Nazir Jan, N. Minallah, Neelam Gohar, Naveed Jan, Shahid Khan, Salahuddin Khan, Mohammad Alibakhshikenari
Nonmetallic minerals like granite and limestone have calcite and biotitic ingredients as their major part which exhibit wonderful absorption features in the visible and short wave range of the electromagnetic spectrum. This research puts emphasis on delineating granite and limestone deposits of the Mardan district through the latest multispectral Landsat‐9 and Sentinel‐2 sensors of which the latter provided 94% mapping accuracy in delineating granites (biotitic bearing minerals) and limestone (calcite‐bearing minerals). The Image processing techniques of minimum noise fraction, which is double cascaded principal components analysis and pixel purity index algorithms proved helpful to bring significant improvements in classification results and in the reduction of noise and data size. The outcomes of the research study show that supervised machine learning algorithms are impactful to map such minerals provided that the data must be well organized and limited in size. The results achieved were verified through validation steps like, (a) Independent reference data of high‐resolution Google Earth maps and (b) Ground survey reports. Arc GIS 10.2 and Envi 5.3 software suite were used to create (a) ground truth points at random for accuracy assessment (b) portraying study area maps (c) Image Processing and Preprocessing tools and (d) implementation of machine learning algorithms. Access to the data and software suite is being provided for open research work.
{"title":"Granite Exposure Mapping Through Sentinel‐2 Visible and Short Wave Infrared Bands","authors":"Nazir Jan, N. Minallah, Neelam Gohar, Naveed Jan, Shahid Khan, Salahuddin Khan, Mohammad Alibakhshikenari","doi":"10.1029/2023rs007864","DOIUrl":"https://doi.org/10.1029/2023rs007864","url":null,"abstract":"Nonmetallic minerals like granite and limestone have calcite and biotitic ingredients as their major part which exhibit wonderful absorption features in the visible and short wave range of the electromagnetic spectrum. This research puts emphasis on delineating granite and limestone deposits of the Mardan district through the latest multispectral Landsat‐9 and Sentinel‐2 sensors of which the latter provided 94% mapping accuracy in delineating granites (biotitic bearing minerals) and limestone (calcite‐bearing minerals). The Image processing techniques of minimum noise fraction, which is double cascaded principal components analysis and pixel purity index algorithms proved helpful to bring significant improvements in classification results and in the reduction of noise and data size. The outcomes of the research study show that supervised machine learning algorithms are impactful to map such minerals provided that the data must be well organized and limited in size. The results achieved were verified through validation steps like, (a) Independent reference data of high‐resolution Google Earth maps and (b) Ground survey reports. Arc GIS 10.2 and Envi 5.3 software suite were used to create (a) ground truth points at random for accuracy assessment (b) portraying study area maps (c) Image Processing and Preprocessing tools and (d) implementation of machine learning algorithms. Access to the data and software suite is being provided for open research work.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"40 13","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139814145","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}
Ka‐band Micro rain Doppler radar is an effective tool to investigate the profiles of precipitation microstructure in terms of the raindrop size distribution (DSD). The DSD parameters that vary appreciably with height are indicative of the associated atmospheric phenomena. Hence the present investigation endeavors to put light on the underlying physical processes responsible for the evolution of varied rain microstructure profiles using micro rain radar (MRR), and radiometric measurements complemented with re‐analysis outputs over an urban tropical location, Kolkata (22.57°N, 88.37°E), India. MRR unravels the prevalence of significant biases in the typical power law relationship (Dm = aRb) between rain rate (R) and mass‐weighted mean drop diameter (Dm) along the rain height, especially during intense convective rain events, above the atmospheric boundary layer (ABL). Consequently, an alternative empirical relation appropriate to account for the R‐Dm variability above the ABL is proposed. Further, radiometric measurements and re‐analysis outputs reveal that the presence of atmospheric instabilities coupled with wind shear impacts above the ABL contributes to the enhanced breakup of raindrops and the deviations in the usual R‐Dm relationship. Thus, the present study intends to highlight the applicability of ground‐based radar measurements over the tropics to devise quantitative precipitation algorithms for reliable rain estimates.
