Signal distortion on VHF/UHF transionospheric paths: First results from the Wideband Ionospheric Distortion Experiment

Cannon, Paul S.; Groves, K. M.; Fraser, David; Donnelly, William J.; Perrier, Kathleen

doi:10.1029/2005rs003369

Cited by 27 publications

(33 citation statements)

References 16 publications

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“…Nickisch [] and Knepp and Nickisch [], for example, present phase screen/diffraction methods in which an electromagnetic wave is propagated through multiple phase “screens” followed by a distance of free space to result in the calculation of the two‐frequency, two‐position mutual coherence function and its 2‐D Fourier transform, termed variously as the “scattering function” or “generalized power spectrum.” These 2‐D model spectra also show parabolic arc structures under some circumstances, most pronounced in the case of a single thin scattering screen as seen, for example, in Figure 11 of Knepp and Nickisch []. They are seen in radar observations, though examples reviewed in preparation of the current work do not show the phenomenon very clearly (e.g., Figure 1 in Nickisch [] showing results from an HF channel probe in northern Greenland and VHF results from an equatorial radar facility presented in Cannon et al []).…”

Section: Introductionmentioning

confidence: 69%

Broadband meter‐wavelength observations of ionospheric scintillation

et al. 2014

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Intensity scintillations of cosmic radio sources are used to study astrophysical plasmas like the ionosphere, the solar wind, and the interstellar medium. Normally, these observations are relatively narrow band. With Low‐Frequency Array (LOFAR) technology at the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) station in northern Finland we have observed scintillations over a three‐octave bandwidth. “Parabolic arcs,” which were discovered in interstellar scintillations of pulsars, can provide precise estimates of the distance and velocity of the scattering plasma. Here we report the first observations of such arcs in the ionosphere and the first broadband observations of arcs anywhere, raising hopes that study of the phenomenon may similarly improve the analysis of ionospheric scintillations. These observations were made of the strong natural radio source Cygnus‐A and covered the entire 30–250 MHz band of KAIRA. Well‐defined parabolic arcs were seen early in the observations, before transit, and disappeared after transit although scintillations continued to be obvious during the entire observation. We show that this can be attributed to the structure of Cygnus‐A. Initial results from modeling these scintillation arcs are consistent with simultaneous ionospheric soundings taken with other instruments and indicate that scattering is most likely to be associated more with the topside ionosphere than the F region peak altitude. Further modeling and possible extension to interferometric observations, using international LOFAR stations, are discussed.

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Section: Introductionmentioning

confidence: 69%

Broadband meter‐wavelength observations of ionospheric scintillation

et al. 2014

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“…In the work of Cannon et al [2006] we described the WIDE experiment, our first results and provided examples of channel scattering functions and estimates of the coherency bandwidths and times. In the work of Rogers et al [2009], a companion to this paper, we describe the TIRPS model in some detail and undertake some detailed cross comparisons between the measurements and the model, thereby providing credence to that model.…”

Section: Discussionmentioning

confidence: 99%

“…Although the measurements were taken near the minimum of the solar activity cycle, strong scintillation was nonetheless observed on several occasions, so providing a wide range of conditions. For each pass the data were processed to generate a series of scattering functions (CSFs) [ Cannon et al , 2006; Rogers et al , 2009] from which the CB and CT could be derived.…”

Section: Wideband Ionospheric Distortion Experimentsmentioning

confidence: 99%

“…Following Cannon et al [2006] and Cannon and Bradley [2003], we have chosen to define the coherency time (CT) and coherency bandwidth (CB) as follows: where ΔB is the Doppler spread and ΔT is the delay spread, both of which are determined from the CSFs. Doppler spreads are calculated for the central 68.3% of the total power in the CSF (integrated across all delay samples) as this represents the root‐mean‐squared spread for a Normal power distribution, equivalent to −2.2 dB from the peak.…”

Section: Coherence Time and Coherence Bandwidth And S4 Measurement Anmentioning

confidence: 99%

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Measurements and simulation of ionospheric scattering on VHF and UHF radar signals: Coherence times, coherence bandwidths, and S₄

