This data set contains an interpolated grid data based on a TIN created from point data which represent individual soundings from hydrographic surveys collected in Coastal bays in 2000 and 2003. Depths are adjusted for tidal stage and referenced to NAVD88 datum
This data set was created in response to the need for more complete and up-to-date bathymetric data in the coastal bays, the Resources Assessment Services, Maryland Geological Survey conducted hydrographic surveys in the Maryland's coastal bays using standard digital bathymetric methods. The objectives for this survey were to: 1) provide consistent, systematic bathymetric coverage of the study areas; and 2) develop a baseline bathymetric data set that may be expanded and/or used for comparison with surveys conducted in the future. This grid was created to provide an easy to use and understand representation of the bathymetric point data and to conform to the polygon representing the 2003 condition of Assateague Island.
This data set is based on the final adjusted soundings from hydrographic surveys collected within the Maryland coastal bays. The surveys were conducted in Assawoman Bay and St. Martin River between May 1and June 28, 2000, in Chincoteague Bay between May 31 and October 1, 2003, and in Isle of Wight Bay between October 2 and October 8, 2003.
These data are not for navigational purposes. The Maryland Department of Natural Resources assumes no liability for uses of these data. Acknowledgment of the Maryland Geological Survey, and the Fisheries Service, both part of the Maryland Department of Natural Resources, and NOAA shall be made in products derived from these data.
7206 National Seashore Lane
Funding for bathymetric data collected in the Northern Coastal Bays of Maryland was provided by the Fisheries Service, Maryland Department of Natural Resources. Financial assistance for the bathymetric survey of Chincoteague Bay was provide by the NOAA Coastal Services Center, NOAA Award No. NA17OC2689.
This grid was interpolated at 10m cell size from a TIN created from bathymetric points collected in 2000 and 2003. The TIN was created with hard break lines at 0 m elevation along bay shorelines from the Maryland and Virginia Coastal bays Shoreline and the Assateague Island National Seashore Coastlines Based on October, 2003 Aerial Photography.
The area covered by the data set includes navigable portions of Assawoman Bay, including Delaware, St. Martin River, Isle of Wight Bay, Sinepuxent Bay, Newport Bay, and the Maryland portion of Chincoteague Bay. This dataset is interpolated from bathymetric soundings and thus includes areas between survey transects.
1) Created bounding polygon. Used Maryland and Virginia Coastal bays Shoreline (MGS_CB_Shoreline19980412) and Assateague Island National Seashore Coastlines Based on October, 2003 Aerial Photography (2003_Assateague_Island). Cut the shoreline in the north and south at the extent of the bathymetric survey. The line was closed at the Ocean City inlet and at the northern and southern extents and the ocean shorelines were removed. Recoded elevation on southern boundary (-2), inlet (-6.5), and northern boundary (-4). This line was converted to a polygon using ArcToolbox. 2) Bay islands were converted to polygons using ArcToolbox. 3) Using the Erase tool in ArcToolbox the bay island were erased from the bay polygon. 4) Created TIN from features (3D Analyst). Using CB_BathyPts2000 as mass points and the height as source depth, MGS_CB_Shoreline19980412 as triangulate: hard line and height source: elevation (0), and the masking polygon without island as a hard clip. cb_bathy_tin_2003 was created. 5) Create raster from TIN (3D Analyst). An analysis mask of the masking polygon was used, with cell size 10 and the extent the same as cb_bathy_tin_2003. Used Convert TIN to Raster command with a cell size of 10, z factor of 1 and the Elevation: attribute. Output cb_bathy_2003.
