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  Subjects -> ELECTRONICS (Total: 156 journals)
Showing 1 - 200 of 277 Journals sorted alphabetically
Advances in Biosensors and Bioelectronics     Open Access   (Followers: 6)
Advances in Electrical and Electronic Engineering     Open Access   (Followers: 2)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Microelectronic Engineering     Open Access   (Followers: 12)
Advances in Power Electronics     Open Access   (Followers: 25)
Aerospace and Electronic Systems, IEEE Transactions on     Hybrid Journal   (Followers: 214)
American Journal of Electrical and Electronic Engineering     Open Access   (Followers: 24)
Annals of Telecommunications     Hybrid Journal   (Followers: 7)
Archives of Electrical Engineering     Open Access   (Followers: 12)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 8)
Bell Labs Technical Journal     Hybrid Journal   (Followers: 23)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 17)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 32)
Biomedical Instrumentation & Technology     Hybrid Journal   (Followers: 6)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 10)
BULLETIN of National Technical University of Ukraine. Series RADIOTECHNIQUE. RADIOAPPARATUS BUILDING     Open Access   (Followers: 1)
Bulletin of the Polish Academy of Sciences : Technical Sciences     Open Access  
Canadian Journal of Remote Sensing     Full-text available via subscription   (Followers: 41)
China Communications     Full-text available via subscription   (Followers: 7)
Circuits and Systems     Open Access   (Followers: 16)
Consumer Electronics Times     Open Access   (Followers: 6)
Control Systems     Hybrid Journal   (Followers: 190)
Edu Elektrika Journal     Open Access  
Electronic Design     Partially Free   (Followers: 79)
Electronic Markets     Hybrid Journal   (Followers: 8)
Electronic Materials Letters     Hybrid Journal   (Followers: 2)
Electronics     Open Access   (Followers: 60)
Electronics and Communications in Japan     Hybrid Journal   (Followers: 8)
Electronics For You     Partially Free   (Followers: 64)
Electronics Letters     Hybrid Journal   (Followers: 25)
Embedded Systems Letters, IEEE     Hybrid Journal   (Followers: 40)
Energy Harvesting and Systems : Materials, Mechanisms, Circuits and Storage     Hybrid Journal   (Followers: 3)
Energy Storage Materials     Full-text available via subscription   (Followers: 1)
EPJ Quantum Technology     Open Access  
EURASIP Journal on Embedded Systems     Open Access   (Followers: 12)
Facta Universitatis, Series : Electronics and Energetics     Open Access  
Foundations and Trends® in Communications and Information Theory     Full-text available via subscription   (Followers: 7)
Foundations and Trends® in Signal Processing     Full-text available via subscription   (Followers: 5)
Frequenz     Hybrid Journal   (Followers: 1)
Frontiers of Optoelectronics     Hybrid Journal   (Followers: 1)
Geoscience and Remote Sensing, IEEE Transactions on     Hybrid Journal   (Followers: 153)
Haptics, IEEE Transactions on     Hybrid Journal   (Followers: 3)
IEEE Antennas and Propagation Magazine     Hybrid Journal   (Followers: 73)
IEEE Antennas and Wireless Propagation Letters     Hybrid Journal   (Followers: 62)
IEEE Journal of Emerging and Selected Topics in Power Electronics     Hybrid Journal   (Followers: 32)
IEEE Journal of the Electron Devices Society     Open Access   (Followers: 9)
IEEE Journal on Exploratory Solid-State Computational Devices and Circuits     Hybrid Journal   (Followers: 1)
IEEE Power Electronics Magazine     Full-text available via subscription   (Followers: 49)
IEEE Transactions on Antennas and Propagation     Full-text available via subscription   (Followers: 54)
IEEE Transactions on Automatic Control     Hybrid Journal   (Followers: 49)
IEEE Transactions on Circuits and Systems for Video Technology     Hybrid Journal   (Followers: 17)
IEEE Transactions on Consumer Electronics     Hybrid Journal   (Followers: 33)
IEEE Transactions on Electron Devices     Hybrid Journal   (Followers: 15)
IEEE Transactions on Information Theory     Hybrid Journal   (Followers: 27)
IEEE Transactions on Power Electronics     Hybrid Journal   (Followers: 56)
IEEE Transactions on Signal and Information Processing over Networks     Full-text available via subscription   (Followers: 7)
IEICE - Transactions on Electronics     Full-text available via subscription   (Followers: 15)
IEICE - Transactions on Information and Systems     Full-text available via subscription   (Followers: 7)
IET Microwaves, Antennas & Propagation     Hybrid Journal   (Followers: 30)
IET Power Electronics     Hybrid Journal   (Followers: 30)
IET Wireless Sensor Systems     Hybrid Journal   (Followers: 17)
IETE Journal of Education     Open Access   (Followers: 4)
IETE Journal of Research     Open Access   (Followers: 11)
IETE Technical Review     Open Access   (Followers: 11)
IJEIS (Indonesian Journal of Electronics and Instrumentation Systems)     Open Access  
Industrial Electronics, IEEE Transactions on     Hybrid Journal   (Followers: 39)
Industry Applications, IEEE Transactions on     Hybrid Journal   (Followers: 10)
Informatik-Spektrum     Hybrid Journal   (Followers: 2)
Instabilities in Silicon Devices     Full-text available via subscription  
Intelligent Transportation Systems Magazine, IEEE     Full-text available via subscription   (Followers: 8)
International Journal of Advanced Research in Computer Science and Electronics Engineering     Open Access   (Followers: 17)
International Journal of Advances in Telecommunications, Electrotechnics, Signals and Systems     Open Access   (Followers: 7)
International Journal of Antennas and Propagation     Open Access   (Followers: 11)
International Journal of Applied Electronics in Physics & Robotics     Open Access   (Followers: 4)
International Journal of Computational Vision and Robotics     Hybrid Journal   (Followers: 4)
International Journal of Computer & Electronics Research     Full-text available via subscription   (Followers: 2)
International Journal of Control     Hybrid Journal   (Followers: 13)
International Journal of Electronics     Hybrid Journal   (Followers: 5)
International Journal of Electronics & Data Communication     Open Access   (Followers: 11)
International Journal of Electronics and Telecommunications     Open Access   (Followers: 12)
International Journal of Granular Computing, Rough Sets and Intelligent Systems     Hybrid Journal   (Followers: 2)
International Journal of High Speed Electronics and Systems     Hybrid Journal  
International Journal of Image, Graphics and Signal Processing     Open Access   (Followers: 10)
International Journal of Nano Devices, Sensors and Systems     Open Access   (Followers: 6)
International Journal of Nanoscience     Hybrid Journal   (Followers: 1)
International Journal of Numerical Modelling: Electronic Networks, Devices and Fields     Hybrid Journal   (Followers: 3)
International Journal of Power Electronics     Hybrid Journal   (Followers: 14)
International Journal of Review in Electronics & Communication Engineering     Open Access   (Followers: 4)
International Journal of Sensors, Wireless Communications and Control     Hybrid Journal   (Followers: 7)
