Broadband and narrowband echosounder signals produce comparable estimates of volume backscattering

Despite the potential benefits for species identification, broadband acoustic data collection has yet to be widely implemented in fisheries surveys. In large parts, this is because it remains unclear whether broadband echo integration produces similar abundance estimates as traditional narrowband data. This work compares the integration of broadband and narrowband data from EK80 transceivers operating at nominal frequencies of 38, 70, 120, and 200 kHz. We sequentially transmitted broadband frequency modulated (FM) and narrowband continuous wave (CW) pings to investigate the relationship between the volume backscattering coefficients measured using the two signal types, ${S_{V,CW}}$ and ${S_{V,FM}}$. ${S_{V,FM}}$ was calculated using two approaches. The first approach calculated the pulse-compressed volume backscatter in the time domain, ${S_V}( t )$, using three different methods for estimating aggregate terms in place of frequency-dependent terms. The second approach calculated the mean volume backscatter in the frequency domain, ${S_V}( f )$. While time-domain estimates provide reasonable first approximations of ${S_{V,FM}}$, calculation of volume backscatter using the mean of ${S_V}( f )$ produces backscatter estimates that are statistically equivalent to those calculated from ${S_{V,CW}}$. These comparisons indicate that broadband signals processed in the frequency domain can be echo integrated for fisheries surveys, maintaining continuity of long-term indices of abundance and biomass.