Depth measurement instruments

The distance from the water surface vertically down to an object is a measurement we refer to as depth. Please note that this measurement should not be confused with the depth of the water itself – which is from the water surface to the bed of the river, canal or ocean.

All research, construction or survey activities underwater (military, commercial or academic) need a measurement of depth in real time or in a time-stamped logged form, so that any data collected and operations conducted can be correctly referenced.

Many oceanographic parameters vary over depth, and many studies require vertical “profiles” to be taken where data points are captured as a sensor package ascends or descends through the water column. For example, Anyone making measurements using acoustics underwater (such as hydrographic surveyors mapping the depth of the seabed using multi-beam echosounders, positioning relative to a network of acoustic beacons, or detecting possible threats), needs knowledge of how the velocity of sound changes with depth in that local environment with a high level of precision to provide the most reliable results.

Underwater vehicles of all types need to know their depth accurately for a number of reasons, the most fundamental being safety. Vehicle components (lights, batteries, connections, motors, sensors etc.) must be protected from the effects of pressure and are designed for a particular maximum depth. Exceeding that depth can cause potentially catastrophic faults, so a real-time knowledge of depth is crucial.

Depth is also a navigational parameter underwater and direct measurement more accurate and reliable than a depth calculated by an external tracking system.

Piezo-electric crystalline materials are used for depth measurements subsea, and these change their resistance with pressure variation in a regular, directly proportional way, allowing instruments to be calibrated against known standards very effectively so that there is consistency and confidence.