Modified Processed Continous Resistivity Profile Data Collected in the Corsica River Estuary, Maryland on May 15 and May 16 on USGS Cruise 07005

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Frequently-anticipated questions:

What does this data set describe?

Title:
Modified Processed Continous Resistivity Profile Data Collected in the Corsica River Estuary, Maryland on May 15 and May 16 on USGS Cruise 07005
Abstract:
Submarine groundwater discharge (SGD) into Maryland's Corsica River Estuary was investigated as part of a larger study to determine the importance of nutrient delivery to Chesapeake Bay via this pathway. Resource managers are concerned about nutrients that are entering the estuary via submarine groundwater discharge from this primarily agricultural watershed that may be contributing to eutrophication, harmful algal blooms, and fish kills. An interdisciplinary U.S. Geological Survey (USGS) science team conducted field operations in the estuary in April and May 2007. Techniques used included continuous resistivity profiling (CRP), piezometer sampling, seepage meter measurements, and collection of a radon tracer time series. Better understanding of the style, locations, and rates of groundwater discharge could lead to improved models and mitigation strategies for estuarine nutrient over-enrichment in the Corsica River Estuary, and other similar settings. More information on the field work can be accessed from the Woods Hole Coastal and Marine Science Center Field Activity webpage: <http://quashnet.er.usgs.gov/data/2007/07005/>
  1. How should this data set be cited?

    Cross, VeeAnn A. , 2010, Modified Processed Continous Resistivity Profile Data Collected in the Corsica River Estuary, Maryland on May 15 and May 16 on USGS Cruise 07005: Open-File Report 2010-1094, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Cross, VeeAnn A. , Bratton, John F. , Worley, Charles R. , Crusius, John, and Kroeger, Kevin D. , 2010, Continuous resistivity profiling data from the Corsica River Estuary, Maryland: Open-File Report 2010-1094, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -76.149864
    East_Bounding_Coordinate: -76.119082
    North_Bounding_Coordinate: 39.086800
    South_Bounding_Coordinate: 39.078067

  3. What does it look like?

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

    Beginning_Date: 15-May-2007
    Ending_Date: 16-May-2007
    Currentness_Reference:
    ground condition of the resistivity data. The associated bathymetry data used in conjunction with the resistivity data is from various dates and has been modified for use with the CRP data.

  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?

    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA 02543-1598

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

Why was the data set created?

This dataset provides modified processed continuous resistivity profile (CRP) data collected on May 15 and 16, 2007 in the Corsica River Estuary by the AGI SuperSting system. These data originally did not have bathymetry data associated wtih the GPS navigation files. These files only represent the data files wtihout bathymetry in the navigation and does not include all files from those two days of collection. Bathymetry is an important part of CRP data processing as the bathymetry allows the use of a water resistivity value. Additional work was done to extract bathymetry information from existing grids to recreate the GPS files so that the data could be processed with that information. This release also acts as a data archive.

How was the data set created?

  1. From what previous works were the data drawn?

    (source 1 of 1)
    Source_Contribution:
    The continuous resistivity profile (CRP) system used on this cruise was an AGI SuperSting marine system described at the website: www.agiusa.com/marinesystem.shtml. The particular system used for this acquisition was a 50-m streamer with an 11 electrode array with electrodes spaced 5 meters apart. The source electrodes are graphite, while the receiver electrodes are 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 potential between electrode pairs in the remaining electrodes. The maximum depth below the water surface the streamer can reach is approximately ¼ the streamer length. So for the 50-m streamer, maximum depth is about 12.5 meters. Each line of data acquisition records several files. The two files necessary for processing are the *.stg and the *.gps file. The STG file contains the resistivity data, while the GPS file contains the navigation information. The navigation system used in concert with the CRP system is a Lowrance LMS-480M with an LGC-2000 GPS antenna and a 200 kHz fathometer transducer. The transducer also contains a temperature sensor. Lowrance indicates the speed of sound used by the system is 4800 feet/second. Both the temperature and depth information are recorded in the logged GPS file. There are instances where no depth or temperature information is recorded due to an equipment problem. The CRP system images the subsurface electrical properties of an estuarine, riverine or lacustrine environment. Resistivity differences can be attributed to subsurface geology (conductive vs less conductive layers) and hydrogeologic conditions with fresh water exhibiting high resistivity and saline conditions showing low resistivity.

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

    Date: Jan-2010 (process 1 of 4)
    Once the navigation was repaired to capture depth values, the processing of the data could start. To see the processes that were used to repair the missing bathymetry, see the metadata for "fixbathyraw" available at: <https://pubs.usgs.gov/of/2010/1094/html/catalog.html> under the CRP data section. The resistivity data were merged with the "fixbathy" navigation data and linearized using AGI's Marine Log Manager software version 1.3.4.217. The GPS offset was set to 0 since there is no offset between the navigation antenna and the resistivity cable tow point. Processed lines in this dataset include L12F1, L24F1, L24F2, L25F1, L26F1, L27F1 (parts 1 and 2), and L28F1. These line names are what the * refers to in the source use and source produced citations. This process step and all subsequent process steps were performed by the same person - VeeAnn A. Cross.

    Person who carried out this activity:

    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA 02543-1598

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

    Data sources used in this process:
    • *_fixbathy.gps
    • *.stg

    Data sources produced in this process:

    • *_linfixbathy.stg
    • *_linfixbathy.dep

    Date: Jan-2010 (process 2 of 4)
    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 cruise instruments deployed in the field at the same time as the CRP data collection recorded water salinity and temperature. Averaging surface water and bottom water values yielded a salinity of 5.8 ppt and a temperature of 22 degrees Celsius. Based on these values, the calculated water resistivity value is 1.0345 ohm-m. This calculation was done using the website <http://www2.sese.uwa.edu.au/~hollings/pilot/denscalc.html>. This value was verified using the tool in VACExtras v. 2.1 - Resistivity - Calc resistivity. This value was added to the appropriate place in the DEP files so that a known water resistivity value would be used in the calculations.

