Glossary

This glossary provides consistent definitions for terms used throughout Subsea Database. Terms are defined in operational context, not academic abstraction.

A

ALARP — As Low As Reasonably Practicable. A risk management principle requiring that risks be reduced to the lowest level that is reasonably practicable given technical, economic, and operational constraints.

AUV — Autonomous Underwater Vehicle. An untethered underwater robot that operates without direct human control.

B

Bailout — Emergency breathing gas supply carried by a diver for emergency ascent.

Bottom time — The time a diver spends at maximum depth during a dive, used for decompression calculations.

C

Chain-of-custody — The documented record of who had custody of data or equipment at each point in time, required for legal and regulatory purposes.

Commercial diving — Professional diving operations performed for commercial purposes, as opposed to recreational or military diving.

D

Decompression — The process of gradually reducing pressure to allow dissolved gases (primarily nitrogen) to safely leave body tissues, preventing decompression sickness.

Digital twin — A digital representation of a physical system that is kept synchronized with the physical system and used for simulation, monitoring, and analysis.

E

Emergency procedures — Pre-defined procedures for responding to emergencies, including equipment failures, medical emergencies, and loss of communication.

F

Failure mode — A specific way in which a system can fail, including the conditions that lead to failure and the consequences of failure.

Failsafe — A system design that causes the system to enter a safe state when a failure occurs.

G

Geospatial confidence — The level of confidence in a position measurement, typically expressed as an uncertainty ellipse or circle.

H

HAZID — Hazard Identification. A structured process for identifying hazards in operations.

HAZOP — Hazard and Operability Study. A structured process for identifying hazards and operability problems.

Heliox — A breathing gas mixture of helium and oxygen, used for deep diving to reduce nitrogen narcosis and decompression requirements.

I

IMCA — International Marine Contractors Association. An industry association that publishes guidelines for marine operations.

INS — Inertial Navigation System. A navigation system that uses accelerometers and gyroscopes to track position and orientation.

L

Latency — The time delay between sending a signal and receiving a response, critical for real-time control systems.

Loss-of-comms — The condition when communication between vehicle and surface is lost, requiring autonomous operation.

M

Manipulator — A robotic arm on an ROV used for work tasks such as tool use, object manipulation, and installation.

N

Nitrox — A breathing gas mixture with higher oxygen content than air, used to reduce nitrogen exposure and extend bottom time.

O

Operational records — Documentation of operational activities, including dive logs, equipment records, and incident reports, required for regulatory compliance and audit.

P

Provenance — The record of where data came from, how it was created, and who handled it, required for data integrity and auditability.

R

ROV — Remotely Operated Vehicle. A tethered underwater robot controlled from the surface.

S

Saturation diving — A diving technique where divers live in a pressurized environment (saturation system) and are transported to work depth in a diving bell, allowing extended work periods without decompression between dives.

Sensor calibration — The process of adjusting sensor readings to match known reference values, with traceability to calibration standards.

Surface-supplied diving — Diving where breathing gas is supplied from the surface through an umbilical, as opposed to self-contained (scuba) diving.

T

Timestamp integrity — The assurance that timestamps are accurate, synchronized, and tamper-resistant, required for auditability and legal purposes.

Tether — The cable connecting an ROV to the surface, carrying power, communication, and sometimes strength member for recovery.

Trimix — A breathing gas mixture of helium, nitrogen, and oxygen, used for very deep diving.

U

Umbilical — The cable connecting a diver or ROV to the surface, carrying breathing gas, communication, and other services.

Uncertainty — The quantitative expression of doubt about a measurement, typically expressed as a confidence interval or standard deviation.

V

Vehicle class — A categorization of underwater vehicles by size, capability, and intended use (e.g., observation-class, work-class, survey-class).

This glossary is living and will be updated as terminology evolves. Terms are defined in operational context to reflect how they are used in practice.