Automatically identification of Equatorial Spread-F occurrence on ionograms Valdir Gil Pillat a,n , Paulo Roberto Fagundes a , Lamartine Nogueira Frutuoso Guimarães b a Laboratório de Física e Astronomia, UNIVAP – Universidade do Vale do Paraíba, 12244-000 São José dos Campos, SP, Brazil b Divisão de Energia Nuclear, IEAv-Instituto de Estudos Avançados,12228-970 São José dos Campos, SP, Brazil article info Article history: Received 18 May 2015 Received in revised form 15 October 2015 Accepted 17 October 2015 Available online 20 October 2015 Keywords: Tropical ionosphere Equatorial spread-F Ionogram Auto scaling abstract F-region large-scale irregularities, also called plasma bubbles, are one of the most interesting equatorial ionospheric phenomena. These irregularities are generated in the equatorial region and afterwards ex- tend to lower latitudes. They are one of the important topics of investigation in equatorial ionosphere electrodynamics and, therefore, are subject to intense theoretical and experimental research. The io- nosonde is the most used scientific equipment to study the ionosphere and the F-region. With ad- vancement of digital ionosonde, it is now possible to carry out an ionospheric sounding with a cadence of 5 min or even with 1-minute cadence. To analyse a large amount of ionograms, more sophisticated tools are needed. Thus, development of algorithms to identify and analyse different aspects of ionograms has become very important to space science researchers. Multiple echoes recorded on ionograms are the signature of these irregularities in the ionograms, usually called Spread-F. Spread-F is classified into three types: range, frequency, and mixed. Thus, automatic identification of Spread-F is important in iono- spheric studies, because studies usually involve the analysis and interpretation of large numbers of io- nograms. The main objective of this paper is to present a new computational tool, based on fuzzy re- lation, designed to automatically identify the occurrence of Spread-F in ionograms. The test was con- ducted in ionograms recorded in the Brazilian sector (São José dos Campos (23.2°S, 45.9°W, dip latitude 17.6°S-low latitude) and Palmas (10.2°S, 48.2°W, dip latitude 5.5°S-near the magnetic equatorial)). The automatic identification of Spread-F occurrence was compared with those obtained manually and good agreement was found. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction In the last few years, ionospheric data have been used quite intensively to help understand space weather and ionosphere electrodynamics. For that reason, the use of computational tools to reduce data processing time has become more important. More- over, the main goal is to process ionograms automatically and, therefore, avoid spending a lot of time scaling ionograms manually and checking if there is any type of Spread-F during a period of time. The ionosonde is a kind of radar and is the most used equipment to investigate and track E and F ionospheric electro- dynamic layers. The Physics and Astronomy Laboratory of the “Universidade do Vale do Paraíba” (UNIVAP) uses an ionosonde of the type “Canadian Advanced Digital Ionosonde” (CADI) (Mac- dougall et al., 1995). The ionosonde transmits radio frequency (RF) signals (1–20 MHz), which are reflected by the lower boundary of the ionosphere, when the transmitted frequency matches the plasma frequency (Figs. 1B and 2B). The time between when the signal was transmitted and received is used to calculate the virtual height (h´F) of the reflecting ionosphere edge, given the assump- tion that the speed of light in the vacuum is equal to the speed of light in the atmosphere. The collected data is stored in files to be visualized in the form of frequency against virtual height, and this set is called an ionogram. In the ionograms, it is possible to ob- serve the bottom-side of the ionosphere vertical profile. The data acquisition time to form one ionogram is usually set to 5 min. That means that in 30 days 8640 ionograms are acquired, which require subsequent analysis. From each ionogram, one may extract several types of information that characterizes the ionosphere. The in- formation extracted include for instance; the base height of the E and F (h′Eeh′F) layers, the critical frequencies of the layers (foE e foF2), among others. Due to the large number of ionograms and the importance of the ionosphere analysis, since the 80 s seve- ral technics have been developed with the goal of automatic Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jastp Journal of Atmospheric and Solar-Terrestrial Physics http://dx.doi.org/10.1016/j.jastp.2015.10.015 1364-6826/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. Fax: þ55 12 3947 1149. E-mail addresses: valdirgp@univap.br (V.G. Pillat), fagundes@univap.br (P.R. Fagundes), guimarae@ieav.cta.br (L.N.F. Guimarães). Journal of Atmospheric and Solar-Terrestrial Physics 135 (2015) 118–125