{"title":"Micro Rain Radar and Radiometric Measurements to Unravel Contrasting Features of Rain Microstructure Below and Above the Boundary Layer","authors":"G. Rakshit, R. Chakraborty, A. Maitra","doi":"10.1029/2023rs007875","DOIUrl":"https://doi.org/10.1029/2023rs007875","url":null,"abstract":"Ka‐band Micro rain Doppler radar is an effective tool to investigate the profiles of precipitation microstructure in terms of the raindrop size distribution (DSD). The DSD parameters that vary appreciably with height are indicative of the associated atmospheric phenomena. Hence the present investigation endeavors to put light on the underlying physical processes responsible for the evolution of varied rain microstructure profiles using micro rain radar (MRR), and radiometric measurements complemented with re‐analysis outputs over an urban tropical location, Kolkata (22.57°N, 88.37°E), India. MRR unravels the prevalence of significant biases in the typical power law relationship (Dm = aRb) between rain rate (R) and mass‐weighted mean drop diameter (Dm) along the rain height, especially during intense convective rain events, above the atmospheric boundary layer (ABL). Consequently, an alternative empirical relation appropriate to account for the R‐Dm variability above the ABL is proposed. Further, radiometric measurements and re‐analysis outputs reveal that the presence of atmospheric instabilities coupled with wind shear impacts above the ABL contributes to the enhanced breakup of raindrops and the deviations in the usual R‐Dm relationship. Thus, the present study intends to highlight the applicability of ground‐based radar measurements over the tropics to devise quantitative precipitation algorithms for reliable rain estimates.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"12 4-5","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139871966","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}
Yi-Jiun Su;John A. Carilli;J. Brent Parham;Xiangning Chu;Ivan A. Galkin;Gregory P. Ginet
Electron density plays an important role in the study of wave propagation and is known to be associated with the index of refraction and radiation belt diffusion coefficients. The primary objective of our investigation is to explore the possibility of implementing an onboard signal processing algorithm to automatically obtain electron densities from the upper hybrid resonance traces of wave spectrograms for future missions. U-Net, developed for biomedical image segmentation, has been adapted as our deep learning architecture with results being compared with those extracted from a more traditional semi-automated method. As a product, electron densities and cyclotron frequencies for the entire DSX mission between 2019 and 2021 are acquired for further analysis and applications. Due to limited space measurements, a synthetic image generator based on data statistics and randomization is proposed as an initial step toward the development of a generative adversarial network in hopes of providing unlimited realistic data sources for advanced machine learning.
{"title":"Electron density specification in the inner magnetosphere from the narrow band receiver onboard DSX","authors":"Yi-Jiun Su;John A. Carilli;J. Brent Parham;Xiangning Chu;Ivan A. Galkin;Gregory P. Ginet","doi":"10.1029/2023RS007907","DOIUrl":"10.1029/2023RS007907","url":null,"abstract":"Electron density plays an important role in the study of wave propagation and is known to be associated with the index of refraction and radiation belt diffusion coefficients. The primary objective of our investigation is to explore the possibility of implementing an onboard signal processing algorithm to automatically obtain electron densities from the upper hybrid resonance traces of wave spectrograms for future missions. U-Net, developed for biomedical image segmentation, has been adapted as our deep learning architecture with results being compared with those extracted from a more traditional semi-automated method. As a product, electron densities and cyclotron frequencies for the entire DSX mission between 2019 and 2021 are acquired for further analysis and applications. Due to limited space measurements, a synthetic image generator based on data statistics and randomization is proposed as an initial step toward the development of a generative adversarial network in hopes of providing unlimited realistic data sources for advanced machine learning.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 2","pages":"1-20"},"PeriodicalIF":1.6,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139753207","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. Schneider;V. Wendt;D. Banys;M. Clilverd;T. Raita
The amplitude of Very Low Frequency (VLF) transmissions propagating from transmitter to receiver between the Earth's surface and the ionospheric D-region is a useful measurement to detect changes in the ionization within the D-region ranging from 60 to 90 km. The VLF signal amplitude is disturbed by geomagnetic, solar, and atmospheric phenomena. To be able to identify perturbations in the VLF signal amplitude, we determine its averaged seasonal variation under quiet solar and geomagnetic conditions. Here it is challenging, that long time series of the VLF signal amplitude show significant jumps and outliers, which are caused artificially by technical adjustments/maintenance work. This paper presents a new approach for processing long VLF data time series over multiple years resulting in level 2 data. The new level 2 data enables the consideration of time series with artificial jumps since the jumps are leveled. Moreover, the outliers are removed by a robust and systematic 2-step outlier filtering. The average seasonal and diurnal variation for different transmitter-receiver combinations can be computed with the new level 2 data by applying a composite analysis. A subsequently applied polynomial fit obtains the quiet time lines for daytime and nighttime, representing the typical seasonal variation under undisturbed conditions of the VLF signal amplitude for each considered link. The developed quiet time lines may serve as a tool to determine perturbations of the VLF signal amplitude with solar and geomagnetic as well as atmospheric origin. Also, they allow comparison of the VLF signal amplitude variation for different transmitter-receiver links.
