Hydrophone networks

The hydrophone network is the survey's principal long-range awareness instrument. It is operated jointly by the Filament Guild, which maintains the cables and repeaters, and the Bathymetric Conservancy, which interprets the data.

What it does

The network is passive. It records sound. Sound at depth carries far further than light, and the deep ocean's acoustic channel preserves long-wavelength signals over thousands of kilometres. The network's operators can, with practice, distinguish a tendering vessel from a passing whale from a Pelagine signal — though the last category is the one the network is least confident about, and least public regarding.

What it does not do

The network does not transmit. There is no equivalent network for sending sound; the survey's outbound communications travel by cable to the surface link, by short-range acoustic modems within an anchorage, or — at the markers — by the protocols set by the Treaty of Marker I.

On the Pelagine question

The network records signals in bands that the Pelagine are known to use. Whether what is recorded constitutes communication, navigation, or something the survey does not have a category for is, by current convention, not the network's question to answer. It is recorded, and stored, and very seldom translated.