Seasonal ionospheric scintillation analysis during increasing solar activity at mid-latitude

NASA Astrophysics Data System (ADS)

Ahmed, Wasiu Akande; Wu, Falin; Agbaje, Ganiyu Ishola; Ednofri, Ednofri; Marlia, Dessi; Zhao, Yan

2017-09-01

Monitoring of ionospheric parameters (such as Total Electron Content and scintillation) is of great importance as it affects and contributes to the errors encountered by radio signals. It thus requires constant measurements to avoid disastrous situation for space agencies, parastatals and departments that employ GNSS applications in their daily operations. The research objective is to have a better understanding of the behaviour of ionospheric scintillation at midlatitude as it threatens the performances of satellite communication, navigation systems and military operations. This paper adopts seasonal ionospheric scintillation scenario. The mid-latitude investigation of ionospheric effect of scintillation was conducted during the increasing solar activity from 2011-2015. Ionospheric scintillation data were obtained from four ionospheric monitoring stations located at mid-latitude (i.e Shenzhen North Station, Beijing Changping North Station Branch, Beijing North Station and Beijing Miyun ground Station). The data was collected from January 2011 to December 2015. There were absence of data due to software problem or system failure at some locations. The scintillation phenomenon was computed using Global Ionospheric Scintillation and TEC Monitoring Model. There are four seasons which existed in China namely: Spring, Summer, Autumn and Winter. The relationship between TEC, amplitude and phase scintillation were observed for each of these seasons. The results indicated that the weak amplitude scintillation was observed as against phase scintillation which was high. Phase scintillation was gradually enhanced from 2011 to 2012 and later declined till 2014. TEC was also at peak around 00:00-10:00 UT (08:00-18:00 LT). The seasonal events temporal density characteristics comply with solar cycle prediction as such it ascended from 2011 to 2013 and then scintillation parameters declined significantly afterwards.

Impact of the ionosphere on an L-band space based radar

NASA Technical Reports Server (NTRS)

Chapin, Elaine; Chan, Samuel F.; Chapman, Bruce D.; Chen, Curtis W.; Martin, Jan M.; Michel, Thierry R.; Muellerschoen, Ronald J.; Pi, Xiaoqing; Rosen, Paul A.

2006-01-01

We have quantified the impact that the ionosphere would have on a L-band interferometric Synthetic Aperture Radar (SAR) mission using a combination of simulation, modeling, Global Positioning System (GPS) data collected during the last solar maximum, and existing spaceborne SAR data.

Characterization of the Ionospheric Scintillations at High Latitude using GPS Signal

NASA Astrophysics Data System (ADS)

Mezaoui, H.; Hamza, A. M.; Jayachandran, P. T.

2013-12-01

Transionospheric radio signals experience both amplitude and phase variations as a result of propagation through a turbulent ionosphere; this phenomenon is known as ionospheric scintillations. As a result of these fluctuations, Global Positioning System (GPS) receivers lose track of signals and consequently induce position and navigational errors. Therefore, there is a need to study these scintillations and their causes in order to not only resolve the navigational problem but in addition develop analytical and numerical radio propagation models. In order to quantify and qualify these scintillations, we analyze the probability distribution functions (PDFs) of L1 GPS signals at 50 Hz sampling rate using the Canadian High arctic Ionospheric Network (CHAIN) measurements. The raw GPS signal is detrended using a wavelet-based technique and the detrended amplitude and phase of the signal are used to construct probability distribution functions (PDFs) of the scintillating signal. The resulting PDFs are non-Gaussian. From the PDF functional fits, the moments are estimated. The results reveal a general non-trivial parabolic relationship between the normalized fourth and third moments for both the phase and amplitude of the signal. The calculated higher-order moments of the amplitude and phase distribution functions will help quantify some of the scintillation characteristics and in the process provide a base for forecasting, i.e. develop a scintillation climatology model. This statistical analysis, including power spectra, along with a numerical simulation will constitute the backbone of a high latitude scintillation model.

Modelling ionospheric scintillation under the crest of the equatorial anomaly

NASA Astrophysics Data System (ADS)

Alfonsi, L.; Wernik, A. W.; Materassi, M.; Spogli, L.

2017-10-01

WAM is realized making use of the plasma density data collected via the retarding potential analyser on board the Dynamics Explorer 2 spacecraft, capable to model the scintillation climatology over the northern hemisphere high latitude ionosphere. More recently, WAM has been tuned to model the ionospheric scintillations also over the equatorial latitudes. The effort has been done to support the CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project in the assessment of the scintillations climatology over Latin America. The concept of the new release of WAM is the same already adopted for the high latitudes: the in situ measurements, supplemented with an ionospheric model and with the irregularity anisotropy model, are treated to describe the morphology of scintillation, provided a suitable propagation model is used. Significant differences have been included in the low latitudes release to account for the anisotropy of the irregularities and for strong scattering regime. The paper describes the new WAM formulation and presents comparisons of the model predictions with the actual measurements collected in Brazil.

L-band nighttime scintillations at the northern edge of the EIA along 95°E during the ascending half of the solar cycle 24

NASA Astrophysics Data System (ADS)

Dutta, Barsha; Kalita, Bitap Raj; Bhuyan, Pradip Kumar

2018-04-01

The characteristics of nighttime ionospheric scintillations measured at the L-band frequency of 1.575 GHz over Dibrugarh (27.5°N, 95°E, MLAT ∼ 17°N, 43° dip) during the ascending half of the solar cycle 24 from 2010 to 2014 have been investigated and the results are presented in this paper. The measurement location is within or outside the zone of influence of the equatorial ionization anomaly depending on solar and geomagnetic activity. Maximum scintillation is observed in the equinoxes irrespective of solar activity with clear asymmetry between March and September. The occurrence frequency in the solstices shifts from minimum in the June solstice in low solar activity to a minimum in the December solstice in high solar activity years. A significant positive correlation of occurrence of scintillations in the June solstice with solar activity has been observed. However, earlier reports from the Indian zone (∼75°E) indicate negative or no correlation of scintillation in June solstice with solar activity. Scintillations activity/occurrence in solstices indicates a clear positive correlation with Es recorded simultaneously by a collocated Ionosonde. In equinoxes, maximum scintillations occur in the pre-midnight hours while in solstices the occurrence frequency peaks just after sunset. The incidence of strong scintillations (S4 ≥ 0.4) increases with increase in solar activity. Strong (S4 ≥ 0.4) ionospheric scintillations accompanied by TEC depletions in the pre-midnight period is attributed to equatorial irregularities whereas the dusk period scintillations are related to the sporadic-E activity. Present results thus indicate that the current location at the northern edge of the EIA behaves as low as well as mid-latitude location.

Full Polarimetric Synthetic Aperture Radar (SAR) Data for ionosphere observation - A comparative study

NASA Astrophysics Data System (ADS)

Mohanty, S.; Singh, G.

2017-12-01

Ionosphere, predominantly, govern the propagation of radio waves, especially at L-band and lower frequencies. Small-scale, rapid fluctuations in the electron density, termed as scintillation phenomenon, cause rapid variations in signal amplitude and phase. Scintillation studies have been done using ground-based radio transmitter and beacon GPS signals. In this work, attempt has been made to utilize full polarimetric synthetic aperture radar (SAR) satellite signal at L-band (1.27 GHz) to develop a new measurement index for SAR signal intensity fluctuation. Datasets acquired from Japan's latest Advanced Land Observation Satellite (ALOS)-2 over the Indian subcontinent on two different dates, with varying ionospheric activities, have been utilized to compare the index. A 20% increase in the index values for a scintillation-affected day has been observed. The result coincides with the nature of ionospheric scintillation pattern typically observed over the equatorial belt. Total electron content values, for the two dates of acquisition, obtained from freely available Ionosphere Exchange (IONEX) data have been used to validate the varying ionospheric activities as well as the trend in index results. Another interesting finding of the paper is the demarcation of the equatorial anomaly belt. The index values are comparatively higher at these latitudes on a scintillation-affected day. Furthermore, the SAR signal intensity fluctuation index has great potential in being used as a preliminary measurement index to identify low frequency SAR data affected by ionospheric scintillation.

Midlatitude Measurements of L-Band Ionospheric Scintillation with the ATS-5 Spacecraft

DOT National Transportation Integrated Search

1975-09-01

The report presents some results of L-band signal level measurements taken from the ATS-5 spacecraft operating in the narrow-band frequency translation mode. The uplink signal was sent from the DOT/TSC/Westford Propagation Facility in Westford, Massa...

Comparisons of COSMIC and C/NOFS GPS Occultation Ionospheric Scintillation Measurements with Ground-based Radar and VHF Measurements

NASA Astrophysics Data System (ADS)

Ruggiero, F. H.; Groves, K. M.; Straus, P. R.; Caton, R. G.; Starks, M. J.; Tanyi, K. L.; Verlinden, M.

2009-12-01

Ionospheric irregularities are known to cause scintillation of trans-ionospheric radio signals and can affect space-based UHF/VHF communications, causing outages, and degrading GPS accuracy and precision. Current capability for characterizing and predicting ionospheric scintillation utilizes a network of ground-based receivers to detect scintillation and then extrapolate for short-term forecasts. Practical limits on deploying the ground receivers limits the accuracy and spatial coverage one can achieve with this approach. A more global approach is to use a set of space-based satellites equipped with GPS receivers, such as the COSMIC satellite constellation, to measure scintillations observed during so-called occultations with GPS satellites. In this paper the signal-to-noise values of GPS L1 signals received on the COSMIC and C/NOFS satellites for the portions of the occultations that are not affected by the terrestrial atmosphere are examined to help identify areas of ionospheric scintillation. Three years of S4 scintillation index values from COSMIC occultations are compared with near-zenith ground-based VHF S4 scintillation measurements from the AFRL SCIntillation Network Decision Aid (SCINDA) network stations. The data are correlated to ascertain the viability of using space-based scintillation measurements to characterize and predict scintillation to ground-based receivers. Several days of COSMIC and C/NOFS data are compared with each other and the ALTAIR radar located on Kwajalein Atoll, Marshall Islands to examine how occultation geometry affects observed scintillation and also to verify techniques that provide an upper bound on the spatial location of the ionospheric irregularities contributing to scintillations observed in the occultations.

VHF Scintillation in an Artificially Heated Ionosphere

NASA Astrophysics Data System (ADS)

Suszcynsky, D. M.; Layne, J.; Light, M. E.; Pigue, M. J.; Rivera, L.

2017-12-01

As part of an ongoing project to characterize very-high-frequency (VHF) radio wave propagation through structured ionospheres, Los Alamos National Laboratory has been conducting a set of experiments to measure the scintillation effects of VHF transmissions under a variety of ionospheric conditions. Previous work (see 2015 Fall AGU poster by D. Suszcynsky et al.) measured the S4 index and ionospheric coherence bandwidth in the 32 - 44 MHz frequency range under naturally scintillated conditions in the equatorial region at Kwajalein Atoll during three separate campaigns centered on the 2014 and 2015 equinoxes. In this paper, we will present preliminary results from the February and September, 2017 High Altitude Auroral Research Project (HAARP) Experimental Campaigns where we are attempting to make these measurements under more controlled conditions using the HAARP ionospheric heater in a twisted-beam mode. Two types of measurements are made by transmitting VHF signals through the heated ionospheric volume to the Radio Frequency Propagation (RFProp) satellite experiment. The S4 scintillation index is determined by measuring the power fluctuations of a 135-MHz continuous wave signal and the ionospheric coherence bandwidth is simultaneously determined by measuring the delay spread of a frequency-modulated continuous wave (FMCW) signal in the 130 - 140 MHz frequency range. Additionally, a spatial Fourier transform of the CW time series is used to calculate the irregularity spectral density function. Finally, the temporal evolution of the time series is used to characterize spread-Doppler clutter effects arising from preferential ray paths to the satellite due to refraction off of isolated density irregularities. All results are compared to theory and scaled for comparison to the 32 - 44 MHz Kwajalein measurements.

Ionospheric Scintillation Induced by Solar Wind Dynamic Pressure Enhancements in the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Coppeans, T.; Zou, S.; Weatherwax, A. T.; Coster, A. J.

2017-12-01

Ionospheric scintillation is the random fluctuation in GPS signal radio waves passing through the ionosphere, a phenomenon that can result in the loss of GPS tracking, but can also reveal information about plasma structures in the ionosphere. Sudden compression of the Earth's magnetosphere by a solar wind dynamic pressure enhancement can cause dramatic changes in the E and F region ionospheric plasma. In this study, we investigate the possible ionospheric scintillation induced by solar wind pressure enhancements using ground-based scintillation receivers located at the McMurdo station and the South Pole station in Antarctica. Various studies of scintillation effects have been carried out, mainly in the northern hemisphere, while the southern hemisphere remains less studied. A pool of storm sudden commencements occurring between Jan. 2011 and Dec. 2014 were sorted based on solar wind dynamic pressure enhancement, background conditions, availability of data, and magnitude of scintillation response. Among the 89 events examined, 14 of them exhibited enhanced scintillation and were selected for detailed examination. Besides the scintillation receivers, other datasets have also been used to carry out the above study, including field-aligned currents from AMPERE, and global GPS TEC. Effects of FACs and TEC/TEC gradients on the generation of these scintillations are studied.

Use of IRI to Model the Effect of Ionosphere Emission on Earth Remote Sensing at L-Band

NASA Technical Reports Server (NTRS)

Abraham, Saji; LeVine, David M.

2004-01-01

Microwave remote sensing in the window at 1.413 GHz (L-band) set aside for passive use only is important for monitoring sea surface salinity and soil moisture. These parameters are important for understanding ocean dynamics and energy exchange between the surface and atmosphere, and both NASA and ESA plan to launch satellite sensors to monitor these parameters at L-band (Aquarius, Hydros and SMOS). The ionosphere is an important source of error for passive remote sensing at this frequency. In addition to Faraday rotation, emission from the ionosphere is also a potential source of error at L-band. As an aid for correcting for emission, a regression model is presented that relates ionosphere emission to the integrated electron density (TEC). The goal is to use TEC from sources such as TOPEX, JASON or GPS to obtain estimates of emission over the oceans where the electron density profiles needed to compute emission are not available. In addition, data will also be presented to evaluate the use of the IRI for computing emission over the ocean.

