What is an example of a 1D sonar?

A simple depth sounder or echosounder is a 1D sonar. These systems simply tell the user the depth directly below the sounder. They are not able to warn the user about the rock, submerged shipping container, sandbar, whale, boat, or other obstacle ahead of the vessel. In the very worst of cases, if the sounder is located in the stern of the vessel, the bow may actually be grounded on an obstacle while the sounder continues to tell the operator that there is still water below the keel.