A PC-BASED COHERENT SONAR FOR EXPERIMENTAL UNDERWATER ACOUSTICS

An important tool for experimental underwater acoustics research is a versatile sonar system for transmitting, receiving, and recording acou stic waveforms. In this paper the design, implementation and performan ce of a variable-frequency (25 kHz to 500 kHz) coherent sonar are pres ented, The significance of the design lies in its simplicity and versa tility, These attributes are a result of a sampling technique that pro vides quadrature samples of the complex envelope of a bandpass signal without analog demodulation using a single A/D converter. Implementati on of the design is accomplished using an ISA bus personal computer (P C), a commercially available digital signal processing (DSP) board, an d a small amount of custom electronics, Performance of the sonar, in t erms of magnitude and phase errors, is determined from wideband noise characterization, a linear-system model, and transmit/receive measurem ents.