By definition, photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images. But what does this all mean?
The goal of photogrammetry is to create a complete 3D model from two-dimensional data (photos) taken from different angles, assembled via a special computer software. The final result can be presented in form of an animation, which can show us the desired area or object from multiple angles or the digital elevation map of terrain. The final 3D model is perfect source for virtual reality and interactive museums. It can also be used to create 3D-printed models of exhibits and relics.
Underwater photogrammetry is specific type of photogrammetry due to underwater environment conditions. Normally you make hundreds of photos for photogrammetry, but underwater supply of gas or sometimes even the amount of dives are limited. The goal here is to collect enough data to construct a model, with similar light conditions, across all photos taken, ideally to shoot all you need in one dive. Of course this is not possible for some projects due size of the site of condition underwater. All of this means your attention will rest solely on the target object, which is why you will need a safety diver. The guy with the most boring, but also the most important job. Your safety diver looks out for you, helps you to keep track of all necessities, so that you can focus on your job. To assure the safest and most effective working conditions possible, one has to not only have a dive plan and proper gear, but also adequate diving experience and skill, though the level required can differ in regard to the site. Often moving in a rather small area of your site, you also need to watch out and take care not to impair/destroy your visibility with unnecessary movements or perculation. And let us not delve into the topic of photogrammetry in caves or flooded mines and other submerget objects (wrecks).
While most cameras are fine and sufficient on the surface, you will need a proper underwater housing as well as lights or flashes in order to work underwater. You need to be familiar with your equipment and have the necessary knowledge of the techniques used to gather the data for the model in the most efficient way. You will not be able to learn it “on the spot”.
There is also the question about the most suitable camera for the job? One for photogrammetry should have high resolution and the option of manually adjusting parameters such as aperture, time and ISO. You can try shooting in “fish mode” but this kind of automatic adjustment will not be enough for what you want to achieve. It is important to take the photos of the object/site in the correct order and with the right amount of overlap. Quality of the images has great impact on the final result and number of details visible.. Even with the best computing software and technology available, if your source data is insufficient, you will not end up with a good model with enough details.