Raw and modified raw continuous resistivity profiling data collected in the Indian River Bay, Delaware, on April 13, 2010, on U.S. Geological Survey Field Activity 2010-006-FA

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 1/4 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 antenna and fathometer transducer were mounted on the starboard side of the boat. The streamer tow point was on the port side aft. The layback offset between the navigation antenna and the first electrode was 17.6 meters on April 13 and 14. On April 15 the antenna and transducer were moved 1.6 m aft changing the layback offset to 16 m. This layback offset is accounted for by the acquisition system. The approximately 2 m lateral offset is not accounted for. The Lowrance 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.

The acquisition controlling command file (*.cmd) was set up indicating an electrode spacing of 1 meter. At the time of data acquisition, a scaling factor of 5 was used to reflect the actual 5 meter electrode spacing of the streamer. The data were transferred from the logging computer using AGISSAdmin software version 1.3.4.198. These files were then emailed from the field to the USGS office in Woods Hole in a single zip file. The data files included in this release are the *.crs, *.cmd, *.gps, and *.stg. The two files essential for processing are the GPS and STG files. The GPS file contains the navigation, and in the case of the Lowrance system also includes water depth and water temperature. The STG file contains the resistivity measurements from each of the electrodes. The CRS file contains the contact resistance readings. The CMD file contains the parameters for data collection. These last two files aren't necessary for data processing, but can be useful in terms of troubleshooting. The field collection and data transfer were done by Emile Bergeron of the USGS.

The first step is to check the navigation in the GPS files. One file - L5F2 - had a sizeable navigation gap of approximately 6 minutes. This file was split into 2 parts effectively eliminating the navigation gap. The resulting new files are L5F2_part1 and L5F2_part2. Both the GPS files and the STG files were split into the new parts. Additionally the navigation in the GPS files were inspected visually. This was done by quickly parsing the GPS text files into comma-delimited text files with a header line, and then viewing the files in ArcMap 9.2. The AWK script used to parse the navigation was awkhold. awkhold:

awkhold:

BEGIN {
FS = ","
}
{
FS = ","
ARGC = 2
depth = -9999
temp = -9999
if ($1=="$GPRMC")
	{
	utctime = $2
	utcdate = $10
	latdeg = substr($4,1,2)
	latmin = substr($4,3,6)
	declat = latdeg + (latmin/60)
	londeg = substr($6,1,3)
	lonmin = substr($6,4,6)
	declon = -1 * (londeg + (lonmin/60))
	if (NR==1) {
		holddepth = -9999
		holdtemp = -9999
		}
	else {
		printf("%s, %s, %9.6f, %9.6f, %5.1f, %5.1f, %s\n", holdutctime, holdutcdate, holddeclon, holddeclat, holddepth, holdtemp, ARGV[2])
	}
	holdutctime = utctime
	holdutcdate = utcdate
	holddeclon = declon
	holddeclat = declat
	holddepth = -9999
	holdtemp = -9999
	}
if ($1=="$SDDPT")
	{
	depthreal = $2
	holddepth = depthreal
	}
if ($1=="$SDMTW")
	{
	tempreal = $2
	holdtemp = tempreal
	}
}
END {
printf("%s, %s, %9.6f, %9.6f, %5.1f, %5.1f, %s\n", holdutctime, holdutcdate, holddeclon, holddeclat, holddepth, holdtemp, ARGV[2])
}

This file was executed by a shell script to effectively batch process all the files in a single folder with the extension gps. The batch processor was dohold.

dohold:

files=`ls *.gps | cut -d. -f1 | tr "[A-Z"] ["a-z"]`
for file in $files
do
	awk -f awkhold $file.gps $file > $file.holds
done

Under Cygwin, all of the *.holds files were concatenated into a single comma-delimited text file and a header line added to the file. The header line added to the text file was: gpstime, gpsdate, longitude, latitude, depth_m, temp_c, line. Using ArcMap 9.2 - Tools - Add XY Data, the comma-delimited text file was added as an event theme to ArcMap. No erroneous points were detected.

Although the navigation fixes themselves were in good condition, the bathymetry data was very sparse. A great deal of work was done to extract the best possible depth value associated with each resistivity GPS reading. This information is outlined in detail in the metadata for jd103gps_bestdepth.shp available at https://pubs.usgs.gov/of/2011/1039/html/ofr2011-1039-catalog.html. In order to effectively process the resistivity data, valid depth values are necessary. This raw dataset contains the original GPS files as well as the "newgps" files that are used in the eventual processing of the data. The first step in generating these "newgps" files was to use XTools Pro version 5.2 within ArcMap 9.2 to export attributes from jd103gps_bestdepth.shp. XTools Pro - Table Operations - Export Table to Text. The fields exported were: gpstime; gpsdate; longitude; latitude; temp_c; line; bestdepth. The output was sent to jd103newgps.txt as an ANSI text file.

The output text file is comma-delimited with a header line. Using VI under Cygwin (a Unix emulator running under Windows OS), the file was edited to remove the header line. Then an AWK script was run to reformat the text file to replicate a GPS file format.

awknewgps:

BEGIN {
FS=","
}
{
FS=","
alltime=$1
alldate=$2
tempc=$5
depth=$7
outfile=$6 "_newgps.gps"
declon=$3 * -1
londeg=int(declon)
lonmin=(declon-londeg)*60
declat=$4
latdeg=int(declat)
latmin=(declat-latdeg)*60
printf("$GPRMC,%06d,A,%02d%06.3f,N,%03d%06.3f,W,000.0,0,%06d,0,W*73\n",alltime,latdeg,latmin,londeg,lonmin,alldate) >> outfile
printf("$SDDPT,%s,0.0*56\n",depth) >> outfile
if (tempc != -9999) {
	printf("$SDMTW,%s,C*01\n",tempc) >> outfile
	}
}

Effectively what this script does is not only format the GPS file, but also output the information to the appropriate filename (which is based on the line name).

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. Moved the minimal source information provided to make it the first process step. 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.