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A discussion on the mode conversion from purely perpendicular upper-hybrid mode waves to LO mode waves in an inhomogeneous plasma

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Mohammad Javad Kalaee, Yuto Katoh

Abstract

We consider the equatorial region of the magnetosphere, where the magnetic field is perpendicular (or near to perpendicular) to the density gradient and mode conversion process from UH to LO-mode waves or reverse process are expected. We review and study the mode conversion from UH (upper hybrid) to LO (left hand polarized ordinary) mode waves by a spatially two dimensional plasma fluid code. Several simulations with different initial wave vectors under the same background plasma condition have been performed. We focus on the conversion efficiency from the UH-mode waves with purely perpendicular wave normal angle to the LO-mode waves, since one of the source of generation UH wave can be Bernstein mode as the purely perpendicular electrostatic waves. For this special case, the UH wave normal is kept in perpendicular direction with respect to the magnetic field, and difficult to be in matching direction for conversion to LO mode. Simulation results show that the mode conversion efficiency in this particular case is very weak, since two branches of Z-mode wave and LO mode wave in the dispersion relation are disconnected. We present a discussion to show that for this case (purely perpendicular propagation) a special angle (except 90°), between the magnetic field and the density gradient is necessary for occurrence of efficient mode conversion. For the case (purely perpendicular propagation and the magnetic field perpendicular to the density gradient), the mode conversion just occurred via the tunneling effect, where a steepness of the inhomogeneity plays an essential role.

A pseudospectral method based robust-optimal attitude control strategy for spacecraft

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Arunava Banerjee, Syed Muhammad Amrr, M. Nabi

Abstract

This paper proposes an optimal integral sliding mode control (ISMC) scheme for attitude regulation of the rigid spacecraft. This control technique is capable of handling inertial matrix uncertainties as well as external disturbances. To incorporate optimality into the robust control law, the ISMC is integrated with Legendre pseudospectral method (LPSM). The minimization of the cost function and constraint handling of the spacecraft is obtained by LPSM, while the ISMC provides disturbance rejection. LPSM is chosen for its relatively high rate of convergence and its capability of solving a wide range of challenging optimal control problems. Theoretical stability analysis of closed loop system using Lyapunov theorem guarantees the convergence of attitude states. A comparative analysis between the proposed LPSM-ISMC and Chebyshev Pseudospectral Method (CPSM) based ISMC, is also presented in this paper. The effectiveness of the proposed robust-optimal control strategy is established through simulation results.

Dynamics modeling and simulation of self-collision of tether-net for space debris removal

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Jiyue Si, Zhaojun Pang, Zhonghua Du, Chun Cheng

Abstract

Tether-net is a new active removal technology for space debris, and its deployment and capture have attracted considerable attention. This study focuses on the dynamics and simulation of self-collision of tether-net. First, the mass-spring-damper method is used to model tether-net and a line–line self-collision detection algorithm is proposed according to the geometric characteristics of tether-net. Thereafter, combined with the nonlinear collision model, the self-collision process of tether-net is studied. Two simulations of the close-up of a net with or without a target are executed to show the difference between considering and not considering the self-collision of tether-net. Results reveal that the capture process of tether-net with consideration for self-collision is different from the one without self-collision, especially after the corners of the net begin to contact each other.

Evaluation of the SSN and F10.7 indices as a cause for performance variation of the IRI 2016 and IRI-Plas 2017 models

