tag:blogger.com,1999:blog-5383877989815914374.post4817313796848148711..comments2023-08-04T22:12:19.547+08:00Comments on Gaffer Tape and Matlab... Its all you need: Analysis of suspected MH370 pings recorded by Ocean ShieldRodney Thomsonhttp://www.blogger.com/profile/11854209436110515025noreply@blogger.comBlogger146125tag:blogger.com,1999:blog-5383877989815914374.post-76284239438033476202015-09-04T05:49:29.061+08:002015-09-04T05:49:29.061+08:00Hi Rodney
I really enjoy your analysis, I'm st...Hi Rodney<br />I really enjoy your analysis, I'm student and i interested to see how you program this analysis in MATLAB<br />is that possible that i see your codes<br />Thank youAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-5759225047453354462015-06-08T18:39:59.608+08:002015-06-08T18:39:59.608+08:00Dear Mr. Thomson: I was pleased to see that you a...Dear Mr. Thomson: I was pleased to see that you are participating on Reddit again on the hydrophone/acoustic issues. Hope your efforts lead to a credible new search area. I had hoped that you could exchange thoughts with "pigdead", Kirill Prostyakov and Dr. Ulich. Glad to see public statements accumulating.<br />Michael Molinaro<br />MIchaelMMolinaro@sbcglobal.netAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-19580537408898675282015-04-17T21:02:21.645+08:002015-04-17T21:02:21.645+08:00I agree that this forum provided lots of valuable ...I agree that this forum provided lots of valuable information, and Rodney T. is to be commended for getting the ball rolling. However, 405 days down the road from the disappearance of MH370, Dr. Ulich is suggesting that the search is still focused on the wrong area. Further, Jeff Wise -- formerly a member of Duncan Steel's investigative team -- believes that MH370 landed safely; see http://jeffwise.net/the-spoof-part-1-why-a-speculative-scenario. So, we are still a long ways from knowing what happened to MH370. Rodney S.Unknownhttps://www.blogger.com/profile/13956397155841450383noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-70317518553112333122015-04-17T08:27:49.671+08:002015-04-17T08:27:49.671+08:00I saw today's post by Dr. Ulich 4/16/15 regard...I saw today's post by Dr. Ulich 4/16/15 regarding contrails likely left by MH370 - https://drive.google.com/file/d/0BzOIIFNlx2aUWEtvSjBVS2JWX0E/view - and remembered I first saw Dr. Ulich posting on the MH370 quest here, Mr. Thomson, in response to your wonderful underwater analysis. You attracted lots of great thinkers<br /><br />Thanks for all the interesting posts. Hope the combined scientific efforts are narrowing down the area to find MH 370<br /><br />Michael Molinaro<br />MIchaelMMolinaro@sbcglobal.netAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-46905349729713390402014-07-14T20:52:01.507+08:002014-07-14T20:52:01.507+08:00G'day Mark, Rodney, and others
Note that the ...G'day Mark, Rodney, and others<br /><br />Note that the new search area document released by the ATSB on 26th June has a short mention of the 'false pings' at around 33kHz.<br /><br />It confirms that the ULB carried on MH370 was a DK-100. I assumed also incorrectly that it was a DK-120 as carried on AF447. Therefore the video of the Black Box Teardown posted by Mike Harrington on Youtube is highly relevant.<br /><br />The exact exact timings of the frequency, pulse train duration, and the interval between pulse trains can only be the result of a crystal controlled resonator.<br /><br />The ripple and the leading and trailing edge of the waveform, and the slow rise time of those edges is not likely the result of any 'turning-off-or-on' of the carrier frequency oscillator, but, instead, artifacts of measurement: <br />i. 40kHz Ultrasonic Transducer receiving the signal unterminated in a load resistor- ringing,<br />ii. reflections in the tank of water,<br />iii.poor impedance matching between the Characteristic Impedance of the Piezo Ceramic Transducer/Aluminium case/Water- resulting in high unloaded Q of the ULB transducer.<br /><br />I've bought several 'watch' crystals, wired up a 'rats nest' Pierce oscillator circuit with a 4069 Hex inverter, stuck them in the freezer compartment of my refrigerator at -12Celcius, running on 1.7Volt, and they still operate withinh 1Hz of there room temperatue frequency.<br /><br />The ULB recovered from CVR of AF4447 was judged to be non functional. Apart from taking X-Rays of part of the PCB the BEA laboratory did not further investigate as to reason for the radically reduced output of the ULB. This is grave shortcoming in the thoroughness of the report.<br /><br />The only genuine case we have for a ULB being 'off' frequency is AI182, and reading the final report, there is only a passing reference as to the cause; a 'crack' on the Transducer element. This was advice sought from the manufacturer during the search. There has never been any further information following up as to cause of this 'off' frequency after the recorders were recovered.<br /><br />Mark MercerAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-56140386571664166472014-06-04T12:22:19.831+08:002014-06-04T12:22:19.831+08:00Hi Rodney,
