This is still a difficult problem in underwater robotics, as Eliot mentioned. However, there are few works out there that are on this line of research.
Confined environments such as natural caves or artificial tunnels pose different challenges but you may be able to use some heuristics to aid your navigation depending the specifics of the application environment.
My PhD work was around this problem back on 2014, and here you can see some results. Although it was an AUV with different sonars, the same concept can be applied with a BR2 ROV and the Ping. However, is true that if more than one sonar is used, it will require different frequencies or precise timing to avoid interference.
It may help clarifying some basic concepts having a look on this paper.
Also, if you want to have a look to these kind of data, we have published them here.