International Journal of Systems, Control and Communications     Hybrid Journal   (Followers: 4)
International Journal of Wireless and Microwave Technologies     Open Access   (Followers: 6)
International Journal on Communication     Full-text available via subscription   (Followers: 13)
International Journal on Electrical and Power Engineering     Full-text available via subscription   (Followers: 8)
International Transaction of Electrical and Computer Engineers System     Open Access   (Followers: 2)
Journal of Biosensors & Bioelectronics     Open Access   (Followers: 3)
Journal of Advanced Dielectrics     Open Access   (Followers: 1)
Journal of Artificial Intelligence     Open Access   (Followers: 8)
Journal of Circuits, Systems, and Computers     Hybrid Journal   (Followers: 4)
Journal of Computational Intelligence and Electronic Systems     Full-text available via subscription   (Followers: 1)
Journal of Electrical and Electronics Engineering Research     Open Access   (Followers: 18)
Journal of Electrical Bioimpedance     Open Access   (Followers: 2)
Journal of Electrical Engineering & Electronic Technology     Hybrid Journal   (Followers: 7)
Journal of Electromagnetic Analysis and Applications     Open Access   (Followers: 6)
Journal of Electromagnetic Waves and Applications     Hybrid Journal   (Followers: 5)
Journal of Electronic Design Technology     Full-text available via subscription   (Followers: 6)
Journal of Electronics (China)     Hybrid Journal   (Followers: 4)
Journal of Energy Storage     Full-text available via subscription  
Journal of Field Robotics     Hybrid Journal   (Followers: 2)
Journal of Guidance, Control, and Dynamics     Full-text available via subscription   (Followers: 136)
Journal of Intelligent Procedures in Electrical Technology     Open Access   (Followers: 3)
Journal of Low Power Electronics     Full-text available via subscription   (Followers: 7)
Journal of Low Power Electronics and Applications     Open Access   (Followers: 6)
Journal of Microwaves, Optoelectronics and Electromagnetic Applications     Open Access   (Followers: 9)
Journal of Nuclear Cardiology     Hybrid Journal  
Journal of Optoelectronics Engineering     Open Access   (Followers: 2)
Journal of Physics B: Atomic, Molecular and Optical Physics     Hybrid Journal   (Followers: 31)
Journal of Power Electronics & Power Systems     Full-text available via subscription   (Followers: 9)
Journal of Semiconductors     Full-text available via subscription   (Followers: 4)
Journal of Sensors     Open Access   (Followers: 22)
Journal of Signal and Information Processing     Open Access   (Followers: 8)
Jurnal Rekayasa Elektrika     Open Access  
Learning Technologies, IEEE Transactions on     Hybrid Journal   (Followers: 14)
Magnetics Letters, IEEE     Hybrid Journal   (Followers: 7)
Majalah Ilmiah Teknologi Elektro : Journal of Electrical Technology     Open Access   (Followers: 2)
Metrology and Measurement Systems     Open Access   (Followers: 4)
Microelectronics and Solid State Electronics     Open Access   (Followers: 15)
Nanotechnology Magazine, IEEE     Full-text available via subscription   (Followers: 31)
Nanotechnology, Science and Applications     Open Access   (Followers: 5)
Networks: an International Journal     Hybrid Journal   (Followers: 5)
Open Journal of Antennas and Propagation     Open Access   (Followers: 8)
Optical Communications and Networking, IEEE/OSA Journal of     Full-text available via subscription   (Followers: 14)
Paladyn, Journal of Behavioral Robotics     Open Access  
Progress in Quantum Electronics     Full-text available via subscription   (Followers: 7)
Pulse     Full-text available via subscription   (Followers: 5)
Radiophysics and Quantum Electronics     Hybrid Journal   (Followers: 2)
Recent Patents on Electrical & Electronic Engineering     Full-text available via subscription   (Followers: 9)
Recent Patents on Telecommunications     Full-text available via subscription   (Followers: 2)
Research & Reviews : Journal of Embedded System & Applications     Full-text available via subscription   (Followers: 4)
Security and Communication Networks     Hybrid Journal   (Followers: 3)
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of     Hybrid Journal   (Followers: 49)
Semiconductors and Semimetals     Full-text available via subscription   (Followers: 1)
Sensing and Imaging : An International Journal     Hybrid Journal   (Followers: 2)
Services Computing, IEEE Transactions on     Hybrid Journal   (Followers: 5)
Software Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 66)
Solid-State Circuits Magazine, IEEE     Hybrid Journal   (Followers: 12)
Solid-State Electronics     Hybrid Journal   (Followers: 8)
Superconductor Science and Technology     Hybrid Journal   (Followers: 2)
Synthesis Lectures on Power Electronics     Full-text available via subscription   (Followers: 3)
Technical Report Electronics and Computer Engineering     Open Access  
Telematique     Open Access  
TELKOMNIKA (Telecommunication, Computing, Electronics and Control)     Open Access   (Followers: 7)
Universal Journal of Electrical and Electronic Engineering     Open Access   (Followers: 6)
Visión Electrónica : algo más que un estado sólido     Open Access  
Wireless and Mobile Technologies     Open Access   (Followers: 5)
Women in Engineering Magazine, IEEE     Full-text available via subscription   (Followers: 12)
Електротехніка і Електромеханіка     Open Access  

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Journal Cover Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of
  [SJR: 1.196]   [H-I: 37]   [49 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1939-1404
   Published by IEEE Homepage  [191 journals]
  • Frontcover
    • Abstract: Presents the front cover for this issue of the publication.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • IEEE Geoscience and Remote Sensing Societys
    • Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and society editors for this issue of the publication.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Information for Authors
    • Abstract: These instructions give guidelines for preparing papers for this publication. Presents information for authors publishing in this journal.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Institutional Listings
    • Abstract: Presents a listing of institutional institutions relevant for this issue of the publication.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Foreword to the Special Issue on “New Challenges and Opportunities
           in Scatterometry”
    • Authors: J. Figa-Saldaña;K. Scipal;D. Long;M. A. Bourassa;W. Wagner;A. Stoffelen;
      Pages: 2083 - 2085
      Abstract: The papers in this special section were presented at the 2016 EUMETSAT and ESA conference which explored recent advances in scatterometry and to prepare for the development and exploitation of MetOp-SG scatterometer data.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Scientific Developments and the EPS-SG Scatterometer
    • Authors: Ad Stoffelen;Signe Aaboe;Jean-Christophe Calvet;James Cotton;Giovanna De Chiara;Julia Figa Saldaña;Alexis Aurélien Mouche;Marcos Portabella;Klaus Scipal;Wolfgang Wagner;
      Pages: 2086 - 2097
