Imaging the Solar Corona during the 2015 March 20 Eclipse using LOFAR

2020 ◽  
Author(s):  
Aoife Maria Ryan ◽  
Peter T. Gallagher ◽  
Eoin P. Carley ◽  
Diana E. Morosan ◽  
Michiel A. Brentjens ◽  
...  
Keyword(s):  
Solar Corona ◽  
Spatial Resolution ◽  
Electromagnetic Waves ◽  
High Spatial Resolution ◽  
Low Frequency ◽  
Angular Width ◽  
Interferometric Imaging ◽  
Low Frequencies ◽  
Point Spread ◽  
Spread Function

<p>The solar corona is a highly-structured plasma which reaches temperatures of more than ~2MK. At low radio frequencies (≤ 400 MHz), scattering and refraction of electromagnetic waves are thought to broaden sources to several arcminutes. However, exactly how source size relates to scattering due to turbulence is still subject to investigation. This is mainly due to the lack of high spatial resolution observations of the solar corona at low frequencies. Here, we use the LOw Frequency ARray (LOFAR) to observe the solar corona at 120-180 MHz using baselines of up to ~3.5 km (~1--2’) during a partial solar eclipse of 2015 March 20. We use a lunar de-occultation technique to achieve higher spatial resolution than that attainable via traditional interferometric imaging. This provides a means of studying source sizes in the corona that are smaller than the angular width of the interferometric point spread function. </p>

scholarly journals LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse

2021 ◽  
Author(s):  
Aoife Maria Ryan ◽  
Peter T. Gallagher ◽  
Eoin P. Carley ◽  
Michiel A. Brentjens ◽  
Pearse C. Murphy ◽  
...  
Keyword(s):  
Solar Corona ◽  
Spatial Resolution ◽  
Solar Eclipse ◽  
Electromagnetic Waves ◽  
Imaging Techniques ◽  
Active Regions ◽  
Density Fluctuations ◽  
Source Size ◽  
Interferometric Imaging ◽  
Low Frequencies

<p>The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.</p><p><br><br></p>

scholarly journals Efficient and Compact Near-Field Coupled Hybrid Antenna Using a Single Radiating Subwavelength Split-Ring Resonator

Electronics ◽  
2019 ◽  
Vol 8 (5) ◽  
pp. 527
Author(s):  
Zinching Dang ◽  
Marco Rahm
Keyword(s):  
Resonance Frequency ◽  
Electromagnetic Waves ◽  
Ring Resonator ◽  
Near Field ◽  
Low Frequency ◽  
Split Ring Resonator ◽  
Dipole Antenna ◽  
Angular Width ◽  
Split Ring ◽  
Broadband Internet

Modern applications in the realms of wireless communication and mobile broadband Internet increase the demand for compact antennas with well defined directivity. Here, we present an approach for the design and implementation of hybrid antennas consisting of a classic feeding antenna that is near-field-coupled to a subwavelength resonator. In such a combined structure, the composite antenna always radiates at the resonance frequency of the subwavelength oscillator as well as at the resonance frequency of the feeding antenna. While the classic antenna serves as impedance-matched feeding element, the subwavelength resonator induces an additional resonance to the composite antenna. In general, these near-field coupled structures are known for decades and are lately published as near-field resonant parasitic antennas. We describe an antenna design consisting of a high-frequency electric dipole antenna at f d = 25 GHz that couples to a low-frequency subwavelength split-ring resonator, which emits electromagnetic waves at f SRR = 10.41 GHz. The radiating part of the antenna has a size of approximately 3.2 mm × 8 mm × 1 mm and thus is electrically small at this frequency with a product k · a = 0.5 . The input return loss of the antenna was moderate at − 18 dB and it radiated at a spectral bandwidth of 120 MHz. The measured main lobe of the antenna was observed at 60 ∘ with a − 3 dB angular width of 65 ∘ in the E-plane and at 130 ∘ with a − 3 dB angular width of 145 ∘ in the H-plane.

scholarly journals Blind Fusion of Hyperspectral Multispectral Images Based on Matrix Factorization

2021 ◽  
Vol 13 (21) ◽  
pp. 4219
Author(s):  
Jian Long ◽  
Yuanxi Peng
Keyword(s):  
Response Function ◽  
Spatial Resolution ◽  
Point Spread Function ◽  
Spectral Response ◽  
Estimation Method ◽  
Hyperspectral Images ◽  
Fusion Method ◽  
Multispectral Images ◽  
Point Spread ◽  
Spread Function

