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[1] Recent advances in underwater vehicle navigation and sonar technology now permit detailed mapping of complex seafloor bathymetry found at mid-ocean ridge crests. Imagenex 881 (675 kHz) scanning sonar data collected during low-altitude ($5 m) surveys conducted with DSV Alvin were used to produce submeter resolution bathymetric maps of five hydrothermal vent areas at the East Pacific Rise (EPR) Ridge2000 Integrated Study Site (9°50 0 N, ''bull's-eye''). Data were collected during 29 dives in 2004 and 2005 and were merged through a grid rectification technique to create high-resolution (0.5 m grid) composite maps. These are the first submeter bathymetric maps generated with a scanning sonar mounted on Alvin. The composite maps can be used to quantify the dimensions of meter-scale volcanic and hydrothermal features within the EPR axial summit trough (AST) including hydrothermal vent structures, lava pillars, collapse areas, the trough walls, and primary volcanic fissures. Existing Autonomous Benthic Explorer (ABE) bathymetry data (675 kHz scanning sonar) collected at this site provide the broader geologic context necessary to interpret the meter-scale features resolved in the composite maps. The grid rectification technique we employed can be used to optimize vehicle time by permitting the creation of high-resolution bathymetry maps from data collected during multiple, coordinated, short-duration surveys after primary dive objectives are met. This method can also be used to colocate future near-bottom sonar data sets within the high-resolution composite maps, enabling quantification of bathymetric changes associated with active volcanic, hydrothermal and tectonic processes.Components: 15,200 words, 26 figures, 2 tables.

Absrml-This paper shows results from our development ofnn extended MATLAU image procesing toolbox, which implements some useful opticnl image processing and mosnicking algorithms found in the literature. We surveyed and selected algorithms from the field which showed promise in application to the underwnler environment. We then enended there nlgorithms to explicitly deai with the unique constraints ufunderwater imagery in the building of our toolbox. As such, the nigorithms implemented include:contrnst limited adaptive hbtogram spedficntion (CIAIIS) to den1 with the inherent nonuniform lighting in underwnter imagery.. Fourier b u d methods for sutle, rotation, und trnmlalion ncovery which provide rohustnes against dissimihr image mgiOnS.. local normalid cordstion for imnge registration to handle the low-fenlure, unstructured environment ofthe sealtoor. mulliresolution pyramidal blending of images to form a romposite senmles mosaic without blurring or loss of detail new image borders. io thw pnper we highlight the mathematicnl formulation behind ench uf these algorithms using consistent noration and n unified framework. We depict some of our M A T L A B toolbox results nith an nssorlment of underwater imagery. Index Tu"-Image processing, mosnicking. MATLAA. 1. I N I K 0 I ) U C I ' I O N NE aspect of our research here at the Deep Submergence 0 Laboratury of the Wood, Hulr Oceanographic Institution IS optical image processing and mosaicking. Pruductiun uf the high resolution, large area imagery of the seafloor required by our end user coniniunity. (geologists. biologists. archaeoiugi,ts.. . ) uould be impossible uere it not for the technique of pliu.tomosaicking whereby a large are3 image is assimilated from tens to hundmds of smaller-foutprint. overlapping images. The propagation of visible light underuater sufkrs from rapid attenuation and scattering. which in combinatiiin uith a limited camera-to-light separation akaiiable on most vehicle platforms. places strung constraints on the abilit) to iniage large a r e a uf the seaRwr optically. Special consideration must he giwn tu the unique cunstraints ssuciated with the underwater environment.Our research in underuater image processing and photumoraicking deals explicitly with these constraints. In this paper we cover Lome successtul techniques in the literature for image processing and mosaicking uhich have k e n extended to deal with unique peculiarities of the underuater enkirunment. The algorithms and order of sections presented in this paper arc:contrast limited adaptive histogram specification (CLAHS) to deal with the inherent nonuniform lighting in underwater imagely.Fourier based methods for scale, rotation, and translation recovery which provide robusmess against dissimilar image regions.. local normalized correlation for image registration to handle the low-feature, unstructured environment of the seafloor.. multiresolution pyramidal blending of images to form a composite seamless mosaic without blurring or loss of detail near image borders. As MATLAB has ...

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Mesobot, an autonomous underwater vehicle, addresses specific unmet needs for observing and sampling a variety of phenomena in the ocean’s midwaters. The midwater hosts a vast biomass, has a role in regulating climate, and may soon be exploited commercially, yet our scientific understanding of it is incomplete. Mesobot has the ability to survey and track slow-moving animals and to correlate the animals’ movements with critical environmental measurements. Mesobot will complement existing oceanographic assets such as towed, remotely operated, and autonomous vehicles; shipboard acoustic sensors; and net tows. Its potential to perform behavioral studies unobtrusively over long periods with substantial autonomy provides a capability that is not presently available to midwater researchers. The 250-kilogram marine robot can be teleoperated through a lightweight fiber optic tether and can also operate untethered with full autonomy while minimizing environmental disturbance. We present recent results illustrating the vehicle’s ability to automatically track free-swimming hydromedusae (Solmissus sp.) and larvaceans (Bathochordaeus stygius) at depths of 200 meters in Monterey Bay, USA. In addition to these tracking missions, the vehicle can execute preprogrammed missions collecting image and sensor data while also carrying substantial auxiliary payloads such as cameras, sonars, and samplers.

Mesobot, a new class of autonomous underwater vehicle, will address specific unmet needs for observing slow-moving targets in the midwater ocean. Mesobot will track targets such as zooplankton, fish, and descending particle aggregates using a control system based on stereo cameras and a combination of thrusters and a variable buoyancy system. The vehicle will also be able to collect biogeochemical and environmental DNA (eDNA) samples using a pumped filter sampler.

Preliminary analysis of near-bottom, high-resolution DSL-120 sidescan and bathymetric data from the median valley in the TAG (Trans-Atlantic Geotraverse) segment near 26°N on the Mid-Atl antic Ridge, and Argo-Il photography from the associated actively venting hydrothermal mound, allows us to evaluate the structural, volcanic, and hydrothermal processes occurring in this area, and to provide baseline constraints on the pre-drilling status of the morphology of the mound and the distribution of venting. These data were collected just 2 months before ODP drilling of the active TAG mound, one of the largest volcanichosted, mid-ocean ridge hydrothermal deposits yet discovered. Sharp discontinuities and strong asymmetry in the morphology and age distribution about the spreading axis suggest a recent episode of preferential accretion of crust to the east. Such episodes have likely contributed to the long-term spreading asymmetry (13 mm/yr to the east, 11 mm/yr to the west) of the TAG segment. The active mound lies within the intersection of a zone of actively developing ridge-parallel (north-northeast) fissures and a series of pre-existing obliquely oriented (east-northeast) faults. The east-northeast faults are not continuous with faults previously described from the upper rift valley walls. This intersecting fault pattern may be important in localizing hydrothermal activity. Contemporaneous tectonic deformation and hydrothermal deposition continue to modify the three-dimensional structure and hydrogeology of the active TAG mound.