在地球表面和电离层 D 区之间从发射器传播到接收器的甚低频（VLF）传输振幅是探测 60 至 90 千米范围内 D 区电离变化的有用测量值。甚低频信号振幅受到地磁、太阳和大气现象的干扰。为了能够识别甚低频信号振幅的扰动，我们测定了其在安静的太阳和地磁条件下的平均季节变化。在这方面具有挑战性的是，甚低频信号振幅的长时间序列会出现明显的跳跃和异常值，这是技术调整/维护工作人为造成的。本文介绍了一种处理多年来长 VLF 数据时间序列的新方法，从而生成 2 级数据。新的第 2 级数据可以考虑具有人为跳变的时间序列，因为跳变是平移的。此外，离群值是通过稳健、系统的两步离群值过滤去除的。利用新的第 2 级数据，可以通过综合分析计算出不同发射机-接收机组合的平均季节和昼夜变化。随后应用多项式拟合得到昼间和夜间的静默时间线，代表了每个考虑链路的甚低频信号振幅在不受干扰条件下的典型季节变化。所绘制的静默时间线可作为一种工具，用于确定甚低频信号振幅的太阳、地磁和大气扰动。此外，还可以对不同发射机-接收机链路的甚低频信号振幅变化进行比较。
{"title":"Processing of VLF amplitude measurements: Deduction of a quiet time seasonal variation","authors":"H. Schneider;V. Wendt;D. Banys;M. Clilverd;T. Raita","doi":"10.1029/2023RS007834","DOIUrl":"10.1029/2023RS007834","url":null,"abstract":"The amplitude of Very Low Frequency (VLF) transmissions propagating from transmitter to receiver between the Earth's surface and the ionospheric D-region is a useful measurement to detect changes in the ionization within the D-region ranging from 60 to 90 km. The VLF signal amplitude is disturbed by geomagnetic, solar, and atmospheric phenomena. To be able to identify perturbations in the VLF signal amplitude, we determine its averaged seasonal variation under quiet solar and geomagnetic conditions. Here it is challenging, that long time series of the VLF signal amplitude show significant jumps and outliers, which are caused artificially by technical adjustments/maintenance work. This paper presents a new approach for processing long VLF data time series over multiple years resulting in level 2 data. The new level 2 data enables the consideration of time series with artificial jumps since the jumps are leveled. Moreover, the outliers are removed by a robust and systematic 2-step outlier filtering. The average seasonal and diurnal variation for different transmitter-receiver combinations can be computed with the new level 2 data by applying a composite analysis. A subsequently applied polynomial fit obtains the quiet time lines for daytime and nighttime, representing the typical seasonal variation under undisturbed conditions of the VLF signal amplitude for each considered link. The developed quiet time lines may serve as a tool to determine perturbations of the VLF signal amplitude with solar and geomagnetic as well as atmospheric origin. Also, they allow comparison of the VLF signal amplitude variation for different transmitter-receiver links.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 2","pages":"1-12"},"PeriodicalIF":1.6,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139753205","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}
Nazir Jan;Nasru Minallah;Neelam Gohar;Naveed Jan;Shahid Khan;Salahuddin Khan;Mohammad Alibakhshikenari
Nonmetallic minerals like granite and limestone have calcite and biotitic ingredients as their major part which exhibit wonderful absorption features in the visible and short wave range of the electromagnetic spectrum. This research puts emphasis on delineating granite and limestone deposits of the Mardan district through the latest multispectral Landsat-9 and Sentinel-2 sensors of which the latter provided 94% mapping accuracy in delineating granites (biotitic bearing minerals) and limestone (calcite-bearing minerals). The Image processing techniques of minimum noise fraction, which is double cascaded principal components analysis and pixel purity index algorithms proved helpful to bring significant improvements in classification results and in the reduction of noise and data size. The outcomes of the research study show that supervised machine learning algorithms are impactful to map such minerals provided that the data must be well organized and limited in size. The results achieved were verified through validation steps like, (a) Independent reference data of high-resolution Google Earth maps and (b) Ground survey reports. Arc GIS 10.2 and Envi 5.3 software suite were used to create (a) ground truth points at random for accuracy assessment (b) portraying study area maps (c) Image Processing and Preprocessing tools and (d) implementation of machine learning algorithms. Access to the data and software suite is being provided for open research work.
