Passive sonars have been around for a very long time

but it has nothing to do with Sat Nav system.

Sat Nav relies on time difference technique (triplet star configuration in standard reception mode) to pinpoint one's location.

Passive sonar can be used to determine emitting source's course, position and speed by analysing transmitter's accoustics and change in accoustics (given the passive sonar's current course/speed). However, accoustics do reflect, scatter, deflect depending on density, surface conditions and ocean water boundaries etc - making pinpointing target no easy feat.

What also makes it difficult is that surface sonar bouys are easily picked up (as Chinese fishermen often do against sonar bouys dropped by American/Japanese P-3Cs) and they scatter with due to oceanic current. It is also very very expensive. Given the number of approaches in the First and Second Island chain, it is not possible to cover all approaches with sonar bouys. On the other hand, if you use sonar that sinks to the ocean floor (as Americans do), you are still subject to fisherman's net catching it and more seriously, you need underwater communication to transmit captured sonar data. Low frequency (long wavelength) transmission is still the only effective mean of communication. However you are restricted in the amount of information you can relay due to low bandwidth offered by low frequency. More seriously, transmission as such would also expose the location of unerwater sonar which invites its destruction and/or obfuscation. Americans get around this issue by using undersea fibre cables (which are often cut by fishermen's net). Again, it is a hugely expensive excercise with questionable result under real war fighting condition (since these cables would be cut in the opening salvo of a hot war).

To monitor such large area as oceans, Ocean Surveillance Satellites and OTH radars are really the main assets with other capabilities such as undersea sonar and MPA (Maritime Patrol Assets) augmenting them.