Processed continuous resistivity profiling data collected in Greenwich Bay, Rhode Island, on May 14, 2009, on U.S. Geological Survey Field Activity 2009-021-FA

After navigation and data assessment, the actual processing of the resisitivity data could start. The resistivity data were merged with the navigation data and linearized using AGI's Marine Log Manager (MLM) software. This used the *.gps and *.stg files or the raw data. (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 1.3.4.217. The GPS offset was set to 16.5 since the offset between the navigation antenna and the first electrode of the resistivity streamer was not accounted for in an acquisition offset. Lateral offset (2.5 meters) is not accounted for. Due to navigation gaps, Line 18 was split into three parts. The line names are what the * refers to in the source used and source produced citation. This process step and all subsequent process steps were performed by the same person - VeeAnn A. Cross.

Each DEP file was checked for anomalous bathymetry values, or duplicated distance along line values, and those lines in the DEP 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 additional instrument was deployed to measure water temperature and salinity. This instrument was a YSI 30 which measured temperature and salinity values at various locations during the survey. See the YSI metadata available from the larger work citation for details on the processing of the YSI data. The values did not vary a great deal, so an average water resistivity value of 0.296 ohm-m was added to all the DEP files for processing.

EarthImager version 2.2.8 was then used to process the data files. The process settings were set to CRP - Saltwater. The *.ini file accompanying the results contains the parameters used during 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. Two JPEG images are generated with each process - 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 use 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, *.xyz and *.utm. 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 is also a file created with a UTM extension which has the same format as the LLT file except it contains the coordinates in UTM eastings and northings in the zone appropriate for the survey line (software determined). In this case that would be UTM, Zone 19. This file was not checked for accuracy as software versions in the past gave erroneous UTM fixes. An example of the file naming convention is as follows: For input files of L5F1_lin.stg and L5F1_lin_wres.dep the resulting series of output files are: L5F1_lin1_trial1.ini; L5F1_lin_AllInvRes.llt; L5F1_lin_AllInvRes.xyz; L5F1_lin_trial1_InvResLong.jpg; L5F1_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. Four files were extremely short and therefore no "roll-along" processing was required. These files were L8F1, L10F1, L18F1_part3 and L19F1. In these cases, the JPEG image and the XYZ data have 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 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. Although temperature was recorded during acquisition, the JPEG plot does not show the temperature profile in the short data files.

Added keywords section with USGS persistent identifier as theme keyword.