What is a backscatter?

Natural History

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VIDEO: How does backscatter help us understand the sea floor? Here's what you need to know in less than a minute. Transcript

Backscatter is the reflection of a signal (such as sound waves or light) back in the direction from where it originated. Backscatter is commonly used in medical ultrasounds to understand characteristics of the human body, but in the world of hydrography and marine science, backscatter from soundwaves helps us understand characteristics of the sea floor.

backscatter image

A backscatter mosaic, which records the strength of the sonar return from the ocean floor, is overlaid on a nautical chart.

NOAA ships equipped with multibeam echo sounders use beams of sound to map the ocean floor. These sonar systems collect two types of 3D data: sea floor depth and backscatter. The sea floor depth, or bathymetry, is computed by measuring the time it takes for the sound to leave the sonar, hit the sea floor, and return to the sonar. Backscatter is computed by measuring the amount of sound that is reflected by the sea floor and received by the sonar.

Different bottom types “scatter” sound energy differently, telling scientists about their relative hardness and roughness. Harder bottom types (like rock) reflect more sound than softer bottom types (like mud), and smoother bottom types (like pavement) reflect more sound than bumpier bottom types (like coral reef).

Combining bathymetry and backscatter data collected by multibeam echo sounders allows scientists to create very detailed 3D maps of the sea floor and the habitats present there. The information is used for multiple purposes, including marine ecosystem protection, coastal hazard preparedness, and navigation safety.

Video Transcript

Backscatter—measure of sound that is reflected by the sea floor and received by the sonar. A stronger return signal indicates a hard bottom such as coral or rocks. A weaker return signal indicates a soft bottom such as mud. Scientists use this information to create detailed 3D maps of the sea floor and the habitats present on the bottom of the ocean with the goal of improving navigation safety and marine ecosystem protection.

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