Underwater depth telemetry

Abstract

An acoustic telemetry system and technique are disclosed for remotely meaing the underwater depth and descent rate of a hydrographic package. Analog signals indicative of hydrostatic pressure exerted on the package and related to its underwater depth are periodically sampled and converted to an N-bit digital word representative of the value of pressure. Each bit of the digital word operates one of a plurality of tone generators of different acoustic frequencies in a narrow band, and the outputs of the tone generators are combined with a reference tone continuously generated to permit resolution of Doppler shifts. Acoustically projected through the water to a remote hydrophone, a composite signal representative of the combined tones is corrected for Doppler shifts by translating the frequency of the signal in accordance with shifts detected in the reference tone. The composite signal is digitally decoded to reproduce the N-bit digital word using a parallel series of frequency detectors each tuned to one of the narrow band acoustic frequencies, and the word is displayed as an indication of underwater depth using a series of latches to ensure a steady data display.