Many of today's sounders use the equivalent of radar's short time constant (STC) circuit, which reduces the receiver's sensitivity to close-in targets, including energy reflected from surface turbulence. Anyone who has manipulated the STC control knows that if the STC is slightly too high, even large targets will disappear. Another major imaging challenge occurs when fish are close to the bottom. The large signal reflection from the sea floor can overwhelm the signal processing circuits in conventional sounders, making the fish close to the sea floor difficult or, in some cases, impossible to see. Other variables are also at play, whether the space between your hull and the sea floor is 20 or 2,000 feet. Seeing the fish can depend on their size, the water temperature or its salinity characteristics.