Garmin 190-00683-00 Manuale Utente

The GSD 21 Sounder Module can help you determine whether the 

bottom is hard or soft. When the sonar sound waves are reflected 

back by the bottom, a hard bottom returns a stronger signal than a 

soft bottom. A thin whiteline indicates a softer bottom, while a thick 

whiteline indicates a harder bottom. Normally, a red line is used 

to show the point where water meets the bottom. This line follows 

the bottom contour, along with any significant objects lying on the 

bottom. The unit uses the whiteline function to make the bottom 

layer information easier to distinguish.

A rough definition of a thermocline is a break in water where 

the 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 378/478 to hear both weak 

and strong signals simultaneously so it can identify fish returns 

under the toughest conditions, such as suspended in thermoclines or 

even hiding near structures. See-Thru

®

 technology allows the  

GSD 21 to “see” through thermoclines and helps locate fish where 

they live. 

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