Consider the diagram below illustrating how A-scans work, why doesn't some of the reflected sound on its way back at the red circle interface reflect again (thereby reducing the signal intensity recorded at the green arrow)?
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Some of the sound waves do get reflected on their way back, which reduces the intensity of the returning echoes. But enough energy is returned to allow imaging to be done nonetheless.
niels nielsen
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They in fact do get reflected multiple times. With each reflection one has (1) reduction of amplitude due to reflection coefficients (absorption, etc) and (2) more geometric spread from the longer propagation path. What you would see is a long series of pulses getting smaller and smaller, and possibly being flipped relative to previous pulses. This diagram is showing you the "leading" pulse from each internal reflection. This might be called a primary return depending on the discipline or text. Some signal processing is needed to separate all these out and make a logical determination of primary and secondary returns.