T. G. Cameron;R. A. D. Fiori;G. W. Perry;J. J. Ruck;T. Thayaparan
Large-scale ionospheric gradients associated with the solar terminator can deflect high frequency (HF) radio waves to off-great circle paths during the morning and evening, negatively impacting technologies reliant on HF radio wave propagation. For example, geolocation algorithms used by scientific and military over-the-horizon radars (OTHRs) generally assume on-great circle propagation, and thus lateral deviations from the great-circle path can lead to positioning errors. In this study, radio wave propagation is simulated via 3D numerical ray traces though an empirical, high-latitude model ionosphere initialized for a variety of times of the day and year to explore and quantify high-latitude off-great circle propagation associated with the solar terminator. Analysis of these simulations show large scale east-west ionospheric gradients due to the solar terminator can cause lateral deviations in north-directed propagation paths exceeding 20° at sunrise and sunset depending on radio wave frequency, though the largest portion of received signal power tends to experience maximum deflections of 5°. An exploration of the dependence of propagation direction on deflection shows that propagation paths parallel to the solar terminator tend to experience the largest deflections. Since the solar terminator at high latitudes is at an angle with respect to north in the winter and summer, propagation paths oriented west or east of north can experience larger deflections than north oriented paths at sunrise and sunset during these times of year. Impacts of these diurnal deflections on the operation of OTHR and scientific radar are discussed, as well as possible strategies for mitigating them.
{"title":"High-latitude off-great circle propagation associated with the solar terminator","authors":"T. G. Cameron;R. A. D. Fiori;G. W. Perry;J. J. Ruck;T. Thayaparan","doi":"10.1029/2023RS007917","DOIUrl":"10.1029/2023RS007917","url":null,"abstract":"Large-scale ionospheric gradients associated with the solar terminator can deflect high frequency (HF) radio waves to off-great circle paths during the morning and evening, negatively impacting technologies reliant on HF radio wave propagation. For example, geolocation algorithms used by scientific and military over-the-horizon radars (OTHRs) generally assume on-great circle propagation, and thus lateral deviations from the great-circle path can lead to positioning errors. In this study, radio wave propagation is simulated via 3D numerical ray traces though an empirical, high-latitude model ionosphere initialized for a variety of times of the day and year to explore and quantify high-latitude off-great circle propagation associated with the solar terminator. Analysis of these simulations show large scale east-west ionospheric gradients due to the solar terminator can cause lateral deviations in north-directed propagation paths exceeding 20° at sunrise and sunset depending on radio wave frequency, though the largest portion of received signal power tends to experience maximum deflections of 5°. An exploration of the dependence of propagation direction on deflection shows that propagation paths parallel to the solar terminator tend to experience the largest deflections. Since the solar terminator at high latitudes is at an angle with respect to north in the winter and summer, propagation paths oriented west or east of north can experience larger deflections than north oriented paths at sunrise and sunset during these times of year. Impacts of these diurnal deflections on the operation of OTHR and scientific radar are discussed, as well as possible strategies for mitigating them.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-17"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141140263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 monostatic high-frequency (HF, 8-20 MHz) radars to study dynamic processes in the ionosphere. SuperDARN provides maps of global-scale ionospheric plasma drift circulation from the mid-latitudes to the poles. The conventional SuperDARN radars consecutively scan through 16 beam directions with a lower limit of 1 minute to sample the entire field of view. In this work, we use the advanced capabilities of the recently developed Borealis digital SuperDARN radar system. Combining a wide transmission beam with multiple narrow reception beams allows us to sample all conventional beam directions simultaneously and to speed up scanning of the entire field-of-view by up to 16 times without noticeable deterioration of the data quality. The wide-beam emission also enabled the implementation of multistatic operations, where ionospheric scatter signals from one radar are received by other radars with overlapping viewing areas. These novel operations required the development of a new model to determine the geographic location of the source of the multistatic radar echoes. Our preliminary studies showed that, in comparison with the conventional monostatic operations, the multistatic operations provide a significant increase in geographic coverage, in some cases nearly doubling it. The multistatic data also provide additional velocity vector components, increasing the likelihood of reconstructing full plasma drift velocity vectors. The developed operational modes can be readily implemented at other fully digital SuperDARN radars.
