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Propagation and Energy Transfer
Published in James D. Taylor, Introduction to Ultra-Wideband Radar Systems, 2020
Robert Roussel-Dupré, Terence W. Barrett
The ionospheric TEC depends on geographical location, time of day, season, and solar and geomagnetic activity. Diurnal variations in TEC during the spring season and high solar activity for three geographical locations corresponding to equatorial, middle, and polar latitudes are shown in Figure 7.10A through C, respectively. These results were obtained by integrating the electron density profiles generated using the International Reference Ionosphere (IRI) code.16 This code generates electron density profiles by interpolating a series of tables developed from synoptic measurements obtained with ionosondes, topside sounders, and incoherent scatter radars. The database in some cases constitutes more than 20 years of measurements taken on an hourly basis. Nevertheless, a recent study of the accuracy with which various ionospheric codes predict the TEC value for any given set of parameters indicated that factors of two deviation from measurement were not uncommon. Thus, the plotted magnitudes of TEC should be taken as indicative of a range of possible values.
Advanced Topic: A Moon-Based Imaging of Earth’s Surface
Published in Kun-Shan Chen, Radar Scattering and Imaging of Rough Surfaces, 2020
As can be seen from Figure 10.14, the synthetic aperture time of the Moon-based SAR can be up to hundreds or even thousands of seconds. In contrast, the synthetic aperture time of the LEOSAR is usually limited to 1–2 s. As a result, it seems that the ionospheric freezing assumption for LEOSAR loses its effect in the Moon-based SAR. To catch a better notion, in Figure 10.15, we plot the measured vertical TEC at Guangzhou, China (113.23°E, 23.16°N), with a synthetic aperture time of 1800 s, a typical value of the Moon-based SAR. The TEC data used in the schematic diagram for the temporal variation of background ionosphere is acquired in October 2016 and reported by International Reference Ionosphere 2012 (IRI 2012) [29].
Research on an ionospheric delay correction method for the interferometric imaging radar altimeter based on improved GIM data
Published in Journal of Spatial Science, 2021
Hongli Miao, Renchao Qu, Peng Mao, Xiangying Miao
For adual-frequency microwave altimeter, the dual-frequency method can be used to obtain the TEC on the signal propagation path in real time in order to correct the ionospheric delay with high accuracy. However, InIRA uses single-frequency transmitters and receivers and not equipped with adual-frequency nadir altimeter for calibration, so only the modeling method can be used to correct the ionospheric error. At present, avariety of ionospheric models have been established, such as the 2016 International Reference Ionosphere (IRI-2016), NeQuick, and Klobuchar models. In addition, the global ionosphere map (GIM) provided by the International GNSS Service (IGS) is an important data product for studying the ionosphere, and its accuracy is higher than that of other ionospheric models (Ansari et al. 2017).
An Observational Review on influence of Intense Geomagnetic Storm on Positional Accuracy of NavIC/IRNSS System
Published in IETE Technical Review, 2020
Mehul V. Desai, Shweta N. Shah
Geomagnetic storm effects on Global Positioning System (GPS) based navigation were observed by many researchers [14–18]. Rao et al. [14], found that in the EIA crest region during the geomagnetic storms on 9–10 November 2004, the TEC value rose to 90 TEC units, which is equivalent to an ionospheric delay of ∼15 m. They also observed the three major geomagnetic storms in 2011, that the TEC values obtained from the Global Navigation Satellite System (GNSS) from the International Reference Ionosphere (IRI) 2007 empirical model at a low-latitude Bangalore (77.51° E, 13.03° N) station in India were significantly enhanced [16]. The IRI model was also applied by Samed et al. [17], and de Abreu et al. [18], to compare GPS TEC over the western Black Sea and Brazilian sector during the unusual solar minimum 2009. Astafyeva et al., showed that the density of Loss of Lock (LoL) increased up to a maximum of 3% during a super storm and 1% when an intense storm occurred [19]. During 2013 high intensity, long duration, continuous AE activity event and TEC enhancements from 25% to 80% compared to quiet time were observed by Negreti et al. [20]. We analyzed the impact of Grid Ionospheric Vertical Error (GIVE) model for improving the positional accuracy of the NavIC/IRNSS system under the quiet and disturbed days [4]. However, the study of the effect of intense and super geomagnetic storms on the positional accuracy of the NavIC/IRNSS system was an open research which is being incorporated in this paper up to certain extent.