MOSAIC8 - Composite sidescan-sonar mosaic collected by the U.S. Geological Survey offshore of the Chandeleur Islands, LA, 2007 (UTM Zone 16N GeoTIFF)

Within XSonar Software (version: none) a median filtering routine (Malinverno and others, 1990) was applied to the raw sidescan-sonar data (.xtf) to remove speckle noise; the filter was 6 pixels across track by 3 pixels along track. The data were further processed to correct for fish altitude, slant and beam artifacts, and then merged with the navigation (Danforth, 1997). These 2007 data were affected by port noise on the following days 20070610-20070619. XSonar was edited to reduce the port highpass value (from 4095 to 2500), in an effort to improve the sonar image. Odd and even sidescan sonar lines were mapped seperately out of XSonar at 1 meter/pixel resolution. Sidescan areas were defined within the cruise domain such that the sonar images mapped in XSonar would be no larger than 200 Mb.

The odd and even area files were imported into PCI Geomatica Software (version 10.1) to be digitally mosaicked together using PCI's OrthoEngine and procedures described in Paskevich (1996). The mosaicking process produces an enhanced, geographically correct, sidescan-sonar mosaic with 1 meter/pixel resolution. The composite mosaic was exported as a GeoTIFF image.

The days that experienced portside noise problems (20070610-20070619) needed further processing to improve the mosaic image. Portside swaths that displayed as 'whiteout' within the mosaicked image had pixel values greater than 200 (out of 256) due to noise, and were deleted using the lasso tool in Adobe Photoshop CS2 (version 9.0.2).

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. Formatting of the cross-references was fixed to meet the metadata standard. Some online links were added to the cross-references. 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.