628 results on '"RADAR"'
Search Results
2. Improving Nowcasting of Convective Development by Incorporating Polarimetric Radar Variables Into a Deep‐Learning Model
- Author
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Hao Huang, Yinghui Lu, Kun Zhao, Xiang Pan, Mingjun Wang, and Haonan Chen
- Subjects
Convection ,Nowcasting ,Meteorology ,Computer science ,business.industry ,Deep learning ,Polarimetry ,law.invention ,Geophysics ,law ,General Earth and Planetary Sciences ,Artificial intelligence ,Radar ,business ,Convective precipitation - Published
- 2021
3. Application of a Radar Echo Extrapolation‐Based Deep Learning Method in Strong Convection Nowcasting
- Author
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Wei Han, Jian Yin, and Zhiqiu Gao
- Subjects
Convection ,QE1-996.5 ,Nowcasting ,business.industry ,Computer science ,Deep learning ,Astronomy ,Echo (computing) ,Extrapolation ,deep learning ,QB1-991 ,Geology ,nowcasting ,Environmental Science (miscellaneous) ,law.invention ,law ,General Earth and Planetary Sciences ,radar echo extrapolation ,Artificial intelligence ,Radar ,business ,Remote sensing - Abstract
Strong convection nowcasting has been gaining importance in operational weather forecasting. Recently, deep learning methods have been used to meet the increasing requirement for precise and timely nowcasting. One of the promising deep learning models is the convolutional gated recurrent unit (ConvGRU), which has been proven to perform better than traditional methods in strong convection nowcasting. Despite its encouraging performance, ConvGRU tends to produce blurry radar echo images and fails to model radar echo intensities that have multi‐modal and skewed distributions. To overcome these disadvantages, we tested the structural similarity (SSIM) and multiscale structural similarity (MS‐SSIM) indexes as loss functions. The SSIM and MS‐SSIM loss functions are composed of luminance, contrast, and structure and provide more information about the intensity, grade, and shape of the radar echo, which can reduce blurring. Due to multi‐layer downscaling, MS‐SSIM extracted more radar echo characteristics, and its extrapolation was the most realistic and accurate among all of the loss function schemes. Only the MS‐SSIM scheme successfully predicted strong radar echoes after 2 h, especially those at the rainstorm level.
- Published
- 2021
4. Calibrating the Amplitude and Phase Imbalances in AgileDARN HF Radar
- Author
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Jingye Yan, Hongbin Qiu, Xing-Guang Deng, Liang Wu, Jie Zhang, Ailan Lan, and Jianping Wu
- Subjects
Main lobe ,Computer science ,business.industry ,Phased array ,Acoustics ,Condensed Matter Physics ,law.invention ,Transmission (telecommunications) ,Side lobe ,law ,Calibration ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Antenna gain ,Radar ,business ,Digital signal processing - Abstract
The Agile Dual Auroral Radar Network (AgileDARN) radar has been developed as an all-digital high-frequency (HF) coherent scatter radar. Based on phased array antenna and digital signal processing techniques, digital beam forming (DBF) is employed for both transmission and reception, which steers toward the desired direction based on the relative phases within the array elements. However, the amplitude and phase imbalances among channels will lead to substantial degradation of DBF performance, including the beam direction deviation, broadening of the main lobe, deteriorated side lobes, antenna gain degradation, and ultimately affects the radar detection accuracy. Here, we present a complete method for calibrating these imbalances in transceivers and linear array elements in AgileDARN radar: internal calibration and external calibration. During the internal calibration, the calibration signals with the same amplitude and phase as the multi-pulse sequence are sent to all transceivers internally. The variance of the outputs illustrates the transceivers' imbalances and can be processed to implement calibration. Further, the meteor echoes and linear least squares fitting method are employed for external calibration, which calibrates the amplitude and phase imbalances among the cables and phased array elements. The technique has been successfully implemented, and we present the results of measured data observed by the AgileDARN HF radar before and after calibration.
- Published
- 2021
5. Real‐Time Thermospheric Density Estimation via Radar and GPS Tracking Data Assimilation
- Author
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Richard Linares and David J. Gondelach
- Subjects
Atmospheric Science ,business.industry ,law ,Gps data ,Global Positioning System ,Environmental science ,Tracking data ,Assimilation (biology) ,Density estimation ,Radar ,business ,law.invention ,Remote sensing - Published
- 2021
6. Three Years of Near‐Coastal Antarctic Iceberg Distribution From a Machine Learning Approach Applied to SAR Imagery
- Author
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Mauro Medeiros Barbat, Hartmut Hellmer, Mauricio M. Mata, Christine Wesche, and Thomas Rackow
- Subjects
010504 meteorology & atmospheric sciences ,Antarctic ice sheet ,Distribution (economics) ,Flux ,Oceanography ,Machine learning ,computer.software_genre ,01 natural sciences ,law.invention ,Geochemistry and Petrology ,law ,Coastal zone ,Earth and Planetary Sciences (miscellaneous) ,14. Life underwater ,Radar ,0105 earth and related environmental sciences ,business.industry ,Future climate ,Iceberg ,Geophysics ,13. Climate action ,Space and Planetary Science ,Remote sensing (archaeology) ,Artificial intelligence ,business ,computer ,Geology - Abstract
Mass loss around the Antarctic Ice Sheet is driven by basal melting and iceberg calving,which constitute the two dominant paths of freshwater flux into the Southern Ocean. Although of similarmagnitude, icebergs play an important and still not fully understood role in the balance of heat andfreshwater around Antarctica. This lack of understanding is partly due to operational difficulties inlarge-scale monitoring in polar regions, despite observational and remote sensing efforts. In this study, anovel machine learning approach, augmented by visual inspection, was applied to three SyntheticAperture Radar (SAR) mosaics of the whole Antarctic continent and its adjacent coastal zone. Althoughoriginally intended for a mapping of the Antarctic continent, the SAR mosaics allow us to document theevolution and distribution of the size (and mass) of icebergs in the pan-Antarctic near-coastal zone for theyears 1997, 2000, and 2008. Our novel algorithm identified 7,649 icebergs in 1997, 13,712 icebergs in 2000,and 7,246 icebergs in 2008 with surface areas between 0.1 and 4,567.82 km2and total masses of 4,641.53,6,862.81, and 5,263.69 Gt, respectively. Large regional variability was observed, although a zonal patterndistribution is present. This has implications for future climate modeling studies that try to estimate thefreshwater flux from melting icebergs, which demands a realistic representation of the interannuallyvarying near-coastal iceberg pattern to initialize the simulations.
- Published
- 2019
7. An HF Software‐Defined Radar to Study the Ionosphere
- Author
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Sven G. Bilén, Salih Mehmed Bostan, Julio Urbina, John D. Mathews, and James K. Breakall
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Signal processing ,Radar system design ,business.industry ,Condensed Matter Physics ,Ionospheric sounding ,law.invention ,Software ,Remote sensing (archaeology) ,law ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Ionosphere ,Radar ,business ,Geology ,Remote sensing - Published
- 2019
8. Melting Layer Attenuation at Ka‐ and W‐Bands as Derived From Multifrequency Radar Doppler Spectra Observations
- Author
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Haoran Li, Dmitri Moisseev, INAR Physics, Radar Meteorology group, and Institute for Atmospheric and Earth System Research (INAR)
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Atmospheric Science ,010504 meteorology & atmospheric sciences ,0211 other engineering and technologies ,02 engineering and technology ,Melting layer ,01 natural sciences ,Spectral line ,law.invention ,Rayleigh regime ,symbols.namesake ,Optics ,law ,Earth and Planetary Sciences (miscellaneous) ,Multi-frequency radar Doppler spectra ,Radar ,Physics::Atmospheric and Oceanic Physics ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,business.industry ,Attenuation ,115 Astronomy, Space science ,Geophysics ,13. Climate action ,Space and Planetary Science ,symbols ,business ,Doppler effect ,Ka-/W-band melting layer attenuation ,Geology - Abstract
The melting layer of precipitation has a major impact on remote sensing and telecommunications. However, there is a shortage of observational studies to validate and constrain the melting layer models especially for high-frequency radar bands. In this paper, we report how multifrequency radar Doppler spectra can be used to retrieve the melting layer attenuation at Ka- and W-bands. The presented analysis is based on identifying Rayleigh scattering regions in radar Doppler spectra measurements where dual-wavelength spectral ratios can be related to differential attenuation. We show that the estimated attenuation at Ka- and W-bands agrees reasonably well with previously reported studies, but there are indications of differences at higher rain rates. We advocate that this technique can be applied to long-term observations to advance our knowledge of the melting process. The parameterizations of melting layer attenuation as a function of rain rate and radar reflectivity are also presented.
