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Guaranteed performance based adaptive attitude tracking of spacecraft with control constraints

Mon, 10/21/2019 - 19:10

Publication date: Available online 18 October 2019

Source: Advances in Space Research

Author(s): Kewei Xia, Hungsun Son

Abstract

The guaranteed performance control problem of spacecraft attitude tracking with control constraint, disturbance and time-varying inertia parameters is investigated. A new saturation function is designed to satisfy different magnitude constraints by introducing a piecewise smooth asymmetric Gauss error function. Based on the mean-value theorem, the constrained problem is transformed into an unconstrained control design subject to an unknown bounded coefficient matrix. To satisfy the constraints by performance functions, a tracking error constrained control is developed based on a hyperbolic arc-tangent asymmetric barrier Lyapunov function (BLF). In the backstepping framework, an adaptive robust control law is proposed by employing a smooth robust term simultaneously counteracting the parametric and non-parametric uncertainties, where the unknown coefficient matrix resulting from the control constraint is compensated by a Nussbaum function matrix. Rigorous stability analysis indicates that the proposed control law realizes the asymptotically tracking of spacecraft attitude and that the tracking error remains in a prescribed set which implies the achievement of the guaranteed transient performance. Numerical simulations validate the proposed theoretical results.

Families of halo orbits in the elliptic restricted three-body problem for a solar sail with reflectivity control devices

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Jia Huang, James D. Biggs, Naigang Cui

Abstract

Solar sail halo orbits designed in the Sun-Earth circular restricted three-body problem (CR3BP) provide inefficient reference orbits for station-keeping since the disturbance due to the eccentricity of the Earth’s orbit has to be compensated for. This paper presents a strategy to compute families of halo orbits around the collinear artificial equilibrium points in the Sun-Earth elliptic restricted three-body problem (ER3BP) for a solar sail with reflectivity control devices (RCDs). In this non-autonomous model, periodic halo orbits only exist when their periods are equal to integer multiples of one year. Here multi-revolution halo orbits with periods equal to integer multiples of one year are constructed in the CR3BP and then used as seeds to numerically continue the halo orbits in the ER3BP. The linear stability of the orbits is analyzed which shows that the in-plane motion is unstable while the out-of-plane motion is neutrally stable and a bifurcation is identified. Finally, station-keeping is performed which shows that a reference orbit designed in the ER3BP is significantly more efficient than that designed in the CR3BP, while the addition of RCDs improve station-keeping performance and robustness to uncertainty in the sail lightness number.

Plasma polarization electric field derived from radio sounding of solar wind acceleration region with spacecraft signals

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Yuri V. Pisanko, Oleg I. Yakovlev

Abstract

Presented is the analytical approximation of averaged solar wind velocity radial dependence in the solar wind acceleration region at heliolatitudes below 60o under low and moderate solar activity. This empirical approximation is based on the data of radio sounding of the solar corona with radio signals from various spacecraft. Deduced is an equation connecting the solar wind velocity radial dependence and the radial dependence of solar wind plasma polarization electric field intensity. This allows constructing a semi-empirical radial dependence of plasma polarization electric field corresponding to the empirical radial dependence of solar wind velocity. Main properties of the semi-empirical dependence, which is based on radio sounding data, are described.

Extending the Arctic Sea Ice Freeboard and Sea Level Record with the Sentinel-3 Radar Altimeters

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Isobel R. Lawrence, Thomas W.K. Armitage, Michel C. Tsamados, Julienne C. Stroeve, Salvatore Dinardo, Andy L. Ridout, Alan Muir, Rachel L. Tilling, Andrew Shepherd

Abstract

In February 2016 and April 2018 the European Space Agency launched the Sentinel-3A and 3B satellites respectively, as part of the European Commission’s multi-satellite Copernicus Programme. Here we process Sentinel-3A waveform data to estimate Arctic sea level anomaly and radar freeboard from November 2017 to April 2018. We compare our results to those from the CryoSat-2 satellite, and find an intermission bias on sea-level anomaly of 2 cm. We also find a mean radar freeboard difference of 1 cm, which we attribute to the use of empirical retrackers to retrieve lead and floe elevations. Ahead of Sentinel-3B waveform data being made available, we use orbit files to estimate the improvement in sampling resolution afforded by the addition of Sentinel-3A and 3B data to the CryoSat-2 dataset. By combining data from the three satellites, grid resolution or time-sampling can be almost tripled compared with using CryoSat-2 data alone.