      Abstract: The second-generation exploitation of meteorological satellite polar system (EPS-SG) C-band-wavelength scatterometer instrument (called SCA), planned for launch in 2022, has a direct heritage from the successful advanced scatterometer (ASCAT) flown on the current EPS satellites. In addition, SCA will represent three major innovations with respect to ASCAT, namely: 1) Cross polarization and horizontal copolarization; 2) a nominal spatial resolution of 25 km; and 3) 20% greater spatial coverage than ASCAT. The associated expected science and application benefits that led the SCA design are discussed with respect to ocean, land, and sea ice applications for near-real time, climate monitoring, and research purposes. Moreover, an option to implement an ocean Doppler capability to retrieve the ocean motion vector is briefly discussed as well. In conclusion, the SCA instrument innovations are well set to provide timely benefits in all the main application areas of the scatterometer (winds, soil moisture, sea ice) and can be expected to contribute to new and more sophisticated meteorological, oceanographic, land, sea ice, and climate services in the forthcoming SCA era.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Three Generations of C-Band Wind Scatterometer Systems From ERS-1/2 to
           MetOp/ASCAT, and MetOp Second Generation
    • Authors: Chung-Chi Lin;Wolfgang Lengert;Evert Attema;
      Pages: 2098 - 2122
      Abstract: The C-band wind scatterometer service to the meteorological community started with the launch of the first European radar satellite ERS-1 on July 17, 1991, followed by its twin-satellite ERS-2 launched on April 21, 1995. The continuity of the ocean surface wind observations after ERS was ensured by the first series of operational polar orbiting meteorological satellites, with MetOp-A and MetOp-B satellites launched on October 19, 2006 and September 17, 2012, respectively. The launch of MetOp-C is planned in 2018 which will ensure a gap-less service until the start of the second generation MetOp mission (MetOp -SG) in 2021/22 for a mission duration of 21 years for the latter. This paper presents an overview of the developments and operations of the ERS and MetOp wind scatterometer systems, concluding with the initial definition of the MetOp-SG scatterometer requirements and design. Technical challenges encountered during the development of the first C-band system (ERS) are briefly described. Lessons learned from the experience of the ERS mission have been reflected in the definition of the MetOp/ASCAT mission, which is currently operated by EUMETSAT. Driven by the progress in the NWP models and increasing demands on providing accurate observations of extreme weather events, such as high intensity storms, the third generation of wind scatterometer on-board MetOp-SG will provide yet higher spatial resolution data with extended wind speed dynamic range. The latter enhancement is enabled by the addition of a cross-polarized backscatter component measurement on top of the VV-polarization capability as implemented in the ERS and MetOp systems.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • The CMOD7 Geophysical Model Function for ASCAT and ERS Wind Retrievals
    • Authors: Ad Stoffelen;Jeroen Adriaan Verspeek;Jur Vogelzang;Anton Verhoef;
      Pages: 2123 - 2134
      Abstract: A new geophysical model function (GMF), called CMOD7, has been developed for intercalibrated ERS (ESCAT) and ASCAT C-band scatterometers. It is valid for their combined incidence angle range and being used to generate wind climate data records. CMOD7 has been developed in several steps as a successor of CMOD5.n. First, CMOD5.n has been adapted to the ASCAT transponder calibration, which is considered more accurate than any ESCAT gain calibration. This results in a linear scaling of the backscatter values. Second, for low winds, there is a clear mismatch between CMOD5.n and the measurements. An independently developed ASCAT C-band GMF, C2013, which performs particularly well for low winds was adopted to improve low winds for the ASCAT incidence angle range. Third, retrievals with CMOD5.n show wind speed probability distribution functions (pdf) that undesirably depend on wind vector cell (WVC) position across the swath. To overcome this effect, a higher order calibration is applied, which matches the wind speed pdfs for all WVCs of ASCAT and ESCAT. The resulting CMOD7 GMF indeed shows overall improved performance on all relevant quality parameters compared to CMOD5.n. It is found that the standard deviations of error for wind speed and wind direction of ASCAT are improved. The same holds for the maximum-likelihood estimates, showing an 8% improved consistency with the local triplet of backscatter measurements. As a consequence, triple collocation with moored buoy and numerical weather prediction winds results in smaller wind vector components and wind direction retrieval errorsim.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • SST Dependence of Ku- and C-Band Backscatter Measurements
    • Authors: Zhixiong Wang;Ad Stoffelen;Franco Fois;Anton Verhoef;Chaofang Zhao;Mingsen Lin;Ge Chen;
      Pages: 2135 - 2146
      Abstract: The normalized radar cross section (NRCS) measured by satellite ocean radar systems is representative of the sea surface roughness at the scale of gravity-capillary waves, which are not only dominated by winds, but also modulated by some secondary factors such as sea surface temperature (SST) and sea surface salinity (SSS). In this paper, the variations of NRCS due to SST changes, depending on scatterometer radar frequency, polarization, and incidence angle, are investigated on the basis of a physics-based radar backscatter model and a dataset of collocated ASCAT C-band and RapidScat Ku-band scatterometer measurements. The study shows that the SST effects are substantial at Ku-band, but rather negligible for C-band NRCS measurements. Furthermore, the SST effects are wind speed dependent and more pronounced in VV polarization and at higher incidence angles. SSS effects, due to dielectric constant, surface tension, and dynamic viscosity variations, on scatterometer winds are limited (within 1%). This study concludes that it is necessary to take SST into account in scatterometer wind retrieval for radar wavelengths smaller than C-band.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Sea State Impacts on Wind Speed Retrievals From C-Band Radars
    • Authors: Justin Edward Stopa;Alexis Aurélien Mouche;Bertrand Chapron;Fabrice Collard;
      Pages: 2147 - 2155
