No abstract

The Automatic Identification System (AIS) is now well established and widely used in commercial shipping. The system originated from a safety mandate but AIS messages have also been shown to be useful from a security situational awareness perspective. In terms of coastal security, AIS messages are often received by land-based receivers positioned along a nation's coastline. The operational range of the receivers is controlled by complex variable VHF propagation characteristics, power of the transmitter, etc. However, certain characteristics of the reception coverage area can be determined from the AIS message receptions themselves. This paper presents an algorithm to compute coverage characteristics using AIS messages. The algorithm is applied to synthetic data with known coverage characteristics, and also real AIS data obtained from the Maritime Safety and Security Information System. Results from the Norwegian, North and Baltic Seas show how the coverage estimate is influenced by the coverage edge, lack of vessel activity, and diversity in the source data.

Analysis of 39 satellite-tracked drifter records from the Newfoundland Grand Banks region has allowed maps of the mean and variable flows to be drawn. The variable currents are particularly large relative to the mean for the shelf, Flemish Cap and in the Newfoundland Basin. The ratio of the mean to variable flow is largest along the path of the Labrador Current. Drifters that either have been released on or migrate onto the Grand Banks remain therefor an average of 71 d. A statistical study of the effect of wind on drifter motion has shown that winds can only account for about 10% of current variability. This result is examined with consideration given to data noise, aliasing and non-stationary conditions. Some drifters that were deployed in the Labrador Current moved onto the shelf and vice versa. These observations have been used to estimate the rate of exchange between the Current and the Grand Banks. Using this exchange rate in a box model, it is calculated that, over the iceberg season, 30% of the bergs will be in the Avalon Channel, 20% on the Grand Banks and 50% in the Labrador Current, in good agreement with the observed distribution. An alternative model based solely on advection is considered as well. The exchange model is also applied to the salinity budget for the Labrador Current with some success. RÉSUMÉ L'étude de 39 relevés provenant de dériveurs suivis par satellite dans la région des Grands bancs de Terre-Neuve a permis de dresser des cartes représentant le courant moyen et ses variabilités. L'intensité des courants variables de la plate-forme continentale, du bonnet flamand et du bassin de Terre-neuve est supérieure à la moyenne. Le rapport entre courant moyen et courant variable est plus important le long de la trajectoire du courant du Labrador. Les dériveurs qu'on rencontre dans la région des Grands bancs y passent en moyenne 71 jours. Une étude statistique de l'effet du vent sur le mouvement des dériveurs a indiqué qu'environ 10 % seulement de la variabilité des courants sont attribuables aux vents. Au moment de l'analyse de ce résultant, on a tenu compte des bruits aléatoires, des problèmes de sous-échantillonnage dans le temps et des conditions non stationnaires. Certains dériveurs du courant du Labrador se sont rendus sur la plate-forme continentale et d'autres ont fait le mouvement inverse. Ces observations ont permis d'estimer le taux d'échange entre le courant et les Grands bancs. En utilisant ce taux d'échange dans le cadre d'un modèle systématique (box model), on calcule que pendant la saison des icebergs, 30 % d'entre eux se trouveront dans le chenal d'Avalon, 20 % sur les Grands bancs et 50 % dans le courant du Labrador, ce qui concorde bien avec la répartition observée. On a également tenu compte d'un autre ATMOSPHERE-OCEAN 23 (3) 1985, 209-227 0705-5900/85/0000-0209S01.25/0 © Canadian Meteorological and Oceanographic Society Downloaded by [5.101.220.201] at 22:50 04 June 2016 210 / Brian Pétrie and Anthony Isenor modèle, basé uniquement sur l'advecticn. Le modèle de Véchange per...

No abstract