Analysis of a long-duration AR throughout five solar rotations: Magnetic properties and ejective events

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Francisco A. Iglesias, Hebe Cremades, Luciano A. Merenda, Cristina H. Mandrini, Fernando M. López, Marcelo C. López Fuentes, Ignacio Ugarte-Urra

Abstract

Coronal mass ejections (CMEs), which are among the most magnificent solar eruptions, are a major driver of space weather and can thus affect diverse human technologies. Different processes have been proposed to explain the initiation and release of CMEs from solar active regions (ARs), without reaching consensus on which is the predominant scenario, and thus rendering impossible to accurately predict when a CME is going to erupt from a given AR. To investigate AR magnetic properties that favor CMEs production, we employ multi-spacecraft data to analyze a long duration AR (NOAA 11089, 11100, 11106, 11112 and 11121) throughout its complete lifetime, spanning five Carrington rotations from July to November 2010. We use data from the Solar Dynamics Observatory to study the evolution of the AR magnetic properties during the five near-side passages, and a proxy to follow the magnetic flux changes when no magnetograms are available, i.e. during far-side transits. The ejectivity is studied by characterizing the angular widths, speeds and masses of 108 CMEs that we associated to the AR, when examining a 124-day period. Such an ejectivity tracking was possible thanks to the mulit-viewpoint images provided by the Solar-Terrestrial Relations Observatory and Solar and Heliospheric Observatory in a quasi-quadrature configuration. We also inspected the X-ray flares registered by the GOES satellite and found 162 to be associated to the AR under study. Given the substantial number of ejections studied, we use a statistical approach instead of a single-event analysis. We found three well defined periods of very high CMEs activity and two periods with no mass ejections that are preceded or accompanied by characteristic changes in the AR magnetic flux, free magnetic energy and/or presence of electric currents. Our large sample of CMEs and long term study of a single AR, provide further evidence relating AR magnetic activity to CME and Flare production.

Correlation between Sunspots and Interplanetary Shocks Measured by ACE during 1998-2014 and Some Estimations for the 22<sup>nd</sup> Solar Cycle and the years between 2015 and 2018 with Artificial Neural Network using the Cavus 2013 model

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Huseyin Cavus, Gokhan Araz, Gani Caglar Coban, Abd-ur Raheem, Aysel I. Karafistan

Abstract

The Advanced Composition Explorer (ACE) spacecraft has measured 235 solar-based interplanetary (IP) shock waves between the years of 1998-2014. These were composed of 203 fast forward (FF), 6 slow forward (SF), 21 fast reverse (FR) and 5 slow reverse (SR) type shocks. These data can be obtained from the Interplanetary Shock Database of Harvard-Smithsonian Centre for Astrophysics. The Solar Section of American Association of Variable Star Observers (AAVSO) is an organization that counts the number of the sunspots. The effects of interplanetary shock waves on some physical parameters can be computed using a hydrodynamical model. There should be some correlations between these effects and the sunspot variations. The major objective of this paper is twofold. The first one is to search these correlations with sunspots given in the database of AAVSO. As expected, high correlations between physical parameters and sunspots have been obtained and these are presented in tables below. The second objective is to make an estimation of these parameters for the 22nd solar cycle and the years between 2015 and 2018 using an artificial neural network. Predictions have been made for these years where no shock data is present using artificial intelligence. The correlations were observed to increase further when these prediction results were included.

Multi-GNSS contributions to differential code biases determination and regional ionospheric modeling in China

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Xiaodong Ren, Jun Chen, Xingxing Li, Xiaohong Zhang