Interesting video. Painful to watch hi...Hi Rodney,<br /><br />Interesting video. Painful to watch his ham handed methods (vises, hammers, not exactly "Mr. Finesse!") Interesting "ring" ceramic transducer. His is a DK100, mine is a more modern DK120 (same type as for MH370)<br /><br />The output signal on mine, in air, is strongest at one small area on one side, certainly not even output around the can as one would expect was the intention of the 360 degree ring.<br /><br />If the DK100 is potted, my DK120 must be as well, so I have no desire to ruin it by taking it apart.<br /><br />It does look like he found a crystal. From his scope trace, (similar to my scope trace) the 37.5 KHz signal does not cut on and off cleanly as would be expected if the oscillator was always running and the output just gated on and off. From the exponential start and stop of the signal, the oscillator is clearly being turned completely off between pings (obviously to save power for the 30 day life)<br /><br />This would imply that a purely analog RC time circuit it used to trigger the subsequent pings as any microcontroller timer, or even a simple digital counter, would not have a clock. (I now doubt there is any uP in the device)<br /><br />They COULD have easily designed a circuit with the clock always on (allowing a digital counter) as any cheap digital watch has a 32 KHz crystal and runs for years.<br /><br />So the ping to ping time interval, so critical to my proposed method for deriving a "second hydrophone" from the recorded data (for getting a position fix) is in some jeopardy.<br /><br />But as I have mentioned, even thought this assumed RC timer is clearly not made for accuracy, as ping repetition accuracy would not be an important design parameter, my hope is that because of stable temperatures and battery voltage, it may turn out to be very stable.<br /><br />establishing this time stability is my primary goal in my upcoming precision time measurements.<br /><br />My frustrating lack of high quality test gear is slowing me down, but will not stop me!<br /><br />Mark ZakAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-44678190952220922202014-06-04T10:25:51.618+08:002014-06-04T10:25:51.618+08:00Hi Mark,
Thanks for continuing your efforts with ...Hi Mark,<br /><br />Thanks for continuing your efforts with this. Even if the signals heard by Ocean Shield were NOT from MH370, what you are doing could help answer some important questions about the transmission behaviour of the ULB in varying environmental conditions.<br /><br /><b>I found that the units "speaker" is apparently mounted to the inside surface on the side of the little can (I excepted to find it on the can end)</b><br /><br />Have a look at the following ULB teardown video and you can actually see the electronics in the end and the ring ceramic around the barrel of the ULB:<br /><br />https://www.youtube.com/watch?v=mQehX0rVYuY&feature=player_detailpage#t=222<br /><br />If you have a high quality recording device (sampling at 96kHz or even 192kHz) and could record the audio received during your testing then I would be very interested in looking at it!Rodney Thomsonhttps://www.blogger.com/profile/11854209436110515025noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-59609339037918293842014-06-04T07:00:08.202+08:002014-06-04T07:00:08.202+08:00Hi Rodney Thomson,
It is very disheartening to h...Hi Rodney Thomson, <br /><br />It is very disheartening to hear that the sound signals are now not thought to come from the black boxes. I will continue my analysis efforts anyway since I have put so much effort into it already. <br /><br />I do not have the signal processing credentials of you or some of the others here, but I am quite a good circuits man, and have designed and developed many data acquisition circuits mostly for aircraft analog transducers, including the 787 Dreamliner.<br /><br />I did get my underwater locator beacon, but have been out of town the last week.<br /><br />I did a quick test of the unit, a DK-120. It is in good working order. By using a small piezo microphone, I found that the units "speaker" is apparently mounted to the inside surface on the side of the little can (I excepted to find it on the can end)<br /><br />My very preliminary test seems to show some changes in the signal amplitude envelop as it ran for about 15 minutes. I need to reconfirm this, but it would indicate an analog type of circuit. Frequency was about 37 KHz (as good as I can measure on an analog scope)<br /><br />As I mentioned, I am endeavoring to make a much more precision pulse time measuring circuit with a good crystal reference (2.5 ppm stability)<br /><br />I will keep this blog updated with my progress.<br /><br />Mark ZakAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-90690279378947062732014-06-02T01:25:38.198+08:002014-06-02T01:25:38.198+08:00Bruce,
