OS51B-0468
The Southernmost Branch of the Lucia Canyon System Offshore Central California: New Insights From High-resolution AUV Bathymetry and Chirp Sub-bottom Profiles
The Lucia Canyon system originates from the edge of a narrow shelf approximately 2 km offshore central California. Five of the six feeder canyons to the Lucia Canyon head adjacent to the main Lucia Canyon and merge on the upper slope. The southernmost branch of the Lucia Canyon, informally referred herein as the Lucia Chica, heads approximately 30 km to the south where the shelf is wider; the Lucia Chica merges with the Lucia Canyon farther down the slope (approximately 1800 m water depth) than the more northerly feeder canyons. The Lucia Chica system is more sinuous, less incised, and smaller in width than the other channels of the Lucia Canyon System. The Lucia Chica represents the latest sedimentation in the structurally confined Sur Basin on the continental slope offshore central California. In contrast to the other canyon systems which direct sediment down the slope, the Lucia Chica veers along the slope. The main channel of the Lucia Chica reaches a depocenter in 1000m water depth where it avulses resulting in varying sinuousity of multiple channel segments and complex depositional architectures. In order to study the mid-slope deposition of the Lucia Chica, we recently conducted a high-resolution multibeam bathymetry, chirp sub-bottom profile, and sidescan survey of the Lucia Chica using an Autonomous Underwater Vehicle (AUV) developed by the Monterey Bay Aquarium Research Institute (MBARI). The resulting bathymetry has a lateral resolution of 1m and a vertical precision of 0.3 m, and the sub-bottom profiles achieve penetrations of up to 40 m. These new data have improved interpretation of the complex sedimentation recognized in low- frequency industry 2D seismic-reflection data archived at the USGS and in surface-towed boomer profiles of the Sur Basin. The AUV survey was conducted with the vehicle at 50 m above the sea floor. The varying confinement and relief of the Lucia Chica sinuous channels is buried by 3 to 4 meters of hemipelagic drape. A new, foraminifera 14C calibrated-age date from a vibracore of this hemipelagic layer yields a sediment accumulation rate of 33.4 cm/ka, indicating that the Lucia Chica was last active about 12 ka at the late OIS 2 rising of sea level.
OS51B-0469
Onboard Decision Making For a New Class of AUV Science
Autonomous Underwater Vehicles (AUVs) are an increasingly important tool for oceanographic research. They routinely and cost effectively sample the water column at depths far beyond what humans are capable of visiting. However, control of these platforms has relied on fixed sequences for execution of pre-planned actions limiting their effectiveness for measuring dynamic and episodic ocean phenomenon. At the Monterey Bay Aquarium Research Institute (MBARI), we are developing an advanced Artificial Intelligence (AI) based control system to enable our AUV's to dynamically adapt to the environment by deliberating in-situ about mission plans while tracking onboard resource consumption, dealing with plan failures by allowing dynamic re-planning and being cognizant of vehicle health and safety in the course of executing science plans. Existing behavior-based approaches require an operator to script plans a priori while anticipating where and how the vehicle will transect the water column. While adequate for current needs to do routine pre-defined transects, it has limited flexibility in dealing with opportunistic science needs, is unable to deal with uncertainty in the oceanic environment and puts undue burden on the mission operators to manage complex interactions between behaviors. Our approach, informed by a decades worth of experience in intelligent control of NASA spacecraft, uses a constraint-based representation to manage mission goals, react to exogenous or endogenous failure conditions, respond to sensory feedback by using AI-based search techniques to sort thru a space of likely responses and picking one which is satisfies the completion of mission goals. The system encapsulates the long-standing notion of a sense-deliberate-act cycle at the heart of a control loop and reflects the goal-oriented nature of control allowing operators to specify abstract mission goals rather than detailed command sequences. To date we have tested T- REX (the Teleo-Reactive Executive) on an MBARI Dorado 21" vehicle with a range of scientific instruments for water-column surveys in Monterey Bay. Results to date are available at http://www.mbari.org/autonomy/TREX/index.htm which are very encouraging. Our year-end goals revolve on mapping unstructured phenomenon such as Ocean Fronts and Thin Layers, which we expect will lead to work in adaptive observatory control and autonomous exploration of hydrothermal vents. http://www.mbari.org/autonomy/TREX/index.htm
OS51B-0470
Hudson Submarine Canyon Head Offshore New York and New Jersey: A Dynamic Interface
