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Publisher: Elsevier   (Total: 3042 journals)

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Showing 1 - 200 of 3042 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 19, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 16, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 81, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 23, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 27, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 328, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription  
Acta de Investigación Psicológica     Open Access   (Followers: 2)
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Acta Pharmaceutica Sinica B     Open Access   (Followers: 2)
Acta Poética     Open Access   (Followers: 4)
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Acupuncture and Related Therapies     Hybrid Journal   (Followers: 3)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
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Additives for Polymers     Full-text available via subscription   (Followers: 20)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 124, SJR: 5.2, h-index: 222)
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Advances in Heat Transfer     Full-text available via subscription   (Followers: 20, SJR: 0.906, h-index: 24)
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Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 4)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.764, h-index: 15)
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Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
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Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 22)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
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Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
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Advances in Pediatrics     Full-text available via subscription   (Followers: 21, SJR: 0.4, h-index: 28)
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Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
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Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
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Advances in Psychology     Full-text available via subscription   (Followers: 58)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 2, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 339, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
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Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 15)
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Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 43, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 308, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 5, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 7, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 422, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 38, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 50, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 5, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 10, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 6)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access  
Algal Research     Partially Free   (Followers: 8, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 5, SJR: 0.776, h-index: 35)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 6, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 46, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 47, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 44, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 34, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 15, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 30, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 24, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 32, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 44, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 179, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 54, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 2)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 23, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 23, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 21, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 33, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 53, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 5)
Anales de Cirugia Vascular     Full-text available via subscription  
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Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 38, SJR: 1.548, h-index: 152)
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Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 153, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
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Journal Cover Advances in Space Research
  [SJR: 0.606]   [H-I: 65]   [339 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 0273-1177
   Published by Elsevier Homepage  [3042 journals]
  • Preface: The International Reference Ionosphere (IRI) at equatorial
           latitudes
    • Authors: Bodo Reinisch; Dieter Bilitza
      First page: 205
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Bodo Reinisch, Dieter Bilitza


      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2017.05.006
       
  • Study of ionospheric topside variations based on NeQuick topside
           formulation and comparisons with the IRI-2012 model at equatorial latitude
           station, Chumphon, Thailand
    • Authors: Punyawi Jamjareegulgarn; Pornchai Supnithi; Kornyanat Hozumi; Takuya Tsugawa
      Pages: 206 - 221
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Punyawi Jamjareegulgarn, Pornchai Supnithi, Kornyanat Hozumi, Takuya Tsugawa
      It is well-known that the equatorial anomaly at equatorial and low latitudes is caused by the fountain effect, therefore, the modeling of topside electron density profiles (EDPs) and the knowledge of electron density distribution in the region are particular challenging. Chumphon station, Thailand, is located within this region. However, at this station, since only an FMCW ionosonde system is installed, the topside EDP cannot be automatically obtained. Therefore, in this work, the topside EDPs are derived using the NeQuick topside formulation of the NeQuick 2 model (namely, NeQuick-derived topside EDPs) and then compared with those of three options of the IRI-2012 model including NeQuick, IRI01-corr, and IRI2001 options. The results show that, at Chumphon station, the NeQuick-derived topside EDPs are generally closer to the topside EDPs of IRI01-corr option in winter season and the topside EDPs of NeQuick option in equinox and summer seasons. When analyzing the topside TEC values obtained from each profile and the IGS TEC, it is found that the topside TEC values integrated from NeQuick-derived topside EDPs and predicted by both IRI01-corr and IRI-2001 options of the IRI-2012 model are sometimes higher than the IGS TEC values observed at Chumphon. In addition, we study the diurnal variations of the scale height computed from NeQuick topside formulation (Hsc ), hmF2 and foF2 parameters. The correlation of Hsc with the parameters hmF2 and the bottomside thickness parameter of NeQuick model (B2bot). The computed Hsc values during daytime are lower than those during nighttime and they show non-linear correlations with hmF2 and B2bot. The main cause of these discrepancies are possibly due to the B2bot expressions used to compute the Hsc .

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2017.03.025
       
  • Comparison of the observed topside ionospheric and plasmaspheric electron
           content derived from the COSMIC podTEC measurements with the IRI_Plas
           model results
    • Authors: Man-Lian Zhang; Libo Liu; Weixing Wan; Baiqi Ning
      Pages: 222 - 227
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Man-Lian Zhang, Libo Liu, Weixing Wan, Baiqi Ning
      In this paper, variations of the topside ionospheric and plasmaspheric electron contents (TPEC) in the altitude range of ∼800 to 20,200km are compared with the IRI_Plas model results for the low (2008) and high (2012) solar activity years using TEC data (podTEC) derived from the upward-looking precise orbit determination antenna on board COSMIC low Earth orbit (LEO) satellites tracking the GPS signals. For each year, the dataset were divided into groups according to four seasons: M-Equinox (March, April), J-Solstice (May June, July and August), S-Equinox (September, October) and D-Solstice (January, February, November, and December). Our study showed that the IRI_Plas model is able to reproduce reasonably well the main features of the observational TPEC’s latitudinal, diurnal as well as seasonal variation tendency when no longitudinal difference is taken into account. However, there exist discrepancies between the observational TPEC and the model results. Except for the daytime hours in the Equinoctial seasons of the high solar activity year 2012 when the IRI_Plas model results showed an overestimation, in general, the IRI_Plas model results underestimate the observational ones, in particular at nighttime hours in the low-latitude region. When the longitudinal difference is taken into account, the comparison study showed that the longitudinal dependence effect shown in the observational TPEC’s seasonal variations was not captured by the IRI_Plas model result. Moreover, the IRI_Plas model results tend to show a double-peak structure in the low-latitude region, a feature not appearing in the observational results.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.10.025
       