Precisely determined the surface displacement by the ionospheric mitigation using the L-band SAR Interferometry over Mt.Baekdu

NASA Astrophysics Data System (ADS)

Lee, Won-Jin; Jung, Hyung-Sup; Park, Sun-Cheon; Lee, Duk Kee

2016-04-01

Mt. Baekdu (Changbaishan in Chinese) is located on the border between China and North Korea. It has recently attracted the attention of volcanic unrest during 2002-2005. Many researchers have applied geophysical approaches to detect magma system of beneath Mt.Baekdu such as leveling, Global Positioning System (GPS), gases analysis, seismic analysis, etc. Among them, deformation measuring instruments are important tool to evaluate for volcanism. In contrast to GPS or other deformation measuring instruments, Synthetic Aperture Radar Interferometry (InSAR) has provided high resolution of 2-D surface displacement from remote sensed data. However, Mt. Baekdu area has disturbed by decorrelation on interferogram because of wide vegetation coverage. To overcome this limitation, L-band system of long wavelength is more effective to detect surface deformation. In spite of this advantage, L-band can surfer from more severe ionospheric phase distortions than X- or C- band system because ionospheric phase distortions are inverse proportion to the radar frequency. Recently, Multiple Aperture Interferometry (MAI) based ionospheric phase distortions mitigation method have proposed and investigated. We have applied this technique to the Mt.Baekdu area to measure surface deformation precisely using L-band Advanced Land Observing Satellite-1(ALOS-1) Phased Array type L-band Synthetic Aperture Radar(PALSAR) data acquiring from 2006 to 2011.

Separating Nightside Interplanetary and Ionospheric Scintillation with LOFAR

NASA Astrophysics Data System (ADS)

Fallows, R. A.; Bisi, M. M.; Forte, B.; Ulich, Th.; Konovalenko, A. A.; Mann, G.; Vocks, C.

2016-09-01

Observation of interplanetary scintillation (IPS) beyond Earth-orbit can be challenging due to the necessity to use low radio frequencies at which scintillation due to the ionosphere could confuse the interplanetary contribution. A recent paper by Kaplan et al. presenting observations using the Murchison Widefield Array (MWA) reports evidence of nightside IPS on two radio sources within their field of view. However, the low time cadence of 2 s used might be expected to average out the IPS signal, resulting in the reasonable assumption that the scintillation is more likely to be ionospheric in origin. To check this assumption, this Letter uses observations of IPS taken at a high time cadence using the Low Frequency Array (LOFAR). Averaging these to the same as the MWA observations, we demonstrate that the MWA result is consistent with IPS, although some contribution from the ionosphere cannot be ruled out. These LOFAR observations represent the first of nightside IPS using LOFAR, with solar wind speeds consistent with a slow solar wind stream in one observation and a coronal mass ejection expected to be observed in another.

Ionospheric Scintillation Effects on GPS

NASA Astrophysics Data System (ADS)

Steenburgh, R. A.; Smithtro, C.; Groves, K.

2007-12-01

. Ionospheric scintillation of Global Positioning System (GPS) signals threatens navigation and military operations by degrading performance or making GPS unavailable. Scintillation is particularly active, although not limited to, a belt encircling the earth within 20 degrees of the geomagnetic equator. As GPS applications and users increases, so does the potential for detrimental impacts from scintillation. We examined amplitude scintillation data spanning seven years from Ascension Island, U.K.; Ancon, Peru; and Antofagasta, Chile in the Atlantic/Americas longitudinal sector at as well as data from Parepare, Indonesia; Marak Parak, Malaysia; Pontianak, Indonesia; Guam; and Diego Garcia, U.K.; in the Pacific longitudinal sector. From these data, we calculate percent probability of occurrence of scintillation at various intensities described by the S4 index. Additionally, we determine Dilution of Precision at one minute resolution. We examine diurnal, seasonal and solar cycle characteristics and make spatial comparisons. In general, activity was greatest during the equinoxes and solar maximum, although scintillation at Antofagasta, Chile was higher during 1998 rather than at solar maximum.

Ionosphere Scintillation at Low and High Latitudes (Modelling vs Measurement)

NASA Astrophysics Data System (ADS)

Béniguel, Yannick

2016-04-01

This paper will address the problem of scintillations characteristics, focusing on the parameters of interest for a navigation system. Those parameters are the probabilities of occurrence of simultaneous fading, the bubbles surface at IPP level, the cycle slips and the fades duration statistics. The scintillation characteristics obtained at low and high latitudes will be compared. These results correspond to the data analysis performed after the ESA Monitor ionosphere measurement campaign [1], [2]. A second aspect of the presentation will be the modelling aspect. It has been observed that the phase scintillation dominates at high latitudes while the intensity scintillation dominates at low latitudes. The way it can be reproduced and implemented in a propagation model (e.g. GISM model [3]) will be presented. Comparisons of measurements with results obtained by modelling will be presented on some typical scenarios. References [1] R. Prieto Cerdeira, Y. Beniguel, "The MONITOR project: architecture, data and products", Ionospheric Effects Symposium, Alexandria (Va), May 2011 [2] Y. Béniguel, R Orus-Perez , R. Prieto-Cerdeira , S. Schlueter , S. Scortan, A. Grosu "MONITOR 2: ionospheric monitoring network in support to SBAS and other GNSS and scientific purposes", IES Conference, Alexandria (Va), May 2015-05-22 [3] Y. Béniguel, P. Hamel, "A Global Ionosphere Scintillation Propagation Model for Equatorial Regions", Journal of Space Weather Space Climate, 1, (2011), doi: 10.1051/swsc/2011004

Ionospheric scintillation detection based on GPS observations, a case study over Iran

NASA Astrophysics Data System (ADS)

Sobhkhiz Miandehi, Sahar; Alizadeh Elizei, M. Mahdi; Schuh, Harald

2017-04-01

Global Positioning System (GPS) which is used extensively for various purposes such as navigation, surveying, remote sensing and telecommunication, is strongly affected by the earth's upper atmosphere, the ionosphere. Ionosphere is a highly variable region with complex physical characteristics in which the density of free electrons are large enough to have considerable effects on signals' propagation travelling through this dispersive medium. As GPS signals travel through the ionosphere, they may experience rapid amplitude fluctuations or unexpected phase changes. This is referred to as ionospheric scintillation. Ionospheric scintillation which is caused by small scale irregularities in the electron density, is one of the dominant propagation disturbances at radio frequency signals. These irregularities severely affect the accuracy and reliability of GPS measurements. Therefore it is necessary to investigate ionospheric scintillation and its effects on GPS observations. The focus of this paper is to detect ionospheric scintillations over Iran's region, during different periods of solar activity and to investigate these effects on GPS observations in more detail. Furthermore the effects of these irregularities on regional modeling of ionosphere over Iran is also investigated. The results show that effectiveness of this phenomenon depends on geographic location, local time and global geomagnetic storm index (kp index). The required data for this investigation are ground based measurements of permanent GPS stations over Iran, established by the National Cartographic Center of Iran (NCC).

The Ionospheric Scintillation Effects on the BeiDou Signal Receiver

PubMed Central

He, Zhijun; Zhao, Hongbo; Feng, Wenquan

2016-01-01

Irregularities in the Earth’s ionosphere can make the amplitude and phase of radio signals fluctuate rapidly, which is known as ionospheric scintillation. Severe ionospheric scintillation could affect the performance of the Global Navigation Satellite System (GNSS). Currently, the Multiple Phase Screen (MPS) technique is widely used in solving problems caused by weak and strong scintillations. Considering that Southern China is mainly located in the area where moderate and intense scintillation occur frequently, this paper built a model based on the MPS technique and discussed the scintillation impacts on China’s BeiDou navigation system. By using the BeiDou B1I signal, this paper analyzed the scintillation effects on the receiver, which includes the acquisition and tracking process. For acquisition process, this paper focused on the correlation peak and acquisition probability. For the tracking process, this paper focused on the carrier tracking loop and the code tracking loop. Simulation results show that under high scintillation intensity, the phase fluctuation could be −1.13 ± 0.087 rad to 1.40 ± 0.087 rad and the relative amplitude fluctuation could be −10 dB to 8 dB. As the scintillation intensity increased, the average correlation peak would decrease more than 8%, which could thus degrade acquisition performance. On the other hand, when the signal-to-noise ratio (SNR) is comparatively lower, the influence of strong scintillation on the phase locked loop (PLL) is much higher than that of weak scintillation. As the scintillation becomes more intense, PLL variance could consequently results in an error of more than 2.02 cm in carrier-phase based ranging. In addition, the delay locked loop (DLL) simulation results indicated that the pseudo-range error caused by strong scintillation could be more than 4 m and the consequent impact on positioning accuracy could be more than 6 m. PMID:27834867

Investigation of ionospheric scintillation at UKM station, Malaysia during low solar activity

NASA Astrophysics Data System (ADS)

Seif, Aramesh; Abdullah, Mardina; Marie Hasbi, Alina; Zou, Yuhua

2012-12-01

In this paper the investigation of the occurrence of ionospheric scintillation with S4≥0.2 was conducted by using a dual-frequency GISTM (GPS Ionospheric Scintillation and TEC monitor) at Universiti Kebangsaan Malaysia station, Malaysia (2.55°N, 101.46°E; geomagnetic: 7.39°S, 173.63°E) between September 2009 and December 2010. The study shows that significant nighttime amplitude scintillation event with 0.4≤S4<0.6 mainly occurred in the months of March, September and October, while significant daytime amplitude scintillation activity took place in November and December with 0.3≤S4<0.5. Moreover, nighttime amplitude scintillation observed at UKM station always occurred with phase scintillations, total electron content (TEC) depletions, rate of change of TEC (ROT) fluctuations and the enhancement of rate of TEC index (ROTI). Nevertheless, during daytime amplitude scintillation, TEC depletions and ROT fluctuations were much weaker than those that occurred during nighttime and this may be caused by small scale irregularities in the E region, called sporadic-E (Es), while the occurrences of nighttime amplitude scintillation maybe caused by the ionospheric irregularities in the F region.

Robust GPS carrier tracking under ionospheric scintillation

NASA Astrophysics Data System (ADS)

Susi, M.; Andreotti, M.; Aquino, M. H.; Dodson, A.

2013-12-01

Small scale irregularities present in the ionosphere can induce fast and unpredictable fluctuations of Radio Frequency (RF) signal phase and amplitude. This phenomenon, known as scintillation, can degrade the performance of a GPS receiver leading to cycle slips, increasing the tracking error and also producing a complete loss of lock. In the most severe scenarios, if the tracking of multiple satellites links is prevented, outages in the GPS service can also occur. In order to render a GPS receiver more robust under scintillation, particular attention should be dedicated to the design of the carrier tracking stage, that is the receiver's part most sensitive to these types of phenomenon. This paper exploits the reconfigurability and flexibility of a GPS software receiver to develop a tracking algorithm that is more robust under ionospheric scintillation. For this purpose, first of all, the scintillation level is monitored in real time. Indeed the carrier phase and the post correlation terms obtained by the PLL (Phase Locked Loop) are used to estimate phi60 and S4 [1], the scintillation indices traditionally used to quantify the level of phase and amplitude scintillations, as well as p and T, the spectral parameters of the fluctuations PSD. The effectiveness of the scintillation parameter computation is confirmed by comparing the values obtained by the software receiver and the ones provided by a commercial scintillation monitoring, i.e. the Septentrio PolarxS receiver [2]. Then the above scintillation parameters and the signal carrier to noise density are exploited to tune the carrier tracking algorithm. In case of very weak signals the FLL (Frequency Locked Loop) scheme is selected in order to maintain the signal lock. Otherwise an adaptive bandwidth Phase Locked Loop (PLL) scheme is adopted. The optimum bandwidth for the specific scintillation scenario is evaluated in real time by exploiting the Conker formula [1] for the tracking jitter estimation. The performance

Analysis of Ionospheric Scintillation Characteristics in Sub-Antarctica Region with GNSS Data at Macquarie Island.

PubMed

Guo, Kai; Liu, Yang; Zhao, Yan; Wang, Jinling

2017-01-12

Ionospheric scintillation has a great impact on radio propagation and electronic system performance, thus is extensively studied currently. The influence of scintillation on Global Navigation Satellite System (GNSS) is particularly evident, making GNSS an effective medium to study characteristics of scintillation. Ionospheric scintillation varies greatly in relation with temporal and spatial distribution. In this paper, both temporal and spatial characteristics of scintillation are investigated based on Macquarie Island's GNSS scintillation data collected from 2011 to 2015. Experiments demonstrate that occurrence rates of amplitude scintillation have a close relationship with solar activity, while phase scintillation is more likely to be generated by geomagnetic activity. In addition, scintillation distribution behaviors related to elevation and azimuth angles are statistically analyzed for both amplitude and phase scintillation. The proposed work is valuable for a deeper understanding of theoretical mechanisms of ionospheric scintillation in this region, and provides a reference for GNSS applications in certain regions around sub-Antarctica.

Analyze and Study Ionospheric Scintillation and Total Electron Content Variability (Ionospheric Studies and TEC Variations).

DTIC Science & Technology

1981-03-01

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A study on multifrequency scintillations near the EIA crest of the Indian zone

NASA Astrophysics Data System (ADS)

Chakraborty, S. K.; Chatterjee, S.; Jana, Debasis

2017-10-01

Occurrence features of ionospheric scintillations at S band (2492.028 MHz) are reported for the first time. The same have been explored in the context of scintillations at VHF (250.650 MHz) and L5 (1176.45 MHz) bands. Observations were carried out during the period April-December, 2015 at Raja Peary Mohan College Centre (RPMC: 22.66° N, 88.4° E), located near the equatorial ionization anomaly (EIA) crest of the Indian longitude zone. Mostly weak (<10 dB), short duration, slow fading rate with shallower slope power spectra characterize the S band scintillations compared to VHF and L5 band. In the severe scintillation conditions of VHF frequent loss of lock in L5 channel is reflected. Fade depth of 4.2 ± 1.3 dB and fade rate ∼9 fades/minute at S band mostly precede the loss of lock at L5 channel. A good correspondence between fade rates at multi frequency band is reflected irrespective of phases of scintillation. Spectral analysis reveals weak scattering is the dominating mechanism for scintillation at S band while VHF and L5 band scintillations are mostly attributed to multiple scattering. The estimated threshold coherence length of <23 m at VHF may be suggested to be a good indicator for occurrence of L5 and S band scintillations. Occurrence of simultaneous multi-satellite multi-frequency scintillations leads to speculation over the failsafe navigation using available IRNSS constellation. The results are discussed in terms of existing theory of evolution, structure and dynamics of electron density irregularities in the low latitude region.

