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}
H. Ohya;T. Suzuki;F. Tsuchiya;H. Nakata;K. Shiokawa
Several studies have examined ionospheric variation associated with meteorites, meteoroids, or meteors based on Global Satellite Navigation System total electron content observations. However, there have been few quantitative studies of the D-region of the ionosphere (60–90 km), which is associated with meteoroids. We investigated variation in the D-region during the passage of a meteoroid over northeastern Hokkaido, Japan, at 11:55:55 UT on 18 October 2018, using very low-frequency (VLF, 3–30 kHz) and low-frequency (LF, 30–300 kHz) signals observed by three transmitters [JJY (40 kHz), JJY (60 kHz), and JJI (22.2 kHz)], at Rikubetsu, Japan. Periodic variation of 100–200 s was observed in the VLF and LF amplitudes upon arrival of the acoustic wave. The vertical seismic velocity of Hi-net and F-net data also showed acoustic waves. Although the main period of the acoustic wave was 0.1–0.5 s in the seismic data, a longer period component (100–200 s) remained during propagation up to the D-region ionosphere. The estimated velocity of the acoustic waves was ∼340 m/s on the ground according to the Hi-net seismic data. The acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectory. Based on the observed propagation time of the acoustic waves and ray tracing results, the acoustic waves propagated obliquely from near the endpoint of the meteoroid trajectory up to a D-region height (about ∼90 km altitude), south of the Rikubetsu receiver.
一些研究根据全球卫星导航系统的电子总含量观测结果，对与陨石、流星体或 流星体有关的电离层变化进行了研究。然而，对与流星体有关的电离层 D 区（60-90 公里）的定量研究却很少。我们利用日本陆别市的三个发射器[JJY（40 kHz）、JJY（60 kHz）和 JJI（22.2 kHz）]观测到的甚低频（VLF，3-30 kHz）和低频（LF，30-300 kHz）信号，研究了 2018 年 10 月 18 日 11:55:55 UT 时一颗流星体经过日本北海道东北部上空时 D 区的变化。在声波到达时，VLF 和 LF 振幅出现了 100-200 秒的周期性变化。Hi-net 和 F-net 数据的垂直地震速度也出现了声波。虽然在地震数据中声波的主要周期为 0.1-0.5 秒，但在向 D 区电离层传播的过程中仍存在一个较长的周期分量（100-200 秒）。根据 Hi-net 地震数据，声波在地面上的速度估计为每秒 340 米。声波起源于流星体轨迹终点（25 公里高度）附近。根据观测到的声波传播时间和射线追踪结果，声波从流星体轨迹的端点附近斜向传播到 D 区高度（约 ∼ 90 千米高度），位于 Rikubetsu 接收器的南面。
{"title":"Variation in the reflection height of VLF/LF transmitter signals in the D-region ionosphere and the possible source: A 2018 meteoroid in Hokkaido, Japan","authors":"H. Ohya;T. Suzuki;F. Tsuchiya;H. Nakata;K. Shiokawa","doi":"10.1029/2023RS007801","DOIUrl":"10.1029/2023RS007801","url":null,"abstract":"Several studies have examined ionospheric variation associated with meteorites, meteoroids, or meteors based on Global Satellite Navigation System total electron content observations. However, there have been few quantitative studies of the D-region of the ionosphere (60–90 km), which is associated with meteoroids. We investigated variation in the D-region during the passage of a meteoroid over northeastern Hokkaido, Japan, at 11:55:55 UT on 18 October 2018, using very low-frequency (VLF, 3–30 kHz) and low-frequency (LF, 30–300 kHz) signals observed by three transmitters [JJY (40 kHz), JJY (60 kHz), and JJI (22.2 kHz)], at Rikubetsu, Japan. Periodic variation of 100–200 s was observed in the VLF and LF amplitudes upon arrival of the acoustic wave. The vertical seismic velocity of Hi-net and F-net data also showed acoustic waves. Although the main period of the acoustic wave was 0.1–0.5 s in the seismic data, a longer period component (100–200 s) remained during propagation up to the D-region ionosphere. The estimated velocity of the acoustic waves was ∼340 m/s on the ground according to the Hi-net seismic data. The acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectory. Based on the observed propagation time of the acoustic waves and ray tracing results, the acoustic waves propagated obliquely from near the endpoint of the meteoroid trajectory up to a D-region height (about ∼90 km altitude), south of the Rikubetsu receiver.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 3","pages":"1-10"},"PeriodicalIF":1.6,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139968763","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}
D. Anish Roshi;Phil Perillat;Felix Fernandez;Hamdi Mani;Benetge Perera;Periasamy K. Manoharan;Luis Quintero;Arun Venkataraman
In this paper we present details of the construction of a wideband, cryogenic receiver and its successful commissioning on the Arecibo Observatory 12m telescope. The cryogenic receiver works in the 2.5–14 GHz frequency range. We upgraded the current narrow band, room temperature receivers of the telescope with the new wideband receiver. The current receiver is built around a Quadruple-Ridged Flared Horn (QRFH) developed by Akgiray et al. (2013, https://doi.org/10.1109/tap.2012.2229953). To mitigate strong radio frequency interference (RFI) below 2.7 GHz, we installed a highpass filter before the first stage low noise amplifier (LNA). The QRFH, highpass filter, noise coupler and LNA are located inside a cryostat and are cooled to 15 K. The measured receiver temperature is 25 K (median value) over 2.5–14 GHz. The system temperature measured at zenith is about 40 K near 3.1 and 8.6 GHz and the zenith antenna gains are 0.025 and 0.018 K/Jy at the two frequencies respectively. We recommend the following improvements to the telescope system: (a) Upgrade the highpass filter to achieve better RFI rejection near 2.5 GHz; (b) Improve aperture efficiency at 8.6 GHz; (c) Upgrade the intermediate frequency system to increase the upper frequency of operation from 12 to 14 GHz.