  • Comparison of GPS-derived TEC with IRI-2012 and IRI-2007 TEC predictions
           at Surat, a location around the EIA crest in the Indian sector, during the
           ascending phase of solar cycle 24
    • Authors: N.C. Patel; S.P. Karia; K.N. Pathak
      Pages: 228 - 237
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): N.C. Patel, S.P. Karia, K.N. Pathak
      This paper presents a comparison of GPS-derived TEC with IRI-2012 and IRI-2007 TEC Predictions at Surat (21.16°N Geographic latitude, 72.78°E Geographic longitude, 12.90°N Geomagnetic latitude) a location around the Equatorial Ionisation Anomaly (EIA) crest in the Indian sector, during the Ascending Phase of Solar Cycle 24, for a period of three years (January 2010–December 2012). In this comparison, plasmaspheric electron content (PEC) contribution to the GPS-TEC has been removed. It is observed that percentage PEC contribution to the GPS-TEC varies from about ∼15% (at the noon local time) to about ∼30% (at the morning local time). From the monthly comparison of GPS-TEC with IRI-TEC, it is observed that, TEC predicted by both the models overestimates in June-2012 and underestimates TEC in November-2011, December-2011 and March-2011. For all other months IRI estimates the TEC well. From the seasonal comparison, it is observed that the peak time appears ∼1-h later than the actual peak time in Winter 2010, Summer 2011, and Equinox 2010 and 2012 (the result suggest that it may be due to discrepancies/disagreement of both the versions of the IRI model in estimating the peak density as well as the thickness and shape parameters of the electron density profiles). For the Summer season, the IRI-TEC estimates the TEC well for all the years. Further, the seasonal variation of the GPS-TEC for all the three years matches well with IRI-2012 model compared to IRI-2007 model. Also, the mean annual TEC is predicted well by both the versions of the IRI model.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.11.026
       
  • A comparison of TEC predicted by IRI-2012 with that measured at three
           different stations in low latitude Indian region for the years
           (2010–2012)
    • Authors: S.P. Karia; N.C. Patel; K.N. Pathak
      Pages: 238 - 249
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): S.P. Karia, N.C. Patel, K.N. Pathak
      The present study reports the comparison of GPS measured Total Electron Content (TEC) with that predicted by the latest IRI-2012 model at three different stations located within the Equatorial Ionization Anomaly region (EIA) in the Indian sector. The data used for the study are retrieved from three different stations, namely, Surat (geographic latitude 21.16°N, geographic longitude 72.78°E; geomagnetic latitude 12.90°N), Hyderabad (geographic latitude 17.25°N, geographic longitude 78.30°E; geomagnetic latitude 8.65°N) and Bangalore (geographic latitude 13.02°N, geographic longitude 77.57°E; geomagnetic latitude 4.58°N). The period of comparison is three years for rising solar activity from 2010 to 2012. Here it is to note that both Hyderabad and Bangalore are IGS station with the station code (HYDE and IISC respectively). The results for the comparison of seasonal variation shows a good agreement between the measured and modeled TEC for all seasons with deviation of (±15 TECU) for all three years at Surat and Bangalore and with a deviation of (±25 TECU) at Hyderabad. Both topside options NeQuick and IRI01-Corr derived nearly equal TEC at all three stations. It is observed that the GPS TEC data shows the EIA crest at (23.5°N) where as the IRI TEC predicts the EIA crest at (19.7°N) on an average for all the years 2010–2012.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.10.022
       
  • A comparison of GPS-TEC with IRI-TEC at low latitudes in China in 2006
    • Authors: Qingtao Wan; Guanyi Ma; Jinghua Li; Xiaolan Wang; Jiangtao Fan; Qi Li; Weijun Lu
      Pages: 250 - 256
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Qingtao Wan, Guanyi Ma, Jinghua Li, Xiaolan Wang, Jiangtao Fan, Qi Li, Weijun Lu
      A comparison between GPS derived total electron content (TEC) and IRI-2012 is studied at low latitudes in China in 2006. 4GPS receivers form a small scale GPS network, and the spatial coverage starts at (26.1°N, 119.3°E) and ends at (22.8°N, 108.3°E), the corresponding magnetic coordinate is from (19.6°N, 191.6°E) to (16.2°N, 180.4°E). The network covers a region at or near the northern crest of the equatorial anomaly with ∼11° and ∼3° in longitude and latitude, respectively. The GPS-TEC is computed with the grid-based method. The ABT-2009 and NeQuick are selected for the bottomside and topside profile model for IRI-2012. There are similar monthly and seasonal variation trends between GPS-TEC and IRI-TEC in 2006, while the peak value of GPS-TEC and IRI-TEC appear at different times. The IRI-TEC is almost larger than GPS-TEC at day time, while the difference is small at night time. The largest difference between GPS-TEC and IRI-TEC can reach 16.5TECU, and the ratio of the largest difference and GPS-TEC is about 65%. The largest latitudinal gradient of GPS-TEC at 22–24°N was 5TECU/deg, while that of IRI-TEC was 2.5TECU/deg. These above results indicate that the IRI-2012 can reproduce the TEC variation trends at low latitudes in China, but the IRI-2012 overestimates the GPS-TEC at day time in this region.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.12.002
       
  • Evaluation of ionospheric height assumption for single station GPS-TEC
           derivation
    • Authors: Weijun Lu; Guanyi Ma; Xiaolan Wang; Qingtao Wan; Jinghua Li
      Pages: 286 - 294
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Weijun Lu, Guanyi Ma, Xiaolan Wang, Qingtao Wan, Jinghua Li
      To investigate the effects of ionospheric single thin layer height on GPS based total electron content (TEC) derivation by a single station, the GPS dual frequency pseudoranges and carrier phases received in Beijing at solar minimum and maximum are used for derivation at different heights through grid method, Kalman filtering method and polynomial method respectively. Detailed analyses proceed to be conducted on derived vertical TEC (VTEC) and estimated instrumental biases as well as residual errors of slant TEC (STEC) and errors of satellite biases, during which derived VTEC is compared with VTEC offered by CODE and IRI2012. VTEC at receiver zenith derived through three methods tends to increase with the height, whereas that through grid method at relatively large height may be unsolvable. Biases estimated via Kalman filtering method and polynomial method are less affected by the height. Those via grid method at height below 400km are similar to those via other two methods, but the errors rise sharply above that value. Under the research condition the optimum height for Kalman filtering method as well as polynomial method at solar minimum is 380km, and 310km at solar maximum, while for grid method the optimum height ranges from 280km to 350km.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2017.01.019
       
