Ship Trackline along which Continuous Resistivity Profile Data were Collected in the Corsica River Estuary, Maryland on May 17, 2007 on USGS Cruise 07005 (RESGPSLNS_JD137.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. 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 ¼ 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 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 "linename" 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. The value written out is the first occurrence of the attribute on the unique "line". The additional attributes carried over were gpstime, depth_m, jday, and gpsdate. This process step, along with all subsequent process steps, was performed by the same person: VeeAnn A. Cross.

In ArcMap 9.2, XTools Pro (v. 5.2) was used to add the line length attribute "len_utm18". In XToolsPro - Table Operations - Calculate Area, Perimeter, Length, Acres and Hectares. Specified the output projection as NAD_1983_UTM_Zone_18N and set the output units as meters. Set the output field name to len_utm18.

Two text attributes were added to the attribute table in ArcMap 9.2. 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.

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.