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Potential role of energetic particle observations in geomagnetic storm forecasting

Thu, 05/16/2019 - 19:10

Publication date: Available online 16 May 2019

Source: Advances in Space Research

Author(s): Dheyaa Ameri, Eino Valtonen

Abstract

We have searched for solar proton events consisting of both solar energetic particles (SEPs) accelerated near the Sun and energetic storm particles (ESPs) accelerated by interplanetary shocks driven by coronal mass ejections (CMEs) and observed near the time when the shock passes the observer. The purpose of this study is to investigate the possibilities and advantages of using energetic particle observations for mid-term (warning time several hours) forecasting of geomagnetic storms or as a support for longer-term forecasting methods based on solar observations. The study period extends from May 1996 to December 2017 covering the entire solar cycle 23 and the major part of solar cycle 24. Using two particle energies, 2 and 20 MeV, we found 95 SEP – ESP events of which 65 were associated with geomagnetic storms with Dst ⩽-50 nT caused by CMEs. We performed correlation analysis between log10|Dst (nT)|and various parameters characterising the particle events or the associated CMEs. We found the best correlations for the single independent variables △tESP-SEP (r=-0.47±0.08), which is the difference between the ESP peak time and SEP onset time, the CME direction parameter DP (r=0.47±0.10), and the logarithm of the maximum ESP energy log10[EESPmax(MeV)] (r=0.44±0.11). Using a linear combination of these three variables improves the correlation (r=0.68±0.07). We suggest that an empirical equation based on these three parameters and requiring only coronagraph observations of CMEs and energetic particle measurements in interplanetary space can be used for mid-term forecasting of geomagnetic storm strengths. We found that 74 % of the strongest storms (Dst ⩽-200 nT) during the study period were associated with energetic particle events. The average warning time and its standard deviation for all geomagnetic storms associated with SEP – ESP events was (15±10) hours.

Rocket Investigation of Current Closure in the Ionosphere (RICCI): A novel application of CubeSats from a sounding rocket platform

Thu, 05/16/2019 - 19:10

Publication date: Available online 15 May 2019

Source: Advances in Space Research

Author(s): Ian J. Cohen, Brian J. Anderson, John W. Bonnell, Robert L. Lysak, Marc R. Lessard, Robert G. Michell, Roger H. Varney

Abstract

The Rocket Investigation of Current Closure in the Ionosphere (RICCI) sounding rocket mission concept will use the novel deployment of multiple CubeSats as miniature sub-payloads to obtain the first direct in-situ measurement of ionospheric closure currents. These ionospheric currents are critical to understanding the nature of atmosphere-ionosphere-magnetosphere coupling and have relevance to space weather parameters such as ionospheric densities, thermospheric heating, and satellite drag. Previous attempts to measure these ionospheric closure current in-situ have been limited by poor attitude knowledge resulting in large uncertainties in the magnetic field measurement that compromise the ability to measure the gradient of the magnetic field beyond the precision necessary to resolve the current densities. To address this, RICCI uses dedicated star trackers and currently-available CubeSat subsystems to obtain the high-precision attitude knowledge necessary to directly measure these elusive currents.

Imaging Strong Blazars with Space VLBI

Thu, 05/16/2019 - 19:10

Publication date: Available online 13 May 2019

Source: Advances in Space Research

Author(s): J. Anton Zensus, Laura Vega-García, Eduardo Ros, Andrei P. Lobanov, Manel Perucho, Gabriele Bruni, Yuri Y. Kovalev

Abstract

The RadioAstron mission has obtained a series of detailed multi-frequency images of the brightest blazars of the radio sky concentrated in three key science programs. We present here results of the program on powerful jets in blazars. In the first two years of the mission, observations of compact relativistic jets in 0836+710, 3C 345, 3C 273, and 4C +69.21 were made at λλ 18, 6, and 1.3 cm. The resulting images have revealed compact emitting regions with brightness temperature in excess of 1013 K and a complex jet structure that can be explained by plasma instability developing in a relativistic outflow.

We present here some highlights of these space-VLBI observations, designed to resolve the innermost regions in these powerful targets and address some of the still unanswered questions on their physical nature.