{"title":"Application of wide-beam transmission for advanced operations of SuperDARN Borealis radars in monostatic and multistatic modes","authors":"R. A. Rohel;P. Ponomarenko;K. A. McWilliams","doi":"10.1029/2023RS007900","DOIUrl":"10.1029/2023RS007900","url":null,"abstract":"The Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 monostatic high-frequency (HF, 8-20 MHz) radars to study dynamic processes in the ionosphere. SuperDARN provides maps of global-scale ionospheric plasma drift circulation from the mid-latitudes to the poles. The conventional SuperDARN radars consecutively scan through 16 beam directions with a lower limit of 1 minute to sample the entire field of view. In this work, we use the advanced capabilities of the recently developed Borealis digital SuperDARN radar system. Combining a wide transmission beam with multiple narrow reception beams allows us to sample all conventional beam directions simultaneously and to speed up scanning of the entire field-of-view by up to 16 times without noticeable deterioration of the data quality. The wide-beam emission also enabled the implementation of multistatic operations, where ionospheric scatter signals from one radar are received by other radars with overlapping viewing areas. These novel operations required the development of a new model to determine the geographic location of the source of the multistatic radar echoes. Our preliminary studies showed that, in comparison with the conventional monostatic operations, the multistatic operations provide a significant increase in geographic coverage, in some cases nearly doubling it. The multistatic data also provide additional velocity vector components, increasing the likelihood of reconstructing full plasma drift velocity vectors. The developed operational modes can be readily implemented at other fully digital SuperDARN radars.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-17"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141047304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Digital RF technology has been developed and has been applied to below 6 GHz wireless applications. By replacing the IC die consumptive RF/analog circuit blocks by digital signal processor and circuit, digital rich/small transceivers can be realized. Since the foundation of this technology is based on the Nyquist theory, the operational frequency of the circuit has been limited by the Nyquist frequency (=1/2 of sampling clock frequency). As a result, the maximum operational RF frequency of existing digital RF technology was below 6 GHz. In this paper, a new direct digital RF technology that utilizes the higher-order Nyquist zones is introduced. This technology enables handling RF signal in beyond Nyquist frequency range which means over 6 GHz range. The results of fabricated 26/28 GHz-band transmitter/receiver are reviewed. Since the transceiver architecture with the proposed technologies does not require an RF local oscillator and up/down converters, it is suitable for microwave/millimeter-wave multi-antenna systems such as next generation satellite on-board digital beam forming and Beyond 5G fully digital Massive multiple-input multiple-output systems.
{"title":"Direct digital RF transceiver technology for millimeter-wave DBF systems","authors":"Noriharu Suematsu","doi":"10.1029/2023RS007802","DOIUrl":"https://doi.org/10.1029/2023RS007802","url":null,"abstract":"Digital RF technology has been developed and has been applied to below 6 GHz wireless applications. By replacing the IC die consumptive RF/analog circuit blocks by digital signal processor and circuit, digital rich/small transceivers can be realized. Since the foundation of this technology is based on the Nyquist theory, the operational frequency of the circuit has been limited by the Nyquist frequency (=1/2 of sampling clock frequency). As a result, the maximum operational RF frequency of existing digital RF technology was below 6 GHz. In this paper, a new direct digital RF technology that utilizes the higher-order Nyquist zones is introduced. This technology enables handling RF signal in beyond Nyquist frequency range which means over 6 GHz range. The results of fabricated 26/28 GHz-band transmitter/receiver are reviewed. Since the transceiver architecture with the proposed technologies does not require an RF local oscillator and up/down converters, it is suitable for microwave/millimeter-wave multi-antenna systems such as next generation satellite on-board digital beam forming and Beyond 5G fully digital Massive multiple-input multiple-output systems.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-10"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141181997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Based on graphical processing unit acceleration, a new method of finite-difference time-domain scheme is proposed to simulate the interaction between electromagnetic waves and magnetized plasma in two-dimensional conditions. In this study, transversely electric and transversely magnetic are computed in time to avoid matrix operations involving Lorentz equations of motion. Compared to Young's method, the new method reduces addition and multiplication by about 63% and 66%, respectively. The simulation results of ionospheric wave propagation show that the new method agrees well with Young's method and the calculation speed is improved significantly.
