I had the pleasure of receiving a demonstration of the CODA UIS (Underwater Inspection System) in St. Petersburg, Florida this week. It is 4 dimensional as it works to provide information on the Height, Width, and Depth (3D) with the fourth dimension, Time, added in.
Basically, it provides a graphic display of the sea floor (or hull, or pilings under the pier) visually in real time - as you are traveling the length of the pier face, it is giving you the visual output at the same time - great for spotting anomalies that you will want to investigate further (such as suspicious objects, divers, etc.).
It can be a mobile platform (outfitted to a small craft) or a static position - the employment method is really limited to the imagination of the user.
For more information, please go to http://www.codaoctopus.com/. Let me know what you think.