Kongsberg Simrad ST90, Reference Manual

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Biomass information pane description
The Biomass information pane displays an index of the biomass in the in the current
Inspection view. The biomass index is the
s
A
value, or Nautical area scattering coefficient
(NASC), measured with unit m 2 /nmi 2 .
How to open
Before you open an information pane, you must first click in an Inspection view to make it
"active". The information provided will only be valid for the selected view.
To open the Biomass information pane, click in the chosen view to activate it, then select the
Biomass
button on the top bar. To close the information pane, select it one more time on the
top bar. You can also select
Close
in the top right corner of the pane.
Note
Information panes are only available for Inspection views.
Description
The digit shown in the Biomass information pane is a calculated index.
If more than one target is located in the acoustic beam at the same depth, it is not
usually possible to resolve them separately. This is often the case with schooling fish
or aggregations of zooplankton. In these cases, echo integration is used to estimate
biomass. Echo integration assumes that the total acoustic energy scattered by a
group of targets is the sum of the energy scattered by each individual target. This
assumption holds well in most cases. The total acoustic energy backscattered by the
school or aggregation is integrated together, and this total is divided by the (previously
determined) backscattering coefficient of a single animal, giving an estimate of the
total number.
http://en.wikipedia.org/wiki/Fisheries_acoustics, March 2015
The ST90 system records all the targets from the smallest plankton to the largest whale. The
biomass value is an indicator to how much fish you currently have in the beam. Every single
fish will emit an echo, and the sum of all these registered echoes are presented as a number.
Smaller organisms such as plankton will also emit echoes, but these are so weak that they
will hardly influence on the total biomass.
The biomass value provides you with information about the fish abundance, and as such
it may help you to decide if it pays off to start fishing. However, you must consider if the
biomass value is a result of large amounts of plankton or bait, or if you have "real fish"
Simrad ST90 Reference Manual