Monday, October 7, 2019

Sonar Performance

There is a strong tendency in the military observer world to accept manufacturer’s claims at face value and, worse, to assume that those claims are absolute and unvarying even as real world conditions vary.  One common example of this tendency is the discussion of sonar performance.  Observers tend to believe that a manufacturer’s maximum range claim is gospel, is always achievable regardless of real world factors, and every object within the claimed range will be unerringly detected.  Of course, nothing could be further from the truth.

Let’s look a bit closer at sonar performance.

I assume that readers have a basic understanding of sonar types and mechanism of operation.  Sonobuoy Tech Systems website provides a good summary of the various sonobuoy/sonar types. (3)

Passive sonar simply listens to all the noise that impinges on its receiver.  It is up to the operator to determine which bits of noise are naturally occurring and which, if any, are manmade.  So, for passive sonobuoys, a target submarine is detected when its noise level rises above that of the background noise for a sufficient period of time and at a sufficient level to be recognized by the sonar analyst (human or software).  Complicating factors include thermoclines, overlapping noise sources such as other ships or biologics, sound reflecting objects, flow noise from water movement over and past objects or over the sea floor, wave noise, channeling phenomena, etc.

In the real world, a single buoy cannot even determine a reliable distance range for the sub. The reasons for this are 1., that the source level is usually not known and 2., that the sound propagation circumstances could differ significantly between positions that may be located only some hundred meters apart. For example, in good conditions, a 100 dB source level could be heard over a distance of several kilometers while the same source level may only be heard over a distance of a few hundred meters at a position where the conditions are poor. (1)

We see then, that passive sonobuoy detections provide a target bearing only – no range, course, or speed.  Over time, and with multiple detections, range, course, and speed can be developed.  Of course, since sonobuoys are fixed locations, either the target has to move or additional sonobuoys have to be deployed to obtain the cross-fixes necessary to develop the target data.

Active sonar suffers from many of the same problems although, in this case, the source noise level and timing is known.  Active sonars provide bearing and range, under good conditions – but not target course or speed.  Over time, with multiple detections, course and speed can be developed.

While sonar detection ranges are classified, we can get some hints from public source data although such hints are exceedingly rare.

DelBalzo and Stangl modeled active sonobuoy performance using detection ranges of 2-8 nm and, in another scenario, 0.6-1.6 nm. (2)

SSQ-15 (B-Size) active sonobuoy (circa 1960) had a range of 2500 yds. (4)

It is important to understand that manufacturer’s claims are valid only under perfect conditions with all physical and environmental factors being favorable in the extreme and no acoustic countermeasures being employed.  It is also necessary to understand that the claims are based on laboratory tests and software simulations.  To the best of my knowledge, no manufacturer has their own modern naval submarine for use in testing.  At times, they may be allowed to take part in Navy sponsored testing but even that, to the best of my knowledge, is rare and only involves submarine surrogates, not real submarines.  DOT&E has repeatedly reported on the lack of fidelity of submarine surrogates so that offers the manufacturer little realistic information.

A further complicating factor is acoustic countermeasures. 

One such measure is the now ubiquitous anechoic tile that all modern submarines are coated with.  Designed to absorb sound, the US Navy believes that a submarine with anechoic tiles has a good chance to remain undetected even by active sonar at all but very short ranges.

A similar measure is the use of bubbles which trap and ‘deaden’ noise.  This can be either air bubbles injected into the water, as in the Navy’s Prairie/Masker system for surface ships or embedded in paint-like coatings which are applied to vessel hulls.

What this means for the purpose of this discussion is that claimed sonar detection ranges are unrealistically optimistic since none take into account acoustic countermeasures.

We see, then, that manufacturer’s sonar detection claims are unrealistic to the point of uselessness.  Divide a manufacturer’s claims by a factor of 10 and you might begin to approach the realistic sonar range performance.

Considering all factors, it seems likely that realistic sonar detection ranges against modern submarines are something on the order of 0-5 miles for active sonar and zero to dozens of miles for passive sonar although we have to note that passive detection at extended ranges requires just the right combination of factors.

The commonly held belief that a single active sonar ping will instantaneously provide a 100% perfect, target quality data picture for many dozens of miles around is pure fantasy.  This belief was epitomized in some of the comments in the previous ASW corvette story (see, “Shallow Water ASW Story”) wherein commenters objected to the use of active sonar by ASW corvettes in the story, believing, incorrectly, that a single ping by the corvette would instantly provide perfect and complete target data with a submarine torpedo launch occurring seconds later.

All of this discussion should also reinforce the negative ‘review’ of the Sea Hunter in a recent post in which I expressed the utter disbelief that a small, low powered Sea Hunter sonar could continuously track a modern submarine when our very best, large, high powered, ship mounted sonars operated by the best analysts backed by state of the art software could not (see, “The Sea HunterMyth”).