Abstract

Due to the limited number and uneven distribution globally of Beidou Satellite System (BDS) stations, the contributions of BDS to global ionosphere modeling is still not significant. In order to give a more realistic evaluation of the ability for BDS in ionosphere monitoring and multi-GNSS contributions to the performance of differential code biases (DCBs) determination and ionosphere modeling, we select 22 stations from Crustal Movement Observation Network of China (CMONOC) to assess the result of regional ionospheric model and DCBs estimates over China where the visible satellites and monitoring stations for BDS are comparable to those of GPS/GLONASS. Note that all the 22 stations can track the dual- and triple- frequency GPS, GLONASS, and BDS observations. In this study, seven solutions, i.e., GPS-only (G), GLONASS-only (R), BDS-only (C), GPS+BDS (GC), GPS+ GLONASS (GR), GLONASS+BDS (RC), GPS+GLONASS+BDS (GRC), are used to test the regional ionosphere modeling over the experimental area. Moreover, the performances of them using single-frequency precise point positioning (SF-PPP) method are presented. The experimental results indicate that BDS has the same ionospheric monitoring capability as GPS and GLONASS. Meanwhile, multi-GNSS observations can significantly improve the accuracy of the regional ionospheric models compared with that of GPS-only or GLONASS-only or BDS-only, especially over the edge of the tested region which the accuracy of the model is improved by reducing the RMS of the maximum differences from 5-15 to 2-3 TECu. For satellite DCBs estimates of different systems, the accuracy of them can be improved significantly after combining different system observations, which is improved by reducing the STD of GPS satellite DCB from 0.243 to 0.213, 0.172, and 0.165 ns after adding R, C, and RC observations respectively, with an increment of about 12.3%, 29.4%, and 32.2%. The STD of GLONASS satellite DCB improved from 0.353 to 0.304, 0.271, and 0.243 ns after adding G, C, and GC observations, respectively. The STD of BDS satellite DCB reduced from 0.265 to 0.237, 0.237 and 0.229 ns with the addition of G, R and GR systems respectively, and increased by 10.6%, 10.4%, and 13.6%. From the experimental positioning result, it can be seen that the regional ionospheric models with multi-GNSS observations are better than that with a single satellite system model.

Separation process of multi-spheres in hypersonic flow

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Seong-Hyeon Park, Gisu Park

Abstract

The separation process of multi-spheres in hypersonic flow has been experimentally investigated. The experiments were conducted in a shock tunnel at a nominal freestream Mach number of 6. Iron or acetal small light spheres with different sizes, varying from 2.38 to 6 mm, were considered. They were mounted by a thin wire. The trajectory of the spheres was analyzed using optical images. By varying the radius and the number of spheres from a single to multiple spheres, the lateral velocity and the separation behavior including the phenomenon known as ‘shock wave surfing’ were measured and analyzed. A new equation to account for the lateral velocity of the multi-spheres was proposed by extending the well-known Passey and Melosh’s theory based on two bodies. The theoretical results were compared with the presented experimental data and a good agreement was found. Using the derived equation, the re-entry trajectory analysis of multi-spheres, that is regarded as the hypothetical break-up, was performed. The ground footprint and downrange due to the separation of the multi-spheres were compared with that of single- and two-spheres. The results showed that as the number of spheres increased, the lateral velocity increased while the ballistic coefficient decreased. This led to a large discrepancy in the ground footprint as well as the downrange when compared to the single sphere. Caution should therefore be exercised in the trajectory analysis when the effect of separation induced due to fragmentation is not considered.

Propagation of grid-scale density model uncertainty to orbital uncertainties

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Fabian Schiemenz, Jens Utzmann, Hakan Kayal

Abstract

Accurate knowledge of the orbital state-vector uncertainty is required for the computation of reliable collision probabilities, the association of tracks, as well as the optimal planning of sensor resources. In low Earth Orbits (LEO) neutral atmospheric density uncertainty is the main contributor to orbital state vector uncertainty. Grid-scale model uncertainty on the other hand is, in most cases, the dominating component of atmospheric density uncertainty.

Prior research in the field of density uncertainty has been broad. Nowadays multiple authors seem to agree that a first-order stochastic Gauss-Markov process, also known as Ornstein-Uhlenbeck process (OUP), is an appropriate stochastic representation for density model uncertainties. While many have studied orbital variations due to stochastic grid-scale density uncertainty, it is believed that the work at hand provides for the first time explicit analytic equations for the estimation of orbital uncertainties due to an underlying Ornstein-Uhlenbeck process that has been optimized for the representation of atmospheric density. It is shown that the long-term in-track position error due to this modified OUP grows with ∼t3.

The presented derivations and their validation build upon prior work by Emmert et al. and Sagnières and Sharf. Numerical Monte-Carlo simulations are used to validate the findings with two different semi-empirical density models. We also demonstrate that the resulting orbital uncertainty due to the modified OUP in atmospheric density can be estimated using a classical OUP in the relative density error.

