Processed Continuous Resistivity Profiles Collected in the Neuse River, May 5, 2005

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Frequently-anticipated questions:

What does this data set describe?

Title:
Processed Continuous Resistivity Profiles Collected in the Neuse River, May 5, 2005
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 Profiles Collected in the Neuse River, May 5, 2005:.

    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: -77.033752
    East_Bounding_Coordinate: -76.936250
    North_Bounding_Coordinate: 35.124350
    South_Bounding_Coordinate: 35.005450

  3. What does it look like?

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

    Calendar_Date: 05-May-2005
    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 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.

  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 files available for this day are L6F1.*, L6F2.*, L7F1.*, L8F1, and L9F1.*.

    (process 2 of 9)
    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.

    Data sources used in this process:

    • L1F1.stg

    Data sources produced in this process:

    • L1F1_rescaled.stg

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

    (process 4 of 9)
    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 L9F1, all of the file was selected for export. This line was run perpendicular to shore, starting at the shore. Exporting the whole line was necessary to get the nearshore values. Because of the length of three of the files, as well as incorporated turns, these files had to be broken up into parts and exported to new STG files, and accompanying DEP files. The DEP file contains the distance along line and bathymetry values. L6F1 was broken into L6F1_part1proc.*, L6F1_part2proc.* L6F2 was broken into L6F2_part1proc.*, L6F2_part2proc.*, L6F3_part3proc.* L7F1 was broken into LF1_part1proc.*, L7F1_part2proc.*

    (process 5 of 9)
    The DEP files were checked for anomalous bathymetry values, and those lines within the DEP file were deleted. For L9F1, the file that was exported in its entirety (which included negative distances along), a depth value of 0.1 was assigned to the first point in the DEP file. In addition, the first distance along point in the DEP 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.

    Data sources used in this process:

    • L6F1_part1proc.dep, L6F1_part2proc.dep, L6F2_part1proc.dep, L6F2_part2proc.dep, L6F2_part3proc.dep, L7F1_part1proc.dep, L7F1_part2proc.dep, L8F1_proc.dep, L9F1_proc.dep

    Data sources produced in this process:

    • L6F1_part1proc_mod.dep, L6F1_part2proc_mod.dep, L6F2_part1proc_mod.dep, L6F2_part2proc_mod.dep, L6F2_part3proc_mod.dep, L7F1_part1proc_mod.dep, L7F1_part2proc_mod.dep, L8F1_procmod.dep, L9F1_procmod.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 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 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.

    (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.

  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-Nov-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 Nov 01 14:39:42 2005