(1)“Submarine Tracking by Means of Passive Sonobuoys”, Kristian Johansson and Per Svensson, FOA-R-97-00440-505-SE, June 1997, ISSN 1104-9154, Div. of Command and Control Warfare Technology, SE-581 11 Linkoping, Sweden,

(2)“Design and Performance of Irregular Sonobuoy Patterns in Complicated Environments”,
Donald R. DelBalzo, Technology Solutions Group, and Kevin C. Stangl, OPNAV N874, 0-933957-38-1 ©2009 MTS,

(3)Sonobuoy Tech Systems website,

(4)“The Evolution of the Sonobuoy from World War II to the Cold War”, Roger A. Holler, U.S. Navy Journal of Underwater Acoustics, Jan-2014,


  1. Is there any published material on what the power input is for any hull mounted sonars? I see AN/SQS-26 had a 240kw output. Has this increased by orders of magnitude?

  2. Thoughts if the Atlantic Undersea Test and Evaluation Center (AUTEC) between Palm Beach, Florida and Nassau, Bahamas able to carry out realistic tests without a stealthy AIP SSK.

    Earlier this year the new AN/SQS-62 VDS, ASW mission module for the LCS, was tested at AUTEC, noticeable that Navy did not install VDS on a LCS class ship for the trials, too noisy?, LCS Freedom class base nearby, homeport in Mayport, Florida.

    Dec 2016, trials with Walrus sub, realistic? don't think Walrus fitted with anechoic tiles

    LFAPS - The Royal Netherlands Navy operational evaluation (OPEVAL) of its new Low Frequency Active Passive Sonar (LFAPS) aboard HMNS VAN AMSTEL, 3,300 t, an M-class (also known as KAREL DOORMAN-class) frigate.
    Conducted OPEVAL over several days in conjunction with a WALRUS-class submarine and an NH90 helicopter fitted with low frequency dipping sonar, the OPEVAL demonstrated LFAP’s capability to detect and track a diesel-electric submarine, both mono- and bi-statically, in challenging conditions in littoral waters. Marine Corps Lt.-Gen. Rob Verkerk, Commander of the Royal Netherlands Navy, used Twitter to express his opinion that the testing represented a “quantum leap in the field of submarine warfare!”
    LFAP Ultra Electronics Maritime Systems hardware and processing software was developed by the Netherlands Organisation for Applied Scientific Research (TNO.)

    1. "LFAPS"

      I know nothing about this other than what's written in open literature which is just manufacturer's claims, essentially. I would remind, however, how every system the Navy has ever tried to develop was praised as being the future of warfare and revolutionizing naval warfare. The reality, of course, is that few succeed and almost none 'revolutionize' naval warfare. So, LFAP may be everything it's claimed to be or, far more likely, it's capable in a limited set of circumstances like most naval warfare systems.

      I have no idea how capable the Walrus class is but I note that it is a 1970's era design.

  3. With more and more man made noise generated out in the ocean with the cargo ships, tanker,etc...wonder how much "quiet " ocean there's left...couldn't a sub just vanish even easier today with all the background noise than in the 60s or 70s? I guess software can help filter it out but you still have wonder if the sub being so quiet, gets filtered out too?!?

    I'm wondering if the advantage is even more in the sub camp than we might commonly assume...

  4. ComNavOps I agree with your assessment regarding manufacturer advertised vs actual active sonar performance.
    I think the advertised performance is simply based on transmit frequencies, theoretical propagation losses, theoretical target strengths vs aspect, transmit source level, receiver array size, and (maybe) theoretical reverberation vs time.
    The underwater truth is far more complex and almost always operates to reduce performance and increase uncertainty. Two big factors are (1) the complexity of the propagation path structure to and from the target and how they all add up in the receiver, made worse by variation over time due to even small changes in source and target depths and relative range as well as bottom depth, and (2) bottom and surface reflections (clutter) - both are time-varying - that can cause unacceptable false alarm levels if the detection threshold is set too low.
    Both (1) and (2) are almost impossible to model currently in a way that could be applied as standard advertised factors so the manufacturers simply leave them out.
    The difference between claimed range performance by large surface ship mounted active mid frequency sonar and the small mid and high frequency sonars intended for the ACTUV program could be related to shorter detection and tracking ranges demanded by CONOPS for a swarm of ACTUVs - that's my guess.
    Separate comment: you have "Active sonars provide bearing and range ... but not target course or speed." Actually, modern active sonar can transmit complex waveform types that can provide a relative speed estimate under good conditions in addition to bearing and range on a single ping.
    Your blog is very informative, keep up the good work!

    1. "Actually, modern active sonar can transmit complex waveform types that can provide a relative speed estimate under good conditions in addition to bearing and range on a single ping."

