Ship tracklines along which continuous resistivity profiling data were collected in the Indian River Bay, Delaware, on April 13, 2010, on U.S. Geological Survey Field Activity 2010-006-FA (JD103GPS_LINES_SPLITS.SHP, Geographic, WGS 84)

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.

In ArcMap 9.2 an ArcMap extension written in Woods Hole (VACExtras, v2.1) was used to convert the individual navigation points to lines. The "Points to Line v2" tool within the extension was used. The user selects an attribute to be the unique identifier used to group the points into a line; in this case, the attribute "line" was used. The script assumes the order of the points in the point shapefile is the order they need to be added to the line, and the projection of the output shapefile is the same as the input point shapefile. The user can also select additional attributes to be carried over to the output polyline shapefile - first occurrence and last occurrence. The first occurrence values written to the output shapefile were gpstime, gpsdate, and bestdepth. The output attributes retain the same name. The last occurrence attributes carried to the output shapefile were gpstime, gpsdate, and bestdepth. The attributes in the output shapefile have "_end" appended to the attribute name. If the original attribute name is more than 6 characters long, the attribute name is truncated to the first 6 characters with the "_end" appended to that. This process step, along with all subsequent process steps, was performed by the same person: VeeAnn A. Cross.

During processing of the data, several lines had to be split during processing to account for sharp turns during the survey. On this day this includes l5f2_part1 and l5f5. A definition query was applied to jd103gps_bestdepth.shp such that only the points associated with each line was viewable. Then VACExtras v. 2.1 - Points 2 Lines v2 was used to generate a polyline shapefile as in the previous process step. The definition query and VACExtras were applied a total of four times - for each individual part. Within the newly generated polyline shapefiles, the "line" attribute was edited to reflect the new linename.

Using ArcMap 9.2 the original polyline shapefile was merged with the newly formed "split" lines using ArcToolbox - Data Management Tools - General - Merge.

Used XTools Pro version 5.2 to add the line length attribute "len_utm18". In XTools Pro - Table Operations - Calculate Area, Perimeter, Length, Acres and Hectares. Specified the output projection as WGS_1984_UTM_18_N and set the output units as meters. Set the output field name to len_utm18.

In ArcMap 9.2 two additional attributes were added to the shapefile: hotlink and hlink2. The attribute "hotlink" will allow the user to hyperlink to the MATLAB JPEG images of the CRP line from within ArcMap. The attribute "hlink2" will allow the user to hyperlink to the EarthImager JPEG image of the long version of the CRP line from within ArcMap. See the entity and attribute overview for instructions on how to implement this feature. Because of the split in some of the lines, not every polyline has a value in these new attributes.

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.