{"title":"Novel scheme for GPU-accelerated finite-difference time-domain simulation of electromagnetic wave interaction with magnetic plasma","authors":"Shimin He;Moran Liu;Ting Feng;Yiyun Wu;Xiang Wang;Chen Zhou;Ting Lan;Haiyin Qing","doi":"10.1029/2023RS007862","DOIUrl":"10.1029/2023RS007862","url":null,"abstract":"Based on graphical processing unit acceleration, a new method of finite-difference time-domain scheme is proposed to simulate the interaction between electromagnetic waves and magnetized plasma in two-dimensional conditions. In this study, transversely electric and transversely magnetic are computed in time to avoid matrix operations involving Lorentz equations of motion. Compared to Young's method, the new method reduces addition and multiplication by about 63% and 66%, respectively. The simulation results of ionospheric wave propagation show that the new method agrees well with Young's method and the calculation speed is improved significantly.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-16"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141057515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emi Tamura;Jack Fried;Sven Herrmann;Paul O'Connor;Eric J. Raguzin;Anze Slosar
The Lunar Surface Electromagnetics Explorer—Night, LuSEE-Night, is a low-frequency radio astronomy experiment that will explore the cosmic Dark Ages signal on the radio-quiet farside of the Moon. The LuSEE-Night carries a radio frequency spectrometer consisting of a set of antennas, analog and digital processing electronics, and will be launched by NASA's Commercial Lunar Payload Services in 2025. The spectrometer is designed to observe the spectrum of the radio sky in the 0.5–50 MHz band. The engineering model (EM) of the four-channel spectrometer has been developed. The EM has been characterized for linearity, gain, noise, and their temperature dependence, confirming that the EM meets all the requirements for LuSEE-Night. Three mitigation techniques have been implemented and verified to suppress self-induced electromagnetic interference. The flight model of the spectrometer is currently being developed and is scheduled to be shipped to the integration site in early 2024.
{"title":"Design and characterization of the engineering model of the spectrometer onboard LuSEE-Night","authors":"Emi Tamura;Jack Fried;Sven Herrmann;Paul O'Connor;Eric J. Raguzin;Anze Slosar","doi":"10.1029/2023RS007925","DOIUrl":"https://doi.org/10.1029/2023RS007925","url":null,"abstract":"The Lunar Surface Electromagnetics Explorer—Night, LuSEE-Night, is a low-frequency radio astronomy experiment that will explore the cosmic Dark Ages signal on the radio-quiet farside of the Moon. The LuSEE-Night carries a radio frequency spectrometer consisting of a set of antennas, analog and digital processing electronics, and will be launched by NASA's Commercial Lunar Payload Services in 2025. The spectrometer is designed to observe the spectrum of the radio sky in the 0.5–50 MHz band. The engineering model (EM) of the four-channel spectrometer has been developed. The EM has been characterized for linearity, gain, noise, and their temperature dependence, confirming that the EM meets all the requirements for LuSEE-Night. Three mitigation techniques have been implemented and verified to suppress self-induced electromagnetic interference. The flight model of the spectrometer is currently being developed and is scheduled to be shipped to the integration site in early 2024.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-20"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141181998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ali Mohandesi;David J. Knudsen;Susan Skone;Richard B. Langley;Andrew W. Yau
Ionospheric density structures at low latitudes range in size from thousands of kilometers down to a few meters. Radio frequency (RF) signals, such as those from global navigation satellite systems, that propagate through irregularities suffer from rapid fluctuations in phase and intensity, known as scintillations. In this study, we use the high-sample-rate measurements of the Swarm Echo (CASSIOPE/e-POP) satellite's GPS Occultation (GAP-O) receiver taken after its antenna was re-oriented to vertical-pointing, simultaneously with e-POP Ion Mass Spectrometer surface current observations as a proxy for plasma density, to obtain the spectral characteristics of GPS signal intensity and in-situ irregularities at altitudes from 350 to 1,280 km. We show that the power spectra of both measurements can generally be characterized by a power law. In the case of density irregularities, the spectral index with the highest occurrence rate is around 1.7, which is consistent with previous studies. Also, all the power spectra of GPS signal intensity in this study show a single spectral index near 2. Moreover, roll-off frequencies estimated in this work range from 0.4 to 2.5 Hz, which is significantly higher than Fresnel frequencies calculated from ground GPS receivers at low latitudes (between 0.2 and 0.45 Hz). Part of this increase is due to the 8 km/s orbital velocity of Swarm Echo near perigee. Another key difference is that variations in the GPS signals in this study are dominated by the topside ionosphere, whereas GPS signals received from ground are affected mostly by the relatively dense F-region plasma in the 250-350 km altitudinal range.
