The technique of using very low frequency signals (VLF-Very Low Frequency) is a very effective tool to study the sudden ionospheric disturbance (SID) due to the fact that the VLF signals are almost entirely reflected at D layer (60 - 90 km altitude) of the ionosphere when disturbance occurs. | Tạp chí Khoa học và Công nghệ 54 (1) (2016) 82-91 STUDY OF SUDDEN IONOSPHERIC DISTURBANCES USING VERY LOW FREQUENCY RECEIVER IN NHA TRANG, VIETNAM Vinh Hao*, Tong Van Tuat, Ngo Van Tam Nha Trang Institute of Technology Research and Application,VAST, 02 Hung Vuong str., Nha Trang * Email: Received: 11 March 2015; Accepted for publication: 14 October 2015 ABSTRACT The technique of using very low frequency signals (VLF-Very Low Frequency) is a very effective tool to study the sudden ionospheric disturbance (SID) due to the fact that the VLF signals are almost entirely reflected at D layer (60 - 90 km altitude) of the ionosphere when disturbance occurs. For the requirement of quickly grasp advanced engineering and technology to master the research equipment, we bravely set a target for manufacturing equipment to serve the research and application. In this paper, the research group would like to present the obtained results of applying the VLF receiver made at Nha Trang Institute of Technology Research and Application to study the sudden ionospheric disturbances. Keywords: VLF signal, VLF receiver, sudden ionospheric disturbance. 1. INTRODUCTION A sudden ionospheric disturbance is a natural phenomenon, in which the Earth's ionosphere is temporarily disturbed by increasing of ionization sources. There are many sources, which creat sudden ionospheric disturbances but the most common source is solar flare. Radiations from solar flares, especially high energy X-rays can take about 8 minutes to the earth [1]. In the day time, free electron density of D-layer is not high enough to reflect VLF waves so they go through the D-layer and are reflected by higher layers (E-layer and F-layer). Energy of VLF waves is decreased strongly by adsorption of D-layer (Figure 1). Daytime Nighttime Nighttime Figure 1. Variation of VLF signal for a quiet day [1]. Study of sudden ionospheric disturbances using very low frequency receiver in Nha Trang, Vietnam At .