Kilometer-Spaced GNSS Array for Ionospheric Irregularity Monitoring

NASA Astrophysics Data System (ADS)

Su, Yang

This dissertation presents automated, systematic data collection, processing, and analysis methods for studying the spatial-temporal properties of Global Navigation Satellite Systems (GNSS) scintillations produced by ionospheric irregularities at high latitudes using a closely spaced multi-receiver array deployed in the northern auroral zone. The main contributions include 1) automated scintillation monitoring, 2) estimation of drift and anisotropy of the irregularities, 3) error analysis of the drift estimates, and 4) multi-instrument study of the ionosphere. A radio wave propagating through the ionosphere, consisting of ionized plasma, may suffer from rapid signal amplitude and/or phase fluctuations known as scintillation. Caused by non-uniform structures in the ionosphere, intense scintillation can lead to GNSS navigation and high-frequency (HF) communication failures. With specialized GNSS receivers, scintillation can be studied to better understand the structure and dynamics of the ionospheric irregularities, which can be parameterized by altitude, drift motion, anisotropy of the shape, horizontal spatial extent and their time evolution. To study the structuring and motion of ionospheric irregularities at the sub-kilometer scale sizes that produce L-band scintillations, a closely-spaced GNSS array has been established in the auroral zone at Poker Flat Research Range, Alaska to investigate high latitude scintillation and irregularities. Routinely collecting low-rate scintillation statistics, the array database also provides 100 Hz power and phase data for each channel at L1/L2C frequency. In this work, a survey of seasonal and hourly dependence of L1 scintillation events over the course of a year is discussed. To efficiently and systematically study scintillation events, an automated low-rate scintillation detection routine is established and performed for each day by screening the phase scintillation index. The spaced-receiver technique is applied to cross

Ionospheric Scintillation Activity Over Ilorin, Nigeria

NASA Astrophysics Data System (ADS)

Oladipo, O. A.; Adeniyi, J. O.; Doherty, P. H.; Radicella, S. M.; Adimula, I. A.; Olawepo, A. O.

2018-02-01

Scintillation of radio waves in the L-band frequency is a regular occurrence at the equatorial and auroral regions at night most especially during high solar activity periods. Scintillation is caused by plasma density irregularities, and this could cause loss of lock of Global Navigation Satellite System (GNSS) signals leading to impairment of the applications that rely on this system. A study on the occurrence of scintillation activity over Ilorin (latitude = 8.48°N, longitude = 4.67°W, and geomagnetic latitude = 1.89°S), Nigeria was done using S4 index data from NovAtel GPStation-2 receiver (2009-2012) and NovAtel GPStation-6 receiver (August 2013 to December 2016) which are both located at this station. The solar maximum period of the solar cycle 24 is located well within the period of this investigation; hence, this study provides opportunity to see the occurrence pattern of scintillation during different seasons as well as the pattern from low solar activity to solar maximum. The results obtained showed that scintillation occurs between 21:00 LT and 04:00 LT at the peak of the occurrence in 2014. The time window of occurrence decreases with decrease in solar activity. Similarly, scintillation activity was observed to be more regular during high solar activity and it has two peaks of occurrence in March and October. A solar activity trend was observed in scintillation occurrence; scintillation activity increases with increase in the level of solar activity.

Ionospheric scintillation effects on single frequency GPS

NASA Astrophysics Data System (ADS)

Steenburgh, R. A.; Smithtro, C. G.; Groves, K. M.

2008-04-01

Ionospheric scintillation of Global Positioning System (GPS) signals threatens navigation and military operations by degrading performance or making GPS unavailable. Scintillation is particularly active within, although not limited to, a belt encircling the Earth within 20 degrees of the geomagnetic equator. As GPS applications and users increase, so does the potential for degraded precision and availability from scintillation. We examined amplitude scintillation data spanning 7 years from Ascension Island, U.K.; Ancon, Peru; and Antofagasta, Chile in the Atlantic/American longitudinal sector as well as data from Parepare, Indonesia; Marak Parak, Malaysia; Pontianak, Indonesia; Guam; and Diego Garcia, U.K. in the Pacific longitudinal sector. From these data, we calculate percent probability of occurrence of scintillation at various intensities described by the S4 index. Additionally, we determine Dilution of Precision at 1 min resolution. We examine diurnal, seasonal, and solar cycle characteristics and make spatial comparisons. In general, activity was greatest during the equinoxes and solar maximum, although scintillation at Antofagasta, Chile was higher during 1998 rather than at solar maximum.

Simulation and analysis of chemical release in the ionosphere

NASA Astrophysics Data System (ADS)

Gao, Jing-Fan; Guo, Li-Xin; Xu, Zheng-Wen; Zhao, Hai-Sheng; Feng, Jie

2018-05-01

Ionospheric inhomogeneous plasma produced by single point chemical release has simple space-time structure, and cannot impact radio wave frequencies higher than Very High Frequency (VHF) band. In order to produce more complicated ionospheric plasma perturbation structure and trigger instabilities phenomena, multiple-point chemical release scheme is presented in this paper. The effects of chemical release on low latitude ionospheric plasma are estimated by linear instability growth rate theory that high growth rate represents high irregularities, ionospheric scintillation occurrence probability and high scintillation intension in scintillation duration. The amplitude scintillations and the phase scintillations of 150 MHz, 400 MHz, and 1000 MHz are calculated based on the theory of multiple phase screen (MPS), when they propagate through the disturbed area.

Ionospheric scintillation studies

NASA Technical Reports Server (NTRS)

Rino, C. L.; Freemouw, E. J.

1973-01-01

The diffracted field of a monochromatic plane wave was characterized by two complex correlation functions. For a Gaussian complex field, these quantities suffice to completely define the statistics of the field. Thus, one can in principle calculate the statistics of any measurable quantity in terms of the model parameters. The best data fits were achieved for intensity statistics derived under the Gaussian statistics hypothesis. The signal structure that achieved the best fit was nearly invariant with scintillation level and irregularity source (ionosphere or solar wind). It was characterized by the fact that more than 80% of the scattered signal power is in phase quadrature with the undeviated or coherent signal component. Thus, the Gaussian-statistics hypothesis is both convenient and accurate for channel modeling work.

First Observations of GNSS Ionospheric Scintillations From DemoGRAPE Project

NASA Astrophysics Data System (ADS)

Alfonsi, L.; Cilliers, P. J.; Romano, V.; Hunstad, I.; Correia, E.; Linty, N.; Dovis, F.; Terzo, O.; Ruiu, P.; Ward, J.; Riley, P.

2016-10-01

The Istituto Nazionale di Geofisica e Vulcanologia leads an international project funded by the Italian National Program for Antarctic Research, called Demonstrator of Global Navigation Satellite System (GNSS) Research and Application for Polar Environment (DemoGRAPE), in partnership with Politecnico di Torino, Istituto Superiore Mario Boella, and with South African National Space Agency and the Brazilian National Institute of Space Physics, as key collaborators. DemoGRAPE is a new prototype of support for the satellite navigation in Antarctica. Besides the scientific interest, the accuracy of satellite navigation in Antarctica is of paramount importance since there is always the danger that people and vehicles can fall into a crevasse during a snowstorm, when visibility is limited and travel is restricted to following specified routes using satellite navigation systems. The variability of ionospheric delay and ionospheric scintillation are two of the primary factors which affect the accuracy of satellite navigation. The project will provide a demonstrator of cutting edge technology for the empirical assessment of the ionospheric delay and ionospheric scintillations in the polar regions. The scope of the project includes new equipment for the recording and dissemination of GNSS data and products installed at the South African and Brazilian bases in Antarctica. The new equipment will facilitate the exchange of software and derived products via the Cloud computing technology infrastructure. The project portal is accessible at www.demogrape.net. We report the first Global Navigation Satellite System (GNSS) signal scintillations observed in Antarctica.

An investigation of methods for updating ionospheric scintillation models using topside in-situ plasma density measurements

NASA Astrophysics Data System (ADS)

Secan, James A.

1991-05-01

Modern military communication, navigation, and surveillance systems depend on reliable, noise-free transionospheric radio-frequency channels. They can be severely impacted by small-scale electron-density irregularities in the ionosphere, which cause both phase and amplitude scintillation. Basic tools used in planning and mitigation schemes are climatological in nature and thus may greatly over- and under-estimate the effects of scintillation in a given scenario. This report summarizes the results of the first year of a three-year investigation into the methods for updating ionospheric scintillation models using observations of ionospheric plasma-density irregularities measured by DMSP Scintillation Meter (SM) sensor. Results are reported from the analysis of data from a campaign conducted in January 1990 near Tromso, Norway, in which near coincident in-situ plasma-density and transionospheric scintillation measurements were made. Estimates for the level of intensity and phase scintillation on a transionospheric UHF radio link in the early-evening auroral zone were calculated from DMSP SM data and compared to the levels actually observed.

Accuracy assessment of Precise Point Positioning with multi-constellation GNSS data under ionospheric scintillation effects

NASA Astrophysics Data System (ADS)

Marques, Haroldo Antonio; Marques, Heloísa Alves Silva; Aquino, Marcio; Veettil, Sreeja Vadakke; Monico, João Francisco Galera

2018-02-01

GPS and GLONASS are currently the Global Navigation Satellite Systems (GNSS) with full operational capacity. The integration of GPS, GLONASS and future GNSS constellations can provide better accuracy and more reliability in geodetic positioning, in particular for kinematic Precise Point Positioning (PPP), where the satellite geometry is considered a limiting factor to achieve centimeter accuracy. The satellite geometry can change suddenly in kinematic positioning in urban areas or under conditions of strong atmospheric effects such as for instance ionospheric scintillation that may degrade satellite signal quality, causing cycle slips and even loss of lock. Scintillation is caused by small scale irregularities in the ionosphere and is characterized by rapid changes in amplitude and phase of the signal, which are more severe in equatorial and high latitudes geomagnetic regions. In this work, geodetic positioning through the PPP method was evaluated with integrated GPS and GLONASS data collected in the equatorial region under varied scintillation conditions. The GNSS data were processed in kinematic PPP mode and the analyses show accuracy improvements of up to 60% under conditions of strong scintillation when using multi-constellation data instead of GPS data alone. The concepts and analyses related to the ionospheric scintillation effects, the mathematical model involved in PPP with GPS and GLONASS data integration as well as accuracy assessment with data collected under ionospheric scintillation effects are presented.

Visual exploration and analysis of ionospheric scintillation monitoring data: The ISMR Query Tool

NASA Astrophysics Data System (ADS)

Vani, Bruno César; Shimabukuro, Milton Hirokazu; Galera Monico, João Francisco

2017-07-01

Ionospheric Scintillations are rapid variations on the phase and/or amplitude of a radio signal as it passes through ionospheric plasma irregularities. The ionosphere is a specific layer of the Earth's atmosphere located approximately between 50 km and 1000 km above the Earth's surface. As Global Navigation Satellite Systems (GNSS) - such as GPS, Galileo, BDS and GLONASS - use radio signals, these variations degrade their positioning service quality. Due to its location, Brazil is one of the places most affected by scintillation in the world. For that reason, ionosphere monitoring stations have been deployed over Brazilian territory since 2011 through cooperative projects between several institutions in Europe and Brazil. Such monitoring stations compose a network that generates a large amount of monitoring data everyday. GNSS receivers deployed at these stations - named Ionospheric Scintillation Monitor Receivers (ISMR) - provide scintillation indices and related signal metrics for available satellites dedicated to satellite-based navigation and positioning services. With this monitoring infrastructure, more than ten million observation values are generated and stored every day. Extracting the relevant information from this huge amount of data was a hard process and required the expertise of computer and geoscience scientists. This paper describes the concepts, design and aspects related to the implementation of the software that has been supporting research on ISMR data - the so-called ISMR Query Tool. Usability and other aspects are also presented via examples of application. This web based software has been designed and developed aiming to ensure insights over the huge amount of ISMR data that is fetched every day on an integrated platform. The software applies and adapts time series mining and information visualization techniques to extend the possibilities of exploring and analyzing ISMR data. The software is available to the scientific community through the

On the occurrence of F region irregularities over Haikou retrieved from COSMIC GPS radio occultation and ground-based ionospheric scintillation monitor observations

NASA Astrophysics Data System (ADS)

Yu, Xiao; Yue, Xinan; Zhen, Weimin; Xu, Jisheng; Liu, Dun; Guo, Shan

2017-01-01

In this paper, the amplitude scintillation index (s4) derived from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) radio occultation (RO) technique and ground-based Ionospheric Scintillation Monitor (ISM) at Haikou station (geographic latitude: 20.0°N, geographic longitude: 110.3°E, and geomagnetic latitude: 10.02°N) is used to investigate the morphology of F region irregularities in the low latitudes of China. The RO events of tangent point within the range of 10-30°N latitude, 70-160°E longitude, and 150-500 km altitude are adopted to analyze the ionospheric scintillation characteristics. The percentage of ionospheric scintillation occurrence is computed to obtain its diurnal variations, seasonal trends, and the dependence on solar and geomagnetic activities. Based on a statistical analysis of a long-term period data set (years 2007 to 2013), we found that the ionospheric scintillation occurrence from both techniques show similar variations. After sunset (18 LT), the scintillation occurrence increases rapidly and reaches the maximum 3 h later. Then it decreases rapidly till 04 LT and remains low level during the daytime. The ionospheric scintillation tends to occur more frequently during vernal and autumnal equinoxes, especially in March-April and September-October. The equinoctial asymmetry could be seen clearly from the ground-based ISM observations. The peak ionospheric scintillation occurrence time varies with seasons. It is reached latest in summer, while in spring it is very close to that in autumn. The nighttime ionospheric scintillation occurrence tends to increase with increasing solar activities. The increasing tendency is more prominent in vernal and autumnal equinoxes than that in summer and winter. In general, the control of geomagnetic activities is apt to inhibit ionospheric scintillation at equinox nighttime. In summer and winter, the geomagnetic activities could either trigger or inhibit the generation of

First light from a kilometer-baseline Scintillation Auroral GPS Array.

