Doppler processing of phase encoded underwater acoustic signals

Abstract

Travel time of an acoustic signal from transmitter to receiver provides a great deal of information about the ocean environment. Variations in the travel time of the signal may be caused by the changes in the sound speed along the path. Since sound speed is a function of pressure, temperature and salinity, measurement of this parameter in acoustic tomography provides a means to observe ocean fluctuations through the use of inverse techniques. The upcoming Heard Island Experiment will attempt to determine the feasibility of measuring global warming by measuring changes in signal travel time that may be caused by temperature changes in the world's oceans. The signals to be transmitted in this experiment are phase encoded maximal-length sequences of various lengths which are well suited to measurement of travel time. The objectives of this thesis are to provide a software package, in C, that will allow participation as a receiver in this experiment, and to provide a general capability to process any maximal-length sequence, transmitted at any carrier frequency and with any reasonable Doppler. A background on wave propagation, maximal-length sequences, and Doppler processing are presented in this thesis.