Image Processing Reference
In-Depth Information
oasis is estimated at 800,000 inhabitants, of which 78% live in urban areas and 22%
in rural areas and villages. The main activity is concentrated on the agricultural sec-
tor (palm trees), but the overall agricultural area is declining due to climatic and
anthropogenic factors such as sand movement, urban encroachment, decrease of the
level of ground water tables, lack of drainage (sabkha), the small size of agricultural
parcels which are not exploited cost-effectively. The climate is arid and the precipita-
tion ranges from 75 to 110 mm.
The site covered in this study was a 40 × 55 km rectangle centered on Al-Ahsa
oasis. Two multi-temporal multispectral Landsat-TM imagery with 30 m spatial
resolution, were used to analyze two points of time: October 1987 and October
2001. Topographic maps at a scale of 1/25,000 and road network map were also
used, along with ground observations.
Data Analysis
:
We performed the following operations: (1) pre-processing of the
two Landsat-TM images, which consisted of image subsetting, geometric correction
according to the parameters of the national grid reference (UTM projection, WGS'84
Datum and Zone 39); (2) land use mapping based on visual interpretation, using
ground observations and the two Landsat images; and (3) analysis of the two land use
maps using GIS in order to investigate the impact of urbanization on other land uses.
Results and Discussion
:
The results of this case study included land use maps at a
scale of 1:100,000, which offered a diagnosis of urban and sub-urban areas at each
period (1987 and 2001). The land use categories include seven thematic classes,
namely: urban areas, urban planning, agricultural lands, sabkha, sand dunes, hills
and water bodies (Mufareh
2002
; Ait Belaid and Mufareh
2002
; Ait Belaid
2003
).
The total area of the study site is approximately 222,000 ha.
One evolution map for the period (1987-2001) was created to illustrate the temporal
evolution of land use categories. During 14 years, urban areas (Fig.
13.5
) have
expanded by 5,326 ha (75%) and agricultural areas by 4,430 ha (22%). During the
same period of time, there was a decrease in the areas of sabkha by 8,063 ha (12%),
urban planning zones by 1,341 ha (27%), sand dunes by 206 ha and hills by 146 ha.
The evolution matrix generated for Al-Ahsa oasis is shown in Table
13.2
. It
illustrates the major land use changes that occurred between 1987 and 2001. It signals
also the land use categories, which are not impacted by any change and vise-versa.
The zero value in the matrix implies no land use change in corresponding classes.
During 14 years, urban areas increased by 5,326 ha, of which 2,746 ha were
converted from sabkha, 1,500 ha from urban planning zones, 972 ha from sand
dunes, and 513 ha from agricultural lands. In contrast, the area of agricultural lands
increased by 4,430 ha, of which 4,480 ha converted from sabkha, 1,654 ha from sand
dunes, 184 ha from urban planning zones, and 119 ha from urban areas. The agri-
cultural lands experienced many transformations. Overall, urban areas and agricultural
lands show an explicit evolution of change during the study period. This expansion
was compensated by a regression of other land use categories, implying that new
sand dunes, sabkha, urban planning uses were developed between 1987 and 2001 but
consumed by urban areas and agricultural lands. In conclusion, Al-Ahsa oasis is