PubMed

Datta-Barua, S; Su, Y; Deshpande, K; Miladinovich, D; Bust, G S; Hampton, D; Crowley, G

2015-05-28

We introduce and analyze the first data from an array of closely spaced Global Positioning System (GPS) scintillation receivers established in the auroral zone in late 2013 to measure spatial and temporal variations in L band signals at 100-1000 m and subsecond scales. The seven receivers of the Scintillation Auroral GPS Array (SAGA) are sited at Poker Flat Research Range, Alaska. The receivers produce 100 s scintillation indices and 100 Hz carrier phase and raw in-phase and quadrature-phase samples. SAGA is the largest existing array with baseline lengths of the ionospheric diffractive Fresnel scale at L band. With an initial array of five receivers, we identify a period of simultaneous amplitude and phase scintillation. We compare SAGA power and phase data with collocated 630.0 nm all-sky images of an auroral arc and incoherent scatter radar electron precipitation measurements, to illustrate how SAGA can be used in multi-instrument observations for subkilometer-scale studies. A seven-receiver Scintillation Auroral GPS Array (SAGA) is now at Poker Flat, Alaska SAGA is the largest subkilometer array to enable phase/irregularities studies Simultaneous scintillation, auroral arc, and electron precipitation are observed.

Integrated Multi-Point Space Plasma Measurements With Four Ionospheric Satellites

NASA Astrophysics Data System (ADS)

Siefring, C. L.; Bernhardt, P. A.; Selcher, C.; Wilkens, M. R.; McHarg, M. G.; Krause, L.; Chun, F.; Enloe, L.; Panholzer, R.; Sakoda, D.; Phelps, R.; D Roussel-Dupre, D.; Colestock, P.; Close, S.

2006-12-01

The STP-1 launch scheduled for late 2006 will place four satellites with ionospheric plasma diagnostics into the same nearly circular orbit with an altitude of 560 km and inclination of 35.4°. The satellites will allow for unique multipoint measurements of ionospheric scintillations and their causes. Both the radio and in-situ diagnostics will provide coverage of low- and mid-latitudes. The four satellites, STPSat1, NPSat1, FalconSat3, and CFE will follow the same ground-track but because of drag and mass differences their relative velocities will be different and vary during the lifetime of the satellites. The four satellites will start close together; separate over a few months and coming back together with near conjunctions at six and eight months. Two satellite conjunctions between NPSat1 and STPSat1 will occur most often, approximately one month apart at the end of the mission. STPSat1 is equipped with CITRIS (sCintillation and TEC Receiver In Space) which will measure scintillations in the VHF, UHF and L-band along with measuring Total Electron Content (TEC) along the propagation path. NPSat1 will carry a three-frequency CERTO (Coherent Electromagnetic Radio TOmography) Beacon which broadcasts phase-coherent signals at 150.012 MHz, 400.032 MHz, and 1066.752 MHz. CITRIS will be able to measure TEC and Scintillations along the orbital path (propagation path from NPSat1 to STPSat1) as well as between the CITRIS and the ground. NPSat1 carries electron and ion saturation Langmuir Probes, while FalconSat3 carries the FLAPS (FLAt Plasma Spectrometer) and PLANE (Plasma Local Anomalous Noise Environment). The in-situ diagnostic complement the CITRIS/CERTO radio techniques in many ways. The CIBOLA Flight Experiment (CFE) contains a wide band receiver covering 100 to 500 MHz. The CFE data can be processed to show distortion of wide-band modulations by ionospheric irregularities. CFE and CITRIS can record ground transmissions from the French DORIS beacons which radiate

Characterization of Ionospheric Dynamics Over The East African Dip Equatorial Region Using GPS-Derived Total Electron Content.

NASA Astrophysics Data System (ADS)

Olwendo, J. O.

2016-12-01

Through a linear combination of GPS satellite range and phase measurement observed on two carrier frequencies by terrestrial based GPS receivers, the ionospheric total electron content (TEC) along oblique GPS signal path can be quantified. Using Adjusted Spherical Harmonic (ASHA) expansion, regional TEC maps over the East Africa sector has been achieved. The observed TEC has been used to evaluate the performance of IRI2007 and NeQuick 2 models over the region. Ionospheric irregularities have been measured and the plasma drift velocity and the East-West extent of the irregularities have also been analyzed by using a Very High Frequency (VHF) receiver system that is closely spaced. The hourly TEC images developed have shown that the Southern Equatorial Ionization Anomaly (EIA) crest over the East African sector lies within the Kenyan region, and the occurrence of scintillation is dependent on how well the anomaly crest forms. Scintillation occurrences are intense at and around the edges of EIA crest due to the presence of high ambient electron densities and sharp TEC depletions. Simultaneous recording of amplitude scintillations at VHF and L-band frequencies reveal two distinct types of scintillation namely; the Plasma Bubble Induced (PBI) and the Bottom Side Sinusoidal (BSS). The PBI scintillations are characterized by high intensity during the post-sunset hours of the equinoctial months and appear at both VHF and L-band frequencies. The BSS type are associated with VHF scintillation and are characterized by long duration patches and often exhibit Fresnel oscillation on the roll portion of the power spectrum, which suggest a weak scattering from thin screen irregularities. The occurrence of post-midnight L-band scintillation events which are not linked to pre-midnight scintillation observations raises fundamental question on the mechanism and source of electric fields driving the plasma depletion under conditions of very low background electron density.

Observational study of ionospheric irregularities and GPS scintillations associated with the 2012 tropical cyclone Tembin passing Hong Kong

NASA Astrophysics Data System (ADS)

Yang, Zhe; Liu, Zhizhao

2016-05-01

This study presents the ionospheric responses observed in Hong Kong to a Typhoon, namely, Tembin, from the aspects of the occurrence of ionospheric irregularities and scintillations, using Global Positioning System (GPS) observations from a ground-based GPS scintillation monitoring station in Hong Kong and from GPS receivers on board the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. The ionospheric irregularities and scintillations are characterized by the rate of total electron content variation index (ROTI) and the amplitude scintillation index S4, respectively. The typhoon Tembin formed over the western North Pacific during 18-30 August 2012 and approached Hong Kong during 24-27 August 2012 with the closest distance 290 km from Hong Kong at around 17 universal time (UT) on 25 August 2012. The ground-based observations indicate that in the nighttime period of 20:00-02:00 local time (LT = UT + 8 h) on 26 August when Tembin passed closely to Hong Kong, the ionospheric irregularities and scintillations of GPS signals were observed in the south of Hong Kong, over the area of 13°N ~ 23°N in latitude and 110°E ~ 120°E in longitude. From the COSMIC observations, it shows that the number of radio occultation scintillation events peaks on 26 August 2012 during the passage of Tembin. Without the presence of strong geomagnetic or solar activity, it is suspected that gravity waves might be generated in the lower atmosphere and likely seed the formation of ionospheric plasma irregularities. This work for the first time from Hong Kong observes the sign of coupling between the lower atmosphere and ionosphere in a tropical cyclone event, combining both ground- and space-based GPS observation data.

Attenuation of Scintillation of Discrete Cosmic Sources during Nonresonant HF Heating of the Upper Ionosphere

NASA Astrophysics Data System (ADS)

Bezrodny, V. G.; Watkins, B.; Charkina, O. V.; Yampolski, Y. M.

2014-03-01

The aim of the work is to experimentally investigate the response of scintillation spectra and indices of discrete cosmic sources (DCS) to modification of the ionospheric F-region by powerful electromagnetic fields with frequencies exceeding the Langmuir and upper hybrid ones. The results of a special experiment on the scintillations of radiation from DCS Cygnus A observed with using the 64-beam imaging riometer located near the Gakona village (Alaska, USA) are here presented. The ionosphere was artificially disturbed by powerful HAARP heater. Under the studied conditions of nonresonant heating of the ionospheric plasma, an earlier unknown effect of reducing the level of DCS scintillation was discovered. The theoretical interpretation has been given for the discovered effect, which using allowed the proposed technique of solving the inverse problem (recovery deviations of average electron density and temperature in the modified region from their unperturbed values).

An Analysis on the TEC Variability and Ionospheric Scintillation at Los Alamos, New Mexico Derived from FORTE-Received LAPP Signals

NASA Astrophysics Data System (ADS)

Huang, Z.; Roussel-Dupre, R.

2003-12-01

The total electron content (TEC) of ionosphere and its electron density irregularities (scintillation) have effects of degradation and disruption on radio signals passed between ground stations and orbiting man-made satellites. With the rapid increase in operational reliance on UHF/VHF satellite communication, it is desirable to obtain understandings of ionosphere TEC variability and scintillation characteristics to improve our ability of predicting satellite communication outages. In this work, data collected from FORTE satellite received LAPP (Los Alamos Portable Pulser) signals during 1998-2002 are used to derive TEC and ionospheric scintillation index at Los Alamos, New Mexico. To characterize in-situ TEC variability at Los Alamos, the FORTE-LAPP derived TECs are analyzed against diurnal, seasonal, solar activity, magnetic storm, and stratospheric warming. The results are also compared with the TEC estimates from the Los Alamos ionospheric transfer function (ITF) implemented with the global ionospheric models (IRI, PIM), and GPS -derived TEC maps. The FORTE-LAPP signals are also analyzed against two important measures of the effect of scintillation on broadband signals, the mean time delay and the time delay jitter. The results are used to examine coherence frequency bandwidth and compared with the predictions from a global scintillation model (WBMOD). The FORTE-LAPP analyzed and WBMOD predicted scintillation characteristics are used to investigate temporal and seasonal behavior of scintillation at Los Alamos.

Zonal Drift Variations and Suppression of Ionospheric Scintillation During St. Patrick's Day Storm Observed by Pingtung SCINDA Station in Taiwan

NASA Astrophysics Data System (ADS)

Su, S. Y.; Nayak, C.; Tsai, L. C.; Caton, R. G.; Groves, K. M.

2016-12-01

Variations of zonal drift and ionospheric VHF scintillations observed by a SCINDA station in Southern Taiwan during the St. Patrick's day geomagnetic storm are studied. Although scintillations were observed for 6 consecutive days before the storm, they were absence during the storm period. Data from VHF receivers, ionosonde and in situ plasma density observations from ESA's SWARM constellation are used to study the ionospheric irregularity/scintillation events in the Taiwanese sector to compare with what happened in the Indian sectors. The absence of scintillation in the Taiwanese sector during the storm period seems to be caused by a reduced pre-reversal enhancement (PRE) electric field from a westward prompt-penetration electric field (PPEF) during the storm. A low post-sunset ionosphere thus becomes unfavorable for the Rayleigh-Taylor instability to occur. On the contrary, the PPEFs were found to strongly enhance the PRE electric field in the Indian sector to cause the ionospheric irregularities/scintillations in the post-sunset sector. Zonal drift variations during the storm time are also discussed in conjunction with the irregularity/scintillation occurrences.

Experimental Evidence on the Dependence of the Standard GPS Phase Scintillation Index on the Ionospheric Plasma Drift Around Noon Sector of the Polar Ionosphere

NASA Astrophysics Data System (ADS)

Wang, Y.; Zhang, Q.-H.; Jayachandran, P. T.; Moen, J.; Xing, Z.-Y.; Chadwick, R.; Ma, Y.-Z.; Ruohoniemi, J. M.; Lester, M.

2018-03-01

First experimental proof of a clear and strong dependence of the standard phase scintillation index (σφ) derived using Global Positioning System measurements on the ionospheric plasma flow around the noon sector of polar ionosphere is presented. σφ shows a strong linear dependence on the plasma drift speed measured by the Super Dual Auroral Radar Network radars, whereas the amplitude scintillation index (S4) does not. This observed dependence can be explained as a consequence of Fresnel frequency dependence of the relative drift and the used constant cutoff frequency (0.1 Hz) to detrend the data for obtaining standard σφ. The lack of dependence of S4 on the drift speed possibly eliminates the plasma instability mechanism(s) involved as a cause of the dependence. These observations further confirm that the standard phase scintillation index is much more sensitive to plasma flow; therefore, utmost care must be taken when identifying phase scintillation (diffractive phase variations) from refractive (deterministic) phase variations, especially in the polar region where the ionospheric plasma drift is much larger than in equatorial and midlatitude regions.

PFISR GPS tracking mode for researching high-latitude ionospheric electron density gradients associated with GPS scintillation

NASA Astrophysics Data System (ADS)

Loucks, D. C.; Palo, S. E.; Pilinski, M.; Crowley, G.; Azeem, S. I.; Hampton, D. L.

2016-12-01

Ionospheric behavior in the high-latitudes can significantly impact Ultra High Frequency (UHF) signals in the 300 MHz to 3 GHz band, resulting in degradation of Global Positioning System (GPS) position solutions and satellite communications interruptions. To address these operational concerns, a need arises to identify and understand the ionospheric structure that leads to disturbed conditions in the Arctic. Structures in the high-latitude ionosphere are known to change on the order of seconds or less, can be decameters to kilometers in scale, and elongate across magnetic field lines at auroral latitudes. Nominal operations at Poker Flat Incoherent Scatter Radar (PFISR) give temporal resolution on the order of minutes, and range resolution on the order of tens of kilometers, while specialized GPS receivers available for ionospheric sensing have a 100Hz observation sampling rate. One of these, ASTRA's Connected Autonomous Space Environment Sensor (CASES) is used for this study. We have developed a new GPS scintillation tracking mode for PFISR to address open scientific questions regarding temporal and spatial electron density gradients. The mode will be described, a number of experimental campaigns will be analyzed, and results and lessons learned will be presented.

Analysis of strong ionospheric scintillation events measured by means of GPS signals at low latitudes during disturbed conditions

NASA Astrophysics Data System (ADS)

Forte, B.

2012-08-01

Drifting structures characterized by inhomogeneities in the spatial electron density distribution at ionospheric heights cause the scintillation of radio waves propagating through. The fractional electron density fluctuations and the corresponding scintillation levels may reach extreme values at low latitudes during high solar activity. Different levels of scintillation were observed on experimental data collected in the Asian sector at low latitudes by means of a GPS dual frequency receiver under moderate solar activity (2005). The GPS receiver used in these campaigns was particularly modified in firmware in order to record power estimates on the C/A code as well as on the carriers L1 and L2. Strong scintillation activity was recorded in the post-sunset period (saturatingS4 and SI as high as 20 dB). Spectral modifications and broadening was observed during high levels of scintillation possibly indicating refractive scattering taking place instead of diffractive scattering. A possible interpretation of those events was attempted on the basis of the refractive scattering theory developed by Uscinski (1968) and Booker and MajidiAhi (1981).