Or perhaps the sources just drifted out of...Bruce,<br /><br />Or perhaps the sources just drifted out of the search area due to currents.<br /><br />I seem to recall seeing a water depth chart showing one corner of the search area being too deep for the Bluefin-21. I believe it is a fairly small percentage of the total search area. In any case, they exhausted the portion of the search area accessible to the Bluefin-21, and they moved on to the next phase involving higher search-rate, lower resolution towed side-scan sonars.Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-62763357127405803372014-06-02T00:53:36.327+08:002014-06-02T00:53:36.327+08:00The other weird thing about Dean's comment is ...The other weird thing about Dean's comment is that there seemingly were areas that they couldn't search because of depth. This is mentioned in the (fascinating to me) video entitled "Autonomous Underwater Vehicle" found at the link. http://video.defence.gov.au/#2b0796aa-8f2c-4eab-83af-3284d2ba28a6,0,DateAddedAnonymoushttps://www.blogger.com/profile/11346143097748716878noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-6191929742506350622014-06-02T00:21:27.076+08:002014-06-02T00:21:27.076+08:00Bobby, I agree. Dean sounded just like me when I m...Bobby, I agree. Dean sounded just like me when I misplace something: I conclude it must have been stolen because I know there could not possibly be anything wrong with my search.<br /><br />On the other hand, I think the fact that they detected the signals more or less right away, and then none in the subsequent 7 weeks, is suggestive that the source was connected with the search (or controlled by someone initially unaware of, or unable to stop its impact on, the search) and didn't get filtered out or turned off for a few days.Anonymoushttps://www.blogger.com/profile/11346143097748716878noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-11142968086124012192014-06-02T00:20:05.511+08:002014-06-02T00:20:05.511+08:00This comment has been removed by the author.Anonymoushttps://www.blogger.com/profile/11346143097748716878noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-52196577880674368792014-05-30T07:06:29.741+08:002014-05-30T07:06:29.741+08:00According to CNN today, the US Navy Deputy Direct...According to CNN today, the US Navy Deputy Director of Ocean Engineering, Michael Dean, says the acoustic signals detected by the TPL did not come from MH370. He said the most likely theory is that they came from the ship or from the TPL. Interestingly, in one interview I saw, he said that the reason this conclusion was drawn was because they had "looked at all the imagery" and found nothing. In other words, he is saying that the absence of visible wreckage in the side-scan sonar images led to the conclusion that the pings heard could not be from the MH370 black boxes. He never mentioned any of the reasons why the acoustic pings might not have come from the ULBs. Some hours, later, Mr. Dean, a civilian, was taken to task by the uniformed Navy for speaking out of turn. They made it clear that they were not saying his conclusions were inaccurate, just that it was the JACC's job to say such things, not the US Navy. <br /><br />Some of Mr. Dean's later quotations regarding possible noise sources seemed like very uninformed speculation to me. I personally believe the most likely source is drifting equipment locator beacons with long-lived batteries, similar to the ones made by Sonotronics..Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-42029604493398979952014-05-29T08:43:18.859+08:002014-05-29T08:43:18.859+08:00[Re-post to fix broken link]
