Processed Continuous Resistivity Profile Data Collected in the Potomac River/Chesapeake Bay on Sept. 8, 2006

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set 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?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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 data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How should this data set be cited?

   Bratton, John F. , and Cross, VeeAnn A. , 2010, Processed Continuous Resistivity Profile Data Collected in the Potomac River/Chesapeake Bay on Sept. 8, 2006: Open-File Report 2009-1151, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

   Online Links:

   • <https://pubs.usgs.gov/of/2009/1151/data/resistivity/proc_resis/sept8_proc.zip>
   • <https://pubs.usgs.gov/of/2009/1151/html/catalog.html>

   This is part of the following larger work.

   Cross, VeeAnn A. , Foster, David S. , and Bratton, John F. , 2010, Continuous Resistivity Profiling and Seismic-Reflection Data Collected in 2006 from the Potomac River Estuary, Virginia and Maryland: Open-File Report 2009-1151, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

   Online Links:

   • <https://pubs.usgs.gov/of/2009/1151/>

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -76.856267

   East_Bounding_Coordinate: -76.362700

   North_Bounding_Coordinate: 38.004733

   South_Bounding_Coordinate: 38.231150

3. What does it look like?

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

   Calendar_Date: 08-Sep-2006

   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?

      This is a point data set.

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

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
      

      Vertical_Coordinate_System_Definition:

      Depth_System_Definition:

      Depth_Datum_Name: Local surface

      Depth_Resolution: 0.1

      Depth_Distance_Units: meters

      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates

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)
   • John F. Bratton
   • VeeAnn A. Cross

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
   Woods Hole Coastal and Marine Science Center
   Woods Hole, MA 02543-1598
   

   (508) 548-8700 x2254 (voice)
   (508) 457-2310 (FAX)
   jbratton@usgs.gov
   

Why was the data set created?

To provide the processed continuous resistivity profile (CRP) data collected on this date by the AGI SuperSting system.

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 100-m streamer with an 11 electrode array with electrodes spaced 10 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. 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 which was not working on Julian Day 249. Lowrance indicates the speed of sound used by the system is 4800 feet/second. On the first day of data collection (Julian Day 249, Sept. 6, 2006) the Lowrance transducer was side-mounted mid-ship on the port side of the boat. The remainder of the cruise the transducer was side-mounted mid-ship of the starboard side of the boat. 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: 2006 (process 1 of 10)

   Once the navigation and raw data were assessed to be okay, the actual processing of the data could start. The resistivity data were merged with the navigation data and linearized using AGI's Marine Log Manager software. (Note that the Marine Log Manager version is different than the software version of the AGISSAdmin software of which it is a part - although shipped together, the software is developed separately). The version of Marine Log Manager used was AGI SSAdmin MLM v 1.3.4. The GPS offset was set to 7.9 meters to account for the difference between the navigation antenna and the resistivity cable tow point. The lines processed on this day are L20F1, L21f1, L22F1, L23F1, L24F1, L25F1, L25F2, L26F1. These line names are what the * refers to in the source used 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:

   • *.gps
   • *.stg

   Data sources produced in this process:

   • *_lin.stg
   • *_lin.dep

   Date: 2006 (process 2 of 10)

   The DEP file was checked for anomalous bathymetry values, or duplicated distance along values, and those lines in the file were deleted.

   Date: 2006 (process 3 of 10)

   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, another system was acquiring data at the same time as the resistivity system. I took the data from that system which included conductivity and temperature measured values of the near surface water and reformatted these data text files that could be loaded into ArcMap as XY Event themes. The reformatting was accomplished with a locally written python script called r_nav.py.

   Data sources used in this process:

   • R720060908083041.RAW
   • R720060908095700.RAW

   Data sources produced in this process:

   • R720060908083041.txt
   • R720060908095700.txt

   Date: 2006 (process 4 of 10)

   These text files were then loaded into ArcMap 9.0 using Tools - Add XY data and setting the projection to Geographic, NAD83. Once the event layers were loaded into ArcMap they were converted to shapefiles using the Data Export option. The individual shapefiles were then merged into a single shapefile representing the Julian Day using ET GeoWizards version 9.

   Data sources used in this process:

   • R720060908083041.txt
   • R720060908095700.txt

   Data sources produced in this process:

   • jd251_pnts.shp

   Date: 2006 (process 5 of 10)

   I then used the resistivity calculator in VACExtras v. 1.95 to convert the temperature and salinity values to resistivity values with the units of ohm-m. The result of the calculation is to add an attribute to the shapefile called "resval". In the event that either the temperature or salinity value is not available, a resval of -9999 is used as the calculated value.

   Data sources used in this process:

   • jd251_pnts.shp

   Data sources produced in this process:

   • jd251_pnts.shp

   Date: 2006 (process 6 of 10)

   I then used the ArcToolbox 9.0 Analysis tools - Proximity - Near tool with the following parameters: input feature - the points containing the calculated water resistivity values; near features - the resistivity tracklines from this particular Julian day; search radius - 40 meters. Running this tool added the fields NEAR_FID and NEAR_DIST to the input point shapefile containing the water resistivity values (jd251_pnts.shp). I chose a 40 meter radius because I wanted to exclude far away values so as not to skew results. The instrument collecting the water conductivity information does not track right on top of the CPR navigation, so comparing the two datasets indicated a 40 meter search radius was appropriate.