First light from a kilometer-baseline Scintillation Auroral GPS Array

PubMed Central

Datta-Barua, S; Su, Y; Deshpande, K; Miladinovich, D; Bust, G S; Hampton, D; Crowley, G

2015-01-01

We introduce and analyze the first data from an array of closely spaced Global Positioning System (GPS) scintillation receivers established in the auroral zone in late 2013 to measure spatial and temporal variations in L band signals at 100–1000 m and subsecond scales. The seven receivers of the Scintillation Auroral GPS Array (SAGA) are sited at Poker Flat Research Range, Alaska. The receivers produce 100 s scintillation indices and 100 Hz carrier phase and raw in-phase and quadrature-phase samples. SAGA is the largest existing array with baseline lengths of the ionospheric diffractive Fresnel scale at L band. With an initial array of five receivers, we identify a period of simultaneous amplitude and phase scintillation. We compare SAGA power and phase data with collocated 630.0 nm all-sky images of an auroral arc and incoherent scatter radar electron precipitation measurements, to illustrate how SAGA can be used in multi-instrument observations for subkilometer-scale studies. Key Points A seven-receiver Scintillation Auroral GPS Array (SAGA) is now at Poker Flat, Alaska SAGA is the largest subkilometer array to enable phase/irregularities studies Simultaneous scintillation, auroral arc, and electron precipitation are observed PMID:26709318

Study of GNSS Loss of Lock Characteristics under Ionosphere Scintillation with GNSS Data at Weipa (Australia) During Solar Maximum Phase.

PubMed

Liu, Yang; Fu, Lianjie; Wang, Jinling; Zhang, Chunxi

2017-09-25

One of the adverse impacts of scintillation on GNSS signals is the loss of lock status, which can lead to GNSS geometry and visibility reductions that compromise the accuracy and integrity of navigation performance. In this paper the loss of lock based on ionosphere scintillation in this solar maximum phase has been well investigated with respect to both temporal and spatial behaviors, based on GNSS observatory data collected at Weipa (Australia; geographic: 12.45° S, 130.95° E; geomagnetic: 21.79° S, 214.41° E) from 2011 to 2015. Experiments demonstrate that the percentage of occurrence of loss of lock events under ionosphere scintillation is closely related with solar activity and seasonal shifts. Loss of lock behaviors under ionosphere scintillation related to elevation and azimuth angles are statistically analyzed, with some distinct characteristics found. The influences of daytime scintillation and geomagnetic storms on loss of lock have also been discussed in details. The proposed work is valuable for a deeper understanding of theoretical mechanisms of-loss of lock under ionosphere scintillation in global regions, and provides a reference for GNSS applications in certain regions at Australian low latitudes.

Study of GNSS Loss of Lock Characteristics under Ionosphere Scintillation with GNSS Data at Weipa (Australia) During Solar Maximum Phase

PubMed Central

Liu, Yang; Fu, Lianjie; Wang, Jinling; Zhang, Chunxi

2017-01-01

One of the adverse impacts of scintillation on GNSS signals is the loss of lock status, which can lead to GNSS geometry and visibility reductions that compromise the accuracy and integrity of navigation performance. In this paper the loss of lock based on ionosphere scintillation in this solar maximum phase has been well investigated with respect to both temporal and spatial behaviors, based on GNSS observatory data collected at Weipa (Australia; geographic: 12.45° S, 130.95° E; geomagnetic: 21.79° S, 214.41° E) from 2011 to 2015. Experiments demonstrate that the percentage of occurrence of loss of lock events under ionosphere scintillation is closely related with solar activity and seasonal shifts. Loss of lock behaviors under ionosphere scintillation related to elevation and azimuth angles are statistically analyzed, with some distinct characteristics found. The influences of daytime scintillation and geomagnetic storms on loss of lock have also been discussed in details. The proposed work is valuable for a deeper understanding of theoretical mechanisms of—loss of lock under ionosphere scintillation in global regions, and provides a reference for GNSS applications in certain regions at Australian low latitudes. PMID:28946676

Sporadic-E Studies by Ionospheric Scintillation Using Ground-Based GPS and Radio Occultation Measurements

NASA Astrophysics Data System (ADS)

Seif, A.; Liu, T. J. Y.; Mannucci, A. J.; Carter, B. A.; Norman, R.

2016-12-01

The Global Navigation Satellite System (GNSS) based radio occultation (RO) technique provides an ideal limb-viewing geometry from space for studying the occurrence of sporadic E (Es). This study focuses on the detection and analysis of Es from RO measurements, to conclusively show the presence of Es's relationship with daytime scintillation. We bring two data sets to bear, using GNSS signal transmissions received on the ground and from space, which provide a unique opportunity to retrieve information about Es. RO signatures of Es and in GHz scintillation are not the same as ground-based signatures of Es. The viewing geometries are approximately orthogonal, which means the irregularity sources are not the same. That is, irregularities responsible for RO scintillations are essentially in a vertical plane, whereas those responsible for ground-based scintillations are essentially in a horizontal plane. Hence, complementary information is available regarding plasma structure in an Es patch. An analysis of combined data sets should prove to be a profitable avenue for research. In this study, we present the occurrence of scintillation using GPS Ionospheric Scintillation and Total Electron Content Monitor (GISTM) systems from two equatorial stations UKM (2.55°N, 101.46°E), and Langkawi (6.19°N, 99.51°E) in Malaysia. To better understand scale size irregularities as well as identify the occurrence of Es, we use COSMIC RO data. Two key findings coming out from our study are 1) According to the characteristics of daytime scintillation analyzed at, UKM and Langkawi stations, scintillation shows no significant TEC depletions and ROTI enhancements. The finding that ROTI does not exceed 0.5 TECU/min during daytime implies that large scale ionospheric irregularities with a scale length of a few kilometers do not exist at these stations. This is a piece of evidence which positively supports that daytime scintillation shows irregularities consistent with thin layer Es and

Validation of measured poleward TEC gradient using multi-station GPS with Artificial Neural Network based TEC model in low latitude region for developing predictive capability of ionospheric scintillation

NASA Astrophysics Data System (ADS)

Sur, D.; Paul, A.

2017-12-01

The equatorial ionosphere shows sharp diurnal and latitudinal Total Electron Content (TEC) variations over a major part of the day. Equatorial ionosphere also exhibits intense post-sunset ionospheric irregularities. Accurate prediction of TEC in these low latitudes is not possible from standard ionospheric models. An Artificial Neural Network (ANN) based Vertical TEC (VTEC) model has been designed using TEC data in low latitude Indian longitude sector for accurate prediction of VTEC. GPS TEC data from the stations Calcutta (22.58°N, 88.38°E geographic, magnetic dip 32°), Baharampore (24.09°N, 88.25°E geographic, magnetic dip 35°) and Siliguri (26.72°N, 88.39°E geographic; magnetic dip 40°) are used as training dataset for the duration of January 2007-September 2011. Poleward VTEC gradients from northern EIA crest to region beyond EIA crest have been calculated from measured VTEC and compared with that obtained from ANN based VTEC model. TEC data from Calcutta and Siliguri are used to compute VTEC gradients during April 2013 and August-September 2013. It has been observed that poleward VTEC gradient computed from ANN based TEC model has shown good correlation with measured values during vernal and autumnal equinoxes of high solar activity periods of 2013. Possible correlation between measured poleward TEC gradients and post-sunset scintillations (S4 ≥ 0.4) from northern crest of EIA has been observed in this paper. From the observation, a suitable threshold poleward VTEC gradient has been proposed for possible occurrence of post-sunset scintillations at northern crest of EIA along 88°E longitude. Poleward VTEC gradients obtained from ANN based VTEC model are used to forecast possible ionospheric scintillation after post-sunset period using the threshold value. It has been observed that these predicted VTEC gradients obtained from ANN based VTEC model can forecast post-sunset L-band scintillation with an accuracy of 67% to 82% in this dynamic low latitude

Validating the use of scintillation proxies to study ionospheric scintillation over the Ugandan region

NASA Astrophysics Data System (ADS)

Amabayo, Emirant B.; Jurua, Edward; Cilliers, Pierre J.

2015-06-01

In this study, we compare the standard scintillation indices (S4 and σΦ) from a SCINDA receiver with scintillation proxies (S4p and | sDPR |) derived from two IGS GPS receivers. Amplitude (S4) and phase (σΦ) scintillation data were obtained from the SCINDA installed at Makerere University (0.34°N, 32.57°E). The corresponding amplitude (S4p) and phase (| sDPR |) scintillation proxies were derived from data archived by IGS GPS receivers installed at Entebbe (0.04°N, 32.44°E) and Mbarara (0.60°S, 30.74°E). The results show that for most of the cases analysed in this study, σΦ and | sDPR | are in agreement. Amplitude scintillation occurrence estimated using the S4p are fairly consistent with the standard S4, mainly between 17:00 UT and 21:00 UT, despite a few cases of over and under estimation of scintillation levels by S4p. Correlation coefficients between σΦ and the | sDPR | proxy revealed positive correlation. Generally, S4p and S4 exhibits both moderate and strong positive correlation. TEC depletions associated with equatorial plasma bubbles are proposed as the cause of the observed scintillation over the region. These equatorial plasma bubbles were evident along the ray paths to satellites with PRN 2, 15, 27 and 11 as observed from MBAR and EBBE. In addition to equatorial plasma bubbles, atmospheric gravity waves with periods similar to those of large scale traveling ionospheric disturbances were also observed as one of the mechanisms for scintillation occurrence. The outcome of this study implies that GPS derived scintillation proxies can be used to quantify scintillation levels in the absence of standard scintillation data in the equatorial regions.

A study of multi-GNSS ionospheric scintillation and cycle-slip over Hong Kong region for moderate solar flux conditions

NASA Astrophysics Data System (ADS)

Luo, Xiaomin; Liu, Zhizhao; Lou, Yidong; Gu, Shengfeng; Chen, Biyan

2017-09-01

This study presents the characteristics of Multiple Global Navigation Satellite System (Multi-GNSS) ionospheric scintillation and cycle-slip occurrence through the analysis of Multi-GNSS data collected by a newly installed receiver located at Sha Tin of Hong Kong from 6 October 2015 to 31 December 2016. This period of time was under a moderate solar activity condition with average sunspot number and F10.7 as 44 and 92, respectively. Considering the frequent occurrence of loss of lock in satellites measurements in the presence of ionospheric scintillation, a rate of geometry-free (ROGF) combination is proposed to take the time gap size between two data arcs into account in the cycle-slip detection. The results show that most ionospheric scintillation events and cycle-slips are observed from 20:00 LT to 0:00 LT. Under the strong scintillation (S4 > 0.6) conditions, it is found that the time series of wide-land (WL) ambiguity NWL and ROGF vary significantly and their range can reach more than 50 cycles and 0.1 m/s, respectively. However, the variations of the NWL and ROGF are generally small under weak scintillation (0.2 < S4 ≤ 0.6) or non-scintillation (S4 ≤ 0.2) conditions. A strong correlation of scintillation and cycle-slip occurrence is also verified by the daily and spatial statistics results. In addition, it is found that on average every 1000 strong scintillation events can result in 200, 124, and 171 cycle-slip occurrences in GPS, GLONASS, and BDS, respectively, whereas these values are 7, 12, and 12 per 1000 under weak scintillation conditions. This study suggests that cautions be taken when GNSS measurements are contaminated by the strong ionospheric scintillation in GNSS applications such as real-time kinematic (RTK) and precise point positioning (PPP).

Methods of alleviation of ionospheric scintillation effects on digital communications

NASA Technical Reports Server (NTRS)

Massey, J. L.

1974-01-01

The degradation of the performance of digital communication systems because of ionospheric scintillation effects can be reduced either by diversity techniques or by coding. The effectiveness of traditional space-diversity, frequency-diversity and time-diversity techniques is reviewed and design considerations isolated. Time-diversity signaling is then treated as an extremely simple form of coding. More advanced coding methods, such as diffuse threshold decoding and burst-trapping decoding, which appear attractive in combatting scintillation effects are discussed and design considerations noted. Finally, adaptive coding techniques appropriate when the general state of the channel is known are discussed.

A multi-instrument case study of high-latitude ionospheric GNSS scintillation due to drifting plasma irregularities

NASA Astrophysics Data System (ADS)

van der Meeren, C.; Oksavik, K.; Moen, J. I.; Romano, V.

2013-12-01

For this study, GPS receiver scintillation and Total Electron Content (TEC) data from high-latitude locations on Svalbard have been combined with several other data sets, including the EISCAT Svalbard Radar (ESR) and allsky cameras, to perform a multi-instrument case study of high-latitude GPS ionospheric scintillations in relation to drifting plasma irregularities at night over Svalbard on 31 October 2011. Scintillations are rapid amplitude and phase fluctuations of electromagnetic signals. GNSS-based systems may be disturbed by ionospheric plasma irregularities and structures such as plasma patches (areas of enhanced electron density in the polar cap) and plasma gradients. When the GNSS radio signals propagate through such areas, in particular gradients, the signals experience scintillations that at best increases positioning errors and at worst may break the receiver's signal lock, potentially resulting in the GNSS receiver losing track of its position. Due to the importance of many GNSS applications, it is desirable to study the scintillation environment to understand the limitations of the GNSS systems. We find scintillation mainly localised to plasma gradients, with predominantly phase scintillation at the leading edge of patches and both phase and amplitude scintillation at the trailing edge. A single edge may also contain different scintillation types at different locations.

Modeling of the Ionospheric Scintillation and Total Electron Content Observations during the 21 August 2017 Total Solar Eclipse

NASA Astrophysics Data System (ADS)

Datta-Barua, S.; Gachancipa, J. N.; Deshpande, K.; Herrera, J. A.; Lehmacher, G. A.; Su, Y.; Gyuk, G.; Bust, G. S.; Hampton, D. L.

