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Black Laser Glossary

Side Scan Sonar Terminology

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There are currently 21 names in this directory
Across Track
Direction on a sonar image perpendicular to the direction of travel

Along Track
Direction on a sonar image parallel to the direction of travel

ASV
Autonomous Surface Vehicle - Unlike radio controlled craft autonomous surface vessels can be programmed or use artificial intelligence to perform missions without human control.

CHIRP
A CHIRP sonar pulse uses multiple frequencies instead of one specific frequency. Think of it as sonar broadband. CHIRP systems have increased range and resolution. CHIRP is an acronym for Compressed High Intensity Radar Pulse. The technology first used for radars was adapted for use underwater in sonars.

Down Imaging®
Down Imaging® (DI) is Humminbird®'s trademarked term for a side scan like image that covers the area directly under the transducer. See Hummibird®'s youtube for a great explanation. A link is available in Black Laser Learning's Humminbird Forum.

First Bottom Return
There point at which the water column meets the data on a side scan image. usually represents a profile of the bottom under the sonar but only when the sonar is steady. Waves changes in altitude or other motion can contribute to an irregular line.

Ground Range
Is the horizontal distance between 2 points which may or may not be at different elevations. If the elevations are different then the slant range (Line of sight) will be longer than the ground range

MEGA
MEGA is Humminbird's name for its' 1.2 MHZ (1200kHz) frequency. A system with MEGA in the model description will have the high resolution 1.2 MHz capability.

Mensuration
In sonar terms Mensuration is the measurement of length, width and height of a contact

Nadir
Lowest point on the celestial sphere below the observer. In side scan sonar terms, the sonar imagery from directly below the side scan sonar transducer. A French word derived from Arabic.

Nadir Zone
Side scan sonar data from directly below the sonar transducer, towfish, AUV or UUV where the grazing angle is more perpendicular reducing shadow length and compressing imagery in the across track.

PMA
Post Mission Analysis - Reviewing sonar data after collection.

SAR
Search and Rescue - SAR is a commonly used acronym by marine police, sheriffs and fire rescue teams.

SAR - 2
Search and Recovery - This version of the acronym is more common with commercial search and salvage.

Side Imaging® Sonar
Side Imaging® (SI) sonar is Humminbird's® registered trademark for the side scan sonar data produced by the Humminbird® sonars.

Side Scan Sonar
Side scan sonar is a specific class of sonar which utilizes acoustic backscatter to produce bottom imagery. Side scan sonar was invented by Dr Harold "Doc" Edgerton and refined for commercial use by his student Marty Klein. Some folks incorrectly use Sidescan or Side-Scan.

Slant Range
Is the range directly from the transducer to the bottom or a target. Using a hull mounted system in 100 feet of water the slant range to an object 35 feet off to the side and on the bottom will be greater than 100 feet (106 ft). So the horizontal distance also known as ground range is 35 feet and the slant range is 106 feet. Slant range is also used with radar and is defined as the line of sight between two points which are not at the same level.

Sonar Range
Is the distance from the transducer and is measured as a slant range.

Sonar Range Setting
In side scan sonars the sonar range setting is the slant range distance from which a single transducer receives data. A sonar set to the 50 meter range will look 50m port and 50m starboard. Total coverage is 2x the range assuming the towfish or vehicle is at the proper elevation above the sea floor.

UUV
Unmanned Underwater Vehicle - Commonly used by military users of autonomous underwater robots.

Water Column
The area of no bottom reflection at the center of a side scan image. The water column color usually represents no sonar return and equals the acoustic shadow color.


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