Real‐time specification of HF propagation support based on a global assimilative model of the ionosphere

Abstract

[1] An HF propagation program, HFNowcast, has been developed that takes advantage of the availability of a real-time global model of the ionosphere to specify in real time the range of frequencies that would be supported on a given HF communications circuit. HFNowcast determines the range of frequency support for a specified circuit, from the lowest usable F layer frequency (FLUF) to the highest (FMUF), together with the E layer ELUF and EMUF. The lack of real-time observations of HF absorption and HF noise at the receiver means that it is not possible to provide real-time specifications of the signalto-noise ratio (SNR), the key parameter for HF communications. The global model (developed by Utah State University (USU)) includes particle E precipitation at high dip latitudes during the night, which often precludes the determination of foF2 and M(3000)F2 and thus the simple determination of propagation support in those regions. The FMUF is therefore derived by first calculating the vertical incidence ionogram at the control point(s) and then transforming that ionogram to the oblique incidence (OI) ionogram for the given circuit/hop length. HFNowcast has been validated favorably against several months of oblique propagation observations on midlatitude circuits, although its day-to-day variability does not match the observations very well, and it tends to underestimate the FMUFs. The systematic differences between the predictions and observations can be attributed directly to limitations of the current version of the USU model of the ionosphere.

Global modeling of the low‐ and middle‐latitude ionospheric D and lower E regions and implications for HF radio wave absorption

“…Another reason for recent interest in the D region is that, as discussed by Eccles et al [], there has been a renewal of interest in the use of HF radio for both defense and commercial applications [see also McNamara et al , ; Ads et al , ]. Further, introducing a new model of HF absorption, Pederick and Cervera [] show that they get more absorption in the 90–100 km layer than the older calculations and that this “contradicts” the classic picture, dating back to work by Appleton and Piggott [].…”

Longitudinal structure in the CHAMP electron densities and their implications for global ionospheric modeling

“…Many of the same issues are expected to arise with empirical models developed by URSI and CCIR (ITU) that fit observations such as foF2 with spherical harmonic functions of the minimum possible order. The information missing from both the assimilative and empirical models of the equatorial ionosphere can be expected to have negative impacts on operational applications such as real‐time HF propagation predictions [see, e.g., Angling et al , 2009; McNamara et al , 2009].…”

Development of an HF selection tool based on the Electron Density Assimilative Model near‐real‐time ionosphere

“…The returned values are obtained by deriving f o F 2 and M(3000) F 2 (see Table 1 for definitions) from the EDAM grid and then applying the MUF estimation algorithm from International Telecommunication Union Radiocommunication Sector ( ITU‐R ) [2007]. A similar project, called HFNowcast [ McNamara et al , 2009], is being undertaken by the U.S. Air Force Research Laboratory (AFRL) using electron density grids from the Utah State University Global Assimilation of Ionospheric Measurements (USU‐GAIM) [ Thompson et al , 2006]. McNamara et al [2009] provide a good exposition of the rationale for providing MUF predictions rather than the more usual signal‐to‐noise ratio (SNR) predictions.…”

“…A similar project, called HFNowcast [ McNamara et al , 2009], is being undertaken by the U.S. Air Force Research Laboratory (AFRL) using electron density grids from the Utah State University Global Assimilation of Ionospheric Measurements (USU‐GAIM) [ Thompson et al , 2006]. McNamara et al [2009] provide a good exposition of the rationale for providing MUF predictions rather than the more usual signal‐to‐noise ratio (SNR) predictions. In summary, in the absence of real‐time noise and absorption measurements, it is not possible to provide real‐time estimates of SNR.…”

“…Testing was conducted by comparing the EDAM533 results with those obtained from the standard Institute of Telecommunications Sciences (ITS) implementation of REC533 and with those obtained by direct ray tracing through IRI2007. Satisfactory comparisons have also been made between EDAM533 and the AFRL HFNowcast program [ McNamara et al , 2009] when both have used identical ionospheric grids (IRI2007; i.e., no assimilation is used).…”