The fusion of low spatial resolution hyperspectral images and high spatial resolution multispectral images in the same scenario is important for the super-resolution of hyperspectral images. The spectral response function (SRF) and the point spread function (PSF) are two crucial prior pieces of information in fusion, and most of the current algorithms need to provide these two preliminary pieces of information in advance, even for semi-blind fusion algorithms at least the SRF. This causes limitations in the application of fusion algorithms. This paper aims to solve the dependence of the fusion method on the point spread function and proposes a method to estimate the spectral response function from the images involved in the fusion to achieve blind fusion. We conducted experiments on simulated datasets Pavia University, CAVE, and the remote sensing images acquired by two spectral cameras, Sentinel 2 and Hyperion. The experimental results show that our proposed SRF estimation method can improve the PSNR value by 5 dB on average compared with other state-of-the-art SRF estimation results. The proposed blind fusion method can improve the PSNR value of fusion results by 3–15 dB compared with other blind fusion methods.

scholarly journals HIGH SPATIAL RESOLUTION OBSERVATIONS OF LOOPS IN THE SOLAR CORONA

2013 ◽  
Vol 772 (2) ◽  
pp. L19 ◽  
Author(s):  
David H. Brooks ◽  
Harry P. Warren ◽  
Ignacio Ugarte-Urra ◽  
Amy R. Winebarger
Keyword(s):  
Solar Corona ◽  
Spatial Resolution ◽  
High Spatial Resolution

scholarly journals Reconstructed spatial resolution and contrast recovery with Bayesian penalized likelihood reconstruction (Q.Clear) for FDG-PET compared to time-of-flight (TOF) with point spread function (PSF)

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Julian M. Rogasch ◽  
Said Suleiman ◽  
Frank Hofheinz ◽  
Stephanie Bluemel ◽  
Mathias Lukas ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Point Spread Function ◽  
Activity Concentration ◽  
Signal To Noise Ratio ◽  
Time Of Flight ◽  
Penalized Likelihood ◽  
Systematic Evaluation ◽  
Point Spread ◽  
Spread Function ◽  
Relative Differences

Abstract Background Bayesian penalized likelihood reconstruction for PET (e.g., GE Q.Clear) aims at improving convergence of lesion activity while ensuring sufficient signal-to-noise ratio (SNR). This study evaluated reconstructed spatial resolution, maximum/peak contrast recovery (CRmax/CRpeak) and SNR of Q.Clear compared to time-of-flight (TOF) OSEM with and without point spread function (PSF) modeling. Methods The NEMA IEC Body phantom was scanned five times (3 min scan duration, 30 min between scans, background, 1.5–3.9 kBq/ml F18) with a GE Discovery MI PET/CT (3-ring detector) with spheres filled with 8-, 4-, or 2-fold the background activity concentration (SBR 8:1, 4:1, 2:1). Reconstruction included Q.Clear (beta, 150/300/450), “PSF+TOF4/16” (iterations, 4; subsets, 16; in-plane filter, 2.0 mm), “OSEM+TOF4/16” (identical parameters), “PSF+TOF2/17” (2 it, 17 ss, 2.0 mm filter), “OSEM+TOF2/17” (identical), “PSF+TOF4/8” (4 it, 8 ss, 6.4 mm), and “OSEM+TOF2/8” (2 it, 8 ss, 6.4 mm). Spatial resolution was derived from 3D sphere activity profiles. RC as (sphere activity concentration [AC]/true AC). SNR as (background mean AC/background AC standard deviation). Results Spatial resolution of Q.Clear150 was significantly better than all conventional algorithms at SBR 8:1 and 4:1 (Wilcoxon, each p < 0.05). At SBR 4:1 and 2:1, the spatial resolution of Q.Clear300/450 was similar or inferior to PSF+TOF4/16 and OSEM+TOF4/16. Small sphere CRpeak generally underestimated true AC, and it was similar for Q.Clear150/300/450 as with PSF+TOF4/16 or PSF+TOF2/17 (i.e., relative differences < 10%). Q.Clear provided similar or higher CRpeak as OSEM+TOF4/16 and OSEM+TOF2/17 resulting in a consistently better tradeoff between CRpeak and SNR with Q.Clear. Compared to PSF+TOF4/8/OSEM+TOF2/8, Q.Clear150/300/450 showed lower SNR but higher CRpeak. Conclusions Q.Clear consistently improved reconstructed spatial resolution at high and medium SBR compared to PSF+TOF and OSEM+TOF, but only with beta = 150. However, this is at the cost of inferior SNR with Q.Clear150 compared to Q.Clear300/450 and PSF+TOF4/16/PSF+TOF2/17 while CRpeak for the small spheres did not improve considerably. This suggests that Q.Clear300/450 may be advantageous for the 3-ring detector configuration because the tradeoff between CR and SNR with Q.Clear300/450 was superior to PSF+TOF4/16, OSEM+TOF4/16, and OSEM+TOF2/17. However, it requires validation by systematic evaluation in patients at different activity and acquisition protocols.

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