{"title":"Power spectral characteristics of in-situ irregularities and topside GPS signal intensity at low latitudes using high-sample-rate swarm echo (e-POP) measurements","authors":"Ali Mohandesi;David J. Knudsen;Susan Skone;Richard B. Langley;Andrew W. Yau","doi":"10.1029/2023RS007885","DOIUrl":"10.1029/2023RS007885","url":null,"abstract":"Ionospheric density structures at low latitudes range in size from thousands of kilometers down to a few meters. Radio frequency (RF) signals, such as those from global navigation satellite systems, that propagate through irregularities suffer from rapid fluctuations in phase and intensity, known as scintillations. In this study, we use the high-sample-rate measurements of the Swarm Echo (CASSIOPE/e-POP) satellite's GPS Occultation (GAP-O) receiver taken after its antenna was re-oriented to vertical-pointing, simultaneously with e-POP Ion Mass Spectrometer surface current observations as a proxy for plasma density, to obtain the spectral characteristics of GPS signal intensity and in-situ irregularities at altitudes from 350 to 1,280 km. We show that the power spectra of both measurements can generally be characterized by a power law. In the case of density irregularities, the spectral index with the highest occurrence rate is around 1.7, which is consistent with previous studies. Also, all the power spectra of GPS signal intensity in this study show a single spectral index near 2. Moreover, roll-off frequencies estimated in this work range from 0.4 to 2.5 Hz, which is significantly higher than Fresnel frequencies calculated from ground GPS receivers at low latitudes (between 0.2 and 0.45 Hz). Part of this increase is due to the 8 km/s orbital velocity of Swarm Echo near perigee. Another key difference is that variations in the GPS signals in this study are dominated by the topside ionosphere, whereas GPS signals received from ground are affected mostly by the relatively dense F-region plasma in the 250-350 km altitudinal range.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-11"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141035540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Runbo Xie;Guang Yang;Yuping Zhang;Dongzhe Han;Meng Huang;Shuai Liu;Wangze Lu
Floods are among the most devastating natural disasters worldwide. Such disasters are often accompanied by strong precipitation and other weather factors, making it more difficult to identify affected areas. Moreover, synthetic aperture radar (SAR) technology can capture images in a 24-hr window and penetrate clouds and fog. Change detection (CD) technology based on SAR images is generally utilized to locate disaster-stricken areas by analyzing the differences between pre- and post-disaster images. However, this method faces two main challenges: the presence of speckle noise, which reduces the difference detection accuracy, and the lack of a suitable SAR data set for flood disaster CD. Therefore, this study proposes a novel two-stage approach for locating flood disaster areas, known as the denoising-change detection approach (D-CDA). The first stage comprises a nine-layer denoising network with an encoder-decoder structure known as the SAR denoising network (SDNet). It utilizes a multiresidual block and a parallel convolutional block attention module to extract features during the encoding process to suppress the noise component. In the second stage, a novel convolution neural network is proposed to detect the changes between bitemporal SAR images, namely, the coordinate attention fused network, which combines the siamese network and UNet++ as the backbone, and fuses coordinate attention modules to enhance the change features. Moreover, a CD data set (Zhengzhou flood data set) was constructed using Sentinel-1 SAR images based on the 2021 flood disaster in Zhengzhou, China. Simulations verify the effectiveness of the proposed method. The experimental results indicate that D-CDA achieves favorable detection performance in locating flood disaster areas.
