Attribute_Accuracy:
Attribute_Accuracy_Report:
The positional accuracy of the sample locations is determined by the accuracy of the raw position data recorded by the GPS and antenna during data collection. DGPS coordinates were obtained using post-processing software packages (National Geodetic Survey On-Line Positioning User Service (OPUS), and Waypoint Product Group GrafNav, version 8.6. Water level readings were corrected to NAVD88 and compared to a nearby National Oceanic and Atmospheric Administration (NOAA) water level station. The total station only provides elevation measurements and does not produce positional data; therefore, no positional data were reported for those samples. The random surface samples (R) were collected using an angle and distance from the bead plot. The angles and distances were reported in the notes section and were approximate locations and should not be considered precise positions. If positions are desired the reader is requested to contact the authors for more information.
Logical_Consistency_Report:
Position and elevation data at each sample site were recorded with Ashtech DGPS receivers and GNSS antennas. Additionally, DGPS data were recorded concurrently throughout the survey at two NGS benchmarks using a similar instrument combination. Due to a local base station malfunction during survey 17CCT05, the nearest Continually Operating Reference Station (CORS) ALDI (PID=DL3486), located on the east end of Dauphin Island, Alabama, was utilized for post-processing. The final sample locations, including elevation, are the post-processed DGPS coordinates processed to the nearest base station; baseline distances for all sample sites were approximately less than 9 kilometers (km), sample elevations from survey 17CCT05 have a baseline upwards of 30 km. Total station samples do not include occupation times, collection times, positional data, or horizontal errors. The random surface samples (R) collected with the total station do not include verified elevations and should be used with caution.
Completeness_Report:
This dataset includes the locations of 1,236 elevation points collected from shorelines, water level logger wells, elevation benchmarks, random surface samples, and net sedimentation tile study sites that were collected from Grand Bay Mississippi from October 2016 to October 2017 (USGS FANs 16CCT07, 17CCT01, 17CCT02, 17CCT03, 17CCT04, and 17CCT05). This dataset is considered complete for the information presented, as described in the abstract section. Users are advised to read the rest of the metadata record carefully for additional details. In some cases, sensor malfunctions or significant errors caused data loss for some sites or FANs. During 17CCT01 a total station was used in some cases and there is no occupation time, collection time, easting, northing, latitude, longitude, verified elevations, or horizontal error.
Positional_Accuracy:
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
All static GPS base station sessions were processed through the OPUS maintained by NGS. The OPUS base station solutions were entered into a spreadsheet to compute a final, time-weighted positional coordinate (latitude, longitude, and ellipsoid height) for each base station. Base station positional error was calculated as the absolute value of the final position minus the session position value. The maximum horizontal error of the base station coordinates used for post-processing the sample locations were 0.00081 s latitude and 0.00063 s longitude for B166, and 0.00054 s latitude and 0.00036 s longitude for 189A. The time-weighted positions for both base stations were compared against the derived coordinates from the first survey (16CCT07). All subsequent survey occupations (17CCT01-17CCT05 produced time weighted averages that were within 3 standard deviations of the first occupation and therefore, for consistency, the 16CCT07 coordinates were used in all post-processing.
Vertical_Positional_Accuracy:
Vertical_Positional_Accuracy_Report:
All static GPS base station sessions were processed through OPUS. The OPUS base station solutions were entered into a spreadsheet to compute a final, time-weighted positional coordinate (latitude, longitude, and ellipsoid height) for each base station. Base station positional error for each GPS session was calculated as the absolute value of the final position minus the session position value. For all base station occupations, the maximum standard deviations of the base station ellipsoid heights were 0.021 m for B166, 0.012 m for 189A and the maximum vertical errors for the base stations were 0.028 m and 0.029 m, respectively. The time-weighted positions for both base stations were compared against the derived coordinates from the first survey (16CCT07), which individually has a standard deviation of 0.007 m (B166) and 0.011 m (189A). All subsequent survey occupations (17CCT01-17CCT04) produced time weighted averages that were within 3 standard deviations of the first occupation and therefore, for consistency, the 16CCT07 coordinates were used in post-processing. Data acquired during survey 17CCT05 was post-processed using data downloaded from the NGS website for CORS station ALDI (
https://www.ngs.noaa.gov/CORS/Sites/aldi.html). The station is located approximately 30 km away from the survey location, causing significant errors due to extended baseline distance. Total station samples are referenced to a benchmark at each of the study sites.
