Time–frequency analysis | Signal processing
Low Frequency Analyzer and Recorder (LOFAR)
Two closely related terms, Low Frequency Analyzer and Recorder and Low Frequency Analysis and Recording bearing the acronym LOFAR, deal with the equipment and process respectively for presenting a visual spectrum representation of low frequency sounds in a time–frequency analysis. The process was originally applied to fixed surveillance passive antisubmarine sonar systems and later to sonobuoy and other systems. Originally the analysis was electromechanical and the display was produced on electrostatic recording paper, a Lofargram, with stronger frequencies presented as lines against background noise. The analysis migrated to digital and both analysis and display were digital after a major system consolidation into centralized processing centers during the 1990s. Both the equipment and process had specific and classified application to fixed surveillance sonar systems and was the basis for the United States Navy's ocean wide Sound Surveillance System (SOSUS) established in the early 1950s. The research and development of systems utilizing LOFAR was given the code name Project Jezebel. The installation and maintenance of SOSUS was under the unclassified code name Project Caesar. The principle was later applied to air, surface and submarine tactical sonar systems with some incorporating the name "Jezebel". (Wikipedia).
