Sunday, April 13, 2014

Automatic detection of MH370 ULB pings

In my earlier post (Analysis of suspected MH370 pings) I manually inspected a audio waveform to determine ping times of arrival. Whilst this is managable for the short segment I looked at, to perform this analysis over many hours or days of recordings would be a bit tedious and probably error prone.

This afternoon I put together a quick MATLAB script to automate this process and ran it over the whole Youtube video audio.

The algorithm is as follows:
  • Read acoustic data from file in 1s segments
  • For each 1s segment use a Hilbert Transform (using FFT) to calculate the envelope of the waveform
  • Calculate noise by smoothing the envelope with a window of length 0.1s (or 10x expected pulse width)
Envelope (red); Smoothed (black)
  • Calculate SNR as the envelope amplitude divided by the noise
  • Locate rising edges in the SNR that exceed the detection threshold (ie start of pulse)
SNR (green) with detected pulse (x)
  • At end of processing plot detection times of arrival module ping interval (1.106s from previous analysis)
Time of Arrival Ping Graph


In the resulting plot that there are 2 distinct sections of coherent detections. The others are false detects from other in-band transients.

Interestingly I had not noticed the 2 individual segments previously, but upon a second listen a distinct discontinuity can be heard hence the 'realignment' of the ping times of arrival. This plot shows that the first segment corresponds to a time where the TPL was going away from the source as the times of arrival are increasing. The second segment has the TPL coming closer to the source near CPA due to the decrease and stabilisation of time of arrival.

14 comments:

  1. This is really interesting analysis. I can only hope the team there in your "backyard" working on the search is as creative and skilled as you are. Thanks for sharing.
    Robert
    Raleigh, NC USA

    ReplyDelete
  2. Dumb question. Can we plot perpendiculars from the segments to suggest the source location?

    ReplyDelete
  3. Thanks Robert! I'm familiar with AJAAC and some of the analysts there. They're a clever bunch and I'm sure they're processing the data they have to extrac the maximum.

    Bruce, spot on mate. That is what I suggest to do at the end of my previous post. I think it is the most accurate way to localise the pinger.

    Even if they only have good CPA data from a single tow track, then the CPA will reduce the along-track error and vastly reduce the potential search area for the CVR/FDR (hopefully the pinder is still attached!)

    ReplyDelete
  4. If the AJAAC uses your methodology, does it seem to you (as it does to me) that if the Bluefin can find it, it is likely to find it sooner rather than later? I.e., because your method seems to suggest a single and precise location?

    ReplyDelete
  5. This comment has been removed by a blog administrator.

    ReplyDelete
  6. Hi Bruce,

    There are limitations to the precision of which you could derive the location of the pinger. The main being the uncertainty in the position of the receiver.

    This position will be estimated based on the depth of the towfish, the length of cable payed out and a model of the drag forces on the cable for the given transit speed and ocean current. I'd expect you could know the position of the receiver to within about 100-200 metres?

    When you add other potential error sources such as acoustic propagation conditions I would be confident you could localise the pinger to within 500m.

    However, this does NOT help the bluefin locate the CVR/FDR as that is not what it is attempting to find. A sidescan sonar operating at 400kHz will be at the limit of its resolution if it were attempting to detect a 30cm wide object.

    It will be looking for larger pieces of debris such as landing gear.

    ReplyDelete
  7. I have been concerned that the search location may have been defined by dubious data refinements from Inmarsat, instead of from the underwater pings but it appears that your confidence in the AJACC analysts is well placed:

    PERTH, Australia— The underwater search of the seabed for debris from Malaysia Airlines Flight 370 is expected to take less time than the previously forecast 6 weeks to 2 months, due to analysis of acoustic data.

    The underwater search area had been significantly narrowed through the detailed acoustic analysis conducted on the four signal detections made by the Towed Pinger Locator on ADV Ocean Shield, Australia’s Joint Agency Coordination Centre, which is leading the multinational search operation, said in a statement.