7206 National Seashore Lane
Hydrographic surveys were conducted using a 17 ft Boston Whaler equipped with a 70 horsepower outboard engine. Track lines followed predetermined NAD83 UTM northing gridlines or easting gridlines, which facilitated navigation of the whaler and allowed survey lines to be easily retraced for quality control and quality assurance (QA/QC) purposes and during future surveys. Track lines were spaced 400 meters apart and extended from shore to shore (generally east-west). Tie-in track lines were run every 1000 meters perpendicular to the shore-to-shore tracks lines. Boundary surveys, following the shoreline, were also conducted to establish boundary (near-shore) conditions. Bathymetric data were collected using an Ashtech Reliance Precision GPS (model SCA-12S; L1 code and carrier) and a Knudsen 320B/P dual frequency echo sounder with sounding frequencies of 200 KHz and 28 KHz. The echo sounder transducer is a KEL771 dual frequency transducer with a 200 KHz beam angle of 4 degrees and a 28 KHz beam angle of 29 degrees. The echo sounder generated acoustic pulses for bottom recognition at a rate of 2 Hz. The pulse width was set to automatically change between 0.2 mS and 0.8 mS depending on the depth of the water. The transmitted acoustic wave reflected off the density gradient separating the water column from the bottom sediment. The returned acoustic wave is received by the transducer, and the time separation between the sent and the returned wave is recorded. This time separation is directly proportional to distance. The recordings were then filtered for points that were outside of the gate window (2 meters) and integrated within the echo sounder to produce an accurate measurement from the transducer to the water/sediment interface. At an average vessel speed of 4 knots, a depth sounding was collected approximately every 1.0 m (3.3 ft) along the survey track-lines. To minimize pitch and roll, the transducer, used for both transmitting the pulse and receiving the echo signal, was mounted off the port side of the whaler, slightly aft of the vessel's center. Because of the size of the boat and safety considerations, surveys were collected during "calm" conditions (waves = 1 ft). The sounding data was stored along with the GPS location and positional latency in a laptop computer. Navigation was provided through a Lowrance GlobalNav 212 GPS interfaced to a Lowrance DGPS beacon receiver. A Starlink MRB-2 DGPS receiver provided DGPS signals to the Ashtech Reliance GPS system. The Ashtech unit was programmed to output location coordinates only if the following criteria were met: 1) position derived from at least six satellites with positions of 15 ° or greater above the horizon; 2) Position dilution of precision (PDOP) less than 5; and 3) DGPS signal less than 30 seconds old. DGPS differential corrections broadcast by the United States Coast Guard provided a real-time horizontal accuracy of 1 to 2 m [3 to 6 feet] using the Cape Henry, Virginia, and Cape Henlopen, Delaware, DGPS sites. The Ashtech GPS, the Lowrance GPS, and the echo sounder were checked against known horizontal and vertical measurements during the survey. The echo sounder was calibrated to obtain speed of sound correction and transducer offset. The HF sounding data from the hydrographic surveys were processed to remove invalid depth data (invalid HF flag), depths less than 0.35 meters, "out of sequence" depths (e.g., fish, water column noise, multiples, etc.), and invalid location coordinates (GPS latency values > 1000 msec). For soundings having the same geographic coordinates, the sounding with the higher latency was removed. Sounding depth values were adjusted to account for the offset of the transducer below the water surface. The offset value was derived from the calibration of the echo sounder. The adjusted sounding depth values were then corrected to account for tide stage and/or wind effects. To determine the actual water level during the time the hydrographic surveys were conducted, water level recorders were installed and operated at several locations within the areas being surveying. Water levels from the water level recorder were interpolated to the exact times depth soundings were taken, and the interpolated water level were subtracted from the adjusted depth soundings, obtaining depths corrected to NAVD88, meters.
7206 National Seashore Lane
Shoreline vectors were digitized from aerial photography taken in multiple years. DELAWARE shoreline was digitized on-screen from the DOQQs (Assawoman Quad) compiled from color infrared photography flown on April 12, 1989, by the National Aerial Photography Program (NAPP). The shoreline was digitized by Darlene Wells using TNTMips software. MARYLAND shoreline was originally extracted from the Maryland Department of Natural Resources wetland delineation maps, which were digitized from digital orthoquarter quads (DOQQs) compiled from color infrared photography flown on April 12, 1989, by the National Aerial Photography Program (NAPP). Metadata for the shorelines may be downloaded from the following website: http://www.mgs.md.gov/coastal/vmap/SLMetadata.html The shoreline was further modified to account for some shoreline changes that occurred between 1989 and 2000/2003. When the boat track lines for the hydrographic surveys collected in 2003 were plotted on top of the shoreline, there were many areas where the boat track crossed over landside of the shoreline, These discrepancies were attributed to changes in shoreline position due to erosion that occurred since 1989 (date of the orthophotoquads). Using AutoCAD and/or ArcMap editor, the shoreline vectors were shifted landward along those areas where the boat track crossed the shoreline. These modifications were done by Darlene Wells, Maryland Geological Survey. Shoreline along bay-side of Assateague Island in northern half of Sinepuxent Bay (from OC inlet to Verrazanno Bridge, and mainland shoreline along Marsh Harbor and Stinky Beach across from OC Inlet) was digitized from Georectified TIFFS of aerial photographs of Assateague Island, taken 3/17/1999. Images were 1 meter resolution. The 1999 TIFFS were obtained from Mark Duffy with the National Park Service, Assateague Island National Seashore. VIRGINIA shoreline: The Virginia portion of Chincoteague Bay shoreline was obtained from VIMS (contact: Sharon Killeen [email@example.com]. The baseline shoreline was developed by digitizing the land-water interface observed on 1994, 1:12,000 color infra-red d digital ortho quarter quadrangles (DOQQ). The rectified aerial photography was provided by the U.S. Geological Survey. Metadata for shorelines may be found at the following website: http://www.vims.edu/ccrm/gis/gisdata.html
Maryland Geological Survey
7206 National Seashore Lane
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.
7206 National Seashore Lane