In situ Imaging

Background
The distribution of particles and other items within liquids is important for various research questions and applications. Examples are:

  • The spatial distribution of very small organisms in the water, caused by the hydrodynamic conditions, influences important biological processes.
  • The mass transport and properties of sediment particles are of interest to coastal researchers.
  • Dispersed plastic particles can be incorporated by organisms.
  • With regard to technical processes, items in liquids may indicate malfunctions.

In situ imaging is suitable for depicting items if the transport liquid is sufficiently transparent. A variety of spatially resolved technical parameters and environmental data may be assigned to a single image. Classical sampling, in contrast, always integrates across a certain area of the water body.

Tasks
Within the research focus "In situ Imaging" the scientists develop imaging systems that magnify objects to varying degrees. A key aspect is to detect freely floating items smaller than two millimetres (e.g. many of the planktonic organisms shown on this web page).

In order to ensure the quality of the image, a motion blur must not occur. Thus, a moving water body should be exposed only briefly but illuminated strongly. The researchers therefore develop specific optical approaches and exposure units and apply them on seagoing expeditions. The detected particles are visualised with spatial resolution and correlated to other sensor data.

The research also focusses on artificial vision: Numerical image descriptions make it possible to identify and distinguish particular items. Here, methods of image processing are combined with techniques of multivariate statistics

Tools
The scientists predominantly use industrial cameras with Gigabit ethernet interface. The images are recorded by data acquisition systems that are either located on board a research vessel or lowered into the water within a pressure-resistant housing.

Units of light emitting diodes set into flash mode serve as light source. Dependent on the intended use, the arrays are put in a certain order or included into reflector systems. Lenses may also be added. If monochromatic light is needed, fluorescence properties are to be visualised or thin layers are to be illuminated, the researchers may use laser. These technologies can be combined and complemented with additional sensors.