Read ship messages and images differently

ZACUBE-2 included an Automatic Identification System, or AIS, reception demonstration using a software-defined radio payload. AIS-equipped ships transmit structured messages. A position report can include coordinates, time, speed and course; other messages carry identity or voyage information. Receiving these messages from orbit extends the places from which reports may be collected, but a decoded message remains a report transmitted by equipment.

An optical image is a different kind of evidence: a detector records light from its field of view. ZACube-2 also carried an imaging demonstration, including a near-infrared K-line instrument associated with fire detection. Do not describe an AIS point on a map as a photograph of a ship, or assume that the imager could resolve every transmitting vessel. Payload purpose, sampling, coverage and validation determine what each product can support.

AMSA explains that different AIS message types arrive at different rates. A position can arrive before a vessel’s name and voyage details. A display that combines them should preserve which fields were reported when. Reception and processing introduce additional times. A current-looking map marker may still represent an older position report.

In a fictional example, a ship reports a speed of ten metres per second. Six hundred seconds later, constant speed along a straight path would imply six kilometres of travel. That is an extrapolation under stated assumptions, not a new measured position. The vessel could change speed or turn. Show the reported point and the predicted position as different kinds of information rather than quietly moving the observation.

A report and a prediction have different times

AIS does not provide a complete physical census of everything on the sea. A vessel might lack suitable equipment, a transmission might not be received or decoded, or a report might be absent from the particular data product. The absence of a point does not prove empty water. It also does not, by itself, prove illegal activity or explain why a transmitter was not heard.

To combine radio and image evidence, compare their times, coverage and position uncertainties first. A scene acquired hours after a report is not a simultaneous confirmation. A wider-area radio receiver and a narrow image footprint may cover different places. A good analyst preserves unmatched observations and explains gaps. The demonstration can inform later maritime systems while remaining distinct from a validated continuous service.