CDP navigation at 500 trace intervals for multichannel boomer seismic-reflection data collected by the U.S. Geological Survey in Vineyard Sound, MA, 2011 (Esri point shapefile, Geographic, WGS 84, 2010-100-FA_Boomer_cdp500.shp)

A SIOSEIS seismic processing software script was used as follows: The raw SEG-D shot files were read with the process SEGDDIN specifying geometrics format; for lines L1 and L2, the process HEADER was used to correct time of day because of random incorrect values of time and position recorded in the header (correct time in the header was needed for the next process); the process GEOM was used to describe the shot and streamer geometries and to calculate the reflection point (CDP) numbers used to gather (sort traces by CDP) the seismic line. Process GEOM was used to set the shot-receiver distance into the trace header of every trace. For lines L1 and L2, GEOM type 6 was specified, which computes a distance from last shot (DFLS) for each shot based on the corrected shot time in the header and the navigation from an ASCII file containing time and position. The ASCII shot navigation file was derived from the HYPACK navigation data. Geom type 9 was specified for line L3, which calculates DFLS based on position in the SEG-D header that was verified to be correct; a normal move out (NMO) applied a travel time correction to each trace based on offset and a velocity of 1500 m/s; process GATHER was used to sort the shot order traces in to traces sorted by the CDP numbers computed by the process GEOM; lastly, the CDP trace gathers were written with the process in SEG-Y rev. 1, IEEE floating point format.

A SIOSEIS script was used to stack the CDP gathers, apply a bandpass filter and automatic gain control. The process DISKIN read the CDP sorted SEG-Y file and renumbered CDP starting at one and incremented CDP number by one. The process STACK was used to sum traces, compute the average amplitude for each trace sample, and write the computed samples to one trace. The trace header values of the first trace in the gather were used for the stacked trace. The process FILTER applied a zero-phase bandpass frequency domain filter between 600 and 2000 Hz with a slope of 48 decibel per octave slope. The process AGC applied an automatic gain control (AGC) with a window length of 5 ms. The computed multiplier for each AGC window was reduced by fifty percent. Lastly, the processed stacked traces were written to disk with the process DISKOX in SEG-Y rev. 1, IEEE floating point format.

A Seismic Unix script was used to read the trace headers of the stacked SEG-Y files and write CDP, source X and Y, year, day, hour minute, seconds only where the original channel number was equal to one (the channel closest to the source). Some CDP gathers did not contain a trace with channel one in the header and were eliminated. The coordinates represent the position of the GPS antenna, which has a constant offset of 10 meters to the source. The source to receiver offset was 22 meters. Half the distance between source and receiver represents the location of the common reflection point. A layback correction of 21 meters was applied to the navigation using an AWK script written by Wayne Baldwin, USGS. An AWK script was used to format the trace navigation with corrected layback positions in a comma-delimited file.

Text files created in the previous step were concatenated into a comma-delimited text file, then imported into ArcMap (version 9.3) using 'Create Feature Class from XY Table' and saved as points (UTM Zone 19, WGS84) in the Esri shapefile format.

The shapefile created in the previous step was converted from points to polylines using VAC Extras Points to Line v2. The 'Line' field was used to define which points were used to generate each polyline feature.

Using ArcToolbox, Linear Referencing Tools, a CDP navigation file was created with points for CDP at even intervals of 500 and with start and end CDP values. First, Create Routes was used to create a polyline calibrated shapefile using the Line field as the Route Identifier and Length as the Measure Source. Calibrate Routes used the output from Create Routes with Line as the Route Identifier Field and the CDP point file for all unique fixes described in process step 4. The Point Identifier Field was Line, the Measured Field was CDP and the Measure Calculation Method was Measures. This created a calibrated polyline shapefile. Hatches were added at the beginning and end of each line, as well as at 500 CDP spacing. This was done in ArcMap 9.3 by opening the layer properties and selecting the Hatches tab. Create a hatch interval of 500 for the Hatch Class, then for Hatch Def(1) place a marker hatch every 1 hatch interval. From the Hatch Class -- Add a Hatch Definition - Add End Hatch Definition and set these to a marker Hatch. By displaying the labels for both Hatch Definitions, a quick comparison between the hatches and the unique trace navigation makes sure things are lining up right. Within ArcMap 9.3 - by going to Tools - Customize - Commands and scrolling down to the Category "Linear Referencing", the icon for the command "Convert Hatches to Graphics can be added to a toolbar. Once this is done, that tool can be used to convert the hatches to graphics. The graphics were converted to a shapefile using XTools Pro version 7.1. XTools Pro - Feature Conversions - Convert Graphics to Shapes. ArcToolbox - Linear Referencing Tools - Locate Features Along Route used the shapefile converted from graphics with input route features; Lines as Route Identifier Field, and 5 meters as Search Radius. A DBF file was output with Line as Route Identifier Field, point as Event Type, and CDP as Measure Field. The rest of options at default were checked. Using ArcMap 9.3 - ArcToolbox - Linear Referencing Tools - Make Route Event Layer to create an event feature. The input used the following parameters: input route features: the output from Calibrate Routes was the Input Route Features; Lines was the Route Identifier Field, and the output was Locate Features Along Route in the Input Event Table; Line was the Route Identifier Field; Point was the Event Type; CDP was the Measure Field. The rest of the option left at default values. The event layer was converted to a shapefile in ArcMap 9.3 by exporting the data (right mouse click on event layer, Data, Export Data) to a temporary shapefile. The temporary shapefile was sorted within ArcMap 9.3 using VAC Extras version 2.1 (an extension written by the USGS in Woods Hole) to sort the shapefile: VAC Extras - FeatConv - Table Sort with the CDP file sorted based on Line and CDP. Line was set as the primary sort field, ascending order. CDP was set as the secondary sort field - ascending order. Output to 2010-100-FA_Boomer_cdp500.shp. Finally, ArcToolbox was used to change from UTM projection to Geographic coordinate system.

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.). Added the DOI link in the Identification section - both as the first link and as part of the Larger Work citation. Fixed the publication date and also the Larger Work citation title to match what is available online. Updated the link to the project page in the abstract as well as the field activity links. The source information was incomplete and had to be modified to meet the standard. Fixed a link in the distribution section. 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.