洪水是全世界最具破坏性的自然灾害之一。这种灾害往往伴随着强降水和其他天气因素，使得确定受灾地区变得更加困难。此外，合成孔径雷达（SAR）技术可在 24 小时内捕捉图像，并能穿透云雾。基于合成孔径雷达图像的变化检测（CD）技术通常通过分析灾前和灾后图像之间的差异来定位受灾地区。然而，这种方法面临两个主要挑战：斑点噪声的存在降低了差异检测的准确性，以及缺乏适用于洪水灾害变化检测的合成孔径雷达数据集。因此，本研究提出了一种新颖的两阶段洪水灾害区域定位方法，即去噪变化检测方法（D-CDA）。第一阶段包括一个具有编码器-解码器结构的九层去噪网络，称为合成孔径雷达去噪网络（SDNet）。它利用多残差块和并行卷积块注意模块，在编码过程中提取特征，以抑制噪声成分。在第二阶段，提出了一种新型卷积神经网络来检测位时 SAR 图像之间的变化，即坐标注意融合网络，它以连体网络和 UNet++ 为骨干，融合坐标注意模块来增强变化特征。此外，基于 2021 年中国郑州洪水灾害，利用 Sentinel-1 SAR 图像构建了 CD 数据集（郑州洪水数据集）。仿真验证了所提方法的有效性。实验结果表明，D-CDA 在洪水灾害区域定位方面具有良好的检测性能。
{"title":"D-CDA: A denoise and change detection approach for flood disaster location from SAR images","authors":"Runbo Xie;Guang Yang;Yuping Zhang;Dongzhe Han;Meng Huang;Shuai Liu;Wangze Lu","doi":"10.1029/2023RS007846","DOIUrl":"https://doi.org/10.1029/2023RS007846","url":null,"abstract":"Floods are among the most devastating natural disasters worldwide. Such disasters are often accompanied by strong precipitation and other weather factors, making it more difficult to identify affected areas. Moreover, synthetic aperture radar (SAR) technology can capture images in a 24-hr window and penetrate clouds and fog. Change detection (CD) technology based on SAR images is generally utilized to locate disaster-stricken areas by analyzing the differences between pre- and post-disaster images. However, this method faces two main challenges: the presence of speckle noise, which reduces the difference detection accuracy, and the lack of a suitable SAR data set for flood disaster CD. Therefore, this study proposes a novel two-stage approach for locating flood disaster areas, known as the denoising-change detection approach (D-CDA). The first stage comprises a nine-layer denoising network with an encoder-decoder structure known as the SAR denoising network (SDNet). It utilizes a multiresidual block and a parallel convolutional block attention module to extract features during the encoding process to suppress the noise component. In the second stage, a novel convolution neural network is proposed to detect the changes between bitemporal SAR images, namely, the coordinate attention fused network, which combines the siamese network and UNet++ as the backbone, and fuses coordinate attention modules to enhance the change features. Moreover, a CD data set (Zhengzhou flood data set) was constructed using Sentinel-1 SAR images based on the 2021 flood disaster in Zhengzhou, China. Simulations verify the effectiveness of the proposed method. The experimental results indicate that D-CDA achieves favorable detection performance in locating flood disaster areas.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 5","pages":"1-18"},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141181888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ben Boyde, Alan Wood, G. Dorrian, Frits Sweijen, Francesco de Gasperin, Maaijke Mevius, Kasia Beser, David Themens
Radio interferometers used to make astronomical observations, such as the LOw Frequency ARray (LOFAR), experience distortions imposed upon the received signal due to the ionosphere as well as those from instrumental errors. Calibration using a well‐characterized radio source can be used to mitigate these effects and produce more accurate images of astronomical sources, and the calibration process provides measurements of ionospheric conditions over a wide range of length scales. The basic ionospheric measurement this provides is differential Total Electron Content (TEC, the integral of electron density along the line of sight). Differential TEC measurements made using LOFAR have a precision of <1 mTECu and therefore enable investigation of ionospheric disturbances which may be undetectable to many other methods. We demonstrate an approach to identify ionospheric waves from these data using a wavelet transform and a simple plane wave model. The noise spectra are robustly characterized to provide uncertainty estimates for the fitted parameters. An example is shown in which this method identifies a wave with an amplitude an order of magnitude below those reported using Global Navigation Systems Satellite TEC measurements. Artificially generated data are used to test the accuracy of the method and establish the range of wavelengths which can be detected using this method with LOFAR data. This technique will enable the use of a large and mostly unexplored data set to study traveling ionospheric disturbances over Europe.