2017-12-01

High concentration of free electrons in the ionosphere can cause fluctuations in incoming electromagnetic waves, such as those from the different Global Navigation Satellite Systems (GNSS). The behavior of the ionosphere depends on time and location, and it is highly influenced by solar activity. The purpose of this study is to determine the impact of a total solar eclipse on the local ionosphere in terms of ionospheric scintillations, and on the global ionosphere in terms of TEC (Total Electron Content). The studied eclipse occurred on 21 August 2017 across the continental United States. During the eclipse, we expected to see a decrease in the scintillation strength, as well as in the TEC values. As a broader impact part of our recently funded NSF proposal, we temporarily deployed two GNSS receivers on the eclipse's totality path. One GNSS receiver was placed in Clemson, SC. This is a multi-frequency GNSS receiver (NovAtel GPStation-6) capable of measuring high and low rate scintillation data as well as TEC values from four different GNSS systems. We had the receiver operating before, during, and after the solar eclipse to enable the comparison between eclipse and non-eclipse periods. A twin receiver collected data at Daytona Beach, FL during the same time, where an 85% partial solar eclipse was observed. Additionally, we set up a ground receiver onsite in the path of totality in Perryville, Missouri, from which the Adler Planetarium of Chicago launched a high-altitude balloon to capture a 360-degree video of the eclipse from the stratosphere. By analyzing the collected data, this study looks at the effects of partial and total solar eclipse periods on high rate GNSS scintillation data at mid-latitudes, which had not been explored in detail. This study also explores the impact of solar eclipses on signals from different satellite constellations (GPS, GLONASS, and Galileo). Throughout the eclipse, the scintillation values did not appear to have dramatic changes

Analysis of the PLL phase error in presence of simulated ionospheric scintillation events

NASA Astrophysics Data System (ADS)

Forte, B.

2012-01-01

The functioning of standard phase locked loops (PLL), including those used to track radio signals from Global Navigation Satellite Systems (GNSS), is based on a linear approximation which holds in presence of small phase errors. Such an approximation represents a reasonable assumption in most of the propagation channels. However, in presence of a fading channel the phase error may become large, making the linear approximation no longer valid. The PLL is then expected to operate in a non-linear regime. As PLLs are generally designed and expected to operate in their linear regime, whenever the non-linear regime comes into play, they will experience a serious limitation in their capability to track the corresponding signals. The phase error and the performance of a typical PLL embedded into a commercial multiconstellation GNSS receiver were analyzed in presence of simulated ionospheric scintillation. Large phase errors occurred during scintillation-induced signal fluctuations although cycle slips only occurred during the signal re-acquisition after a loss of lock. Losses of lock occurred whenever the signal faded below the minimumC/N0threshold allowed for tracking. The simulations were performed for different signals (GPS L1C/A, GPS L2C, GPS L5 and Galileo L1). L5 and L2C proved to be weaker than L1. It appeared evident that the conditions driving the PLL phase error in the specific case of GPS receivers in presence of scintillation-induced signal perturbations need to be evaluated in terms of the combination of the minimumC/N0 tracking threshold, lock detector thresholds, possible cycle slips in the tracking PLL and accuracy of the observables (i.e. the error propagation onto the observables stage).

Growth of L-band scintillation at anomaly crest station in association with strong TEC gradient: A study covering wide solar activity period

NASA Astrophysics Data System (ADS)

Pathak, K.; Devi, M.; Barbara, A. K.; Zahan, Y.

2018-01-01

The paper aims at to study the sources associated with growth of L band scintillation over Guwahati, an Appleton anomaly region. Starting with the analysis of diurnal and seasonal characteristic features of scintillation from a minimum sunspot number (Rz) of 10 to a maximum of 140, the paper shows that scintillations are more likely to develop during high solar activity period. It also highlights the explosive increase in occurrence of scintillation from post sunset to pre midnight hours in vernal equinoctial months when the background TEC is 50% more than on a normal day, accompanied by enhanced TEC decay rate. The role of equatorial anomaly effects through EXB drift processes are brought into discussion as possible sources on the growth of small scale irregularities leading to such scintillations.

Growth of L-band scintillation at anomaly crest station in association with strong TEC gradient: A study covering wide solar activity period

NASA Astrophysics Data System (ADS)

Pathak, K.; Devi, M.; Barbara, A. K.; Zahan, Y.

2018-07-01

The paper aims at to study the sources associated with growth of L band scintillation over Guwahati, an Appleton anomaly region. Starting with the analysis of diurnal and seasonal characteristic features of scintillation from a minimum sunspot number (Rz) of 10 to a maximum of 140, the paper shows that scintillations are more likely to develop during high solar activity period. It also highlights the explosive increase in occurrence of scintillation from post sunset to pre midnight hours in vernal equinoctial months when the background TEC is 50% more than on a normal day, accompanied by enhanced TEC decay rate. The role of equatorial anomaly effects through EXB drift processes are brought into discussion as possible sources on the growth of small scale irregularities leading to such scintillations.

Suppression of ionospheric scintillation during St. Patrick's Day geomagnetic super storm as observed over the anomaly crest region station Pingtung, Taiwan: A case study

NASA Astrophysics Data System (ADS)

Nayak, Chinmaya; Tsai, L.-C.; Su, S.-Y.; Galkin, I. A.; Caton, R. G.; Groves, K. M.

2017-07-01

In this paper, we investigate the reasons behind the absence of ionospheric VHF scintillation over Pingtung, Taiwan during the March 17, 2015 St. Patrick's Day geomagnetic storm. What makes it more interesting is the fact that the absence of scintillation on the storm day was preceded by observations of scintillation for 6 consecutive days before the storm. A combination of data from VHF receivers, ionosonde and in situ plasma density observations from European Space Agency (ESA)'s SWARM constellation were used for this purpose. Also, global hmF2 maps obtained from International Reference Ionosphere (IRI) Real-Time Assimilative Mapping (IRTAM) were utilised for a better picture of the ionospheric conditions. The main driver behind the absence of the scintillation in the Taiwanese sector was a reduced pre-reversal enhancement (PRE) electric field caused due to westward prompt-penetration electric field (PPEF). This caused the post-sunset ionosphere to drift downwards in altitude causing unfavourable conditions for Rayleigh-Taylor instability. On the contrary, the PPEFs were found to strongly enhance the PRE electric fields in the Indian sector leading to ionospheric irregularities/scintillations in the post-sunset sector.

Low and Mid-Latitude Ionospheric Irregularities Studies Using TEC and Radio Scintillation Data from the CITRIS Radio Beacon Receiver in Low-Earth-Orbit

NASA Astrophysics Data System (ADS)

Siefring, C. L.; Bernhardt, P. A.; Huba, J.; Krall, J.; Roddy, P. A.

2009-12-01

Unique data on ionospheric plasma irregularities from the Naval Research Laboratory (NRL) CITRIS (Scintillation and TEC Receiver in Space) instrument will be presented. CITRIS is a multi-band receiver that recorded TEC (Total Electron Content) and radio scintillations from Low-Earth Orbit (LEO) on STPSat1. The 555+/5 km altitude 35° inclination orbit covers low and mid-latitudes. The measurements require propagation from a transmitter to a receiver through the F-region plasma. CITRIS used both 1) satellite beacons in LEO, such as the NRL CERTO (Coherent Electromagnetic Radio TOmography) beacons and 2) the global network of ground-based DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) beacons. The TEC measurements allow for tracking of ionospheric disturbances and irregularities while the measurements of scintillations can simultaneously characterize their effects. CITRIS was operated in a complementary fashion with the C/NOFS (Communication/Navigations Outages Forecasting System) satellite during most of its first year of operations. C/NOFS carries a three-frequency 150/400/1067 MHz CERTO beacon and is dedicated to the study of Spread-F. In the case of Spread-F, ionospheric irregularities start with large scale size density gradients (100s of km) and cascade through complex processes to short scale sizes (10s of meters). It is typically the 100m-1km scale features that harm communication and navigation systems through scintillations. A multi-sensor approach is needed to completely understand this complex system, such as, the combination of CITRIS remote radio sensing and C/NOFS in-situ data. Several types of irregularities have been studied including Spread-F and the newly discovered dawn-side depletions. Comparisons with the physics based SAMI3 model are being performed to help our understanding of the morphology of the irregularities.

Atmospheric Drag, Occultation `N' Ionospheric Scintillation (ADONIS) mission proposal. Alpbach Summer School 2013 Team Orange

NASA Astrophysics Data System (ADS)

Hettrich, Sebastian; Kempf, Yann; Perakis, Nikolaos; Górski, Jędrzej; Edl, Martina; Urbář, Jaroslav; Dósa, Melinda; Gini, Francesco; Roberts, Owen W.; Schindler, Stefan; Schemmer, Maximilian; Steenari, David; Joldžić, Nina; Glesnes Ødegaard, Linn-Kristine; Sarria, David; Volwerk, Martin; Praks, Jaan

2015-02-01

The Atmospheric Drag, Occultation `N' Ionospheric Scintillation mission (ADONIS) studies the dynamics of the terrestrial thermosphere and ionosphere in dependency of solar events over a full solar cycle in Low Earth Orbit (LEO). The objectives are to investigate satellite drag with in-situ measurements and the ionospheric electron density profiles with radio occultation and scintillation measurements. A constellation of two satellites provides the possibility to gain near real-time data (NRT) about ionospheric conditions over the Arctic region where current coverage is insufficient. The mission shall also provide global high-resolution data to improve assimilative ionospheric models. The low-cost constellation can be launched using a single Vega rocket and most of the instruments are already space-proven allowing for rapid development and good reliability. From July 16 to 25, 2013, the Alpbach Summer School 2013 was organised by the Austrian Research Promotion Agency (FFG), the European Space Agency (ESA), the International Space Science Institute (ISSI) and the association of Austrian space industries Austrospace in Alpbach, Austria. During the workshop, four teams of 15 students each independently developed four different space mission proposals on the topic of "Space Weather: Science, Missions and Systems", supported by a team of tutors. The present work is based on the mission proposal that resulted from one of these teams' efforts.

A study of simultaneous scintillation observations by Chinese FY-2 geostationary meteorological satellite and VHF coherent radar measurements over South China

NASA Astrophysics Data System (ADS)

Zuo, X.; Yu, T.; Xia, C.

2016-12-01

It's a good place for South China to monitor ionospheric scintillation, which are situated near the northern crest of the equatorial ionosphere anomaly. The temporal variation characteristics of Amplitude scintillations of Chinese FY-2 geostationary meteorological satellite (86.5°E) observed at Guangzhou (23.2°N, 113.3°E, dip 18°N) during the period from July 2011 to June 2013 are present. The scintillation occurrence and intensity increase dramatically at September and October in FY-2 satellite link. The scintillation observations of FY-2 geostationary satellite observed at Guangzhou and simultaneous VHF (47.5MHz) coherent radar measurements from Sanya (18.3°N, 109.6°E, dip 13°N) during equinoctial months of 2011 and 2012 are used for a coordinated study for the relationship between the L-band scintillation patches on the propagation path of FY-2 satellite and the extended 3-m irregularity structures known as plumes over South China. The results showed good coincidence of the plumes with scintillation patches in most events. In case study, the zonal drift velocity of the irregularities was estimated by comparison of the onset times of the scintillation and plume and the irregularities were found to drift eastwards at a speed ranging about tens of meters to one hundred meters per second. From the derived value of drift speed and duration of scintillation events, the irregularity patches were found to have east-west extent about a few hundred kilometers. On the other hand, if the plumes on the radar maps occurred at lower altitudes, the associated irregularities would not be able to reach the IPP of the satellite and generate L-band scintillations there. Weak scintillations were observed on FY-2 link without any plume structure on radar backscatter maps occasionally.

Statistical evaluation of GLONASS amplitude scintillation over low latitudes in the Brazilian territory

NASA Astrophysics Data System (ADS)

de Oliveira Moraes, Alison; Muella, Marcio T. A. H.; de Paula, Eurico R.; de Oliveira, César B. A.; Terra, William P.; Perrella, Waldecir J.; Meibach-Rosa, Pâmela R. P.

2018-04-01

The ionospheric scintillation, generated by the ionospheric plasma irregularities, affects the radio signals that pass through it. Their effects are widely studied in the literature with two different approaches. The first one deals with the use of radio signals to study and understand the morphology of this phenomenon, while the second one seeks to understand and model how much this phenomenon interferes in the radio signals and consequently in the services to which these systems work. The interest of several areas, particularly to those that are life critical, has increased using the concept of satellite multi-constellation, which consists of receiving, processing and using data from different navigation and positioning systems. Although there is a vast literature analyzing the effects of ionospheric scintillation on satellite navigation systems, the number of studies using signals received from the Russian satellite positioning system (named GLONASS) is still very rare. This work presents for the first time in the Brazilian low-latitude sector a statistical analysis of ionospheric scintillation data for all levels of magnetic activities obtained by a set of scintillation monitors that receive signals from the GLONASS system. In this study, data collected from four stations were used in the analysis; Fortaleza, Presidente Prudente, São José dos Campos and Porto Alegre. The GLONASS L-band signals were analyzed for the period from December 21, 2012 to June 20, 2016, which includes the peak of the solar cycle 24 that occurred in 2014. The main characteristics of scintillation presented in this study include: (1) the statistical evaluation of seasonal and solar activity, showing the chances that an user on similar geophysical conditions may be susceptible to the effects of ionospheric scintillation; (2) a temporal analysis based on the local time distribution of scintillation at different seasons and intensity levels; and (3) the evaluation of number of

Assessment of GPS Multifrequency Signal Characteristics During Periods of Ionospheric Scintillations from an Anomaly Crest Location

NASA Astrophysics Data System (ADS)

Goswami, S.; Paul, K. S.; Paul, A.

2017-09-01

Multifrequency GPS transmissions have provided the opportunity for testing the applicability of the principle of frequency diversity for scintillation mitigation. Published results addressing this issue with quantified estimates are not available in literature, at least from the anomaly crest location of the Indian longitude sector. Multifrequency scattering within the same L band is often the attributed cause behind simultaneous decorrelated signal fluctuations. The present paper aims to provide proportion of time during scintillation patches that decorrelations are found across GPS L1, L2, and L5 frequencies associated with high S4, corresponding high values of scattering coefficients, and large receiver position deviations thereby seriously compromising the performance of satellite-based navigation system. Results from the anomaly crest station at Calcutta indicate maximum 40% of scintillation time during February-April 2014 and 33% during August-October 2014 that the signals are decorrelated. It is important to note that it is only during these time intervals that the principle of frequency diversity could be applied for scintillation mitigation.

