Which factor has the greatest effect on the amount of gain required to obtain an echo sounder reading?

• A. Type of bottom
• B. Water depth
• C. Temperature
• D. Salinity

Answer: (A)

The key idea is that gain must match the strength of the returned echo. The most important factor here is the bottom type because it determines how much of the transmitted sound is reflected back to the transducer. A hard, rocky or coarse bottom reflects a large portion of energy, producing a strong echo that needs less gain to be detected. A soft, muddy bottom reflects much less energy, giving a weak echo and requiring more gain to obtain a readable signal. Water depth, temperature, and salinity do influence signal propagation a bit, but their effect on the necessary gain is smaller compared with how reflective the bottom is.