Ocean Circulation and Climate Dynamics
The basis of oceanographic research is the measurement of physical, chemical and biological parameters. Until a few decades ago it was necessary for ships to sail to the site of scientific interest and take in situ measurements. This was and is very time-consuming, laborious and costly. The technical development of electronics, sensors and computers has led to rapid change, especially in recent years.
Since the 1950s, oceanographers have used moored instrumentation to autonomously record measurements over a period of up to 3 years. The data could then only be analyzed after recovery of the mooring. Satellite measurements have provided a major leap forward since the 1970s where large portions of the ocean can be surveyed in a short amount of time, and the data became available for further analysis within minutes or hours. Unfortunately, many of the oceanographic parameters of interest are not accessible by satellites, and the interior of the ocean remains largely hidden from a satellite’s view. In the last ten years, there have been huge advances in satellite-linked phones, high-performance and energy-saving microelectronics and new materials which enabled the development of a new generation of oceanographic instrumentation. For example, floats and gliders measure independently for months and years, drifting with the ocean currents, or sailing along predetermined courses. They are capable of sending their data at regular intervals via satellite to a land-based receiving station.
Ship based observations
The observing physical oceanography group is mainly working on data measured directly in the ocean, so-called in-situ data. This means that open ocean cruises onboard the big research vessels still remain the highlights in the professional life of Physical Oceanographers. All publications and all results are somehow based on data gathered during these cruises.
Different instruments and measurement techniques are utilised onboard the research vessels. Most important are:
- CTD Probe
Even during the early cruises of the first “Meteor” in the South Atlantic during the 1920s, profiles of temperature and salinity were taken from the surface all the way down to the ocean floor, several thousand meters deep. Those measurements, tedious and time-consuming using buckets and reversing thermometers, more
- ADCP Current Meter
Nowadays, most current measurements are taken acoustically, i.e. by using the so-called Doppler effect: The frequency of a reflected acoustic signal changes as the target (or reflector) moves relative to the sound source (transponder). This phenomenon is well known as the sound of a passing car more
- Micrstructure Profiler
The microstructure profiler is an instrument designed to measure velocity shear and temperature variability on vertical scales of less than a millimeter and simultaneously record other physical parameters of the ocean. The profiler is more
- Tracer Release
The open ocean tracer release experiment is an accurate method to investigate the turbulent vertical mixing and horizontal dispersion in the ocean. The experiment starts with the release of a chemical compound, concentrations of which are detectable even when strongly diluted. With time, the tracer patch spreads horizontally and vertically, its spread monitored by several cruise campaigns. more
A mooring describes a measurement platform with autonomously registering sensors at various depths where the entire platform is “moored” at a fixed location by a bottom weight (often made of discarded railroad wheels). The mooring consists of steel wire or synthetic rope which holds the sensors plus associated buoys made of glass or foam to provide sufficient buoyancy to keep the mooring upright.
Close to the bottom but above the anchor are acoustic releases which allow the controlled release of the instrumented part of the mooring at the end of the scheduled deployment period. The buoyant flotation brings the instruments plus the steel wire to the sea surface to be recovered by the attending research vessel. Most of the data are immediately retrieved on the ship, the instruments are checked, calibrated and refurbished, ... more
Floats, Glider and AUV
The youngest group of oceanographic instruments is characterized by their operation being largely independent from oceanographers and research vessels. Floats, Gliders and AUVs (Autonomous Underwater Vehicle) are the logical development of several decades of oceanographic instruments. They combine more