A GPS sonobuoy localization system

Abstract

A GPS localization system is described that uses the precision navigation signal but does not require a SAASM decoding unit in the sonobuoy. The system operates by retransmitting a selected 1 MHz portion of the GPS L1 or L2 signal spectrum from the sonobuoy to a Master Control Station (MCS). By offsetting the selected spectrum about 2 MHz from the center frequency of the GPS band, both the current P(Y) signal and the new M-code signal can be accommodated. By cross-correlating the retransmitted signal with the same signal received at a remote site a differential delay can be computed for each visible satellite. This delay defines a prolate spheroid with one focus at the satellite and the other at the remote site. The intersection of the measured prolate spheroid with the oblate spheroid approximation of the sea surface defines a closed curve on the surface of the ocean on which the sonobuoy lies. Two additional satellite measurements or two additional measurements of the same satellite from a moving remote site such as an airplane then locates the sonobuoy uniquely.