  • Variations of B0 and B1 with the solar quiet Sq-current system and
           comparison with IRI-2012 model at Ilorin
    • Authors: S.A. Bello; M. Abdullah; N.S.A. Hamid; A. Yoshikawa; A.O. Olawepo
      Pages: 307 - 316
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): S.A. Bello, M. Abdullah, N.S.A. Hamid, A. Yoshikawa, A.O. Olawepo
      The ionospheric thickness (B0) and shape (B1) are bottomside profile parameters introduced by the International Reference Ionosphere (IRI) model. We have validated these parameters with the latest version of the IRI-2012 model and compared them with the solar quiet of geomagnetic H-component (SqH). The B0, B1 and SqH are calculated from the measurements obtained from digisonde DPS-4 sounder and the Magnetic Data Acquisition System (MAGDAS) magnetometer, respectively at Ilorin (geo latitude 8.50°N, geo longitude 4.68°E, and Magnetic dip 4.1°S) an equatorial station in the African sector. The study was for the year 2010, a year of low solar activity (with 27-day averaged solar index, F10.7=80sfu). The results show that B0 for the entire months was higher during the daytime than during the night time. On the other hand, the magnitude of B1during the daytime period is lower than nighttime values and exhibit oscillatory pattern. By comparing the experimental observations of the profile parameters with the IRI-2012 model prediction, we found that B0 was fairly represented by the IRI model options during the nighttime period while discrepancies exist between the model estimates and the experimental values during the morning till midday. A close agreement exists between the observed B1 values and IRI model options. We observed a positive and significant correlation coefficient between B0 and SqH indicating a plausible relationship between these parameters while a weak and negative correlation coefficient between B1 and SqH was observed. We concluded that the difference in the relationship of SqH and the profile parameters B0 and B1 observed can be attributed to their sensitivity to the electric field which is responsible for the E × B drift which in turn modulate the height of the F2.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2017.02.003
       
  • A new expression for computing the bottomside thickness parameter and
           comparisons with the NeQuick and IRI-2012 models during declining phase of
           solar cycle 23 at equatorial latitude station, Chumphon, Thailand
    • Authors: Punyawi Jamjareegulgarn; Pornchai Supnithi; Kornyanat Watthanasangmechai; Tatsuhiro Yokoyama; Takuya Tsugawa; Mamoru Ishii
      Pages: 329 - 346
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Punyawi Jamjareegulgarn, Pornchai Supnithi, Kornyanat Watthanasangmechai, Tatsuhiro Yokoyama, Takuya Tsugawa, Mamoru Ishii
      This paper proposes a new expression for computing the bottomside thickness parameter at equatorial latitude station, Chumphon (10.72°N, 99.37°E), Thailand. Its diurnal variations from 2004 to 2006 at this location are then studied. The proposed expression is derived based on two experimental data sources: FMCW ionosonde and dual-frequency GPS system, and some expressions of the NeQuick 2 model. Hence, after both the bottomside thickness parameter computed by the proposed equation, B2bot_Pro, and the bottomside shape parameter (namely, B1_Pro in this work) are computed, the bottomside electron density and the height where the bottomside electron density drops down to be 24% of the NmF2 (namely, h0.24) can be computed and shown in this work using the analytical functions of the IRI model. Moreover, the diurnal variations of the B2bot_Pro are compared with those computed from the NeQuick model, B2bot_NeQ, and the predicted B0 of the IRI-2012 model with ABT-2009 and Bil-2000 options (namely, “B0_ABT” and “B0_Bil”, respectively). The averaged, minimum, and maximum values of percentage deviations among these bottomside thickness parameters are also computed and shown in this work. Our results show that the diurnal variations of B2bot_Pro at Chumphon station have the following patterns: they start to increase during nighttime to the first peaks during pre-sunrise hours, and then decrease abruptly to their minimum values during sunrise hours. Afterward, they increase again to reach the second peaks around local noontime and fall gradually to their starting times during 20–04 LT. The diurnal variations of B2bot_Pro follow generally the same trends as those of the B2bot_NeQ and the B0_ABT, except pre-sunrise hours. The pre-sunrise peaks and sunrise collapses in both the B2bot_NeQ and the B0_ABT can be found occasionally. On the other hand, the diurnal variations in B2bot_Pro differ from those in B0_Bil due to the flattened variation in B0_Bil and the pre-sunrise peaks as well as sunrise collapses in B0_Bil disappear. The pre-sunrise peaks of the B2bot_Pro at the Chumphon station are higher than those of the B2bot_NeQ, the B0_ABT, and the observed B0 at other regions. Furthermore, the percentage deviations between the B2bot_Pro and the B0_ABT (PD_B2B0ABT) are mostly lower than 30% for all seasons of the studied years, opposite to the other percentage deviations studied in this work. The proposed B2bot_Pro parameters in this work follow a similar trend to the B2bot_NeQ and the B0_ABT, but it is not conclusive that the proposed values are equivalent to them.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.11.003
       
  • On improvement in representation of foE in IRI
    • Authors: Zhe Yang; Nicholas Ssessanga; Lan Thi Tran; Dieter Bilitza; Prasert Kenpankho
      Pages: 347 - 356
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Zhe Yang, Nicholas Ssessanga, Lan Thi Tran, Dieter Bilitza, Prasert Kenpankho
      Improvements in representation of foE for use in the International Reference Ionosphere (IRI) model are investigated. The IRI model currently depends on the 12-month running mean of sunspot number to estimate the foE. Using the F10.7 daily and F10.7_81 indices as the new model drivers, results are compared to ionosonde measurements at low, mid and high latitudes during solar minimum and solar maximum. Results show that the IRI model estimates the foE parameter better at low-mid latitudes than at high latitudes, specifically during solar maximum. Using the F10.7 indices to derive the IRI model improves estimates of foE, specifically at low-mid latitudes. The F10.7_81 index was found to perform better than the daily F10.7 index. Improvements during solar maximum and during solar minimum were on average 3.5% and 1%, respectively. Therefore, the F10.7_81 index is recommended as IRI model driver for foE estimates.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.11.008
       
  • NmF2 trends at low and mid latitudes for the recent solar minima and
           comparison with IRI-2012 model
    • Authors: L. Perna; M. Pezzopane; R. Ezquer; M. Cabrera; J.A. Baskaradas
      Pages: 363 - 374
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): L. Perna, M. Pezzopane, R. Ezquer, M. Cabrera, J.A. Baskaradas
      The ionospheric electron density peak (NmF2) is analyzed for the recent minima of solar activity for two mid-latitude stations, Rome (41.8°N, 12.5°E, geomagnetic latitude 41.7°N, Italy) and Gibilmanna (37.9°N, 14.0°E, geomagnetic latitude 37.6°N, Italy), and for the low-latitude station of Tucumán (26.9°S, 294.6°E, geomagnetic latitude 17.2°S, Argentina), located in the south ridge of the equatorial ionization anomaly. An inter-minima comparison reveals that from an ionospheric point of view the last minimum of solar activity (minimum 23/24) was peculiar, with values of NmF2 lower than those recorded during the previous minima for all the stations and all the hours of the day. A more pronounced decrease is observed at Tucumán than at Rome and Gibilmanna. The study of the winter and semi-annual anomaly shows that at mid-latitude stations the winter anomaly is not visible only for the years 2008 and 2009, which represent the deeper part of the prolonged and anomalous last solar minimum. The same is for the semi-annual anomaly. A comparison with the version 2012 of the International Reference Ionosphere model (IRI) is also carried out. The results reveal that for low solar activity the model works better at mid latitudes than at low latitudes, confirming the problems of IRI in correctly representing the low-latitude ionosphere. Nevertheless, using as input updated values of the solar and geomagnetic indices, no loss of accuracy is detected in the IRI performances for the last solar minimum with respect to the previous ones, both at mid and low latitudes.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.09.025
       
