Predictions of HF system performance for propagation through disturbed ionospheres measured using low-Earth-orbit satellite radio beacon tomography

Abstract

The CERTO radio beacon on the C/NOFS satellite sends VHF/UHF radio signals at 150 and 400 MHz to provide measurements of integrated electron density or Total Electron Content (TEC) by an east-west chain of ground receivers in Peru. Computerized Ionospheric Tomography (CIT) is used to convert the TEC data into two-dimensional images of electron densities with maximum 5 × 5 km resolution in Longitude-Altitude space. These images are updated every 95 min as the C/NOFS satellite passes over the receiver network in its low-latitude orbit with an inclination of 12°. The 2-D, high-resolution images of the ionosphere are used to predict the impact of equatorial plasma structures on HF propagation of radar and radio signals. Electron density measurements from the NRL radio tomography chain across Peru are used for simulations of the performance by HF one-way links. HF rays from transmitter to receiver are traced through the electron density images produced by radio beacon tomography. Eight separate paths are found between a transmitter and ground receiver separated by 2000 km. A total of 36 backscatter echoes are found with unique group delay, Doppler frequency shift, phase delay, and echo amplitude. This multipath effect explains the range and Doppler spreading of observations for HF monostatic radar propagation through F layer irregularities. This type of analysis is useful for prediction and interpretation of range and Doppler observations from HF systems including over-the-horizon and SuperDARN radars, HF Geolocation Arrays, and HF communications networks.

Radiotomography and HF ray tracing of the artificially disturbed ionosphere above the Sura heating facility

“…As of now, such experiments can be carried out, e.g., using the ePOP payload onboard the Canadian CASSIOPE satellite [ Siefring et al , ]. Similar experiments with the ePOP satellite have been proposed by Bernhardt et al [] using the coherent electromagnetic radio tomography beacon and the radio receiver instrument on the satellite to detect the effects natural irregularities on HF radio transmissions.…”

“…Similar studies, e.g., for the region of the northern crest of equatorial anomaly are presented in Kryukovsky and Kiryanova []. The HF ray‐tracing technique has also be employed for natural irregularities at the equator measured with satellite beacon tomography [ Bernhardt et al , ].…”

An FDTD Investigation of Orthogonality and the Backscattering of HF Waves in the Presence of Ionospheric Irregularities

“…For these models to be sufficiently accurate, two conditions must be satisfied. First, the spatial resolution must be less than the Fresnel diffraction scale (Bernhardt et al, 2014; Rino, 2011). Second, any material objects in the spatial domain of interest must be larger than the wavelength of the incident wave (Smith et al, 2020).…”

“…Many numerical methods have been used to study the backscattering process and better map the location of irregularities from observed data (Bernhardt et al, 2014; Cervera & Harris, 2014; Chisham et al, 2008; Greenwald et al, 1995; Liu et al, 2012). The majority of these models are based on ray tracing, an approach that treats the HF waves as rays and only tracks the primary direction of energy flow.…”

“…The modeling in this paper is unique because it is run at a sufficiently high resolution to examine how small‐scale irregularities that are comparable to the HF's wavelength affect the backscattering of the signal. To the author's knowledge, ray tracing models of HF waves with ionospheric irregularities are run at a coarse resolution (Bernhardt et al, 2014; Cervera & Harris, 2014; Chisham et al, 2008; Greenwald et al, 1995; Liu et al, 2012). The modeling results in this paper will show that these small‐scale irregularities, which are accounted for in the FDTD model, have a significant impact on where orthogonality occurs.…”