Acoustic Backscattering Properties of Polymetallic Nodules from the Indian Ocean Basin: Results from a Laboratory Measurement

The abundance of deep-sea polymetallic nodules (PMN) can be assessed effectively using acoustic backscatter data. Controlled experiments can help us understand this capability in greater detail enabling us to optimize the sonar operating parameters for better performance. However, it is difficult to obtain PMN from deep-sea regions in sufficient quantities to study them in controlled conditions. We explore the possibility of replacing these PMN with artificial nodules by comparing the acoustic backscatter intensities of artificial nodules and PMN from the Indian Ocean Basin in a laboratory experiment. Results from our laboratory measurements reveal that the backscatter intensity from a bentonite sediment layer covered with PMN/artificial nodules, is significantly higher than returns from bentonite with no nodule coverage. Furthermore the intensity of acoustic backscatter from artificial nodules matches that of actual PMN. This indicates that for future studies, we can use these artificial nodules as proxies in place of real PMN to perform initial acoustic testing.