{"title":"Granite exposure mapping through Sentinel-2 visible and short wave infrared bands","authors":"Nazir Jan;Nasru Minallah;Neelam Gohar;Naveed Jan;Shahid Khan;Salahuddin Khan;Mohammad Alibakhshikenari","doi":"10.1029/2023RS007864","DOIUrl":"10.1029/2023RS007864","url":null,"abstract":"Nonmetallic minerals like granite and limestone have calcite and biotitic ingredients as their major part which exhibit wonderful absorption features in the visible and short wave range of the electromagnetic spectrum. This research puts emphasis on delineating granite and limestone deposits of the Mardan district through the latest multispectral Landsat-9 and Sentinel-2 sensors of which the latter provided 94% mapping accuracy in delineating granites (biotitic bearing minerals) and limestone (calcite-bearing minerals). The Image processing techniques of minimum noise fraction, which is double cascaded principal components analysis and pixel purity index algorithms proved helpful to bring significant improvements in classification results and in the reduction of noise and data size. The outcomes of the research study show that supervised machine learning algorithms are impactful to map such minerals provided that the data must be well organized and limited in size. The results achieved were verified through validation steps like, (a) Independent reference data of high-resolution Google Earth maps and (b) Ground survey reports. Arc GIS 10.2 and Envi 5.3 software suite were used to create (a) ground truth points at random for accuracy assessment (b) portraying study area maps (c) Image Processing and Preprocessing tools and (d) implementation of machine learning algorithms. Access to the data and software suite is being provided for open research work.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 2","pages":"1-12"},"PeriodicalIF":1.6,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139873974","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}
Ka-band Micro rain Doppler radar is an effective tool to investigate the profiles of precipitation microstructure in terms of the raindrop size distribution (DSD). The DSD parameters that vary appreciably with height are indicative of the associated atmospheric phenomena. Hence the present investigation endeavors to put light on the underlying physical processes responsible for the evolution of varied rain microstructure profiles using micro rain radar (MRR), and radiometric measurements complemented with re-analysis outputs over an urban tropical location, Kolkata (22.57°N, 88.37°E), India. MRR unravels the prevalence of significant biases in the typical power law relationship (D m = aR b ) between rain rate (R) and mass-weighted mean drop diameter (D m ) along the rain height, especially during intense convective rain events, above the atmospheric boundary layer (ABL). Consequently, an alternative empirical relation appropriate to account for the R-D m variability above the ABL is proposed. Further, radiometric measurements and re-analysis outputs reveal that the presence of atmospheric instabilities coupled with wind shear impacts above the ABL contributes to the enhanced breakup of raindrops and the deviations in the usual R-D m relationship. Thus, the present study intends to highlight the applicability of ground-based radar measurements over the tropics to devise quantitative precipitation algorithms for reliable rain estimates.
