1 URSI AP-RASC 2019, New Delhi, India, 09 - 15 March 2019 Detection of TID activity from ionogram virtual height variations H. Haralambous *, T. Leontiou, Frederick University, Nicosia, Cyprus, e-mail: eng.hh@frederick.ac.cy, eng.lt@frederick.ac.cy Abstract Travelling Ionospheric Disturbances (TIDs) constitute a specific phenomenon that can be excited by space weather or driven by other processes acting below the ionosphere. Independent of their source, the effects imposed by TIDs in the ionosphere are very detrimental to an array of user technologies. TechTIDE (http://techtide.space.noa.gr/) is a project funded by the European Commission Horizon 2020 research and innovation program that aspires to establish a pre-operational system to demonstrate reliability of a set of TID (Travelling Ionospheric Disturbances) detection methodologies to issue warnings of the occurrence of TIDs over the region extending from Europe to South Africa. One of these detection methodologies is based on the height-time-reflection intensity (HTI) methodology applied on Digisonde ionograms to infer TID activity over Digisonde stations. In this paper we describe the steps for the implementation of this technique in the frames of TechTIDE. 1. Introduction Travelling Ionospheric Disturbances (TIDs) are plasma density fluctuations that propagate as waves through the ionosphere at a wide range of velocities and frequencies and play an important role in the exchange of momentum and energy between various regions of the upper atmosphere. TIDs constitute a specific phenomenon that can be excited by space weather or driven by other processes acting below the ionosphere. Independent of their source, the effects imposed by TIDs in the ionosphere are very detrimental to an array of user technologies and in particular for Real Time Kinematic (RTK) and Wide Area Real Time Kinematic (WARTK) as the enhanced TID disturbance of the ionosphere is directly translated to user positioning error. Large-scale TIDs (LSTIDs) associated with auroral and geomagnetic activity propagating with wavelengths of 1000 to 3000 km and velocities of 300 – 1000 m/s have the most dramatic effect on such systems. The height-time-reflection intensity (HTI) methodology is similar to the technique producing range-time intensity (RTI) radar displays within a given time interval. The application of this method in TechTIDE enables the identification and tracking of the TID activity over each Digisonde station by using the actual ionograms produced over each station. This technique considers an ionogram as a ‘‘snapshot’’ of reflected intensity as a function of virtual height and Digisonde signal frequency, and it uses a sequence of ionograms to compute an average HTI plot, (for a given frequency bin) that is essentially a 3-D plot of reflected signal-to-noise ratio in dB as a function of height within a given time interval. This display reveals dynamic changes in the ionosphere. Figure 1: HTI plots over Nicosia (left), Athens (middle) and Pruhonice (right) for December 7, 2016. Figure 1 depicts TID-like variations on typical HTI plots corresponding to a Digisonde frequency band, of 2.0-4.0 MHz for three stations over Europe. The periodicity of the dominant wave activity is estimated by applying spectral analysis to points of maximum intensity reflected at certain F-region virtual heights indicated by black dots on these HTI plots. In the present paper, using ionograms obtained by the DPS-4D Digital ionosonde (Digisonde) at the lower mid-latitude European station near Nicosia, Cyprus (35 o N, 33 o E geographic; magnetic dip. 29.38°N). we demonstrate the main concepts behind this technique as implementated in the frames of TechTIDE project and we apply it during two geomagnetic storm events that triggered TID activity. 2. Methodology The HTI method uses raw ionograms (Figure 2a) in order to estimate the optimal frequency bin within which the F- region trace of the ionograms will be processed at each instant during a 24 hour interval. For each ionogram at the appropriate frequency bin a virtual height profile of signal strength is obtained (indicated by different colour in Figure 2b).