Site analysis in the Argentinean Andean region for the placement of astrophysical observatories and solar photovoltaic power plants. The case of the “Leoncito 2” site

Thu, 05/16/2019 - 19:10

Publication date: Available online 13 May 2019

Source: Advances in Space Research

Author(s): M.M. Freire, L.S. Della Ceca, M.I. Micheletti, I. Novara, B. Garcia, A. Mancilla, GM. Salum, E. Crinó, RD. Piacentini

Abstract

After a detailed search for possible sites where to place astrophysical facilities in Argentinean Andean region, a location labeled as LEO 2 (31°24’22” S, 69°29’32” W, 1630 masl)is proposed. It is placed near the largest Astronomical Observatory of Argentina: Complejo AStronómico El LEOncito (CASLEO). Its advantages are: a good altitude to detect the maximum development of cosmic ray showers, high spectral transmittance to UV and visible ranges, very low aerosol content (mean particle concentration measured at ground with an optical particle counter PM2.5 = 1.52 µg.m-3and PM>2.5= 6.83 µg.m-3, mean Aerosol Optical Depth at 550 nm = 0.027 (measured from space using the SeaWiFS instrument on board of the SeaStar NASA satellite). A local meteorological analysis was done, using data measured in situ, which shows a typical desertic site with the following mean annual (std. dev.) values:mean annual temperature 18.93 (7.66) °C, mean annual relative humidity 28.76 (20.55)%, low/ moderate mean annual average wind speed 11.63 (8.78) Km/h, low mean water content (0.73 cm) and rather low mean cloud coverage fraction (cloud coverage fraction): 0.29 (0.02) (for the period 2003 - 2016 from Aqua/NASA satellite MODIS device) and 0.25 (0.01) (for the period 2000 – 2016, Terra/NASA satellite MODIS device).Concerning the conditions for the placement of photovoltaic solar power plants, some positive aspects that can be remarked are a large rather flat available surface (336 Km2) with very good levels of annual mean horizontal solar irradiation: Global (2334 KWh.m-2per year), Direct(3127 KWh.m-2per year) and Diffuse (394 KWh.m-2per year). Optimum angle to place solar panels at this site is determined and the global tilted solar irradiation is calculated (2689 KWh.m-2per year). In comparison with an African (Ouarzazate, Morocco) and Asian (Dubai) sites, the analysed site present better annual irradiation levels being the Global horizontal irradiation at the Argentinean site 8.1% and 10.3% higher than those calculated for the African and Asian site respectively. Also, a comparison is made of different solar cells (monocrystalline Si, polycrystalline Si and perovskite), through the calculation of the generated photocurrent (mean produced solar photovoltaic current per unit cell surface), considering the atmospheric and solar radiation parameters found for the studied site. We thus conclude that the proposed site in the Andes range is well suited for the placement of Astrophysical facilities, as well as Photovoltaic solar power plants.

RadioAstron orbit determination and evaluation of its results using correlation of space-VLBI observations

Thu, 05/16/2019 - 19:10

Publication date: Available online 13 May 2019

Source: Advances in Space Research

Author(s): M.V. Zakhvatkin, A.S. Andrianov, V.Yu. Avdeev, V.I. Kostenko, Y.Y. Kovalev, S.F. Likhachev, I.D. Litovchenko, D.A. Litvinov, A.G. Rudnitskiy, M.A. Shchurov, K.V. Sokolovsky, V.A. Stepanyants, A.G. Tuchin, P.A. Voitsik, G.S. Zaslavskiy, V.E. Zharov, V.A. Zuga

Abstract

A crucial part of a space mission for very-long baseline interferometery (VLBI), which is the technique capable of providing the highest resolution images in astronomy, is orbit determination of the mission?s space radio telescope(s). In order to successfully detect interference fringes that result from correlation of the signals recorded by a ground-based and a space-borne radio telescope, the propagation delays experienced in the near-Earth space by radio waves emitted by the source and the relativity effects on each telescope?s clock need to be evaluated, which requires accurate knowledge of position and velocity of the space radio telescope. In this paper we describe our approach to orbit determination (OD) of the RadioAstron spacecraft of the RadioAstron space-VLBI mission. Determining RadioAstron?s orbit is complicated due to several factors: strong solar radiation pressure, a highly eccentric orbit, and frequent orbit perturbations caused by the attitude control system. We show that in order to maintain the OD accuracy required for processing space-VLBI observations at cm-wavelengths it is required to take into account the additional data on thruster firings, reaction wheel rotation rates, and attitude of the spacecraft.We also investigate into using the unique orbit data available only for a space-VLBI spacecraft, i.e. the residual delays and delay rates that result from VLBI data processing, as a means to evaluate the achieved OD accuracy. We present the results of the first experience of OD accuracy evaluation of this kind, using more than 5,000 residual values obtained as a result of space-VLBI observations performed over 7 years of the RadioAstron mission operations.

