{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,23]],"date-time":"2026-06-23T19:41:34Z","timestamp":1782243694468,"version":"3.54.5"},"reference-count":42,"publisher":"World Scientific Pub Co Pte Lt","issue":"02","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Adv. Adapt. Data Anal."],"published-print":{"date-parts":[[2009,4]]},"abstract":"<jats:p> Instantaneous frequency (IF) is necessary for understanding the detailed mechanisms for nonlinear and nonstationary processes. Historically, IF was computed from analytic signal (AS) through the Hilbert transform. This paper offers an overview of the difficulties involved in using AS, and two new methods to overcome the difficulties for computing IF. The first approach is to compute the quadrature (defined here as a simple 90\u00b0 shift of phase angle) directly. The second approach is designated as the normalized Hilbert transform (NHT), which consists of applying the Hilbert transform to the empirically determined FM signals. Additionally, we have also introduced alternative methods to compute local frequency, the generalized zero-crossing (GZC), and the teager energy operator (TEO) methods. Through careful comparisons, we found that the NHT and direct quadrature gave the best overall performance. While the TEO method is the most localized, it is limited to data from linear processes, the GZC method is the most robust and accurate although limited to the mean frequency over a quarter wavelength of temporal resolution. With these results, we believe most of the problems associated with the IF determination are resolved, and a true time\u2013frequency analysis is thus taking another step toward maturity. <\/jats:p>","DOI":"10.1142\/s1793536909000096","type":"journal-article","created":{"date-parts":[[2009,4,8]],"date-time":"2009-04-08T04:55:25Z","timestamp":1239166525000},"page":"177-229","source":"Crossref","is-referenced-by-count":556,"title":["ON INSTANTANEOUS FREQUENCY"],"prefix":"10.1142","volume":"01","author":[{"given":"NORDEN E.","family":"HUANG","sequence":"first","affiliation":[{"name":"Research Center for Adaptive Data Analysis, National Central University, Chungli, Taiwan 32001, Republic of China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"ZHAOHUA","family":"WU","sequence":"additional","affiliation":[{"name":"Department of Meteorology &amp; Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL 32306, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"STEVEN R.","family":"LONG","sequence":"additional","affiliation":[{"name":"NASA Goddard Space Flight Center, Ocean Sciences Branch\/Code 614.2, Wallops Flight Facility, Wallops Island, VA 23337, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"KENNETH C.","family":"ARNOLD","sequence":"additional","affiliation":[{"name":"Department of Electric and Computer Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"XIANYAO","family":"CHEN","sequence":"additional","affiliation":[{"name":"The First Institute of Oceanography, SOA, Qingdao 266061, People's Republic of China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"KARIN","family":"BLANK","sequence":"additional","affiliation":[{"name":"Code 564, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"219","published-online":{"date-parts":[[2011,11,20]]},"reference":[{"key":"rf1","first-page":"548","volume":"41","author":"Shekel J.","journal-title":"Proc. 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