Bottom Classification - BioSonics, Inc

Bottom scattering is a complex physical phenomenon. Movement of the vessel has an effect on the convolution
of the transducer beam pattern function and the oblique back reflection function of the bottom. If we extract
from the first and second bottom echo components of an echo signal related to the hardness and roughness of
the seabed, then the clusters boundaries (rectangular fields) representing different bottom categories can be
established in x/y coordinates (see Figure 6). The hardness signature is estimated by taking the integral of the
echo envelope of the second bottom echo (E2) squared and the roughness signature is estimated by taking the
integral of the second part of first bottom echo (E1).
Figure 6. Projection of Hardness (E2) and Roughness (E1) signatures in the VBT software and classification
fields (clusters) in x/y coordinates.
This method of bottom classification using the first and second bottom echo energy integral was developed and
published first by Orlowski (1984). Additional research was done by Chivers (1990). The method was
commercialized first by Rox-Ann. This is the B2 method implemented in the VBT software.
2.4. First Echo Division Method
Hardness and roughness signatures can be extracted from the first bottom echo. The following are distinct
phases of the bottom echo formation (see Figure 7):
• Phase 1 - Attack - from the moment the pulse reaches the bottom until the time when the bottom is
reached by the back slope of the pulse.
• Phase 2 - Decay - from the end of the attack phase and lasting until the time when the front of the pulse
reaches the boundary of the ideal beam pattern.
• Phase 3 - Release - lasting until the time when the pulse completely enters the bottom.
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