Hudson Canyon is the largest submarine canyon on the U. S. Atlantic continental margin. Having completed a surface ship multi-beam bathymetric map of the Hudson Canyon region (resolution 100m; http://pubs.usgs.gov/of/2004/1441/index/html), we report preliminary results of mapping portions of the canyon head (75 square km, water depth 200-500 m) using the Eagle Ray autonomous underwater vehicle (Explorer 27- BO1-2200 AUV, ISE Ltd.) of the University of Southern Mississippi. The AUV was equipped with a Simrad EM2000 multi-beam sonar system and flown 50 m above the seafloor for resolution (3 m), and with a CTD to map water column properties. Shipboard CTD casts were also made and water sampled from the shelf break (depth 200 m) to the upper continental rise (3000 m) for detection of methane. The canyon head is of interest as an essential fish habitat (squid, hake, tilefish, and lobster) that may contribute to sustain a regional fishery and that may conduct sediment to the ocean basin. A shallow trough, the Hudson Shelf Valley, extends ~185 km across the continental shelf connecting the mouth of the Hudson River to the canyon head where it indents the seaward edge of the shelf. The canyon head bifurcates with branch 1 (6 km-long) oriented NW-SE aligned with the Shelf Valley, and branch 2 (4 km-long) oriented N-S. The two branches merge into a segment 10 km-long oriented NW-SE aligned with branch 1. Branch 1 has symmetric walls with mean inclinations of 10 degrees and smooth seafloor, suggesting that it is presently inactive and accumulating a cover of hemipelagic sediment. In contrast, the walls of both the N-S branch 2 and of the contiguous NW-SE segment are asymmetric. The walls of the NW-SE segment have a mean inclination of 15 degrees and exhibit semicircular escarpments 800-900 m long and 600-700 m wide, separated by narrow ravines perpendicular to the canyon axis. Slump blocks with sharp rims occur where N-S branch 1 joins the NW- SE segment. Two circular depressions (diameter 100 and 300 m; relief c.15 m; depths 345 m and 390 m) occur at the base of the SW wall of the segment and may be collapse features related to gas discharge evidenced by a high methane anomaly at the shelf edge. The head of Hudson Canyon encompasses diverse habitats and is a dynamic interface between shelf and slope processes. We thank NOAA's National Undersea Research Program for support.
OS51B-0471
Hybrid Fluorometric Flow Analyzer for Underway Measurement of Ammonia in Seawater
A Hybrid Flow Analyzer (HFA) has been developed as a robust, highly sensitive instrument for the determination of ammonia in seawater. The instrument uses two syringe pumps to handle reagents and sample, respectively. The flow configuration is a hybrid between flow injection (FI) and sequential injection (SI) schemes. This hybrid flow analyzer spends most of its time in the continuous flow mode, providing the traditional FI advantages of baseline stability and high sensitivity while the SI mode in the remaining time provides flexibility and robustness for reagent and sample handling. The hybrid fluorometric flow analyzer has a linear dynamic range of 0-10 uM (r2 = 0.9987), with the limit of detections (3xSD) at 1 nM. The response changes by only 2.2% from 0 to 35 salinity. Moreover, the method has no refractive index effect, which is quite useful for seawater measurement. The method has been used to examine the spatial distribution of ammonia in wastewater outfalls off the coasts of Florida.
OS51B-0472
Adaptive Water Sampling based on Unsupervised Clustering
Autonomous Underwater Vehicles (AUVs) are widely used for oceanographic surveys, during which data is collected from a number of on-board sensors. Engineers and scientists at MBARI have extended this approach by developing a water sampler specialy for the AUV, which can sample a specific patch of water at a specific time. The sampler, named the Gulper, captures 2 liters of seawater in less than 2 seconds on a 21" MBARI Odyssey AUV. Each sample chamber of the Gulper is filled with seawater through a one-way valve, which protrudes through the fairing of the AUV. This new kind of device raises a new problem: when to trigger the gulper autonomously? For example, scientists interested in studying the mobilization and transport of shelf sediments would like to detect intermediate nepheloïd layers (INLs). To be able to detect this phenomenon we need to extract a model based on AUV sensors that can detect this feature in-situ. The formation of such a model is not obvious as identification of this feature is generally based on data from multiple sensors. We have developed an unsupervised data clustering technique to extract the different features which will then be used for on-board classification and triggering of the Gulper. We use a three phase approach: 1) use data from past missions to learn the different classes of data from sensor inputs. The clustering algorithm will then extract the set of features that can be distinguished within this large data set. 2) Scientists on shore then identify these features and point out which correspond to those of interest (e.g. nepheloïd layer, upwelling material etc) 3) Embed the corresponding classifier into the AUV control system to indicate the most probable feature of the water depending on sensory input. The triggering algorithm looks to this result and triggers the Gulper if the classifier indicates that we are within the feature of interest with a predetermined threshold of confidence. We have deployed this method of online classification and sampling based on AUV depth and HOBI Labs Hydroscat-2 sensor data. Using approximately 20,000 data samples the clustering algorithm generated 14 clusters with one identified as corresponding to a nepheloïd layer. We demonstrate that such a technique can be used to reliably and efficiently sample water based on multiple sources of data in real-time.
