Port blockade and commercial shipping denial monitoring

SAR vessel detection cross-referenced with AIS gaps reveals whether a declared naval blockade is holding. Berth occupancy, anchorage density and cargo-handling signatures complete the picture where transponders go dark.

Sensors

Sentinel-1 SAR (C-band, ESA): 5 x 20 m resolution in Interferometric Wide Swath mode, 250 km swath. Revisit of 6 days at the equator with a single satellite, 3 days with both; shorter over mid-latitudes due to orbit geometry. Detects vessels down to roughly 30 m length in calm sea states. Cloud-transparent and day/night capable. Free archive from 2014.
ICEYE SAR (X-band, commercial): Spotlight mode delivers approximately 0.5 m resolution; strip mode 3 m. Constellation of over 30 satellites as of 2024, enabling tasked revisit of under 1 hour over a specific target with scheduling. Detects smaller vessels than Sentinel-1 and resolves deck-level structure useful for ship-type classification.
Maxar WorldView-2 (optical, 0.46 m pan): Sub-half-metre panchromatic resolution resolves individual containers, crane positions and vehicle movements on quaysides. Confirms whether cargo-handling equipment is active. Dependent on cloud-free conditions; single-pass revisit over a given port is typically 1 to 3 days with tasking priority.
Planet Dove (optical, 3 m): Daily global revisit at 3 m resolution. Useful for tracking anchorage occupancy counts and detecting new arrivals between SAR passes, though vessel classification is limited at this resolution. Provides temporal density that higher-resolution assets cannot match economically.
AIS (Automatic Identification System, cross-reference context): Mandatory for vessels over 300 GT under SOLAS. Spire and similar operators collect AIS via low-Earth-orbit receivers. Gaps between expected and observed transmissions, combined with SAR-detected positions, are the primary method for identifying transponder-off or spoofed vessels. Not a sensor; a data layer.

What a blockade actually looks like from 500 km up

A functioning blockade suppresses commercial arrivals. The observable signatures are straightforward in principle: berths that were occupied fall empty, anchorage density drops, crane cycles cease, and the port's vessel-traffic rhythm collapses toward zero. SAR imagery makes this measurable without any cooperation from the parties involved.

Sentinel-1 provides the baseline. Its C-band radar returns a bright point for any metal hull above roughly 30 m in calm to moderate sea states, regardless of weather or time of day. Over a monitored port, a time series of Sentinel-1 scenes going back to 2014 establishes the pre-blockade norm: typical berth occupancy, anchorage count, and vessel size distribution. Deviation from that norm is the signal. The method does not require classified data; it requires consistent geometry and a long archive, both of which Sentinel-1 provides at no cost.

The AIS gap technique and its published pedigree

AIS is mandatory for commercial vessels above 300 gross tonnes under the SOLAS convention. When a vessel that should be transmitting goes silent, and a SAR return appears at a position consistent with its last known track, the inference is straightforward: the ship is present but has switched off its transponder. This cross-referencing technique is not novel. UN Panel of Experts reports on sanctions regimes, including those covering North Korea and Libya, have cited exactly this method to document illicit cargo movements, lending it a degree of evidentiary standing that purely commercial intelligence products rarely achieve.

The practical workflow compares space-based AIS collection (from operators such as Spire, whose satellites receive AIS globally) against SAR-detected vessel positions. A ship appearing in SAR with no corresponding AIS record within the expected position error budget is flagged as a dark vessel. Aggregated over weeks, the count of dark vessels calling at a blockaded port gives a direct measure of blockade leakage.

Cargo handling is harder to hide than the ships themselves

Even when a vessel's identity is obscured, its activity at the quayside is not. High-resolution optical imagery from WorldView-2 resolves individual ship-to-shore cranes, their boom angles, and the presence of containers or bulk cargo on the apron. A crane at 45 degrees with a container suspended is unambiguous evidence of active discharge or loading. A row of cranes at rest, with empty aprons, confirms that vessels at berth are not transferring cargo.

This matters because a blockade's legal and strategic effect depends on cargo denial, not merely vessel exclusion. A vessel anchored offshore without offloading is a different situation from one completing a full discharge. Optical analysis distinguishes the two. The constraint is cloud cover: in persistently overcast regions or seasons, optical confirmation may be delayed by days. SAR can detect the vessel; it cannot, at Sentinel-1 resolutions, reliably confirm crane activity. That gap is where commercial SAR at ICEYE's 0.5 m spotlight resolution starts to earn its cost.

Where the method fails, and by how much

Honesty about limits is not a disclaimer; it is the foundation of any credible intelligence product. The primary gap is temporal. Sentinel-1's 3 to 6 day revisit means a vessel can arrive, discharge, and depart within a single revisit window without ever appearing in an image. Commercial SAR constellations narrow this gap considerably: ICEYE's published constellation size supports sub-hourly revisit over a tasked point, but sustained tasking of a single port at that cadence is expensive and competes with other priorities.

