Magnetometers

Magnetometers are used to measure anomalies in the earth’s magnetic field. These can be due to local geologic features or manmade objects in the area (i.e., ship wrecks). Underwater magnetometers are typically towed behind a ship.
Proton magnetometers operate on the principal that the protons in all atoms are spinning on an axis aligned with the magnetic field. Ordinarily, protons tend to line up with the earth’s magnetic field. When subjected to an artificially-induced magnetic field, the protons will align themselves with the new field. When this new field is interrupted, the protons return to their original alignment with the earth’s magnetic field. As they change their alignment, the spinning protons precess, or wobble, much as a spinning top does as it slows down. The frequency at which the protons precess is directly proportional to the strength of the earth’s magnetic field.
Overhauser magnetometers use electronproton coupling to produce stronger precession signals than conventional proton precession magnetometers. Optically pumped magnetometers (Cesium, Potasium, and Rubidium) make even more precise measurements of magnetic fields by determining the frequency of radio waves required to change the transparency of a glass vapor cell containing gaseous metal that is exposed (or pumped) to polarized light of very specific wavelength.
Meteorological Sensors (met sensors): Exchanges across the air-sea interface, including heat and fresh water, couple the ocean and atmosphere and are of major interest in studies of global climate. Met sensors on either research vessels or buoys include those used to measure sea surface temperature, air temperature, wind speed and direction, barometric pressure, solar and long-wave radiation, humidity and
precipitation. From these measurements, accurate estimates of air-sea fluxes can be made.
Motion Sensors measure heave, pitch and roll – typically on surface vessels. Correcting for vessel motion is critical for multi-beam hydrographic surveys, for high-accuracy acoustic positioning systems and for other applications. Most are based on three orthogonal accelerometers of which there are several types having different accuracies at different costs. Older systems, some of which are still in use, are based on pendulums.
For less dynamic or static applications, tilt sensors can be used to measure the angle of inclination. These are commonly used on subsea vehicles or instruments resting on the seafloor. Electrolytic tilt sensors use a sealed glass vial partially filled with a conductive fluid. Several metal electrodes go through the glass into the fluid filled chamber. As the sensor tilts, the surface of the fluid remains level due to gravity. The fluid is electrically conductive, and the conductivity between the two electrodes is proportional to the length of electrode immersed in the fluid. Electrically, the sensor is similar to a potentiometer, with resistance changing in proportion to tilt angle. Single and dual axis sensors are available.