Initially, echounders were merely used for measuring the depth beneath the vessel or for detecting fish. One type of echosounder utilized a special type of transducer that gave a longer 'tail' to the echo of an undulating bottom. However, this effect could be caused by rocks or by sandy humps so, although it was useful, it could not be considered to classify the type of bottom. In recent years, computer development has led to far greater analyses of the echoes returned from targets. One of these developments is the introduction of the bottom discrimination echosounder (also known under the trade name Roxann).