Highlights• ML algorithms can classify water and sea ice characteristics in the coastal Arctic.• Spring freshet runoff over sea ice is optically distinct from surface melt ponds.• Time-series analyses of satellite ima...
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On ocean general circulation scales, vertical velocitywis extremely small, O(10−5) smaller than the horizontal velocity in scale. Nevertheless, it is of great importance to advective–diffusive and vorticity balances....
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On ocean general circulation scales, vertical velocitywis extremely small, O(10−5) smaller than the horizontal velocity in scale. Nevertheless, it is of great importance to advective–diffusive and vorticity balances. In order to better understand the relationship between the cross-isopycnal (diapycnal) velocity, the mixing, andw, in a nonideal ocean in which some mixing and density sources are present, the velocity vector is decomposed into isopycnal and diapycnal components. Applying this decomposition to the exact continuity (mass conservation) equation, it is shown that while the diapycnal divergence is in principle the first correction to the isopycnal divergence for general circulation scales, the observational uncertainties in the isopycnal velocity are large enough that the diapycnal divergence cannot in practice be determined. Using these results, the horizontally averaged near-vertical (diapycnal) velocity computed by Wunsch et al. in a model of the South Pacific (28–43°S) is reconsidered. It is shown that the calculation of diapycnal velocity from isopycnal mass convergence is not consistent with uncertainties in the isopycnal velocity and that the implied mixing cannot be accounted for with simple diffusion models and salt-fingering alone.
Reliable simultaneous localization and mapping (SLAM) algorithms are necessary for safety-critical autonomous navigation. In the communication-constrained multi-agent setting, navigation systems increasingly use point...
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Deep-sea agglutinated foraminifera have been quantitatively examined from 28 coretop samples from seven box cores collected in June, 1983, at the HEBBLE (High Energy Benthic Boundary Layer Experiment) Site (40°27...
Deep-sea agglutinated foraminifera have been quantitatively examined from 28 coretop samples from seven box cores collected in June, 1983, at the HEBBLE (High Energy Benthic Boundary Layer Experiment) Site (40°27′N, 62°20′W, 4815–4825 m depth) and HEBBLE Shallow Site (40°53′N, 63°44′W, 4185 m depth) on the Nova Scotian continental rise. Samples from the relatively tranquil HEBBLE Shallow Site can be distinguished from the HEBBLE Site on the basis of their microfauna. A Q-mode VARIMAX factor analysis of species-frequency data delineates three major faunal assemblages: 1. (1) A faunal assemblage from the HEBBLE Site dominated by Ammobaculties sp. cf. A. americanus. This assemblage exhibits lowest species diversity (suggesting a disturbed community) and strongly associated with box cores containing fine-grained, laminated sediments. 2. (2) An assemblage associated with box cores from the HEBBLE Meadow dominated by Saccammina tubulata, Psammosphaera sp., cf. P. fusca, a coarsely grained species of Psammosphaera and Reophax sp. 1. 3. (3) A fauna occurring at the HEBBLE Shallow Site, dominated by Hormosinella distans, with Reophax bacillaris and Ammobaculites agglutinans unique to the assemblage. This fauna displays a higher ratio of calcareous to agglutinated species, significantly higher species diversity, lower variability and a greater proportion of hormosinids and species utilizing finer grains than samples from the HEBBLE Site, which is interpreted as reflecting environmental stability. Marked heterogeneity exists among agglutinated foraminiferal assemblages within box cores. At the HEBBLE Meadow, within-box-core faunal variability exceeds between-box-core variability, suggesting that environmental factors influencing the distribution of species are patchy on a scale of approximately 40 cm.
Turbo equalizers have been exploited for underwater wireless communication due to their excellent practical performance. As the equalizer is adaptive, it is possible to take advantage of the soft information available...
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ISBN:
(纸本)9781467350518
Turbo equalizers have been exploited for underwater wireless communication due to their excellent practical performance. As the equalizer is adaptive, it is possible to take advantage of the soft information available from the decoder in the adaptation process. In this paper, we consider a method to do this and compare it with the use of soft information in feedback, which is a method that has been considered in the past. Data from the KAM11 experiment demonstrates that using soft information in adaptation can improve performance over using it only in feedback. We also consider combining these different approaches and how this affects performance.
In the context of three-row bathymetric sidescan sonars, a coherent source direction estimator (CSDE) is proposed to resolve two sources from different direction. This method is compared with the ESPRIT-based approach...
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In the context of three-row bathymetric sidescan sonars, a coherent source direction estimator (CSDE) is proposed to resolve two sources from different direction. This method is compared with the ESPRIT-based approach using different sonar models. The simulations show that CSDE works very well for highly coherent sources and at the signal-to-noise ratio above 10dB while the ESPRIT-based method is quite robust for the incoherent source signal model. In addition, CSDE gives the source time series estimation on the basis of the direction estimation as well.
Describes the development and verification of a six degree of freedom, non-linear simulation model for the REMUS AUV, the first such model for this platform. In this model, the external forces and moments resulting fr...
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Describes the development and verification of a six degree of freedom, non-linear simulation model for the REMUS AUV, the first such model for this platform. In this model, the external forces and moments resulting from hydrostatics, hydrodynamic lift and drag, added mass, and the control inputs of the vehicle propeller and fins are all defined in terms of vehicle coefficients. The paper briefly describes the derivation of these coefficients. The equations determining the coefficients, as well as those describing the vehicle rigid-body dynamics, are left in non-linear form to better simulate the inherently non-linear behavior of the vehicle. Simulation of the vehicle motion is achieved through numeric integration of the equations of motion. The simulator output is then verified against vehicle dynamics data collected in experiments performed at sea. The simulator is shown to accurately model the motion of the vehicle. The paper concludes with recommendations for future model validation experiments.
We present an integrated framework for joint estimation and pursuit of dynamic features in the ocean, over large spatial scales and with multiple collaborating vehicles relying on limited communications. Our approach ...
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We make two contributions toward integrated monitoring over large spatial scales, with multiple collaborating vehicles. Our focus is dynamic ocean features such as fronts and plumes. To support strong networked-contro...
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ISBN:
(纸本)9781467363563
We make two contributions toward integrated monitoring over large spatial scales, with multiple collaborating vehicles. Our focus is dynamic ocean features such as fronts and plumes. To support strong networked-control designs, we first develop a clean linear time-invariant framework for tracking features, that directly couples the global structure of the process to vehicle positioning. To address the packet loss inherent in underwater acoustic communications, we then extend the synthesis technique of Imer et al. [1] to the case where measurements and control commands suffer loss with differing statistics among the multiple channels. Simulations show that the integrated feedback system achieves good performance in front tracking.
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