Kısa Dalga (Kd) Haberleşmesi İçin Doppler Kaymasının Kestirilmesi
Ionosphere has a great importance on radio wave propagation. Thanks to the high electron density it contains, it forms reflective ionosphere layers. Ionosphere enables High Frequency (HF) Communication by reflecting radio waves in the frequency range of 3-30 MHz. Ionosphere varies in time and location due to many factors such as solar radiation effect, geomagnetic or seismic activities. The variability in the ionosphere causes the Doppler shift on the received signal. The Doppler frequency shift effects the communication quality, negatively. Therefore, the Doppler shift on the received signal must be detected. One of the prominent ways for measuring the Doppler shift is using ionosonde equipments. Ionosonde equipments measure Doppler shift of a signal transmitted through the zenith direction from the transmitter. These equipments are expensive and their installation, maintenance require special attention. Furthermore, the ionosonde network over the world is not spatially dense enough. In this study, a technique is proposed to estimate Doppler shift on the received signal based on ray tracing when there is no measurement equipment like ionosonde. Thus, the structure of the ionosphere should be analyzed. One of the important parameters thativ characterize the ionosphere is the Total Electron Content (TEC). First, 2- Dimensional TEC maps are constructed by using the IONOLAB–MAP tool which spatially interpolates the Vertical TEC (VTEC) estimates obtained from the European Reference Frame (EUREF) network. To model the ionosphere, the widely used IRI-Plas model was used. Next, a 3-Dimensional electron density profile is generated by inputting inputting the TEC estimates to the IRI-Plas model. Eventually, a close-to real situation electron density profile is obtained in which ray tracing can be performed. These profiles can be constructed periodically with a period as low as 30 seconds. By processing two consequent snapshots together and calculating the propagation paths caused by motion of the reflective ionosphere layers, Doppler shift is estimated. The proposed technique is tested by comparing the results to the Doppler measurements taken at the Digital Portable Sounder (DPS) ionosonde equipment at Pruhonice, Czech Republic.