According as the cathodic protection system on board results in an extremely low frequency（ELF） electric field

a marine electric field sensor based on virtual instruments is devised to complete the measurement of the ELF electric field.On the other hand

due to the conductivity of seawater

the ELF electric field produced by ship under water will attenuate speedily with the increase of its propagation distance

will be baffled readily by environmental noises.Therefore

a line enhancement computation method

based on adaptive harmonic wavelet

is proposed.Experimental results demonstrate that this method is workable to effectively separate the faint and narrow-banded axis frequency electric field signals from background noises.