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Glossary Sonar Terms
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Display, FSTN: FSTN is an acronym for Film Super-Twist Nematic. FSTN is a
monochrome display technology characterized by black, high-contrast pixels. All
monochrome fixed mount Humminbird® products use FSTN technology.
DualBeam PLUS™: DualBeam PLUS™ is a Humminbird® sonar configuration that
uses two sonar beams simultaneously, and combines the information from both
beams into one view by overlapping the data on-screen, or shows each beam
individually side by side, or permits each beam to be viewed individually full screen.
Feature Memory: Feature Memory is a Humminbird® feature that retains the user's
menu settings in permanent memory. Settings are retained even when the unit is
powered off indefinitely.
Fish Arch: A Fish Arch is the apparent "arch" that appears on the display when any
object moves through the sonar cone. The arch results from a gradual decrease in
distance to an object as it moves into the sonar cone. The distance to an object
changes due to the conical shape of the sonar beam, which causes the distance to
be greater at the edges of the beam than at the center of the beam. When this
distance change is graphed on the display, an arch appears.
Fish ID+™: Fish ID+™ is a Humminbird® feature that uses advanced sonar
processing algorithms to determine if a detected object is likely to be a fish. When
the sonar signal from an object meets strict parameters, the unit draws a Fish
Symbol (or icon) and the digital depth of the target. On DualBeam and DualBeam
PLUS™ units, fish detected in the narrow center beam are shown as shaded
symbols, and fish detected in the wider beam are shown as hollow symbols.
Fish Symbol: A Fish Symbol is the graphic that is displayed on the screen when Fish
ID+™ determines that a sonar return is likely to be a fish. See Fish ID+™.
Freeze Frame: Freeze Frame is a Humminbird® feature that pauses the sonar
scrolling so that the image on screen can be studied with greater detail. See
Instant Image Update.
Frequency: Frequency is a measure of the number of sound wave cycles per second
of a sound impulse transmitted underwater. A typical frequency for fishfinders is
200 kHz, which offers a good balance of performance under many conditions.
Lower frequencies, 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: Grayscale is the use of varying shades of gray to represent the strength
of the sonar signal on the display , and is a very intuitive method of presenting
information. Traditionally, the strongest sonar signals are represented in black, and
progressively weaker signals are represented in progressively lighter shades of gray.
Grayscale, Inverse: Inverse Grayscale is a Humminbird® feature that reverses the
correlation of sonar signal strength and the shade of gray typically used to
represent it. The strongest sonar signals are represented by "white", and
progressively weaker signals are represented in progressively darker shades of gray.
While somewhat counter-intuitive, this method makes the sonar images crisper,
and has the benefit of enhancing the apparent sensitivity because the weaker
signals appear bolder. Inverse grayscale works well in very clear water. Debris-laden
water often appears as a lot of clutter on the screen.
Instant Image Update: Instant Image Update is a Humminbird® feature that
updates all the sonar information on the display when Sensitivity and a variety of
sonar settings (Bottom View, Range, etc.) are modified. This differs from the
traditional functionality that only updates the new sonar information collected after
the setting change. Instant Image Update permits more accurate fine-tuning of the