De Robertis, A., and Higginbottom, I. 2007. A post-processing technique to estimate the signal-to-noise ratio and remove echosounder background noise. – ICES Journal of Marine Science, 64: 1282–1291. A simple and effective post-processing technique to estimate echosounder background-noise levels and signal-to-noise ratios (SNRs) during active pinging is developed. Similar to other methods of noise estimation during active pinging, this method assumes that some portion of the sampled acoustic signal is dominated by background noise, with a negligible contribution from the backscattered transmit signal. If this assumption is met, the method will provide robust and accurate estimates of background noise equivalent to that measured by the receiver if the transmitter were disabled. It provides repeated noise estimates over short intervals of time without user intervention, which is beneficial in cases where background noise changes over time. In situations where background noise is dominant in a portion of the recorded signal, it is straightforward to make first-order corrections for the effects of noise and to estimate the SNR to evaluate the effects of background noise on acoustic measurements. Noise correction and signal-to-noise-based thresholds have the potential to improve inferences from acoustic measurements in lower signal-to-noise situations, such as when surveying from noisy vessels, using multifrequency techniques, surveying at longer ranges, and when working with weak acoustic targets such as invertebrates and fish lacking swimbladders.

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Multibeam echo sounder systems allow the in situ observation of swimming and foraging behavior and give insights into the ecology of fish at the individual level. In Lake Opeongo, Ontario, 16 adult lake trout Salvelinus namaycush were surgically implanted with ultrasonic tags, released, and studied by means of mobile fisheries acoustics. The transmitted pulses from the ultrasonic tags could be detected and displayed within the multibeam echogram in real time. Tagged lake trout were relocated on 131 occasions over 12 d, for a total of 11.7 h of echogram observations. From these events we observed and quantified the spatial relationships of individual lake trout to other fish targets, schools of cisco Coregonus artedi, and the surrounding habitat. We found that all but one tagged lake trout spent at least a portion of their time close to the lake's bottom, but interestingly, many made rapid vertical swimming movements into the water column. These burst vertical movements were sometimes targeted at schools of cisco, such attacks always occurring from below the schools. During such interactions, the lake trout showed distinct peaks in swimming speed when they were between 2.4 and 6.4 m from the schools; we interpret this as the range of their reactive distance in the field. Some of the lake trout were also found to travel alongside of or to actively swim toward other fish targets, whereas others were more solitary. This type of information, made possible by the integration of fisheries acoustics and biotelemetry technology, gives us a fuller understanding of the ecology of aquatic predators and their prey and provides the direct measurements needed to quantify the bioenergetics of lake trout in their natural environment.

Echoview is a hydroacoustic data analysis software package, widely used in the fisheries research and stock assessment communities. Originally developed to handle a variety of single-beam sonar data formats, Echoview has been extended to support multibeam data. Multibeam data logging, lossless compression, and real time beamforming and display are some of the software’s core features. Multibeam data has an additional dimension compared to single-beam data, and a 3D data viewer has been developed providing 3D visualizations of the seabed and fish schools detected by built-in algorithms. Since the multibeam module is just one of many software modules of the Echoview package, data from other sources such as single-beam sonar systems and current profilers can be combined and analyzed together with the multibeam data. The combination of coincident fish density estimates from calibrated single-beam backscatter data with school volume estimates from multibeam data will represent a significant improvement in stock assessment methods. Ongoing research and development will make it possible for Echoview to follow and even set new trends in multibeam water-column data analysis for fisheries research. Features under development include calibration, vessel motion compensation, improved feature detection, and enhanced and animated 3D displays.

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