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Yekoye Asmare Tariku

Abstract

This paper mainly focuses on the evaluation of efficiency of the Sunspot Number (SSN) and the 10.7 cm Solar Radio Flux (F10.7) indices as a cause for the variation of the performance of the latest versions of the International Reference Ionosphere model (IRI 2016 with NeQuick, IRI01-corr and IRI2001 options for the topside electron density) and the IRI Extended to the Plasmasphere (IRI-Plas 2017) for the modeling of the Total Electron Content (TEC). The Global Positioning System (GPS)-derived TEC data obtained from the dual frequency GPS receivers located at Observation Rock, OBSR (geog 46.90°N, 238.18°W, Geom. 52.46°N) and Husband, HUSB (44.12°N, 238.15°W, Geom. 49.73°N) in the West Pacific region during the recent solar maximum (2012-2014) years have been considered for the validation of the performance of the models. The results show that both the GPS-derived TEC (GPS VTEC) and modelled (IRI 2016 and IRI-Plas 2017 VTEC) seasonal diurnal values tend to peak at 00:00 UT (16:00 LT) and 20:00 (12:00 LT) with the highest being observed mostly at 20:00 (12:00 LT); while, their minima are mostly observed at about 13:00 UT (05:00 LT). In addition, in utilizing the SSN, the best performance is generally observed in the June solstice months, especially by the IRI-Plas 2017 model. However, for the equinoctial and December solstice months, the best performance is generally observed by the IRI 2016 model with NeQuick and IRI01 options. It has also been shown that the root-mean-square deviations between the GPS-derived and modelled VTEC diurnal variation in using the F10.7 index are generally less than those of the SSN option in all months, revealing that both the IRI 2016 and IRI-Plas 2017 models generally show better performance using F10.7 index than the SSN. Hence, the F10.7 option is recommended for better TEC modeling employing the IRI 2016 and IRI-Plas 2017 models during the recent solar maximum years over the West Pacific region. In addition, both models cannot effectively estimate the geomagnetic storm time TEC variation.

Study of the relative geoeffectiveness of high-speed solar wind streams of different speed and different durations

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): F. Mustajab, Badruddin, H. Asiri

Abstract

We consider high speed streams (HSS) identified from 16 years (1996–2011) of continuous solar wind plasma and field data. We compare the geomagnetic response of the HSS of different speed and different durations based on statistical distribution, the superposed epoch analysis as well as the regression analysis. We analyse the geomagnetic responses of the HSS of different speed and durations together with the solar wind plasma and field data. The observed differences in the amplitudes, time profiles and recovery characteristics of geomagnetic disturbances during the passage of the HSS of different speed and durations are compared with the differences in the simultaneous solar wind plasma/field behaviour. Implications of these results on the solar wind-magnetosphere coupling are discussed.

Invariance of conveying capacity for drilling into lunar soil simulant

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Tao Chen, Zhen Zhao, Stephen R. Schwartz, Caishan Liu, Qi Wang

Abstract

In this paper, we study the conveying dynamics in the helical groove of an auger drilling into lunar simulant. We demonstrate that the stress-coupling effect of the conveyed granules by the groove of a drill auger plays a significant role on the dynamics of conveyance. For this, a discrete element method (DEM) is adopted first to uncover the motion and the stress characteristics of conveyed granules in a working auger. Then, a simplified dynamic model following the stress characteristics of DEM is established. The simplified model can not only reflect the results by the discrete element method, but can also explain well the proportional relationship between the maximum conveying rate and the rotating speed of the auger in the experiment (Zhao et al., 2019).

Smart-RTK: Multi-GNSS kinematic positioning approach on android smart devices with Doppler-smoothed-code filter and constant acceleration model

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Kaishi Zhang, Wenhai Jiao, Liang Wang, Zishen Li, Jianwen Li, Kai Zhou

