Application of CDMA modulated signals in seafloor remote sensing

The paper investigates the application of digital modulation access technique called Code Division Multiple Access (CDMA) to remote sensing of a seafloor. In a traditional sonar, the next ping cannot be sent until the echo from previous transmission has been received by the sonar transducer. As a result, such a sonar system is characterized by low duty ratio what causes the decrease of data resolution especially for larger depths. Using the CDMA modulation technique, may reduce pulse repetition rate. In the CDMA technique, each sonar pulse consists of several multiple narrow pulses, where each is encoded with a phase shift 0 or đ based on a spreading code. The paper presents the performance investigation results for this modulation scheme as applied both to transmitted and seafloor backscattered signal. The bottom backscattering was modeled numerically for typical bottom material and morphology. The advantages and constraints of the proposed technique were discussed in the context of echo detection and usefulness in acoustic seafloor characterization.