Instrumentation to Measure the Depth/Time Fluctuations in Acoustic Pulses Propagated through Arctic Internal Waves

Abstract

Instrumentation for measuring the evolution of volume-scattered acoustic signals in both depth and time is described. Measurements were taken for 12 days during the spring of 1985 with transmitters and receivers suspended beneath arctic pack ice in the Beaufort Sea. These acoustic measurements were made simultaneously with extensive oceanographic measurements taken by other investigators during the Arctic Internal Wave Experiment (AIWEX). A depth cycling vertical array of three receivers and a single fixed horizontal receiver 100 m transverse to the propagation path were deployed 6.43 km from moored transmitters. A vertical depth cycle of 51 m produced a synthetic vertical aperture of 153 m. Pulses spanning three octaves in acoustic frequency (2, 4, 8, 16 kHz) were used. The scattered field was sampled more often at 8 and 16 kHz to assure sufficient sampling (better than Nyquist) of the space/time fluctuations. Ten Gbytes of acoustic pulse receptions were recorded on optical disk for later processing. The measurements provide a unique two-dimensional (space/time) dataset for testing theories of acoustic volume scattering due to internal waves and finestructure.