CNN is now reporting...[Re-post to fix broken link]<br /><br />CNN is now reporting: "The four acoustic pings at the center of the search for Malaysia Airlines Flight 370 for the past seven weeks are no longer believed to have come from the plane's black boxes, a U.S. Navy official told CNN . . . Our best theory at this point is that (the pings were) likely some sound produced by the ship ... or within the electronics of the Towed Pinger Locator." See http://www.cnn.com/2014/05/28/world/asia/malaysia-airlines-pinging/index.html?hpt=hp_t1Unknownhttps://www.blogger.com/profile/13956397155841450383noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-17473415302721274972014-05-29T08:30:49.201+08:002014-05-29T08:30:49.201+08:00CNN is now reporting: "The four acoustic pin...CNN is now reporting: "The four acoustic pings at the center of the search for Malaysia Airlines Flight 370 for the past seven weeks are no longer believed to have come from the plane's black boxes, a U.S. Navy official told CNN . . . Our best theory at this point is that (the pings were) likely some sound produced by the ship ... or within the electronics of the Towed Pinger Locator." See http ://www.cnn.com/2014/05/28/world/asia/malaysia-airlines-pinging/index.html?hpt=hp_t1 Rodney S.Unknownhttps://www.blogger.com/profile/13956397155841450383noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-17288160850086195792014-05-28T23:12:56.279+08:002014-05-28T23:12:56.279+08:00It would be great if someone has already done this...<b> It would be great if someone has already done this for the same model ULB as in MH370.</b><br />There was someone earlier in the thread that claimed to have purchased an ULB for testing (M. Zak). I have not heard any further outcomes.<br /><br />I'm personally tempted to get one myself as we have an environmental chamber and pressure chamber (5000msw) at work that I could put the ULB in and measure the properties of the transmitted signals with varying temperature and pressure. You could also pull it apart and measure the transmit voltage response of the ceramic (ie power output over various frequencies).<br /><br />It is certainly possible that the signals detected could be from:<br />- Ocean Shield itself (stray sounder harmonic or some other interfering source)<br />- A long life locator beacon similar to the type you mentioned<br /><br />Even if the signals observed by Ocean Shield on the TPL-25 are conclusively found not to have come from MH370, then it still wasn't a waste of time to search the area. I mean, the resources were available and where else would we look?<br /><br />I'm just annoyed that there is no conclusive answer as yet :)<br /><br />Rodney Thomsonhttps://www.blogger.com/profile/11854209436110515025noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-74507872997758319202014-05-28T22:40:40.398+08:002014-05-28T22:40:40.398+08:00Mr. Thomson,
I have enjoyed our back-and-forth co...Mr. Thomson,<br /><br />I have enjoyed our back-and-forth conversation very much indeed. I was so pleased to find someone who had a lot of expertise in sonar signal processing. Your information on off-resonance power output is very interesting. It would be great if someone has already done this for the same model ULB as in MH370.<br /><br />By the way, there is a company in Tucson, Arizona called Sonotronics that makes acoustic transmitters. Here is a link to a data sheet on what they call equipment locators that use frequencies from 30-40 kHz with 161.5 dB output, a six month battery life, and a 4 km detection range. They also produce shorter-range beacons with up to 48 month battery life.<br /><br />http://sonotronics.com/wp-content/uploads/2010/07/EMT-01_data_sheet3.pdf<br /><br />Perhaps drift net fishermen use locator beacons like these on their nets, and some (pieces?) of them are lost and drift long distances. It's very hard to understand how 30-day beacons could be so numerous as to explain the multitude of detections in the search area, but perhaps equipment beacons, which are not encoded and don't operate at very high sonar frequencies, are at least part of the explanation.<br /><br />Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-79595057902079737942014-05-28T14:32:31.057+08:002014-05-28T14:32:31.057+08:00No thankyou Bobby, I always enjoy an entertaining ...No thankyou Bobby, I always enjoy an entertaining back-and-forth discussion.<br /><br />I tend to agree with your first two bullet points regarding SNR and source level off-frequency being reduced. Of the acoustic transmitters we use at work, they tend to have -3dB transmission points at about ±10% of resonance. IE For a resonant frequency of 20kHz then the transmit response falls 3dB below the peak at less than 18kHz and above 22kHz. <br /><br />Now that is a broad generalisation but suggests the output power of an ULB at 10% below its resonant frequency could be at least 3dB lower.