Trimmed Processed Continuous Resistivity Point Data from Cape Cod National Seashore, Feb. 28, 2006

The data were transferred from the logging computer via AGISSAdmin software. The data files available for this day are l1*, l2*, l3*, l4*, l5*, l6*, l8*, l9*, l10*, l11*, l12*, l13*, l14*, and l15*. ***Of note, on lines 1 and 2, during acquisition the distance between the cable connection point and the first electrode was entered as 10 meters instead of -10 meters. This can be adjusted when reading the data into Marine Log Manager for linearization.

$GPRMC lines with the GPS file that had bad time stamps or were otherwise corrupt were deleted.

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). In some instances, only a portion of the line was exported for processing. In particular, turns are removed before processing. (AGISSAdmin version 1.33.182) ***Note. When reading in l1 and l2, the GPS offset needs to be set to 10 to account for an incorrect acquisition parameter indicating the distance between the cable connection point and the first electrode.

In most cases, nearshore values were very important. For that reason, the whole linearized STG file was selected for export. This applied in the following lines: l1, l2, l4, l5, l6, l9, l11, l12 and l14. The way the Marine Log Manager software works, the first value exported is where at least one of the electrodes has a known navigational fix. But the rest of the streamer electrodes at this position have a negative distance along line. When this export option is chosen, no DEP file is output. In order to create a DEP file, a second export file is needed. This one selects only positive electrode positions for export.

The linearized STG file with negative values is processed with EarthImager version 2.01 in order to determine the most negative position (available from the final XYZ output file). Once this is done, I can create a navigation fix for that negative distance along line. Based on the trackline created from the GPS data, I run an ArcView 3.3 avenue script (extendline.ave) which uses a straight-line tow path assumption of the first 2 points to create an additional point at the negative distance input. Essentially I extend the line at the start of the line.

With this new point I can modify the DEP file generated by the positive only electrode position export. I add in the negative distance along, as well as all the supplemental information, including the header information describing the latitude and longitude position of the start of line. So now I have a linearized STG file, as well as the accompanying DEP file for those files with negative distances along line.

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

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. On this survey, an instrument was used periodically to measure water conductivity. This value was converted to appropriate resistivity units and added to the DEP file. A value of 0.2 was used in all the files.

EarthImager version 2.0.1 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 6%; L2Norm; CRP processing using a 60% overlap.

The results of the processing are JPEG images of the resistivity profile (a short and extended version); an XYZ file containing the distance along, depth, apparent resistivity (ohm-m); an LLT file which contains longitude, latitude, depth, and resistivity value; a UTM file which contains easting, northing, depth, resistivity value. The JPEG files produced uses a color scale that is based on the data from that particular file. This particular version of EarthImager defaults to using the latitude and longitude values along the x-axis to mark electrode positions. Another pair of long and short JPEG images was exported which use the distance along values for the electrode positions on the X-axis.

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 "matlabimages" folder.

The XYZ output file was also loaded into Matlab with the DEP file so that those resistivity values in the water column could be removed. The extrapolated value at the sediment water interface was exported, as well as all the values in the original XYZ file below the DEP line. These new XYZ files are in the folder "trimxyz".

An avenue script (createatdistance.ave) was used in ArcView 3.3 to read the trimmed XYZ files, and based on the distance along value, extract the geographic X and Y position based on the polyline trackline. The result is a point shapefile containing each line of information in the XYZ file.

Each individual trimmed XYZ shapefile was merged into a single point shapefile.

Edits to the metadata were made to fix any errors that MP v 2.9.30 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. The source citation information is inferred from other information in the metadata and was not part of the original metadata file. Source time period of content was inferred from the time period of the dataset. Needed to add link to data in the distribution section. Other minor edits were probably performed (title, publisher, publication place, etc.). 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.