Type_of_Source_Media: hard disk
Originator: U.S. Geological Survey
Publication_Date: Unpublished material
Title: Raw CRP Data
Source_Citation_Abbreviation: raw crp data
Source_Currentness_Reference: ground condition
These data were acquired with an AGI SuperSting Marine system that is described at the website: www.agiusa.com/marinesystem.shtml. The particular system used for this acquisition was an 11 electrode array with electrodes spaced 5 meters apart. The potential electrodes are made of graphite, with the remaining electrodes 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 potentials between electrode pairs in the remaining electrodes. Each line of data acquisition records several files. The two files necessary for processing are the *.stg and *.gps file. The STG file contains the resistivity data, while the GPS file contains the navigation information.
The data were transferred from the logging computer via AGISSAdmin software. The data files available for this day are L6F1.*, L6F2.*, L6F3.*, L7F1.*, L8F1.*, and L9F1.*.
Line L6F1 had navigation issues that were handled in the following way:
1) The GPS files were processed using an AWK script to parse out the navigational information from the $GPRMC string and concatenated into a single file. This comma delimited text file was then imported as a table into ArcView 3.3, loaded as an event theme, and then converted to a shapefile.
2) The allgps shapefile was copied to a new shapefile (tempall) and a field called record was added. This field was filled with the record number so that each point had a unique identifier.
3) The extension pathfind.avx (Path, with Distance and Bearings, v. 3.2) was loaded into the ArcView project. Clicking on the pathfind button brings up a dialog. Select the shapefile (tempall) and the ID field and SERIES field. In this case, both are the "record" field in the shapefile. For the RESULTS table, I checked the option RESULTS table and Join results with Theme Attribute table. Select NO LINES for connection lines. ***Because I think in terms of meters, not decimal degrees for distance measure, I had set the View Properties to UTM, Zone 18, NAD83 projection. The joined shapefile table was then exported to a text file.
4) This exported text file was then reloaded as a table, added as an event theme, and converted to a shapefile. Three new fields are now in the shapefiles as a result of the pathfind extension: To_ID, Cent_Bear, Cent_Dist. (The record field is the fromID). The navigation problem, which manifests itself as the same fix for a long period of time is now readily obtainable. The Cent_Bear value becomes -999 and the Cent_Dist is 0.000. This happened to gps_fixing.shp
5) Three new fields are added to the shapefile: new_dist, new_bear, sum_dist. The new_dist field is for the value that I want to be between each navigation point, assuming the ship is traveling at a constant speed. This value is calculated by using the Cent_dist value that appears right after the 0 values, divided by the number of -999 azimuth values plus 1. That Cent_dist value records the large distance jump once the navigation started acquiring valid values. For example, if there are 9 values of -999, then I divide the large distance value by 10. This resulting value needs to be placed in the 2nd -999 row, through to one row after the lat -999 value (in the new_dist column).
6) The sum_dist field simply sums the distance covered by each new distance section. Select the records from a section for an individual line that needs this calculation. Use the calculate button (table must be in edit mode) and enter the equation: sum_dist = new_dist *([To_ID]-xxxx] where xxxx is the record field value of the first row in the selection.
7) To properly populate the new_bear field, I used the extension dist_az_tools. For each gap, I measured the azimuth between the last good point and the point where the gps started working again. This value was then placed into the appropriate section.
8) I decided to do the rest of the processing on the individual lines that need the repairs. I selected all the points from each line of interest and saved them as a new shapefile resulting in: templ2f1.shp, templ3f1.shp, templ5f1.shp. **Because my distance and azimuth readings are based on the shapefile being projected, I exported the files as projected shapefiles.
9) The distance_azimuth tool now lets me create a new shapefile based on distances and azimuths. Run the tool for each new shapefile, select the second option (Input theme, using unique distances and azimuths). Next window, select the shapefile with the DISTANCE FIELD being sum_dist, and the AZIMUTH FIELD being new_bear. Select all the fields for the new shapefile. What the script does is take the point and move it to a new location based on the distance and azimuth as specified in those fields. The result is that only points that need moving have values other than zeros in the sum_dist and new_bear fields, therefore those are the only points that are actually moved. The new shapefile was called: templ6f1_fix.shp
10) Because this shapefile is projected, I needed to convert it back to geographic. I used ArcToolbox (9.0) to define the projection as UTM, Zone 18, NAD83, and then reprojected it to Geographic, NAD83. Resulting file was: templ6f1_fixgeog.shp.
11) This geographic shapefile was loaded back into ArcView 3.3 and I used a modified form of the addxycoo.ave script to add back in the xy (latitude, longitude) fields. The modification to the script had it write 6 decimal places instead of 5.
12) I then "turned off" all the fields except the ones I needed: col_time, col_date, depth_m, temp, x-coord, y-coord and exported the table to a comma delimited text file. This file was: l6f1_gpsfix.txt.
13) I then took this text file and ran it through the awk script "awknewgps" to output a repaired GPS file for use with Marine Log Manager.
Of note, even though the navigational fixes are duplicates in the original GPS file, the fathometer and temperature values are assumed to be valid.
Edits to the metadata were made to fix any errors that MP v 2.9.34 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.). The source information was incomplete and had to be modified to meet the standard. The process steps without process dates had the date set to unknown. The distributor information needed to be added, along with the distribution format and network resource. 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.
Contact_Organization: U.S. Geological Survey
Contact_Position: Marine Geologist
Contact_Person: VeeAnn A. Cross
Address_Type: Mailing and Physical
Contact_Voice_Telephone: 508-548-8700 x2251
Address: 384 Woods Hole Road
City: Woods Hole