Developing an Open-Source Analysis Pipeline for a Glider-Based Acoustic Zooplankton Fish Profiler (AZFP)

Multi-frequency acoustic sensors such as the Acoustic Zooplankton Fish Profiler (AZFP) simultaneously observe marine species of various sizes and trophic levels. As such, they are now routinely being used to augment or replace traditional vessel-based sampling. When acoustic sensors are integrated into underwater autonomous vehicles such as gliders, they can record data at a wider depth range and over longer time periods than vessel-based sampling. The AZFP requires specialized processing and software packages that can be expensive to purchase or subscribe to. Additionally, software packages are typically designed for vessel hull-mounted acoustic sensors, and therefore are limited in application to vertically profiling platforms including gliders. This study utilized modern, free open-source software, originally developed for vessel-based acoustic sampling (Echopype), and developed a pipeline to extend Echopype for processing novel glider-based AZFP acoustic data. Echopype is a free acoustic processing package that, with alterations, can be used as an alternative to other packages such as Echoview, the proprietary software that is frequently used for processing these types of datasets. Using a case study focused on Antarctic krill, we then compared processed data outputs of Echopype and Echoview. The adapted Echopype processing method was able to reproduce the results that Echoview accomplished in calculating and plotting acoustic backscatter strength recorded by a glider-mounted AZFP. However, this correlation became weaker with more complexity integrated into the data processing stream, particularly in the comparison of data outputs after applying seafloor masking and krill swarm detection. Therefore, future efforts to address these more complex analysis features would further improve Echopype application to glider-based acoustic data.