Enhanced sidescan-sonar TIFF images in a UTM projection on the inner continental shelf off the northern Oregon and southern Washington

Sidescan-sonar data were collected using an EdgeTech sidescan-sonar system and logged to a Triton QMIPS data acquisition system. The EdgeTech system acquired data at a rate of 7.5 pulses/sec yielding a total swath width of 200m (100m range to each side of the sidescan-sonar towfish). The digital sidescan-sonar data were processed and mapped to provide proper geographic orientation of the data. Although the EdgeTech system is a dual-frequency system (100kHz and 500kHz), this particular study only processed and used the 100kHz data. The processing steps of the sidescan-sonar data included; subsampling the raw sidescan-sonar data using a median filtering routine to suppress speckle noise and reduce file size, and correcting for slant-range distortion, signal attenuation, and dropped sonar lines using the XSonar software package (Danforth et al., 1991). The sidescan-sonar data was then mapped into its proper geographic location at a resolution of 2 m/pixel using techniques summarized by Paskevich (1996).  The study area was broken into 4 areas (area1 being the northenmost, area4 the southernmost) so that each individual area would be a workable file size within the remote sensing software package PCI. Because this particular study consists of reconnaissance lines spaced approximately 5km apart, no mosaicking steps were applied.  Line crossings had no adjustments or shifts applied to the geographic position of the data. Some of the 1997 sidescan-sonar data was collected in an 8-bit format. These files were tone-matched to the 16-bit data. After tone matching, an enhancement was applied to all the sidescan sonar imagery such that the maximum pixel value is 254 with the minimum pixel value of 0. The imagery was then transferred to a background of 255. Rectangular segments of each of the 4 areas from each year of surveying were then exported as TIFF image files with associated world files for georeferencing. Images in a geographic coordinate system were then reprojected to a UTM projection. Due to the large size of the TIF images, they were compressed with the program GZIP such that the filenameconforms to the 8.3 format. An example of a filename is ar1_1.gz.

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.). The original metadata was available in HTML only, so had to be reformatted. The citation in the identification section was completely redone, including adding links to the data and larger work citation. Added ISO 19115 Topic Category keywords. The standard order process section in the distribution was modified to include the link to the data. 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.