The Mixing Zephyr Pages

Mixing Zephyr Program
Notes on Reduction of Data from Mesotech Scanning Sonar

A Mesotech Scanning Sonar is installed on the vehicle in a downlooking postion. The instrument is capable of stepping in 0.225 degree increments, although for typical survey parameters faster scans at 0.9 degree increments are appropriate. The data returned consists of two way travel times for each of the pings transmitted during a sector scan over an adjustable angle.

During the Mixing Zephyr program, the system was generally running and logging during all operations. In addition, short dedicated surveys were run in the MEF during Dives 2930 and 2934, the first over the Bastille complex and the second over Grotto and Lobo.

Data Reduction

A number of processing steps are necessary to translate the instrumental data into a representation of the topography of the vent field: Dan Scheirer, when at UC Santa Barbara, developed a number of programs to complete these steps which can be found in $ZEPHYR/mesoproc. However, in analyzing some of the initial data manually we recognized some problems in the data structure; these are discussed elsewhere. Thus, we have not devoted substantial amounts of time to working up the data we acquired, as Scheirer intends to repair his code and provide us with a revised version. However we did some manual processing of the data to inspect data quality and the adequacy of our survey designs. From these results we were able to construct along course profiles, similar to the waterfall display common on swath mapping sonars. In instances where heading was in a narrow band, we have mapped with them, however making no correction for vehicle attitude. These corrections, while important, are of the same order of magnitude as the uncertainty in the navigation and so while not a final product, the resulting imagery shows major features reasonably well.

This is an example from the Bastille area viewed from just south of west. In the far right the west wall of the axial valley rises (grading to cyan and blue). In the center foreground are the sulfide structures that make up the Bastille complex (blues and magenta). Note the steep southern walls and the less steep northern slopes. The valley floor to the north of Bastille once away from the wall if quite flat; a significant depression is seen to the south of the complex. The viewpoint is toward heading 275, azimuth 45 degrees.

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