      Abstract: Scatterometers, a proven technology, provide ocean wind speeds and directions that are essential in operational forecasts, monitoring of the climate, and scientific applications. While the missions and geophysical model functions are performing well, challenges remain. We analyze data from advanced scatterometer (ASCAT) aboard MetOp-A and the advanced synthetic aperture radar (ASAR) aboard Envisat, both of which operate in the C-band, against the in situ buoy wind speeds. We observe large variability in the wind speed residuals. Through analysis of these residuals, we find that they are related to sea state effects and atmospheric stability. The sea state dependence created by low-frequency swells is more pronounced for the lower incidence angles in ASCAT. In ASAR with a fixed angle of 23°, the sea state dominates the wind speed errors and these trends increase with the significant wave height. We observe that wind speeds from ASAR and ASCAT have a close resemblance, which helps us to extrapolate our findings. The synergy between the two technologies can be further exploited to improve wind speed retrievals. Future scatterometer missions, such as the next MetOp, will operate with the wider range of incidence angles (including lower angles) to increase their coverage together, have higher spatial resolution, and obtain measurements closer to the coasts. In these cases, high-resolution SAR data can aide in the understanding of the radar response.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Toward an Improved Wind Inversion Algorithm for RapidScat
    • Authors: Wenming Lin;Marcos Portabella;Ad Stoffelen;Anton Verhoef;
      Pages: 2156 - 2164
      Abstract: The sea-surface winds from the RapidScat scatterometer (RSCAT) onboard the International Space Station (ISS) have been produced using the Pencil-beam scatterometer Wind Processor (PenWP) since December 2014. An inversion residual or Maximum Likelihood Estimator (MLE-) based quality control (QC) algorithm is included in PenWP to distinguish between goodand poor-quality winds. Generally, the QC-accepted RSCAT winds are in good agreement with both the Advanced Scatterometer (ASCAT) winds and the European Centre for Medium-range Weather Forecasting (ECMWF) model output. In contrast, the QC-rejected winds present an overall positive bias with respect to ASCAT and ECMWF winds, mainly due to the impact of rain. However, it has been recently found that a considerable portion (>5%) of RSCAT QC-rejected contains anomalously low retrieved speeds (ω 10 m/s) according to ASCAT/ECMWF. This paper attempts to sort out the cause for these spuriously low winds. A revised MLE inversion with prefiltering the anomalous backscatters is proposed to correct the mentioned inversion issue. The impact of such improved inversion on the retrieved RSCAT winds is evaluated using both the collocated ASCAT and ECMWF winds. The results show that the proposed algorithm improves the wind retrieval of the spuriously low wind cases remarkably, while preserving about 4.7% of the nominal QC-rejected data (0.25% in total).
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Evaluating and Extending the Ocean Wind Climate Data Record
    • Authors: Frank J. Wentz;Lucrezia Ricciardulli;Ernesto Rodriguez;Bryan W. Stiles;Mark A. Bourassa;David G. Long;Ross N. Hoffman;Ad Stoffelen;Anton Verhoef;Larry W. O'Neill;J. Tomas Farrar;Douglas Vandemark;Alexander G. Fore;Svetla M. Hristova-Veleva;F. Joseph Turk;Robert Gaston;Douglas Tyler;
      Pages: 2165 - 2185
      Abstract: Satellite microwave sensors, both active scatterometers and passive radiometers, have been systematically measuring near-surface ocean winds for nearly 40 years, establishing an important legacy in studying and monitoring weather and climate variability. As an aid to such activities, the various wind datasets are being intercalibrated and merged into consistent climate data records (CDRs). The ocean wind CDRs (OW-CDRs) are evaluated by comparisons with ocean buoys and intercomparisons among the different satellite sensors and among the different data providers. Extending the OW-CDR into the future requires exploiting all available datasets, such as OSCAT-2 scheduled to launch in July 2016. Three planned methods of calibrating the OSCAT-2 σo measurements include 1) direct Ku-band σo intercalibration to QuikSCAT and RapidScat; 2) multisensor wind speed intercalibration; and 3) calibration to stable rainforest targets. Unfortunately, RapidScat failed in August 2016 and cannot be used to directly calibrate OSCAT-2. A particular future continuity concern is the absence of scheduled new or continuation radiometer missions capable of measuring wind speed. Specialized model assimilations provide 30-year long high temporal/spatial resolution wind vector grids that composite the satellite wind information from OW-CDRs of multiple satellites viewing the Earth at different local times.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Long-Term Scatterometer Wind Climate Data Records
    • Authors: Anton Verhoef;Jur Vogelzang;Jeroen Verspeek;Ad Stoffelen;
      Pages: 2186 - 2194
      Abstract: The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Ocean and Sea Ice Satellite Application Facility (OSI SAF) produces near-real-time scatterometer ocean vector winds since almost 20 years already. Data from the European remote sensing satellites (ERS-1 and ERS-2 scatterometer), QuikSCAT (SeaWinds), Metop (ASCAT), Oceansat 2 (OSCAT), and RapidScat on the International Space Station have been, or are being, produced. The OSI SAF scatterometer products, produced at the Royal Netherlands Meteorological Institute, provide superior comparison to both buoy and numerical weather prediction (NWP) datasets. Moreover, the wind processing software is publicly available through the EUMETSAT NWP SAF. An increasing amount of users employs scatterometer wind data for climate studies. However, the wind retrieval algorithms have been continuously improved over the years and the currently existing archives of near-real-time data are not always suitable to fulfill the need for homogeneous datasets spanning a longer period of time. Currently, only few validated vector wind climate datasets are available. Therefore, the OSI SAF is reprocessing several offline datasets. This paper is focusing on two climate data records from SeaWinds and ASCAT winds, which together span the period from 1999 to 2014. The data are compared to the NWP model and buoy winds. The stability of the wind characteristics is assessed and an attempt is made to attribute temporal changes to climatological and NWP model changes over time.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Cone Metrics: A New Tool for the Intercomparison of Scatterometer Records
    • Authors: Maria Belmonte Rivas;Ad Stoffelen;Jeroen Verspeek;Anton Verhoef;Xavier Neyt;Craig Anderson;
      Pages: 2195 - 2204
      Abstract: With an eye on the generation of a long-term climate record of ocean winds, soil moisture, and sea ice extents across the C-band ERS and ASCAT scatterometer spans, a new calibration tool termed cone metrics has been developed. The new method is based on monitoring changes in the location and shape of the surface of maximum density of ocean backscatter measurements, also known as “the wind cone.” The cone metrics technique complements established calibration approaches, such as rain forest and NWP ocean calibration, through the characterization of linear as well as nonlinear beam offsets, the latter via wind cone deformations. Given instrument evolution, proven stability, and the monitoring by transponders, we take ASCAT-A data over 2013 as absolute calibration reference. This paper describes the new method and its application as intercalibration tool in the context of the reprocessing activities for ERS-1 and ERS-2. Cone metrics succeeds at establishing the linear and nonlinear corrections necessary to homogenize the ASCAT and ERS C-band records down to 0.05 dB.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Platform and Across-Swath Comparison of Vorticity Spectra From QuikSCAT,