AIS spoofing is a growing problem. Vessels increasingly transmit false positions, making the gap-detection method less reliable when the transmitted position is plausible but wrong. SAR provides the ground truth that defeats spoofing, but only at the moments of imaging. Between passes, a spoofing vessel is effectively invisible to the cross-reference method. Sea state also degrades SAR vessel detection: in high sea states, wave clutter masks smaller returns, and vessels under roughly 50 m may fall below the detection threshold. Finally, distinguishing vessel type from SAR alone is uncertain at Sentinel-1 resolution; a bulk carrier and a tanker of similar length produce similar returns. ICEYE spotlight imagery and optical confirmation are needed for confident type classification.

Building an enforcement baseline: what a monitoring programme looks like

Effective blockade monitoring is not a single image; it is a structured time series. The analytic architecture starts with a pre-blockade baseline covering at minimum 12 months of SAR scenes, establishing the statistical distribution of berth occupancy, anchorage count and vessel size. Once a blockade is declared, each new acquisition is compared against that baseline. Departures beyond two standard deviations trigger a review.

Optical tasking is scheduled on a risk-prioritised basis: when SAR detects an anomalous vessel arrival, a WorldView-2 or ICEYE spotlight task is placed for the next available clear-sky pass. The output is a structured incident log, not a raw imagery dump. Each entry records the SAR detection time, the AIS status of the detected vessel, any optical confirmation of cargo handling, and a confidence rating. That log is the document that matters in a sanctions or legal context. Satellize structures its analytics outputs to meet this kind of evidentiary standard, informed by the same published UN methodology its analysts draw on. The Tonga crop-estimation programme demonstrated the same principle at the other end of the spectrum: rigorous method documentation matters as much as the sensor data itself.

Spoofing, small craft and the limits of open data

Two vessel categories largely escape this framework. Small craft below roughly 30 m, including fishing boats, dhows and fast patrol craft, fall below Sentinel-1's practical detection floor in anything other than calm conditions. They are also exempt from SOLAS AIS requirements, so there is no transponder record to cross-reference. Monitoring small-craft traffic requires either very-high-resolution SAR tasking at high cadence or persistent optical surveillance, both of which are costly and operationally intensive.

The open-data boundary is the other structural limit. Sentinel-1 and Planet Dove data are free or low-cost, but the AIS feeds from commercial aggregators, the ICEYE tasking, and the WorldView-2 acquisitions all carry licence costs that scale with monitoring area and cadence. A government client building a sustained blockade-monitoring capability should budget for a hybrid architecture: free Sentinel-1 as the persistent baseline, with commercial SAR and optical triggered by anomaly detection rather than scheduled continuously. That architecture keeps cost proportional to threat activity rather than flat.

Typical figures

SAR spatial resolution (Sentinel-1 IW)	5 x 20 m (range x azimuth)
SAR spatial resolution (ICEYE Spotlight)	~0.5 m
Optical resolution (WorldView-2 pan)	0.46 m
Sentinel-1 revisit (dual satellite)	3 days at mid-latitudes; 6 days at equator
ICEYE revisit (tasked, constellation)	Sub-1 hour over a tasked point (scheduled)
Minimum detectable vessel (Sentinel-1, calm sea)	~30 m hull length
AIS archive depth (commercial aggregators)	Typically 5+ years; Sentinel-1 SAR archive from 2014
Cloud penetration	SAR: full; optical: cloud-free passes only
Delivery formats	GeoTIFF, GeoJSON vessel detections, structured incident log (PDF/XLSX), GIS-ready vector layers
Latency (SAR detection to alert)	2 to 6 hours post-acquisition for automated detection pipelines

Analytics Satellize can run

Dark vessel identification	SAR vessel detection cross-referenced against space-based AIS; vessels with SAR return and no AIS record within position error budget flagged as transponder-off. Method class: SAR-AIS fusion, as documented in UN Panel of Experts sanctions reports.	Structured incident log with vessel position, SAR acquisition time, AIS status and confidence rating; delivered as GeoJSON and PDF summary
Berth occupancy time series	Automated SAR ship detection over defined berth polygons; occupancy count and vessel length estimates derived from each acquisition. Baseline established from pre-event archive.	Weekly occupancy chart with anomaly flags; GIS layer of berth polygons with occupancy history
Anchorage density monitoring	SAR and Planet Dove daily optical used to count vessels in defined anchorage zones. Statistical comparison against 12-month pre-blockade baseline.	Time-series chart and alert when count deviates beyond defined threshold; delivered as dashboard feed or scheduled report
Cargo-handling activity assessment	High-resolution optical analysis (WorldView-2) of crane boom angles, container apron occupancy and vehicle presence on quaysides. Manual and semi-automated interpretation.	Per-incident optical assessment report with annotated imagery and activity classification (active discharge / idle / indeterminate)
Vessel type classification	ICEYE spotlight SAR at ~0.5 m for deck-structure discrimination; optical confirmation where available. Classification against known vessel silhouette libraries.	Vessel type annotation appended to dark vessel incident log
Blockade leakage index	Aggregated dark vessel call count and cargo-handling events normalised against pre-blockade traffic baseline. Expressed as a percentage of pre-blockade activity volume.	Monthly summary report with trend line and confidence interval; suitable for policy or legal use

Sources

Who does the work

We can get this done for you. Satellize runs its own analyst desk and a strong science team. You do not buy a data feed and work out what it means; our people source the imagery, run the analysis described on this page, and hand you the answer with its confidence limits stated. Discuss this requirement.