  • Ionospheric peak height at the magnetic equator: Comparison between
           ionosonde measurements and IRI
    • Authors: Takashi Maruyama; Guanyi Ma; Takuya Tsugawa; Pornchai Supnithi; Tharadol Komolmis
      Pages: 375 - 380
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Takashi Maruyama, Guanyi Ma, Takuya Tsugawa, Pornchai Supnithi, Tharadol Komolmis
      The ionospheric peak height in the F layer (hmF2) varies with not only thermospheric conditions but also dynamic processes in the upper atmosphere. At mid-latitudes, the field-aligned diffusion and recombination loss determine the hmF2 in the absence of applied vertical drift. Vertical drifts displace the hmF2 to a new equilibrium position in conjunction with the field-aligned redistribution of the plasma. In the vicinity of the magnetic equator, however, the equilibrium state would be different from low and mid-latitudes because the direct vertical coupling of plasma through the diffusion process is not allowed. Thus the behavior of hmF2 cannot be simply an extrapolation of that at low latitudes. In this paper, ionosonde measurements of the hmF2 near the magnetic equator and off-equatorial latitudes are compared with the IRI output.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.10.013
       
  • Solar cycle variation of ionospheric parameters over the low latitude
           station Hainan, China, during 2002–2012 and its comparison with IRI-2012
           model
    • Authors: G.J. Wang; J.K. Shi; Z. Wang; X. Wang; E. Romanova; K. Ratovsky; N.M. Polekh
      Pages: 381 - 395
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): G.J. Wang, J.K. Shi, Z. Wang, X. Wang, E. Romanova, K. Ratovsky, N.M. Polekh
      The low latitude ionospheric data observed by digisonde at Hainan station (19.5°N, 109.1°E) in a whole solar activity cycle period from 2002 to 2012 within Ap<20 have been analyzed to explore the diurnal, seasonal, annual variations and solar activity dependences of the ionospheric peak parameters (foF2, hmF2, and Chapman scale height Hm), as well as some quantitative comparison with IRI-2012 modeling predictions. The results show that the winter anomaly in the daytime foF2 appears at different levels of solar activity. The semiannual anomaly in the daytime and nighttime foF2 with two maxima in equinox seasons is present. The foF2 have a close correlation with a solar activity factor F107P=(F107+F107A)/2 and the correlation coefficients (r) in their diurnal variation are around 0.7. The slope of foF2 varying with F107P in daytime is usually smaller than in nighttime. The afternoon and evening hmF2 show good correlation with F107P (their r values exceed 0.6), but hmF2 at other time are low or poor related to F107P. The prominent character of hmF2 in equinox and summer seasons is its strong increase at sunset in high solar activity period, which may be due to pre-reversal enhancement (PRE) of local electric field. We also note that hmF2 values around midnight slightly decrease with increasing F107P index in equinox seasons. The diurnal variation of Hm usually has two peaks around noontime and pre-sunrise. The daytime Hm has an annual variation with maximum in summer and minimum in winter. Moreover, the dependence of the daytime Hm on solar activity is not strong due to meridional wind and other factors. The above results over Hainan are considerably different from those reported over Millstone Hill, which is attributed to their different geomagnetic locations. The quantitative results compared between IRI-2012 model predictions and observations show that the predicted foF2 values are basically underestimated and the magnitude of their deviations obviously increases with increasing solar activity. The predicted hmF2 obtained with measured M(3000)F2 inputs in low and moderate solar activity agree well with the observed ones. However, their deviations in high solar activity are significantly magnified.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.12.013
       
  • Variability of ionospheric parameters during solar minimum and maximum
           activity and assessment of IRI model
    • Authors: D.K. Sharma; Malini Aggarwal; Ananna Bardhan
      Pages: 435 - 443
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): D.K. Sharma, Malini Aggarwal, Ananna Bardhan
      The ionospheric parameters (electron and ion plasma temperatures (Te and Ti) and total ion density, Ni) as obtained by the Indian SROSS-C2 satellite (altitude ∼500km) have been investigated during low (year 1995, F10.7 ∼77 sfu) and high (year 2000, F10.7 ∼177 sfu) solar activity periods. The region under study spans over 5°S-30°N geomag. latitude and 60–100°E geog. longitude over the Indian sector. The observations are compared with the modelled values using IRI-2007 and IRI-2012 versions to assess model predictability. We found that minimum plasma temperatures (Te and Ti) in nighttime gets twice hotter whereas maximum temperatures in early morning gets reduced by half (cooler) when the solar flux gets doubled indicating a direct relation of Te and Ti with solar flux, F10.7 in nighttime but inverse in the morning hours. The ion density (Ni) exhibits solar activity dependence throughout the day and increases by one order when solar activity gets doubled. The modelled Te and Ti are found in agreement to the observed values for high solar activity over both the regions. Whereas the discrepancy exists during low solar activity period over both the regions with over-/under-estimated values in nighttime/morning and noontime respectively. The latest IRI-2012 model improves the nighttime Te and Ti whereas the modelled Ni is found in complete agreement to the observations.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.11.027
       
