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Data/Event Type | Average Latency (between start time and when it appears in Skylight) |
|---|---|
AIS positions & Last Known Position | Majority within minutes (see here for more detail) |
Entry Events | 1 hour |
Standard Rendezvous | 1 hour |
Vessel Detections from Night Lights | 2 hours |
Vessel Detections from Sentinel-1 Satellite Radar | 3-6 hours |
Vessel Detections from Sentinel-2 Optical Imagery | 3-6 hours |
Dark Rendezvous | 4 hours |
Fishing | 6 hours |
Last Known Positions: computed in real time and displayed in Skylight within a few minutes of receiving AIS transmissions from that vessel
Entry Events: these are computed in near real time. Internal processing of AIS data will delay the display of entries within Skylight on average by 1 hour. However, the rate of latency can vary and may be as high as almost 6-hours. The event start time will always reflect the time when the event started, not when it was first displayed in Skylight.
Tracks: these are computed in real-time, but if vessels are traveling at roughly the same speed and same heading since the last ping, then a new track segment will not display until one of those elements changes
Note: Last known position (#1) will always update
Standard Rendezvous: the algorithm requires the vessels to be together for at least 30 minutes. Internal processing of AIS data will delay the display of Standard Rendezvous within Skylight on average by 1 hour. However, the rate of latency can vary and may be as high as almost 6-hours. The event start time will always reflect the time when the event started, not when it was first displayed in Skylight.
Night Lights Detections have delays on average of 2 hours.
Satellite Radar Detections have delays of several hours. See subpages for details:
SENTINEL-1 (average of 3-6 hours)
Dark Rendezvous: the model requires at least 15 minutes of rendezvous activity. However, the internal processing of AIS data for dark rendezvous has a latency of a little more than 4-hours on average. (Note, the rate of latency can vary and may be as high as 7-hours). The event start time will always reflect the time when the event started, not when it was first displayed in Skylight.
Fishing: in general, the event is displayed in Skylight as soon as it’s generated. However, the internal processing of AIS data for fishing events has a latency of almost 6-hours on average. (Note, the rate of latency can vary and may be as high as 7-hours). The event start time will always reflect the time when the event started, not when it was first displayed in Skylight.
Potential Dark Activity: the algorithm requires no AIS transmissions for 6 or 18 hours (depending on the Transmission class). Internal processing of AIS data will delay the display of Potential Dark Activity within Skylight on average by 1 hour. However, the rate of latency can vary and may be as high as almost 6-hours. The event start time will always reflect the time when the event started, not when it was first displayed in Skylight.
Port Visits: these are updated once daily, so there can be up to a 24 hour delay.
AIS Delays from Spire
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Spire’s AIS feed is not always real-time particularly when collected by their satellite receivers. For their whole feed (including terrestrial data), 99% of data comes within minutes/1 hour. However when we look at data from satellite receivers, a significant amount (>30%) is received more than 1 hour later.
Below is more detail from Spire as of March 2024 about messages picked up by their satellite receivers, using an arbitrary time interval (20-27 February, 2024) , and looking at latency between timestamp and our ingestion time.
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97.55% of all messages are ingested in 6 hours after AIS message is transmitted
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0.26% of messages are delivered between 1-2 days latency and no message is delivered later than 2 days in this time frame.
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Median latency was 45 minutes & 95th percentile
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was under 4 hours.
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