{"title":"Micro rain radar and radiometric measurements to unravel contrasting features of rain microstructure below and above the boundary layer","authors":"Gargi Rakshit;Rohit Chakraborty;Animesh Maitra","doi":"10.1029/2023RS007875","DOIUrl":"10.1029/2023RS007875","url":null,"abstract":"Ka-band Micro rain Doppler radar is an effective tool to investigate the profiles of precipitation microstructure in terms of the raindrop size distribution (DSD). The DSD parameters that vary appreciably with height are indicative of the associated atmospheric phenomena. Hence the present investigation endeavors to put light on the underlying physical processes responsible for the evolution of varied rain microstructure profiles using micro rain radar (MRR), and radiometric measurements complemented with re-analysis outputs over an urban tropical location, Kolkata (22.57°N, 88.37°E), India. MRR unravels the prevalence of significant biases in the typical power law relationship (D\u0000<inf>m</inf>\u0000 = aR\u0000<sup>b</sup>\u0000) between rain rate (R) and mass-weighted mean drop diameter (D\u0000<inf>m</inf>\u0000) along the rain height, especially during intense convective rain events, above the atmospheric boundary layer (ABL). Consequently, an alternative empirical relation appropriate to account for the R-D\u0000<inf>m</inf>\u0000 variability above the ABL is proposed. Further, radiometric measurements and re-analysis outputs reveal that the presence of atmospheric instabilities coupled with wind shear impacts above the ABL contributes to the enhanced breakup of raindrops and the deviations in the usual R-D\u0000<inf>m</inf>\u0000 relationship. Thus, the present study intends to highlight the applicability of ground-based radar measurements over the tropics to devise quantitative precipitation algorithms for reliable rain estimates.","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":"139812178","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}
Mohamed O. Shammat;Bodo W. Reinisch;Ivan Galkin;Philip J. Erickson;Jay A. Weitzen;William C. Rideout
This paper introduces the Peak Density Thickness (PDT) formalism, a novel approach to representing the F2 layer's vertical electron density profile in the ionosphere. It diverges from the conventional “pointed-peak” model by suggesting a “broad-peak” or “flat-nose” profile where plasma density remains constant within an altitude interval χ. This theory is backed by independent observations, including a comprehensive data set from the Millstone Hill Incoherent Scatter Radar at the MIT Haystack observatory, spanning from 1993 to 2023, which illustrates the presence and diurnal variation of PDT. A single-day intensive cross-verification using Digisonde Portable Sounder DPS4D soundings of the sub-peak ionosphere has shown remarkable agreement in the measurements of the lower boundary of the χ interval and the peak density. This study suggests incorporating the flat-nose section χ into the F-region profile formalism. Such a shift could improve the accuracy of topside specifications derived from ground-based ionosonde measurements, enhancing our understanding of ionospheric plasma dynamics.
{"title":"Characterizing plasma peak density thickness in the ionosphere: A single-site multi-instrument study","authors":"Mohamed O. Shammat;Bodo W. Reinisch;Ivan Galkin;Philip J. Erickson;Jay A. Weitzen;William C. Rideout","doi":"10.1029/2023RS007658","DOIUrl":"10.1029/2023RS007658","url":null,"abstract":"This paper introduces the Peak Density Thickness (PDT) formalism, a novel approach to representing the F2 layer's vertical electron density profile in the ionosphere. It diverges from the conventional “pointed-peak” model by suggesting a “broad-peak” or “flat-nose” profile where plasma density remains constant within an altitude interval χ. This theory is backed by independent observations, including a comprehensive data set from the Millstone Hill Incoherent Scatter Radar at the MIT Haystack observatory, spanning from 1993 to 2023, which illustrates the presence and diurnal variation of PDT. A single-day intensive cross-verification using Digisonde Portable Sounder DPS4D soundings of the sub-peak ionosphere has shown remarkable agreement in the measurements of the lower boundary of the χ interval and the peak density. This study suggests incorporating the flat-nose section χ into the F-region profile formalism. Such a shift could improve the accuracy of topside specifications derived from ground-based ionosonde measurements, enhancing our understanding of ionospheric plasma dynamics.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 1","pages":"1-13"},"PeriodicalIF":1.6,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139095956","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}
Jishnu N. Thekkeppattu;Randall B. Wayth;Marcin Sokołowski
Performance of digitally beamformed phased arrays relies on accurate calibration of the array by obtaining gains of each antenna in the array. The stations of the Square Kilometer Array-Low (SKA-Low) are such digital arrays, where the station calibration is currently performed using conventional interferometric techniques. An alternative calibration technique similar to holography of dish based telescopes has been suggested in the past. In this paper, we develop a novel mathematical framework for holography employing tensors, which are multi-way data structures. Self-holography using a reference beam formed with the station under test itself and cross-holography using a different station to obtain the reference beam are unified under the same formalism. Besides, the relation between the two apparently distinct holographic approaches in the literature for phased arrays is shown, and we show that under certain conditions the two methods yield the same results. We test the various holographic techniques on an SKA-Low prototype station Aperture Array Verification System 2 (AAVS2) with the Sun as the calibrator. We perform self-holography of AAVS2 and cross-holography with simultaneous observations carried out with another station Engineering Development Array 2. We find the results from the holographic techniques to be consistent among themselves as well as with a more conventional calibration technique.