{"title":"Wavelet Analysis of Differential TEC Measurements Obtained Using LOFAR","authors":"Ben Boyde, Alan Wood, G. Dorrian, Frits Sweijen, Francesco de Gasperin, Maaijke Mevius, Kasia Beser, David Themens","doi":"10.1029/2023rs007871","DOIUrl":"https://doi.org/10.1029/2023rs007871","url":null,"abstract":"Radio interferometers used to make astronomical observations, such as the LOw Frequency ARray (LOFAR), experience distortions imposed upon the received signal due to the ionosphere as well as those from instrumental errors. Calibration using a well‐characterized radio source can be used to mitigate these effects and produce more accurate images of astronomical sources, and the calibration process provides measurements of ionospheric conditions over a wide range of length scales. The basic ionospheric measurement this provides is differential Total Electron Content (TEC, the integral of electron density along the line of sight). Differential TEC measurements made using LOFAR have a precision of <1 mTECu and therefore enable investigation of ionospheric disturbances which may be undetectable to many other methods. We demonstrate an approach to identify ionospheric waves from these data using a wavelet transform and a simple plane wave model. The noise spectra are robustly characterized to provide uncertainty estimates for the fitted parameters. An example is shown in which this method identifies a wave with an amplitude an order of magnitude below those reported using Global Navigation Systems Satellite TEC measurements. Artificially generated data are used to test the accuracy of the method and establish the range of wavelengths which can be detected using this method with LOFAR data. This technique will enable the use of a large and mostly unexplored data set to study traveling ionospheric disturbances over Europe.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"28 24","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140364463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Jaron, I. Martí-Vidal, M. Schartner, J. González-García, E. Albentosa-Ruiz, S. Bernhart, J. Böhm, J. Gruber, S. Modiri, A. Nothnagel, V. Pérez-Díez, T. Savolainen, B. Soja, E. Varenius, M. H. Xu
Radio telescopes with dual linearly polarized feeds regularly participate in Very Long Baseline Interferometry. One example is the VLBI Global Observing System (VGOS), which is employed for high-precision geodesy and astrometry. In order to achieve the maximum signal-to-noise ratio, the visibilities of all four polarization products are combined to Stokes I before fringe-fitting. Our aim is to improve cross-polarization bandpass calibration, which is an essential processing step in this context. Here we investigate the shapes of these station-specific quantities as a function of frequency and time. We observed the extra-galactic source 4C 39.25 for 6 hours with a VGOS network. We correlated the data with the DiFX software and analyzed the visibilities with PolConvert to determine the complex cross-bandpasses with high accuracy. Their frequency-dependent shape is to first order characterized by a group delay between the two orthogonal polarizations, in the order of several hundred picoseconds. We find that this group delay shows systematic variability in the range of a few picoseconds, but can remain stable within this range for several years, as evident from earlier sessions. On top of the linear phase-frequency relationship there are systematic deviations of several tens of degrees, which in addition are subject to smooth temporal evolution. The antenna cross-bandpasses are variable on time scales of ∼1 hr, which defines the frequency of necessary calibrator scans. The source 4C 39.25 is confirmed as an excellent cross-bandpass calibrator. Dedicated surveys are highly encouraged to search for more calibrators of similar quality.
