Navigation, bathymetry, and water temperature points of ship position during continuous resistivity profile data collection in Northport Harbor on Long Island, New York in May, 2008 (RESGPSPNTS_NORTHPORT.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.

The data were transferred from the logging computer via AGISSAdmin software version 1.3.2.165. These files were then transferred via a thumb drive to the processing computer. The files included in this publication 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 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. Due to a large navigation gap, L38F1 had to be split into two parts with the new filename prefix for the GPS and STG files being L38F1_part1 and L38F1_part2. This process step, along with all subsequent process steps, was performed by the same person: VeeAnn A. Cross.

An AWK script was used to extract the navigation, bathymetry, and temperature information recorded in each individual GPS data file for each day of data acqusition.

AWK script "awkhold":
BEGIN {
FS = ","
}
{
FS = ","
ARGC = 2
depth = -9999
temp = -9999
if ($1=="$GPRMC")
	{
	utctime = $2
	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, %9.6f, %9.6f, %5.1f, %5.1f, %s\n", holdutctime, >holddeclon, holddeclat, holddepth, holdtemp, ARGV[2])
	}
	holdutctime = utctime
	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, %9.6f, %9.6f, %5.1f, %5.1f, %s\n", holdutctime, holddeclon, >holddeclat, holddepth, holdtemp, ARGV[2])
}

This AWK script was initialized by "dogps" - shell script run under CYGWIN v. 1.5.1 (UNIX like environment that runs under Windows). This is the script used for the May 12 data collection:

files=`ls *.gps | cut -d. -f1`
for file in $files
do
	awk -f awkhold $file.gps $file >> day1gps.txt
done

The script not only parses the GPS navigation, but concatenates the results into a single file. This script was repeated for day 2 and day 3 (May 13 and May 14 respectively) with the output directed to day2gps.txt and day3gps.txt.

VI (v. 7.2) under CYGWIN was used to add the appropriate header line and the comma-delimited text file was imported to ArcMap 9.2: Tools - Add XY Data. The X field is longitude; Y field is latitude, and the Coordinate System was defined as Geographic, WGS84. This "Event Theme" was converted to a shapefile by right-mouse clicking on the layer - Data - Export Data. The resulting shapefiles were day1gps.shp, day2gps.shp and day3gps.shp.

Using ArcMap 9.2 the following attributes were added to the shapefiles: location, streamer, jday, and col_date.

Using ArcMap 9.2 - ArcToolbox - Data Management Tools - General - Merge Input datasets: day1gps.shp day2gps.shp day3gps.shp
Output: resgpspnts_northport.shp
In the field mapping section I renamed depth to depth_m and tempc to temp_c
I had the following definition query set up in day1gps: "line" <> '7' Although I processed the GPS file, the navigation was bad and the data unusable.
I had the following definition query set up in day2gps: "line" <> 'L8F2' AND "line" <> 'L9F1' AND "line" <> 'L9F2' Those points had bad longitude values and needed to be excluded.

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.