OS51B-0473
Using a Towed Vehicle to Identify Oceanographic Features: Triaxus Onboard the R/V Point Sur
Using a Towed Vehicle to Identify Oceanographic Features: Triaxus Onboard the R/V Point Sur Scientific demand to sample macro and micro scale dynamic processes in near coastal and open ocean environments by means of a single medium have furthered technological advances in towed undulating vehicles. One of the newer towed vehicles available to researchers using UNOLS vessels is the Triaxus. This vehicle has a large payload capacity, can be towed at relatively fast speeds (up to 8 knots), and can provide power to user supplied instruments. The Triaxus has been deployed from the R/V Point Sur and other vessels to effectively identify a variety of oceanographic features. Some of these features include: plume front propagation, locating and examining micro scale mixing events, illustration of mixed layer restratification in the presence of strong lateral density gradients, as well as the mapping of 3-dimensional variability of various aspects of the water column. In this work we present preliminary Triaxus tow data collected throughout a range of investigations utilizing an assortment of instrumentation to demonstrate the ability and effectiveness of this vehicle to identify and investigate a wide range of oceanographic features. http://marineops.mlml.calstate.edu/ptsur.html
OS51B-0474
Recent Advances in Deep-Sea in situ Geochemical Measurements by ROV Deployed Laser Raman Spectroscopy.
Raman spectroscopy is a valuable analytical technique for making in situ geochemical measurements. It is applicable to liquids, solids and gases; requires little or no sample preparation; and is rapid with typical analysis times of several minutes or less. These features combine to make it an ideal technique for deployment and use on remotely operated vehicles in a variety of applications. We report results from our second generation laser Raman spectrometer (DORISS2), developed in conjunction with Kaiser Optical Systems, Inc., which is both lighter and more robust than the original design. Packaged within a single titanium pressure housing rated to 4000m, DORISS2 has a floating optical bench which minimizes misalignments and preserves instrument calibration both during and between dives. The pressure compensated fiber optic cables have improved signal strength from 8% to 88% at 1024 m greatly reducing the time required to acquire a sample spectrum and allowing the detection of lower concentrations of trace components. Development of the precision underwater positioner (PUP) has enabled the spectroscopic analysis of opaque targets where a focusing precision of +/- 0.1 mm is required. This has allowed us to investigate the composition of authigenic minerals (such as hydrothermal vent precipitates) and gas hydrates in their native and undisturbed condition, such as the massive outcrops on the seafloor at Barkley Canyon, or to inspect the fine-scale inhomogeneities that occur in seafloor synthesis experiments conducted in Monterey Bay. The recent development of a single axis positioner (SAP) has allowed us to use DORISS2 when payload weight is an issue, in places where the seafloor is too steep to safely deploy PUP, or where operational conditions (such as an overhanging ledge) are too restrictive and where PUP does not fit. The SAP adds a new degree of flexibility we have not previously had and has even permitted the analysis of scale carotenoids in a live rock fish with no apparent harm to the organism.
OS51B-0475
Reconstruction of Coastal-Scale Ocean Fields in an Upwelling Region
Coastal upwelling is an ecologically important ocean process. In this presentation, we first extract the upwelling mode in Monterey Bay from satellite and aircraft sea surface temperature (SST) measurements during the AOSN II Experiment in August 2003. Then we evaluate autonomous underwater vehicles' (AUVs') capability of capturing the upwelling mode and reconstructing the ocean field. The upwelling mode features colder water at the upwelling centers at Cape Ano Nuevo and Point Sur. Its amplitude correlates well with the oceanic upwelling index (based on wind stress measurement). The upwelling mode accounts for 56% of the total variance, hence is by far the principal mode. Surface temperature measurements made by Dorado, Spray, and Slocum AUVs constituted a data set independent of the satellite & aircraft SST data set. One metric to evaluate the AUVs' survey performance is how much of the upwelling mode they captured. Using the AUVs' SST data only, we estimate the upwelling mode's amplitude. It closely tracks the upwelling mode's amplitude estimated by satellite & aircraft SST, and also correlates quite well with the upwelling index, up to August 24. For the last week in August, the correlations decrease considerably, which we think is due to the AUVs' larger distances from the upwelling centers. This study reveals the upwelling mode from SST measurements, and also provides insight to improving AUVs' surveys for capturing ocean processes.