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What else can I help you with?
Why can't radar be used under water?
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)
Are Decca Radar Lobes radiation safe?
There is continuing debates about "Non-Ionising Radiation" and the safety issues; although more particularly for cell phones and urban emitters rather then DECCA RADAR and DECCA Navigation emitters (note DECCA is the Chinese work for RADAR, comes from the British company that pioneered DECCA navigation). Non-Ionising Radiation is the kind of Radiation that does not strip Ions from bio-chemical bonds unlike other more harmful radiations like Gamma, Nuclear Radiation. RF radiation waves are Non-Ionising, however specific frequencies can be more readily absorb by some parts of the body then others. This is to do with resonant frequencies for body tissues and the one quarter wavelength in the RF wave it self. The rate of absorb-ion is known as the SAR (Specific Absorption Rate). The general recommendations are not to stare directly into RF beams or expose soft tissues for very long periods of time and short ranges to the emitters. Some medical practitioners believe that some frequencies have a risk at close ranges for developing cataracts etc. It is also important to understand that RF power lowers as a function of range by a "range squared law", so the power drops off quite quickly with range. Other factors are amount of exposure you receive (long term) and the frequency and power you are being exposed to (the dose). In the RADAR case it is also important to remember that they use high gain antenna, and this means that the radiation is mostly in one direction and much less in others. In the DECCA navigation emitter case the energy level is less power and is more omni directional. The RADAR case's concentrated beams maybe scanned and the RF Power maybe pulsed (not constant). The Radar beams should be arranged to not point directly into inhabitants at close ranges, and the specific range is dependant on the mean power scan rate and range against the frequency. RADARs are arranged in this way. In the DECCA navigation case the RF is Continuous, and given the range of properagation is quite far you would expect the power levels also to be much higher, however the frequency is quite low at 70 - 130 kHz and lower frequency propagate much better then higher ones so the power level can be much less. It is also believed to be much less harmful risk as these frequencies are far away from water and bio-chemical resonates. However, if you work with RF and/or RADAR it is impotent to remember that repeated exposure can harmful and that the Microwave Oven was discovered by a scientist that melted a chocolate bar in is pocket because it was in a radio beam at very close range. I do not now if he suffered as a result of it but I assume the chocolate bar was not consumed.
