Processed Continuous Resistivity Profiles Collected in the Neuse River, May 4, 2005

Metadata:

• Identification_Information
• Data_Quality_Information
• Distribution_Information
• Metadata_Reference_Information

Identification_Information:

Citation:

Citation_Information:

Originator: John F. Bratton

Originator: VeeAnn A. Cross

Publication_Date: 2005

Title:

Processed Continuous Resistivity Profiles Collected in the Neuse River, May 4, 2005

Online_Linkage:

<http://pubs.usgs.gov/of/2005/1306/data/2005/proc_resis/may4_proc.zip>

Larger_Work_Citation:

Citation_Information:

Originator: VeeAnn A. Cross

Originator: John F. Bratton

Originator: Emile Bergeron

Originator: Jeff K. Meunier

Originator: John Crusius

Originator: Dirk Koopmans

Publication_Date: 2005

Title:

Continuous Resistivity Profiling Data from the Upper Neuse River Estuary, North Carolina, 2004-2005

Series_Information:

Series_Name: Open-File Report

Issue_Identification: 2005-1306

Publication_Information:

Publication_Place: Woods Hole Science Center, Woods Hole, MA

Publisher: U.S. Geological Survey, Coastal and Marine Geology Program

Online_Linkage: <http://pubs.usgs.gov/of/2005/1306>

Description:

Abstract:

The Neuse River Estuary in North Carolina is a broad, V-shaped water body located on the southwestern end of Pamlico Sound. This estuary suffers from severe eutrophication for which several water quality models have recently been developed to aid in the management of nutrient loading to the estuary. In an effort to help constrain model estimates of the fraction of nutrients delivered by direct ground-water discharge, continuous resistivity profile (CRP) measurements were made during the spring of 2004 and 2005. CRP is used to measure electrical resistivity of sediments, a property that is sensitive to difference in salinity of submarine ground water. The 2004 and 2005 surveys used floating resistivity streamers of 100 m and 50 m respectively. The depth penetration of the streamers is approximately 20% of the streamer length which translates to approximately 20-25 m with the 100 m streamer and 12-14 m with the 50 m streamer. These data were processed using AGI's EarthImager 2D software. CRP data enables the mapping of the extent and depth of the fresher ground water within the estuary.

Purpose:

To provide resistivity data as collected by the AGI SuperSting system and processed with EarthImager software.

Time_Period_of_Content:

Time_Period_Information:

Single_Date/Time:

Calendar_Date: 20050504

Currentness_Reference: ground condition

Status:

Progress: Complete

Maintenance_and_Update_Frequency: None planned

Spatial_Domain:

Bounding_Coordinates:

West_Bounding_Coordinate: -77.020917

East_Bounding_Coordinate: -76.812000

North_Bounding_Coordinate: 35.102200

South_Bounding_Coordinate: 34.936783

Keywords:

Theme:

Theme_Keyword_Thesaurus: General

Theme_Keyword: CMGP

Theme_Keyword: coastal

Theme_Keyword: Coastal and Marine Geology Program

Theme_Keyword: Continuous Resistivity Profiling

Theme_Keyword: CRP

Theme_Keyword: ground-water

Theme_Keyword: marine resistivity

Theme_Keyword: submarine ground-water

Theme_Keyword: U.S. Geological Survey

Theme_Keyword: USGS

Theme_Keyword: Woods Hole Science Center

Theme_Keyword: Open-File Report

Theme_Keyword: OF 2005-1306

Place:

Place_Keyword_Thesaurus: General

Place_Keyword: Neuse River

Place_Keyword: North America

Place_Keyword: North Carolina

Place_Keyword: Pamlico Sound

Place_Keyword: United States

Access_Constraints: none.

Use_Constraints:

The U.S. Geological Survey must be referenced as the originator of the dataset in any future products or research derived from these data.

Point_of_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: John F. Bratton

Contact_Organization: U.S. Geological Survey

Contact_Address:

Address_Type: mailing and physical address

Address: 384 Woods Hole Rd.

City: Woods Hole

State_or_Province: MA

Postal_Code: 02543-1598

Contact_Voice_Telephone: (508) 548-8700 x2254

Contact_Facsimile_Telephone: (508) 457-2310

Native_Data_Set_Environment:

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 9.0.0.535

Data_Quality_Information:

Lineage:

Source_Information:

Source_Contribution:

These data were acquired with an AGI SuperSting Marine system that is described at the website: www.agiusa.com/marinesystem.shtml. The particular system used for this acquisition was an 11 electrode array with electrodes spaced 5 meters apart. The potential electrodes are made of graphite, with the remaining electrodes stainless steel. A dipole-dipole configuration was used for the data collection in which two fixed current electrodes are assigned with the measurement of voltage potentials between electrode pairs in the remaining electrodes. Each line of data acquisition records several files. The two files necessary for processing are the *.stg and *.gps file. The STG file contains the resistivity data, while the GPS file contains the navigation information.