Occurrence and zonal drifts of small-scale ionospheric irregularities over an equatorial station during solar maximum - Magnetic quiet and disturbed conditions

NASA Astrophysics Data System (ADS)

Muella, M. T. A. H.; de Paula, E. R.; Kantor, I. J.; Rezende, L. F. C.; Smorigo, P. F.

2009-06-01

A statistical study of L-band amplitude scintillations and zonal drift velocity of Fresnel-scale ionospheric irregularities is presented. Ground-based global positioning system (GPS) data acquired at the equatorial station of São Luís (2.33°S, 44.21°W, dip latitude 1.3°S), Brazil, during the solar maximum period from March 2001 to February 2002 are used in the analysis. The variation of scintillations and irregularity drift velocities with local time, season and magnetic activity are reported. The results reveal that for the near overhead ionosphere (satellite elevation angle >45°) a broad maximum in the occurrence of scintillation is seen from October to February. In general, weak scintillations (S 4 < 0.4) dominated (>90%) during equinox (March-April; September-October) and December solstice (November-February) quiet time conditions and, many of the scintillations, occurred during pre-midnight hours. The mean zonal velocities of the irregularities are seen to be ˜30 m s -1 larger near December solstice, while during the equinoctial period the velocities decay faster and the scintillations tend to cease earlier. On geomagnetically disturbed nights, scintillation activity seems to be strongly affected by the prompt penetration of magnetospheric electric fields and disturbance dynamo effects. On disturbed days, during the equinox and December solstice seasons, the scintillations tend to be suppressed in the pre-midnight hours, whereas during June solstice months (May-August) the effect is opposite. In the post-midnight period, the mostly marked increase in the scintillation occurrence is observed during the equinox months. The results show that during disturbed conditions only one type of storm (when the main phase maximum takes place during the daytime hours) agrees with the Aarons' description, that is the suppression of L-band scintillations in the first recovery phase night. The results also reveal that the storm-time irregularity drifts become more

Effects of diffraction by ionospheric electron density irregularities on the range error in GNSS dual-frequency positioning and phase decorrelation

NASA Astrophysics Data System (ADS)

Gherm, Vadim E.; Zernov, Nikolay N.; Strangeways, Hal J.

2011-06-01

It can be important to determine the correlation of different frequency signals in L band that have followed transionospheric paths. In the future, both GPS and the new Galileo satellite system will broadcast three frequencies enabling more advanced three frequency correction schemes so that knowledge of correlations of different frequency pairs for scintillation conditions is desirable. Even at present, it would be helpful to know how dual-frequency Global Navigation Satellite Systems positioning can be affected by lack of correlation between the L1 and L2 signals. To treat this problem of signal correlation for the case of strong scintillation, a previously constructed simulator program, based on the hybrid method, has been further modified to simulate the fields for both frequencies on the ground, taking account of their cross correlation. Then, the errors in the two-frequency range finding method caused by scintillation have been estimated for particular ionospheric conditions and for a realistic fully three-dimensional model of the ionospheric turbulence. The results which are presented for five different frequency pairs (L1/L2, L1/L3, L1/L5, L2/L3, and L2/L5) show the dependence of diffractional errors on the scintillation index S4 and that the errors diverge from a linear relationship, the stronger are scintillation effects, and may reach up to ten centimeters, or more. The correlation of the phases at spaced frequencies has also been studied and found that the correlation coefficients for different pairs of frequencies depend on the procedure of phase retrieval, and reduce slowly as both the variance of the electron density fluctuations and cycle slips increase.

Impact of multiple frequency scattering on GNSS performance under adverse ionospheric conditions

NASA Astrophysics Data System (ADS)

Das, Aditi; Paul, Ashik

One of the major deterrents to successful implementation of SBAS may be linked to sharp latitudinal gradients of ionization occurring during the daytime and intense Space Weather events in the post sunset hours, affecting transionospheric satellite links particularly in the equatorial region. These phenomena have the potential to cause serious damage to the technological infrastructure on which society relies. GPS modernization program is focused on addition of a new navigation signal L5 to the GPS constellation. The L5 is exclusively reserved for aviation navigation services and is designed with a protected spectrum, higher power, and greater bandwidth to support life-critical and high performance applications. Overall robustness of this dual-frequency mechanism to ionospheric scintillations could be ascertained through a study of correlated scintillations. Understanding the correlation of signal fades across two frequencies is important to assess their collective mitigation effectiveness. The Indian Regional Navigational Satellite System (IRNSS) will operate at L1 (1575.42 MHz), L5 (1176.45 MHz) and S-band (2492.42 MHz) frequencies. A multi-constellation, multi-frequency GNSS receiver is operational at University of Calcutta, Calcutta, India (22.58deg N, 88.38deg E geographic; magnetic dip: 32deg N) since April 2013. Special emphasis was given to analyzing signals from satellite vehicles equipped to transmit L5 frequency. On April 12, 2013, amplitude scintillation and associated fluctuations in carrier-to-noise ratios (CNO) were noted on SV1 link during 14:15-14:50UT from Calcutta. The S4 indices at the three frequencies, L1, L2 and L5, were affected to different extent with L2 and L5 values showing close correspondence and L1 suffering least scintillations. Correlation coefficient of S4 and carrier-to-noise ratios (CNO) between different combination of frequencies (L1:L2, L2:L5; L1:L5) were calculated at 3 minutes interval during periods of scintillation. As L2

Day and nighttime L-Band amplitude scintillations during low solar activity at a low latitude station in the South Pacific region

NASA Astrophysics Data System (ADS)

Prasad, Ramendra; Kumar, Sushil

2017-12-01

A morphological study of GPS L-band amplitude scintillations observed at a low latitude station, Suva (18.1°S, 178.4°E), Fiji, during low solar activity year 2010 of solar cycle 24, has been presented. Out of a total of 480 scintillation events recorded during 2010, 84.4% were weak (0.2 ≤ S4 < 0.3), 14.6% moderate (0.3 ≤ S4 < 0.45) and only 1% strong (0.45 ≤ S4). The amplitude scintillations were most pronounced in the local daytime with January registering the highest occurrence. Seasonal analysis revealed maximum scintillation occurrence during summer as compared to winter and equinox seasons. The daytime scintillation with a maximum in the summer is consistent with localized blanketing sporadic E observations and could also be possibly due to lightning activity around the observing station. Annual percentage occurrence shows that scintillations occurred mostly in the daytime with peak occurrence at around 05:00-09:00 LT. The daytime strong scintillation events were not associated with vTEC depletions and phase scintillations, but the signal to noise ratio during the scintillation events decreased with increase in scintillation index (S4). However, the post-midnight strong amplitude scintillations were associated with vTEC depletions and phase scintillations indicative of large scale irregularities (spread-F). The geomagnetic activity effect showed enhanced occurrence on geomagnetically disturbed days as compared to quite conditions. The geomagnetic storm effect on scintillations for 17 storms of different strengths (Dst ≤ 50 nT) during 2010-2011 showed an increase in the occurrence of post-storm scintillations, on the days following the storm.

Experimental Plan for Conducting Ionospheric Scintillation Measurements Using ATS Geostationary Satellites at 136 and 1550 MHz

DOT National Transportation Integrated Search

1973-04-01

An experimental plan for conducting ionospheric scintillation measurements using the geostationary Applications Technology Satellites at 136 MHz and 1550 MHz is presented. A remote unmanned data collection platform is proposed together with detailed ...

Scintillation Observations and Response of The Ionosphere to Electrodynamics (SORTIE)

NASA Astrophysics Data System (ADS)

Crowley, G.

2015-12-01

The Scintillation Observations and Response of The Ionosphere to Electrodynamics, or SORTIE, mission is a 6U NASA Heliophysics CubeSat designed to study the ionosphere at altitudes below 400km. The SORTIE mission is being developed by a team including ASTRA (lead institution), AFRL, University of Texas at Dallas (UTD), COSMIAC (Satellite Integrator), and Boston College. SORTIE will address cutting-edge science in the area of ionospheric dynamics. The SORTIE mission will address the following science questions: Q1) Discover the sources of wave-like plasma perturbations in the F-region ionosphere. Q2) Determine the relative role of dynamo action and more direct mechanical forcing in the formation of wave-like plasma perturbations. To address these questions we plan to fly a CubeSat with novel sensors that measure key plasma parameters in a circular, low to middle inclination orbit near 350-400 km altitude. The sensors include an ion velocity meter (built by UTD) and a Planar Langmuir Probe (built by AFRL). The SORTIE mission plan is to describe the distribution of wave-like structures in the plasma density of the ionospheric F-region. In doing so, the SORTIE team will determine the possible role of these perturbations in aiding the growth of plasma instabilities. SORTIE will provide (1) the initial spectrum of wave perturbations which are the starting point for the RT calculation; (2) measured electric fields which determine the magnitude of the instability growth rate near the region where plasma bubbles are generated; (3) initial observations of irregularities in plasma density which result from RT growth. SORTIE results will be used as input to PBMOD, an assimilative first-principles physical model of the ionosphere, in order to predict evolution of EPBs. In this presentation, we will review the science objectives, provide an overview of the spacecraft and instrument design, and present a concept of operations plan.

Climatology of the scintillation onset over southern Brazil

NASA Astrophysics Data System (ADS)

Sousasantos, Jonas; de Oliveira Moraes, Alison; Sobral, José H. A.; Muella, Marcio T. A. H.; de Paula, Eurico R.; Paolini, Rafael S.

2018-04-01

This work presents an analysis of the climatology of the onset time of ionospheric scintillations at low latitude over the southern Brazilian territory near the peak of the equatorial ionization anomaly (EIA). Data from L1 frequency GPS receiver located in Cachoeira Paulista (22.4° S, 45.0° W; dip latitude 16.9° S), from September 1998 to November 2014, covering a period between solar cycles 23 and 24, were used in the present analysis of the scintillation onset time. The results show that the start time of the ionospheric scintillation follows a pattern, starting about 40 min earlier, in the months of November and December, when compared to January and February. The analyses presented here show that such temporal behavior seems to be associated with the ionospheric prereversal vertical drift (PRVD) magnitude and time. The influence of solar activity in the percentage of GPS links affected is also addressed together with the respective ionospheric prereversal vertical drift behavior. Based on this climatological study a set of empirical equations is proposed to be used for a GNSS alert about the scintillation prediction. The identification of this kind of pattern may support GNSS applications for aviation and oil extraction maritime stations positioning.

Space-Based Three-Dimensional Imaging of Equatorial Plasma Bubbles: Advancing the Understanding of Ionospheric Density Depletions and Scintillation

DTIC Science & Technology

2012-03-28

Scintillation 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Comberiate, Joseph M. 5e. TASK NUMBER 5f. WORK...bubble climatology. A tomographic reconstruction technique was modified and applied to SSUSI data to reconstruct three-dimensional cubes of ionospheric... modified and applied to SSUSI data to reconstruct three-dimensional cubes of ionospheric electron density. These data cubes allowed for 3-D imaging of

Sub-Ionospheric Measurements of the Ocean, Atmosphere, and Ionosphere from the CARINA Satellites

NASA Astrophysics Data System (ADS)

Bernhardt, P. A.; Montgomery, J. A., Jr.; Siefring, C. L.; Gatling, G.

2016-12-01

New satellites designed to fly between 150 and 250 km has been constructed to study a wide range of geophysical topics extending from the ocean to the topside ionosphere. The key features of the CARINA satellites are (1) the ability of sustain long duration (60 day) orbits below the F-Layer ionosphere, (2) download large quantities of data (10 GBytes) per pass over a ground station, and (3) a heritage instrument payload comprised of an Electric Field Instrument (EFI) with full range measurements from 3 to 13 MHz, a Ram Langmuir Probe (RLP) the measures ion density from 102 to 106 cm-3 with 10 kHz sample rate, an Orbiting GPS Receiver (OGR) providing overhead total electron content and satellite position and the Wake Retro Reflectors (WRR) that use laser ranging for precise orbit determination. Each letter in "CARINA" represents one of the science objectives. "Coastal" ocean wave remote sensing of the sea surface wave height spectrum derived from HF surface wave scatter to the satellite. Assimilation ionospheric models are supported by Global measurements of GPS total electron count (TEC) and in situ plasma density for updating data driven ionospheric models (GAIM, IDA3D, etc.). Radio wave propagation and interactions determine the impact of the bottomside ionosphere on HF ray trajectories, the effects of ionospheric irregularities that yield UHF/L-band scintillations and ionospheric modifications by high power HF waves. Ionospheric structures such are sporadic-E and intermediate layers, traveling ionospheric disturbances (TID's) and large scale bottomside fluctuations in the F-layer are directly measured by CARINA sensors. Neutral drag is studied along the orbit through reentry modeling of drag coefficients and neutral density model updates. Finally, Atmospherics and lightning knowledge is acquired through studies of lightning EM pulses and their impact on ionosphere. Two CARINA satellites separated by 2000 km flying above 50 degree inclination represents the

Ionosphere scintillations associated with features of equatorial ionosphere

NASA Technical Reports Server (NTRS)

Chandra, H.; Vats, H. O.; Sethia, G.; Deshpande, M. R.; Rastogi, R. G.; Sastri, J. H.; Murthy, B. S.

1979-01-01

Amplitude scintillations of radio beacons aboard the ATS-6 satellite on 40 MHz, 140 MHz and 360 MHz recorded during the ATS-6 phase II at an equatorial station Ootacamund (dip 4 deg N) and the ionograms at a nearby station Kodaikanal (dip 3.5 deg N) are examined for scintillation activity. Only sporadic E events, other than Es-q, Es-c or normal E are found to be associated with intense daytime scintillations. Scintillations are also observed during night Es conditions. The amplitude spread is associated with strong scintillations on all frequencies while frequency spread causes weaker scintillations and that mainly at 40 MHz.

