Processed Continuous Resistivity Profile Collected in the Neuse River, April 19, 2004

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Frequently-anticipated questions:

What does this data set describe?

Title:
Processed Continuous Resistivity Profile Collected in the Neuse River, April 19, 2004
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.
  1. How should this data set be cited?

    Bratton, John F. , and Cross, VeeAnn A. , 2005, Processed Continuous Resistivity Profile Collected in the Neuse River, April 19, 2004:.

    Online Links:

    This is part of the following larger work.

    Cross, VeeAnn A. , Bratton, John F. , Bergeron, Emile, Meunier, Jeff K. , Crusius, John, and Koopmans, Dirk, 2005, Continuous Resistivity Profiling Data from the Upper Neuse River Estuary, North Carolina, 2004-2005: Open-File Report 2005-1306, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -76.729717
    East_Bounding_Coordinate: -76.713317
    North_Bounding_Coordinate: 34.972333
    South_Bounding_Coordinate: 34.966467

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 19-Apr-2004
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

    2. What coordinate system is used to represent geographic features?

  7. How does the data set describe geographic features?

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    John F. Bratton
    U.S. Geological Survey
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700 x2254 (voice)
    (508) 457-2310 (FAX)

Why was the data set created?

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

How was the data set created?

  1. From what previous works were the data drawn?

    (source 1 of 1)
    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 stainless steel electrode array with electrodes spaced 10 meters apart. 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.

  2. How were the data generated, processed, and modified?

    (process 1 of 9)
    The data were transferred from the logging computer via AGISSAdmin software. The data file available for this day is N2.*.

    (process 2 of 9)
    A section of the STG file was removed due to bad time stamps (between records 1913 and 1920). $GPRMC lines within the GPS file that had bad time stamps or were otherwise corrupt were also deleted.

    Person who carried out this activity:

    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov

    Data sources used in this process:
    • N2.stg and N2.gps

    Data sources produced in this process:

    • N2_mod.stg and N2_mod.gps

    (process 3 of 9)
    The data were merged with navigation and linearized using AGI's Marine Log Manager software.

    (process 4 of 9)
    The file was then exported to a new STG file, and accompanying DEP file. The DEP file contains the distance along line and bathymetry values.

    Data sources used in this process:

    • N2_mod.stg

    Data sources produced in this process:

    • N2proc.stg, N2proc.dep

    (process 5 of 9)
    The DEP file was checked for anomalous bathymetry values and those lines in the file were deleted.

    Data sources used in this process:

    • N2proc.dep

    Data sources produced in this process:

    • N2proc_mod.dep

    (process 6 of 9)
    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 conductivity data readings during the survey.

    Data sources used in this process:

    • N2proc_mod.dep

    Data sources produced in this process:

    • N2proc_wres.dep

    (process 7 of 9)
    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 8 of 9)
    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. **Caution: The XYZ output filename does not contain the trial number, so the processing technique is a function of the folder it resides in.

    Data sources produced in this process:

    • N2proc_AllInvRes.xyz, N2proc_trial1_InvResShort.jpg, N2proc_trial2_InvResShort.jpg

    (process 9 of 9)
    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.

    Data sources used in this process:

    • N2proc_AllInvRes.xyz

    Data sources produced in this process:

    • N2proc_defwres.jpg, N2proc_wres.jpg

  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

  5. How consistent are the relationships among the observations, including topology?

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

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.

  1. Who distributes the data set?[Distributor contact information not provided.]

  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    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.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 01-Sep-2005
Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
384 Woods Hole Rd.
Woods Hole, MA 02543-1598

(508) 548-8700 x2251 (voice)
(508) 457-2310 (FAX)
vatnipp@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.8.6 on Tue Sep 13 12:06:45 2005