Time filter

Source Type

Kongsberg, Norway

This work explores the potential for extending tide gauge time series from the Permanent Service for Mean Sea Level (PSMSL) using historical documents, PSMSL ancillary data, and by developing additional composite time series using near neighbor tide gauges. The aim was to increase the number, completeness, and geographical extent of records covering most or all of the twentieth century. The number of at least 75% complete century-scale time series have been approximately doubled over the original PSMSL data set. In total, over 4800 station years have been added, with 294 of these added to 10 long Southern Hemisphere records. Individual century-scale acceleration values derived from this new extended data set tend to converge on a value of 0.01±0.008 mm/yr2. This result agrees closely with recent work and is statistically significant at the 1 sigma level. Possible causes of acceleration and errors are briefly discussed. Results confirm the importance of current data archeology projects involving digitization of the remaining archives of hard copy tide gauge data for sea level and climate studies. © 2014. American Geophysical Union. All Rights Reserved. Source

Sabetzadeh M.,Certus Software v and v Center | Nejati S.,Certus Software v and v Center | Briand L.,Certus Software v and v Center | Mills A.-H.E.,Kongsberg Maritime
Proceedings of IEEE International Symposium on High Assurance Systems Engineering | Year: 2011

Safety-critical embedded systems often need to undergo a rigorous certification process to ensure that the safety risks associated with the use of the systems are adequately mitigated. Interfaces between software and hardware components (SW/HW interfaces) play a fundamental role in these systems by linking the systems' control software to either the physical hardware components or to a hardware abstraction layer. Subsequently, safety certification of embedded systems necessarily has to cover the SW/HW interfaces used in these systems. In this paper, we describe a Model Driven Engineering (MDE) approach based on the SysML language, targeted at facilitating the certification of SW/HW interfaces in embedded systems. Our work draws on our experience with maritime and energy systems, but the work should also apply to a broader set of domains, e.g., the automotive sector, where similar design principles are used for (SW/HW) interface design. Our approach leverages our previous work on the development of SysML-based modeling and analysis techniques for safety-critical systems [4]. Specifically, we tailor the methodology developed in our previous work to the development of safety-critical interfaces, and provide step-bystep and practical guidelines aimed at providing the evidence necessary for arguing that the safety-related requirements of an interface are properly addressed by its design. We describe an application of our proposed guidelines to a representative safety-critical interface in the maritime and energy domain. © 2011 IEEE. Source

Brekke E.,National University of Singapore | Hallingstad O.,University Graduate Center | Glattetre J.,Kongsberg Maritime
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

Tracking methods attempt to follow the movement of a target of interest while suppressing irrelevant clutter. A particularly troublesome source of clutter is wakes that appear behind the target. This problem arises in sonar tracking of human divers, in the tracking of boats using surveillance radars, and also in radar tracking of ballistic missiles. Previous research has integrated a solution to this problem in the popular probabilistic data association filter (PDAF). A new solution to this problem in the same framework is proposed here. While previous research has used an approach described as probabilistic editing, the new solution solves the wake problem in a Bayesian framework by means of marginalization. Monte-Carlo simulations show that the new solution provides significantly increased robustness as compared with both the standard PDAF and the probabilistic editing approach. As the new solution has improved theoretical underpinnings, we hope that it can be useful for further research on tracking in the presence of wake clutter. © 1965-2011 IEEE. Source

Brekke E.,Norwegian University of Science and Technology | Brekke E.,University Graduate Center | Hallingstad O.,Norwegian University of Science and Technology | Hallingstad O.,University Graduate Center | Glattetre J.,Kongsberg Maritime
IEEE Journal of Oceanic Engineering | Year: 2010

Harbor surveillance above and below the sea surface depends on sensors such as surveillance radar and multibeam sonar. These sensors attempt to detect and track moderately observable targets such as small boats or human divers in environments which often are characterized by heavy-tailed backgrounds. Target tracking in heavy-tailed environments is challenging even for moderate signal-to-noise ratios (SNRs) due to the increased frequency of target-like outliers. A tracking method operating in such an environment should exploit as much of the data as possible to ensure robustness. Still, conventional tracking methods rely on kinematic measurements such as range, bearing, and Doppler only. The performance of the tracking method can be improved by using the backscattered signal strengths together with the kinematic measurements. This is done in the probabilistic data association filter with amplitude information (PDAFAI). We propose new conservative amplitude likelihoods for the PDAFAI with improved robustness compared to existing methods. The first likelihood works by incorporating the uncertainty of the background estimate. The second likelihood explicitly treats the background as heavy tailed using the K-distribution. Extensive and realistic Monte Carlo simulations show that both our conservative likelihoods give significant reductions in track loss. Furthermore, we provide a quantitative evaluation of the difficulties encountered by tracking methods in heavy-tailed clutter. To the best of our knowledge, such an analysis does not yet exist in the open literature. © 2010 IEEE. Source

Naess A.,Norwegian University of Science and Technology | Stansberg C.T.,MARINTEK AS | Batsevych O.,Kongsberg Maritime
Journal of Offshore Mechanics and Arctic Engineering | Year: 2011

The paper presents a study of the extreme value statistics related to measurements on a scale model of a large tension leg platform (TLP) subjected to random waves in a wave basin. Extensive model tests were carried out in three irregular sea states. Time series of the motion responses and tether tension were recorded for a total of 18 three hour tests (full scale). In this paper we discuss the statistics of the measured tether tension. The focus is on a comparison of two alternative methods for the prediction of extreme tether tension from finite time series records. One method is based on expressing the extreme value distribution in terms of the average upcrossing rate (AUR). The other is a novel method that can account for statistical dependence in the recorded time series by utilizing a cascade of conditioning approximations obtained by defining the average conditional exceedance rates (ACER). Both methods rely on introducing a specific parametric form for the tail part of the extreme value distribution. This is combined with an optimization procedure to determine the parameters involved, which allows prediction of various extreme response levels. © 2012 American Society of Mechanical Engineers. Source

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