           ASCAT-A, OSCAT, and ASCAT-B Scatterometers
    • Authors: Heather M. Holbach;Mark A. Bourassa;
      Pages: 2205 - 2213
      Abstract: In the last few years, there has been tremendous improvement in the calibration of ocean surface vector winds from scatterometers and polarimetric radiometers. This is the first detailed investigation of across-swath consistency in scatterometer-derived (i.e., QSCAT, ASCAT-A, OSCAT, and ASCAT-B) vorticity (curl of the ocean surface vector winds). Spatial derivatives of the winds fields are very important for atmospheric boundary-layer processes, upper ocean forcing, and deep ocean forcing. Improvements in wind calibration imply improvements in derivatives of these winds; however, it does not imply consistency. This study demonstrates near consistency in across-swath vorticity and near consistency between platforms.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Comparison of SeaWinds Backscatter Imaging Algorithms
    • Authors: David G. Long;
      Pages: 2214 - 2231
      Abstract: This paper compares the performance and tradeoffs of various backscatter imaging algorithms for the SeaWinds scatterometer when multiple passes over a target are available. Reconstruction methods are compared with conventional gridding algorithms. In particular, the performance and tradeoffs in conventional “drop in the bucket” (DIB) gridding at the intrinsic sensor resolution are compared to high-spatial-resolution imaging algorithms such as fine-resolution DIB and the scatterometer image reconstruction (SIR) that generate enhanced-resolution backscatter images. Various options for each algorithm are explored, including considering both linear and dB computation. The effects of sampling density and reconstruction quality versus time are explored. Both simulated and actual data results are considered. The results demonstrate the effectiveness of high-resolution reconstruction using SIR as well as its limitations and the limitations of DIB and fine-resolution DIB.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Validation and Cross-Validation Methods for ASCAT
    • Authors: Craig Anderson;Julia Figa-Saldaña;John Julian William Wilson;Francesca Ticconi;
      Pages: 2232 - 2239
      Abstract: The advanced scatterometer (ASCAT) is a fan beam scatterometer carried on board the Metop series of satellites. Its primary objective is to measure ocean backscatter for the retrieval of ocean wind vectors. Two ASCAT instruments (ASCAT-A and ASCAT-B) are operational and are independently calibrated using a number of ground-based transponders. The first seven years of data from ASCAT-A have recently been processed into a climate data record. This paper describes a number of methods for cross-validating the data from the two instruments and for assessing the quality and stability of the climate data record. The methods are based on backscatter from the Amazon rainforest, mean backscatter from the open ocean, comparison of measured and modeled ocean backscatter, and ocean cone metrics. These methods show that the climate data record, which covers the period January 2007 to March 2014, has a very high stability (with trends around 0.005 dB per year), good absolute and relative calibration (better than 0.1 dB), and a good across swath calibration (peak to peak variation of less than 0.1 dB). For operational data covering the period April 2015 to March 2016, the methods indicate that ASCAT-B backscatter is around 0.1-0.2 dB higher than ASCAT-A (depending on which beam is considered). This difference is due to a combination of factors: minor changes in calibration algorithms, a minor change in the behavior of the ASCAT-A internal calibration system, and the strategy used to update calibration files in the processing system.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Assessing Vegetation Dynamics Over Mainland Australia With Metop ASCAT
    • Authors: Mariette Vreugdenhil;Sebastian Hahn;Thomas Melzer;Bernhard Bauer-Marschallinger;Christoph Reimer;Wouter Arnoud Dorigo;Wolfgang Wagner;
      Pages: 2240 - 2248
      Abstract: Recently, the slope and curvature estimation of the backscatter-incidence angle relationship within the TU Wien retrieval algorithm has been improved. Where previously only climatologies of the slope and curvature parameters were available, i.e., one value for every day of year, slope and curvature are now calculated for every day. This enables the retrieval of time series of vegetation optical depth (τa) from backscatter observations. This study demonstrates the ability to detect interannual variability in vegetation dynamics using τa derived from backscatter provided by the advanced scatterometer on-board Metop-A. τa time series over Australia for the period 2007-2014 are compared to leaf area index (LAI) from SPOT-VEGETATION by calculating the rank correlation coefficient (τa) for original time series and anomalies. High values for τa are found over bare soil and sparse vegetation in central Australia with median τa values of 0.78 and 0.58, respectively. Forests and ephemeral lakes and rivers impact the retrieval of τa, and the negative values for τa are found in these areas. Looking at the annual averages of τa, LAI, and surface soil moisture, significantly high values are found for the anomalously wet years 2010 and 2011. Patterns in the increased τa correspond to regions with increased soil moisture and LAI. Values for τa and LAI are anomalous especially in sparsely vegetated regions, where the flush of grasses increases τa and LAI. Regions with enough precipitation and higher woody vegetation component show a smaller increase in 2010 and 2011. This study demonstrates the skill of τ-, and subsequently of scatterometers, to monitor the vegetation dynamics thanks to the multiincidence angle observation capability.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Radar Remote Sensing of Agricultural Canopies: A Review
    • Authors: Susan C. Steele-Dunne;Heather McNairn;Alejandro Monsivais-Huertero;Jasmeet Judge;Pang-Wei Liu;Kostas Papathanassiou;
      Pages: 2249 - 2273
      Abstract: Observations from spaceborne radar contain considerable information about vegetation dynamics. The ability to extract this information could lead to improved soil moisture retrievals and the increased capacity to monitor vegetation phenology and water stress using radar data. The purpose of this review paper is to provide an overview of the current state of knowledge with respect to backscatter from vegetated (agricultural) landscapes and to identify opportunities and challenges in this domain. Much of our understanding of vegetation backscatter from agricultural canopies stems from SAR studies to perform field-scale classification and monitoring. Hence, SAR applications, theory, and applications are considered here too. An overview will be provided of the knowledge generated from ground-based and airborne experimental campaigns that contributed to the development of crop classification, crop monitoring, and soil moisture monitoring applications. A description of the current vegetation modeling approaches will be given. A review of current applications of spaceborne radar will be used to illustrate the current state of the art in terms of data utilization. Finally, emerging applications, opportunities and challenges will be identified and discussed. Improved representation of vegetation phenology and water dynamics will be identified as essential to improve soil moisture retrievals, crop monitoring, and for the development of emerging drought/water stress applications.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Triple Collocation Analysis of Soil Moisture From Metop-A ASCAT and SMOS