    Data sources used in this process:

    • *.dep

    Data sources produced in this process:

    • *_wres.dep

    Date: Jan-2010 (process 3 of 4)
    EarthImager version 2.2.8 build 562 was then 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 negative resistivity, smooth model inversion; finite element method; Cholesky decomposition; Dirichlet boundary condition; thickness incremental factor: 1.1; depth factor: 1.1; max number of CG iterations: 100; stop criteria: number of iterations 8; max RMS 3%; error reduction 5%; L2Norm; CRP processing using a 65% overlap. These INI files can be loaded in EarthImager to help maintain consistent processing parameters for other datasets. When the files are processed, numerous files are generated. Because of the "roll-along" nature of the processing, each line takes several iterations of processing which are then combined into a single output. The output consists of numerous files including JPEG images and text files representing the XYZ position of each resistivity value. There are four JPEG image generated with each process when possible - a long version with the x-axis labeled with distance along line (in meters) and a corresponding short version of the same information. Additionally, there is a long version with the x-axis labeled with latitudes and longitudes and the corresponding short version with the same information. The JPEG files produced uses a color scale for the resistivity that is based on the data extent from that particular file. When temperature is available, the JPEG images also include a plot of temperature along the line. In addition to the JPEG images, there are text files with the extensions of *.llt, and *.xyz. Each of these is a text file. The LLT file has four columns of information: longitude in decimal degrees, latitude in decimal degrees, depth in meters, and resistivity value in ohm-m. The XYZ file has three columns of information: distance along line in meters, depth in meters, and resistivity value in ohm-m. There was also a file created with a UTM extension, but the eastings and northing values were invalid so was omitted from this collection (software bug). An example of the file naming convention is as follows: For input files of L3F1_lin.stg and L3F1_lin_wres.dep the resulting series of output files are: L3F1_lin1_trial1.ini; L3F1_lin_AllInvRes.llt; L3F1_lin_AllInvRes.xyz; L3F1_lin_trial1_InvResLong.jpg; L3F1_lin_trial1_InvResShort.jpg. You can process an individual line as many times as you want and the software places the results in incrementing folder names starting with trial1. These data represent trial2, which is the processing with the water resistivity value. In addition, the DEP (if used in processing) is written to the results folder. In the case of the extremely short files, no "roll-along" processing was required. In these cases, the JPEG images and the XYZ data had to be saved manually. First, just the inverted resistivity line is displayed using View - Inverted Resistivity Section. Then the image can be saved using File - Save Image and only the linear labled image was saved. And finally, the XYZ data had to be saved manually using File - Save Data in XYZ format. The XYZ output file extension is DAT instead of XYZ.

    Data sources used in this process:

    • *_linfixbathy.stg
    • *_linfixbathy_wres.dep

    Data sources produced in this process:

    • *.ini
    • *.llt
    • *.xyz or *.dat
    • *.jpg

    Date: Jan-2010 (process 4 of 4)
    The XYZ output file was then loaded into Matlab version 7.5.0.342 (R2007b), along with the depth information from the DEP file, 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 "matlabimages" folder. These JPEG images include a black line within the resistivity profile which represents the sediment water interface based on the depth values from the DEP file. The local Matlab script used to load the data was cp_corsica.m, while the local Matlab script used to export the JPEG image was exportfig.m.

    Data sources used in this process:

    • *.xyz or *.dat
    • *_linfixbathy_wres.dep

    Data sources produced in this process:

    • matlabimages/*.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?

    The navigation system used was a Lowrance 480M with an LGC-2000 Global Positioning System (GPS) antenna. The antenna was located at the anchor point for the resistivity streamer, which is also directly above the fathometer transducer mount point. The GPS system is published to be accurate to within 10 meters.

  3. How accurate are the heights or depths?

    The vertical accuracy of these files is a function of several factors. First of all is the accuracy of the original bathymetry dataset from which the depth values were extracted. And second is the offset applied to this bathymetry value to essentially add in the tidal component. Specific tide values were not acquired, but rather the grid bathymetry values were compared to actual valid fathometer reading to estimate and offset. These factors combine to detract from the vertical accuracy, making it probably more than 1 meter.

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

    This data reprocessing represents the lines missing the majority of fathometer data from the original GPS files. These files include: L12F1, L24F1, L24F2, L25F1, L26F1, L27F1_par1, L27F1_part2, and L28F1. L12F2 and L13F1 were omitted from this list because the lines were so short (L13F1 was only 62 meters long).

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

    Each line of data was handled in the same manner to capture valid bathymetry data.

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 public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset.

  1. Who distributes the data set? (Distributor 1 of 1)

    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA 02543-1598

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

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

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    Neither the U.S. government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

  4. How can I download or order the data?

  5. What hardware or software do I need in order to use the data set?

    The data are provided in a WinZip compressed file. The user must have software capable of uncompressing the archive. In addition, portions of the processed data are available in a format compatible with AGI Geosciences EarthImager software. The user must have software capable of reading the AGI format in order to process these data. The data are also available in an XYZ ASCII format.

Who wrote the metadata?

Dates:
Last modified: 13-Dec-2010
Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
Woods Hole Coastal and Marine Science Center
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 2.9.6 on Tue Dec 14 10:55:15 2010