Vertical profile data in oceanography usually refers to measurements of ocean properties (e.g., temperature, salinity, density) against depth (from the surface downwards). These instruments are important because the vertical structure of the ocean (temperature gradient, thermocline, stratification) greatly determines ocean currents, mixing, and physical dynamics. The Mechanical Bathythermograph (MBT) is one of the classic instruments used to measure sea temperature against depth up to the upper ocean layer. MBTs have been in use since the mid-20th century and were widely used before modern instruments such as CTDs and XBTs became dominant.
The Vertical Profile Data is equipped with:
Vertical profile data is usually accompanied by a number of metadata and parameters, for example:
- Depth or pressure at each measurement point
- Sea temperature at each depth
- Horizontal location (latitude, longitude)
- Measurement time/date
- Instrument identification, calibration, and additional metadata (e.g., sea conditions during measurement)
- Standard data format (e.g., UBT for MBT)
Therefore, vertical profile data is not just temperature-depth numbers, but also includes information for correct interpretation (e.g., error correction, instrument metadata, location, time).
The main function of these Mechanical Bathythermograph is
Some of the main functions of MBT include,
- Measuring temperature profiles against depth in the upper ocean layer, so we can find out how the temperature changes from the surface downwards.
- Determining the thermal structure of the ocean, including thermocline depth, temperature gradient, and mixed layer.
- As historical data: MBT provides records of past ocean temperatures, which are useful for long-term studies of ocean climate change and ocean heat.
- Supporting estimates of thermal transport or thermal flux in the ocean, when combined with other data such as current velocity. For example, in studies of the Makassar Current in Indonesia, MBT is used in conjunction with CTD and XBT data to create representative temperature profiles.
However, due to limitations in accuracy and depth, MBT is often replaced by more sophisticated instruments in modern research.
Types of Mechanical Bathythermograph
Actually, MBT itself is a type of instrument (mechanical bathythermograph). However, there are several variations or generations and ways of using it:
- Classic/traditional MBT, a mechanical instrument with a liquid-metal thermometer and mechanical recorder.
- Modified/newer version of MBT, with improved calibration and more accurate sensors.
- MBT differs from XBT (Expendable Bathythermograph), XBT is a disposable instrument released from a ship, not retrieved, and uses a different method.
So, although there are not as many “types of MBT” as there are variations in modern instruments, variants usually refer to generations, sensor designs, or recording methods.
Main Components of Mechanical Bathythermograph
- Liquid-in-metal thermometer, This is a temperature measuring element containing a liquid (e.g., mercury or other metal) that reacts to temperature changes.
- Mechanical recorder (indication on a slide/glass plate), As the instrument descends through the water column, the temperature causes expansion or displacement of the thermometer element, which is recorded mechanically (e.g., on a glass slide).
- Waterproof casing or housing (housing / pressure case), Protects internal components from water pressure and marine conditions (corrosion).
- Cable or hook rope / winch, Used from the ship to lower and raise the device or control the depth.
- Brake or stop mechanism / depth control, To stop the device at the target depth or slow down its speed.
- Metadata and calibration system, Additional components such as calibration scales, device identification, and calibration records to correct system errors.
These components work together to produce a temperature vs. depth curve.
How Dart Buoy Work
- Preparation and calibration of equipment
Before use, the MBT is calibrated in the laboratory to ensure temperature and depth accuracy. Metadata about the calibration date is recorded.
2. Deployment of equipment into the sea
The equipment is released from the ship and lowered into the water, usually slowly so that the temperature recording against depth is accurate.
3. Recording temperature against depth
As the MBT moves down (or sometimes up), the thermometer element records the temperature, and the recording mechanism (glass slide or mechanical recorder) records the temperature value against position (the associated depth). Since water pressure increases with depth, depth can be linked to pressure.
4. Stopping or retrieving the device
After reaching the target depth (e.g., 200–250 m), the device may be stopped and then retrieved to the surface to retrieve the recorded data.
5. Data extraction and conversion
Mechanical recording data is read (e.g., glass slides are scanned) and then converted to digital format: temperature vs. depth. This data is supplemented with metadata on location, time, and sea conditions.
6. Correction and processing
Because MBTs are known to have systematic errors (bias in temperature and depth), data profiles are usually corrected using standard methods before being used in analysis.
7. Data interpretation and use
Once the data is clean, the temperature versus depth curve can be used to analyze thermoclines, stratification, and other parameters.
Dart Buoy strengths and weaknesses
Strengths
The Mechanical Bathythermograph (MBT) has a number of advantages and disadvantages that are important to understand in the context of its use. In terms of its strengths, the MBT makes a significant contribution to providing extensive historical data. This instrument has been in use since the mid-20th century, enabling it to produce records of past sea surface temperatures that are useful for marine climatology and long-term climate change studies. In addition, the relatively simple and fully mechanical design of the MBT allows it to be used without the need for complex electronic technology, making it suitable for use in an era before modern instruments were developed. The data generated by MBTs is also widely stored in global oceanographic databases, such as the World Ocean Database, which is an important source for global research. Furthermore, MBTs are adequate for studying the thermal structure of the upper ocean, particularly to a depth of about 200–250 meters, so they remain relevant for certain analyses.
Weakness
However, despite its advantages, MBT also has several disadvantages. Measurement accuracy is often limited due to systematic errors (bias) in both temperature and depth recordings, so the data needs to undergo a correction process before it can be used. This instrument is also only effective at depths of 250–285 meters, so it cannot reach deeper layers of the ocean. Its vertical measurement resolution is relatively low because the recording mechanism is still mechanical, so the distance between measurement points is less detailed than modern instruments such as CTD. The MBT data processing process is also quite complicated, because mechanically recorded data requires manual reading and additional corrections. In addition, MBT cannot be used automatically or continuously for long periods of time because it must be operated directly from a ship, unlike modern instruments that can be installed for long-term observation. Another disadvantage is its limitation in dealing with extreme sea conditions, such as high waves or severe turbulence, which can interfere with the data recording process.
Writer : Talitha Aprillia Ensu
