GIS and Remote Sensing Based Analysis of the Built-up Area Change in the Ria Formosa Barrier Islands (Portugal)
Carlos Loureiro Ferreira1, Tiago Garcia2, Óscar Ferreira3, João Alveirinho Dias3
1 CIMA, Universidade do Algarve (PT)
2 CIMA/CIACOMAR, Universidade do Algarve (PT)
3 Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve
(PT)
Data about land use is an essential element of
the planning process because it can contribute to a better knowledge of the
spatial arrangements and patterns of human activities and the need to modify
them for environmental planning purposes (Treitz, 2004). Analyses of land use
change with remotely sensed imagery have been done extensively for urban planning,
most part of the times using aerial photographs (Carlson, 2003). In the last
years, remote sensing data have been coupled with GIS creating a valuable analysis
tool and source of detailed spatial information upon which sound planning decisions
can be made (Prenzel, 2004).
In this abstract we present the objectives and proposed methods for a research
study that uses GIS and remote sensing, aiming to create land use databases
to assess the impact of the increasing human occupation in the evolution of
the Ria Formosa barrier islands.
The Ria Formosa barrier island system is composed by two peninsulas and five
islands, separated by six tidal inlets, extending along approximately 55 km
in the Southern coast of Portugal (Fig. 1). The system presents a high degree
of morphologic variability which has been constricted by housing and urban infrastructures
and also by heavy coastal engineering structures (jetties for inlet stabilization
and seawalls for coastal erosion protection).
Fig 1 - Geographical location of the study area (adapted from Vila-Concejo et al., 2004)
The proposed research will consider four main objectives:
· To accurately measure the variation of built-up land uses in the Ria
Formosa barrier islands for the last 54 years (1947-2001).
· To identify areas of change and the type of change that has occurred
(e.g., new constructions, conversions, restorations, demolitions), aiming to
understand its driving pressures.
· To compare the morphologic evolution of the Ria Formosa barrier islands
with the built-up land-use intensification in order to assess their mutual impact.
· To establish near future scenarios based upon the land use data collected
and the expected shoreline evolution trends.
The generation of the land use databases is based on photo-interpretation of
aerial photographs by "on screen" digitizing with ArcGIS software.
Aerial photographs were selected for this study because they provide an appropriate
combination of spatial resolution and temporal coverage. The aerial photograph
sets that are being used (1947, 1958, 1969, 1972, 1976, 1989, 1996, 2001) allow
to follow the growing of the built-up area since the period when it was still
incipient, until today, being observed the proliferation of houses, roads, parking
lots and tourist related infrastructures.
Pre-processing of the digital images comprehended the scanning of the analogue
aerial photograph sets at different resolutions, in order to preserve a ground
resolution of 1 m/pixel. The digital images obtained were georectified with
ER Mapper software, and then integrated into the GIS.
The next step of this study will be the "on screen" digitizing for
database generation. In this process vector-based databases of polygons will
be created for buildings, roads, and other artificial surfaces. A reference
database will derive from the most recent flight (2001) and the remaining will
be done by downdating, i.e. the 2001 database will be overlapped on screen with
the 1996 images and then the information for the 1996 database will be extracted.
This procedure will be repeated for the following datasets, enabling the harmonization
between the reference (2001) and the historical databases. The reference database
will be supplemented with ancillary data about the buildings and the artificial
surfaces (e.g. approximate age, construction material and occupation pattern).
Fig 2 - Change in the built-up area between 1947 and 2001 in Farol Beach (Culatra Island)
The proposed method for database generation adapts
the one developed by the Project MOLAND (Monitoring Land Use/Cover Dynamics
- http://moland.jrc.it), carried out by the Land Management Unit of the Institute
for Environment and Sustainability of the European Commission Joint Research
Centre, although using a more detailed spatial scale and adjusting it for built-up
land use in coastal zones.
By providing a spatial tool that can be used for assessing, monitoring and modelling
urban development and its interactions with the environmental dynamics of the
barrier island system, this research can present an important contribute to
the coastal zone planning and management of the study area.
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