These data represent a series of mean high water shorelines collected on Assateague Island National Seashore (ASIS), appended into one shapefile. The shoreline surveys are collected using an Trimble ProXR GPS mounted on an ATV, and range in dates from December of 1994 to the most recent updated survey of December, 2006. Depending on the time of year and intended purpose, some surveys contain ocean, inlet and bay shorelines, while some surveys only contain ocean shorelines. Additionally, some surveys contain all of ASIS, while some contain only shorelines in the Maryland district.
The dynamic nature of coastal barriers such as Assateague Island is a defining characteristic, influencing nearly every aspect of their ecology. Fundamentally disturbance driven systems, barrier islands and their endemic biota are continually shaped by physical forces on a time scale vastly accelerated in comparison to mainland systems. Because of the rapid pace and scope of change, long term monitoring is crucial towards understanding natural barrier island conditions as well as anthropogenic influences. This appended shoreline dataset was created to aid in data use and distribution. Shorelines are also stored and available as individual line shapefiles, which are available through contacting ASIS (asis_gis@nps.gov).
These shorelines are also stored as individual line shapefiles, which contain more detailed positional information and specific time and date attributes. These data can be available through contacting ASIS (asis_gis@nps.gov).
ground condition
None
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ASIS
Attributes are accurate as recorded by the Trimble ProXR GPS and TSC1 handheld data-logger.
Most of the data in this file were checked at 1:2000 for topological inconsistency in the line, and all inconsistent topology was amended. Some gaps are present and have not been amended. Multiple data points were deleted.
This dataset includes surveys that cover the following extents: the entire ocean shoreline of Assateague Island; the ocean shoreline within the Maryland portion of Assateague Island; the ocean shoreline of the northern most 10 kilometers of Assateague Island; the northern 10 kilometers of the bayside shoreline of Assateague Island; and the southern most 6-8 km of bay shoreline, in the Virginia portion of Assateague Island.
Horizontal precision was reported as sub-meter. All positions were post-processed and points where 68% precisions exceeded 1 meter were not exported. Positions with a PDOP of 6.0 or greater were not exported. 60 of 14645 positions were filtered out because PDOP was over 6.0. Positions were collected at known reference points during each survey. These positions were compared with the published coordinates of the reference points and did not vary more than 1 meter horizontal distance from the published location.
see report
Surveys along the ocean shoreline were accomplished by driving a 4 wheel ATV at a relatively constant speed along the identified high tide line. For the purposes of this monitoring program, the actual ocean "shoreline" was defined as the average position of the most recent high tide, evidenced by the obvious wet/dry sand line or deposited wrack. The GPS receiver was configured to record positions at a very short interval (1 position every 1 seconds) for the best representation of the shoreline position. This survey (Ocean and Bayside) was conducted shortly after the daily high tide at the Lewes Delaware Water Level Station (8557380). (20061116: 4.58 ft at 00530; 20061117: 4.40 at 0542; 20061120: 5.13 at 0806; 20061121: 5.28 at 0836) Mean normal high tide at Lewes Delaware is 4.08 feet. Logical consistency was checked in ArcMap v 9.1. The antenna was mounted on the left side of the ATV above the front left wheel. The Maryland bay shoreline was collected by walking along the water line from the inlet to km4.25 after high tide on 20061120 and from km 4.25 to km 8.5 on 20061121. The Virginia Toms Cove bay shoreline was collected by walking along the water line from the old Coast Guard Station to the beginning of marsh near the Toms Cove Visitors Center. All data was real-time differentially corrected using beacon signals from Annapolis, MD or Driver, VA. Data was also differentially post-processed using data from the VIMS (Wachapreague, VA) and Horn Point, MD CORS stations.
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After data collection, each survey is manipulated in ArcGIS so it can be appended into this master database of ASIS GPS shorelines (asis_shorelines.shp). Line features are split between shoreline types (Bay, Inlet, Mudflat, Ocean, etc.) so that no features contain more than on type of shoreline. The features with the same shoreline type are then merged together, resulting in one unique feature for each type of shoreline, per survey. These features now represent multiple GPS events and dates, so the GPS specific fields are deleted from the survey attribute table, and the following fields are added and filled in: Type (shoreline type), Year, Month, Day, Season (all of which represent the final date of shoreline collection for the associated feature), and Comments. The survey is then simply appended to the master dataset using the 'Append' tool in ArcToolbox.
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Internal feature number.
ESRI
Feature geometry.
ESRI
Type of water body providing prevailing processes on the stretch of shoreline.
ASIS Resource Management
Shoreline borders a bay.
ASIS Resource Management
Shoreline borders an ocean.
ASIS Resource Management
Shoreline borders an inlet.
ASIS Resource Management
Shoreline borders a mudflat.
ASIS Resource Management
Year of data collection
ASIS Resource Management
Month of the year during which data collection occurred
ASIS Resource Management
January
Calendar
February
Calendar
March
Calendar
April
Calendar
May
Calendar
June
Calendar
July
Calendar
August
Calendar
September
Calendar
October
Calendar
November
Calendar
December
Calendar
One of the numbered 24-hour periods into which a week, month, or year is divided.
The American Heritage Dictionary
Season of data collection.
ASIS Resource Management
Months of December, January, and February.
ASIS Resource Management
Months of March, April, and May
ASIS Resource Management
Months of June, July, and August
ASIS Resource Management
Months of September, October, and November
ASIS Resource Management
comments recorded during data collection and/or data processing
ASIS Resource Management
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The National Park Service shall not be held liable for improper or incorrect use of the data described and/or contained herein. These data and related graphics (i.e. "GIF or JPG" format files) are not legal documents and are not intended to be used as such. The information contained in these data is dynamic and may change over time. The data are not better than the original sources from which they are derived. It is the responsibility of the data user to use the data appropriately and consistent within the limitations of geospatial data in general and these data in particular. The related graphics are intended to aid the data user in acquiring relevant data; it is not appropriate to use the related graphics as data. The National Park Service gives no warranty, expressed or implied, as to the accuracy, reliability, or completeness of these data. It is strongly recommended that these data are directly acquired from an NPS server and not indirectly through other sources which may have changed the data in some way. Although these data have been processed successfully on computer systems at the National Park Service, no warranty expressed or implied is made regarding the utility of the data on other systems for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data.
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