   Data sources used in this process:

   • jd251_pnts.shp
   • resnavlns_jd251.shp

   Data sources produced in this process:

   • jd251_pnts.shp

   Date: 2006 (process 7 of 10)

   I then created a text field called "resline" within the point shapefile using the attribute table option - Add field. I then joined the point shapefile to the polyline shapefile using the NEAR_FID attribute in the point shapefile and the FID attribute from the polyline shapefile. I selected all records within the joined table where NEAR_FID <> -1. the -1 is what is put for a point that doesn't fall near a line within the search radius (in the Near tool). I then copied over the line name attribute value from the polyline shapefile to the resline attribute within the point shapefile.

   Data sources used in this process:

   • jd251_pnts.shp
   • resnavlns_jd251.shp

   Date: 2006 (process 8 of 10)

   By selecting all the records for a given CRP line I can do the statistics to calculate the mean of the calculated water resistivity values. First I use the properties of the shapefile to define a definition query that will exclude all resistivity values that equal -9999 since this is essentially a NODATA value. Once this is done, the mean value is then used as the water resistivity value within the DEP file for that particular CRP line. This value is added to the appropriate location within the DEP file, and this file is then saved as *_lin_wres.dep where the * refers to the original line name. (* on this day refers to L20F1, L21f1, L22F1, L23F1, L24F1, L25F1, L25F2, L26F1).

   Data sources used in this process:

   • *_lin.dep

   Data sources produced in this process:

   • *_lin_wres.dep

   Date: 2006 (process 9 of 10)

   EarthImager version 1.9.9 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 element 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. 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 two JPEG image generated with each process - a long version and a short version. The JPEG files produced uses a color scale for the resistivity that is based on the data extent from that particular file. 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 L1F1_lin.stg and L1F1_lin_wres.dep the resulting series of output files are: L1F1_lin1_trial1.ini; L1F1_lin_AllInvRes.llt; L1F1_lin_AllInvRes.xyz; L1F1_lin_trial1_InvResLong.jpg; L1F1_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. In addition, the STG and DEP used as input to the processing software are written to the results folder.

   Data sources used in this process:

   • *_lin.stg
   • *_lin_wres.dep

   Data sources produced in this process:

   • *.ini
   • *.llt
   • *.xyz
   • *.jpg

   Date: 2009 (process 10 of 10)

   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_100m_potomac.m, while the local Matlab script used to export the JPEG image was exportfig.m.

   Data sources used in this process:

   • *.xyz
   • *_lin_wres.dep

   Data sources produced in this process:

   • matlabimages/*.jpg

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

   Advanced Geosciences, Inc., 2005, Instruction Manual for EarthImager 2D, version 1.9.0, Resistivity and IP inversion software.

   Online Links:

   • <http://www.agiusa.com/>

   Advanced Geosciences, Inc., 2003, Instruction Manual for the Marine Log Manager Module of the Administrator for SuperSting Software, Release 1.3.7.

   Online Links:

   • <http://www.agiusa.com/>

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 primary navigation system used was a Lowrance 480M with an LGC-2000 Global Positioning System (GPS) antenna. The antenna was located 7.9 meters forward of the anchor point for the resistivity streamer, and approximately 3 meters forward of the fathometer transducer. These offsets were not entered into the GPS system. Additionally, because of navigation and fathometers issues, periodically the ship's navigation system was used to supplement these data. The ship had a Differential GPS (DGPS) system with the antenna placed in the same location as the Lowrance antenna. The fathometer was located (hull-mounted) roughly directly below the antenna, so no horizontal offset. Because of the mixture of systems, the accuracy is on the order of 20 meters.

3. How accurate are the heights or depths?

   On this day the bathymetric values were collected by the Lowrance fathometer. This fathometer was mounted mid-ship on the starboard side of the boat. The Lowrance manufacturer indicates the speed of sound used by the system to convert to depths is 4800 feet/second. All values are assumed to be accurate to within 1 meter.

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

   All usable data collected on this day was processed. The processed files are included in this dataset.

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

   All the data files were checked and handled in the same manner.

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)
   John F. Bratton
   U.S. Geological Survey
   Woods Hole Coastal and Marine Science Center
   Woods Hole, MA 02543-1598
   

   (508) 548-8700 x2254 (voice)
   (508) 457-2310 (FAX)
   jbratton@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?
   • Availability in digital form:

     Data format:	The WinZip file contains all the processed CRP data from Sept. 8, 2006 as well as the associated metadata files. in format WinZip (version 9.0) Size: 21.4 MB
     Network links:	<https://pubs.usgs.gov/of/2009/1151/data/resistivity/proc_resis/sept8_proc.zip> <https://pubs.usgs.gov/of/2009/1151/html/catalog.html>
     Media you can order:	DVD-ROM (Density 4.75 GBytes) (format UDF)

   • Cost to order the data: None.

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

   The user must have software capable of uncompressing the WinZip file.

Who wrote the metadata?

Dates:

Last modified: 21-Jun-2009

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:

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