Abstract

Global Navigation Satellite System (GNSS), once dedicated to military and geodetic applications, is entering civilian life with the development of low-cost internal multi-GNSS chips in mass-market smart devices. The recently enabled Application Programming Interface (API) to GNSS raw measurement in Android Nougat operating system, make it possible to implement precise positioning technology on Android smart devices, such as Real-Time Kinematic Positioning (RTK) and Precise Point Positioning (PPP). An optimized kinematic positioning approach on Android smart devices with Doppler-Smoothed-Code (DSC) filter and Constant Acceleration (CA) model is assessed in this paper. In this optimized approach, DSC filter is used to reduce the code measurement noise, which is extremely high on smart devices and CA model is used to accurately predict the kinematic state of smart devices. The optimized approach is named Smart-RTK for its applicability to smart devices, respectively. The performance of the Smart-RTK approach is validated by two Google/HTC Nexus 9 tablets separately under stationary, walking, and vehicular condition. The numerical experiments show the significant improvement on positioning accuracy and continuity. The positioning Root Mean Square Error (RMSE) in horizontal component reaches about 0.3–0.6 m in stationary condition and 0.4–0.7 m in walking condition, improved by about 85% compared with that of chipset original solutions. In the subsequent vehicular experiment, the horizontal positioning RMSE is about 0.85 m, 50% better than that of chipset solutions.

Abnormal behaviour of sporadic E-layer during the total solar eclipse of 22 July 2009 near the crest of EIA over India

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): Prabhakar Tiwari, Navin Parihar, Adarsh Dube, Rajesh Singh, S. Sripathi

Abstract

In this study we present the behaviour of sporadic E-layer during a total solar eclipse (TSE) which occurred during the dawn/sunrise hours over a site located in the path of totality. A Canadian Advanced Digital Ionosonde (CADI) was operated at Allahabad (25.4° N, 81.9° E), a low latitude station located near the crest of equatorial ionization anomaly (EIA) in the Indian subcontinent to study the ionospheric effects of 22 July 2009 TSE. Corresponding to the eclipse period, a gradual increase of ftEs (top frequency of Es layer) in the 4–5 MHz range was seen on the control days. On 22 July (the TSE day), correlated changes in ftEs coinciding with the TSE progression was noted – (i) sharp decrease near first and second contact of TSE, (ii) an increase after first and second contact, and (iii) wavelike fluctuations in ftEs variation during eclipse hours and beyond. Much higher ftEs values were noted during the TSE hours in comparison to that seen on usual days. Strong blanketing Es layer developed during the TSE hours and persisted for slightly longer duration than its usual occurrence time. Near the TSE totality, slight lowering of the base height of Es layer was also noted.

A solar electron event model in near-Earth space

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Jian-zhao Wang, Ying Wang, Shu-wu Dai, Chen Wang, Ji-nan Ma, Xiao-yu Jia, Yan-cun Li, Dai Tian, Jia-wen Qiu

Abstract

A new solar electron event model is developed based on Virtual Timeline Method (VTM). We study events individually by analyzing the 17-year data of 3DP instrument on WIND spacecraft. This model is established in different solar cycle phases and is based on statistics of duration, fluence, and waiting time of solar electron events. The fluences follow a log-normal distribution and logarithmic durations fit well with logarithmic fluences linearly. We prove that waiting times of events significantly deviates from the Poisson process by investigating the stationary and event independence property of Poisson distribution. After a comparison study on waiting times, we choose the Lévy distribution in solar minimum and maximum years. During solar minimum, the event frequency is much lower than that of solar maximum, but the event magnitude is independent of solar cycle period. Large events also happen in solar minimum years. In different solar cycle phases, this model can output a spectrum with confidence level and mission duration by generating many series of virtual timelines composed of many pseudo-events based on Monte Carlo method. On the other hand, spectra in solar minimum years are softer than that in solar maximum years. The fluences in solar maximum years are about one order of magnitude higher than that in solar minimum years in a given mission period. We also compare this model with Interplanetary Electron Model (IEM) quantitatively and prove that this model is advanced.

The capability analysis of the bistatic radar system based on Tianlai radio array for space debris detection

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Jiawei Li, Pengqi Gao, Ming Shen, You Zhao

Abstract

The bistatic radar system has been one of the effective methods to detect the space debris in low earth orbit (LEO). Tianlai radio array with cylindrical-parabolic antennas is designed for dark energy detection, which has large field of view and high sensitivity, offering a fan-beam during the observation. We propose a bistatic radar system, which consists of Tianlai radio array and an incoherent scattering radar (ISR) assumed as a transmitter in the Qujing city of China, to detect space debris. In this paper, we calculate and analyze the detection capabilities of this system. The results show the bistatic radar system has the potential to detect small space debris of less than 10 cm in LEO. We provide a space debris detection method to obtain the position of the cross-beam satisfying the observation requirement with the TLE data of the space debris. The method can solve the problem of space synchronization between the radio array and ISR. We used the long-short baseline method of the radio array to locate the space target. The relationship among positioning error, the azimuth and the elevation angle are also discussed.