Ascent Guidance Law for a Horizontal Take-Off Vehicle with a Multi-Combined Cycle Engine

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Hongyu Zhou, Xiaogang Wang, Wenzhao Shan, Naigang Cui

Abstract

This paper researches the ascent guidance law for the vehicle with a multi-combined cycle propulsion. The guidance law comprises two parts, namely, the off-line optimal trajectories generation and online guidance. With respect to the off-line part, disturbances are discretized and incorporated into the trajectory optimization problem; subsequently, a set of trajectories is calculated to constitute a database. To quickly obtain a database that comprises a large number of trajectories, a novel ascent profile is proposed with respect to height and velocity. Based on this profile, only inequity constraints exist in the optimization model, and the original optimization problem is converted to a parameter searching problem. The optimal trajectories are calculated using a hybrid optimization method that comprises a particle swarm optimization (PSO) method and the Hooke-Jeeves (HJ) method. With respect to online guidance, the profile is updated using a radial basis function neural network (RBFNN) based on the current flight states and the database. Simulation validates the efficiency of the proposed optimization method by comparing the method with the pseudospectral method; the robustness of the guidance law is also validated using Monte Carlo simulation.

Differential code bias estimation based on uncombined PPP with LEO onboard GPS observations

Mon, 10/21/2019 - 19:10

Publication date: Available online 16 October 2019

Source: Advances in Space Research

Author(s): Peiyuan Zhou, Zhixi Nie, Yan Xiang, Jin Wang, Lan Du, Yang Gao

Abstract

Differential Code Bias (DCB) is an essential correction that must be provided to the Global Navigation Satellite System (GNSS) users for precise position determination. With the continuous deployment of Low Earth Orbit (LEO) satellites, DCB estimation using observations from GNSS receivers onboard the LEO satellites is drawing increasing interests in order to meet the growing demands on high-quality DCB products from LEO-based applications, such as LEO-based GNSS signal augmentation and space weather research. Previous studies on LEO-based DCB estimation are usually using the geometry-free combination of GNSS observations, and it may suffer from significant leveling errors due to non-zero mean of multipath errors and short-term variations of receiver code and phase biases. In this study, we utilize the uncombined Precise Point Positioning (PPP) model for LEO DCB estimation. The models for uncombined PPP-based LEO DCB estimation are presented and GPS observations acquired from receivers onboard three identical Swarm satellites from February 1 to 28, 2019 are used for the validation. The results show that the average Root Mean Square errors (RMS) of the GPS satellite DCBs estimated with onboard data from each of the three Swarm satellites using the uncombined PPP model are less than 0.18 ns when compared to the GPS satellite DCBs obtained from IGS final daily Global Ionospheric Map (GIM) products. Meanwhile, the corresponding average RMS of GPS satellite DCBs estimated with the conventional geometry-free model are 0.290, 0.210, 0.281 ns, respectively, which are significantly larger than those obtained with the uncombined PPP model. It is also noted that the estimated GPS satellite DCBs by Swarm A and C satellites are highly correlated, likely attributed to their similar orbit type and space environment. On the other hand, the Swarm receiver DCBs estimated with uncombined PPP model, with Standard Deviation (STD) of 0.065, 0.037 and 0.071 ns, are more stable than those obtained from the official Swarm Level 2 products with corresponding STD values of 0.115, 0.101, and 0.109 ns, respectively. The above indicates that high-quality DCB products can be estimated based on uncombined PPP with LEO onboard observations.

Annual, seasonal and diurnal variations of integrated water vapor using GPS observations over Hyderabad, a tropical station

Mon, 10/21/2019 - 19:10

Publication date: Available online 14 October 2019

Source: Advances in Space Research

Author(s): Nirmala Bai Jadala, Miriyala Sridhar, Nirvikar Dashora, Gopa Dutta

Abstract

This paper presents annual, seasonal and diurnal variations of integrated water vapor (IWV) derived from Global Positioning System (GPS) measurements for a tropical site, Hyderabad (17.4˚ N, 78.46˚ E). The zenith wet delay (ZWD) due to the troposphere has been computed using GPS observations and collocated meteorological data. ZWD is converted to IWV with very little added uncertainty. Mean monthly IWV values show maximum in July (∼ 50 kg m-2) and minimum in December (∼ 15 kg m-2). Fast Fourier Transform (FFT) and Harmonic analyses methods have been adopted to extract amplitudes and phases of diurnal (24 h), semi-diurnal (12 h) and ter-diurnal (8 h) oscillations which yielded comparable results. Amplitude of the 24 h component is observed to be maximum in spring whereas 12 h and 8 h components maximize in summer. A cross-correlation study between available daily IWV values and corresponding surface temperatures over one year produced a good correlation coefficient (0.44). The correlation obtained for different seasons got reduced to 0.25, 0.02, -0.39 and 0.21 for winter, spring, summer and autumn seasons respectively. The correlation between IWV and rainfall is poor. The coefficients obtained for the whole year is 0.05 and - 0.13 for the rainy season.

