Preliminary Inter-comparison of AIS Data and Optimal Ship Tracks

Abstract

Optimal ship tracks computed via the VISIR model are compared to tracks recorded by the Automatic Identification System (AIS). The evaluation regards 43 tracks in the Southern Atlantic Ocean, sailed during 2016-2017 by different bulk carriers. In this exercise, VISIR is fed by wave analysis fields from the Copernicus Marine Environment Monitoring Service (CMEMS). In order to reproduce vessel speed loss in waves, a new methodology is developed, where kinematic information from AIS is fusioned with wave information from CMEMS. Resulting VISIR tracks are analyzed along with AIS tracks in terms of their topological features and duration. The tracks exhibit quite diverse topological shapes, including orthodromic, loxodromic, and other paths with complex and dynamic diversions. The distribution of AIS to VISIR track durations is analyzed in terms of several parameters, such as the AIS to VISIR track length and their Fréchet distance. Model features of VISIR affecting the results are discussed and future developments suggested by the results are outlined.

VISIR-1.b: ocean surface gravity waves and currents for energy-efficient navigation

“…However, advances in operational oceanography have revealed a high level of variability in the water flow at numerous spatial and temporal scales (Pinardi et al, 2015). This is indicated by ocean drifter data, which are also affected by wind (Maximenko et al, 2012), satellite altimetry, which just provides the geostrophic component of the currents (Pascual et al, 2006), and model computations, whose capacity to represent mesoscale variability depends on spatial discretisation along with other factors (Fu and Smith, 1996;Sandery and Sakov, 2017). More recently, even animal-borne measurements have been used to characterise ocean currents, particularly in the polar regions (Roquet et al, 2013).…”

In response to RC1

“…By computing both spatial and temporal discrepancies between VISIR and AIS tracks, we could infer that optimization likely took place in several but not all tracks. While the method by Mannarini et al (2019) is still in its infancy, we believe its extension to a larger statistics could contribute to shed light on questions like the one posed in this Referee's comment.…”

“…Nevertheless, we recently addressed this question by comparing VISIR optimal tracks vs. reported ship tracks per AIS (Automated Identification System) data, for a route in the Southern Ocean (Mannarini et al, 2019). By computing both spatial and temporal discrepancies between VISIR and AIS tracks, we could infer that optimization likely took place in several but not all tracks.…”

Graph-Search and Differential Equations for Time-Optimal Vessel Route Planning in Dynamic Ocean Waves

“…For open-sea navigation, which is well outside the zone where ship acceleration/deceleration transients usually occur, this is an acceptable approximation. A recent evaluation of time-optimal trajectories computed by VISIR and actually sailed trajectories in the Southern Atlantic Ocean was conducted in [72]. These preliminary results indicate that only part of the actually sailed trajectories are to some extent optimized.…”