Lineage:
Process_Step:
Process_Description:
GPS base stations were erected on two NGS benchmarks located within the Grand Bay National Estuarine Research Reserve (GBNERR), B166 (PID DO5987) and 189A (PID DO5977). Ashtech Z-Xtreme DGPS receivers recorded the 12-channel full-carrier-phase positioning signals (L1/L2) from satellites via a Thales choke-ring antenna at the base stations. A similar instrument combination (Ashtech Z-Xtreme receiver and Ashtech GNSS antenna) was used for the rover GPS systems. The base receiver and the rover receiver record their positions concurrently at 1 s recording intervals throughout the survey. A stop-and-go rapid-static survey technique was used, with a static occupation. For FAN 17CCT01, total station measurements were collected instead of using DGPS . The total station measures the sloping distance of an object to the instrument. A temporary USGS-installed benchmark was surveyed before collecting marsh data to get a static reference point. This reference point was then used to determine elevation for the rest of the samples.
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Chelsea A. Stalk
Contact_Position: Researcher III
Contact_Address:
Address_Type: mailing and physical
Address: 600 4th Street South
City: St.Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: cstalk@contractor.usgs.gov
Process_Step:
Process_Description:
The final, time weighted coordinates from 16CCT07 for the GPS base stations were imported into GrafNav, versions 8.6 (Novatel Waypoint Product Group) and the data from the rover GPS were post-processed to the concurrent GPS session data from the nearest base station; baseline distances for all sample sites were less than 9 km and dependent upon site location. The GPS data were acquired in the NAD83 geocentric datum. Due to a local base station malfunction, data from survey 17CCT05 were post-processed using concurrent CORS data from the neared station, ALDI (baseline distance 30 km).
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Chelsea A. Stalk
Contact_Position: Researcher III
Contact_Address:
Address_Type: mailing and physical
Address: 600 4th Street South
City: St.Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: cstalk@contractor.usgs.gov
Process_Step:
Process_Description:
The exported file from GrafNav was converted using the NOAA VDatum software conversion tool version 3.6 (
http://vdatum.noaa.gov/). The sample locations were transformed from the GPS acquisition datum of NAD83 horizontal and vertical, to NAD83, Universal Transverse Mercator (UTM) Zone 16 North (16N) horizontal reference frame and the NAVD88 orthometric elevation, using the NGS geoid model 2012A (GEOID 12A).
Contact_Information:
Contact_Person_Primary:
Contact_Person: Chelsea A. Stalk
Contact_Position: Researcher III
Contact_Address:
Address_Type: mailing and physical
Address: 600 4th Street South
City: St.Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8000
Contact_Electronic_Mail_Address: cstalk@contractor.usgs.gov
Process_Step:
Process_Description:
Elevation data from all trips were compiled into tabular digital datasets (Comma separated values [CSV] format). Data with errors in collection or processing were flagged and noted as such in the published data file.
Process_Date: 2018
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Kathryn Smith
Contact_Position: Researcher III
Contact_Address:
Address_Type: mailing and physical
Address: 600 4th Street South
City: St.Petersburg
State_or_Province: FL
Postal_Code: 33701
Country: USA
Contact_Voice_Telephone: 727-502-8073
Contact_Electronic_Mail_Address: kelsmith@usgs.gov
Process_Step:
Process_Description:
Added keywords section with USGS persistent identifier as theme keyword.
Process_Date: 20201013
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: VeeAnn A. Cross
Contact_Position: Marine Geologist
Contact_Address:
Address_Type: Mailing and Physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2251
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: vatnipp@usgs.gov