{"title":"A cryogenic wideband (2.5–14 GHz) receiver system for the Arecibo Observatory 12 m telescope","authors":"D. Anish Roshi;Phil Perillat;Felix Fernandez;Hamdi Mani;Benetge Perera;Periasamy K. Manoharan;Luis Quintero;Arun Venkataraman","doi":"10.1029/2023RS007839","DOIUrl":"10.1029/2023RS007839","url":null,"abstract":"In this paper we present details of the construction of a wideband, cryogenic receiver and its successful commissioning on the Arecibo Observatory 12m telescope. The cryogenic receiver works in the 2.5–14 GHz frequency range. We upgraded the current narrow band, room temperature receivers of the telescope with the new wideband receiver. The current receiver is built around a Quadruple-Ridged Flared Horn (QRFH) developed by Akgiray et al. (2013, https://doi.org/10.1109/tap.2012.2229953). To mitigate strong radio frequency interference (RFI) below 2.7 GHz, we installed a highpass filter before the first stage low noise amplifier (LNA). The QRFH, highpass filter, noise coupler and LNA are located inside a cryostat and are cooled to 15 K. The measured receiver temperature is 25 K (median value) over 2.5–14 GHz. The system temperature measured at zenith is about 40 K near 3.1 and 8.6 GHz and the zenith antenna gains are 0.025 and 0.018 K/Jy at the two frequencies respectively. We recommend the following improvements to the telescope system: (a) Upgrade the highpass filter to achieve better RFI rejection near 2.5 GHz; (b) Improve aperture efficiency at 8.6 GHz; (c) Upgrade the intermediate frequency system to increase the upper frequency of operation from 12 to 14 GHz.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 3","pages":"1-11"},"PeriodicalIF":1.6,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140277606","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}
Electromagnetic exposure caused by mobile communication signals has always been a cause of concern. Due to the cost and inconvenience of professional measurement equipment, researchers have turned to smartphone APPs to study and assess the electric field strength caused by mobile communication signals. However, existing cell phone-based measurements have two weaknesses. First, no system architecture suitable for large-scale crowdsourced testing has been proposed. Second, since smartphone sensors cannot measure electric field strength directly, existing methods for converting the received signal power of the phone and electric field strength have errors of more than 5 dB. This paper proposes a measurement and calibration method for electric field strength of mobile communication signals based on a smartphone app and gradient boosting decision tree (GBDT). This method consists of a downlink signal acquisition system based on an APP and a calibration model based on GBDT to convert received signal power into electric field strength. The experimental results show that the proposed model achieves a R 2 score of 0.93 and a MAE of 0.97 dB. Compared with the existing methods, our method improves the calibration accuracy by 4 dB, enabling large-scale, low-cost, and high-precision direct measurement of the electric field strength of mobile communication signals.
{"title":"Measurement and calibration of EMF: A study using phone and GBDT for mobile communication signals","authors":"Sheng Zeng;Weiwei Chen;Yuhang Ji;Liping Yan;Xiang Zhao","doi":"10.1029/2023RS007890","DOIUrl":"10.1029/2023RS007890","url":null,"abstract":"Electromagnetic exposure caused by mobile communication signals has always been a cause of concern. Due to the cost and inconvenience of professional measurement equipment, researchers have turned to smartphone APPs to study and assess the electric field strength caused by mobile communication signals. However, existing cell phone-based measurements have two weaknesses. First, no system architecture suitable for large-scale crowdsourced testing has been proposed. Second, since smartphone sensors cannot measure electric field strength directly, existing methods for converting the received signal power of the phone and electric field strength have errors of more than 5 dB. This paper proposes a measurement and calibration method for electric field strength of mobile communication signals based on a smartphone app and gradient boosting decision tree (GBDT). This method consists of a downlink signal acquisition system based on an APP and a calibration model based on GBDT to convert received signal power into electric field strength. The experimental results show that the proposed model achieves a R\u0000<sup>2</sup>\u0000 score of 0.93 and a MAE of 0.97 dB. Compared with the existing methods, our method improves the calibration accuracy by 4 dB, enabling large-scale, low-cost, and high-precision direct measurement of the electric field strength of mobile communication signals.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 2","pages":"1-13"},"PeriodicalIF":1.6,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139918642","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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