Sadly the towed pinger locator (TPL-25) is omni directional.

But by analysing the inter-ping interval you can determine a CPA point. Something below I wrote on reddit about this technique:

Due to the pulse length (10ms) there is an inherent 100Hz bandwidth in the signal, which is equivalent to the frequency shift you would expect if moving at 4m/s. In other words, Doppler measurements of a single pulse is NOT going to be useful in attempting to localise.

However, because the pinger has a relatively stable repetition rate (about 1.106s from what I could see) you can do a cool trick to localise it (assuming the source is stationary):

- Perform a pass over the area of interest (ie where the pinger is) - measure the ping times of arrival (either manually with waveform inspection or write an envelope detector) - plot the ping times of arrival versus the time of arrival modulo ping interval. ie in MATLAB: plot(toa, mod(toa, 1.106), '.'); - The plot indicates the relative distance from the source / receiver. Hopefully the plot should contain a local minimum representing a closest point of approach (ie like http://imgur.com/v1ZclaX ). This means that the source lies in a line perpendicular to the vessels course centred at the location of the receiver (ie TPL-25) at CPA time - Perform another pass over the area of interest on a course perpendicular to the first - measure the ping times of arrival and look for CPA as before - You should now have two intersecting lines. Guess what should be at the intersection? :)

This relies on having a stable ping repetition rate.

BTW this is the author of the linked post here :)

Rodney

Edit: @ISL has hit the nail on the head there. Hyperbolic trilateration using multiple simultaneous receivers is the way to go. RAAF will be trying this with sonobuoys deployed from P3-C Orions

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