V.L.F. RELATIVE NAVIGATION

An experimental long-range relative navigation system has been employed on the research vessel Atlantis II of the Woods Hole Oceanographic Institution during cruise 8 to the Indian Ocean in 1963 and Cruise 15 which circumnavigated the globe in 1965. The very low frequencies (V.L.F.) transmitted by stations having stabilized carriers are attenuated to a much lesser degree than higher frequencies and can be received throughout the world. The V.L.F. transmissions provide navigational information from the comparison of the received signals of two or more stations with a precision oscillator which serves as a reference. Geographical changes result in phase changes which may be computed to longitude and latitude. Since a known starting point is required, the system is relative. The Atlantis II was able to obtain the loan of a satellite navigation set from the U.S. Navy for Cruise 15. Reference points were supplied several times each day to the V.L.F. system, if needed. Best positioning agreed to within 1-3 nautical miles from best ships position under favourable conditions. The system also was able to provide (1) a measure of ships drift on station, (2) precise time and frequencies for the digital computer, data acquisition system, clocks and recorders, and (3) a calibration of the electromagnetic log while at sea.