of urban vegetation and economic activity distress.
In this study social parameters of planning units of the City of Colombo in Sri Lanka has been related with the density of urban vegetation so that the areas having a poor environmental condition could be easily recognised. Further it is shown that this relation could be represented by a relation between a proposed index UI and MSAVI both computed using Landsat TM data so that these areas could be continually monitored using satellite data. UI is strongly related to social and other parameters of development while MSAVI is related to the vegetation density.
The study area was limited to the Municipal Council Limits of the city of Colombo which has an area 37.7 sq.km with a population of 635000. Figure 1 shows the planning units within the city. The vegetation within the city consists of parks, grasslands, mixed agricultural crops, mangroves deep and shallow marshes and artificial green. The distribution of vegetaion within the city is shown in figure 2 which is an urban vegetation map of 1981 and was used in this study.
Figure 1 Planning units within Colombo City
Figure 2 Distribution of Urban Vegetation in Colombo City, 1981
Table 1 Social and environmental parameters
2.0 Data used in the study
2.1 Conventional Data
To compute the density vegetation in the respective planning units an urban vegetation map of 1981 of Colombo City (Fig.2) was used. A map showing the planning units within the city was scanned and registered with other spatial data to compute by using a 1:12672 building cover map of 1970. Population and housing data of 1993 and slum and shanty population data of 1981 was used in the analysis.
2.2 Remote Sensing Data
A Landsat TM scene over the colombo materopolitan regon quired on the 12 the February 1992 was used in the analysis.
2.2.1 the proposed Index UI
The proposed index UI was computed as shown below using Landsat TM band 7 and 4.
UI is strongly related to the density of building cover (UD) as could be seen the figure 10 in section 4.1. To obtain this figure the scanned image of the building cover map and themap showing the planing units have been registered with the Landsat TM image. Figure in section 4.1 show how UI is related to social parameters of this urban area.
2.2.2 The modified soil adjusted vegetation index (MSAVI)
The Modified Soil Adjusted Vegetation Index (MSAVI) has been proposed by Qi et al [2] minimise soil background influences on NDVI. It increases the dynamic range of the vegetation sensitivity. MSAVI is defined and used in this study as shown below.
where B4 and B3 refer to Landsat TM Bands 4 and 4 and 3 respectively.
