I am saying that you are taking sonar detection as granted, and it is not granted, not even by longest shot there is. Sonar is not magic, same as radar is not magic, and nothing is granted. Sry to pierce your bubble on that one. You all make mistake by assuming detection, first thing they tell you is "assume nothing". My point is military always assumes enemy will pass its radar coverage and its sonar coverage.
Nothing s granted. : )
It is a game of chances.
It took same time to found it : )
The principle is simple:the linear array of hydrophones dramaticaly increase the directional sensitivity .
Not just a bit, but extremly.
If the sonar is towed ,then that makes the detection less than optimal, like if you want to look around then you have to turn, but if you turn then the sonar cable will follow an arc. If it follow an arce then it can not work as linear array .
additionaly you can have different currents, temperature gradients, salt level, speed and so on.
But if the sonar system planted to the seabed then one will not make to much difference, but you have a layered system.
as the enemy submarine wandering deeper and deeper it will pass several high gain beam area.
And to make it better, the seabed sonars can "learn" the typical behaviour of the surrounding water.Like a noise source (survey ship or submarine) going throught the water perioidcaly, and creating a map of typical propagational maps for given period of day/year.
To make the problem more deeper, the sound waves propagation interestingly in the water.
It is not like in the air, where the sound going up, but it going down.
Means the seabed sonars more effective than the surface ones.
With a posseidon P-8 you have less chance for detection than with a pre installed seabed sonar system. Simply due to the basic laws of mother nature.
Oh ,and this is the reason why the sonar installation needs submarine.
The sonar array has to be perfectly strait, and has to face the pre defined direction .
Additionaly the sonar installation can works as multistatic active sonar system as a bonus . : )