- Published
- 2019
9. The Relationship of Cloud Number and Size With Their Large‐Scale Environment in Deep Tropical Convection
- Author
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Martin Bergemann, Alain Protat, Sugata Narsey, Valentin Louf, and Christian Jakob
- Subjects
Convection ,Scale (ratio) ,business.industry ,Tropics ,Cloud computing ,law.invention ,Geophysics ,law ,Climatology ,General Earth and Planetary Sciences ,Environmental science ,Radar ,business ,Tropical convection - Published
- 2019
10. Gap Filling of High‐Resolution Soil Moisture for SMAP/Sentinel‐1: A Two‐Layer Machine Learning‐Based Framework
- Author
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Nick Duffield, Hanzi Mao, Binayak P. Mohanty, and Dhruva Kathuria
- Subjects
010504 meteorology & atmospheric sciences ,Mean squared error ,0208 environmental biotechnology ,High resolution ,02 engineering and technology ,Machine learning ,computer.software_genre ,01 natural sciences ,law.invention ,symbols.namesake ,law ,Radar ,Water content ,0105 earth and related environmental sciences ,Water Science and Technology ,Gap filling ,Radiometer ,business.industry ,Pearson product-moment correlation coefficient ,020801 environmental engineering ,Brightness temperature ,symbols ,Environmental science ,Artificial intelligence ,business ,computer - Abstract
As the most recent 3 km soil moisture product from the Soil Moisture Active Passive (SMAP) mission, the SMAP/Sentinel-1 L2_SM_SP product has a unique capability to provide global-scale 3 km soil moisture estimates through the fusion of radar and radiometer microwave observations. The spatial and temporal availability of this high-resolution soil moisture product depends on concurrent radar and radiometer observations which is significantly restricted by the narrow swath and low revisit schedule of the Sentinel-1 radars. To address this issue, this paper presents a novel two-layer machine learning-based framework which predicts the brightness temperature and subsequently the soil moisture at gap areas. The proposed method is able to gap-fill soil moisture satisfactorily at areas where the radiometer observations are available while the radar observations are missing. We find that incorporating historical radar backscatter measurements (30-day average) into the machine learning framework boosts its predictive performance. The effectiveness of the two-layer framework is validated against regional hold-out SMAP/Sentinel-1 3 km soil moisture estimates at four study areas with distinct climate regimes. Results indicate that our proposed method is able to reconstruct 3 km soil moisture at gap areas with higher Pearson correlation coefficient (47%/35%/20%/80% improvement of mean R, at Arizona/Oklahoma/Iowa/Arkansas) and lower unbiased Root Mean Square Error (20%/10%/7%/26% improvement of mean ubRMSE) when compared to the SMAP 33 km soil moisture product. Additional validation against airborne data and in-situ data from soil moisture networks is also satisfactory.
- Published
- 2019
11. Reconstruction of Cloud Vertical Structure With a Generative Adversarial Network
- Author
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Jussi Leinonen, Tianle Yuan, and Alexandre Guillaume
- Subjects
Structure (mathematical logic) ,010504 meteorology & atmospheric sciences ,Computer science ,business.industry ,Imaging spectrometer ,Cloud computing ,010502 geochemistry & geophysics ,computer.software_genre ,01 natural sciences ,Convolutional neural network ,Field (computer science) ,law.invention ,Geophysics ,law ,Range (statistics) ,General Earth and Planetary Sciences ,Satellite ,Data mining ,Radar ,business ,computer ,0105 earth and related environmental sciences - Abstract
We demonstrate the feasibility of solving atmospheric remote sensing problems with machine learning using conditional generative adversarial networks (CGANs), implemented using convolutional neural networks (CNNs). We apply the CGAN to generating two-dimensional cloud vertical structures that would be observed by the CloudSat satellite-based radar, using only the collocated Moderate-Resolution Imaging Spectrometer (MODIS) measurements as input. The CGAN is usually able to generate reasonable guesses of the cloud structure, and can infer complex structures such as multilayer clouds from the MODIS data. This network, which is formulated probabilistically, also estimates the uncertainty of its own predictions. We examine the statistics of the generated data, and analyze the response of the network to each input parameter. The success of the CGAN in solving this problem suggests that generative adversarial networks are applicable to a wide range of problems in atmospheric science, a field characterized by complex spatial structures and observational uncertainties.
- Published
- 2019
12. Correction of Ionospheric Distortion on HF Hybrid Sky‐Surface Wave Radar Calibrated by Direct Wave
- Author
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Wang Longgang, Xianchang Yue, Qing Zhou, Lan Zhang, and Xingbin Wu
- Subjects
Physics ,010504 meteorology & atmospheric sciences ,business.industry ,Phase (waves) ,020206 networking & telecommunications ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Background noise ,symbols.namesake ,Optics ,Surface wave ,law ,Distortion ,Wave radar ,0202 electrical engineering, electronic engineering, information engineering ,symbols ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,Ionosphere ,business ,Doppler effect ,0105 earth and related environmental sciences - Abstract
The performance of the high-frequency hybrid sky-surface wave radar is often degraded due to the distortion of radar echoes induced by time-varying ionosphere. Here a modified S-transform method based on the direct wave for ionosphere decontamination of high-frequency hybrid sky-surface wave radar is presented. First, we extract the time-varying-ionosphere-distorted phase of the echoes from the direct wave of high-frequency hybrid sky-surface wave radar by using the modified S-transform. Then this phase function is used to decontaminate the ionosphere distortion of radar echo at each range bins. Simulations and experimental data are conducted to validate the performance of the proposed method on decontaminating the distortion. The experimental data are acquired by Wuhan Universitys ocean state measuring and analyzing radar. A mass of radar data is processed and analyzed, demonstrating that the decontamination effect is statistically significant. The method is not only effective to remove the Doppler shift of direct wave and Bragg peaks caused by ionosphere but also able to narrow the broadened direct wave and Bragg peaks. Meanwhile, the SNR is improved in most range bins; the background noise is reduced detectably, sometimes significantly; and some isolated radar echoes near direct wave or Bragg peaks are recovered or enhanced. These results indicate that the proposed decontamination algorithm works well.
- Published
- 2019
13. Characterizing the Representativity Error of Cloud Profiling Observations for Data Assimilation
- Author
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O. Stiller and Mark D. Fielding
- Subjects
Profiling (computer programming) ,Atmospheric Science ,business.industry ,Cloud computing ,law.invention ,Geophysics ,Lidar ,Data assimilation ,Space and Planetary Science ,law ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,Radar ,business ,Remote sensing - Published
- 2019
14. Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere
- Author
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David Morgan, David Andrews, D. Pitoňák, Andrew Kopf, Christopher M. Fowler, D. A. Gurnett, Laila Andersson, and František Němec
- Subjects
010504 meteorology & atmospheric sciences ,MARSIS ,Electron ,01 natural sciences ,Physics::Geophysics ,law.invention ,Geochemistry and Petrology ,law ,Earth and Planetary Sciences (miscellaneous) ,Radar ,Physics::Atmospheric and Oceanic Physics ,0105 earth and related environmental sciences ,Martian ,Spacecraft ,business.industry ,Mars Exploration Program ,Geophysics ,Depth sounding ,Computer Science::Graphics ,Space and Planetary Science ,Physics::Space Physics ,Astrophysics::Earth and Planetary Astrophysics ,Ionosphere ,business ,Geology - Abstract
We use more than 10years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to der ...