The CALorimetric Electron Telescope (CALET) on the International Space Station

Thu, 05/16/2019 - 19:10

Publication date: Available online 13 May 2019

Source: Advances in Space Research

Author(s): Shoji Torii, Pier Simone Marrocchesi, for the CALET collaboration

Abstract

The CALorimetric Electron Telescope (CALET) space experiment, developed by Japan in collaboration with Italy and the United States, is a high-energy astroparticle physics mission installed on the International Space Station (ISS). The primary goals of the CALET mission include investigating on the possible presence of nearby sources of high-energy electrons, studying the details of galactic particle propagation and searching for dark matter signatures. During a two-year mission, extendable to five years, CALET can measure the flux of cosmic-ray electrons (including positrons) to 20 TeV, gamma-rays to 10 TeV and nuclei with Z=1 to 40 up to 1,000 TeV. The instrument consists of two layers of segmented plastic scintillators for cosmic-ray charge identification (CHD), a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter (IMC) and a 27 radiation length thick lead-tungstate calorimeter (TASC). CALET has sufficient depth, imaging capabilities and excellent energy resolution to allow for a clear separation between hadrons and electrons and between charged particles and gamma rays. The instrument was launched on August 19, 2015 to the ISS with the H-II Transfer Vehicle 5 (HTV-5) and installed on the Japanese Experiment Module-Exposed Facility (JEM-EF) on August 25. Since the start of operations in mid-October, 2015, a continuous observation has been going on mainly by triggering high energy (>10 GeV) showers without any major interruption. The number of triggered events above 10 GeV is nearly 20 million per month. By using the data obtained during the first two years, we give a summary of CALET observations: 1) Electron+Positron energy spectrum, 2) Proton and Nuclei spectrum, 3) Gamma-ray observation, with results of the performance study on orbit. We also present the results of observations of the electromagnetic counterparts to LIGO-VIRGO gravitational wave events and high-energy counterparts to GRB events measured with the CALET Gamma-ray Burst Monitor (CGBM).

Interstellar Scintillation, ISS, and Intrinsic Variability of Radio AGN

Thu, 05/16/2019 - 19:10

Publication date: Available online 13 May 2019

Source: Advances in Space Research

Author(s): David L. Jauncey, Jun Yi Koay, Hayley Bignall, Jean-Pierre Macquart, Tapio Pursimo, Marcello Giroletti, Talvikki Hovatta, Sebastian Kiehlmann, Barney Rickett, Anthony Readhead, Walter Max-Moerbeck, Harish Vedantham, Cormac Reynolds, James Lovell, Roopesh Ojha, Lucyna Kedziora-Chudczer

Abstract

We investigate the relationship between the 5 GHz interstellar scintillation (ISS) and the 15 GHz intrinsic variability of the compact, radio-selected active galactic nuclei (AGN) common to the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory blazar flux density monitoring program. As part of this investigation, we also re-examine the reported intrinsic nature of the February 1990 VLA observations of the blazar S5 0716+714. We are also examining the presence of IDV/ISS in the Owens Valley 15 GHz flux density monitoring data. We find a significant relationship between the Owens Valley 15 GHz modulation index and the MASIV modulation index. We also discuss the implications of these findings for RadioAstron.

