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Satellite Imagery and Visualization of the Exumas, Great Bahama Bank - From Analog for Carbonate Sand Reservoirs

Ellis, James 1; Harris, P. Mitch 2
1 Ellis GeoSpatial, Walnut Creek, CA.
2 Chevron Energy Technology Company, San Ramon, CA.

We hope to promote interest in the Exuma Islands and surrounding carbonate sand bodies of Great Bahama Bank by making readily available a set of processed satellite images, offshore/onshore digital elevation model (DEM), and interpretation maps organized into a GIS, along with examples of how this data can be visualized and used for geological interpretation. To increase accessibility, improve learning, and promote spatially accurate feedback, the stack of images, color-coded DEM, and geologic maps were exported from GIS into easier and more flexible viewing programs such as GoogleEarth and GeoPDF.

The clearest satellite images of the Exumas 1984-2005 were acquired and processed. Image processing was undertaken to maximize apparent water penetration and delineate submerged features. The primary images are 28.5-m Landsat TM, 15-m ASTER, and 0.6 m Quickbird. The processed scenes were georeferenced to a base image in GIS, creating a stack of co-registered images that can be effectively used for change detection. Masks were created for water and land to enable integration of different images and maps. A digital bathymetric map was created from water depths estimated from the spectral characteristics of a Landsat TM image. This offshore depth map was integrated with an onshore DEM derived from NASA Space Shuttle elevation data (SRTM) for the islands.

Different water depths were selected, color-coded, and visualized in the GIS to illustrate the distribution and morphometry of flood tidal deltas, ebb deltas, and sand flats and island-attached sands. Various satellite images and maps were draped on the DEM within the GIS to provide perspective views and improve understanding of spatial relationships for the flood tidal delta lobes, tidal channels, occurrence of tidal channels and beaches through time (1967-2005), and Pleistocene/Holocene landforms.

Shroud Cay was selected to evaluate the effectiveness of spectral classification for mapping sand flats and other island features, and the high resolution (2.4 m pixel) multispectral Quickbird satellite imagery was utilized. The spectral classification map revealed a consistent pattern of depositional environments related to subtle elevation differences. Emergent features (Pleistocene and Holocene island ridges) can also be mapped in detail using satellite imagery, maps, and the corrected SRTM onshore DEM. The Landsat TM, ASTER, and Quickbird data were processed to accentuate onshore variations in vegetation.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009