A Multi-Hydrophone Digital Acoustic Buoy System with In-Situ FFT Processing

Two major problems have been historically associated with self-contained analog acoustic data acquisition buoy systems. First, analog tape recorder characteristics bound the obtainable dynamic range and time base stability of the recorded data. Second, post-processing of the data tapes to obtain the required acoustic information can be both time consuming and expensive. To address these problems, a new buoy system has been developed at NUSC. Acoustic data from each of eight hydrophones is digitized with an instantaneous dynamic range of more than 72 dB available over the frequency range 4-350 Hz. The acoustic data is Hanning weighted and Fast Fourier Transformed to yield spectral results in 2 Hz increments. These spectral results are stored in both complex and ensemble averaged forms on a digital cartridge tape. All spectra are calibrated with respect to absolute sound pressure level. The first at-sea test of the system occurred in September 1983 at a deep water location near the Bermuda Islands. In this paper we will describe the SEACAL buoy system and acoustic results from the 1983 sea test.