2009

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[1] Irregularities in the electron density of the ionosphere cause phase and amplitude scintillation on transionospheric VHF and UHF radar signals, particularly at lower radio frequencies. The design of radar and other transionospheric systems requires good estimates of the coherence bandwidth (CB) and coherence time (CT) imposed by a turbulent ionosphere. CB and CT measurements of the equatorial ionosphere, made using the Advanced Research Project Agency Long-range Tracking and Identification Radar 158 MHz and 422 MHz phase coherent radar located on Kwajalein (9.4°N, 167.5°E), are presented as a function of the two-way S 4 scintillation index at 422 MHz The log linear regression equations are CT = 1.46 exp(À1.40 S 4 ) s at 158 MHz and CT = 2.31 exp(À1.10 S 4 ) s at 422 MHz. CT also varies by a factor of 2-3 depending on the effective scan velocity through the ionosphere, v eff . The CT and CB, as a function of S 4 , have been compared to those from the Trans-Ionospheric Radio Propagation Simulator, a phase screen model. A close agreement is achieved using appropriate values of v eff and midrange values of phase spectral index and outer scale. Validation of CB is, however, limited by insufficient radar chirp bandwidth. Formulating the model in terms of the two-way S 4 index (an easily measurable parameter) rather than more fundamental phase screen parameters (which are difficult to obtain), improves its utility for the systems engineer. The frequency dependencies (spectral indices) of S 4 and of CT are also presented to allow interpolation and some extrapolation of these results to other frequencies.

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“…For WIDE tracking scans, the radar was operated with a transmitted pulse bandwidth at VHF of 7 MHz and at UHF of 18 MHz providing a range resolution of 32 and 12.5 m, respectively. The pulse repetition frequency (or radar sampling rate) varied during the scans but was typically in the range of 300 Hz [ Cannon et al , 2006]. Raw data collected in tracking mode were reduced by MIT Lincoln Laboratory (MIT/LL) and provided to the experiment collaborators including full amplitude, phase, and target range information for each frequency.…”

Section: Computing Tec From Altair Tracking Scansmentioning

confidence: 99%

Simulating the effects of scintillation on transionospheric signals with a two‐way phase screen constructed from ALTAIR phase‐derived TEC

et al. 2009

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Severe scintillation on transionospheric radio signals caused by small‐scale plasma irregularities can greatly disrupt wideband communication, surveillance, and navigation systems. Development of techniques to mitigate the effects of scintillation requires accurate characterization of the ionospheric propagation channel. To achieve this goal, multiple campaigns were conducted as part of the joint U.S. ‐UK Wideband Ionospheric Distortion Experiment to obtain ionospheric signatures from various instruments located on Kwajalein Atoll. We use tracking data from the VHF/UHF Advanced Research Project Agency Long‐Range Tracking and Instrumentation Radar for overflights of passive calibration spheres in low‐Earth orbit to demonstrate the validity of a one‐dimensional (1‐D) phase screen model to represent the propagation channel through a disturbed ionosphere. The 1‐D phase screen is constructed from radar phase‐derived estimates of the total electron content. We present a detailed comparison of simulated radar cross section after propagation through the phase screen with observed radar returns under both disturbed and quiet ionospheric conditions. Successful reproduction of radar amplitude enhancements and fades adds to our understanding of small‐scale plasma irregularities and moves us toward our goal of providing precise predictions of radar system performance. Doing so will allow for the development of better mitigation/compensation algorithms for detrimental ionospheric effects. Result from this study also provide an assessment of the tools required for incorporating in situ density measurements along with phase screen theory into situational awareness products to offer an accurate nowcast/forecast of system impacts to users in the communication, navigation, and surveillance communities.

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Signal distortion on VHF/UHF transionospheric paths: First results from the Wideband Ionospheric Distortion Experiment

Cited by 27 publications

References 16 publications

Broadband meter‐wavelength observations of ionospheric scintillation

Broadband meter‐wavelength observations of ionospheric scintillation

Measurements and simulation of ionospheric scattering on VHF and UHF radar signals: Coherence times, coherence bandwidths, and S₄

Simulating the effects of scintillation on transionospheric signals with a two‐way phase screen constructed from ALTAIR phase‐derived TEC

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Signal distortion on VHF/UHF transionospheric paths: First results from the Wideband Ionospheric Distortion Experiment

Cited by 27 publications

References 16 publications

Broadband meter‐wavelength observations of ionospheric scintillation

Broadband meter‐wavelength observations of ionospheric scintillation

Measurements and simulation of ionospheric scattering on VHF and UHF radar signals: Coherence times, coherence bandwidths, and S4

Simulating the effects of scintillation on transionospheric signals with a two‐way phase screen constructed from ALTAIR phase‐derived TEC

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Measurements and simulation of ionospheric scattering on VHF and UHF radar signals: Coherence times, coherence bandwidths, and S₄