The velocity of electromagnetic radiation depends on the refractive index of the medium in which they are travelling. If the refractive index varies with frequency (or wavelength) - which is true for many media, including sea water - then the velocity will also vary. See the discussion about dispersion in this wikipedia article.

Thanks to JohnDG for his answer. I will study the refered documents.

First of all the sea water absorbs the electromagnetic waves except on some windows:

16 Hz frequency and blue visible band. The speed of electromagnetic wave in water is slower than in vacuum, but there is a good chance that telepatic waves go faster and this is mattr of perception. Ar you trying to devlop underwater communication system? what is wrong with system based on sonic signal? if you have time to wait for response.

Stan

Hi Stan,

Thanks for your answer. Would you please tell me about the reference for which you said about 16 Hz.

Regards,

Afshin