Chokepoint transits
Analyze vessel movement through four maritime chokepoints with AIS evidence, and understand the non-confirming Sentinel-1 catalog boundary.
Axiom Overwatch uses AIS positions and corridor geometry to analyze vessel movement through four maritime chokepoints: Bab-el-Mandeb, the Strait of Hormuz, the southern Suez approaches, and Cape Agulhas.
The supported confirmation posture is AIS-only. Overwatch can also query the Copernicus Sentinel-1 catalog to learn whether radar imagery may exist near a place and time, but a catalog result does not identify a vessel, process image pixels, or confirm a transit.
Do not treat SAR catalog coverage as evidence that a vessel crossed a corridor. Pixel detection and AIS-to-SAR confirmation are not part of the supported production workflow.
When to use this
Use chokepoint analysis to:
- Review AIS-observed approaches and passages through a named corridor.
- Compare a vessel's projected route with later AIS positions.
- Investigate stale or missing AIS while keeping the evidentiary gap explicit.
- Check whether Sentinel-1 products may exist for an independent imagery workflow.
For vessel-level routing without corridor semantics, use Route forecasts. For catalog availability near one location and time, use the SAR coverage API.
Current operating boundary
| Capability | Current documentation contract |
|---|---|
| AIS position and route evidence | Supported. Use observed positions and route forecasts to reason about a vessel's movement. |
| Chokepoint corridor geometry | Supported for the four configured corridors on this page. |
| AIS-based transit conclusion | Supported when the conclusion is backed by AIS evidence. |
| Sentinel-1 catalog lookup | Supported through the authenticated SAR coverage endpoint. It reports product availability and timing metadata. |
| Radar pixel detection | Not a supported production capability. |
| Automatic AIS-to-SAR vessel match | Not a supported production capability. |
| SAR-confirmed or SAR-only dark transit | Do not claim from the current product surface. |
The chokepoints
| Corridor key | Name | Analytical boundary |
|---|---|---|
bab-el-mandeb | Bab-el-Mandeb / Red Sea South | Strait between Yemen and Djibouti, connecting the Gulf of Aden and Red Sea. |
hormuz | Strait of Hormuz / Northern Gulf | Passage between the Persian Gulf and Gulf of Oman. |
suez-s | Southern Suez approaches / Red Sea North | Southern approach to the canal; surface analysis does not imply coverage inside the land-locked canal. |
cape-agulhas | Cape Agulhas / Southern Africa | Atlantic–Indian Ocean rounding corridor used for detour analysis. |
Each corridor has an analysis polygon plus approach and exit geometry. A projected path can indicate that a vessel is likely to enter a corridor; later AIS positions provide the evidence for whether the vessel was observed continuing through it.
AIS analysis workflow
Start with recent AIS
Confirm that the vessel has a recent position, course, and speed. A stale, stationary, or heading-less position cannot support a reliable forward projection.
Project the route
Use the vessel's latest AIS state and route forecast to evaluate whether its path intersects a configured chokepoint.
Watch for observed positions
Compare the projected approach with later AIS positions in or beyond the corridor. Keep the projection and observation timestamps separate.
State the evidence
Describe an observed transit only when AIS supports it. If the vessel stops reporting, record an AIS gap rather than upgrading the gap to a radar-confirmed or dark transit.
Using Sentinel-1 catalog coverage
The SAR coverage endpoint accepts a location, time, and radius, then queries the Copernicus catalog for matching Sentinel-1 products. Its response can answer questions such as:
- Did the catalog return a product near this place and time?
- When was the closest cataloged pass?
- Is the product listed as online?
- How strong is the timing-and-coverage potential for a separate investigation?
It cannot answer:
- Which vessel appears in an image.
- Whether any ship-like pixel exists.
- Whether a cataloged product was downloaded or processed.
- Whether an AIS gap is a sanctions-evasion event.
- Whether a vessel completed a chokepoint transit.
The repository contains readiness-oriented SAR code and data structures, including a default-disabled monitor and an unavailable detector scaffold. Their presence is not launch evidence. Re-verify feature configuration, processing, and reviewed precision evidence before documenting any future SAR confirmation capability.
Interpret missing AIS carefully
An AIS gap is an absence of expected position reports, not proof of concealment. Weather, terrestrial receiver coverage, equipment state, congestion, and operational behavior can all affect reporting.
When the evidence is incomplete:
- Preserve the last observed AIS position and timestamp.
- Keep route projections labeled as projections.
- Use other Overwatch signals as corroborating context, not as a substitute observation.
- Treat catalog coverage as a pointer for independent imagery analysis.
- Avoid assigning a vessel identity to radar imagery without a separately validated detection and matching workflow.
Continue with AIS coverage, Route forecasts, and the SAR coverage API.
Route forecasts
Per-vessel ETA distributions and great-circle waypoint sequences for vessels in transit — methodology behind Overwatch expected arrivals and route maps.
Pairwise encounter extraction
How Axiom Overwatch detects vessel-to-vessel encounters from AIS and produces per-pair, per-timestep CPA, TCPA, and risk geometry.