A new multi-target tracking algorithm for a large number of orbiting objects

Thu, 05/16/2019 - 19:10

Publication date: Available online 13 May 2019

Source: Advances in Space Research

Author(s): E. Delande, J. Houssineau, J. Franco, C. Frueh, D. Clark, M. Jah

Abstract

This paper presents the filter for Hypothesised and Independent Stochastic Populations (HISP), a multi-object joint detection/tracking algorithm derived from a recent estimation framework for stochastic populations, in the context of Space Situational Awareness. Designed for multi-object estimation problems where the data association between tracks and collected observations is moderately ambiguous, the HISP filter has a linear complexity with the number of objects and the number of observations. Because of its scalable complexity, the HISP filter is a promising solution for the construction of a large-scale catalogue of Resident Space Objects. We illustrate the HISP filter on a challenging surveillance scenario built from real data for 115 satellites of PlanetLabs’ Dove constellation, and simulated observations collected from two sensors with limited coverage and measurement noise, in the presence of false positives and missed detection.

Effects of vertical accuracy of digital elevation model (DEM) data on automatic lineaments extraction from shaded DEM

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): Ayman Soliman, Ling Han

Abstract

Remote sensing data, such as satellite images, and remote sensing derived digital elevation models (DEMs) are credited by simplifying many geological processes that require costly and laborious field work, such as lineament extraction. Furthermore, the recent increase in the availability of DEMs from many free open sources as well as their advantages over satellite imagery have promoted their wide application as remote sensing methods for lineament extraction. The quality of a DEM affects the results of its application, and this quality is controlled by its vertical accuracy and spatial resolution. The objectives of this study were to assess and verify the effects of the vertical accuracies of DEMs on lineament extraction. The area around Baoji city, Shaanxi province, China, was selected as a case study and the lineaments were automatically extracted using the LINE algorithm of PCI Geomatica from three DEMs with different vertical accuracies: tri stereo ZY3 imagery derived DEM, SRTM1V3, and ASTGDEMV2. All of these DEMs have 1″ spatial resolution (approx. 30 m). The results showed that the vertical accuracy of the applied DEM affects the number, length, and density of the extracted lineaments, where these quantities increase with increasing vertical accuracy of the DEM.

Finite Element Analysis for Nightside Transfer Function Lunar Electromagnetic Induction Studies

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): H. Fuqua Haviland, G.T. Delory, I. de Pater

Abstract

The global electromagnetic induction response of the Moon has been solved numerically for several electrical conductivity profiles using the finite-element method. Here we demonstrate the capability and applicability in both two and three spatial dimensions for any input magnetic field time series measured at the Moon. We discuss the applicability of a vacuum approximation to the induced magnetic field response to the lunar plasma environment and the challenges of isolating geomagnetic induced fields including the interaction with the lunar wake structure. We perform three validation analyses comparing our vacuum model response to analytic solutions: (1) the time domain response to a step impulse or tangential discontinuity within the solar wind, (2) the time domain response to a ramp driving function, and (3) the broadband frequency domain response. We fit the analytic solutions to a root-mean-square error of better than 1% for all cases. We analyze the accuracy range and demonstrate our model’s capability of resolving interior structure from Apollo magnetometer data. We present the first time domain numerical solution of the induced magnetic field response of the Moon in vacuum for any driving input signal and any interior conductivity profile, building on previous Apollo era work. Lastly, we discuss the trade-offs between model accuracy and performance, which is of particular concern for large datasets and iterative optimizations. The transfer function method developed here is applicable to other airless body two-point magnetometer measurements including Apollo, ARTEMIS, and future lunar geophysical networks.

Mapping the chlorophyll-<em>a</em> horizontal gradient in a cascading reservoirs system using MSI Sentinel-2A images

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): Fernanda Watanabe, Enner Alcântara, Nariane Bernardo, Caroline de Andrade, Ana Carolina Gomes, Alisson do Carmo, Thanan Rodrigues, Luiz Henrique Rotta

Abstract

In this work, we investigated the trophic gradient in three reservoirs cascading in Tietê River, Southeast Brazil, based on their chlorophyll-a (chl a) concentration. The goal of this study was to identify spatial patterns in the chl a distribution, which are associated with the filtration process caused by reservoir cascade. Hence, maps of chl a content were developed considering a short time series of MSI Sentinel-2A images (2016–2018). A chl a prediction algorithm was applied to images, whose calibration was done from data collected during a severe drought (2014), which led to intense harmful algal blooms (HABs) and after the drought (2016). The outcomes showed that 20 m spatial resolution of MSI Sentinel-2A images are suitable in estimating pigment concentration in small and middle reservoirs. In addition, the Sen2cor atmospheric correction tool exhibited good performance in removing the scattering effects. Its application in retrieving the chl a content also presented good results. Besides reservoir order in the cascade, the storage system showed to be a factor that also affects the trophic state in downstream impoundments.

