How to set up a stereo BRUV system?

[marine....@gmail.com]

What is involved in setting up a stereo BRUV system?

Cheers

[Euan Harvey]

The principals of setting up a stereo-video system are reasonably straight forward.

You need to carefully choose your cameras.  If you can, get progressive scan high definition cameras that will record the best image quality you can.  A bigger sensor is better than a smaller one. The cameras want to have the ability to switch off image stabilsation.

Once you know the cameras you can get information on the sensor size, the pixel size and spacing on sensor and the focal length of the cameras (will you need a wide angle adapter?).  Using this information it is possible to determine the distance you need between the cameras and the convergence angle to optimise the system for the area you want to sample and for the accuracy and precision you require.

 

One of the main issues with constructing a stereo-video making the system stable. The housings need to be mounted very securely to the base bar so there is no movement at all.   You should be able to grab housing with your hand and really try and shift it and see no movement at all in any direction.  Similarly, the camera must relocate back into the housing at exactly the same place.  For the last 20 years we have used relocating pins to ensure the camera front port  goes back into the camera housing in exactly the same place.  The other thing that we do is mount the camera to the front port.  This means that any movement associated with taking the camera in and out of the housing to change batteries or memory cards is minimised.  Without doing this you ned to recalibrate at the start and end of every deployment. 

This is also one of the major issues with using cameras like the GoPros and the Sony Action Cams.  There is no way to be certian that the cameras are going back into the housings in exactly the same place every time.  Consequently, you may have large measurement and precision errors which are associated with the camera system not being stable.

 

There are two papers on this subject which I have attached.  I hope this helps.

 

Harvey, E. and Shortis, M. R. 1998. Calibration stability of an underwater stereo-video system: Implications for measurement accuracy and precision.  Marine Technology Society Journal, 32(2): 3-17.

 

Shortis, M. R., Miller, S., Harvey, E. S. and Robson, S. 2000 - An analysis of the calibration stability and measurement accuracy of an underwater stereo-video system used for shellfish surveys. Geomatics Research Australasia, 73: 1-24.