A vessel that goes dark is hiding from the record

There is a habit of treating missing data as the absence of information. For automatic identification system (AIS) tracks, the opposite is closer to true. A vessel that broadcasts continuously tells you where it is. A vessel that goes dark tells you something about what it intends — provided you have kept enough of the record to know that the silence is unusual.

Silence has a shape

A gap is only legible against a baseline. If you know a strait’s ordinary rhythm — who transits, how fast, how often they report — then a three-hour absence at a particular chokepoint is not noise. It is a signal with edges.

1. Establish the baseline rhythm of the corridor.
2. Flag absences that depart from it, weighted by place.
3. Score the departure, and keep the score where others can check it.

Where to stand

The analyst’s job is to choose a vantage from which the silence becomes information. That vantage is usually temporal: you have to have been watching long enough that the gap is surprising.

A gap in the data is data — if you have kept the record long enough to be surprised by it.

This is what an open, reproducible method buys you. Not certainty — a place to stand, and a record someone else can stand on after you.