Processed continuous resistivity profile (CRP) data below the sediment water interface from Manhasset Bay on Long Island, New York collected from May 15 to May 17, 2008 (MANHASSETALL_RESBELOWSED.SHP)

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. Two different streamers were used for data collection - not simultaneously. One streamer was a 50-m streamer with an 11 electrode array with electrodes spaced 5 meters apart. The other streamer was a 15-m streamer with an 11 electrode array with electrodes spaced 1.5 meters apart. In both cases, 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, while the 15 meter streamer can reach about 3.75 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. 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.

A MATLAB script (justbelowsed.m) was run on the processed CRP files to generate files with just the resistivity values that fall below the sediment water interface, and an extrapolated value at the sediment water interface. Two files from the processed resistivity data are needed for this script: the XYZ output from the EarthImager processing which has distance along line (meters), depth of resistivity reading (meters), and resistivity value (ohm-m); and the DEP file that contains distance along line (meters) and water depth values (meters). Because some lines are short and don't require a "roll-along" processing technique, the XYZ information is contained in a file with the DAT extension. The MATLAB script combines the two data files (processed resistivity and depth files) such that the output is only the resistivity values that fall at or below the sediment water interface. This script was written by the USGS (VeeAnn A. Cross) in Woods Hole, MA. In order to have a resistivity value at the sediment water interface, the software usually has to interpolate resistivity values. The version of MATLAB used for these data was MATLAB 7.5.0.342 (R2007b). An example of the script usage in MATLAB is: justbelowsed('L10F1_lin_AllInvRes.xyz','L10F1_lin_wres.dep') The output is: L10F1_lin_AllInvRes_jbsed.xyz This resulting XYZ file has 5 columns of information: distance along line (meters); depth below water surface (meters); depth below sediment/water interface (meters); resistivity value (ohm-m); log(10) resistivity value. This process step and all subsequent process steps were performed by the same person - VeeAnn A. Cross.

Using ArcView 3.3 and the avenue script resist_jbsed_nan.ave (script written by VeeAnn Cross at the USGS in Woods Hole, MA) these XYZ files are converted to shapefiles. This script requires that the navigation for the resistivity line be a polyline shapefile and present in the view. The script prompts the user for the polyline shapefile in the view that they want to use, then prompts the user to browse for the xyz resistivity file. The script then creates a new point shapefile, with a point along the polyline at each value of X specified in the xyz file. The y and z values, as well as longitude and latitude are added to the point shapefile. This requires that the view be projected, as the distance in the xyz file is in meters. This script will work on a single line polyline shapefile (ie the nav for a survey line is alone in a shapefile) or on a selected line within a polyline shapefile. The result is a point shapefile with 11 columns of information. The Id attribute is automatically generated upon creation of a shapefile, the line attribute is the line name as indicated within the polyline shapefile that the program prompts the user for, dist is the distance along line attribute carried over from the MATLAB file, the attributes of location information (latitude, longitude, utmx, utmy) are calculated by the tool, the attributes depth, dep_b_sed, resvalue, and reslogval are carried over from the MATLAB file. The Entity and Attribute section further describes these attributes and their units. This particular script had to handle NaN values generated by MATLAB where the CRP data only contained information in the water column because the water was too deep for the resistivity streamer to penetrate the sediment water interface.

Then using the geoprocessing extension that comes with ArcView 3.3, the individual point shapefiles for each line of collection were merged into a single point shapefile for each day of collection.

Using ArcMap 9.2 - ArcToolbox - Data Management Tools - Projections and Transformations - Define Projection define the projection of the point shapefiles as Geographic, WGS84.

Combine the individual days of the resbelowsed files into a single shapefile. Within ArcMap 9.2, using ArcToolbox - Data Management Tools - General - Merge input files: day4all_resbelowsed, day5all_resbelowsed, day6all_resbelowsed; output: manhassetall_resbelowsed.shp. Left field mapping at the defaults.

Edits to the metadata were made to fix any errors that MP v 2.9.36 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). Attempted to modify http to https where appropriate. Reordered the links in the identification section to have a landing page link as the first link. Updated the link to the field activity. Moved the minimal source information provided to make it the first process step. The distribution format name was modified in an attempt to be more consistent with other metadata files of the same data format. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent.

Added keywords section with USGS persistent identifier as theme keyword.