  • Diurnal variations of the ionospheric electron density height profiles
           over Irkutsk: Comparison of the incoherent scatter radar measurements, GSM
           TIP simulations and IRI predictions
    • Authors: G.A. Zherebtsov; K.G. Ratovsky; M.V. Klimenko; V.V. Klimenko; A.V. Medvedev; S.S. Alsatkin; A.V. Oinats; R.Yu. Lukianova
      Pages: 444 - 451
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): G.A. Zherebtsov, K.G. Ratovsky, M.V. Klimenko, V.V. Klimenko, A.V. Medvedev, S.S. Alsatkin, A.V. Oinats, R.Yu. Lukianova
      The long-duration continuous Irkutsk incoherent scatter radar (ISR) measurements allowed us to obtain the monthly averaged height-diurnal variations of the electron density in the 180–600km altitudinal range for 4 four seasons (winter, spring, summer, autumn) and for two solar activity levels (low and moderate). Considering these electron density variations as “quiet ionosphere patterns” we compared them with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) simulations and the International Reference Ionosphere (IRI) predictions. It was found that some observational features revealed from the ISR measurements are reproduced nicely by both the theoretical and empirical models, and some features agree better with the GSM TIP than with IRI. None of the models is able to reproduce a detailed multi-peak behavior of the electron density observed by ISR at ∼300km and above for the spring and autumn under low solar activity, while for the spring the GSM TIP tends to reproduce the morning and daytime peaks at the same local times as they are seen from the ISR observations.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.12.008
       
  • Comparative study of COSMIC/FORMOSAT-3, Irkutsk incoherent scatter radar,
           Irkutsk Digisonde and IRI model electron density vertical profiles
    • Authors: K.G. Ratovsky; A.V. Dmitriev; A.V. Suvorova; A.A. Shcherbakov; S.S. Alsatkin; A.V. Oinats
      Pages: 452 - 460
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): K.G. Ratovsky, A.V. Dmitriev, A.V. Suvorova, A.A. Shcherbakov, S.S. Alsatkin, A.V. Oinats
      The long-duration continuous Irkutsk incoherent scatter radar observations allowed us to collect 337 electron density vertical profiles obtained almost simultaneously with the radar and the COSMIC in the radar vicinity. The COSMIC electron density profiles were compared with those from the radar, Digisonde, and the IRI model. The comparison included 4 seasons and 2 solar activity levels (low and moderate). The number of simultaneous cases was ∼10 times more than in the previous incoherent scatter radar comparisons. In the case of the bottomside characteristics (peak density and bottomside electron content), the deviations between the COSMIC and the ground-based facilities data may be interpreted as the COSMIC measurement errors without significant systematic biases and with root-mean-square values that are ∼1.4–1.6 times smaller those that from the IRI model prediction. In the case of the topside characteristics (topside electron content and ionospheric electron content), the IRI model overestimates the COSMIC data by 0.6–0.8tecu on average, and the COSMIC overestimates the Irkutsk incoherent scatter radar data by 1.0–1.1tecu on average. The percentage differences between the radar and COSMIC in the topside electron content can reach 80%. In terms of the root-mean-square deviation, the COSMIC and the radar agree better than each of them agrees with the IRI model.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.12.026
       
  • Comparison of midlatitude ionospheric F region peak parameters and topside
           Ne profiles from IRI2012 model prediction with ground-based ionosonde and
           Alouette II observations
    • Authors: G.I. Gordiyenko; A.F. Yakovets
      Pages: 461 - 474
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): G.I. Gordiyenko, A.F. Yakovets
      The ionospheric F2 peak parameters recorded by a ground-based ionosonde at the midlatitude station Alma-Ata [43.25N, 76.92E] were compared with those obtained using the latest version of the IRI model (http://omniweb.gsfc.nasa.gov/vitmo/iri2012_vitmo.html) for quiet geomagnetic conditions of winter (January), equinoxes (March and September), and summer (July) months of 2008–2010. It was found that for the Alma-Ata (Kazakhstan) location, the IRI2012 model describes well the morphology of seasonal and diurnal variations of the ionospheric critical frequency (foF2) and peak density height (hmF2) monthly medians. The model errors in the median foF2 prediction (percentage deviations between the median foF2 values and their model predictions) were found to vary approximately in the range from about −20% to 34% and showed a stable overestimation in the median foF2 values for daytime in January and July and underestimation for day- and nighttime hours in the equinoctial months. The comparison between the ionosonde hmF2 and IRI results clearly showed that the IRI overestimates the nighttime hmF2 values for March and September months, and the difference is up to 30km. The daytime Alma-Ata hmF2 data were found to be close to the IRI predictions (deviations are approximately ±10–15km) in winter and equinoctial months, except in July when the observed hmF2 values were much more (from approximately 50–200km). The comparison between the Alouette foF2 data and IRI predictions showed mixed results. In particular, the Alouette foF2 data showed a tendency to be overestimated for daytime in winter months similar to the ionosonde data; however, the overestimated foF2 values for nighttime in the autumn equinox were in disagreement with the ionosonde observations. There were large deviations between the observed hmF2 values and their model predictions. The largest deviations were found during winter and summer (up to −90km). The comparison of the Alouette II electron density profiles with those predicted by the adapted IRI2012 model in the altitude range hmF2 of the satellite position showed a great difference in the shape of the Alouette-, NeQuick-, IRI02-coorr, and IRI2001-derived Ne profiles, with overestimated Ne values at some altitudes and underestimated Ne values at others. The results obtained in the study showed that the observation–model differences were significant especially for the real observed (not median) data. For practical application, it is clearly important for the IRI2012 model to be adapted to the observed F2-layer peak parameters. However, the model does not offer a simple solution to predict the shape of the vertical electron density profile in the topside ionosphere, because of the problem with the topside shape parameters.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2017.01.006
       
  • Application of the nudged elastic band method to the point-to-point radio
           wave ray tracing in IRI modeled ionosphere
    • Authors: I.A. Nosikov; M.V. Klimenko; P.F. Bessarab; G.A Zhbankov
      Pages: 491 - 497
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): I.A. Nosikov, M.V. Klimenko, P.F. Bessarab, G.A Zhbankov
      Point-to-point ray tracing is an important problem in many fields of science. While direct variational methods where some trajectory is transformed to an optimal one are routinely used in calculations of pathways of seismic waves, chemical reactions, diffusion processes, etc., this approach is not widely known in ionospheric point-to-point ray tracing. We apply the Nudged Elastic Band (NEB) method to a radio wave propagation problem. In the NEB method, a chain of points which gives a discrete representation of the radio wave ray is adjusted iteratively to an optimal configuration satisfying the Fermat’s principle, while the endpoints of the trajectory are kept fixed according to the boundary conditions. Transverse displacements define the radio ray trajectory, while springs between the points control their distribution along the ray. The method is applied to a study of point-to-point ionospheric ray tracing, where the propagation medium is obtained with the International Reference Ionosphere model taking into account traveling ionospheric disturbances. A 2-dimensional representation of the optical path functional is developed and used to gain insight into the fundamental difference between high and low rays. We conclude that high and low rays are minima and saddle points of the optical path functional, respectively.

