15-Minute Navigation for Seismic-Reflection Data Collected in Eastern Rhode Island Sound in 1975 (A75_6NAV_SORT.SHP)

LORAN-C time delays (chain 9930) from the R/V Asterias Cruise ASTR75-June Logbook were converted in a batch to latitude and longitude (WGS84 projection) using LoranGPS 6.2 using the X and Z chains and selecting the output as decimal degrees.

Latitudes and longitudes converted by LoranGPS were copied into an Excel file containing additional information (date, time, line number, comments). Lines are named using the following convention: for instance, 25Ab signifies the line 25A, section b (capital letters are part of the line name as recorded on the seismic records, lower case letters refer to sections of the line that were split during data collection or during scanning). Lines were cut during scanning when they were too long to scan all at once.

Time delays were manually corrected because LoranGPS does not apply a correction to time delays using the 9930 chain. Latitudes and longitudes and time delays for 10 points in eastern Rhode Island Sound (RIS) were plotted by hand on the original trackline chart. The differences between the plots of latitude/longitude and time delays were measured and averaged. The average correction, +1.2 for TD1 and -3.1 for TD2, a distance of about 1.3 km, was applied to the time delays.

The corrected time delays were run through LoranGPS to obtain latitudes and longitudes, which were copied into the Excel file. Added field 'Minutes', the time in minutes after midnight, to the Excel file using the following calculation: (int ([time value]/100)*60) + [time value] - ((int([time value]/100))*100) where the field 'Time' is used as the time value. Added field 'Line_temp', a line identification used to create the file a75_6lines2.shp.

Data from the Excel file were added to ArcMap 9.2 (tools, add xy data) and converted to a shapefile (data, export data) and the projection was defined as geographic WGS84. Attributes LineSeg, CommentSeg, Source, and Cruise_ID were added to the shapefile. Several points were added from the a75_6_1minnav_sort.shp file to correspond to line end points generally cut during scanning. These points are noted in the source field.

Used Table Sort tool in VACExtras version 1.91 to sort the data such that points are sorted primarily by LineSeg and secondarily by Time.

Edits to the metadata were made to fix any errors that MP v 2.9.32 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.). Minor fixes to the attribute format for some attributes were needed. 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.