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How does Skylight determine the identity of a vessel detection?
When viewing vessel detections in Skylight, you’ll note that some are labeled “AIS Correlated Vessel Detection” while others are “Dark Vessel Detection”.
Using an algorithm, Skylight matches AIS points with vessel detections to identify and display vessel metadata information for any vessel that can be matched or ‘correlated’ with AIS. If there are no AIS points near the detection, it’s considered a Dark Vessel Detection and no vessel metadata is displayed .
In the below illustration, 1 and 3 are vessel detections and 2 is an AIS point. The Skylight correlation algorithm has determined the AIS point 2 was likely transmitted by the vessel in detection 1. Detection 1 is labeled AIS Correlated Detection and the vessel data available from AIS is displayed.
There is no AIS ping near detection 3 so the Skylight algorithm labels that detection “Dark Vessel Detection” and no additional vessel data is displayed.
(Skylight is contractually prohibited from sharing raw AIS points. Therefore, we do not display AIS point transmissions as shown above within Skylight.)
The Skylight correlation process searches over a circle centered on each vessel detection for overlaps. All intersecting segments from every vessel’s search radius will be used to compute all predicted vessel positions. AIS pings from vessels further than 1500 meters from the location of a vessel detection are disregarded as possible matches.
Why would a detection be labeled ‘Dark’ and then later be correlated?
As a near real-time system, Skylight displays the most up-to-date information available at the time. Sometimes additional updated AIS data is received or internal Skylight processes are completed after vessels are detected in our non-AIS sources. As a result, Skylight may learn There are two primary reasons this happens:
More AIS data is received after Skylight already checked for AIS tracks in the vicinity of the detection
Skylight uses track “segments” rather than individual AIS pings to look for AIS vessels in the vicinity of a detection. Because of the way track “segments” are generated, sometimes it takes longer for a track segment to appear near the detection.
If Skylight learns that a detection previously marked as ‘dark’ “dark” can be correlated . Skylight will display the detection as soon as it’s available and update the correlation status as additional information is available.
There may be instances in Skylight when a vessel event is displayed and a nearby Night Lights detection displays as dark. Skylight reruns the correlation service every 24 hours to attempt to identify any dark detections that can now be identified with updated AIS data.
It is very rare for the opposite scenario to occur: for previously correlated detections to be updated to darkdue to one of the above reasons, it will try to update that correlation. Skylight checks for updated AIS data in the vicinity of dark vessels every 24 hours. Because Skylight is focused on displaying information as near real time as possible, it processes the image to identify vessels as soon as possible, even if it means that some of those dark detections may be possible to correlate with AIS over time. For this reason, we always recommend checking dark detections in Skylight with data you have in other tools (e.g. AIS data from other tools, VMS, radar).