Radar is the use of a transmitted electromagnetic pulse and the evaluation of reflections to determine what is in the signal's field. Sea water conducts electricity pretty well, and anything that conducts electricity like that will absorb the electromagnetic energy of the radar (as well as reflect some of it) and not allow it to penetrate it to an significant degree. It would be like trying to see through the densest fog you've ever been in at night while using a flashlight. Almost nothing more than a couple of feet away will be visible. The dielectric constant of water is not good for RF propagating but Air is. Air has a very good dielectric constant of RF properagation, as does a vacuum. However water is good for propagating sound will although it propagates much slower the RF weaves, the distance that sound waves (which is a pressure waves) travel is vastly longer then Radio Waves (which is electromagnetic waves) would in water. For this reason SONAR is used for echo location in place of RADAR underwater, and it is worth noting that because SONAR waves propagate slower the radio waves a lot of Radar Techniques have already been proven on SONAR application before they are on RADAR one as the time base is slower. (Richard Rudd-Orthners)
Decca Radar Lobes emit non-ionizing radiation, which is generally considered safe for human health. However, prolonged exposure at close proximity can potentially cause tissue heating and other effects. It is recommended to follow safety guidelines and maintain a safe distance from the radar equipment to mitigate any potential risks.