      PubDate: 2017-06-15T07:57:21Z
      DOI: 10.1016/j.asr.2016.12.003
       
  • Robust double gain unscented Kalman filter for small satellite attitude
           estimation
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Lu Cao, Weiwei Yang, Hengnian Li, Zhidong Zhang, Jianjun Shi
      Limited by the low precision of small satellite sensors, the estimation theories with high performance remains the most popular research topic for the attitude estimation. The Kalman filter (KF) and its extensions have been widely applied in the satellite attitude estimation and achieved plenty of achievements. However, most of the existing methods just take use of the current time-step’s priori measurement residuals to complete the measurement update and state estimation, which always ignores the extraction and utilization of the previous time-step’s posteriori measurement residuals. In addition, the uncertainty model errors always exist in the attitude dynamic system, which also put forward the higher performance requirements for the classical KF in attitude estimation problem. Therefore, the novel robust double gain unscented Kalman filter (RDG-UKF) is presented in this paper to satisfy the above requirements for the small satellite attitude estimation with the low precision sensors. It is assumed that the system state estimation errors can be exhibited in the measurement residual; therefore, the new method is to derive the second Kalman gain K k 2 for making full use of the previous time-step’s measurement residual to improve the utilization efficiency of the measurement data. Moreover, the sequence orthogonal principle and unscented transform (UT) strategy are introduced to robust and enhance the performance of the novel Kalman Filter in order to reduce the influence of existing uncertainty model errors. Numerical simulations show that the proposed RDG-UKF is more effective and robustness in dealing with the model errors and low precision sensors for the attitude estimation of small satellite by comparing with the classical unscented Kalman Filter (UKF).

      PubDate: 2017-06-27T03:36:18Z
       
  • Estimation of inertial characteristics of tumbling spacecraft using
           constant state filter
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Chuan Ma, Honghua Dai, Jianping Yuan
      Reconstruction of dynamical parameters is one of the main challenges faced in the on-orbit servicing missions for defunct spacecraft. And the quaternion plays a major role in parameterizations of the dynamical model. In this paper, the analytical solution of the quaternion differential equations of a tumbling symmetrical object is derived. Given this solution, a constant state filter is proposed for inertial characteristics estimation and attitude prediction of tumbling spacecraft. The key idea of the present filter is to replace dynamic variables by the undetermined constant parameters of the analytical solution. These parameters are estimated during the filtering process and then used to calculate the dynamic variables of the spacecraft. Furthermore, they are also utilized to determine the inertial characteristics and predict the future attitude motions. Compared with traditional EKFs, the constant state filter shows good performance when the measurement sampling interval is large or a priori estimation of the state is unavailable, because the dynamic model and observation model are transformed into approximate linear forms by utilizing the constant state vector. Numerical simulations verify the convergence and precision of the proposed filter.

      PubDate: 2017-06-27T03:36:18Z
       
  • Scoring sensor observations to facilitate the exchange of space
           surveillance data
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): M. Weigel, H. Fiedler, T. Schildknecht
      In this paper, a scoring metric for space surveillance sensor observations is introduced. A scoring metric allows for direct comparison of data quantity and data quality, and makes transparent the effort made by different sensor operators. The concept might be applied to various sensor types like tracking and surveillance radar, active optical laser tracking, or passive optical telescopes as well as combinations of different measurement types. For each measurement type, a polynomial least squares fit is performed on the measurement values contained in the track. The track score is the average sum over the polynomial coefficients uncertainties and scaled by reference measurement accuracy. Based on the newly developed scoring metric, an accounting model and a rating model are introduced. Both models facilitate the exchange of observation data within a network of space surveillance sensors operators. In this paper, optical observations are taken as an example for analysis purposes, but both models can also be utilized for any other type of observations. The rating model has the capability to distinguish between network participants with major and minor data contribution to the network. The level of sanction on data reception is defined by the participants themselves enabling a high flexibility. The more elaborated accounting model translates the track score to credit points earned for data provision and spend for data reception. In this model, data reception is automatically limited for participants with low contribution to the network. The introduced method for observation scoring is first applied for transparent data exchange within the Small Aperture Robotic Telescope Network (SMARTnet). Therefore a detailed mathematical description is presented for line of sight measurements from optical telescopes, as well as numerical simulations for different network setups.

      PubDate: 2017-06-27T03:36:18Z
       
  • New fundamental parameters for attitude representation
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Russell P. Patera
      A new attitude parameter set is developed to clarify the geometry of combining finite rotations in a rotational sequence and in combining infinitesimal angular increments generated by angular rate. The resulting parameter set of six Pivot Parameters represents a rotation as a great circle arc on a unit sphere that can be located at any clocking location in the rotation plane. Two rotations are combined by linking their arcs at either of the two intersection points of the respective rotation planes. In a similar fashion, linking rotational increments produced by angular rate is used to derive the associated kinematical equations, which are linear and have no singularities. Included in this paper is the derivation of twelve Pivot Parameter elements that represent all twelve Euler Angle sequences, which enables efficient conversions between Pivot Parameters and any Euler Angle sequence. Applications of this new parameter set include the derivation of quaternions and the quaternion composition rule, as well as, the derivation of the analytical solution to time dependent coning motion. The relationships between Pivot Parameters and traditional parameter sets are included in this work. Pivot Parameters are well suited for a variety of aerospace applications due to their effective composition rule, singularity free kinematic equations, efficient conversion to and from Euler Angle sequences and clarity of their geometrical foundation.