<br /><br />The observed pulse period <b>does</b> match the pinger specs (not less than 0.9Hz or less than 1.111s interval) and is also consistent with a 'golden sample' measured at 1.08s interval after the Air France 447 unit was recovered and tested:<br />http://www.bea.aero/fr/enquetes/vol.af.447/cvr.ulb.examination.report.pdf<br /><br />If I get hold of the raw data then I am sure I will have more to say about the matter. I know of a few people that HAVE been analysing the recordings, one of whom (ex submariner sonar operator involved in the search) does not believe the signals originated from a ULB. Unfortunately I can only base my own opinions from the information available!Rodney Thomsonhttps://www.blogger.com/profile/11854209436110515025noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-12818685739300343602014-05-28T05:55:29.911+08:002014-05-28T05:55:29.911+08:00Hi, Rodney. Here's a link to a new seafloor m...Hi, Rodney. Here's a link to a new seafloor map that plots the general location of the two acoustic ping detections and other points of interest, just in case I am not the last one to see it. http://news.agu.org/press-release/seafloor-experts-publish-new-view-of-zone-where-malaysia-airlines-flight-370-might-lie/ Here's my latest off-the-wall question: the map gives the location of Deep Sea Drilling Project Site 256, which is marked by a gray dot roughly equidistant from the two ping locations. Apparently this site was marked by a beacon when it was drilled in 1972. http://www.deepseadrilling.org/26/volume/dsdp26_09.pdf Might its location still be marked by a beacon, and if so . . . .Anonymoushttps://www.blogger.com/profile/11346143097748716878noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-13125441086843953952014-05-28T03:52:25.149+08:002014-05-28T03:52:25.149+08:00Mr. Thomson,
Additional comments:
The ~ 2 ms ext...Mr. Thomson,<br /><br />Additional comments:<br /><br />The ~ 2 ms extra time delay until the first echo arrives would be caused by a reflection with a round-trip path length difference (in air at 343 m/s) of about 0.7 m. Judging from the video, there appear to be several possibilities for this reflection, including the equipment rack or a shelf/table next to it.<br /><br />The 20 ms time delayed return would require a 7 m path length. This could be a flat wall or ceiling or perhaps a “cube corner reflector” where two walls meet the ceiling/floor. One or more of these about 3.5 m away seems quite plausible. The cube corner reflections may be stronger because they do not suffer normal spreading loss. It depends on the wavelength and how far the mike is from the speaker.<br /><br />I summary, I would say that all of the complexity of the waveforms is explainable by playback room echoes. The only remaining mystery in this data set is the two mis-timed pulses, and I don’t think the solution is hiding in the recording we have.<br /><br />The remaining reliable evidence (from this data set alone) related to the source is as follows:<br /><br />• Many of the pulses have very high SNRs, implying the source is probably much closer than the 4.2 km to the bottom.<br />• The 33.3 kHz frequency is too far away from 37.5 kHz to be from the ULB because the high Q of the crystal will only permit faint transmissions at frequencies significantly different from the crystal resonance, whereas high amplitude signals are frequently observed.<br />• The observed pulse period of ~1.108 s is not consistent with the expected 1.0 s, although one could argue that it changed from the factory settings by an undetermined mechanism.<br />• We cannot determine the source speed or whether or not it was static. All we can say is that the speed was not much greater than the ship speed.<br /><br />Mr. Thomson, I want to thank you for providing me the data and the results of your analysis. Unless you can identify some new approach, I think we have extracted all the reliable information we can from this data set. I would love to look at either the uncontaminated 33 kHz or the 27 kHz data to see what the waveforms actually look like and if there are multiple sources. Please let me know if you can somehow obtain copies.<br />Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-70034691539105836022014-05-28T03:50:57.961+08:002014-05-28T03:50:57.961+08:00Mr. Thomson,
Your message gave me an “AHA!!” mo...Mr. Thomson, <br /><br />Your message gave me an “AHA!!” moment. <br /><br />Of course you are correct that, if the re-recording was done with an open mike in the playback room, then room echoes at 3.3 kHz will be added that will contaminate the true signal.<br /><br />Here is the list of my original questions with some answers that arise if we assume, with good reason, that playback room echoes (at 3.3 kHz) are added to the undersea acoustic recording during the re-recording process:<br /><br />• Why is the complex waveform so stable when the TPL is constantly moving?