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Data Series 968

Land-Cover Types, Shoreline Positions, and Sand Extents Derived From Landsat Satellite Imagery, Assateague Island to Metompkin Island, Maryland and Virginia, 1984 to 2014

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Nineteen Landsat 5 Thematic Mapper (TM) and four Landsat 8 Operational Land Imager (OLI) image acquisition dates were selected for analysis (table 1). Landsat standard data products, processed using the Level 1 Product Generation System (LPGS), were downloaded from the USGS Earth Resources Observation and Science (EROS) Center data archives. Image acquisition dates correspond to 5-year intervals beginning in 1984 supplemented with additional images from intervening years for which high-resolution aerial photography was also analyzed (Guy, 2015). If available, spring (April preferred) and late fall (November preferred) image acquisition dates were used for each analysis year. Monthly water levels measured at the long-term tide gage at Ocean City Inlet, Maryland show the smallest average seasonal deviation from mean sea level during these months (Zervas, 2009); in addition, analysis of spring and fall scenes provides information on seasonal variation in vegetation response. The spring and fall images were supplemented with additional scenes corresponding to aerial photography acquisition dates (Guy, 2015). A gap in imagery dates from August 31, 2011, to April 14, 2013, corresponding to the decommissioning of the Landsat 5 TM mission and the first data available from the recently launched Landsat 8 OLI mission. Data from the Landsat 7 Enhanced Thematic Mapper Plus (ETM+) satellite are available for this time period; however, data gaps exist over the study area in all Landsat 7 images acquired since May 2003 due to the failure of the scan line corrector (U.S. Geological Survey, 2012), limiting the use of these data in quantitative land-change analyses.

Compared to the high-resolution aerial photography (1-foot to 2-m pixel resolution) analyzed by Guy (2015), the location of features such as digitized shoreline or sand-line positions derived from satellite-based Landsat imagery (30-m pixel resolution for reflective bands used in land-cover classification) may be less precise; however, Landsat imagery offers several advantages over aerial photography datasets. Each Landsat scene covers an area approximately 175 km by 183 km, minimizing the number of images necessary to encompass large study areas and making Landsat data ideal for regional- or landscape-scale analyses. Landsat images are acquired every 16 days, enabling trends analyses at varying scales (for example, seasonal, annual, and decadal), whereas aerial photography missions are flown at irregular intervals. Because Landsat images include multiple infrared bands in addition to the visible red, blue, and green spectrum, various classification algorithms can be used to differentiate between land-cover or habitat types, and shoreline positions and land-cover boundaries can easily be extracted from the classed imagery; these features are commonly hand-digitized from aerial photographs.

Table 1. Landsat 5 and Landsat 8 image acquisition dates used in this study.
Date Scene Sensor Comment
11/24/1984 LT50140331984329PAC13
Landsat 5
04/28/1989 LT50140331989118AAA04
Landsat 5 Guy (2015) imagery acquired 04/12/1989
10/05/1989 LT50140331989278XXX01
Landsat 5
04/26/1994 LT50140331994116XXX02
Landsat 5 Guy (2015) imagery acquired 03/20/1994
11/04/1994 LT50140331994308XXX02
Landsat 5
05/10/1999 LT50140331999130AAA02
Landsat 5
11/18/1999 LT50140331999322AAA02
Landsat 5
04/05/2004 LT50140332004096GNC02
Landsat 5
11/15/2004 LT50140332004320GNC01
Landsat 5 Guy (2015) imagery acquired 11/05/2004
06/11/2005 LT50140332005162GNC01
Landsat 5 Guy (2015) imagery acquired 06/08/2005 and 06/15/2005
11/02/2005 LT50140332005306GNC01
Landsat 5
05/16/2007 LT50140332007136GNC01
Landsat 5
06/17/2007 LT50140332007168GNC01
Landsat 5 Guy (2015) imagery acquired 06/22/2007
04/16/2008 LT50140332008107GNC01
Landsat 5 Guy (2015) imagery acquired 05/25/2008
11/26/2008 LT50140332008331EDC00
Landsat 5
03/18/2009 LT50140332009077GNC01
Landsat 5 Guy (2015) imagery acquired 06/26/2009 and 08/07/2009
04/25/2011 LT50140332011115GNC01
Landsat 5
07/14/2011 LT50140332011195EDC00
Landsat 5 Guy (2015) imagery acquired 05/30/2011 and 06/02/2011
08/31/2011 LT50140332011243GNC01
Landsat 5 Hurricane Irene passes offshore of Maryland-Virginia coastline 08/28/2011
Hurricane Sandy passes offshore of Maryland-Virginia coastline 10/29/2012
04/14/2013 LC80140332013104LGN01
Landsat 8 Guy (2015) imagery acquired 03/15/2013
09/05/2013 LC80140332013248LGN00
Landsat 8 Guy (2015 imagery acquired 09/05/2013
04/01/2014 LC80140332014091LGN00
Landsat 8
10/26/2014 LC80140332014299LGN00
Landsat 8 October 2014 Nor-Easter impacts Maryland-Virginia coastline 10/22/2014

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