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Another factor influencing images is the sonar frequency. As the speed of sound in water is relatively constant, at higher frequencies, the sound wavelengths are shorter. As sonar echo strength is proportional to target roughness at the wavelength of the sonar source, higher frequencies pick out finer roughness better, as seen in the previous images.
Man-made objects show up well in sidescan sonar images; they usually have high acoustic impedance, and nice crisp sharp edges and corners as reflectors. However, as the image below shows, it's shape, not the intensity, that separates this plane from the surrounding rocks (see Figure 7).
Brief History of Sonar Development (page 4 of 4)
Figure 7. Man-made objects show up well in sidescan sonar images.