Analysis of deterministic and stochastic models of GPS stations in the Crustal Movement Observation Network of China

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): Shuguang Wu, Guigen Nie, Jingnan Liu, Changhu Xue, Jing Wang, Haiyang Li, Fengyou Peng

Abstract

The Crustal Movement Observation Network of China (CMONOC) has been accumulating GPS observation data for nearly 20 years since its trial operation in March 1999. It is an important task to comprehensively utilize the existing data from different research organizations and institutes, which will be beneficial to the research field of geosciences. Focusing on GPS coordinate time series of 27 CMONOC stations, this paper analyses the change of its characteristics before and after land surface environmental loading corrections (ELCs) and further studies the effect of surface displacements derived from environmental loadings on deterministic and stochastic models in this long-term GPS coordinate time series. Results show that the annual periodic signal in environmental loading displacement series may reasonably explain the seasonal signals in the vertical components of CMONOC stations but fails to account for the annual variation in the horizontal components. After ELCs, velocity estimations of 63.0% of station components decrease, while velocity uncertainties have an increasing trend. Non-integer spectral indices of GPS coordinate time series have also changed, especially in the vertical component. The optimal noise models in 14.8% of station components have changed, and the two principal models are WN+FN and WN+PL. The amplitudes of white noise and random walk noise have not been weakened, while the amplitude of flicker noise in the vertical component has reduced by 17.8% on average. Velocity uncertainties have a certain linear correlation with annual average rainfall and latitudes of these CMONOC stations, and the correlation with latitudes is stronger than with rainfall. Through a comprehensive analysis of the deterministic and stochastic models contained in the GPS time series, we may gain a further understanding of the features of crustal deformation in China.

Turbopause Range Measured by the Method of the Artificial Periodic Irregularities

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): A.V. Tolmacheva, N.V. Bakhmetieva, G.I. Grigoriev, M.N. Egerev

Abstract

A new opportunity for estimating the level of the turbopause is presented. It is based on the method of determining atmospheric parameters using artificial periodic irregularities of the ionospheric plasma (the API techniques). The obtained data show the presence of variations of the level of the turbopause. Experiments were carried out using SURA heating facility (56.1°N, 46.1°E) for API creation. Above the observation point the turbopause region occupies the altitude interval between 94 and 106 km. There are changes in the level of the turbopause during the day: in the evening hours the turbopause level can go down. Temporal variations of the turbopause level are observed. They are compared with variations in the atmospheric parameters at these heights.

The Legacy of PAMELA

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): Piergiorgio Picozza, Laura Marcelli

Abstract

PAMELA, a medium-sized experiment for the detection of cosmic rays, took data in space from 2006 to 2016. Composed of a magnetic spectrometer and several auxiliary detectors, the instrument compensated the reduced dimensions with the high performance of the individual detectors to obtain high-precision measurements over a range of energy from tens of MeV/n to 1 TeV/n.

In ten years of operation PAMELA revealed very interesting features in cosmic rays, namely in the fluxes of protons, helium, electrons, that might change our basic vision of the mechanisms of production, acceleration and propagation of cosmic rays in the Galaxy. Amazing and stimulating have been the measurements of cosmic antiproton and positron fluxes that have allowed the nature of dark matter to be probed in a new way, suggesting new ideas and setting strong constraints to the models. The constant monitoring of the solar activity and the detailed study of the solar modulation of cosmic rays for a long period have boosted important improvements to the comprehension of the heliosphere mechanisms. PAMELA also measured the radiation environment around the Earth and discovered an antiproton radiation belt.

