What is underwater photogrammetry
Underwater photogrammetry is a technique for creating 3D models of underwater objects, which uses underwater photos and their appropriate processing using specialized software.
What is the difference between underwater photogrammetry and terrestrial photogrammetry?
Underwater photogrammetry, due to the fact that part of the process takes place underwater, brings with it many challenges related to underwater photography. These include low or variable water transparency and, consequently, underwater visibility; the disappearance of colors with depth related to the absorption phenomenon; and finally, challenges related to diving or the use of underwater robots (ROVs).
What is underwater photogrammetry used for?
Underwater photogrammetry is currently used in several fields:
Underwater archaeology
Underwater photogrammetry is used in underwater archaeology primarily in two ways. The first is the documentation of archaeological discoveries that have not yet been thoroughly investigated. Someone discovers something for the first time and it needs to be documented in advance in order to show it to the world, or to obtain money for underwater archaeological research. When there is money, a plan of action and all the required permits, underwater photogrammetry is used for the second time, this time for detailed documentation of underwater archaeological sites. Sometimes this is done once, but more and more often regular monitoring of how these places change over time is also used.
After completing their research, archaeologists publish their results. Thanks to modern technology, they can now publish 3D models online so that they are accessible to everyone. But more and more often they decide to publish models in museums, in the form of 3D prints, which are slowly replacing old models and dioramas. There are also museums where visitors can visit underwater archaeological sites in virtual or augmented reality.
Here is an example of the use of underwater photogrammetry in archaeology. This is a 3D model of an ancient Roman wreck that lies 45m underwater, near the islet of Šćedro in Croatia. We made it a few years ago for the University of Split and the Ministry of Culture and Media of the Republic of Croatia.
Documentation of flooded mines and underwater caves
Flooded mines are remnants of human activity, often long and related to local culture, tradition and economy. So even if they are no longer used, they still constitute cultural heritage, and the more time passes, the more they are forgotten and the more destroyed by the forces of nature. Hence the need to document this heritage by creating three-dimensional maps of mines that most likely no human will ever walk in again.
But cave and mine divers will enter into these places. And it is also for them and with their involvement that maps of flooded mines are currently being created, as maps of underwater tourist attractions, or not fully explored places for exploration.
A great example is the Maria Concordia Mine 3d Scan project implemented by the Submerged Foundation.
It’s similar with underwater caves. These are often places that cave divers visit, and it’s with their help that 3D models are created. Until now, they only had drawn maps, sometimes photos of characteristic points taken by others, sometimes films. Now, thanks to underwater photogrammetry, they can have 3D maps of entire networks of tunnels and chambers. If a cave is entirely explored, they can have a complete map. If it’s partially unexplored, it also makes it easier for them to find out where to explore further. Scientists studying such caves can also benefit from 3D maps, especially if they don’t dive in caves themselves.
Maps for divers and diving centers
It is estimated that there are about 9 million active recreational divers in the world. People who are passionate about exploring the underwater world. There are many wreck enthusiasts among them, actually so many that some countries, such as Malta, have decided to sink old ships with divers in mind.
Knowing the diving business from the inside, I can say with full responsibility that until now one of its weakest links in planning safe and enjoyable dives was the availability of up-to-date and detailed maps of dive sites. But this is slowly changing, because new technologies, such as underwater photogrammetry, mean that more and more popular diving locations are well mapped, some already in 3D. We have also contributed to this, with our 3D map of the P31 wreck , which is located near the island of Comino, in Malta.
Marine Conservation and Research
Underwater photogrammetry is useful in this field for scanning both entire areas and individual marine organisms or colonies of organisms. Scanned areas are, for example, coral reefs, which can then be studied based on 3D models without entering the water. With the help of underwater photogrammetry, it is also possible to regularly create models of the same reefs and thus monitor the changes occurring on them over time. On the other hand, scanning individual organisms or colonies of organisms includes, from example, precise scanning of individual corals, the monitoring of which can supplement data collected from monitoring the entire reef. Below is a photogrammetric model of a coral reef in the Maldives , created by the Submerged Foundation.
Oil and Gas Industry
In this area, underwater photogrammetry, often using surface-operated vehicles (ROVs), is primarily concerned with inspecting and monitoring underwater infrastructure such as pipelines and platforms to ensure they are still operational and safe to use.
What is the future of underwater photogrammetry?
This is certainly a field that will develop and popularize. Hardware will become smaller and easier to use, and software will use artificial intelligence to speed up photo processing and facilitate the creation of even complex models. However, for a long time, a human will be needed for all this, especially at the photography stage. In any case, underwater photogrammetry, just like photography today, will be available to everyone and will accompany all maritime-related industries.
Of course, over time there will be autonomous robots taking underwater photos for us, but people will still be involved at the planning stage of their mission. Sooner, however, improved robots will be used for underwater exploration of places that are still inaccessible to them today. Therefore, there are many more discoveries waiting for us under water!
Mariusz Milka
Digital Heritage and Underwater Photogrammetry Specialist