{"title":"Cross-Polarization Gain Calibration of Linearly Polarized VLBI Antennas by Observations of 4C 39.25","authors":"F. Jaron, I. Martí-Vidal, M. Schartner, J. González-García, E. Albentosa-Ruiz, S. Bernhart, J. Böhm, J. Gruber, S. Modiri, A. Nothnagel, V. Pérez-Díez, T. Savolainen, B. Soja, E. Varenius, M. H. Xu","doi":"10.1029/2023rs007892","DOIUrl":"https://doi.org/10.1029/2023rs007892","url":null,"abstract":"Radio telescopes with dual linearly polarized feeds regularly participate in Very Long Baseline Interferometry. One example is the VLBI Global Observing System (VGOS), which is employed for high-precision geodesy and astrometry. In order to achieve the maximum signal-to-noise ratio, the visibilities of all four polarization products are combined to Stokes <i>I</i> before fringe-fitting. Our aim is to improve cross-polarization bandpass calibration, which is an essential processing step in this context. Here we investigate the shapes of these station-specific quantities as a function of frequency and time. We observed the extra-galactic source 4C 39.25 for 6 hours with a VGOS network. We correlated the data with the DiFX software and analyzed the visibilities with PolConvert to determine the complex cross-bandpasses with high accuracy. Their frequency-dependent shape is to first order characterized by a group delay between the two orthogonal polarizations, in the order of several hundred picoseconds. We find that this group delay shows systematic variability in the range of a few picoseconds, but can remain stable within this range for several years, as evident from earlier sessions. On top of the linear phase-frequency relationship there are systematic deviations of several tens of degrees, which in addition are subject to smooth temporal evolution. The antenna cross-bandpasses are variable on time scales of ∼1 hr, which defines the frequency of necessary calibrator scans. The source 4C 39.25 is confirmed as an excellent cross-bandpass calibrator. Dedicated surveys are highly encouraged to search for more calibrators of similar quality.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"34 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140325684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The complex refractive index and reflectance of an epidermis-equivalent phantom were evaluated in the terahertz-frequency region. The complex refractive indices of the epidermis and the epidermis-equivalent phantom, made using ultrapure water, mineral oil, glycerin fatty acid ester, and agar, were measured using a terahertz time-domain spectrometer. The complex refractive indices of the epidermis and the epidermis-equivalent phantom were in agreement. However, their mean reflectances had a difference of approximately 3%. The difference disappeared on adding surface roughness to the epidermis-equivalent phantom. Thus, we found that roughness of the surface of the epidermis-equivalent phantom was required to ensure a match of the reflectance of the phantom with that of the epidermis at frequencies from 0.2 THz to 0.6 THz.
{"title":"Spectroscopic evaluation of epidermis-equivalent phantom in terahertz-frequency region","authors":"Maya Mizuno;Shota Yamazaki;Tomoaki Nagaoka","doi":"10.1029/2023RS007809","DOIUrl":"10.1029/2023RS007809","url":null,"abstract":"The complex refractive index and reflectance of an epidermis-equivalent phantom were evaluated in the terahertz-frequency region. The complex refractive indices of the epidermis and the epidermis-equivalent phantom, made using ultrapure water, mineral oil, glycerin fatty acid ester, and agar, were measured using a terahertz time-domain spectrometer. The complex refractive indices of the epidermis and the epidermis-equivalent phantom were in agreement. However, their mean reflectances had a difference of approximately 3%. The difference disappeared on adding surface roughness to the epidermis-equivalent phantom. Thus, we found that roughness of the surface of the epidermis-equivalent phantom was required to ensure a match of the reflectance of the phantom with that of the epidermis at frequencies from 0.2 THz to 0.6 THz.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 3","pages":"1-6"},"PeriodicalIF":1.6,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140400482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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