honig@ics.UCI.EDU (David A. Honig) (09/06/89)
From: "David A. Honig" <honig@ics.UCI.EDU> In article <27084@amdcad.AMD.COM> broman@trout.nosc.mil (Vincent Broman) writes: >By comparing the signals arriving at each individual hydrophone, one >can estimate useful parameters, e.g. the azimuthal angle of arrival of >the sound rays relative to the sensor. "SOund NAvigation and Ranging" >is a slight misnomer for such a sensor, because the range to the >target cannot usually be estimated by means of one passive detection, Question: Can the dispersion (frequency-dependant propogation velocity) of sound through water be used to measure range with a single measurement? Seems that you could, if the target emitted a broadband signal and you knew the dispersion characteristics of water. -- David A Honig
broman@schroeder.nosc.mil (Vincent Broman) (09/07/89)
From: broman@schroeder.nosc.mil (Vincent Broman) Can the frequency dependence of sound speed in water enable passive sonar ranging? I doubt it. It would be difficult to compute a time-difference from signals found in two different frequency bins, because you don't know that the two signals were identical and simultaneous when they were emitted. Sound speed depends on many factors, e.g. temperature, pressure, and salinity. The sound energy measured in one incoming beam of sound may be a mixture of several signals which travelled over different propagation paths, possibly originating from several sources. Ocean acoustics deals with some very dirty data. If one has prior intelligence on the strength of an emitted signal, then the transmission loss in signal power might be compared to a model of the attenuation and refraction expected in the current ocean environment to produce information on the length of the signal propagation path. The resulting probability density on range can be strange and multimodal. If your array of hydrophones is in the near field of the sound source, one may estimate range from the curvature of the sound wave fronts. Generally, such towed array passive ranging methods produce usable results only under limited conditions. Vincent Broman, code 632, Naval Ocean Systems Center, San Diego, CA 92152, USA Phone: +1 619 553 1641 Internet: broman@nosc.mil Uucp: sdcsvax!nosc!broman
malloy@nprdc.navy.mil (Sean Malloy) (09/08/89)
From: malloy@nprdc.navy.mil (Sean Malloy) In article <27140@amdcad.AMD.COM> broman@schroeder.nosc.mil (Vincent Broman) writes: >Can the frequency dependence of sound speed in water enable passive >sonar ranging? Under the right conditions (basically, deep enough water for the effect to work) you can get rough ranging data from picking up a passive sonar contact in the convergent zones. Convergence zones are rings around the listening ship where the noise emitted downward by a vessel is refracted back up by the pressure differential at increasing depth to the surface some miles away. The sound can then be reflected from the surface and make another 'hop'; several such hops may be made under ideal conditions. In water over 12,000 feet deep, convergence zone information can be approximated as follows (the actual distances and widths depend on water conditions, but these numbers can be used for rough examples): Convergence Zone Zone Distance Zone Width First 30 nm. 3 nm. Second 60 nm. 6 nm. Third 90 nm. 9 nm. You're not going to get _good_ range information from a CZ contact, but you can get a good enough track to lob a missile out to take a look if your sonarman IDs the contact as hostile. Sean Malloy | "The proton absorbs a photon Navy Personnel Research & Development Center | and emits two morons, a San Diego, CA 92152-6800 | lepton, a boson, and a malloy@nprdc.navy.mil | boson's mate. Why did I ever | take high-energy physics?"
dfkling@cs.washington.edu (Dean F. Kling) (09/13/89)
From: dfkling@cs.washington.edu (Dean F. Kling) > Question: Can the dispersion (frequency-dependant propogation velocity) of > sound through water be used to measure range with a single measurement? > Seems that you could, if the target emitted a broadband signal and you > knew the dispersion characteristics of water. > -- > David A Honig The biggest problem is that seawater is decidedly non-uniform so that the dispersal and refraction effects would be impossible to sort out. Range determination with passive sonar is not a particularly difficult problem to solve if you have sufficient bearing information over time and based on the relative geometry of the target and own ship. Dean F. Kling cs.washington.edu