Disaggregation of modis land surface temperature in urban areas using improved thermal sharpening techniques

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): Ruchi Bala, Rajendra Prasad, Vijay Pratap Yadav

Abstract

Applications of satellite thermal images are usually impeded by the low spatial resolution, leading to the development of various downscaling techniques. The thermal sharpening model based on the relationship between LST and Normalized Difference Vegetation Index (NDVI) was developed which shows good results in agricultural areas but may not be applicable for urban areas. Therefore, the present study focuses on determining improved downscaling techniques that shows good results in different urban regions. Hence, the performance of six different indices, namely NDVI, Enhanced Vegetation Index (EVI), Normalized Difference Built-up Index (NDBI), Urban Index (UI), Normalized Difference Soil Index (NDSI) and Normalized Difference Water Index (NDWI) were compared for thermal sharpening using Disaggregation of Radiometric Temperature (Distrad) Model over four different cities in India i.e. Bikaner, Hyderabad, Vadodara and Varanasi. LST obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors (930 m) were disaggregated to the spatial resolution of Landsat 8 Thermal Infrared Sensor (TIRS) (100 m) and compared with the Landsat LST. The performance of NDBI was found better as compared to other indices in the four cities having Root Mean Square Error (RMSE) = 1.54 K, 1.24 K, 1.10 K and 1.03 K, respectively. Further, NDBI was used for disaggregation using two robust regression techniques i.e. Least Median Square Regression (LMSR) and Bi-square regression which shows better results as compared to that of Distrad model in the four study sites. Bi-square regression method shows RMSE values of 1.30 K, 1.21 K, 0.98 K and 0.97 K, respectively for the four study sites. The LMSR and Bi-square regressions are less sensitive to outliers resulting in increased accuracy of downscaled LST.

Detecting the Angular Momentum of the Galactic Dark Halo

Thu, 05/16/2019 - 19:10

Publication date: Available online 11 May 2019

Source: Advances in Space Research

Author(s): Angelo Tartaglia

Abstract

General relativity predicts the presence of a gravito-magnetic component of the gravitational interaction induced by a rotating mass. It is currently assumed that our galaxy (as well as the others) is immersed in a dark halo. If so, it is reasonable to expect the halo to rotate, then to produce a gravito-magnetic field. Here we present a proposal to measure such effect exploiting the fully relativistic version of the Sagnac effect. When an electromagnetic signal is led to travel along a spacely closed path immersed in a gravito-magnetic field the time of flight for a complete turn depends on the direction of rotation. The proposed physical loop would be based on the Lagrange points of the Sun-Earth pair. An evaluation of the sensitivity of such a measurement, together with a discussion of more opportunities that the experiment would offer is also presented.

Observation of mesospheric wave using collocated OH airglow temperature and radar wind measurements over Indian low latitude

Thu, 05/16/2019 - 19:10

Publication date: Available online 10 May 2019

Source: Advances in Space Research

Author(s): R.N. Ghodpage, Alok Taori, O.B. Gurav, P.T. Patil, S. Gurubaran, Devendraa Siingh, G.P. Naniwadekar

Abstract

We analyzed the mesospheric winds and temperature data for investigating the waves scaling from the period of few hours to several hours (and few days) based on the airglow observations at Kolhapur (16.8oN, 74.2oE, 10.6oN dip. lat.). The data presented in this study are collected using medium frequency radar and Multispectral Scanning Photometer at low latitude station Kolhapur. We scrutinized the wind and temperature relation of these waves for the observed period from January to May 2011. The data of 56 clear nights were collected and out of which 22 nights of data shows a conspicuous wavelike features. The nocturnal variability reveals the prominent wave signatures with a period which range from 7 to 12 hour (h) as a dominant nocturnal wave. The presence of quasi 2.8 to 4 days waves with significant amplitudes is also detected. The comparison of the winds and temperatures suggests the temperature waves to be near in phase with meridional wind component and a time delayed relation with the zonal wind component.

Assessing outdoor thermal comfort of English Bazar Municipality and its Surrounding, West Bengal, India