<br /><br />The waveform is complex because there are echoes (reflections) from the floor, walls, ceiling, table/shelf, etc. (perhaps half a dozen or more) of varying amplitudes and time delays. In addition, there is no Doppler shift since they are static. The one feature that apparently moved a bit might be from a nearby person who moved.<br /><br />• Why does the pulse amplitude vary significantly from pulse to pulse on time scales of several seconds?<br /><br />Your experience is apparently that these “fades” are observed to occur in undersea paths, and that is likely the explanation here also. I don’t think room echoes can create this result.<br /><br />• What mechanism produces the largest 33 kHz amplitudes in the first ~5 cycles?<br /><br />The reason it is the loudest is that it is from the direct path during re-recording and does not suffer reflection loss.<br /><br />• Why do the peaks in the pulse envelope decrease ~ exponentially during the entire pulse? [Note that each successive envelope peak is lower than the previous one.]<br /><br />Later returns are experiencing more spreading loss from the loudspeaker source and will be fainter roughly as inverse time delay squared. So the decay may actually be sort of 1/t^2 rather than EXP(-t/a).<br /><br />• Why is there a “gap” about one ms wide from 17-18 ms and then several cycles of 33 kHz from 17-18 ms that appear to be very stable in time?<br /><br />Gaps can appear either by destructive interference or by echo separations longer than the pulse length. The stability arises from the static nature of the room echoes.<br /><br />• What mechanism produces the “leftover” pulses, and are they associated with the 1.108 ms pulse train source? There are two very-high SNR examples at 26.236 s and 59.947 s. In addition, there are numerous possible pulses at 20.611, 28.585, 34.179, 36.375, 37.272, 38.158, 50.236, 51.215, 52.320, and 59.081 s.<br /><br />You are correct is observing that the two “leftover” pulses occur just before “missing” pulses in the 1.108 ms pulse train. I doubt that any of the other times I listed above are real returns. They may very well be just noise. I would guess that it would be difficult to do this time shifting by manually editing either the original recording or the re-recording. I cannot think of any rational act to do this, but I suspect it is caused by something done after the data were originally recorded. In other words, I don’t think it is “real” and due to the source, and it is certainly not caused by room echoes.<br /><br />• Is there a second source present in these data?<br /><br />I would say probably not. I think the two leftover pulses are due to mishandling of data and are not due to a second source because there are only two, they look just like the other pulses in the train, and they are off from the train timing by exactly the same time difference, despite the fact that they occurred at least several tens of seconds apart.<br />Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-43386009587511194852014-05-27T22:13:21.798+08:002014-05-27T22:13:21.798+08:00I am by no means suggesting the following statemen...I am by no means suggesting the following statements are correct, but I thought I would suggest some alternatives<br /><br /><b>1. Why is the complex waveform so stable when the TPL is constantly moving?</b><br />The transfer-function of the room in which the recording was made could be the dominant factor in the envelope modulation.<br /><br /><b>2. Why does the pulse amplitude vary significantly from pulse to pulse on time scales of several seconds?</b><br />Unfortunately most of the pingers I deal with at work are attached to platforms that are either fast moving underwater or stationary bobbing near the surface.<br /><br />In both cases there can be significant differences in received amplitudes across multiple pings, typically due to aspect dependance of the source or interaction with the surface.<br /><br /><b>3. What mechanism produces the largest 33 kHz amplitudes in the first ~5 cycles?</b><br />The first 20s segment doesn't show this effect significantly however the second segment does. One explanation is simple human psychology. If you were showing off detections to a third party you would highlight the best SNR detections. It is possible the playback started at the strongest detections and tailed off.<br /><br />Unfortunately we are looking at only 40 seconds worth of data so we have to extrapolate somewhat.<br /><br /><b>4. Why do the peaks in the pulse envelope decrease ~ exponentially during the entire pulse?</b><br />If the signals are from an ULB nearing the end of its battery life, then the transmit voltage may drop during transmission of the waveform (however it is a very short signal and seems unlikely). Also if the battery level was decreasing then you would expect the transmit power to be reduced and thus expect low SNR received signals (if at all!).