Activación de las emociones durante la interacción del proceso aprendizaje-enseñanza

Measurement, or observation, of ship traffic is required in order to quantify the statistics to complete the model from the previous section. Quantitative measurement of ship dynamic response and performance has been an integral part of sea-trials and design verification. The effort by the IMO to improve the maneuvering performance by standard requirements led to the installation of position reference systems of adequate accuracy during sea-trials making performance data available as in the case of the Esso Osaka and Esso Bernica.

2.2. MEASUREMENT OF SHIP TRAFFIC 23

Figure 2.1.1: The simple model for a single traffic-pattern with straight sections intercon- nected by circular turn sections shown in bold. The statistical variables are shown on the vessel imprints along the traffic-pattern.

GPS introduced a standardized measurement source for the ship position, and has become an integral part of the on-board navigational equipment. The deployment of positioning systems on ship has been focused on determining the ships position for use in navigation with the possibility to record the data for later use. The availability of high accuracy GPS implementations has brought increased accuracy to the measurement of ship traffic, but GPS in isolation has had little impact on the quantification of traffic as the measurements are isolated to a single ship. The autonomous nature of ships implies that a large effort to collect data recording devices would have been required in order to rely solely on the GPS reference system to produce a coherent data of regional ship traffic. There are two distinct system architectures for observation of ship traffic, centralized observation (remote sensing) and distributed collection of local measurements. This distinction is seen in Figure 2.2.1 where distributed collection is represented by AIS. AIS has the potential to solve the problem of collecting position logs from different vessels but will degrade the accuracy of the GPS measurements due to the limited payload in a singe AIS message. Another distinction between these two collection regimes lines in the effort required to accommodate the observer. A centralized observation relies on querying every ship for its position whereas the distributed approach accommodates the observer by listening to the ongoing exchange of messages.

2.2.1

Purpose built systems

The alternative to a systematic collection of GPS position logs has been to construct shore- based measurement systems to remotely determine and track the position of vessels. Such systems have been constructed using infra-red closed circuit TV (CCTV) (Gluver and Olsen, 2001), radar (Pedersen, 2002; Yao et al., 2010) and laser range finding (Zalewski and Montewka, 2007; Gucma and Montewka, 2005). Purpose built monitoring systems were long the only reasonable alternative for shore-based traffic measurement. The ad- ditional hardware required for these systems require investment in equipment and time. The accuracy of purpose built systems can be as good as the hardware allows, with laser based range-finding the most accurate but the drawback are the required investment, the

(a) Basic architecture of remote monitoring of ship traffic by a centralized observer. The quality of the measurement data depends on the observer and the technical abilities of the system obtain accurate measurements at a distance.

(b) Autonomous exchange of AIS transmis- sions between vessels, there is no significant difference between an observer and a vessel which is observed.

Figure 2.2.1: The different architectures between central observation of ship traffic and distributed measurements broadcasted over AIS

temporary nature of the installation, the sensitivity to prevailing weather conditions but more importantly the centralized nature of the systems.

The underlying architecture of purpose built systems are that of a centralized observer as seen in Figure 2.2.1a. The observer must classify the objects in the area, observe the state (position) of objects and record them. This system architecture place several functions at the observer in addition to the pure record keeping function. This system architecture has an impact on both the quality and quantity of measurements available form these systems. The infrared CCTV is limited by the resolution of the CCTV signal which has implications for the resolution of the position estimate. Observations form laser range finding will give high-fidelity measurements of speed and position, but is limited by visual conditions and the number of objects required to be observed simultaneously. Radar is the most robust of these techniques as it allows observation of all the objects in range but is also the most expensive. The accuracy of radar is highly dependent on the type of radar in use and the range to the object of interest and a direct recording of the radar output is a technical challenge, and also subject to stringent access controls (Yao et al., 2010). All the systems described previously are based on direct observations and can have issues with coverage due to the local topography.

2.2.2

The automatic identification system

The automatic identification system (AIS) for ships was introduced to augment radar ob- servations with broadcasted vessel positions unaffected by local radar shadows. Radar was long the primary information source of the position of other vessels, while electronic and celestial navigation provided the global position of the local ship. The quality of the local position service was greatly increased with the introduction of GPS while the qual- ity of position information of other vessels continued to be determined by the capabilities

2.3. DATA COLLECTION, PROCESSING AND RECONSTRUCTION 25