- Published
- 2019
15. Vertical Coupling From the Lower Atmosphere to the Ionosphere: Observations Inferred From Indian MST Radar, GPS Radiosonde, Ionosonde, Magnetometer, OLR (NOAA), and SABER/TIMED Instrument Over Gadanki
- Author
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A. K. Patra, T. K. Ramkumar, Priyanka Ghosh, Som Sharma, and P. Pavan Chaitanya
- Subjects
Coupling ,Meteorology ,Magnetometer ,business.industry ,law.invention ,Atmosphere ,Geophysics ,Space and Planetary Science ,law ,Radiosonde ,Global Positioning System ,Radar ,Ionosphere ,business ,Ionosonde ,Geology - Published
- 2019
16. Characterizing Vertical Particle Structure of Precipitating Cloud System from Multiplatform Measurements of A-Train Constellation
- Author
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Maki Kikuchi and Kentaroh Suzuki
- Subjects
business.industry ,Cloud computing ,law.invention ,Geophysics ,Lidar ,law ,Remote sensing (archaeology) ,General Earth and Planetary Sciences ,Environmental science ,Particle ,Satellite ,Precipitation ,Radar ,business ,Remote sensing ,Constellation - Abstract
形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2018-12-14, 資料番号: PA1910015000
- Published
- 2018
17. Comparing Satellite‐ and Ground‐Based Observations of Cloud Occurrence Over High Southern Latitudes
- Author
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Cameron McErlich, Adrian McDonald, Alex Schuddeboom, and Israel Silber
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Meteorology ,business.industry ,Cloud computing ,01 natural sciences ,law.invention ,Latitude ,Geophysics ,Altitude ,Lidar ,Space and Planetary Science ,law ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,Satellite ,Radar ,business ,0105 earth and related environmental sciences - Abstract
The 2B-CLDCLASS-LIDAR R05 (2BCL5) and the raDAR/liDAR (DARDAR) satellite retrievals of cloud occurrence are compared as a function of altitude and latitude. The largest disparities are observed at ...
- Published
- 2021
18. Refractivity‐From‐Clutter Capable, Software‐Defined, Coherent‐on‐Receive Marine Radar
- Author
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Luyao Xu, Joshua Compaleo, and Caglar Yardim
- Subjects
010504 meteorology & atmospheric sciences ,business.industry ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,020206 networking & telecommunications ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,Signal ,GeneralLiterature_MISCELLANEOUS ,Power (physics) ,law.invention ,Software ,Marine radar ,Remote sensing (archaeology) ,law ,0202 electrical engineering, electronic engineering, information engineering ,General Earth and Planetary Sciences ,Environmental science ,Clutter ,Atmospheric duct ,Electrical and Electronic Engineering ,Radar ,business ,0105 earth and related environmental sciences ,Remote sensing - Abstract
Refractivity-from-clutter (RFC) is a technique for remote sensing of the lowest portion of vertical atmospheric refractivity profile, particularly evaporation and surface-based ducts. It uses the sea-surface backscattered radar signal to estimate the ducting conditions. The Lower Atmospheric Propagation (LATPROP) radar is a software-defined, coherent-on-receive remote sensing system built on a low-cost, commercial off-the-shelf marine radar platform operating at 9.41 GHz. The system is designed to specifically operate as a RFC-capable platform sensitive to low clutter power returns from the sea surface. This paper examines the appropriate radar design, system modifications, and radar signal processing steps, and provides a comparison with existing RFC-capable systems. The LATPROP system was deployed during the Coupled Air-Sea Processes and electromagnetic Ducting Research West Campaign that took place off of the coast of Southern California during October 2017 and was shown to accurately capture the effects of the ducting conditions.
- Published
- 2021
19. A Deep Learning Approach to Radar‐Based QPE
- Author
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Jung-Lien Chu, Chiao‐Wei Chang, Ting-Shuo Yo, Hung-Chi Kuo, and Shih-Hao Su
- Subjects
quantitative precipitation estimation ,Quantitative precipitation estimation ,QPESUMS ,lcsh:Astronomy ,business.industry ,Deep learning ,lcsh:QE1-996.5 ,Environmental Science (miscellaneous) ,Machine learning ,computer.software_genre ,Convolutional neural network ,law.invention ,lcsh:QB1-991 ,lcsh:Geology ,machine learning ,law ,convolutional neural networks ,General Earth and Planetary Sciences ,Environmental science ,volume‐to‐point ,Artificial intelligence ,Radar ,business ,computer ,radar - Abstract
In this study, we propose a volume‐to‐point framework for quantitative precipitation estimation (QPE) based on the Quantitative Precipitation Estimation and Segregation Using Multiple Sensor (QPESUMS) Mosaic Radar data set. With a data volume consisting of the time series of gridded radar reflectivities over the Taiwan area, we used machine learning algorithms to establish a statistical model for QPE in weather stations. The model extracts spatial and temporal features from the input data volume and then associates these features with the location‐specific precipitations. In contrast to QPE methods based on the Z–R relation, we leverage the machine learning algorithms to automatically detect the evolution and movement of weather systems and associate these patterns to a location with specific topographic attributes. Specifically, we evaluated this framework with the hourly precipitation data of 45 weather stations in Taipei during 2013–2016. In comparison to the operational QPE scheme used by the Central Weather Bureau, the volume‐to‐point framework performed comparably well in general cases and excelled in detecting heavy‐rainfall events. By using the current results as the reference benchmark, the proposed method can integrate the heterogeneous data sources and potentially improve the forecast in extreme precipitation scenarios.
- Published
- 2021
20. Frequency Selection to Avoid Medium Effects on RCS of Conducting Objects With Plane E Wave Polarization
- Author
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Hosam El-Ocla
- Subjects
Physics ,Scattering ,Turbulence ,business.industry ,Frequency dependence ,Condensed Matter Physics ,Polarization (waves) ,law.invention ,Optics ,law ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,business - Published
- 2020
21. On Modeling of Quad‐Polarization Radar Scattering From the Ocean Surface With Breaking Waves
- Author
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Vladimir Kudryavtsev, Xiaolu Zhao, Biao Zhang, and William Perrie
- Subjects
Synthetic aperture radar ,Physics ,business.industry ,Scattering ,Breaking wave ,Microwave scattering ,Oceanography ,Polarization (waves) ,law.invention ,Geophysics ,Optics ,Space and Planetary Science ,Geochemistry and Petrology ,law ,Earth and Planetary Sciences (miscellaneous) ,Radar ,business - Published
- 2020
22. F 3 Layer Characteristics Revealed by the Jicamarca Incoherent Scatter Radar: First Results
- Author
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A. K. Patra, Bodo W. Reinisch, and K. Venkatesh
- Subjects
Geophysics ,Optics ,Space and Planetary Science ,law ,business.industry ,Incoherent scatter ,Radar ,business ,Layer (electronics) ,Geology ,law.invention - Published
- 2020
23. Agile Adaptive Radar Sampling of Fast‐Evolving Atmospheric Phenomena Guided by Satellite Imagery and Surface Cameras
- Author
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Katia Lamer, Pavlos Kollias, Edward P. Luke, and Mariko Oue
- Subjects
Surface (mathematics) ,business.industry ,Sampling (statistics) ,law.invention ,Geophysics ,law ,General Earth and Planetary Sciences ,Environmental science ,Satellite imagery ,Precipitation ,Radar ,business ,Remote sensing ,Agile software development - Published
- 2020
24. Spaceborne Cloud and Precipitation Radars: Status, Challenges, and Ways Forward
- Author
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Katia Lamer, Daniel Watters, Mircea Grecu, Lihua Li, Alessandro Battaglia, Pavlos Kollias, Richard Roy, Matthew Lebsock, Simone Tanelli, Kinji Furukawa, Ranvir Dhillon, Kamil Mroz, and Gerald M. Heymsfield
- Subjects
010504 meteorology & atmospheric sciences ,Computer science ,Doppler radar ,Cloud computing ,Precipitation ,Review Article ,cloud microphysics ,010502 geochemistry & geophysics ,01 natural sciences ,Radio spectrum ,Convective Processes ,Radio Science ,law.invention ,Spaceborne radar ,law ,Geodesy and Gravity ,Water cycle ,Radar ,Review Articles ,convection ,0105 earth and related environmental sciences ,Constellation ,Remote sensing ,Atmosphere Monitoring with Geodetic Techniques ,business.industry ,Doppler ,Physical Modeling ,Radar Atmospheric Physics ,Geophysics ,Atmospheric Processes ,Hydrology ,business ,Clouds and Aerosols ,Regional Modeling ,Natural Hazards ,radar - Abstract
