Modern photogrammetric methods like image mosaicking or 3D reconstruction (see e.g. [4]) allow to use images taken by optical cameras to accurately measure distances or volumes of objects in a scene of interest. In order to achieve consistent and large-scale maps that are not bent, biased or disrupted, it is important to understand the geometric properties of the underwater camera. At best, refraction at underwater housings is avoided, e.g. by centering a camera perfectly in a dome port[3]. We have developed methods to support this centering [1,2,3].

For flat ports and other settings where light rays change their direction during their way from the scene into the sensor, it is important to calibrate the overall camera system properly[1,4]. A possible solution is to explicitly model light refraction at the underwater housing port, which avoids systematic errors in later measurements. The required parameters can be obtained by calibration.

Stay tuned, we are preparing to make our camera calibration toolbox available !

Based on such a calibration, it is possible to apply methods like refractive 3D reconstruction [4] to images captured at the seafloor and compute a virtual, digital 3D model of the scene, that can be viewed interactively.

If you would like to calibrate a flat port camera for underwater usage, please have a look at our instructions, which are also available as an Ocean Best Practise document. See below for more resources on underwater cameras calibration, refraction and simulation:

Related Publications:

[1] M.She, D.Nakath, Y.Song, K.Köser:
Refractive Geometry for Underwater Domes.
ISPRS Journal of Photogrammetry and Remote Sensing, Volume 183, Pages 525-540, Elsevier, 2022. doi 10.1016/j.isprsjprs.2021.11.006
[Open Access Article]

[2] D.Nakath, M.She, Y.Song, K.Köser:
An Optical Digital Twin for Underwater Photogrammetry.
Journal of Photogrammetry, Remote Sensing and Geoinformation Science (90), pp. 69–81, Springer, 2022, doi 10.1007/s41064-021-00190-9
[Open Access Article]   [GEODT Supplementary Material and Toolkit]

[3] She M., Song Y., Mohrmann J., Köser K.: Adjustment and Calibration of Dome Port Camera Systems for Underwater Vision. In: Fink G., Frintrop S., Jiang X. (eds) Pattern Recognition. DAGM GCPR 2019. Lecture Notes in Computer Science, vol 11824. Springer, Cham (preprint pdf)
doi 10.1007/978-3-030-33676-9_6

[4] Anne Jordt, Kevin Köser, Reinhard Koch:
Refractive 3D reconstruction on underwater images
Methods in Oceanography, Volumes 15–16, April–July 2016, Pages 90-113, ISSN 2211-1220, doi 10.1016/j.mio.2016.03.001