Propagation in seawater. transmission of electromagnetic energy through the ocean is practically impossible at high frequencies because of the high attenuation rates encountered. for seawater, take a = 4 s-m-1, epsilon r = 81. and mu r = 1. respectively. show that seawater is a good conductor for frequencies much less than -890 mhz. for frequencies less than 100 mhz. calculate, as a function of frequency (in hz), the approximate distance over which the amplitude of the electric field is reduced by a factor of 10.