The relative frequency response, as derived from individually separated targets on cod, saithe and Norway pout
Abstract
The relative frequency response is an important acoustic feature used to characterise acoustic
targets. This response has been defined as the sv, volume backscattering coefficient, for a specific
frequency relative to that of a reference frequency (38 kHz). The acoustic data commonly used in
these calculations are derived from integrated measurements in a region containing multiple
targets. In this study the relative frequency responses at 18, 38, 70, 120, and 200 kHz have
additionally been measured using filtered target strength data on all frequencies. The spatial
comparability of the sv-data is thus avoided, while the single-target detection becomes a new
challenge. Target strength was extracted from in situ measurements, using calibrated and digitised
data from a Simrad EK60 with split-beam transducers transmitting simultaneously at all five
frequencies. Selected series with nearly pure catches of Atlantic cod (Gadus Morhua L.), saithe
(Pollachius virens L.) and Norway pout (Trisopterus esmarkii L.) were analysed. The frequency
response derived by the new method is compared with standard integration method.
Publisher
ICESSeries
ICES CM documents2004/R:16