      PubDate: 2017-06-27T03:36:18Z
       
  • Polarimetric SAR Interferometry based modeling for tree height and
           aboveground biomass retrieval in a tropical deciduous forest
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Shashi Kumar, Unmesh G. Khati, Shreya Chandola, Shefali Agrawal, Satya P.S. Kushwaha
      The regulation of the carbon cycle is a critical ecosystem service provided by forests globally. It is, therefore, necessary to have robust techniques for speedy assessment of forest biophysical parameters at the landscape level. It is arduous and time taking to monitor the status of vast forest landscapes using traditional field methods. Remote sensing and GIS techniques are efficient tools that can monitor the health of forests regularly. Biomass estimation is a key parameter in the assessment of forest health. Polarimetric SAR (PolSAR) remote sensing has already shown its potential for forest biophysical parameter retrieval. The current research work focuses on the retrieval of forest biophysical parameters of tropical deciduous forest, using fully polarimetric spaceborne C-band data with Polarimetric SAR Interferometry (PolInSAR) techniques. PolSAR based Interferometric Water Cloud Model (IWCM) has been used to estimate aboveground biomass (AGB). Input parameters to the IWCM have been extracted from the decomposition modeling of SAR data as well as PolInSAR coherence estimation. The technique of forest tree height retrieval utilized PolInSAR coherence based modeling approach. Two techniques – Coherence Amplitude Inversion (CAI) and Three Stage Inversion (TSI) – for forest height estimation are discussed, compared and validated. These techniques allow estimation of forest stand height and true ground topography. The accuracy of the forest height estimated is assessed using ground-based measurements. PolInSAR based forest height models showed enervation in the identification of forest vegetation and as a result height values were obtained in river channels and plain areas. Overestimation in forest height was also noticed at several patches of the forest. To overcome this problem, coherence and backscatter based threshold technique is introduced for forest area identification and accurate height estimation in non-forested regions. IWCM based modeling for forest AGB retrieval showed R2 value of 0.5, RMSE of 62.73 (t ha−1) and a percent accuracy of 51%. TSI based PolInSAR inversion modeling showed the most accurate result for forest height estimation. The correlation between the field measured forest height and the estimated tree height using TSI technique is 62% with an average accuracy of 91.56% and RMSE of 2.28m. The study suggested that PolInSAR coherence based modeling approach has significant potential for retrieval of forest biophysical parameters.

      PubDate: 2017-06-27T03:36:18Z
       
  • Autonomous rock detection on mars through region contrast
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Xueming Xiao, Hutao Cui, Meibao Yao, Yang Tian
      In this paper, we present a new autonomous rock detection approach through region contrast. Unlike current state-of-art pixel-level rock segmenting methods, new method deals with this issue in region level, which will significantly reduce the computational cost. Image is firstly splitted into homogeneous regions based on intensity information and spatial layout. Considering the high-water memory constraints of onboard flight processor, only low-level features, average intensity and variation of superpixel, are measured. Region contrast is derived as the integration of intensity contrast and smoothness measurement. Rocks are then segmented from the resulting contrast map by an adaptive threshold. Since the merely intensity-based method may cause false detection in background areas with different illuminations from surroundings, a more reliable method is further proposed by introducing spatial factor and background similarity to the region contrast. Spatial factor demonstrates the locality of contrast, while background similarity calculates the probability of each subregion belonging to background. Our method is efficient in dealing with large images and only few parameters are needed. Preliminary experimental results show that our algorithm outperforms edge-based methods in various grayscale rover images.

      PubDate: 2017-06-27T03:36:18Z
       
  • Effect of grain size distribution on stress-strain behavior of lunar soil
           simulants
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Mehmet Murat Monkul, Amina Dacic
      Geotechnical behavior of the lunar soils is important for engineering analyses regarding various aspects of the future extraterrestrial settlement plans including lunar exploration and construction. Many lunar soil simulants had been produced so far, in order to resemble lunar soils and conduct such analyses. The goal of this study is to investigate how and to what extent the variations in the grain size distribution of different lunar soil simulants affect their shear strength and volume change behaviors, both of which are quite important for constitutive modeling and geotechnical design. Static simple shear tests were conducted on four lunar soil simulants that were reproduced in terms of original gradation characteristics. The results indicate that various gradational parameters, such as mean grain size, coefficient of uniformity and fines content influence the shear strength, the amount of volumetric dilatancy, and the rate of dilatancy of simulant specimens in different levels when they were compared at the same density or void ratio. The possible reasons behind such different levels of influence were also discussed by focusing on the initial fabric of specimens achieved before shearing and the interaction between silt and sand matrices in the simulants.

      PubDate: 2017-06-27T03:36:18Z
       
  • Latitudinal and MLT dependence of the seasonal variation of geomagnetic
           field around auroral zone
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Jin Zhu, Aimin Du, Jiaming Ou, Wenyao Xu
      Seasonal variation of geomagnetic field around auroral zone is analyzed in terms of geomagnetic latitude, magnetic local time (MLT) and geomagnetic condition in this study. The study uses horizontal component (H) of geomagnetic field obtained from 6 observatories located in geomagnetic latitude of 57.8°N–73.8°N along 115°E longitudinal line. The results indicate that seasonal variations of geomagnetic field around auroral zone are different combinations of annual and semiannual variations at different latitudinal ranges. Both annual and semiannual variations show distinct MLT dependency: (1) At dayside auroral latitudes (around 72°N geomagnetic latitude), geomagnetic field shows distinct annual variation under both quiet and disturbed conditions. Furthermore, the annual component is mainly contributed by data of dusk sector. (2) At nightside auroral latitudes (around 65°N), geomagnetic field shows semiannual dominated seasonal variation. Under quiet conditions the annual component is comparable to the semiannual component, while under disturbed conditions, the semiannual component is twice as much as the annual component. Under quiet conditions, the semiannual component is mainly contributed by 1300–1400 MLT, while the annual component has two peaks: one is around 1100–1300 MLT and the other is around 2000–2200 MLT. Under disturbed conditions, the semiannual component is mainly contributed by data around midnight, while the annual component is mainly contributed by dusk sector. (3) At subauroral latitudes (around 60°N), annual variation is comparable to semiannual variation under both quiet and disturbed conditions. Both annual and semiannual components show similar MLT dependencies as that of nightside auroral latitudes.

      PubDate: 2017-06-27T03:36:18Z
       
  • Ingestion of FORMOSAT-3/COSMIC GPS data into La Plata Ionospheric Model: A
           preliminary assessment
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): J. Federico Conte, Claudio Brunini
      La Plata Ionospheric Model (LPIM; Brunini et al., 2011) has been upgraded to a new stage enabling the ingestion of sTEC values retrieved from GPS receivers on board the FORMOSAT-3 Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites, in order to determine corrections to the global mean values of the ionosphere F2 layer critical frequency, f o F 2 (related to the peak density, N m F 2 ) and the F2 layer peak height, h m F 2 . Once the corrections were computed, La Plata Ionospheric Model determined new f o F 2 and h m F 2 values which were used to reproduce ionospheric electron density profiles depending on Universal Time, geographical coordinates, and solar and geomagnetic activity levels. These new profiles were compared with those obtained using LPIM but without COSMIC-GPS data ingestion and against International Reference Ionosphere (IRI) profiles; while the new values of the F2 peak parameters were compared with ionosonde measurements. These comparisons served to show that the incorporation of COSMIC-GPS data seems to provide LPIM with a better capability to render a more reliable representation of the F2 layer of the ionosphere. Consequently, results of the data ingestion process, as well as intra-technique and against IRI and observations comparisons are described, and general conclusions are presented. The most important being that: • Without data ingestion LPIM tends to overestimate N m F 2 and to slightly underestimate h m F 2 . • LPIM has improved its representation of the F2 peak of the ionosphere.

