Detection of false AIS messages for the improvement of maritime situational awareness

International audienceThe Automatic Identification System (AIS) was initially designed for safety and security of navigation purposes. However it was progressively also used for other objectives, such as surveillance, and thus led to the discovery of behaviors such as the falsification of the AIS messages by people that have been carrying out illegal activities and will to keep their activities up in an hidden way. In addition, the messages contain erroneous data and undergo spoofing attacks. The paper introduces the quality dimensions of data that shall be used in a quality assessment of AIS messages, in order to point out the dubious ones. The principles of a methodological approach for the detection of such data errors and falsifications are introduced

Data Quality Assessment for Maritime Situation Awareness

International audienceThe Automatic Identification System (AIS) initially designed to ensure maritime security through continuous position reports has been progressively used for many extended objectives. In particular it supports a global monitoring of the maritime domain for various purposes like safety and security but also traffic management, logistics or protection of strategic areas, etc. In this monitoring, data errors, misuse, irregular behaviours at sea, malfeasance mechanisms and bad navigation practices have inevitably emerged either by inattentiveness or voluntary actions in order to circumvent, alter or exploit such a system in the interests of offenders. This paper introduces the AIS system and presents vulnerabilities and data quality assessment for decision making in maritime situational awareness cases. The principles of a novel methodological approach for modelling, analysing and detecting these data errors and falsification are introduced

Accounts from a Claims Reuse Experience: Design of an Airline Fares Tracker

Previous research efforts have led to the establishment of a repository of claims as reusable knowledge entities. Through the analysis, design, and prototyping of a notification system aimed at monitoring airfares across time, airlines, and location, this paper presents the various work-products resulting from a scenario-based design approach coupled with the Claims Reuse Library to support reuse-centric claims analysis. Finally, we share our experience and findings using the Claims Reuse Library as a core to knowledge transfer

Design of freeform diffraction gratings: performance, limitations and potential applications

Spectroscopy is a key technique in astronomy and nowadays most major telescopes include at least one spectrograph in their instrument suite. The dispersive element is one of the most important components and it defines the pupil size, spectral resolution and efficiency. Different types of dispersive elements have been developed including prisms, grisms, VPH and echelle gratings. In this paper, we investigate the design and optimization possibilities offered by metallic freeform gratings using diamond machining techniques. The incorporation of power in a diffraction grating enables several functionalities within the same optical component, such as the combination of dispersion, focusing and field reformat. The resulting benefit is a reduction in the number of surfaces and therefore, an improvement in the throughput. Freeform surfaces are also interesting for their enhanced optical performance by allowing extra degree of freedom in the optimization. These degrees of freedom include the shape of the substrate but also additional parameters such as the pitch or the number of blaze angle. Freeform gratings used as single optical component systems also present some limitations such as the trade-off between optical quality versus field of view or the spectral range versus spectral resolution. This paper discusses the possibility offered by the design of freeform gratings for low to medium spectral resolution, in the visible and near-infrared, for potential applications in ultra-compact integral field spectrographs

Maritime monitoring

The maritime environment still represents an unexploited potential for modelling, management and understanding of mobility data. The environment is diverse, open but partly ruled, and covers a large spectrum of ships from small sailing-boats to super tankers which generally exhibit type-related behaviours. Similarly to terrestrial or aerial domains, several real-time positioning systems, such as the Automatic Identification System (AIS), have been developed for keeping track of vessel movements. However the huge amounts of data provided by these reporting systems are rarely used for knowledge discovery. This chapter aims at discussing different aspects of maritime mobilities understanding. This chapter enables readers to, first, understand the intrinsic behaviour of maritime positioning systems and then proposes a methodology to illustrate the different steps leading to trajectory patterns for the understanding of outlier detection

The HR image slicer for GNIRS at Gemini North: optical design and performance

GNIRS (Gemini Near-InfraRed Spectrograph) is a multi-function spectrograph at Gemini North telescope offering four observational modes in the spectral range of 0.8 to 5.4 µm. It provides 2-pixel spectral resolutions from 1,200 up to 18,0000 and has single disperser and cross-disperser modes yielding simultaneous spectral bandwidths from 40 nm to 1,650 nm. GNIRS presented three existing modes: long-slit (50-100" slit), cross-dispersed (5-7" slit) and low resolution (LR) Integral Field Unit (IFU) (3.15" x 4.80") and it is now being upgraded with a fourth mode allowing high resolution (HR) IFU spectroscopy using an image slicer optimised for fully adaptively corrected images over a field of view of 2.25 arcsec2 (1.80" x 1.25") covered by 25 slices of 410 µm width offering a spatial sampling of 0.05 x 0.05 arscec2 with a diffraction limited optical quality. The proposed layout meets specifications and some challenging design constraints: it shall be contained within the same envelope defined by the LR image slicer (0.1 x 0.2 x 0.1 m3 ), the input and output focal-ratios of both image slicers shall be the same and at exact positions but providing different anamorphic magnifications and preserving the optical quality. The length of the generated slit will be similar to the length of the slit in long-slit mode to maximise detector use and avoid vignetting. This communication presents the optical design and performance of the high resolution image slicer compliant with all specifications and constraints and it shows some design adaptations adopted in order to facilitate its manufacturing in metal at Durham University

Efficient AIS Data Processing for Environmentally Safe Shipping

Reducing ship accidents at sea is important to all economic, environmental, and cultural sectors of Greece. Despite an increase in traffic and national monitoring, ships formulate routes according to their best judgment risking an accident. In this study we take a dataset spanning in 3 years from the AIS (Automatic Identification System) network, which is transmitting in public a ship's identity and location with an interval of seconds, and we load it in a trajectory database supported by the Hermes Moving Objects Database (MOD) system. Presented analysis begins by extracting statistics for the dataset, both general (number of ships and position reports) as well as safety related ones. Simple queries on the dataset illustrate the capabilities of Hermes and allow to gain insight on how the ships move in the Greek Seas. Analysis of movement based on an Origin-Destination matrix between interesting areas in the Greek territory is presented. One of the newest challenges that emerged during this process is that the amount of the positioning data is becoming more and more massive. As a conclusion, a preliminary review of possible solutions to this challenge along with others such as dealing with the noise in AIS data is mentioned and we also briefly discuss the need for interdisciplinary cooperation.This research was partially supported by AMINESS project funded by the Greek government (www.aminess.eu). Cyril Ray was supported by a Short Term Scientific Mission performed at the University of Piraeus by the COST Action IC0903 on “Knowledge Discovery from Moving Objects” (http://www.move-cost.info). IMIS Hellas (www.imishel las.gr) kindly provided the AIS dataset for research purposes

Traitement continu des requêtes dépendantes de la localisation dans des environnements intérieurs

Cet article développe une représentation de données spatiales d’un environnement intérieur dit “indoor” qui tient compte des dimensions contextuelles centrées sur l’utilisateur et aborde les enjeux de gestion de données mobiles. Un modèle de données “indoor” hiérarchique et sensible au contexte est proposé. Cette conception hiérarchique favorise un traitement adaptatif et efficace des requêtes dépendantes de la localisation. Un langage de requêtes continues est développé et illustré par des exemples de requêtes. Cette approche de modélisation est complétée par le développement d’algorithmes de traitement continu des requêtes de recherche de chemin hiérarchique et des requêtes de zone sur des objets mobiles en “indoor”. Une étude expérimentale des solutions développées a été menée pour évaluer la performance et le passage à l’échelle à l’égard des propriétés intrinsèques des solutions proposées