Invited Article: Digital beam-forming imaging riometer systems

Honary, F.; Marple, S.; Barratt, Keith; Chapman, Peter; Grill, Martin; Nielsen, E.

doi:10.1063/1.3567309

Cited by 19 publications

(18 citation statements)

References 23 publications

(26 reference statements)

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“…The ''Churchill line'' of seven riometers labelled in Figure 1 lies close to the 94°W geographic meridian (±2°) from Taloyoak (talo) in the north to Pinawa (pina) in the south. These data were complemented by measurements from the zenithal beam of the Imaging Riometer for Ionospheric Studies (IRIS) (Browne et al 1995;Honary et al 2011) operated by Lancaster University at Kilpisjärvi, Finland in conjunction with the Sodankylä Geophysical Observatory (SGO). The data were processed using the Multi-Instrument Analysis (MIA) software package (Marple & Honary 2004).…”

Section: Riometer Measurementsmentioning

confidence: 99%

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Rogers

Honary

2015

J. Space Weather Space Clim.

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Space weather events may adversely affect high frequency (HF) radio propagation, hence the ability to provide nowcasting and forecasting of HF radio absorption is key for industries that rely on HF communications. This paper presents methods of assimilating 30 MHz radio absorption measurements into two types of ionospheric polar cap absorption (PCA) model to improve their performance as nowcasting tools. Type 1 models calculate absorption as m times the square root of the flux of solar protons above an energy threshold, E t . Measurements from 14 riometers during 94 solar proton events (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) are assimilated by optimising the day and night values of m by linear regression. Further non-linear optimisations are demonstrated in which parameters such as E t are also optimised and additional terms characterise local time and seasonal variations. These optimisations reduce RMS errors by up to 36%. Type 2 models incorporate altitude profiles of electron and neutral densities and electron temperatures. Here the scale height of the effective recombination coefficient profile in the D-region is optimised by regression. Furthermore, two published models of the rigidity cut-off latitude (CL) are assessed by comparison with riometer measurements. A small improvement in performance is observed by introducing a 3-h lag in the geomagnetic index K p in the CL models. Assimilating data from a single riometer in the polar cap reduces RMS errors below 1 dB with less than 0.2 dB bias. However, many highlatitude riometers now provide absorption measurements in near-real time and we demonstrate how these data may be assimilated by fitting a low-order spherical harmonic function to both the measurements and a PCA model with optimised parameters.

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Section: Riometer Measurementsmentioning

confidence: 99%

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Rogers

Honary

2015

J. Space Weather Space Clim.

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“…An indication of the scale of this difference may be observed by comparing CNA measurements from coaxial vertical beams of different beam widths. In Figure , the blue lines present data for the narrow central beam of the IRIS imaging riometer at Kilpisjärvi, Finland, (3 dB beam width = 12.8° [ Honary et al , ]), while the red points present the absorption from the wide beam (60° width) formed from a single crossed‐dipole antenna at the same location. This widebeam antenna— supplied by La Jolla Sciences of Solana Beach, California—is also used by riometers of the NORSTAR array.…”

Section: Resultsmentioning

confidence: 99%

Improving the twilight model for polar cap absorption nowcasts

et al. 2016

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During solar proton events (SPE), energetic protons ionize the polar mesosphere causing HF radio wave attenuation, more strongly on the dayside where the effective recombination coefficient, αeff, is low. Polar cap absorption models predict the 30 MHz cosmic noise absorption, A, measured by riometers, based on real‐time measurements of the integrated proton flux‐energy spectrum, J. However, empirical models in common use cannot account for regional and day‐to‐day variations in the daytime and nighttime profiles of αeff(z) or the related sensitivity parameter, m=Atrue/J. Large prediction errors occur during twilight when m changes rapidly, and due to errors locating the rigidity cutoff latitude. Modeling the twilight change in m as a linear or Gauss error‐function transition over a range of solar‐zenith angles (χl < χ < χu) provides a better fit to measurements than selecting day or night αeff profiles based on the Earth‐shadow height. Optimal model parameters were determined for several polar cap riometers for large SPEs in 1998–2005. The optimal χl parameter was found to be most variable, with smaller values (as low as 60°) postsunrise compared with presunset and with positive correlation between riometers over a wide area. Day and night values of m exhibited higher correlation for closely spaced riometers. A nowcast simulation is presented in which rigidity boundary latitude and twilight model parameters are optimized by assimilating age‐weighted measurements from 25 riometers. The technique reduces model bias, and root‐mean‐square errors are reduced by up to 30% compared with a model employing no riometer data assimilation.

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“…The weighted fit gives a slope of 0.54 and intercept of 0.02. The lower value is expected, as this is what has been experienced between the IRIS system which is based on a noise‐balancing system compared to the AIRIS system in Andøya which is a digital system and in which beam forming is done via FPGA (similar to KAIRA) [ Honary et al , ]. This discrepancy remains under investigation.…”

Section: Comparisonsmentioning

confidence: 99%

“…This technique has been explored for the purposes of riometry, where complications due to sidelobe response [Hagfors et al, 2003] were corrected using tapering. Imaging riometers to date have often been filled-aperture multibeam systems [Honary et al, 2011].…”

Section: All-sky Interferometric Riometrymentioning

confidence: 99%

All‐sky interferometric riometry

et al. 2015

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The first implementation of a Fourier-based interferometric riometry technique for measuring electron density induced ionospheric opacity at VHF radio frequencies is presented. Unlike multibeam riometers, which form discrete beams on the sky, the interferometric technique permits all-sky sampling of incoming cosmic radio noise emissions resulting in a spatially continuous radiogram of the entire sky. The map of the received power at each time may then be compared to the equivalent map from a "quiet day," allowing the morphology of ionospheric absorption of cosmic radio noise to be ascertained. In this work, the high-latitude Kilpisjärvi Atmospheric Imaging Receiver Array was used to carry out the first interferometric riometry measurements in late 2013, producing all-sky absorption maps of space-weather-related ionization in the D region.

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Invited Article: Digital beam-forming imaging riometer systems

Cited by 19 publications

References 23 publications

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Improving the twilight model for polar cap absorption nowcasts

All‐sky interferometric riometry

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