Spectral analysis on the solar parameters and empirical orthogonal functions of foF2 data obtained by singular value decomposition

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Junmi Gogoi, Kalyan Bhuyan

Abstract

The geomagnetic storm is an important weather issue in the earth’s ionosphere-magnetosphere system. Many linear and nonlinear systems are involved in this earth-space environment. In order to understand the nonlinearly evolving dynamical system of magnetosphere and ionosphere, Time series analysis of foF2 data, Disturbance Storm Index Dst, Geomagnetic activity Index Ap and some other parameters during various solar cycles has been carried out in this work. The hourly data of critical frequency of F2 layer (foF2) for three ionosonde stations [Townsville (TV51R) 19.7°S, 146.9°E; Canberra (CB53N) 35.3°S, 149.1°E; Juliusruh (JR055) 54.6°N, 13.4°E] have been noted for 4 solar cycles viz., Solar Cycle 20, 21, 22 and 23. Hourly time series analysis has been performed to achieve some functional approaches such as statistical, analytical and spectral approach etc. to examine for the presence of periodicities in the data. Time Series is a sequential set of data which can be measured over time, and since the data being used for this work had been recorded as a function of time under various conditions, the appearance of missing observations in time series data is a very common issue. Different series may require different approaches to estimate these missing values. As such, to vanquish the problem of missing data we have attempted to estimate the missing value of foF2 data for various stations using the technique of Singular Value Decomposition (SVD). Another important method, Lomb Scargle Periodogram (LSP) has been performed on the Empirical Orthogonal Functions (EOFs) u1 and u2 (that has been obtained by SVD) along with the solar parameters such as solar flux f10.7, sun spot number (SSN) etc. and geomagnetic indices such as Dst index, Kp index & Ap index etc. for the four solar cycles to find the correlation, if any. For all the plots after performing LSP the power has been found out at 99% confidence level to see how much significant the generated data with respect to the parameters is. The periodicity obtained after performing LSP are divided into three terms namely:– (a) short-term periodicity, in which 27 days periodicity is found to be prominent, (b) mid-term periodicity, in which 1.3 year periodicity is found to be very common and (c) long-term periodicity, in which 11 years periodicity is very regular in almost among all the parameters and in the EOFs.

Geocentric Baltic Sea level changes along the southern coastline

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Adam Łyszkowicz, Anna Bernatowicz

Abstract

Sea level is a unique indicator in climate impact studies on any changes on the surface of the Earth. Traditionally, tide gauges allow observation of relative (relative to land) sea level changes at specific locations with a high resolution in time. Common method of sea level determination in XXI century is the combination of tide gauge observations with satellite observation data. So determined sea level changes are absolute changes and they are referred to the beginning of the ITRF system.

Geocentric changes in the Baltic Sea level are monitored, inter alia, by the SONEL network. This network system does not include the southern coast of the Baltic Sea. The aim of this work is to fill this gap and to compute geocentric changes in the Baltic Sea at the stations: Hel, Władysławowo, Łeba, Ustka, Kołobrzeg, Świnoujście.

The tide gauge data needed for the analysis were made available by the Institute of Meteorology and Water Management and the GNSS data was taken from web page Nevada Geodetic Laboratory. The analysis of the time series of tide gauge and GNSS observations was carried out using the TSAnalyzer software. We assumed that GNSS and tide gauge series have a seasonal signal (annual plus semi-annual) and a trend. First the outliers were removed from observation, then the jumps were viewing. The trend, annual and semi-annual terms were calculated for GNSS and tide gauge series.