Spaceborne radars offer a unique three‐dimensional view of the atmospheric components of the Earth's hydrological cycle. Existing and planned spaceborne radar missions provide cloud and precipitation information over the oceans and land difficult to access in remote areas. A careful look into their measurement capabilities indicates considerable gaps that hinder our ability to detect and probe key cloud and precipitation processes. The international community is currently debating how the next generation of spaceborne radars shall enhance current capabilities and address remaining gaps. Part of the discussion is focused on how to best take advantage of recent advancements in radar and space platform technologies while addressing outstanding limitations. First, the observing capabilities and measurement highlights of existing and planned spaceborne radar missions including TRMM, CloudSat, GPM, RainCube, and EarthCARE are reviewed. Then, the limitations of current spaceborne observing systems, with respect to observations of low‐level clouds, midlatitude and high‐latitude precipitation, and convective motions, are thoroughly analyzed. Finally, the review proposes potential solutions and future research avenues to be explored. Promising paths forward include collecting observations across a gamut of frequency bands tailored to specific scientific objectives, collecting observations using mixtures of pulse lengths to overcome trade‐offs in sensitivity and resolution, and flying constellations of miniaturized radars to capture rapidly evolving weather phenomena. This work aims to increase the awareness about existing limitations and gaps in spaceborne radar measurements and to increase the level of engagement of the international community in the discussions for the next generation of spaceborne radar systems., Key Points Current spaceborne radars offer a unique three‐dimensional view of the atmospheric component of the Earth's hydrological cycleCurrent spaceborne radar have limitations with respect to observations of low‐level clouds, midlatitude/high‐latitude precipitation, and convectionRecent advances in radar technology will enable filling current science gaps
- Published
- 2020
25. Impacts of Humidity Adjustment Through Radar Data Assimilation Using Cloud Analysis on the Analysis and Prediction of a Squall Line in Southern China
- Author
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Mingjun Wang, Ming Xue, and Yujie Pan
- Subjects
moisture adjustment ,Meteorology ,business.industry ,lcsh:Astronomy ,lcsh:QE1-996.5 ,Humidity ,cloud analysis ,Cloud computing ,Environmental Science (miscellaneous) ,Reflectivity ,law.invention ,lcsh:QB1-991 ,lcsh:Geology ,Data assimilation ,Southern china ,law ,reflectivity ,General Earth and Planetary Sciences ,Environmental science ,squall line ,Radar ,business ,Squall line ,data assimilation - Abstract
This study examines the impacts of humidity adjustment in a cloud analysis system on the analysis and forecast of a squall line that occurred in southeast China on 23–24 April 2007. Radial velocity data are assimilated using the ARPS three‐dimensional variational system while reflectivity data are assimilated by a cloud analysis system. Experiments with two different humidity adjustment schemes are performed, with the original and enhanced versions. Another experiment does not adjust moisture. Both schemes generally decrease the humidity in front of the convective line and increase the humidity within the convective and stratiform regions of squall line compared to no humidity adjustment, and the original scheme produces the higher humidity within precipitation regions, especially the stratiform region. Both schemes improve the forecast of squall line structure, including the leading convective line, a transition zone, and a trailing stratiform region. Among the three experiments, the enhanced scheme produces the highest precipitation forecast skill. The latent heating rates are also diagnosed to investigate the microphysical responses to the humidity adjustment. The cooling outside of the observed precipitation regions corresponding to the humidity reduction also acts to suppress spurious precipitation. Water vapor condensation into cloud water and cloud water evaporation generally dominate the latent heating/cooling below the freezing level. Compared to the enhanced scheme, the original scheme releases much more latent heat in the middle troposphere, causing more warming. This is linked to the higher cloud water condensation rate, due to the higher amount of moisture addition/adjustment by the original scheme.
- Published
- 2020
26. A Deep Learning‐Based Methodology for Precipitation Nowcasting With Radar
- Author
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Lei Chen, Yuan Cao, Junping Zhang, and Leiming Ma
- Subjects
precipitation nowcasting ,Nowcasting ,Meteorology ,business.industry ,lcsh:Astronomy ,Deep learning ,group normalization ,lcsh:QE1-996.5 ,deep learning ,Environmental Science (miscellaneous) ,law.invention ,lcsh:QB1-991 ,lcsh:Geology ,law ,General Earth and Planetary Sciences ,Environmental science ,Artificial intelligence ,Precipitation ,Radar ,business ,convolutional LSTM - Abstract
Nowcasting and early warning of severe convective weather play crucial roles in heavy rainfall warning, flood mitigation, and water resource management. However, achieving effective temporal‐spatial resolution nowcasting is a very challenging task owing to the complex dynamics and chaos. Recently, an increasing amount of research has focused on utilizing deep learning approaches for this task because of their powerful abilities in learning spatiotemporal feature representation in an end‐to‐end manner. In this paper, we present convolutional long short‐term memory with a layer called star‐shape bridge to transfer features across time steps. We build an end‐to‐end trainable model for the nowcasting problem using the radar echo data set. Furthermore, we propose a raining‐oriented loss function inspired by the critical success index and utilize the group normalization technique to refine the convergence performance in optimizing our deep network. Experiments indicate that our model outperforms convolutional long short‐term memory with the cross entropy loss function and the conventional extrapolation method.
- Published
- 2020
27. OptimalFRegion Electron Density for the PolarDARN Radar Echo Detection Near the Resolute Bay Zenith
- Author
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P. V. Ponomarenko, A. V. Koustov, David R. Themens, C. J. Graf, and R. G. Gillies
- Subjects
Electron density ,010504 meteorology & atmospheric sciences ,business.industry ,Echo detection ,Condensed Matter Physics ,01 natural sciences ,Refraction ,F region ,law.invention ,Optics ,law ,0103 physical sciences ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,business ,010303 astronomy & astrophysics ,Bay ,Zenith ,Geology ,0105 earth and related environmental sciences - Published
- 2018
28. Antenna Array Simulation and Detection Performance Analysis of Sanya Prototype Incoherent Scatter Radar
- Author
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Kai Yuan, Lingqi Zeng, Ming Yao, Hailong Zhao, Xiaohua Deng, Chen Li, and Feng Ding
- Subjects
Physics ,Time delay and integration ,010504 meteorology & atmospheric sciences ,business.industry ,0211 other engineering and technologies ,Incoherent scatter ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Antenna array ,Optics ,law ,Approximation error ,General Earth and Planetary Sciences ,Detection performance ,Electrical and Electronic Engineering ,Antenna gain ,Radar ,business ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences - Published
- 2018
29. The Challenge of Identifying Controls on Cloud Properties and Precipitation Onset for Cumulus Congestus Sampled During MC3E
- Author
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Scott E. Giangrande and David B. Mechem
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,business.industry ,Simulation modeling ,Cloud computing ,Forcing (mathematics) ,010502 geochemistry & geophysics ,01 natural sciences ,law.invention ,Geophysics ,Space and Planetary Science ,law ,Climatology ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,Precipitation ,Radar ,business ,0105 earth and related environmental sciences - Published
- 2018
30. VHF Radar Images of Artificial Field-Aligned Ionospheric Irregularities in the Subauroral E Region
- Author
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D. L. Hysell, J. Munk, and M. J. McCarrick
- Subjects
Physics ,010504 meteorology & atmospheric sciences ,business.industry ,Coherent backscattering ,Condensed Matter Physics ,Sporadic E propagation ,01 natural sciences ,Radiation pattern ,law.invention ,Optics ,law ,Radar imaging ,0103 physical sciences ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Ionosphere ,Radar ,010306 general physics ,business ,Beam (structure) ,Zenith ,0105 earth and related environmental sciences - Abstract
Artificial E-region field-aligned plasma density irregularities (AFAIs) have been generated using the HAARP ionospheric modification facility in Gakona and observed with a 30-MHz coherent scatter radar imager in Homer, Alaska. The AFAIs were generated using a distinctive, twisted-beam antenna pattern that illuminated a particularly broad volume overhead. The broad beam facilitates studies of natural sporadic E layer patches when they are present. The center of the pattern was pointed at different angles between zenith and magnetic zenith to examine the effects on the AFAI morphology. Radar images of AFAIs generally resemble the radiation pattern of the HF source, but the irregularities are strongest within a narrow range of zenith angles bounded approximately by the Spitze angle. A number of factors which might influence AFAI generation and detection are examined. The most important is most likely the requirement for the pump mode to have a standing-wave component for thermal parametric instability to operate.