Quantitative Analyses of Complexity and Nonlinear trend of Radio Refractivity Gradient in the troposphere

Mon, 10/21/2019 - 19:10

Publication date: Available online 14 October 2019

Source: Advances in Space Research

Author(s): A.O. Adelakun, J.S. Ojo, O.V. Edward

Abstract

In this paper, the complexity and nonlinear trends of Radio Refractivity Gradient (RRG) in the troposphere over selected locations in Nigeria are analyzed and discussed extensively. The RRG is an important parameter in estimating path clearance and propagation effects such as ducting, surface reflection and multi-path on terrestrial line of-sights links. Also, radio wave signal propagating in the troposphere is affected by unpredictability of a weather condition which includes the variations of meteorological parameters such as temperature, pressure and relative humidity. The complex state of the atmosphere, which is the medium for the transmission of radio signals tend to have very strong influence such as scintillation, ducting, e.t.c on the quality of the radio signal, amplitude and phase. Variations in the meteorological parameters also induce variations in the refractive index of the atmosphere which in-turn results in the effect known as radio refractivity. For effective prediction and modeling of radio signal propagation, one should be able to characterize the nature and predictability of the computed RRG information. Chaotic Quantifiers (CQ) such as Phase Plot Reconstruction (PPR), Average Mutual Information (AMI), False Nearest Neighbor (FNN), Recurrence Plot (RP) and Recurrence Quantification Analyses (RQA) are used to assess the RRG. The information reveal, however, is based on the prediction techniques, design and frequency planning of microwave networks which may be useful for optimum performances during atmospheric turbulence.

Mesoscale Eddy Variability and its Linkage to Deep Convection over the Bay of Bengal using Satellite Altimetric Observations

Mon, 10/21/2019 - 19:10

Publication date: Available online 11 October 2019

Source: Advances in Space Research

Author(s): Heather L. Roman-Stork, Bulusu Subrahmanyam, Corinne B. Trott

Abstract

In the Bay of Bengal (BoB), surface circulation is strongly influenced by the Indian Monsoon and notable local eddying that modulates the East India Coastal Current (EICC). In this study, we apply an eddy tracking algorithm to 25 years (1993-2018) of satellite altimetric observations to identify, analyze, and track mesoscale eddies in the BoB from their generation to dissipation. We compare the characteristics and trajectories of these eddies during the southwest (SW) and northeast (NE) monsoon seasons and during the pre- and post-SW monsoon periods to better understand the seasonality of the local eddy field. We find high eddy generation in the eastern BoB associated with instability induced by coastal Kelvin waves and the westward propagating Rossby waves, but we found the most robust eddies in the western BoB around the EICC. Ocean heat content (OHC) in the BoB was compared with warm-core eddies and we find that warm-core eddies drive changes in OHC. We also compared the eddy field during strong and weak SW monsoon forcing and with varying Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) conditions, finding a statistically significant relationship with warm-core eddies and sea surface temperatures (SSTs; R2 = 91%) and outgoing longwave radiation (OLR; R2 = 88%) during periods of strong ENSO and IOD forcing. To understand the impact of these eddies on local atmospheric convection we found the composite surface structure of anticyclonic and cyclonic eddies of warm-core and cold-core SSTs, finding a close relationship between the eddy-composite SSTs and OLR.