The results of the work are calculated geocentric changes in the Baltic Sea level along southern coast and they are at a level of 0.3 mm/year except Ustka where it reach value 4.68 mm/year.

Designing observation scheme in X-ray pulsar-based navigation with probability ellipsoid

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Haoye Lin, Bo Xu, Jingxi Liu

Abstract

The accuracy in pulsar-based navigation system can be improved with a well-designed observation scheme. In this paper, based on the idea that minimises the size of position probability ellipsoid at each updating time, four strategies are put forward for determining observation order. As the calculation of posterior probability ellipsoid only requires a priori orbit information, the observation scheme can be designed during preliminary mission analysis. These strategies can be employed in both situations with single detector and multiple detectors. Numerical simulations show that the proposed observation strategies achieve good performance.

Data-driven modelling of the Van Allen Belts: The 5DRBM model for trapped electrons

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Lionel Métrailler, Guillaume Bélanger, Peter Kretschmar, Erik Kuulkers, Ricardo Pérez Martínez, Jan-Uwe Ness, Pedro Rodriguez, Mauro Casale, Jorge Fauste, Timothy Finn, Celia Sanchez, Thomas Godard, Richard Southworth

Abstract

The magnetosphere sustained by the rotation of the Earth’s liquid iron core traps charged particles, mostly electrons and protons, into structures referred to as the Van Allen Belts. These radiation belts, in which the density of charged energetic particles can be very destructive for sensitive instrumentation, have to be crossed on every orbit of satellites traveling in elliptical orbits around the Earth, as is the case for ESA’s INTEGRAL and XMM-Newton missions. This paper presents the first working version of the 5DRBM-e model, a global, data-driven model of the radiation belts for trapped electrons. The model is based on in situ measurements of electrons by the radiation monitors on board the INTEGRAL and XMM-Newton satellites along their long elliptical orbits for respectively 16 and 19 years of operations. This model, in its present form, features the integral flux for trapped electrons within energies ranging from 0.7 to 1.75 MeV. Cross-validation of the 5DRBM-e with the well-known AE8min/max and AE9mean models for a low eccentricity GPS orbit shows excellent agreement, and demonstrates that the new model can be used to provide reliable predictions along widely different orbits around Earth for the purpose of designing, planning, and operating satellites with more accurate instrument safety margins. Future work will include extending the model based on electrons of different energies and proton radiation measurement data.

The Atmospheric Coupling and Dynamics Across the Mesopause (ACaDAMe) mission

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): D. Janches, A.W. Yu, M.A. Krainak, C. Gardner, B. Kaifler, S. Etemad, D.C. Fritts, S.D. Eckermann, R.L. Collins, E.C.M. Dawkins, R.S. Lieberman, D.R. Marsh, G. Liu, W. Jarvis

Abstract

The Atmospheric Coupling and Dynamics Across the Mesopause (ACaDAMe) is a mission designed to uniquely address critical questions involving multi-scale wave dynamics at key space weather (SWx) “gateway altitudes” of the mesosphere and lower thermosphere (MLT) at ~70–150 km. ACaDAMe observes with a nadir-pointing resonant lidar that utilizes the fluorescence of atomic Na present in the MLT. By tuning a laser to the Na absorption wavelength (589 nm), ACaDAMe would perform very high resolution measurements of temperature and Na densities across the mesopause during both day and night. In this manner, Na is used as tracer for observing and characterizing MLT waves generated by tropospheric weather that represent the dominant terrestrial source of energy and momentum affecting space weather and transport of mesospheric species.