- Published
- 2018
31. Combining InSAR and GPS to Determine Transient Movement and Thickness of a Seasonally Active Low‐Gradient Translational Landslide
- Author
-
Thomas C. Pierson, David L. George, Zhong Lu, Rebecca Kramer, and Xie Hu
- Subjects
010504 meteorology & atmospheric sciences ,business.industry ,0211 other engineering and technologies ,Landslide ,02 engineering and technology ,Geodesy ,01 natural sciences ,law.invention ,Geophysics ,Remote sensing (archaeology) ,law ,Interferometric synthetic aperture radar ,Global Positioning System ,General Earth and Planetary Sciences ,Movement (clockwork) ,Transient (oscillation) ,Low gradient ,Radar ,business ,Geology ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences - Published
- 2018
32. Cloud Properties Observed From the Surface and by Satellite at the Northern Edge of the Southern Ocean
- Author
-
Simon P. Alexander and Alain Protat
- Subjects
Atmospheric Science ,Virga ,010504 meteorology & atmospheric sciences ,Meteorology ,business.industry ,Cloud top ,Cloud computing ,010502 geochemistry & geophysics ,01 natural sciences ,law.invention ,Geophysics ,Altitude ,Lidar ,Space and Planetary Science ,law ,Earth and Planetary Sciences (miscellaneous) ,Satellite ,Glacial period ,Radar ,business ,Geology ,0105 earth and related environmental sciences - Abstract
A Raman depolarization lidar was deployed at Cape Grim, Australia (40.7°S, 144.7°E), at the northern edge of the Southern Ocean from July 2013 to February 2014 from which we determine cloud boundaries, cloud phase, ice virga, and cloud effective top heights. We compare surface-based lidar with results from the raDAR/liDAR (DARDAR) data set within 1,000 km of Cape Grim. DARDAR combines information from the CloudSat and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instruments. We extract single-layer clouds that are sufficiently thin for signal to be present on the farside of the cloud and which have a liquid cloud top phase. These conditions maximize the likelihood that both surface-based lidar and DARDAR are observing the full vertical extent of the same clouds. Differences in low-level cloud occurrence frequencies for these single-layer clouds reveal that DARDAR underestimates cloud at 0.2â€"1.0 km altitude by a factor of 3 compared with the surface-based lidar. When multiple cloud decks are present, the underestimate in this altitude region is around 2.5 times. Heterogeneous glaciation observed by the Cape Grim lidar in midlevel stratiform supercooled water clouds is similar to that reported by previous surface-based observations adjacent to the Southern Ocean, with half of these clouds precipitating ice at cloud top temperatures of −20°C. This transition occurs around -15°C in the DARDAR data set, and this difference is likely due to the reduced sensitivity of surface-based lidar in detecting precipitating ice compared with what a surface-based radar could observe.
- Published
- 2018
33. Refraction and Faraday rotation in the incoherent scatter radar technique
- Author
-
Boris G. Shpynev
- Subjects
Physics ,010504 meteorology & atmospheric sciences ,business.industry ,Incoherent scatter ,Condensed Matter Physics ,Radiolocation ,01 natural sciences ,Refraction ,law.invention ,symbols.namesake ,Optics ,law ,0103 physical sciences ,Faraday effect ,symbols ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,Ionosphere ,Wideband ,business ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Line (formation) - Abstract
In this paper we consider the radiolocation equation for the Incoherent Scatter Radar (ISR) method, the equation accounts for refraction effect and Faraday rotation in the VHF frequency domain. Our research shows that we cannot ignore refraction in processing the incoherent scatter data when lag-product is used to obtain the ionospheric characteristics. Effect of refraction can explain some uncertainties that arise during processing and interpretation of the ISR data. This effect shows that together with the "ion line" of incoherent scatter spectrum, a relatively small "electron line" also plays a significant role in forming the ionosphere response. The “electron line” behaves as an additional "radar induced" wideband radiolocation signal affected by refraction and Faraday rotation; it depends on the ionosphere temperature and ion composition. The presence of a wideband “electron line” produces specific distortions of the ISR spectrum during 3D-forming of the ionosphere response inside the ISR antenna diagram pattern. During testing, we found that the signal from the ISR “electron line” can be measured at much higher altitudes comparing to the “ion line”. Hence, to improve the incoherent scatter technique, we can take the “electron line” and refraction into account.
- Published
- 2017
34. Interferometer angle-of-arrival determination using precalculated phases
- Author
-
J. P. Younger and Iain M. Reid
- Subjects
010504 meteorology & atmospheric sciences ,Direction finding ,business.industry ,Phase (waves) ,020206 networking & telecommunications ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Azimuth ,Interferometry ,Optics ,law ,Angle of arrival ,Lookup table ,0202 electrical engineering, electronic engineering, information engineering ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,Antenna (radio) ,business ,Algorithm ,Computer Science::Information Theory ,0105 earth and related environmental sciences ,Mathematics - Abstract
A method has been developed to determine the angle-of-arrival (AoA) of incident radiation using pre-computed lookup tables. The phase difference between two receiving antennas can be used to infer AoA as measured from the pair baseline, but there will be more than one possible solution for antenna spacings greater than or equal to half a wavelength. Larger spacings are preferable to minimize mutual coupling of elements in the receive array and to decrease the relative uncertainty in measured phase difference. We present a solution that uses all unique antenna pairs to determine probabilities for all possible azimuth and zenith values. Prior to analysis, the expected phase differences for all AOAs are calculated for each antenna pair. For a received signal, histograms of possible AoAs for each antenna pair phase difference are extracted and added to produce a two dimensional probability density array that will maximize at the true value of the AoA. A benefit of this method is that all possible antenna pairs are utilized, rather than the restriction to specific pairs along baselines used by some interferometer algorithms. Numerical simulations indicate that performance of the suggested algorithm exceeds that of existing methods, with the benefit of additional flexibility in antenna placement. Meteor radar data has been used to test this method against existing methods, with excellent agreement between the two approaches. This method of AoA determination will allow the construction of low-cost interferometric direction finding arrays with different layouts, including construction of difficult terrain and three-dimensional antenna arrangements.
- Published
- 2017
35. Distributed sensing of ionospheric irregularities with a GNSS receiver array
- Author
-
K. Deshpande, Seebany Datta-Barua, Yang Su, and Gary S. Bust
- Subjects
Scintillation ,Drift velocity ,010504 meteorology & atmospheric sciences ,business.industry ,Incoherent scatter ,Condensed Matter Physics ,Geodesy ,01 natural sciences ,law.invention ,law ,GNSS applications ,Physics::Space Physics ,0103 physical sciences ,Global Positioning System ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,Ionosphere ,business ,010303 astronomy & astrophysics ,Geology ,Noise (radio) ,0105 earth and related environmental sciences ,Remote sensing - Abstract
We present analysis methods for studying the structuring and motion of ionospheric irregularities at the sub-kilometer scale sizes that produce L-band scintillations. Spaced receiver methods are used for Global Navigation Satellite System (GNSS) receivers' phase measurements over approximately sub-kilometer to kilometer-length baselines for the first time. The quantities estimated by these techniques are: plasma drift velocity, diffraction anisotropy magnitude and orientation, and characteristic velocity. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts through linearization about the estimated values of the state. Five receivers of the Scintillation Auroral Global Positioning System (GPS) Array (SAGA) provide 100 Hz power and phase data for each channel at L1 frequency. The array is sited in the auroral zone at Poker Flat Research Range, Alaska. A case study of a single scintillating satellite observed by the array is used to demonstrate the spaced receiver and uncertainty estimation process. A second case study estimates drifts as measured by multiple scintillating channels. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30-minute period are made and compared to a collocated incoherent scatter radar, and show good agreement in horizontal drift speed and direction during periods of scintillation for which the characteristic velocity is less than the drift velocity.
