Bathymetric ArcRaster Grid of Apalachicola Bay and St. George Sound, Florida (25m)

These data were collected under a cooperative mapping program between the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration Office for Coastal Management (NOAA\OCM), and the Apalachicola National Estuarine Research Reserve (NERR). The primary objectives of this program were to collect marine geophysical data to develop a suite of seafloor maps to better define the extent of oyster habitats, the overall seafloor geology of the bay and provide updated information for management of this resource. In addition to their value for management of the bay's oyster resources, the maps also provide a geologic framework for scientific research and the public.

High-resolution bathymetry, backscatter intensity, and seismic profile data were collected over 230 square kilometers of the floor of the bay. The study focused on Apalachicola Bay and Western St. George Sound portions of the estuary mostly in depths > 2.0 meters.

Original contact information:

Contact Name: Brian Andrews

Contact Org: U.S. Geological Survey

Title: Geographer

Phone: 508-548-8700 x2348

Email: bandrews@usgs.gov

The purpose of this dataset is to produce a bathymetric grid of the area within the survey boundary in St. George Sound and Apalachicola Bay.

The purpose of these data is to represent the swath bathymetry in a courser grid cell resolution but cover the gaps between survey lines. In shallow areas less than 2m deep the digitized seafloor from the ASV seismic data was used to provide single beam bathymetry.

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These data are a bathymetric grid of Apalachicola Bay and St. George Sound generated from swath sounding gridded at 5m. Refer to processing steps under data quality section for detailed methods.

NOAA manages much of the data to users of digital geographic data. NOAA is in no way condoning or endorsing the application of this data for any given purpose.It is the sole responsibility of the user to determine whether or not the data is suitable for the intended purpose. It is also the obligation of the user to apply the data in an appropriate and conscientious manner.NOAA provides no warranty,nor accepts any liability occurring from any incomplete,incorrect, or misleading data, or from any incorrect,incomplete, or misleading use of the data. Much of the data is based on and maintained with ARC/GIS software developed by the Environmental Systems Research Institute (ESRI).In addition, much of the information presented uses conventions and terms popularized by ARC/GIS and its user community. NOAA in no way represents the interests of ESRI,nor acts as agents for them. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Data can be downloaded via the World Wide Web (WWW);

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Data are not intended for navigational use.

These data should not be used at resolutions for which it is not intended.

Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 9.2.2.1350

DGPS is assumed to be accurate within 1-2 meters. Standard GPS is assumed accurate within 5-10 meters. 99% of the positional data is DGPS. Unless noted, all GPS/DGPS data is referenced to WGS84 (NAD83). The configuration of the fathometer is as follows: the transducer on the RAFAEL was mounted on a pole at the vessel's bow. Offset between the bow mount and GPS antenna is measured. On ASV IRIS, the subbottom profiler used to measure water depth was mounted directly below the GPS antenna. No measurements were taken of ship's pitch, yaw, heave, or change in draft due to water and fuel usage. Motion of the fathometer is not measured. Horizontal accuracy of the fathometer is assumed to be within +/- 3 meters.

Ship motion was recorded with a TSS DMS 2-05 Attitude Sensor, mounted on a head above the interferometric Submetrix 2000 Series transducers. Navigation was recorded using Real Time Kinematic Differential Global Positioning System (RTK-DGPS). The interferometric sonar is an angle-measuring system; depth accuracy decreases with increasing horizontal range. The combined angular accuracy of the Submetrix 2000 Series and the TSS DMS 2-05 attitude sensor is documented as 0.1 degrees. Assuming a constant angular accuracy, and using the International Hydrographic Standard (IHO) of a required 0.3 meter accuracy in < 30 meter water depth, all data collected within the survey fall within the IHO accuracy standards. However, vertical accuracy is also directly affected by the accuracy of both the navigation system and tidal measurements. RTK DGPS vertical accuracy is assumed to be 0.2 meters. Tidal elevations were derived from RTK -DGPS heights sent from a survey-specific base station located on St. George Island.

The base station occupied a temporary monument. The x & y positions were calculated for that location using a 3 day average of 12 hour data sets using the Online Positioning User Service (OPUS, National Geodetic Survey) solution. Tidal elevations were calculated from NOAA Tidal Station #8728690 using the same OPUS solution and then applied to the corrected elevations for the base station at St. George Island. Antenna heights were referenced to Mean Lower Low Water (MLLW) for easier comparison of NOAA nautical charts.

Soundings were gridded in OMG SwathEd software using the entire swath width across track to achieve maximum coverage at the scale of the entire Apalachicola Bay/St. George Sound survey area. Although the soundings were manually edited, small data spikes may exist at outer edges of some swaths.

Pockmark features that appear in the dredge channel of the intracoastal waterway fairways are artifacts of the processing methods used to generate a continuous surface from swath bathymetry collected on lines spaced 100m apart.

These data have not been quantitatively compared to previous hydrographic data, although they generally agree with qualitative comparison of published NOAA charts.