These are able to occupy, on a monthly basis, all the 48 hydrographic sections that took the WHP 12 years to do once. We acquire data from this widely dispersed network via satellite telemetry. It is something of a wonder to follow the intricate patrol pattern of the Slocums assigned to the various sections. For example, there are ten assigned to patrol a section along 24N in the Atlantic. Each patrols a six degree segment of longitude.
Pairs meet once a month to do an intercalibration.
Sometimes we schedule an intricate cotillion-like dance of the Sentinel Slocums in which they interchange patrols, thus obtaining, over the course of a year, a complete intercalibration of all Slocums on the section. We also have special Calibration Standard Slocums that wander randomly about the patrol lines, like the inspectors on a subway system, calibrating all Slocums that they encounter. Each Slocum reports into Mission Control via satellite about six times a day. The satellite also reports on the Slocum's position, which informs us how much the float has been set by the ocean currents it encounters and permits its automatic pilot to be reset according to a course-correction algorithm. During the day, the casts terminate at different depths and sometimes the floats dwell for a period at the bottom of the cast, so it is possible to recover information about the vertical model structure of the currents.