For all the intelligent discourse earlier in this thread regarding Doppler effects of electromagnetic waves, the mention of Doppler with respect to sound waves is curiously missing even though the effect is far more pronounced. The odds of getting precisely a 37.5 kHz return in an extremely noisy ocean are pretty low, at any considerable distance from the source.
Right, it wasn't exactly 37.5 kHz. It was 33.2kHz. They believe this is still indicative of the pingers, as the AF447 was transmitting at ~34kHz. But the cadence/interval of both pings (1Hz) did match, that's why they believe it is a legit detection.
re the Chinese RIB, I believe that was a handheld detector. (the kind the Chinese have is designed for shallow water/handheld use e.g. by a diver)