Profiling Float: Buoyancy-Driven Ocean Diving

Mission

MANUAL CONTROL

Buoyancy Piston

Oil-bladder volume Δ_V 0 mL

Park depth target 600 m

Thermocline depth 120 m

Telemetry

Depth

0 m

Vertical rate

0.0 cm/s

Seawater ρ(z)

1023 kg/m³

Net buoyancy

0.0 N

Float volume vs. seawater displaced

11.00 L

How it works

A profiling float (the real technology behind the 4,000-unit international Argo array) carries no propeller. It dives and surfaces purely by changing its own volume with a small hydraulic pump that pushes oil into or out of an external bladder, which shifts its average density relative to the surrounding seawater:

Archimedes' principle:  F_b = ρ_sea(z) · g · V(z)
Weight:                 F_g = m · g
Net force:              F = F_b − F_g − ½ C_d A ρ_sea(z) v|v|
Motion:                 m dv/dt = F,   dz/dt = v

Seawater density ρ_sea(z) is not constant with depth. It rises through the thermocline as temperature falls, and rises further at depth from the (small) compressibility of water under pressure:

ρ_sea(z) = ρ_surf + (ρ_deep − ρ_surf) · sigmoid((z − z_thermocline)/150)
           + 0.0022 · z        [pressure compressibility term]

Oil-bladder volume slider — retracting oil (negative ΔV) shrinks the float, its average density exceeds ρ_sea and it sinks; extending oil (positive ΔV) does the opposite. A real Argo float shifts only ~200–300 mL against an ~11 L hull to move.
Park depth — the depth a real float drifts at between dives, riding the local current for days while sampling temperature and salinity; here it also sets the autonomous mission's turnaround depth.
Thermocline depth — where the sharp temperature/density transition sits; a shallower thermocline means the float meets denser water sooner, changing where its sink rate slows down.
Autonomous Profile — runs the real Argo duty cycle: descend → park & drift → descend to profile depth → ascend to the surface (to transmit data by satellite) → repeat.

Simulation time here runs about 60× faster than reality — a real Argo descent to 1,000 m takes on the order of hours; the vertical rate readout is still the true instantaneous physical speed (v = dz/dt), just reached sooner on screen.

Profiling float Marine snow (drift)

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