Thu, 05/16/2019 - 19:10

Publication date: Available online 10 May 2019

Source: Advances in Space Research

Author(s): Sk. Ziaul, Swades Pal

Abstract

The present study intended to analyze the spatio-temporal outdoor thermal condition during the winter, summer and post-monsoon seasons of 2010 and 2016 by using Discomfort Index (DI) and Physiological Equivalent Temperature (PET) in the English Bazar Municipality (India). DI value has been computed based on air temperature and relative humidity data retrieved from satellite imageries and mobile field survey, while PET value has been produced with the RayMan Model. Result of DI reveals that built up area experienced partially uncomfortable-Cold (C) in winter, extremely uncomfortable in summer and partially uncomfortable-W in post-monsoon both in 2010 and 2016.But the areal extension under these discomfort zone significantly increased in 2016 compare to 2010, for example area under extreme uncomfortable and partially uncomfortable zones-Warm (W) was 3281.4 ha and 983.07 ha respectively in 2010 but it increased 4815.83 ha and 3291.74 ha respectively in 2016. Mean monthly PET value ranges from 15°C to27 °C. But in extreme hours, 58.78 % area of the town experienced strong cold stress with the range of PET of9 to 11 °C in winter season. In summer seasons 82.41 %, 16.91%, and 0.67 % areas respectively fall under the physiologically strong, extreme and scorching type of heat stress.

Classification of Hyperspectral Imagery with a 3D Convolutional Neural Network and J-M Distance

Thu, 05/16/2019 - 19:10

Publication date: Available online 10 May 2019

Source: Advances in Space Research

Author(s): Chunxing Wang, Nan Ma, Yanfang Ming, Quan Wang, Jinfeng Xia

Abstract

A three-dimensional convolutional neural network (3D-CNN) is proposed and applied to the identification of land types from hyperspectral images. Due to the advantages of the combined use of the spectral-spatial features of hyperspectral imagery, high accuracy identification of most objects can be realized. However, too many wavelengths increase information redundancy between adjacent bands and interfere with classification accuracy to some extent, complicating achievement of better results for the identification of ground objects with relatively small differences in spectral and spatial domains. To solve such problems, in this paper, the Jeffries-Matusita (J-M) distance is introduced to select effective bands to reduce the redundancy of spectral information for identifying objects with similar features. This method is based on a 3D-CNN considering pixel spectral and spatial information. The optimal band combination algorithm based on the J-M distance is first used to extract spectral features of hyperspectral data while reducing feature dimensions. Then, the 3D-CNN is applied to mine spectral and spatial features from the hyperspectral images. Finally, a Softmax classifier is used to classify land types based on the high-level features learned by the 3D-CNN. Experiments were carried out on data from an area of north-western Indiana and a Pavia university scene. In such images, some objects have very similar spectral and spatial features. The results were compared with the current 3D-CNN land type classification and show that both methods can achieve high-precision identification of most land types, but for objects with similar features, the method proposed in this article has obvious advantages.

RATAN-600 and RadioAstron reveal the neutrino-associated blazar TXS&nbsp;0506+056 as a typical variable AGN

Thu, 05/16/2019 - 19:10

Publication date: Available online 9 May 2019

Source: Advances in Space Research

Author(s): Yu.A. Kovalev, N.S. Kardashev, Y.Y. Kovalev, K.V. Sokolovsky, P.A. Voitsik, P.G. Edwards, A.V. Popkov, G.V. Zhekanis, Yu.V. Sotnikova, N.A. Nizhelsky, P.G. Tsybulev, A.K. Erkenov, N.N. Bursov

Abstract

The possible association with the high-energy neutrino event IceCube-170922A has sparked interest in the blazar TXS 0506+056. We present 72 instantaneous 1–22 GHz spectra measured over the past 20 years with the RATAN-600 telescope and compare them with the results of observations of 700 variable Active Galactic Nuclei (AGN) studied within the same program. The recent radio flare of TXS 0506+056 started from a minimum in 2013 and reached its first peak in December 2017 and a second peak in May-June 2018. This was the third strong radio flare in this source since 1997. The spectrum remains nearly flat during the flares. The spectral shape and variability pattern observed in TXS 0506+056 are typical for variable AGN. RadioAstron Space VLBI observations in 2013–2015 did not detect TXS 0506+056 on space-ground baselines of more than 9 Earth diameters. However, an observation on 23 September 2015 resulted in the detection of interferometric signal on 6 Earth diameter baselines at 18 cm close to the detection limit. We consider the possibility that TXS 0506+056 and other AGN may accelerate relativistic protons more efficiently than electrons. Relativistic protons are necessary to produce both the high-energy neutrinos observed in the IceCube Observatory and the high AGN brightness temperatures implied by the RadioAstron detection. They may also provide the main contribution to the observed synchrotron radiation of parsec-scale AGN jets. This supports the suggestion that relativistic protons may play a much more important part in extragalactic astrophysics than earlier anticipated.

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