What are sound images?

The term “sound image” has several definitions and applications. It may be a visual representation of audio phenomenon, or it may relate to the arbitrary character of representation in linguistics.
In acoustics, sound image may be a photographic representation of a sound, for example as it occurs on a film’s sound track. The “image” may also be a representation of a sound, such as the recorded version in contrast to the actual sound. The term may also relate to the relationship between visual and audio, such as the kinds of images that particular sounds suggest.
Ferdinand de Saussure, the pioneer of structural linguistics, used the term in a different way. In defining a “sign,” he distinguished between the concept that it represented and the sound image that it represented. For every idea that the human mind holds, it must arbitrarily attach a means of representing it. While the concepts are very similar across cultures, the representations differ widely because they are arbitrary. One common example is “tree.” While plants with a trunk, branches, and leaves occur in most parts of the world, the use of the sound-image “tree” in English compared to “arbol” in Spanish is arbitrary.

Sound images refer to the visual representations of radar pulses, usually digital, to present a picture of what is happening in places we cannot see.
One of the most commonly understood examples of sound imaging is ultrasound technology, used to "see" inside the human body. Ultrasound imagery is used for a variety of medical applications, but is often associated with pregnancy. Ultrasound imagery allows physicians to "see" a fetus in the womb to determine important things like due dates, size, sex, and possible birth defects.
Similarly, sonar applications allow us to see where we would not otherwise be able to see—for example, in deep ocean environments. Through sonar technologies, we are able to send a sound pulse toward the earth and record its bounce-back rate to determine depth. The application of sonar along the ocean floor can create profiles of ridges and valleys to offer us a better understanding of what is happening deep underwater.
For more information on sonar technology, check out the NOAA Ocean Explorer link, which offers several great pictures produced by sonar technology.