The application of the tasseled cap transformation and feature knowledge for the extraction of coastline information from remote sensing images

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Chao Chen, Juan Bu, Yuhuan Zhang, Yue Zhuang, Yanli Chu, Jiachen Hu, Biyun Guo

Abstract

The coastline is the dividing line between the ocean and land. Monitoring coastline dynamics is of crucial importance because it provides essential information for understanding the coastal response to contemporary climate change and human impacts. Real-time monitoring of coastlines has increasingly depended on remote sensing images at high temporal and spatial resolutions. In this study, a method combining the tasseled cap transformation (TCT) and feature knowledge is proposed to extract coastline information. Because traditional remote sensing methods cannot be used where total suspended sediment content is high, land and ocean separation was carried out using the wetness component of the Otsu method. A mathematical morphology analysis was used to remove the influence of lakes, rivers, and ships. Coastlines with shorter length were eliminated, and intermittent coastlines were connected based on a coordinate geometry description (such as length, distance, and direction). For the period of 2000–2018, Landsat-5 TM (Thematic Mapper) and Landsat-8 OLI (Operational Land Imager) images of the Zhoushan Islands, China, were used to extract coastline information using a method combining TCT and feature knowledge. A comparison of the results with reference data obtained by visual interpretation shows that the average of producer accuracy and user accuracy are 93.62% and 96.15%, respectively, and the average of length error was 2.45%. Therefore, the proposed method was effective in delineating the boundary between land and ocean and more effective than traditional methods in areas with high suspended sediment concentrations.

Quality assessment of GPS, Galileo and BeiDou-2/3 satellite broadcast group delays

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Ningbo Wang, Zishen Li, Oliver Montenbruck, Chengpan Tang

Abstract

The quality of broadcast group delays (BGDs) transmitted in the navigation messages of the Global Positioning System (GPS), BeiDou-2/3 and Galileo is assessed by comparison with multi-GNSS differential code bias (DCB) products generated at the Chinese Academy of Sciences (CAS). An automatic DCB (AutoDCB) realignment procedure is presented to handle discontinuities within individual BGD/DCB series. The analysis is performed over a four-year period starting from January 2014. For GPS, the consistency between broadcast timing group delays (TGDs) and CAS MGEX DCBs is 0.25 ns, and the corresponding values are 0.05, 0.3 and 0.45 ns for L1C/A, L2C and L5Q inter-signal corrections (ISCs), respectively. The best agreement between GPS L2C ISCs and CAS MGEX C1W-C2L DCBs is emphasized. The inconsistency between broadcast and post-processed C2I-C6I DCBs (=TGD1) is found to decrease from 1.5 to 0.45 ns across the entire BeiDou-2 constellation since late July 2017, indicating a significant quality improvement of BeiDou-2 transmitted TGD1 parameters. A systematic offset of around 4.0 ns is found between TGD1 reference datums of BeiDou-3 and BeiDou-2 constellations, which needs to be removed in the combined BeiDou-2/3 B1I single-frequency or B1I+B3I dual-frequency standard positioning applications. Aside from the increasingly improved repeatability of broadcast E1-E5a/5b delays, an overall agreement at the level of 0.1–0.4 ns is achieved between Galileo transmitted value and DCB metadata from European GNSS Agency (GSA) for the in-orbit validation (IOV) satellites. In the comparison of Galileo BGDs and CAS MGEX DCBs, the consistency is at the level of 0.4 and 0.3 ns for IOV and full operation capability (FOC) satellites, respectively. The requirement of the routine assessment of broadcast group delays is also emphasized, in particular for newly launched satellites of new constellations.

A new hierarchical method for automatic road centerline extraction in urban areas using LIDAR data