           Against JRA-55 and ERA-Interim
    • Authors: Kengo Miyaoka;Alexander Gruber;Francesca Ticconi;Sebastian Hahn;Wolfgang Wagner;Julia Figa-Saldaña;Craig Anderson;
      Pages: 2274 - 2284
      Abstract: This study investigates the quality of Advanced Scatterometer (ASCAT) surface soil moisture (SSM) retrievals with respect to other SSM products derived from the passive Soil Moisture and Ocean Salinity (SMOS) mission and two reanalysis datasets, i.e., the JRA-55 and the ERA-Interim. In particular, the purposes of this study are to 1) characterize the global error structure of the satellite products, 2) understand the spatiotemporal variability of SSM at global scale, and 3) investigate in which areas the assimilation of satellite data may add value to reanalysis. For these purposes, we applied standard statistical methods as well as triple collocation analysis (TCA) for estimating signal-to-noise ratios (SNR). In line with previous studies, we find large and spatially variable biases between all four datasets, but overall spatiotemporal dynamics as reflected in Hovmöller diagrams agree well. With the exception of arid and semiarid environments, ASCAT performs better than SMOS in terms of both its correlation with the models and the SNR. As a result of TCA, we recognize the potential areas for assimilation of ASCAT data, characterized by a high SNR of the satellite data compared to the models, to be the savanna regions in Africa and Central Asia, southwestern North America, and eastern Australia.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • A Review of the Applications of ASCAT Soil Moisture Products
    • Authors: Luca Brocca;Wade T. Crow;Luca Ciabatta;Christian Massari;Patricia de Rosnay;Markus Enenkel;Sebastian Hahn;Giriraj Amarnath;Stefania Camici;Angelica Tarpanelli;Wolfgang Wagner;
      Pages: 2285 - 2306
      Abstract: Remote sensing of soil moisture has reached a level of good maturity and accuracy for which the retrieved products are ready to use in real-world applications. Due to the importance of soil moisture in the partitioning of the water and energy fluxes between the land surface and the atmosphere, a wide range of applications can benefit from the availability of satellite soil moisture products. Specifically, the Advanced SCATterometer (ASCAT) on board the series of Meteorological Operational (Metop) satellites is providing a near real time (and long-term, 9+ years starting from January 2007) soil moisture product, with a nearly daily (sub-daily after the launch of Metop-B) revisit time and a spatial sampling of 12.5 and 25 km. This study first performs a review of the climatic, meteorological, and hydrological studies that use satellite soil moisture products for a better understanding of the water and energy cycle. Specifically, applications that consider satellite soil moisture product for improving their predictions are analyzed and discussed. Moreover, four real examples are shown in which ASCAT soil moisture observations have been successfully applied toward: 1) numerical weather prediction, 2) rainfall estimation, 3) flood forecasting, and 4) drought monitoring and prediction. Finally, the strengths and limitations of ASCAT soil moisture products and the way forward for fully exploiting these data in real-world applications are discussed.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Polar Applications of Spaceborne Scatterometers
    • Authors: David G. Long;
      Pages: 2307 - 2320
      Abstract: Wind scatterometers were originally developed for observation of near-surface winds over the ocean. They retrieve wind indirectly by measuring the normalized radar cross section (σ°) of the surface, and estimating the wind via geophysical model function relating σ° to the vector wind. The σ° measurements have proven to be remarkably capable in studies of the polar regions where they can map snow cover; detect the freeze/thaw state of forest, tundra, and ice; map and classify sea ice; and track icebergs. Further, a long time series of scatterometer σ° observations is available to support climate studies. In addition to fundamental scientific research, scatterometer data are operationally used for sea-ice mapping to support navigation. Scatterometers are, thus, invaluable tools for monitoring the polar regions. In this paper, a brief review of some of the polar applications of spaceborne wind scatterometer data is provided. The paper considers both C-band and Ku-band scatterometers, and the relative merits of fan-beam and pencil-beam scatterometers in polar remote sensing are discussed.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • The ASCAT 6.25-km Wind Product
    • Authors: Jur Vogelzang;Ad Stoffelen;Richard D. Lindsley;Anton Verhoef;Jeroen Verspeek;
      Pages: 2321 - 2331
      Abstract: The advanced scatterometer (ASCAT) wind data processor (AWDP) produces ocean surface vector winds from radar measurements by the ASCAT on board the Metop satellites. So far, the ASCAT-coastal product with a grid size of 12.5 km has been the one with the highest resolution. Version 2.4 of AWDP, released May 2016, offers the possibility to process wind data on a 6.25 km grid. In this paper, the true spatial resolution and accuracy of that product is assessed using various methods. The crucial parameter is the radius of the area used to aggregate individual backscatter observations to a wind vector cell (WVC) level. A value of 7.5 km, half of that for ASCAT-coastal, appears to be the best compromise between resolution and accuracy. Spatial responses from multiple radar cross-section measurements are combined to cumulative responses, and show that the ASCAT-6.25 product has a spatial resolution of about 17 km, better than the 28 km found for the ASCAT-coastal product. The accuracy of the ASCAT-6.25 product is estimated using comparison with collocated buoys, triple collocation analysis, and a new method based on spatial variances. These methods show consistently that the ASCAT-6.25 product contains about 0.2 m2/s2 more noise in the wind components than the ASCAT-coastal product, due to the smaller number of individual measurements contributing to the average radar cross section in a WVC. The ASCAT-6.25 product is intended for applications that demand a spatial resolution as high as possible, like the study of dynamical mesoscale phenomena.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • ASCAT Ultrahigh-Resolution Wind Products on Optimized Grids
    • Authors: Jur Vogelzang;Ad Stoffelen;
      Pages: 2332 - 2339