Gravity Wave Mixing Effects on the OH*-layer

Mon, 10/21/2019 - 19:10

Publication date: Available online 11 October 2019

Source: Advances in Space Research

Author(s): E. Becker, M. Grygalashvyly, G.R. Sonnemann

Abstract

Based on an advanced numerical model for excited hydroxyl (OH*) we simulate the effects of gravity waves (GWs) on the OH*-layer in the upper mesosphere. The OH* model takes into account 1) production by the reaction of atomic hydrogen (H) with ozone (O3), 2) deactivation by atomic oxygen (O), molecular oxygen (O2), and molecular nitrogen (N2), 3) spontaneous emission, and 4) loss due to chemical reaction with O. This OH* model is part of a chemistry-transport model (CTM) which is driven by the high-resolution dynamics from the KMCM (Kühlungsborn Mechanistic general Circulation Model) which simulates mid-frequency GWs and their effects on the mean flow in the MLT explicitly. We find that the maximum number density and the height of the OH*-layer peak are strongly determined by the distribution of atomic oxygen and by the temperature. As a results, there are two ways how GWs influence the OH*-layer: 1) through the instantaneous modulation by O and T on short time scales (a few hours), and 2) through vertical mixing of O (days to weeks). The instantaneous variations of the OH*-layer peak altitude due to GWs amount to 5-10 km. Such variations would introduce significant biases in the GW parameters derived from airglow when assuming a constant pressure level of the emission height. Performing a sensitivity experiment we find that on average, the vertical mixing by GWs moves the OH*-layer down by ∼2-7 km and increases its number density by more than 50%. This effect is strongest at middle and high latitudes during winter where secondary GWs generated in the stratopause region account for large GW amplitudes.

Probing afternoon detached aurora and high-latitude trough based on DMSP observations

Mon, 10/21/2019 - 19:10

Publication date: Available online 10 October 2019

Source: Advances in Space Research

Author(s): Su Zhou, Kazuo Shiokawa, Igor Poddelsky, Yuqing Chen, Jin Zhang

Abstract

The present work displays the observations of an afternoon detached aurora along with ionospheric high-latitude trough. The event was observed by DMSP F17 on 19 September 2014. The afternoon detached aurora was isolated from the auroral oval and was located between 12:00–18:00 magnetic local time (MLT) and 65°–70° geomagnetic latitude (MLAT). Particle observations indicate that the afternoon detached aurora was produced by energetic ring current ions with energies above ∼10 keV where the main ion energy was likely to be above the upper limit of DMSP measurement (∼30 keV). Magnetometer observation from the ground implies that the energetic ions were likely scattered by EMIC waves. Both the detached aurora and the auroral oval are found to be well inside the high-latitude trough with MLAT between ∼64° and ∼76° (68°– 80° GLAT). The auroral oval corresponds to a westward (sunward) plasma drift. It is expected that the westward drift transports the low-density plasma in the nightside toward the dayside, leading to the high-latitude trough formation. The afternoon detached aurora was well equatorward of the high-latitude trough, and the corresponding plasma drift was nearly zero. The plasma associated with the detached aurora is expected to be stagnant, and broaden the high-latitude trough equatorward.

Energy spectra of abundant cosmic-ray nuclei in the NUCLEON experiment

Mon, 10/21/2019 - 19:10

Publication date: Available online 10 October 2019

Source: Advances in Space Research

Author(s): V. Grebenyuk, D. Karmanov, I. Kovalev, I. Kudryashov, A. Kurganov, A. Panov, D. Podorozhny, A. Tkachenko, L. Tkachev, A. Turundaevskiy, O. Vasiliev, A. Voronin

Abstract

The NUCLEON satellite experiment is designed to directly investigate the energy spectra of cosmic-ray nuclei and the chemical composition (Z = 1–30) in the energy range of 2–500 TeV. The experimental results are presented, including the energy spectra of different abundant nuclei measured using the new Kinematic Lightweight Energy Meter (KLEM) technique. The primary energy is reconstructed by registration of spatial density of the secondary particles. The particles are generated by the first hadronic inelastic interaction in a carbon target. Then additional particles are produced in a thin tungsten converter, by electromagnetic and hadronic interactions. The deconvolution of spectra was performed. Statistical errors were presented.

Establishment of atmospheric weighted mean temperature model in the polar regions

