Earth Observation Based Assessment of Area Changes Related to Hurricane Events – The Dauphin Island DEVELOP Case Study
Raymond White, University of South Alabama (project lead)
Walter Clark, University of South Alabama
Stephanie Heimann, University of South Alabama
Josh Stodghill, Edward Via College of Osteopathic Medicine
Hunter Winstanley, University of South Alabama
Barrier islands are elongated sand-based coastal landforms that are separated by open water from the main land. These coastal features are often at high risk to shoreline erosion. Barrier islands are dynamic landforms and driven by long shore currents causing sand to constantly shift in terms of location and volumetric quantity. Hurricanes and other severe coastal storms can greatly accelerate the erosion and shoreline change of a barrier island. Dauphin Island is a prominent barrier island located in the Gulf of Mexico off of the coast of Alabama. The island protects Alabama’s main land coastline during hurricane events by effectively acting as a barricade to storm impacts. It is home to an Audubon Bird Sanctuary and supports Mobile County’s economy with its tourism industry. The island has experienced constant erosion and rebuilding over the past few decades.
This study briefly discussed herein builds upon a previous DEVELOP project completed in the fall of 2009. The previous study utilized Landsat and ASTER imagery to create 21 land cover maps of Dauphin Island between the years of 1983 and 2009. Results from the previous project indicated that Dauphin Island’s land and vegetation area has been in a gradual state of decline over the last two-and-one-half decades. This project added to these findings by increasing the observed study period to 1972-2010 and by incorporating multidate Lidar elevation imagery to measure island change at a finer spatial scale. The main objectives of this study were to 1) Measure land area change of the island from 1972 to 2010, with special emphasis on the area surrounding the bird sanctuary and Dauphin Island’s fishing pier, which recently has been unusable since the merging of Sand Island to Dauphin Island. 2) Measure vegetation area change on the island from 1972 to 2010. 3) Investigate the impact of hurricanes on the island’s land and vegetation area change. 4) Provide the results of this study to the Dauphin Island Park and Beach Board (DIP&BB).
The following remote sensing data have been used in this study: Multispectral Scanner (MSS) aboard the Landsat 1-3 satellites, the Thematic Mapper (TM) aboard the Landsat 4-5 satellites, the ASTER instrument aboard the Terra satellite, and the Advanced Land Imager (ALI) aboard the EO-1 satellite. Landsat TM and MSS, and ALI data were obtained from the USGS Earth Resources Observation and Science (EROS) Center. ASTER imagery was acquired through NASA’s Warehouse Inventory Search Tool (WIST). These data were utilized to observe the land and vegetation area change.
To assess land area change, unsupervised classifications of island land cover were performed using ERDAS Imagine. To assess shoreline erosion in the areas of interest, the bird sanctuary and fishing pier, Experimental Advanced Airborne Research Lidar (EAARL) and Airborne Topographic Mapper (ATM) LIDAR images were analyzed in ESRI’s ArcGIS. The imagery was provided by the USGS. Normalized Difference Vegetation Index (NDVI) products were computed for each observed date to assess the change in vegetated area. In select years containing major hurricane events, land and vegetated area was assessed both before and after the tropical cyclone activity.
This study found that both land area and vegetated area have gradually declined for the past three-and- one- half decades. The results also help illustrate the relationship between area change and known hurricane events. We can clearly recognize this relationship within the areas of special interest. We found that most of the erosion that occurred around the bird sanctuary’s shoreline happened after 2004. This change is apparently due to impacts from Hurricanes Ivan (2004), Hurricane Dennis (2005) and Hurricane Katrina (2005). Another major point to note is the significant movement of Sand Island, a smaller island south of Dauphin Island, to the west after Hurricane Katrina in 2005. Not only do these results yield similar erosion trends to previous studies of Dauphin Island, they also demonstrate the utility of remotely sensed data to assist in the spacio-temporal synoptic studies of barrier islands.
The Dauphin Island Park and Beach Board (DIP&BB) maintains the Dauphin Island campground, the Dauphin Island fishing pier, Fort Gains, the public beach, the Audubon Bird Sanctuary, as well as several small parks. This project assists the DIP&BB by improving land management strategies and restoration monitoring through enhanced decision-making support. It also expands the user community of NASA Earth science data products by linking Earth observations, students, and local communities.
Dr. Bernard Eichold II – Mobile County Health Department, Health Officer
Dr. Jim Connors – University of South Alabama, Professor
Dr. George Crozier – Dauphin Island Sea Lab
Karen Jordan – University of South Alabama, Instructor
Joe Spruce – Computer Science Corporation, Stennis Space Center
Dr. Kenton Ross – Science Systems & Applications, Inc., NOAA National Environmental Satellite, Data, and Information Service (NESDIS)
For more information about the DEVELOP National Program and other student projects, please visit http://develop.larc.nasa.gov.by