      PubDate: 2017-06-27T03:36:18Z
       
  • Mars entry guidance based on an adaptive reference drag profile
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Zixuan Liang, Guangfei Duan, Zhang Ren
      The conventional Mars entry tracks a fixed reference drag profile (FRDP). To improve the landing precision, a novel guidance approach that utilizes an adaptive reference drag profile (ARDP) is presented. The entry flight is divided into two phases. For each phase, a family of drag profiles corresponding to various trajectory lengths is planned. Two update windows are investigated for the reference drag profile. At each window, the ARDP is selected online from the profile database according to the actual range-to-go. The tracking law for the selected drag profile is designed based on the feedback linearization. Guidance approaches using the ARDP and the FRDP are then tested and compared. Simulation results demonstrate that the proposed ARDP approach achieves much higher guidance precision than the conventional FRDP approach.

      PubDate: 2017-06-27T03:36:18Z
       
  • Interstellar protonated molecular species
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Emmanuel E. Etim, Prasanta Gorai, Ankan Das, Elangannan Arunan
      Majority of the known interstellar cations are protonated species believed to be the natural precursors for their corresponding neutral analogues formed via the dissociative recombination process. The protonation of a neutral species can occur in more than one position on the molecular structure thus resulting in more than one proton binding energy value and different protonated species for the same neutral species. In the present work, ab initio quantum calculations are employed to calculate accurate proton binding energies for over 100 neutral interstellar molecules of which majority of the neutral molecules are protonated in more than one position. From the results, protonated species resulting from a high proton binding energy prefers to remain protonated rather than transferring a proton and returning to its neutral form as compared to its analogue that gives rise to a lower proton binding energy (PBE) from the same neutral species. For two protonated species resulting from the same neutral molecule, the one that results in a higher PBE is more stable as compared to its counterpart that is responsible for the lower PBE for the same neutral species. Here, the most stable species are highlighted for all the systems considered.
      Graphical abstract image

      PubDate: 2017-06-27T03:36:18Z
       
  • Quantification of LSS using the persistent homology in the SDSS fields
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Yuki Kimura, Koji Imai
      Using galaxy samples from the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12), we first estimate the topology of cosmic large-scale structure (LSS) by means of a new method of persistent homology which captures the size and robustness of the void structure in a compact and meaningful manner. To avoid cosmic variance, we create three volume-limited subsamples, which contain more than 2000 galaxies in different redshift slices (Δz =0.01). The result shows the clearer differences from the topology of uniform distribution as the redshift decreases, and supports the scenario of modern cosmology that the LSS has been formed through the growth in time of an initial density perturbation. Future work will include an analysis for different types of galaxies and a comparison with N-body simulation to constrain cosmological models.

      PubDate: 2017-06-27T03:36:18Z
       
  • Realization of hydrodynamic experiments on quasi-2D liquid crystal films
           in microgravity
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3
      Author(s): Noel A. Clark, Alexey Eremin, Matthew A. Glaser, Nancy Hall, Kirsten Harth, Christoph Klopp, Joseph E. Maclennan, Cheol S. Park, Ralf Stannarius, Padetha Tin, William N. Thurmes, Torsten Trittel
      Freely suspended films of smectic liquid crystals are unique examples of quasi two-dimensional fluids. Mechanically stable and with quantized thickness of the order of only a few molecular layers, smectic films are ideal systems for studying fundamental fluid physics, such as collective molecular ordering, defect and fluctuation phenomena, hydrodynamics, and nonequilibrium behavior in two dimensions (2D), including serving as models of complex biological membranes. Smectic films can be drawn across openings in planar supports resulting in thin, meniscus-bounded membranes, and can also be prepared as bubbles, either supported on an inflation tube or floating freely. The quantized layering renders smectic films uniquely useful in 2D fluid physics. The OASIS team has pursued a variety of ground-based and microgravity applications of thin liquid crystal films to fluid structure and hydrodynamic problems in 2D and quasi-2D systems. Parabolic flights and sounding rocket experiments were carried out in order to explore the shape evolution of free floating smectic bubbles, and to probe Marangoni effects in flat films. The dynamics of emulsions of smectic islands (thicker regions on thin background films) and of microdroplet inclusions in spherical films, as well as thermocapillary effects, were studied over extended periods within the OASIS (Observation and Analysis of Smectic Islands in Space) project on the International Space Station. We summarize the technical details of the OASIS hardware and give preliminary examples of key observations.

      PubDate: 2017-06-27T03:36:18Z
       
  • List of Referees
    • Abstract: Publication date: 1 August 2017
      Source:Advances in Space Research, Volume 60, Issue 3


      PubDate: 2017-06-27T03:36:18Z
       
  • The effect of QBO on foE
    • Authors: Ramazan
      Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2
      Author(s): Ramazan Atıcı, Selçuk Sağır
      In the present work, the relationship with QBO of difference (ΔfoE=foEmea −foEIRI) between critical frequency (foE) values of ionospheric E-region, measured at Darwin and Casos Island stations and calculated by IRI-2012 ionospheric model, is statistically investigated. A multiple regression model is used as statistical tool. The “Dummy” variables (“DummyWest” and “DummyEast” represent westerly QBO values and easterly QBO values, respectively) are added to model in order to see the effect of westerly and easterly QBO. In the result of calculations, it is observed that the changes in ΔfoE about 50–52% can be explained by QBO at both stations. The relationship between QBO and ΔfoE is negative at both stations. The change of 1ms−1 in whole set of QBO leads to a decrease of 0.008MHz at Casos Island station and 0.017MHz at Darwin station in ΔfoE. Directions of QBO have an effect on ΔfoE at the Darwin station, but they’ve not any effect on ΔfoE at Casos Island station. It is thought that the difference values in the foE are due to not to be included in the IRI-model of all parameters affecting the critical frequency value. Thus, QBO which is not included to IRI-model can have an effect on foE and more accurate results can be obtained by IRI model if the QBO is included in this model calculations.

      PubDate: 2017-06-15T07:57:21Z
       
  • List of Referees
    • Abstract: Publication date: 15 July 2017
      Source:Advances in Space Research, Volume 60, Issue 2


      PubDate: 2017-06-15T07:57:21Z
       
 
 
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