      Fascinating. I haven't seen that. Do you have a reference I could look at?

    2. FWIW Raytheon state the new AN/SQS-62 VDS is all digital and can transmit "any type of waveform" Navy want.

    3. No online reference for sonar waveform design, sorry, you'd have to get a textbook on basic radar or sonar (the principles are the same).
      The single frequency sonar pulse gives relative motion using the Doppler frequency shift and a rough estimate of contact range based on timing of the echo reception, but the sonar reverberation at the transmit frequency is terrible unless the target is moving at a high relative speed separating the Doppler-shifted echo out of the reverberation.
      The volume occupied by the ship-based receive array or the length of the ship-towed receive towed array gives contact bearing resolution, but if the ship is moving then the reverberation seen by the receiver is spread in frequency due its own Doppler component, making detection of a Doppler shifted moving object more difficult.
      Hence one advantage of sonobuoys that don't move while receiving active pings.
      Standard sonar processing uses "pulse compression" from a transmit pulse that sweeps up or down in frequency enabling the receiver to get a big gain in range estimate against reverb, but unfortunately no Doppler information.
      More modern sonars transmit waveforms that add Doppler sensitivity to ranging capability - one example is the Costas waveform*. Please let me know if you have any questions.

    4. That's quite fascinating and thanks for the link! I note the linked article is from 2009. Typically, actual field applications lag research by many years. Is this type of waveform actually in use on field sonars, do you know? For example, the SQS-62 will not see service until the Navy's new FFG enters service and I'm sure there will be the usual new equipment pains to debug.

      My interpretation of "any kind of waveform" is FM and CW as for the Thales Captas VDS although perhaps the SQS-62 will have the ability to transmit more complex waveforms?

    5. Sorry, you are right. My statement "More modern sonars transmit waveforms that add Doppler sensitivity to ranging capability" statement should be "More modern sonars may in future transmit waveforms ..." Current sonars likely still use the same basic pulses - CW and FM - that together give Doppler and range estimates on a contact and which were used in the US Navy's SQS-26.*
      * (search on the term "FM" in this document)

    6. Fair enough! The technology is still quite fascinating and well worth keeping an eye on. The links are quite interesting and thank you for them! At a very cursory glance, I note the mention of a sonar-only scout ship (no weapons) for ASW which was briefly considered and dropped. I had been unaware of that but I note that it is exactly what the Navy now intends to do with the Medium Displacement Unmanned Surface Vessel (MDUSV). I'll have to look into that topic much closer.

      All in all, good comments, good links. Thanks for the contributions. The last report, in particular will make for some interesting reading and I look forward to it.

    7. Anon, what's your assessment of the balance between improved sonar detection technology and improved sonar countermeasures (anechoic tiles, bubble impregnated coatings, etc.). Has that altered the balance between ship and sub or merely made both sides equally more complex without changing the fundamental balance?

    8. Very sorry I don't know enough to be of help here.

  5. (Don McCollor)...we need a better way to detect subs than sonar - I have no suggestions...

    1. There's been a lot of research on chemical and other means of detection and tracking. Supposedly, Soviet subs have been seen with some type of chemical sensor. I don't know whether anything has proven out yet, though.

    2. It's from the South China Morning Post, so you definitely need to take this with a grain of salt, Don:

      The Navy has also been working on getting the airborne laser mine detecting package to work as an ASW asset. It's theoretically promising, but there are significant hurdles to get it to operational effectiveness - SCMP credits DARPA with developing a laser mapper than can see 200 feet below the surface.

      The technology isn't quite there yet, but once it gets there, being able to 3d image the sea underneath you is going to be a massive gamechanger for ASW and MCM.

    3. "The technology isn't quite there yet, but once it gets there, being able to 3d image the sea underneath you is going to be a massive gamechanger for ASW and MCM."

      I don't think so, at least not for the foreseeable future. Satellite data collection is not an instantaneous, real time, visual exercise other than for actual cameras. Radar mapping or, in this case, some kind of 3D imaging, consists of multiple scans/passes of the sensor and tons of data which is analyzed and, eventually, assembled into a coherent picture. By the time this process plays out and the data could be transmitted through layers of military hierarchy to a ship or aircraft that could use the information, the sub would be long gone.

    4. @ComNavOps: if Ghiskey Wolf is talking about using ASW helos or MPA to do the laser 3d imaging, that removes a lot of the time lag.

      You're probably right that we won't see this for the foreseable future; ASW lidar has been in the works for decades now.

  6. "if Ghiskey Wolf is talking about using ASW helos or MPA to do the laser 3d imaging, that removes a lot of the time lag."

    That is correct, yes. I don't see sats being tactically relevant for ASW lidar due to the time lag, but they'd be useful for creating a mapping baseline that you can compare the present picture to for anomalies (you could also do the same thing with MPA, of course).


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