Originally Posted by GarageYears
However I do wonder why the pinger frequency is so high?
37.5kHz = 5.5dB/km attenuation
9kHz = 0.5dB/km <<< 10 times less, or potentially 10 times the detection range.
The figures for detection have been discussed before, recently and a year ago. At 4km depth the probability of detection from Emeraude, even from directly above, was probably less than good. I expect that they were using every vessel they had available.
30-50kHz falls in an area of decreasing or minimum ambient noise (depending on depth). That is a good thing for typical scenarios where a plane goes down in shallow water near an airport; also the attenuation is not as big a factor in shallow water.
Certainly 9-15kHz would be a better range. This is the band commonly used for deep water transponders. The problem is that the typical transducers are about 1/2 liter in volume and weigh a kilogram or more. Aircraft designers are concerned with weight. BEA (or some other agency?) has called for lower frequency as a result of this accident.
Originally Posted by RR_NDB
Pingers are VERY simple devices. And not costly.
Itīs "performance" can be (easily) improved.
Why not (for longer range airliners) use extra pinger(s) with specs. like:
- Better (mech.) survivability (not a tiny one attached to a CSMU)
- Increased duty cycle (allowing RX DSP)
- Better frequency spec. (<1%)
- At another (lower) frequency
- Battery capacity (also) up to 90 days
Weight. All of the items listed add weight; some add a lot. I'm not saying that they aren't good or possible things to do, but I'm sure that's why they have been avoided in the past.