Mon, 10/21/2019 - 19:10

Publication date: Available online 10 October 2019

Source: Advances in Space Research

Author(s): Shuaimin Wang, Tianhe Xu, Wenfeng Nie, Jian Wang, Guochang Xu

Abstract

Due to the special geographical location and extreme climate environment, the polar regions (Antarctic and Arctic) have an important impact on global climate change. Atmospheric weighted mean temperature (Tm) is a crucial parameter in the retrieval of precipitable water vapor (PWV) from the zenith wet delay (ZWD) of ground-based Global Navigation Satellite System (GNSS) signal propagation. In this paper, the correlation between weighted mean temperature and surface temperature (Ts) is studied firstly. It is shown that the correlation coefficients between Tm and Ts are 0.93 in the Antarctic and 0.94 in the Arctic. The linear regression Tm model and quadratic function Tm model of the Antarctic and the Arctic are established respectively using the radiosonde profiles of 12 stations in the Antarctic and 58 stations in the Arctic from 2008 to 2015. The accuracies of the linear regression Tm model, the quadratic function Tm model and GPT2w Tm model which is a state-of-the-art global Tm model are verified using the radiosonde profiles from 2016 to 2018 in the Antarctic and Arctic. Root Mean Square (RMS) errors of the linear regression Tm model, the quadratic function Tm model and GPT2w Tm model in the Antarctic are 3.07 K, 2.87 K and 4.32 K respectively, and those in the Arctic are 3.53 K, 3.38 K and 4.82 K, which indicates that the quadratic function Tm model has a higher accuracy compared to linear regression Tm model, and the accuracies of the two regional Tm models are better than that of GPT2w Tm model in the polar regions. In order to better evaluate the accuracy of Tm in the PWV retrieval, the PWV values of radiosondes are used for comparisons as the reference value. The RMS errors of PWV derived from the two Tm models are similar for 1.28 mm in the Antarctic and 1 mm in the Arctic respectively. In addition, the spatial and temporal variation characteristics of Tm are analyzed in the polar regions by spectral analysis of Tm data using fast Fourier transform. The results show that the Tm has obvious seasonality and annual periodicity in the polar regions, and the maximum difference between warm season and cold season is about 45 K. After comparing and analyzing the influences of latitude, longitude and elevation on the Tm in the polar regions, it is found that latitude and elevation have a greater influence on the Tm than the longitude. As the latitude and elevation increase, the Tm decreases, and vice versa in the polar regions.

Corsica: A 20-Yr Multi-Mission Absolute Altimeter Calibration Site

Mon, 10/21/2019 - 19:10

Publication date: Available online 9 October 2019

Source: Advances in Space Research

Author(s): P. Bonnefond, P. Exertier, O. Laurain, T. Guinle, P. Féménias

Abstract

Initially developed for monitoring the performance of TOPEX/Poseidon and follow-on Jason legacy satellite altimeters, the Corsica geodetic facilities that are located both at Senetosa Cape and near Ajaccio have been developed to calibrate successive satellite altimeters in an absolute sense. Since 1998, the successful calibration process used to calibrate most of the oceanographic satellite altimeter missions has been regularly updated in terms of in situ instruments, geodetic measurements and methodologies. In this study, we present an assessment of the long-term stability of the in situ instruments in terms of sea level monitoring that include a careful monitoring of the geodetic datum. Based on this 20-yr series of sea level measurements, we present a review of the derived absolute Sea Surface Height (SSH) biases for the following altimetric missions based on the most recent reprocessing of their data set: TOPEX/Poseidon and Jason-1/2/3, Envisat and ERS-2, CryoSat-2, SARAL/AltiKa and Sentinel-3A&B. For the longest time series the standard error of the absolute SSH biases is now at a few millimeters level which is fundamental to maintain the high level of confidence that scientists have in the global mean sea level rise.

On the uncertainty associated with validating the global mean sea level climate record

Mon, 10/21/2019 - 19:10

Publication date: Available online 9 October 2019

Source: Advances in Space Research

Author(s): Christopher S. Watson, Benoit Legresy, Matt A. King

Abstract

Satellite altimetry provides the ongoing sea level climate data record that provides evidence for one of the most significant manifestations of climate change on Earth. External and independent validation of satellite altimetry is a core component of mission design, providing confidence in such a seminal climate record. The global tide gauge network, corrected for the effects of vertical land motion, forms one of a suite of approaches used to validate satellite altimetry. Used as a tool to identify potential systematic error, the altimeter minus tide gauge approach ultimately leads to an improved geophysical data record through iterative diagnosis, correction and reprocessing of the mission record. A recent example includes the detection of a small but significant drift in the early part of the record associated with the TOPEX record. Here, we return to the approach that quantified the apparent drift in the TOPEX record and focus on further elucidating the uncertainty of that technique as a function of mission duration. We show that approximately 2.9 years is required to reach a validation uncertainty of ±1 mm/yr (1σ). This result appears optimistic by a factor of 1.5 to 2.2 in comparison to an error budget approach reported in the literature. Our results highlight the challenge of validating the altimeter record using a sparse and irregularly distributed network of tide gauges and points towards possible areas of future improvement in the validation approach.

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