<br /><br /><b>5. Why is there a “gap” about one ms wide from 17-18 ms and then several cycles of 33 kHz from 17-18 ms that appear to be very stable in time?</b><br />Reflection of some sort?<br /><br /><b>Mr. Thomson, you could again assist my continuing analysis if you could provide files of the data snippets at 26.236 and at 59.947</b><br />I have uploaded the bandpass filtered version of the file below:<br />https://drive.google.com/file/d/0B0JtIJ1UMWxqbktCQVZKYkx0ams/edit?usp=sharing<br /><br />The unfiltered MP3 is here:<br />https://drive.google.com/file/d/0B0JtIJ1UMWxqb0d6Wnc5c1hHY3M/edit?usp=sharingRodney Thomsonhttps://www.blogger.com/profile/11854209436110515025noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-45121549893199314942014-05-27T21:40:44.839+08:002014-05-27T21:40:44.839+08:00Hi Bobby, thanks again for the detailed analysis o...Hi Bobby, thanks again for the detailed analysis of the pings.<br /><br /><b>6. (the first 6!) There are at least 2, and possibly more, high-SNR recorded pulses that occur at times not obviously associated with the train of 1.108 ms period pulses. They occur at 26.236 s and 59.948 ms.</b><br />The interesting thing is that those high SNR pulses are not in addition to the expected ping in the 1.108s interval, but instead seem to replace it in those cases. I don't think it would be due to a reflection. It is unlikely that the propagation path would change so wildly from one pulse to the next.<br /><br /><b>6. The waveform feature that occurs from 10.5-12 ms after the onset appears to be fixed in time in this data set. It is about a half-dozen cycles of ~33 kHz.</b><br />Tonight I realised that there is another effect that we are not considering that could produce ~2ms delays. The signal recorded is firstly transmitted via the laptop speaker, propagates through the medium sized room (with metal walls) before being recorded on the iPhone or whatever was used.<br /><br />Just something to consider.Rodney Thomsonhttps://www.blogger.com/profile/11854209436110515025noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-53828037347739593152014-05-27T07:22:19.488+08:002014-05-27T07:22:19.488+08:00Mr. Thomson,
First, let me describe my backgrou...Mr. Thomson, <br /><br />First, let me describe my background a bit. I have a BS and a MS in EE, and a PhD in EE & Astronomy. I was Chief Engineer at several radio and optical observatories and a Research Professor of Astronomy at the University of Arizona. I have published about a hundred research papers. Then I worked in the defense business as Chief Scientist at a Fortune 500 company. I built quite a few lidar and sodar systems for the US Navy and Army. Most of my more recent work was in airborne detection of sea mines and submarines using active pulsed laser imaging. I am now retired and therefore have some time to spend on projects like this - analyzing an acoustic recording without much in the way of ground truth data.<br /><br />After spending several days analyzing just this snippet of data (less than a minute), I can appreciate why it is taking the search group so long to come to firm conclusions. We are looking at a fraction of one percent of the total detection data, and our task is quite a bit easier, although conceptually we have the same hurdles to understand and overcome.<br /><br />Here is a list of the additional questions about this data set that need to be answered to have a fairly complete understanding of the observed waveforms:<br /><br />1. Why is the complex waveform so stable when the TPL is constantly moving?<br />2. Why does the pulse amplitude vary significantly from pulse to pulse on time scales of several seconds?<br />3. What mechanism produces the largest 33 kHz amplitudes in the first ~5 cycles?<br />4. Why do the peaks in the pulse envelope decrease ~ exponentially during the entire pulse? [Note that each successive envelope peak is lower than the previous one.]<br />5. Why is there a “gap” about one ms wide from 17-18 ms and then several cycles of 33 kHz from 17-18 ms that appear to be very stable in time?<br />6. What mechanism produces the “leftover” pulses, and are they associated with the 1.108 ms pulse train source? There are two very-high SNR examples at 26.236 s and 59.947 s. In addition, there are numerous possible pulses at 20.611, 28.585, 34.179, 36.375, 37.272, 38.158, 50.236, 51.215, 52.320, and 59.081 s.<br />7. Is there a second source present in these data?<br /><br />Mr. Thomson, you could again assist my continuing analysis if you could provide files of the data snippets at 26.236 and at 59.947. That would allow me to fit my waveform model and to compare the parameter values to those of some others in the 1.108 s period pulse train. Perhaps that will give us a clue as to whether or not they are distant echoes or instead are from a second source.<br />Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.comtag:blogger.com,1999:blog-5383877989815914374.post-78994046819930431292014-05-27T06:26:19.683+08:002014-05-27T06:26:19.683+08:00Mr. Thomson,
