Abstract-This paper addresses the design of mobile sensor networks for optimal data collection. The development is strongly motivated by the application to adaptive ocean sampling for an autonomous ocean observing and prediction system. A performance metric, used to derive optimal paths for the network of mobile sensors, defines the optimal data set as one which minimizes error in a model estimate of the sampled field. Feedback control laws are presented that stably coordinate sensors on structured tracks that have been optimized over a minimal set of parameters. Optimal, closed-loop solutions are computed in a number of low-dimensional cases to illustrate the methodology. Robustness of the performance to the influence of a steady flow field on relatively slow-moving mobile sensors is also explored.

Underwater gliders are autonomous vehicles that profile vertically by controlling buoyancy and move horizontally on wings. Gliders are reviewed, from their conception by Henry Stommel as an extension of autonomous profiling floats, through their development in three models, and including their first deployments singly and in numbers. The basics of glider function are discussed as implemented by University of Washington in Seaglider, Scripps Institution of Oceanography in Spray, and Webb Research in Slocum. Gliders sample in the archetypical modes of sections and of "virtual moorings." Preliminary results are presented from a recent demonstration project that used a network of gliders off Monterey. A wide range of sensors has already been deployed on gliders, with many under current development, and an even wider range of future possibilities. Glider networks appear to be one of the best approaches to achieving subsurface spatial resolution necessary for ocean research.

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Abstract-Operations with multiple autonomous underwater vehicles (AUVs) have a variety of underwater applications. For example, a coordinated group of vehicles with environmental sensors can perform adaptive ocean sampling at the appropriate spatial and temporal scales. We describe a methodology for cooperative control of multiple vehicles based on virtual bodies and artificial potentials (VBAP). This methodology allows for adaptable formation control and can be used for missions such as gradient climbing and feature tracking in an uncertain environment. We discuss our implementation on a fleet of autonomous underwater gliders and present results from sea trials in Monterey Bay in August, 2003. These at-sea demonstrations were performed as part of the Autonomous Ocean Sampling Network (AOSN) II project.

A full-scale adaptive ocean sampling network was deployed throughout the month-long 2006 Adaptive Sampling and Prediction (ASAP) field experiment in Monterey Bay, California. One of the central goals of the field experiment was to test and demonstrate newly developed techniques for coordinated motion control of autonomous vehicles carrying environmental sensors to efficiently sample the ocean. We describe the field results for the heterogeneous fleet of autonomous underwater gliders that collected data continuously throughout the month-long experiment. Six of these gliders were coordinated autonomously for 24 days straight using feedback laws that scale with the number of vehicles. These feedback laws were systematically computed using recently developed methodology to produce desired collective motion patterns, tuned to the spatial and temporal scales in the sampled fields for the purpose of reducing statistical uncertainty in field estimates. The implementation was designed to allow for adaptation of coordinated sampling patterns using human-in-theloop decision making, guided by optimization and prediction tools. The results demonstrate an innovative tool for ocean sampling and provide a proof of concept for an important field robotics endeavor that integrates coordinated motion control with adaptive sampling. C

Subsurface float and surface drifter observations illustrate the structure, evolution, and eventual demise of 10 North Brazil Current (NBC) rings as they approached and collided with the Lesser Antilles in the western tropical Atlantic Ocean. Upon encountering the shoaling topography east of the Lesser Antilles, most of the rings were deflected abruptly northward and several were observed to completely engulf the island of Barbados. The near-surface and subthermocline layers of two rings were observed to cleave or separate upon encountering shoaling bathymetry between Tobago and Barbados, with the resulting portions each retaining an independent and coherent ringlike vortical circulation. Surface drifters and shallow (250 m) subsurface floats that looped within NBC rings were more likely to enter the Caribbean through the passages of the Lesser Antilles than were deeper (500 or 900 m) floats, indicating that the regional bathymetry preferentially inhibits transport of intermediate-depth ring components. No evidence was found for the wholesale passage of rings through the island chain.

The earth's largest oceanic rings are formed by the retroflecting North Brazil Current (NBC) near 8ЊN in the western tropical Atlantic. The NBC flows northward across the equator and past the mouth of the Amazon River entraining river-influenced shelf water along its nearshore edge. Enhanced phytoplankton production associated with the nutrient-rich Amazon discharge results in near-surface chlorophyll gradients that delineate the trajectory of the retroflecting NBC. These large-scale gradients, visible from space using Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color imagery, enable visualization of NBC rings during the initial phases of their evolution and northwestward translation. Observations of 18 NBC rings identified between September 1997 and September 2000 are summarized. Six rings formed each year. Although nearly circular at formation the rings quickly deformed as they translated at speeds near 15 cm s Ϫ1 toward the Caribbean Sea. Typical core radii of rings near 55ЊW were 100 km and 150 km in the across-and alongshore dimensions, respectively. The contribution of each ring to intergyre mass transport (1.0 Ϯ 0.4 Sv) was estimated using SeaWiFS derived surface areas and an estimate of vertical penetration (600 m) based on in situ tracer observations. Several rings were observed (using satellite-tracked surface drifters in combination with SeaWiFS imagery) to violently collide with the Lesser Antilles. At least one ring maintained an organized circulation while passing directly over the island of Barbados. * Contribution Number 10462 of the Woods Hole OceanographicInstitution.