above described embodiments is unacceptably high the double multiplex processing improves channel separation when additional system complexity is warranted an optical sensor array transmitter receiver 84 includes a quantity of n laser sources 86 and n electronic modulators 88 each laser source 86 having its own distinct wavelength u03bb i and modulated by a corresponding modulator 88 with its own different modulation signal s i where i ranges from 1 to n therefore each laser source 86 has an output with its own distinct wavelength and modulation signal each modulation signal s i for each modulator 88 has its own distinct and different periodic variation in amplitude which modulates its corresponding laser source 86 in frequency proportional to the rae of change in modulation signal s i amplitude modulation signals s i may assume various periodic waveforms but sawtooth waveforms are preferred since they cause linear periodic shifts in frequency for their respective laser sources 86 each laser source 86 is connected to n different fiber optic sensors 90 mounted in a towed fiber optic array 92 via a fiber optic input line 94 which passes through a tow cable 96 and couples to each sensor 90 by a fiber optic input coupler 98 the n 2 sensors 90 are arranged into n sensor groups 91 so that each laser source 86 connects to one and only one sensor 90 in each sensor group 91 as a result a total of n electronic modulators 88 modulate n.