This is a LOFAR (LOw Frequency Analysis and Ranging) type sonobuoy. The first sonobuoy in this series was the SSQ-41 introduced in 1965. The output is displayed on a waterfall display (Wiki: Spectrogram) with Frequency on the horizontal axis and time changing on the vertical axis. These displays from a LOFAR sonobuoy were called LofarGrams. The British LOFAR was the SSQ-48 (aka: T24501) Jezebel (passive listening SONAR) (Sonobuoy Ref 7, pg 59)
Unlike the AN/CRT-1 sonobuoy where the lower frequency limit is 300 Hz (First version) or 100 Hz (version A and later) the LOwer Frequency limit on the LOFAR series sonobuoy is between 1.2 and 5.3 Hz at absolute sound-pressure level of -170 dB referenced to 1 µPa at 1 meter. Between 2.1 Hz and 8 Hz at -160 dB and between 10.1 Hz and 20 Hz at -150 dB. This allows hearing sounds that travel much greater distances and also indicate things like propeller shaft RPM. The upper limit is 2,400 Hz which is a little lower than the common 3,000 Hz upper limit for human speech, but there is no speech to be heard underwater, so the upper limit is set based on the types of sounds that are underwater and that a human operator can hear.
LOFAR sonobuoys are the natural evolution of the non-directional sonobuoy that started with the AN/CRT-1. The simplicity translates into the lowest cost of the family of sonobuoys and so probably is the most used.
CNU-239/E Shipping Tube
Fig 3 Label visible from outside
when mounted in plane.
Fig 4 Depth 60 or 400 Feet
Fig 5 1, 3 or 8 Hours operation
Fig 6 threads for Cartridge Actuated Device (CAS).
This electrically activated gas generator will burst the
thin membrane in the launch tube and force the sonobuoy
out of the aircraft. This is the "top side" of the sonobuoy
when mounted in the belly of an aircraft.
In the movie Hunt for Red October (IMDB) the SAPS (Signal Algorithmic Processing System) was said to be based on the earth sciences and the Exxon research patent is for a similar system. Sonograms (Wiki) were developed for a number of applications (Wiki), one of which was the VoicePrint.
3439155 Filtering system, Alexander Warren A, Exxon Production Research Co, Priority: 1 May 1963, Pub: 15 Apr 1969, 708/191, 324/76.29, 359/560, 356/71, 324/76.36 - spectral analysis for oil exploration.
3611411 Spectrum-analyzing recorder, Allan K Mccombs, Stephen L Moshier, Stanley R Rich, Listening Inc, 5 Oct 1971, 346/35, 324/76.31, 346/150.1 - aimed at human hearing analysis
4231103 Fast Fourier transform spectral analysis system employing adaptive window, John E. Timm, Secretary Of The Navy, 28 Oct 1980, 708/404 - applies digital methods
University of Bergen - Department of Earth Science - Electronics Workshop - Sonobuoys & SSQ-57A
P-3C Orion Maritime Patrol, United States of America -
Research Gate: LOFAR sonobuoy localization algorithm based on the measurements of amplitude and frequency -
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