Publication date: 1 November 2019

Source: Advances in Space Research, Volume 64, Issue 9

Author(s): Sayyed Abdullah Kianejad Tejenaki, Hamid Ebadi, Ali Mohammadzadeh

Abstract

Road detection and road extraction are important and challenging issues in the fields of photogrammetry and remote sensing. Researchers have conducted wide research in this regard based on multispectral images and achieved relatively useful results. Image-data driven methods have some shortcomings such as shadows, eliminating small and long vehicles, geometric distortions, and occlusions. In recent years, in order to overcome the above limitations and complexities, several attempts have been done based on LIDAR data. The present paper proposes an automatic hierarchical road detection and extraction method. The main goal of this research is to increase the level of continuity of the road detection and extraction processes. This method includes the preprocessing of intensity data using a local minima filter, applying the Mean Shift segmentation to the refined intensity data, and finally integrating it with various nDSM-based Products. The proposed method involves not only considering both small and long vehicles as road features but also neglecting some parts of large parking lots based on the nearby neighborhood of parked vehicles as much as possible as non-road features. The next step was the process of road centerline extraction by adopting a Voronoi-diagram based approach and then removing dangle lines in several iterations. The proposed method was applied to the Vaihingen and Toronto datasets (ISPRS). The completeness of the two datasets is 95.85% and 88%, and the correctness of these datasets are 83.68% and 72.2%, respectively. The results were indicative of the great potential of the proposed method for effective road centerline extraction in urban areas.

Radiative cooling due to NO at 5.3 <math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg" class="math"><mrow><mi mathvariant="normal">μ</mi></mrow></math>m emission as observed by TIMED/SABER over Asian sector

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): Gaurav Bharti, M.V. Sunil Krishna, Vir Singh

Abstract

The effect of geomagnetic storms on the peak emission of NO Volume Emission Rate (NO VER) at 5.3 μm, in mesosphere and lower thermosphere (MLT) region, is studied over the Asian sector during 26–29 September 2011 (storm 1) and 18–21 February 2014 (storm 2). The data for peak emission of NO VER is obtained from SABER instrument onboard the NASA’s TIMED satellite. The SABER retrieved data along with the neutral densities obtained from NRLMSISE-00 model have been used to study the latitudinal and longitudinal variation of peak NO VER during the storm period. The variations induced in the peak emission of NO VER is understood with the help of fluctuations in neutral species and the resulting changes in chemistry. It has been found that the peak emission of NO VER is strongly influenced by the storm conditions. The peak emission of NO VER at 5.3 μm is found to be maximum at higher latitudes during the storms. However, the magnitude of peak NO VER gradually decreases towards the equator during the storms. The modeled atomic oxygen number density shows depletion at the higher latitudes corresponding to peak altitude of NO VER. There is a negative correlation between the peak emission of NO VER and Dst index during the main phase of the storm. The peak emission of NO VER and modeled atomic oxygen number density shows the positive correlation at the equator region, while negative correlation at the higher latitudes. At higher latitudes modeled atomic oxygen number density shows positive correlation with Dst index, while negative correlation at the equator. The correlation factors obtained between various parameters related to the storm time radiative cooling strongly support the existing understanding of the variation of NO VER during extreme space weather events.

New techniques for retrieving the [O(<sup>3</sup>P)], [O<sub>3</sub>] and [CO<sub>2</sub>] altitude profiles from dayglow oxygen emissions: Uncertainty analysis by the Monte Carlo method

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): Valentine Yankovsky, Ekaterina Vorobeva, Rada Manuilova

Abstract

This study presents methods for retrieving the altitude profiles of atomic oxygen, [O(3P)], ozone, [O3], and carbon dioxide, [CO2], concentrations in the daytime mesosphere and lower thermosphere (MLT) in the framework of the YM2011 model of the electronic-vibrational oxygen kinetics. The emissions of singlet oxygen molecules O2(b1Σ+g, v ≤ 2), O2(a1Δg, v = 0) and the O(1D) atom are used as proxy of the [O(3P)], [O3] and [CO2]. For all the proposed techniques, we compare the uncertainty values of the retrieved [O(3P)], [O3] and [CO2], obtained by the Monte Carlo method, with estimations obtained by the sensitivity analysis method in the earlier works. For all the above mentioned methods for retrieving the [O(3P)], [O3] and [CO2] profiles, we obtained analytical expressions that include the concentrations of excited substances considered as proxies. In addition, the optimal altitude ranges for using these remote sensing methods were determined based on the results of numerical experiments by the Monte Carlo method.

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