      Abstract: The accuracy and spatial resolution of ultrahigh-resolution wind products derived from full-resolution ASCAT radar cross-section measurements are determined by the size and shape of the aggregation area. Current high-resolution products (ASCAT-coastal and ASCAT-6.25) are defined on a regular swath grid (size 12.5 and 6.25 km, respectively) and use a circular aggregation area (15 and 7.5 km radius resp.). For ASCAT-6.25, such approach leads to poor radar sampling, causing noise in the retrieved winds, and poor beam overlap, causing geophysical errors. More regular radar sampling and improved beam overlap can be obtained by using a grid that is synchronized with respect to the ASCAT mid-beam full-resolution measurements. This results in a new generation of ASCAT wind products. It is shown that a product on a 5.6 km grid size (on average) with optimized radar sampling compares better to buoys than ASCAT-6.25, but at the cost of an irregular grid and slightly degraded spatial resolution.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Improved Use of Scatterometer Measurements by Using Stress-Equivalent
           Reference Winds
    • Authors: Jos de Kloe;Ad Stoffelen;Anton Verhoef;
      Pages: 2340 - 2347
      Abstract: Numerical weather prediction (NWP) and buoy ocean surface winds show some systematic differences with satellite scatterometer and radiometer wind measurements, both in statistical results and in local geographical regions. It is possible to rescale these reference winds to remove certain aspects of these systematic differences. Space-borne ocean surface winds actually measure ocean surface roughness, which is related more directly to stress. Air mass density is relevant in the air-sea momentum transfer as captured in the stress vector. Therefore, apart from the already common “neutral wind correction” for atmospheric stratification, also a “mass density wind correction” is investigated here to obtain a better correspondence between satellite stress measurements and buoy or NWP winds. The bicorrected winds are called stress-equivalent winds. Stress-equivalent winds do not strongly depend on the drag formulation used and provide a rather direct standard for comparison and assimilation in user applications. This paper presents details on how this correction is performed and first results that show the benefits of this correction mainly in the extratropical regions.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Dynamic Characterization of the Incidence Angle Dependence of Backscatter
           Using Metop ASCAT
    • Authors: Sebastian Hahn;Christoph Reimer;Mariette Vreugdenhil;Thomas Melzer;Wolfgang Wagner;
      Pages: 2348 - 2359
      Abstract: Observing a target from different look and incidence angles is one of the key features of the Advanced Scatterometer (ASCAT) on-board the series of Metop satellites. The incidence angle dependency of backscatter plays an important role in extracting useful information for the retrieval of geophysical parameters. The TU Wien change detection algorithm exploits the multiangle measurement capabilities of ASCAT to retrieve relative surface soil moisture content. In the TU Wien algorithm, the incidence angle dependence of backscatter is characterized with a second-order polynomial and its coefficients are estimated from several years of data due to robustness. Recently, however, it has been shown by Melzer [1], that a kernel smoother (KS) holds promise to characterize the polynomial coefficients on an interannual basis. In this study, we tested the performance and robustness of the KS globally, by comparing the results obtained from ASCAT on-board Metop-A and Metop-B independently. Overall, a good agreement has been found between Metop-A and Metop-B confirming a robust interannual estimation of the incidence angle dependence of backscatter using the KS. However, in two cases, the prevailing conditions on the ground complicated the estimation: areas with very low signal variation and sandy deserts. An analysis of Hovmöller diagrams provided insight into seasonal variations, also revealing small remaining biases between the instruments. The dynamic characterization of the incidence angle dependence of backscatter allows to study the temporal evolution in more detail and, at the same time, moving a step further on the vegetation correction in the TU Wien soil moisture algorithm.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Analysis of Radio Frequency Interference in Metop ASCAT Backscatter
           Measurements
    • Authors: Francesca Ticconi;Craig Anderson;Julia Figa-Saldaña;John Julian William Wilson;Helmut Bauch;
      Pages: 2360 - 2371
      Abstract: The advanced scatterometer (ASCAT) is a radar system carried on board the ESA/EUMETSAT METOP series of satellites. It is designed for the purpose of retrieving wind field over oceans. It also provides information on surface soil moisture content and sea ice. Although ASCAT uses a linear frequency modulated pulse with a center frequency of 5.255 GHz (C-band), it is subject to radio frequency interference (RFI). This paper analyses seven years of ASCAT data and shows an increase of the number of noise outliers and an increase of the noise background level over specific land areas. This suggests that the outliers are not a natural occurrence, but are due to RFI from ground-based equipments. As regards the observed increase of the noise background level, it is not straightforward to associate possible RFI sources which could have caused it. However, since the ASCAT has a dynamic range of about 30 dB, the worse measured increase of 1 dB in the noise floor has almost no impact on performance, in particular, on soil moisture retrieval. In addition, the effect of the noise outliers on the estimate of the ASCAT receiver filter shape function used in the processing is also examined and is found to introduce errors of up to 0.4 dB. However, the occurrence of the noise outliers is generally very low, typically two out of 60 000 noise measurements per day, so the impact on the operational use of ASCAT data for wind vector retrieval is limited.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Spatial Resolution and Precision Properties of Scatterometer
           Reconstruction Algorithms
    • Authors: Liling Liu;Xiaolong Dong;Wenming Lin;Jintai Zhu;Di Zhu;
      Pages: 2372 - 2382
      Abstract: Various reconstruction methods have been used to enhance the spatial resolution of scatterometer data. Most of the image reconstructions are two-dimensional problems, which combine multiple passes of overlapping data over the temporally homogeneous surface, and thus are only suitable for land and ice applications. This paper attempts to address the one-dimensional reconstruction to enhance the azimuth resolution of scatterometer data using a single pass of observations. Since the range resolution determined by the on-board dechirping technique is generally up to several hundred meters, the one-dimensional reconstruction is adequate for certain near real-time ocean applications, such as the development of coastal scatterometer winds. Three well-known reconstruction algorithms, including additive algebraic reconstruction technique (AART), multiplicative algebraic reconstruction technique (MART), and scatterometer image reconstruction (SIR), are evaluated. The spatial resolution and the reconstruction precision resolved by each algorithm are separately analyzed using the local impulse response and Monte Carlo methods. The dependence of the spatial resolution and the reconstruction precision on a variety of parameters, such as the mean backscatter coefficient and its variance, the beamwidth of spatial response function (SRF), and the SRF function type, is evaluated using a simulation framework. In particular, the tradeoff between the spatial resolution and the reconstruction precision is examined for three algorithms. The results show that SIR offers the quickest convergence and lowest noise.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Toward Scatterometer Winds Assimilation in the Mesoscale HARMONIE Model