- Published
- 2017
36. A case study of microphysical structures and hydrometeor phase in convection using radar Doppler spectra at Darwin, Australia
- Author
-
Laura Riihimaki, Tyler J. Thorsen, Edward P. Luke, Jennifer M. Comstock, and Qiang Fu
- Subjects
Convection ,010504 meteorology & atmospheric sciences ,0211 other engineering and technologies ,Diabatic ,Cloud computing ,02 engineering and technology ,01 natural sciences ,law.invention ,symbols.namesake ,law ,Ka band ,Radar ,Astrophysics::Galaxy Astrophysics ,Physics::Atmospheric and Oceanic Physics ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Remote sensing ,business.industry ,Attenuation ,Geophysics ,Lidar ,symbols ,General Earth and Planetary Sciences ,business ,Doppler effect ,Geology - Abstract
To understand the microphysical processes that impact diabatic heating and cloud lifetimes in convection, we need to characterize the spatial distribution of supercooled liquid water. To address this observational challenge, vertically pointing active sensors at the Darwin Atmospheric Radiation Measurement (ARM) site are used to classify cloud phase within a deep convective cloud in a shallow to deep convection transitional case. The cloud cannot be fully observed by a lidar due to signal attenuation. Thus we develop an objective method for identifying hydrometeor classes, including mixed-phase conditions, using k-means clustering on parameters that describe the shape of the Doppler spectra from vertically pointing Ka band cloud radar. This approach shows that multiple, overlapping mixed-phase layers exist within the cloud, rather than a single region of supercooled liquid, indicating complexity to how ice growth and diabatic heating occurs in the vertical structure of the cloud.
- Published
- 2017
37. High‐latitude GPS phase scintillation from E region electron density gradients during the 20–21 December 2015 geomagnetic storm
- Author
-
Irfan Azeem, Don L. Hampton, Geoff Crowley, Marcin Pilinski, Diana Loucks, and Scott Palo
- Subjects
Geomagnetic storm ,Electron density ,Scintillation ,010504 meteorology & atmospheric sciences ,business.industry ,GPS signals ,Geodesy ,01 natural sciences ,Physics::Geophysics ,law.invention ,Geophysics ,Space and Planetary Science ,law ,Physics::Space Physics ,0103 physical sciences ,Global Positioning System ,Environmental science ,Emission spectrum ,Radar ,Ionosphere ,business ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Remote sensing - Abstract
A novel operating mode for PFISR has been developed to support the study of GPS L1 scintillations arising from electron density gradients over Alaska. Previous authors have combined GPS scintillation data with either PFISR or multi-spectral imagery in this region. This analysis combines all three techniques to determine both gradient parameters as well as the most likely ionospheric source, including a conjunction analysis between GPS signals and known PFISR beams. This approach was used to study scintillation events observed in December 2015. These events were recorded during the recovery phase of a geomagnetic storm that ensued on December 20th when the Earth passed through the path of a solar CME (DST minimum near -170nT, Kp peak of 7). Two scintillation events were detected through analysis of the phase scintillation index (σϕ), calculated from an ASTRA CASES GPS receiver at Poker Flat. Values of σϕ≃0.5 and σϕ≃1.6 cycles were recorded for these events. Concurrently, an experiment on PFISR was run to discern the electron density along the GPS signal line of site; and, the imager observed the 428.7nm, 557.7nm and 630.0nm emission lines during the experiment window. From the ratios of derived emission intensities, estimates of precipitating particle energies were made allowing confirmation of the altitudes associated with the electron density peaks determined using raw radar returns from PFISR. Results indicate that temporal and spatial electron density gradients existed along the signal's path during periods of highest scintillation, which resulted from impact ionization from auroral particle precipitation at E region altitudes.
- Published
- 2017
38. Radar observations of thermal plasma oscillations in the ionosphere
- Author
-
Phil Perillat, Erhan Kudeki, Juha Vierinen, David L. Hysell, Michael P. Sulzer, and Björn Gustavsson
- Subjects
Physics ,Electron density ,010504 meteorology & atmospheric sciences ,business.industry ,Incoherent scatter ,Electron ,Plasma ,Plasma oscillation ,01 natural sciences ,law.invention ,Geophysics ,Optics ,Physics::Plasma Physics ,law ,Physics::Space Physics ,0103 physical sciences ,General Earth and Planetary Sciences ,Arecibo Observatory ,Ionosphere ,Radar ,business ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
Incoherent scatter radar observations of ionospheric plasmas rely on echoes from electron density fluctuations with properties governed by the dispersion relations for ion-acoustic and Langmuir waves. Radar observations of echoes associated with Langmuir waves (plasma lines) from thermal plasma are weak and only a few near-thermal level measurements have been reported. Plasma line echoes are typically only observed with existing radars only when the Langmuir waves are enhanced by suprathermal electrons. A new observation technique has been developed which is sensitive enough to allow observations of these echoes without the presence of suprathermal electrons up to at least 1000 km. This paper presents recent observations from the Arecibo Observatory 430-MHz incoherent scatter radar which show plasma-line echoes during the night when no suprathermal enhancement is expected to be present. The observations are compared with theory, and the results are found to be in agreement with classical incoherent scatter theory for thermal plasmas. The theoretical ratio of the ion line and plasma line power spectral density is within approximately 3 dB of the predicted value. The finding adds a new observational capability, allowing electron density to also be observed at night using the plasma line well into the top side of the ionosphere, increasing the accuracy of the electron density measurement.
- Published
- 2017
39. A machine learning nowcasting method based on real-time reanalysis data
- Author
-
Wei Zhang, Lei Han, Yinjing Lin, Hailei Feng, Juanzhen Sun, and Yuanyuan Xiu
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Nowcasting ,Computer science ,Doppler radar ,02 engineering and technology ,Machine learning ,computer.software_genre ,01 natural sciences ,law.invention ,law ,Classifier (linguistics) ,0202 electrical engineering, electronic engineering, information engineering ,Earth and Planetary Sciences (miscellaneous) ,Radar ,0105 earth and related environmental sciences ,business.industry ,Expert system ,Support vector machine ,Geophysics ,Space and Planetary Science ,Convective storm detection ,Data analysis ,020201 artificial intelligence & image processing ,Artificial intelligence ,business ,computer - Abstract
Despite marked progress over the past several decades, convective storm nowcasting remains a challenge because most nowcasting systems are based on linear extrapolation of radar reflectivity without much consideration for other meteorological fields. The variational Doppler radar analysis system (VDRAS) is an advanced convective-scale analysis system capable of providing analysis of 3-D wind, temperature, and humidity by assimilating Doppler radar observations. Although potentially useful, it is still an open question as to how to use these fields to improve nowcasting. In this study, we present results from our first attempt at developing a Support Vector Machine (SVM) Box-based nOWcasting (SBOW) method under the machine learning framework using VDRAS analysis data. The key design points of SBOW are as follows: 1) The study domain is divided into many position-fixed small boxes and the nowcasting problem is transformed into one question, i.e., will a radar echo > 35 dBZ appear in a box in 30 minutes? 2) Box-based temporal and spatial features, which include time trends and surrounding environmental information, are constructed; and 3) The box-based constructed features are used to first train the SVM classifier, and then the trained classifier is used to make predictions. Compared with complicated and expensive expert systems, the above design of SBOW allows the system to be small, compact, straightforward, and easy to maintain and expand at low cost. The experimental results show that, although no complicated tracking algorithm is used, SBOW can predict the storm movement trend and storm growth with reasonable skill.
