| Glossary | Sonar Terms |
Beam (Sonar Beam) The wide,
Bottom Contour The profile of the bottom graphed to the display as the depth changes.
Bottom Hardness The density (or composition) of the bottom. Varying levels of hardness can be determined by interpreting the “thickness“ of the main sonar return. Hard returns appear thin and black, softer returns appear thicker and less black. It is important to note that a sonar return from a sloping bottom can have the appearance of a softer bottom.
Cavitation The effect of air bubbles created as the propeller rotates and the boat moves through the water.
Cone Angle The angular measurement of the sonar beam at a specific dB down point (i.e.
Dead Zone The area of the sonar beam that receives the sonar signal after the main bottom return.Fish and other objectsclose to the bottom that fall withinthe dead zone will probably not be visible in the sonar beam. Precision sonar beams, such as the Humminbird® 20° beam, have a smaller dead zone than wider sonar beams.
Decibel The measurement for sound pressure level, or “intensity”ofthe sonar return. See dB Down Point.
dB Down Point The standard decibel level at which the sonar cone angle is measured,and is written as “@
Display, FSTN (Film
Frequency A measure of the number of sound wave cycles per second of a sound impulse transmitted underwater. A typical frequencyfor fishfinders is 200 kHz, which offers a good balance of performance under many conditions.Lowerfrequencies, such as 50 kHz, are capable of penetrating to greater depths, but with less resolution. Higher frequencies, such as 455 kHz, offer greater resolution, but are limited in depth performance. Humminbird® uses a variety of frequencies that are optimized for specific applications.
Grayscale The use of varying shades of gray to represent the strength of the sonar signal on the display. Traditionally, the strongest sonar signals are represented in black, and progressively weaker signals are representedin progressivelylighter shades of gray.
Noise The unintentional, external sound waves that interfere with the optimal operation of sonar. Noise appears as random “dots“ on the display and is caused by a variety of sources. Many Humminbird® products have a Noise Filter menu setting that allows the user to clear the screen of noise that is difficult to eliminate (also, see Troubleshooting).
Pixels The “picture elements“, or small square blocks, that make up the image on the LCD. Measured as a vertical by horizontal number (i.e. 640V x 320H), this key specification typically indicates the quality of resolution. In fishfinders, the total resolution (vertical multiplied by horizontal) is often less important than the “Vertical Pixel“ resolution because a greater number of vertical pixels provide finer resolutionof targets detected by sonar. Sonar information on the horizontal axis can vary greatly, depending on boat speed and the Chart Speed setting.
Glossary - Sonar Terms | 144 |