Overview

A Speed Range Event identifies AIS-transmitting vessels traveling within a specific range of speed (e.g., 1-4 knots). The vessel must keep that speed for a certain distance or time. These events are dependent on having a defined Area of Interest. 

Speed Range Events will start generating from the time of configuration (it is not possible to generate historical data retroactively).

Why Use This? 

• To monitor areas with high-speed restrictions to prevent vessel strikes into whales and other marine mammals (e.g. vessel speed rules on the US East Coast for the protection of North Atlantic Right Whales)
• To monitor possible anchoring around reefs or other zones where vessels should not be stopped
• As a proxy for fishing behavior in lieu of/in addition to Fishing Events 
  • In some areas Fishing Events do not capture the fishing activities on AIS desired by the user because the AI model was not trained on the tracks that represent these behavior in that area. 

Algorithm

The algorithm to detect vessels traveling within certain speeds is configured by the user. There are two approaches, by time or distance.

The first step is to determine the speed of interest (e.g., certain fishing behaviors may occur between 1-4 knots.). The second step is to determine the duration of the observed speed 

• By distance - nautical miles (nm), kilometers (km) or miles (mi). 
• By time - hours or minutes

A Speed Range event will end when the vessel breaks the range. This is determined by calculating a rolling average for the last X minutes or distance (same parameter as what was set for the event) and monitoring when the average falls outside of the defined range. This approach ensures events are not ended too early by an anomalous movement, and that events also do not go on forever when the vessel has significantly altered its speed behavior. 

In the examples above, the Speed Range events would lapse when 

• The average speed for the last 2 NM falls outside 1-4 knots
• The average speed for the last 30 minutes falls outside 1-4 knots

Event Details

Standard information

Vessels' information - name, MMSI, Type based on AIS data, IMO, Length based on AIS data

Date and time of the event

Location (lat/lon)

Event history - number of times Skylight has detected this behavior from this vessel

Additional information

Defined Speed Range - The user-configured speed range and duration (time/distance) (e.g., 2-5 knots for at least 1nm)

Average Speed Range - The average speed of vessel, and how long the vessel was observed, within the specified range of speed (e.g., 2.2 knots for 1 hour, 22 minutes)

Area - The name of the relevant Area of Interest

Latency

Speed range events are computed in real time and may be available in just a few minutes following the time conditions are met (i.e., a vessel observed traveling within a speed range for a certain duration) depending on AIS signal. 

Average latency is 1 hour.