Home Articles Overlay Analysis of GIS Layers to Evaluate Changes on AL Sammalyah Island

Overlay Analysis of GIS Layers to Evaluate Changes on AL Sammalyah Island

Salem Essa


Salem Essa
Geology Department
U.A.E. University, Al-Ain, U.A.E.
[email protected]

Ronald Loughland, Mohamed E. Khogali, Abdulmunem Darwish
Environmental Research Department,
Emirates Heritage Club,
Abu Dhabi, U.A.E.

Building a GIS database for AL Sammalyah Island will assist in planning the conservation and management of the natural resources and the development of ecotourism activities on the island.

The island has witnessed high rates of change in land use in the past few years; environmental management approaches have been implemented since the mid 1990s with a vision for improving the decision making process and providing quick and accurate services to researchers and the ecotourism community in general. The building of an integrated spatial database, during the current phase, is an important step towards the achievement of the actual research objectives. A spatial database containing 15 GIS layers was built; both raster and vector layers were integrated; the data is projected in the UTM zone 40N. The outcome of the change detection analysis task, conducted during the first phase of the project, was also added to the database. The integration of multi-scale aerial photographs in a GIS database is of great importance and has a high cost to benefit ratio.

The objectives of the present study are summarized below:

  • Evaluation of the change rates and extent during study period;
  • Creation of GIS layers related to the environment of the island;
  • Building a spatial GIS database for optimal land resource management of the island.

BACKGROUND
The creation of a spatial GIS database is a major objective of the actual study. To emphasize the issues related to the management of the island resources, multi date large scale aerial photographs were scanned, georectified and integrated into the spatial database. Six different dates were considered, the only available data!, mid-1970s, mid-1980s, 1999, 2000 and 2005 aerial photographs with spatial resolution 1 to 2 meters. Vector data were derived from the 1999 and 2005 by on-screen digitization to evaluate the change occurred on the island during this active period of management and laying down of infrastructures on the island.

A total of 11 different GIS layers were produced namely: roads, roundabouts, footpaths/tracks, buildings, breaks/bays/ports/ petrol station, palm trees, mangroves, shrubs, water bodies, water channels, and barren land. A DEM will be generated and added to the database on a later stage because cuts, filling, and the creation of new artificial hills continue to be done during our study.

The basic principle in using remotely sensed data for change detection is that: changes in the objects of interest will result in changes in reflectance values or local textures that are separable from changes caused by other factors such as differences in atmospheric conditions, illumination and viewing angles, and soil moistures.

STUDY AREA
AL Sammalyah is located at approximately 24o 26’10″N – 24o 28’56?N and 54o 29’22?E – 54o 34’12?E (figure1). Situated in the Arabian Gulf, about 12 km north east of Abu Dhabi Island near (Um al-Nar Island) area and just opposite Shati’-Al Raha beach, is characterized by its rich ecosystems and marine life. The Island area covers about 14 square kilometers. Soil texture is dominated by sand, with high salt content reaching 31.5% TSS on the surface, being mostly Chloride soluble salts giving a white colour to the soils of the island, which produces high brightness levels on satellite imagery operating in the visible portion of the EMR, however the very narrow mangrove soils surrounding the island have dark color because of high content of organic carbon content. The Island is a natural reserve containing high biodiversity, mangroves (Avicenna marina), including: Arthrocnemum macrostachyum, Seidlitzia rosmarinus, Suaeda vermiculata, and Cyperus conglomerates.

A change detection analysis using multi-sensor and multi-temporal aerial photographs and satellite imagery can help in emphasizing changes in Land Use/Land Cover (LULC) that has occurred since the establishment of the DER in 1996, and to assess the degree of success in the implementation of the DER’s mandate in protecting and developing the ecosystems of the island.