WhitelineThe GSD 20 or GSD 21 can help you determine whether the bottomis hard or soft. When the sonar sound waves are reflected backby the bottom, a hard bottom returns a stronger signal than a softbottom. A thin whiteline indicates a softer bottom, while a thickwhiteline indicates a harder bottom. Normally, a red line is usedto show the point where water meets the bottom. This line followsthe bottom contour, along with any significant objects lying on thebottom. The unit uses the whiteline function to make the bottomlayer information easier to distinguish.Whiteline OffWhiteline OnThickWhiteline: HardbottomThermoclinesA rough definition of a thermocline is a break in water wherethe water temperature changes faster than the water above it.Thermoclines are shown as the weakest colors.One of the unique features offered by Garmin is See-Thru®technology, which allows the GPSMAP 376C to hear both weak andstrong signals simultaneously so it can identify fish returns underthe toughest conditions, such as suspended in thermoclines or evenhiding near structures. See-Thru technology allows the GSD 20 orGSD 21 to “see” through thermoclines and helps locate fish wherethey live.Thermocline114 GPSMAP 376C Owner’s ManualSETTING UP AND USING SONAR > U NDERSTANDING SONAR190-00508-00_0C.indd 114 11/6/2006 9:47:44 AM