    • Authors: Gert-Jan Marseille;Ad Stoffelen;
      Pages: 2383 - 2393
      Abstract: Data assimilation (DA) experiments have been conducted with the high-resolution limited-area model HirLAM Aladin Regional Mesoscale Operational NWP In Euromed (HARMONIE), which is operational at most weather centers, which are part of the European HirLAM consortium. Recently, the assimilation of scatterometer ocean surface winds was introduced, showing limited forecast skill improvement. Possible explanations are discussed. These include model bias and the time mismatch between observation and analysis time, which introduces nonnegligible correlated errors in a three-dimensional (3-D) variational assimilation system. Also, ignoring the time mismatch increases the innovation, i.e., the observation minus background (model short-term forecast), by about 20% for scatterometer winds. The use of observations as point observations in most DA systems needs reconsideration for mesoscale DA. The introduction of observation operators, taking into account the instrument footprint, would improve the innovation by about 5% for scatterometer winds. Additional directions for improved use of observations in HARMONIE are discussed based on the notice that DA is an inherent deterministic concept. Hence, the selection of the spatial scale for deterministic DA should depend primarily on the 4-D observation coverage rather than the effective model resolution.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Assimilating Advanced Scatterometer Winds in a High-Resolution Limited
           Area Model Over Northern Europe
    • Authors: Teresa Valkonen;Harald Schyberg;Julia Figa-Saldaña;
      Pages: 2394 - 2405
      Abstract: Satellite-based scatterometer ocean surface wind measurements have been shown to improve global weather forecasts through data assimilation. However, these scatterometer data are not yet widely assimilated operationally in high-resolution regional models. This paper demonstrates the impact of assimilating Advanced Scatterometer (ASCAT) winds on the analysis and forecasts in observation system experiments using the convection-resolving operational HARMONIE-AROME model system over Northern Europe. At high latitudes, ASCAT provides dense observational data of meteorological phenomena, such as cold-air mesocyclones, particular in this region. Observation errors for ASCAT used in assimilation were found to be consistent with what was found in analysis of observation versus model background statistics, and no spatial error correlations were found on the 50 km separation distances. The largest impact of the assimilation of ASCAT winds was found over the ocean and in the coastal regions. Forecast verification against synoptic observations at coastal stations showed on average improvements for mean sea-level pressure and to some extent for 10-m wind speed on short forecast range. This varied only a little when changing the assimilation settings. Decreasing the data thinning distance from 100 to 50 km further improved forecasts, while shortening the assimilation window from 3 to 1 h did not yield a consistent forecast impact. The observation system experiments have confirmed that scatterometer winds contribute to improved analysis and forecasts in high-resolution regional modeling. This demonstrates general applicability of scatterometer observations for improving weather forecasts at high latitudes.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Estimating Random Errors of Scatterometer, Altimeter, and Model Wind Speed
           Data
    • Authors: Saleh Abdalla;Giovanna De Chiara;
      Pages: 2406 - 2414
      Abstract: Scatterometer and altimeter wind data are very important for data assimilation and verification of numerical weather prediction models. Standard deviation of absolute random errors can be estimated using the triple collocation technique. However, error correlations between various wind sources (e.g., due to data assimilation) complicate the error estimation. A method is used to alleviate the impact of error correlations between the scatterometer and the model that assimilates such data. Using twenty-two datasets of triplet composed of Jason-2 altimeter, Metop-A/B scatterometers (ASCAT-A/B, respectively), and ECMWF model analysis and forecasts (1 altimeter × 2 scatterometers × 11 model analysis and forecasts = 22 datasets) covering a period of two years from August 2013 to July 2015, the correlation coefficient between the errors of scatterometers and the model analysis was found to be about 0.33 for those datasets. This correlation reduces with forecast lead time until it almost vanishes at day seven. Altimeter and scatterometer errors are not correlated. The standard deviation of wind speed random errors of Jason-2, ASCAT-A/B, and the IFS analysis are estimated as 0.7, 0.8, and 0.9 m/s, respectively. As expected, there was no difference between ASCAT-A and ASCAT-B results.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
  • Improving the Assimilation of Scatterometer Wind Observations in Global
           NWP
    • Authors: Giovanna De Chiara;Massimo Bonavita;Stephen J. English;
      Pages: 2415 - 2423
      Abstract: This study aims at improving the assimilation of scatterometer wind observations in global Numerical Weather Prediction (NWP) model by refining the background quality control and optimizing the observation sampling strategy. To improve the background quality control, different Huber Norm distribution implementations are tested and compared against the current “Gaussian plus flat” distribution. Sensitivity experiments show that the usage of the Huber Norm distribution improves the analysis and forecasts. The benefit is mainly seen in the lower model levels in the tropics and extra-tropical Southern Hemisphere. The optimal wind sampling is investigated by testing several combinations of thinning scheme and observation error standard deviation. The impact is demonstrated with a large sample and illustrated by a case study. The case study shows the impact of different settings on the analysis and forecast of a tropical cyclone. A revised wind sampling setting, where four times more observations and a higher observation error than the current operational one are used, showed slightly positive impact on the European Centre for Medium-Range Weather Forecasts (ECMWF) global NWP analyses and forecasts.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
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    • Pages: 2424 - 2424
      Abstract: Advertisement, IEEE.
      PubDate: May 2017
      Issue No: Vol. 10, No. 5 (2017)
       
 
 
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