**7.5. Signal aliasing**

Strong echoes from close‐in ranges can alias into distant range cells in systems that transmit while receiving. This "ringing" phenomenon produces spurious echoes in distant range cells that can be erroneously interpreted to be tsunami echoes. These far‐out spurious echoes are easily distinguished from real tsunami echoes, as they appear at the same time as the real tsunami echoes from close‐in ranges. If they were caused by a real tsunami, they would appear earlier at distant ranges. Also current amplitudes extracted from the spurious echoes are usually independent of depth. Fundamental, linear shallow‐water wave physics [1, 6] shows that the current amplitudes always decrease with depth. Observations from Chile of the Japan tsunami [4], discussed in Section 3.4.3, appear to show indications of "ringing."