    ReplyDelete
  8. Rodney, do you have any further comment on the progress of the search and the likelihood of success? If they are running perpendiculars off of four signal detections instead of two, presumably they have more prime search areas to cover. On the other hand, if the perpendiculars intersect at significantly different points, that tends to suggest that all of the signals may be false positives, does it not?

    ReplyDelete
  9. According to the latest JACC media release, "The focused underwater search area is defined as a circle of 10km radius around the second Towed Pinger Locator detection which occurred on 8 April." This sounds to me as though the intersecting perpendicular search, if any, have come up dry so to speak. Does that sound correct?

    ReplyDelete
  10. @Bruce:
    I get the feeling they may not have obtained enough data to localise using this technique. To do so requires pre/post CPA measurements from a single run and if you look at the detection locations (http://www.abc.net.au/news/image/5378120-3x2-700x467.jpg) they only have 1 good long run which MAY encompass a CPA.

    However they can still get an estimate of relative velocity to the source location at each of the pinger reception locations based on tow speed and the resulting ping interval (assuming the transmitted ping interval stayed consisten across the 3 days)

    ReplyDelete
  11. Rodney,
    You cant apply that algorithm in this case, In order for it to be used There must be an underwater mapping of the Ocean Sub sea. I ahve all the analysis on that issue including an Indian Ocean Acoustic Model close to SAR zone.

    Indian acts like no other and at that depth, that is the pinger, pitch diminished by the elements Plz contact me @felinenut asap, thanks

    ReplyDelete
  12. @prose072

    I don't want to come across as mean, but in reading your response, and looking at your conversations on Twitter, it is apparent to me that you do not have much first hand experience in underwater acoustics.

    Your memarciniak.wordpress.com site appears to be full of incoherent bold claims about "Data". I only hope a relative of those lost on MH370 do not stumble onto the site and mistake it for science as they may be given false hope.

    ReplyDelete
  13. This comment has been removed by the author.

    ReplyDelete
    Replies
    1. Rodney,

      I worked in the Deep-water Offshore oil industry for 20 years directional drilling, I fully understand propagation and frequency. My word press is simply a summary. I have been advising JACC since March 20th, prior to JACC formation in Data analysis.

      Thats not why I asked you to contact me, however I must clarify your assumption. As you may know, when you assume you, make an ass-outa-u-me y, So lets not do that.

      Furthermore, I have the Data analysis of the Indian Ocean and I have all document studies on the issue since the ULB was designed by the USA. I didnt say your math was wrong. What I said was the algorithm can NOT be applied in this case as that is a FACT.. and thatspart of why the additional errors occurred. See Report and Study completed in the Indian Ocean and the additional studies on this matter as far back as 1968 dealing strictly with ULP and designs.

      When theres an unexplained event applied to technology, first you go back to the design and research and development as well as the history on natural freq or naturally Occurring Frequencies, all of which in this case do not apply, as for P.ing 1 the freq just isnt dead ringer, the DB's are way to high and as for remaining issues that affect the frequency .....thats science by standard and well documented on the ULB from the outset and the Indian Ocean Study also confirms all information I have. My report is first and foremost is the the right and responsibility to be provided to the JACC which is so large it is being recompiled with appendixes annexes.

      I didnt write to tell you any that, I do not "Piss on someone tell them its raining" as facts can NOT be disputed, nor are they argumentative. So I am done with that and I hope we are clear as to who or what my background to come into question.

      As for the what you did to split the process is the correct approach, however, due to the environment in the SAR zone the signal can not be propagated nor that algorithm applied as it diminish the freq and its pulses.

      Again, I didnt write you for a discussion. My contact with you for a simple reason, and that is to ask you If you have audio files on the Actual ULB from Ocean Shield Ping 1 in particular and others in their entirety in order to save me the time to submit authorization for release to myself exclusively, until authorized otherwise from KL.

      The last I have known, No public release was made except a clip on TV. So if we could get back on the right foot instead of snapping them off with that crocodile bite, I would appreciate that information or a response at least so I may have my authorization fast tracked. Thank-you very much and have a great day!! ;->

      Delete