What is an example of a 2D sonar?

Other systems that are called Forward Looking Sonars do actually look forward but they are only able to discern information in 2 dimensions. Generally, they can tell the user that there is an object at a particular bearing and range, but they cannot tell the user if the object is at the surface, in the water column, or on the sea bottom. They simply have one horizontal slice through the water. These systems are unable to tell the user if the object is 5 feet below the surface or 50 feet below the surface. Some 2D systems even go as far as to have a second array giving one vertical slice through the water. However, in this configuration, the vertical slice can only give the user information about the range and depth of an object, it cannot tell the user at what bearing the object is located ahead of the vessel. Even the most advanced 2D system cannot correlate between the vertical and horizontal slice.