Acoustic Data Acquisition And Processing Systems

Acoustic oceanography places special demands on high speed, high volume data collection and processing. Digital audio equipment provides opportunity for high quality digital recording of acoustic signals. Systems typically include one or more acoustic transducers from which signals are recorded through an audio PCM (pulse code modulation) unit onto a VCR (video cassette recorder), recording two 16-bit channels at 44.1 kHz each for up to 8 hours (Fig. la). System variations involve modifications to the PCM to allow input of additional digital data on the VCR recording and to extract the decoded serial data on playback in order to convert it to parallel for input to a computer. Different configurations may multiplex the analogue inputs (Fig. lb), or enter digital data directly into the encoder (Fig. IC). Playback systems allow the PCM to decode and error-correct the data for processing by computers (Fig 2a). The data is recovered from VCR in stream mode at the same data rate at which it was recorded (i.e. 176 K bytes per second). Real-time techniques to handle the data volume and rapid processing allow data to be stored onto 9 track tape (Fig. 3a); overviewed using histograms (Fig. 3b); windowed on selective events (Fig. 3c); averaged and processed in other ways using DSP (digital signal processing) hardware (Fig. 2b). These algorithms greatly compress the data, reducing it by 10 to 1000 times depending on the application. a n a l o g i n p u t s P C M V C R (a1