- Published
- 2017
40. Fault geometry inversion and slip distribution of the 2010Mw7.2 El Mayor‐Cucapah earthquake from geodetic data
- Author
-
Roland Bürgmann, Mong-Han Huang, Eric J. Fielding, Jianbao Sun, J. Alejandro Gonzalez-Ortega, Andrew M. Freed, and H. Dickinson
- Subjects
010504 meteorology & atmospheric sciences ,business.industry ,Trough (geology) ,Geodetic datum ,Geometry ,Slip (materials science) ,010502 geochemistry & geophysics ,Geodesy ,01 natural sciences ,Subpixel rendering ,law.invention ,Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,law ,Interferometric synthetic aperture radar ,Earth and Planetary Sciences (miscellaneous) ,Global Positioning System ,Radar ,business ,Geology ,Smoothing ,Seismology ,0105 earth and related environmental sciences - Abstract
Author(s): Huang, MH; Fielding, EJ; Dickinson, H; Sun, J; Gonzalez-Ortega, JA; Freed, AM; Burgmann, R | Abstract: The 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake in Baja, California, and Sonora, Mexico, had primarily right-lateral strike-slip motion and a minor normal-slip component. The surface rupture extended about 120 km in a NW-SE direction, west of the Cerro Prieto fault. Here we use geodetic measurements including near- to far-field GPS, interferometric synthetic aperture radar (InSAR), and subpixel offset measurements of radar and optical images to characterize the fault slip during the EMC event. We use dislocation inversion methods and determine an optimal nine-segment fault geometry, as well as a subfault slip distribution from the geodetic measurements. With systematic perturbation of the fault dip angles, randomly removing one geodetic data constraint, or different data combinations, we are able to explore the robustness of the inferred slip distribution along fault strike and depth. The model fitting residuals imply contributions of early postseismic deformation to the InSAR measurements as well as lateral heterogeneity in the crustal elastic structure between the Peninsular Ranges and the Salton Trough. We also find that with incorporation of near-field geodetic data and finer fault patch size, the shallow slip deficit is reduced in the EMC event by reductions in the level of smoothing. These results show that the outcomes of coseismic inversions can vary greatly depending on model parameterization and methodology.
- Published
- 2017
41. Oblique Reflections of Mars Express MARSIS Radar Signals From Ionospheric Density Structures: Raytracing Analysis
- Author
-
David Andrews, D. A. Gurnett, František Němec, Andrew Kopf, and David Morgan
- Subjects
Spacecraft ,business.industry ,Oblique case ,MARSIS ,Mars Exploration Program ,Geophysics ,law.invention ,Depth sounding ,Space and Planetary Science ,Geochemistry and Petrology ,law ,Mars express ,Earth and Planetary Sciences (miscellaneous) ,Radar ,Ionosphere ,business ,Geology - Abstract
Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar sounder on board the Mars Express spacecraft revealed oblique reflections coming systematically from apparently stable dens ...
- Published
- 2019
42. New capabilities of the upgraded EISCAT high-power HF facility
- Author
-
Assar Westman, Jussi Markkanen, Andrew Senior, and Michael T. Rietveld
- Subjects
010504 meteorology & atmospheric sciences ,business.industry ,Computer science ,Incoherent scatter ,Electrical engineering ,Effective radiated power ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Antenna array ,law ,Harmonics ,0103 physical sciences ,General Earth and Planetary Sciences ,Waveform ,Radio frequency ,Electrical and Electronic Engineering ,Radar ,Antenna gain ,business ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Remote sensing - Abstract
The high-power HF (High Frequency) facility (commonly known as Heating) near Tromso, Norway, which is an essential part of the EISCAT (European Incoherent SCATter) Scientific Association, has been upgraded in certain key areas in recent years. It is one of only four similar facilities in the world operating at present. An updated description of the facility is given, together with scientific motivation and some results. The main high-power parts such as transmitters, feed-system and antennas remain essentially the same as built in the late 1970s. The improvements are in the areas of radio frequency waveform generation, computer control and monitoring. In particular, fast stepping in frequency is now possible, an important aspect in examining features close to harmonics of the electron gyrofrequency. One antenna array has been modified to allow reception to implement an HF radar mode for mesospheric and magnetospheric probing. More realistic modelling of the antenna gain gives improved estimates of the total effective radiated power for both wanted and unwanted circular polarizations. Results are presented using these new capabilities, but their full scientific potential has yet to be achieved.
- Published
- 2016
43. An effective method for incoherent scattering radar's detecting ability evaluation
- Author
-
Ming Yao, Xiaohua Deng, and Lu Ziqing
- Subjects
Physics ,010504 meteorology & atmospheric sciences ,Pulse-Doppler radar ,business.industry ,0211 other engineering and technologies ,Incoherent scatter ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Continuous-wave radar ,Signal-to-noise ratio ,Optics ,Radar engineering details ,law ,General Earth and Planetary Sciences ,Effective method ,Electrical and Electronic Engineering ,Ionosphere ,Radar ,business ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Remote sensing - Published
- 2016
44. Using GNSS signals as a proxy for SAR signals: Correcting ionospheric defocusing
- Author
-
Matthew Angling, D.P. Belcher, Christopher R. Mannix, and Paul S. Cannon
- Subjects
Point spread function ,Synthetic aperture radar ,010504 meteorology & atmospheric sciences ,02 engineering and technology ,01 natural sciences ,Physics::Geophysics ,law.invention ,law ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Radar ,Point target ,Physics::Atmospheric and Oceanic Physics ,0105 earth and related environmental sciences ,Remote sensing ,Physics ,Scintillation ,business.industry ,Astrophysics::Instrumentation and Methods for Astrophysics ,020206 networking & telecommunications ,Condensed Matter Physics ,Geodesy ,Amplitude ,GNSS applications ,Physics::Space Physics ,Global Positioning System ,General Earth and Planetary Sciences ,business - Abstract
Ultrahigh frequency space-based synthetic aperture radar (SAR) can suffer from the degrading effects of a scintillating ionosphere which modulates both the phase and the amplitude of the radar signal. In this paper, we use Global Navigation Satellite System (GNSS) signals to synthesize an L-band SAR point spread function (PSF). The process of transforming the GNSS signal to the equivalent SAR PSF is described. The synthesized PSF is used to explore the possibility of using a phase correction determined from a point target in a SAR image to correct the ionospheric degradation. GNSS data recorded on equatorial Ascension Island during scintillation events are used to test the feasibility of this approach by applying a phase correction to one GNSS receiver from another located along a magnetic east-west baseline. The peak-to-sidelobe ratios of the synthesized L-band SAR point spread functions before and after the correction are compared, and it is shown that this approach improves the L-band PSF over distances of ~3000 m in the ionosphere, corresponding to 6000 m on the ground.
- Published
- 2016
45. Dual-polarization radar signatures in snowstorms: Role of snowflake aggregation
- Author
-
Susanna Lautaportti, Sanghun Lim, Jani Tyynelä, and Dmitri Moisseev
- Subjects
Physics ,Atmospheric Science ,Ice crystals ,business.industry ,Cloud physics ,Snow ,law.invention ,Computational physics ,Geophysics ,Optics ,13. Climate action ,Space and Planetary Science ,law ,Phase (matter) ,Earth and Planetary Sciences (miscellaneous) ,Weather radar ,Precipitation ,Radar ,Snowflake ,business - Abstract
In this article a potential role of snowflake growth by aggregation on formation of dual-polarization radar signatures in winter storms is discussed. We advocate that the observed bands of increased values of specific differential phase (Kdp) can be linked to the onset of aggregation. These bands are caused by high number concentrations of oblate relatively dense ice particles and take place in regions where an ice phase “seeder-feeder” is active. On the other hand, the differential reflectivity (Zdr) bands, in absence of detectable Kdp values, are observed in the areas where crystal growth is the dominating snow growth mechanism and ice particle number concentration is lower. This distinction in underlying processes explains why Kdp and Zdr bands are not always observed at the same time. Furthermore, based on surface observations of snowflakes, it is determined that early aggregates, consisting of a small number of ice crystals, are oblate. These oblate particles could contribute to the reported dual-polarization radar signatures in snow, especially to the Kdp. This could help to explain why, where observed at the same type, Kdp and Zdr bands do not match and the altitude of the peak value of Kdp is usually lower than the Zdr one. It also means that dual-polarization radar signatures of snowflakes may depend on a stage of aggregation.