{"title":"Calibration of an SKA-low prototype station using holographic techniques","authors":"Jishnu N. Thekkeppattu;Randall B. Wayth;Marcin Sokołowski","doi":"10.1029/2023RS007847","DOIUrl":"10.1029/2023RS007847","url":null,"abstract":"Performance of digitally beamformed phased arrays relies on accurate calibration of the array by obtaining gains of each antenna in the array. The stations of the Square Kilometer Array-Low (SKA-Low) are such digital arrays, where the station calibration is currently performed using conventional interferometric techniques. An alternative calibration technique similar to holography of dish based telescopes has been suggested in the past. In this paper, we develop a novel mathematical framework for holography employing tensors, which are multi-way data structures. Self-holography using a reference beam formed with the station under test itself and cross-holography using a different station to obtain the reference beam are unified under the same formalism. Besides, the relation between the two apparently distinct holographic approaches in the literature for phased arrays is shown, and we show that under certain conditions the two methods yield the same results. We test the various holographic techniques on an SKA-Low prototype station Aperture Array Verification System 2 (AAVS2) with the Sun as the calibrator. We perform self-holography of AAVS2 and cross-holography with simultaneous observations carried out with another station Engineering Development Array 2. We find the results from the holographic techniques to be consistent among themselves as well as with a more conventional calibration technique.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 1","pages":"1-14"},"PeriodicalIF":1.6,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139376181","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 Spitze phenomenon is closely related to the Earth's magnetic field, and characterizes high-frequency (HF) rays propagating in the ionosphere. Specifically, when the reflection conditions are satisfied, HF rays are reflected perpendicular to the Earth's magnetic field. Studying the HF rays reflected from the Spitze region is important to indirectly learn about the ionosphere magnetic properties. The 3D numerical ray-tracing method is a widely used HF rays inversion technique. However, the conventional 3D Haselegrove numerical ray-tracing method can not trace the ordinary rays in the Spitze region back to the ground. Therefore, we improved the conventional ray-tracing method based on Poeverlein's diagram. The improved method can change the ordinary rays' propagation directions when they travel very close to the Spitze reflection point. In this way, the ordinary rays' propagation interruption caused by the Spitze can be eliminated. An example showing the ordinary and extraordinary rays traced by the conventional and improved ray-tracing methods under the quiet ionosphere is provided to validate the improvement. In addition, three disturbed ionospheric backgrounds with large-scale, medium-scale, and small-scale TIDs are designed to simulate various HF rays for further validation. The simulation results show that the Spitze exists in the quiet and disturbed ionosphere, and the improved ray-tracing method can properly solve the Spitze effects on the traced ordinary rays.
{"title":"An improved 3D numerical ray-tracing method for solving the spitze effects based on poeverlein's diagram","authors":"Huan Song;Haiyin Qing;Jiyao Xu","doi":"10.1029/2022RS007583","DOIUrl":"10.1029/2022RS007583","url":null,"abstract":"The Spitze phenomenon is closely related to the Earth's magnetic field, and characterizes high-frequency (HF) rays propagating in the ionosphere. Specifically, when the reflection conditions are satisfied, HF rays are reflected perpendicular to the Earth's magnetic field. Studying the HF rays reflected from the Spitze region is important to indirectly learn about the ionosphere magnetic properties. The 3D numerical ray-tracing method is a widely used HF rays inversion technique. However, the conventional 3D Haselegrove numerical ray-tracing method can not trace the ordinary rays in the Spitze region back to the ground. Therefore, we improved the conventional ray-tracing method based on Poeverlein's diagram. The improved method can change the ordinary rays' propagation directions when they travel very close to the Spitze reflection point. In this way, the ordinary rays' propagation interruption caused by the Spitze can be eliminated. An example showing the ordinary and extraordinary rays traced by the conventional and improved ray-tracing methods under the quiet ionosphere is provided to validate the improvement. In addition, three disturbed ionospheric backgrounds with large-scale, medium-scale, and small-scale TIDs are designed to simulate various HF rays for further validation. The simulation results show that the Spitze exists in the quiet and disturbed ionosphere, and the improved ray-tracing method can properly solve the Spitze effects on the traced ordinary rays.","PeriodicalId":49638,"journal":{"name":"Radio Science","volume":"59 1","pages":"1-13"},"PeriodicalIF":1.6,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139095996","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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