Sediment profile imaging (SPI) | Flanders Marine Institute

Flanders Marine Institute

Platform for marine research

Sediment profile imaging (SPI)

Sediment Profile Imaging (SPI) is an underwater device that images the top layers of the seafloor in a vertical cross-section. This technique provides investigators with high resolution images in the seafloor/water interface of aquatic sediments in a much quicker and efficient way than using traditional sampling methods (box cores, piston cores, etc.). The SPI can image 15 to 20 cm of the sediment surface. This image gives both quantitative and qualitative information about the biological (bioturbation, epifauna), chemical (redoxdepths) and physical (stratification, human/natural disturbance) nature of the sediment. By making a series of images over various time periods, information about how organisms behave or how the structure of sediment changes through time can be obtained. The SPI can be used in both marine and fresh water as in an estuary up to a depth of 4000 m.

How does the SPI work?

The working principle of the SPI seems simple: once the frame with the camera is been placed on the seafloor, one lowers the prism and a photograph of the sediment layers is made. However, a lot of pressure-resistant and unusual instruments are used to do this.

Operation of the SPI. © VLIZ

The frame of the SPI is comprised of a galvanized steel frame with hinged mud doors. These mud doors provide an advantage in locations mainly existing of soft sediment because they are used to add surface area to the base frame and prevent the frame from sinking into the bottom. To enable the lowering of the prism in a variety of bottom sediments, the frame may be loaded with up to 113 kg of lead weights. A penetrometer is attached to one of the frame rods to aid in selecting the amount of weight needed to obtain a good image of the sediment layers. The prism assembly that is pushed into the ocean flooris made of stainless steel and filled with distilled water. The front edge of the prism is very sharp to be able to cut through the sediment. The front of the prism is made forms a gasketed plexiglass. Inside, an inclined mirror reflects the image to the camera lens. The camera, electronics and battery are located in a cylinder that serves as pressure housing. The bottom end cap has flash tube mounted and is located just above the prism. To control the descent speed of the frame, a hydraulic cylinder assembly is needed. This cylinder is filled with oil and is mounted between the main frame and the prism. To limit the penetration of the prism to the desired depth, penetration stops are mounted on the frame rods. A rubber wiper blade cleans the prism window as it penetrates and again as it is withdrawn.

SPI with indications of the various components. ©VLIZ

VLIZ added two small videocameras to the left and right of the prism. This allows people on the research vessel to follow where the SPI-device lands and makes it possible to take picture of the seafloor before the prism is pushed down.

  Advantages and the working of a SPI system


Usefulness of the SPI?

  • The SPI provides clear images of fine-grained aquatic sediments. Especially in estuaries where water turbidity levels are high, the SPI proves its usefulness.
  • Picture quality is independent from ambient water clarity
  • Image qualtiy is independent from the water depth
  • Additional sensors or camera scan be easily mounted on the basic SPI camera frame.

Some studies:

  • Evaluation of dumping dredging material:

SPI recordings were executed by the Institute for Agricultural and Fisheries Research (ILVO) at loswal S1 (at Vlakte van de Raan).
(The results of this research have not yet been processed or reported).

  • Evaluation of sediment changes in relation to sandextraction:

De Backer A. et al., 2014

  • Study of the changes in sedimentstructures and biological activity before and after fishery activities:

This research is in the framework of the EU-project BENTHIS.
For more information and SPI images: click here.
During this research, a movie is made using the SPI system on the RV Simon Stevin.

Technical details

The SPI that VLIZ has put at the disposal is a 3731-D Camera System and contains the following features:

  • Nikon D7100 Digital Camera
  • 16 Gigabyte CF Card
  • 35mm, f2.0 lens (52,5mm 35mm equivalent)
  • Electronics/strobe board with frame counter
  • Pressure Proof housing
  • Sliding, water filled prism with adjustable weights
  • Hydraulic piston to control penetration rate
  • Stainless steel tubular frame with hinged mud doors, tubular stainless main frame, aluminium housing assembly and prism.
  • Main battery: 12V, 3 amp-hour sealed rechargeable battery. A fully charged battery can easily make 300 images.  
  • Controlling computer for added cameras: Macartney Luxus Compact Media Controller

Dimensions of the SPI. ©VLIZ

For more technical specifications: click here

How to borrow a SPI?

For more information about our rental service, please contact VLIZ

Use and conditions

Note: if you use the SPI of VLIZ as a scientist, please refer to it in your publications as: 'This work was supported by data & infrastructure provided by the Flanders Marine Institute (VLIZ)'.