Merged GLORIA sidescan and Hydrosweep pseudo-sidescan: Processing and creation of digital mosaics

We have replaced the usual band of poor-quality data in the near-nadir region of our GLORIA long-range sidescan-sonar imagery with a shaded-relief image constructed from swath bathymetry data (collected simultaneously with GLORIA) which completely cover the nadir area. We have developed a technique to enhance these ''pseudo-sidescan'' images in order to mimic the neighbouring GLORIA backscatter intensities. As a result, the enhanced images greatly facilitate the geologic interpretation of the adjacent GLORIA data, and geologic features evident in the GLORIA data may be correlated with greater confidence across track. Features interpreted from the pseudo-sidescan may be extrapolated from the near-nadir region out into the GLORIA range where they may not have been recognized otherwise, and therefore the pseudo-sidescan can be used to ground-truth GLORIA interpretations. Creation of digital sidescan mosaics utilized an approach not previously used for GLORIA data. Pixels were correctly placed in cartographic space and the time required to complete a final mosaic was significantly reduced. Computer software for digital mapping and mosaic creation is incorporated into the newly-developed Woods Hole Image Processing System (WHIPS) which can process both low- and high-frequency sidescan, and can interchange data with the Mini Image Processing System (MIPS) most commonly used for GLORIA processing. These techniques are tested by creating digital mosaics of merged GLORIA sidescan and Hydrosweep pseudo-sidescan data from the vicinity of the Juan Fernandez microplate along the East Pacific Rise (EPR).