- Published
- 2015
46. Improved range and lag coverage for radar measurements of overspread targets by unmatched filtering of alternating codes
- Author
-
Björn Gustavsson and T. Grydeland
- Subjects
Backscatter ,Pulse-Doppler radar ,business.industry ,Computer science ,Autocorrelation ,Incoherent scatter ,Condensed Matter Physics ,law.invention ,Continuous-wave radar ,Optics ,law ,Range (statistics) ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Radar ,business ,Algorithm ,Decoding methods - Abstract
We propose that by using unmatched decoding for alternating codes, estimates of the autocorrelation function of the backscatter can be estimated at ranges between those resolved by matched filtering. The number of additional correlation estimates obtained in this way is twice that obtained using matched filtering, although each estimate contributes with only a quarter of the power in comparison. This leads to improvements in code performance by a factor of 1.5, and an increase in the speed of incoherent scatter radar experiments by the same factor.
- Published
- 2015
47. An investigation comparing ground‐based techniques that quantify auroral electron flux and conductance
- Author
-
A. Stromme, S. R. Kaeppler, James H. Hecht, Mark Conde, Michael J. Nicolls, Stanley C. Solomon, and Don L. Hampton
- Subjects
Physics ,business.industry ,Incoherent scatter ,Flux ,Energy flux ,Electron ,Computational physics ,law.invention ,Geophysics ,Earth's magnetic field ,Optics ,Space and Planetary Science ,law ,Radar ,Ionosphere ,business ,Characteristic energy - Abstract
We present three case studies that examine optical and radar methods for specifying precipitating auroral flux parameters and conductances. Three events were chosen corresponding to moderate nonsubstorm auroral activity with 557.7 nm intensities greater than 1kR. A technique that directly fits the electron number density from a forward electron transport model to alternating code incoherent scatter radar data is presented. A method for determining characteristic energy using neutral temperature observations is compared against estimates from the incoherent scatter radar. These techniques are focused on line-of-sight observations that are aligned with the local geomagnetic field. Good agreement is found between the optical and incoherent scatter radar methods for estimates of the average energy, energy flux, and conductances. The Pedersen conductance predicted by Robinson et al. (1987) is in very good agreement with estimates calculated from the incoherent scatter radar observations. However, we present an updated form of the relation by Robinson et al. (1987), ΣH/ΣP=0.57〈E〉0.53, which was found to be more consistent with the incoherent scatter radar observations. These results are limited to similar auroral configurations as in these case studies. Case studies are presented that quantify auroral electron flux parameters and conductance estimates which can be used to specify the magnitude of energy dissipated within the ionosphere resulting from magnetospheric driving.
- Published
- 2015
48. Application of particle swarm optimization method to incoherent scatter radar measurement of ionosphere parameters
- Author
-
Xin Wu, Tie-Jun Chen, Li-Li Wu, Jing Liang, and Qihou Zhou
- Subjects
Physics ,business.industry ,Incoherent scatter ,Particle swarm optimization ,Spectral density ,Spectral line ,law.invention ,Computational physics ,Power (physics) ,Geophysics ,Quadratic equation ,Optics ,Space and Planetary Science ,law ,Radar ,Ionosphere ,business - Abstract
Simultaneous derivation of multiple ionospheric parameters from the incoherent scatter power spectra in the F1 region is difficult because the spectra have only subtle differences for different combinations of parameters. In this study, we apply a particle swarm optimizer (PSO) to incoherent scatter power spectrum fitting and compare it to the commonly used least squares fitting (LSF) technique. The PSO method is found to outperform the LSF method in practically all scenarios using simulated data. The PSO method offers the advantages of not being sensitive to initial assumptions and allowing physical constraints to be easily built into the model. When simultaneously fitting for molecular ion fraction (fm), ion temperature (Ti), and ratio of ion to electron temperature (γT), γT is largely stable. The uncertainty between fm and Ti can be described as a quadratic relationship. The significance of this result is that Ti can be retroactively corrected for data archived many years ago where the assumption of fm may not be accurate, and the original power spectra are unavailable. In our discussion, we emphasize the fitting for fm, which is a difficult parameter to obtain. PSO method is often successful in obtaining fm, whereas LSF fails. We apply both PSO and LSF to actual observations made by the Arecibo incoherent scatter radar. The results show that PSO method is a viable method to simultaneously determine ion and electron temperatures and molecular ion fraction when the last is greater than 0.3.
- Published
- 2015
49. Scale‐aware parameterization of liquid cloud inhomogeneity and its impact on simulated climate in CESM
- Author
-
Xin Xie and Minghua Zhang
- Subjects
Atmospheric Science ,Scale (ratio) ,business.industry ,Cloud computing ,Atmospheric sciences ,Shape parameter ,law.invention ,Atmosphere ,Geophysics ,Space and Planetary Science ,law ,Earth and Planetary Sciences (miscellaneous) ,Atmospheric instability ,Gamma distribution ,Environmental science ,Liquid water path ,Radar ,business ,Astrophysics::Galaxy Astrophysics ,Physics::Atmospheric and Oceanic Physics - Abstract
Using long-term radar-based ground measurements from the Atmospheric Radiation Measurement Program, we derive the inhomogeneity of cloud liquid water as represented by the shape parameter of a gamma distribution. The relationship between the inhomogeneity and the model grid size as well as atmospheric condition is presented. A larger grid scale and more unstable atmosphere are associated with larger inhomogeneity that is described by a smaller shape parameter. This relationship is implemented as a scale-aware parameterization of the liquid cloud inhomogeneity in the Community Earth System Model (CESM) in which the shape parameter impacts the cloud microphysical processes. When used in the default CESM1 with the finite-volume dynamic core where a constant liquid inhomogeneity parameter was assumed, it reduces the cloud inhomogeneity in high latitudes and increases it in low latitudes. This is due to both the smaller (larger) grid size in high (low) latitudes in the longitude-latitude grid setting of CESM and the more stable (unstable) atmosphere. The single-column model and general circulation model sensitivity experiments show that the new parameterization increases the cloud liquid water path in polar regions and decreases it in low latitudes. An advantage of the parameterization is that it can recognize the spatial resolutions of the CESM without special tuning of the cloud water inhomogeneity parameter.
- Published
- 2015
50. Studies of the ionospheric turbulence excited by the fourth gyroharmonic at HAARP
- Author
-
Paul A. Bernhardt, Alexander Koloskov, Yu Morton, G. M. Milikh, M. Ruohoniemi, A. A. Sopin, Yu. M. Yampolski, A. V. Zalizovski, William A. Bristow, Carl L. Siefring, K. Chiang, Konstantinos Papadopoulos, S. Taylor, Alireza Mahmoudian, S. Briczinski, and A. Najmi
- Subjects
Physics ,Total electron content ,High Frequency Active Auroral Research Program ,business.industry ,Terminator (solar) ,Geophysics ,Effective radiated power ,law.invention ,Optics ,Space and Planetary Science ,law ,Physics::Space Physics ,Waveguide (acoustics) ,Radar ,Ionosphere ,business ,Ionosonde - Abstract
A study is presented of artificial ionospheric turbulence (AIT) induced by HF heating at High Frequency Active Auroral Research Program (HAARP) using frequencies close to the fourth electron gyroharmonic, in a broad range of radiated powers and using a number of different diagnostics. The diagnostics include GPS scintillations, ground-based stimulated electromagnetic emission (SEE), the HAARP ionosonde, Kodiak radar, and signals received at the Ukrainian Antarctic Station (UAS). The latter allowed analysis of waves scattered by the AIT into the ionospheric waveguide along Earth's terminator, 15.6 mm from the HAARP facility. For the first time, the amplitudes of two prominent SEE features, the downshifted maximum and broad upshifted maximum, were observed to saturate at ~50% of the maximum HAARP effective radiated power. Nonlinear effects in slant total electron content, SEE, and signals received at UAS at different transmitted frequencies and intensities of the pump wave were observed. The correlations between the data from different detectors demonstrate that the scattered waves reach UAS by the waveguide along the Earth's terminator, and that they were injected into the waveguide by scattering off of artificial striations produced by AIT above HAARP, rather than via direct injection from sidelobe radiation.
- Published
- 2015
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