I wanted to update you on my progres...Mr. Thomson,<br /><br />I wanted to update you on my progress, or lack of it, and summarize what is known at this point regarding the one acoustic recording we have been analyzing.<br /><br />Here's what I think we know about the data set:<br /><br />1. There are more than 30 periodic acoustic pulses about 10 ms long that occur at a pulse frequency of about 33.3 kHz and with a period of about 1.108 ms.<br /><br />2. Slight period variations are detected, and, assuming they are caused by Doppler effect, they are consistent with a relatively modest line-of-sight speed (< 1 knot) that is a fraction of the assumed TPL speed of 2-3 knots.<br /><br />3. The ~ 33 kHz observed waveform is least 13 ms long, and possibly as long as 20 ms.<br /><br />4. Many of the pulses have very high SNRs. <br /> <br />[If we assume the TPL was at 300 m depth when these data were originally recorded, this result implies that the source is likely to be much closer to the TPL than the bottom at a water depth of ~ 4.5 km, and probably was closer than 2-3 km. During the whole detection interval, the TPL depth was between 300 m and 1400 m.]<br /><br />5. The waveform is quite complex, with all high-SNR samples showing a distinct and relatively stable modulation of the 33 kHz amplitude with several (2-4) cycles of modulation. <br /><br />[The only explanation I can offer at this time is interference from an echo (and possibly from two echoes). In addition, the slight time delay of the principal echo constrains the reflection to occur quite close to the source. If we assume the cause of the relection that creates the echo is the sea surface or the ship hull, that implies that the source is at a very shallow depth, probably < 10 meters. Of course, wreckage near a UBL on the bottom could also reflect the pulse and produce a modulated waveform, but it is difficult to explain the high SNRs as well as the 2+ hours of detection that was reported with a static source on the bottom. It would be very enlightening to know if the Ocean Shield was moving with the current or against it when this recording was made. An ocean current of 1-2 knots in the right direction would allow a drifting (not necessarily swimming) source to stay within detection range for hours.]<br /><br />6. There are at least 2, and possibly more, high-SNR recorded pulses that occur at times not obviously associated with the train of 1.108 ms period pulses. They occur at 26.236 s and 59.948 ms.<br /><br />[Note that both of these occur 827/828 ms after the previous pulse in the 1.108 ms period pulse train (at 25.409 and 59.120 seconds) or 280 ms before the next 1.108 second train pulse. There's a big clue here staring us in the face, but I'm not sure what it means. It could mean that sometimes, depending on the geometry of a reflector, that a strong echo is heard with either ~420 m less or ~1800 m more path length. However, the fact that this exact delay occurs in two different data sessions has me wondering if some other mechanism is the cause.]<br /><br />6. The waveform feature that occurs from 10.5-12 ms after the onset appears to be fixed in time in this data set. It is about a half-dozen cycles of ~33 kHz.<br /><br />[The simplest explanation is that the transmitted pulse is indeed 10 ms long and the primary echo is delayed by ~ 2 ms during the entire recording. Thus the waveform after 10 ms is predominantly the end of the echo(es).]<br /><br />7. My analysis shows the peak of the waveform envelope feature in the region from 6-9 ms shifts systematically toward the pulse onset by about 1/2 ms during the first data session and then shifts later in time also by about 1/2 ms during the second session. <br /><br />[This may be due to changing relative Doppler velocity. My model shows this interference peak to shift ~ 1/2 ms later in time with about a 3/4 m/s velocity increase in the echo relative to the direct wave. So a shift earlier in time means the echo velocity is lower relative to the direct path velocity in the first data session, and then in the opposite direction in the second session.]<br /><br />A list of questions I am addressing will follow.<br />Anonymoushttps://www.blogger.com/profile/00096432483009098499noreply@blogger.com