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DEPTHX: Underwater Mapping and Imaging of Deep Karst Shafts

Marcus Gary1, Nathaniel Fairfield2, William Stone3, David Wettergreen2, George Kantor2, and John M. Sharp1
1 The University of Texas at Austin, Austin, TX
2 Carnegie Mellon University, Pittsburg
3 Stone Aerospace, Austin, TX

El Zacatón, Mexico, the deepest known underwater karst shaft (cenote) in the world extends at least 329 meters below the water table and the full lateral extent at depth is unknown at this time. We hypothesize that local Pleistocene extrusive volcanism has accelerated dissolution and diagenesis in these Mid-Cretaceous carbonate rocks.

The Deep Phreatic Thermal Explorer (DEPTHX) is a completely autonomous robotic probe being designed as a prototype vehicle that would someday explore sub-ice oceans of Jupiter's moon Europa searching for extra-terrestrial life. This NASA funded project is testing the initial DEPTHX probe in El Zacatón cenote, which is hydrothermal and teeming with microbial communities.

The primary task of DEPTHX is to image and map the physical geometry of the karst feature using an array of sonar transducers. Simultaneous Localization and Mapping (SLAM) is used to create a virtual representation created as a 3D evidence grid in which each 3D cell (or voxel) stores the likelihood that that particular cell is occupied.

In May 2005, a preliminary data set was collected in the El Zacatón cenote using a drop sonde equipped with a circular array of 32 pencil beam sonar transducers. The drop sonde was lowered to a max depth of 200 meters and precise geospatial data was collected down to 280 meters. The visualization of these data reveals a deep shaft extending vertically into the subsurface that is roughly 110 meters in diameter at the top and 60 x 100 meters below 85 meters depth.