Process_Step:

Process_Description:

The data were transferred from the logging computer via AGISSAdmin software. The data files available for this day are L2F1.*, L3F1.*, L4F1.*, and L5F1.*.

Process_Step:

Process_Description:

When the data were acquired, a scaling factor of 5 was used. However, because the initialization file already defined the electrodes as being 5 meters apart, this had the affect of indicating the electrodes were 25 meters apart. Therefore, Marine Log Manager was used to rescale the STG file, by using a scale factor of 0.2, to return the electrodes to the appropriate spacing.

Source_Used_Citation_Abbreviation: L1F1.stg

Source_Produced_Citation_Abbreviation: L1F1_rescaled.stg

Process_Step:

Process_Description:

The data were merged with navigation and linearized using AGI's Marine Log Manager software.

Process_Step:

Process_Description:

In most cases, only that portion of the linearized file that had positive distance along values was exported to the new STG file. In the case of L3F1, L4F1, and L5F1, the entire file was selected for export. These lines were run perpendicular to shore, starting at the shore. Exporting the whole line was necessary to get the nearshore values. Because of the length of one of the files, as well as incorporated turns, L2F1 is broken up and exported to 4 new STG files, and accompanying DEP files. The DEP file contains the distance along line and bathymetry values.

Process_Step:

Process_Description:

The DEP files were checked for anomalous bathymetry values, and those lines within the DEP file were deleted. For L3F1, L4F1, and L5F1, the file that was exported in its entirety (which included negative distances along line), had a depth value of 0.1 assigned to the first point in the DEP file. In addition, the first distance along point in the DEP file was modified to be the same as the first point in the XYZ output of a test processing. This was done to ensure that the entire inversion had a water column constraint.

Source_Used_Citation_Abbreviation:

L2F1_part1proc.dep, L2F1_part2proc.dep, L2F1_part3proc.dep, L2F1_part4proc.dep

Source_Produced_Citation_Abbreviation:

L2F1_part1proc_mod.dep, L2F1_part2proc_mod.dep, L2F1_part3proc_mod.dep, L2F1_part4proc_mod.dep

Process_Step:

Process_Description:

EarthImager software does not require that a default resistivity value for the water column be supplied in the DEP file. If one is not supplied, then it calculates a value based on the first electrode pair. For this reason, the data were processed without a value supplied (in the folder def_wres), and with a value supplied (in the folder wres). The average water resistivity value was calculated based on YSI temperature and salinity data readings recorded during the survey. The average temperature and average salinity values over the STG survey area were plugged into a JavaScript calculator to determine conductivity. The website (<http://ioc.unesco.org/oceanteacher/resourcekit/M3/Converters/SeaWaterEquationOfState/Sea%20Water%20Equation%20of%20State%20Calculator.htm>) was used for this purpose. The inverse of the conductivity value was then used as the average resistivity value.

Process_Step:

Process_Description:

EarthImager version 1.9.0 was used to process the data files. The *.ini file accompanying the results contains the parameters used during the processing. These parameters include: minimum voltage: 0.02 minimum abs(V/I): 2E-5 max repeat error: 3% min apparent res: 0.03 max apparent res: 1000 max reciprocal error: 5% remove spikes smooth model inversion finite difference method Cholesky decomposition Dirichlet boundary condition thickness incremental factor: 1.1 depth factor: 1.1 number of iterations: 8 stop criteria: max RMS 3%, error reduction 5%, L2Norm CRP processing using a 65% overlap

Process_Step:

Process_Description:

The results of the processing are a JPEG image of the resistivity profile, and an XYZ file containing the distance along, depth, apparent resistivity (ohm-m). The first pass at processing (Trial1) used the default water resistivity value, while the second pass (Trial2) used the average water resistivity value in the DEP file. The JPEG file produced uses a color scale that is based on the data from this particular file.

Process_Step:

Process_Description:

The XYZ output file was then loaded into Matlab, along with the depth information, to create a new JPEG image with the same color scale for all the data files. In this manner, the JPEG images can be compared directly. Care was taken to try to get the vertical and horizontal scales uniform as well, although this was not always possible due to Matlab limitations. These images reside in the Matlab images folder. Part of the filename (defwres vs wres), as well as information within the image indicates if the default water resistivity (defwres) data file was used or an average water resistivity (wres) value.

Distribution_Information:

Resource_Description: Downloadable Data

Distribution_Liability:

These data were prepared by an agency of the United States Government. Neither the United States government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Although all data published in this report have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data, software, or related materials.

Metadata_Reference_Information:

Metadata_Date: 20051101

Metadata_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: VeeAnn A. Cross

Contact_Organization: U.S. Geological Survey

Contact_Position: Marine Geologist

Contact_Address:

Address_Type: mailing and physical address

Address: 384 Woods Hole Rd.

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

Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata

Metadata_Standard_Version: FGDC-STD-001-1998

Metadata_Time_Convention: local time

Metadata_Extensions:

Online_Linkage: <http://www.esri.com/metadata/esriprof80.html>

Profile_Name: ESRI Metadata Profile