Skylight receives mostly real-time AIS data from SPIRE and near-real-time data from satellite radar satellites. Some elements need little manipulation before they are displayed in the platform which creates minimal delay. Others can have added delay because of processing requirements.
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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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99.74% are transmitted within a day
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time
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Median latency
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was 45 minutes & 95th percentile
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was under 4 hours.
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