A video plankton recorder (VPR) is towed underwater video microscope

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

 system, which photographs small to fine-scale structure of plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

, from 50 micrometers and up to a few centimeters in size. A VPR consists of five general components: cameras (with magnifying optics ), strobe, additive sensor and flight control, underwater platform and interface software for plankton identification.

Technical aspects

In order to obtain high-quality and low-noise images, charge-coupled device

Charge-coupled device

A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

 (CCD) sensors are used in the camera

Camera

A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

 system. In the early design system, the CCD cameras were mounted in one of the arm of the platform. The developments in the recent years made the cameras system possible to be mounted in the platform body along with other sensors and flight control. The magnification power on the cameras should be vary, with high magnification

Magnification

Magnification is the process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a calculated number also called "magnification"...

 power on the camera, we can obtain detail observation result on the plankton sample, such as protozoan that has <1 µm resolution . In other hand, the high magnification is able to identify plankton into genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 level while low magnification of the camera will provide the rare and larger taxa.

The xenon strobe (red-filtered 80 W) provides the VPR systems with the Lighting

Lighting

Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...

 to support the work of the video camera. It is placed in the other side of the platform arm. This design is intended to provide the area between camera and strobe as undisturbed water volume for continuous observation in the VPR system.

As a complex system, VPR can also carry several oceanographic sensors in the same time such as, CTD, transmissometer, fluorometer and flowmeter. These sensors enable the system to measure temperature, conductivity, depth, flow measurement

Flow measurement

Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways.Positive-displacement flow meters acumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow...

, fraction of light in the water and the fluorescence

Fluorescence

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

.

The housing or platforms for this instrument is varying depend on the purpose of the survey. These are the particular platform that has been tested and used to mount the VPR:

1. Towed device
2. Remotely operated underwater vehicle(ROV)
3. Autonomous underwater vehicle
   Autonomous Underwater Vehicle
   An autonomous underwater vehicle is a robot which travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles...
   
    (AUV)
4. Autonomous profiling mooring

The improvements of imaging system to observe, calculate and measure plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

 in the ocean enable the detail observation on the specific plankton community. This early development was conducted by enumerating and counting the silhouette

Silhouette

A silhouette is the image of a person, an object or scene consisting of the outline and a basically featureless interior, with the silhouetted object usually being black. Although the art form has been popular since the mid-18th century, the term “silhouette” was seldom used until the early decades...

 photography of plankton, the result then is processed with software package such as Matlab

MATLAB

MATLAB is a numerical computing environment and fourth-generation programming language. Developed by MathWorks, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages,...

.

Imaging software

figure from Benfield, M.C., et al
The most important part in VPR is the plankton identification software. Any developments of the software should improve the required task performed by VPR. In a nutshell, the software should have the ability of:

1. Importing the plankton images database
   Database
   A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
   
    in to the system.
2. Validate the object and evaluate from the background of the sample. This qualification should include the capability of the software to discriminate unknown object from plankton.
3. Identify and classify the samples therefore plankton can be distinguished from each other.
4. Presenting the result in the form of; abundance, size of distribution and biomass.

Observation result

The study conducted by Benfield, M.C., et al has discovered that VPR provided comparable data on the taxonomic composition of the plankton compared to physical plankton survey taken by MOCNESS

MOCNESS

MOCNESS is the acronym for Multiple Opening/Closing Net and Environmental Sensing System and is a net system for plankton in the ocean. The system is towed behind a research vessel with a speed of 1.5 knots and consists of five to twenty nets with a mesh size from 64 µm to 3 mm and an...

.

The figure in the right side shows us the general trends in abundance and detail scale patchiness along the observation area.

Advantage and Disadvantages

Although a VPR has a drawback for not being able to identify plankton into species level, the advantages to use this instrument has gone beyond its limitation to provide us with convenient and accurate result. The high resolution result on plankton taxa observation along with synchronized measurement environmental variables from another oceanographic sensor attached in VPR body can be considered as the milestone of this device. In addition, since the observation is conducted visually by photographing the sample, the observation of delicate plankton and gelatinous species can be done accurately without having them destroyed in the net.

Gallery

Source of Picture Gallery