Identification of scintillation signatures on GPS signals originating from plasma structures detected with EISCAT incoherent scatter radar along the same line of sight

PubMed Central

Coleman, Chris; Skone, Susan; Häggström, Ingemar; Mitchell, Cathryn; Da Dalt, Federico; Panicciari, Tommaso; Kinrade, Joe; Bust, Gary

2017-01-01

Abstract Ionospheric scintillation originates from the scattering of electromagnetic waves through spatial gradients in the plasma density distribution, drifting across a given propagation direction. Ionospheric scintillation represents a disruptive manifestation of adverse space weather conditions through degradation of the reliability and continuity of satellite telecommunication and navigation systems and services (e.g., European Geostationary Navigation Overlay Service, EGNOS). The purpose of the experiment presented here was to determine the contribution of auroral ionization structures to GPS scintillation. European Incoherent Scatter (EISCAT) measurements were obtained along the same line of sight of a given GPS satellite observed from Tromso and followed by means of the EISCAT UHF radar to causally identify plasma structures that give rise to scintillation on the co‐aligned GPS radio link. Large‐scale structures associated with the poleward edge of the ionospheric trough, with auroral arcs in the nightside auroral oval and with particle precipitation at the onset of a substorm were indeed identified as responsible for enhanced phase scintillation at L band. For the first time it was observed that the observed large‐scale structures did not cascade into smaller‐scale structures, leading to enhanced phase scintillation without amplitude scintillation. More measurements and theory are necessary to understand the mechanism responsible for the inhibition of large‐scale to small‐scale energy cascade and to reproduce the observations. This aspect is fundamental to model the scattering of radio waves propagating through these ionization structures. New insights from this experiment allow a better characterization of the impact that space weather can have on satellite telecommunications and navigation services. PMID:28331778

Identification of scintillation signatures on GPS signals originating from plasma structures detected with EISCAT incoherent scatter radar along the same line of sight

NASA Astrophysics Data System (ADS)

Forte, Biagio; Coleman, Chris; Skone, Susan; Häggström, Ingemar; Mitchell, Cathryn; Da Dalt, Federico; Panicciari, Tommaso; Kinrade, Joe; Bust, Gary

2017-01-01

Ionospheric scintillation originates from the scattering of electromagnetic waves through spatial gradients in the plasma density distribution, drifting across a given propagation direction. Ionospheric scintillation represents a disruptive manifestation of adverse space weather conditions through degradation of the reliability and continuity of satellite telecommunication and navigation systems and services (e.g., European Geostationary Navigation Overlay Service, EGNOS). The purpose of the experiment presented here was to determine the contribution of auroral ionization structures to GPS scintillation. European Incoherent Scatter (EISCAT) measurements were obtained along the same line of sight of a given GPS satellite observed from Tromso and followed by means of the EISCAT UHF radar to causally identify plasma structures that give rise to scintillation on the co-aligned GPS radio link. Large-scale structures associated with the poleward edge of the ionospheric trough, with auroral arcs in the nightside auroral oval and with particle precipitation at the onset of a substorm were indeed identified as responsible for enhanced phase scintillation at L band. For the first time it was observed that the observed large-scale structures did not cascade into smaller-scale structures, leading to enhanced phase scintillation without amplitude scintillation. More measurements and theory are necessary to understand the mechanism responsible for the inhibition of large-scale to small-scale energy cascade and to reproduce the observations. This aspect is fundamental to model the scattering of radio waves propagating through these ionization structures. New insights from this experiment allow a better characterization of the impact that space weather can have on satellite telecommunications and navigation services.

Identification of scintillation signatures on GPS signals originating from plasma structures detected with EISCAT incoherent scatter radar along the same line of sight.

PubMed

Forte, Biagio; Coleman, Chris; Skone, Susan; Häggström, Ingemar; Mitchell, Cathryn; Da Dalt, Federico; Panicciari, Tommaso; Kinrade, Joe; Bust, Gary

2017-01-01

Ionospheric scintillation originates from the scattering of electromagnetic waves through spatial gradients in the plasma density distribution, drifting across a given propagation direction. Ionospheric scintillation represents a disruptive manifestation of adverse space weather conditions through degradation of the reliability and continuity of satellite telecommunication and navigation systems and services (e.g., European Geostationary Navigation Overlay Service, EGNOS). The purpose of the experiment presented here was to determine the contribution of auroral ionization structures to GPS scintillation. European Incoherent Scatter (EISCAT) measurements were obtained along the same line of sight of a given GPS satellite observed from Tromso and followed by means of the EISCAT UHF radar to causally identify plasma structures that give rise to scintillation on the co-aligned GPS radio link. Large-scale structures associated with the poleward edge of the ionospheric trough, with auroral arcs in the nightside auroral oval and with particle precipitation at the onset of a substorm were indeed identified as responsible for enhanced phase scintillation at L band. For the first time it was observed that the observed large-scale structures did not cascade into smaller-scale structures, leading to enhanced phase scintillation without amplitude scintillation. More measurements and theory are necessary to understand the mechanism responsible for the inhibition of large-scale to small-scale energy cascade and to reproduce the observations. This aspect is fundamental to model the scattering of radio waves propagating through these ionization structures. New insights from this experiment allow a better characterization of the impact that space weather can have on satellite telecommunications and navigation services.

Distributed sensing of ionospheric irregularities with a GNSS receiver array

NASA Astrophysics Data System (ADS)

Su, Yang; Datta-Barua, Seebany; Bust, Gary S.; Deshpande, Kshitija B.

2017-08-01

We present analysis methods for studying the structuring and motion of ionospheric irregularities at the subkilometer scale sizes that produce L band scintillations. Spaced-receiver methods are used for Global Navigation Satellite System (GNSS) receivers' phase measurements over approximately subkilometer to kilometer length baselines for the first time. The quantities estimated by these techniques are plasma drift velocity, diffraction anisotropy magnitude and orientation, and characteristic velocity. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts through linearization about the estimated values of the state. Five receivers of SAGA, the Scintillation Auroral Global Positioning System (GPS) Array, provide 100 Hz power and phase data for each channel at L1 frequency. The array is sited in the auroral zone at Poker Flat Research Range, Alaska. A case study of a single scintillating satellite observed by the array is used to demonstrate the spaced-receiver and uncertainty estimation process. A second case study estimates drifts as measured by multiple scintillating channels. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30 min period are compared to a collocated incoherent scatter radar and show good agreement in horizontal drift speed and direction during periods of scintillation for which the characteristic velocity is less than the drift velocity.

Complex Dynamics of Equatorial Scintillation

NASA Astrophysics Data System (ADS)

Piersanti, Mirko; Materassi, Massimo; Forte, Biagio; Cicone, Antonio

2017-04-01

Radio power scintillation, namely highly irregular fluctuations of the power of trans-ionospheric GNSS signals, is the effect of ionospheric plasma turbulence. The scintillation patterns on radio signals crossing the medium inherit the ionospheric turbulence characteristics of inter-scale coupling, local randomness and large time variability. On this basis, the remote sensing of local features of the turbulent plasma is feasible by studying radio scintillation induced by the ionosphere. The distinctive character of intermittent turbulent media depends on the fluctuations on the space- and time-scale statistical properties of the medium. Hence, assessing how the signal fluctuation properties vary under different Helio-Geophysical conditions will help to understand the corresponding dynamics of the turbulent medium crossed by the signal. Data analysis tools, provided by complex system science, appear to be best fitting to study the response of a turbulent medium, as the Earth's equatorial ionosphere, to the non-linear forcing exerted by the Solar Wind (SW). In particular we used the Adaptive Local Iterative Filtering, the Wavelet analysis and the Information theory data analysis tool. We have analysed the radio scintillation and ionospheric fluctuation data at low latitude focusing on the time and space multi-scale variability and on the causal relationship between forcing factors from the SW environment and the ionospheric response.

Ionospheric Coherence Bandwidth Measurements in the Lower VHF Frequency Range

NASA Astrophysics Data System (ADS)

Suszcynsky, D. M.; Light, M. E.; Pigue, M. J.

2015-12-01

The United States Department of Energy's Radio Frequency Propagation (RFProp) experiment consists of a satellite-based radio receiver suite to study various aspects of trans-ionospheric signal propagation and detection in four frequency bands, 2 - 55 MHz, 125 - 175 MHz, 365 - 415 MHz and 820 - 1100 MHz. In this paper, we present simultaneous ionospheric coherence bandwidth and S4 scintillation index measurements in the 32 - 44 MHz frequency range collected during the ESCINT equatorial scintillation experiment. 40-MHz continuous wave (CW) and 32 - 44 MHz swept frequency signals were transmitted simultaneously to the RFProp receiver suite from the Reagan Test Site at Kwajalein Atoll in the Marshall Islands (8.7° N, 167.7° E) in three separate campaigns during the 2014 and 2015 equinoxes. Results show coherence bandwidths as small as ~ 1 kHz for strong scintillation (S4 > 0.7) and indicate a high degree of ionospheric variability and irregularity on 10-m spatial scales. Spread-Doppler clutter effects arising from preferential ray paths to the satellite due to refraction off of isolated density irregularities are also observed and are dominant at low elevation angles. The results are compared to previous measurements and available scaling laws.

Further Investigations of Ionospheric Total Electron Content and Scintillation Effects on Transionospheric Radiowave Propagation

DTIC Science & Technology

1998-02-12

HAARP ). 14. SUBJECT TERMS Global Positioning System (GPS), High Frequency Active Auroral Research Program ( HAARP ), ionosphere, radiowave...Scintillation Simulation 23 4.10 Automated Calibrations 23 5. HAARP Activities 24 5.1 Development of HAARP Diagnostics 24 5.2 Facilitation of... HAARP Operations and Broader Scientific Collaborations 27 5.3 Public Relations 28 6. Publications 30 References 30 Acronyms and Initials 30 Appendix

Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly

NASA Astrophysics Data System (ADS)

de Lima, G. R. T.; Stephany, S.; de Paula, E. R.; Batista, I. S.; Abdu, M. A.; Rezende, L. F. C.; Aquino, M. G. S.; Dutra, A. P. S.

2014-06-01

Ionospheric scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.

New Opportunities for Remote Sensing Ionospheric Irregularities by Fitting Scintillation Spectra

NASA Astrophysics Data System (ADS)

Carrano, C. S.; Rino, C. L.; Groves, K. M.

2017-12-01

In a recent paper, we presented a phase screen theory for the spectrum of intensity scintillations when the refractive index irregularities follow a two-component power law [Carrano and Rino, DOI: 10.1002/2015RS005903]. More recently we have investigated the inverse problem, whereby phase screen parameters are inferred from scintillation time series. This is accomplished by fitting the spectrum of intensity fluctuations with a parametrized theoretical model using Maximum Likelihood (ML) methods. The Markov-Chain Monte-Carlo technique provides a-posteriori errors and confidence intervals. The Akaike Information Criterion (AIC) provides justification for the use of one- or two-component irregularity models. We refer to this fitting as Irregularity Parameter Estimation (IPE) since it provides a statistical description of the irregularities from the scintillations they produce. In this talk, we explore some new opportunities for remote sensing ionospheric irregularities afforded by IPE. Statistical characterization of irregularities and the plasma bubbles in which they are embedded provides insight into the development of the underlying instability. In a companion paper by Rino et al., IPE is used to interpret scintillation due to simulated EPB structure. IPE can be used to reconcile multi-frequency scintillation observations and to construct high fidelity scintillation simulation tools. In space-to-ground propagation scenarios, for which an estimate of the distance to the scattering region is available a-priori, IPE enables retrieval of zonal irregularity drift. In radio occultation scenarios, the distance to the irregularities is generally unknown but IPE enables retrieval of Fresnel frequency. A geometric model for the effective scan velocity maps Fresnel frequency to Fresnel scale, yielding the distance to the irregularities. We demonstrate this approach by geolocating irregularities observed by the CORISS instrument onboard the C/NOFS satellite.

Optical imaging of airglow structure in equatorial plasma bubbles at radio scintillation scales

NASA Astrophysics Data System (ADS)

Holmes, J. M.; Pedersen, T.; Parris, R. T.; Stephens, B.; Caton, R. G.; Dao, E. V.; Kratochvil, S.; Morton, Y.; Xu, D.; Jiao, Y.; Taylor, S.; Carrano, C. S.

2015-12-01

Imagery of optical emissions from F-region plasma is one of the few means available todetermine plasma density structure in two dimensions. However, the smallest spatial scalesobservable with this technique are typically limited not by magnification of the lens or resolutionof the detector but rather by the optical throughput of the system, which drives the integrationtime, which in turn causes smearing of the features that are typically moving at speeds of 100m/s or more. In this paper we present high spatio-temporal imagery of equatorial plasma bubbles(EPBs) from an imaging system called the Large Aperture Ionospheric Structure Imager(LAISI), which was specifically designed to capture short-integration, high-resolution images ofF-region recombination airglow at λ557.7 nm. The imager features 8-inch diameter entranceoptics comprised of a unique F/0.87 lens, combined with a monolithic 8-inch diameterinterference filter and a 2x2-inch CCD detector. The LAISI field of view is approximately 30degrees. Filtered all-sky images at common airglow wavelengths are combined with magneticfield-aligned LAISI images, GNSS scintillation, and VHF scintillation data obtained atAscension Island (7.98S, 14.41W geographic). A custom-built, multi-constellation GNSS datacollection system was employed that sampled GPS L1, L2C, L5, GLONASS L1 and L2, BeidouB1, and Galileo E1 and E5a signals. Sophisticated processing software was able to maintainlock of all signals during strong scintillation, providing unprecedented spatial observability ofL band scintillation. The smallest-resolvable scale sizes above the noise floor in the EPBs, as viewed byLAISI, are illustrated for integration times of 1, 5 and 10 seconds, with concurrentzonal irregularity drift speeds from both spaced-receiver VHF measurements and single-stationGNSS measurements of S4 and σφ. These observable optical scale sizes are placed in thecontext of those that give rise to radio scintillation in VHF and L band signals.

Very High-Frequency (VHF) ionospheric scintillation fading measurements at Lima, Peru

NASA Technical Reports Server (NTRS)

Blank, H. A.; Golden, T. S.

1972-01-01

During the spring equinox of 1970, scintillating signals at VHF (136.4 MHz) were observed at Lima, Peru. The transmission originated from ATS 3 and was observed through a pair of antennas spaced 1200 feet apart on an east-west baseline. The empirical data were digitized, reduced, and analyzed. The results include amplitude probability density and distribution functions, time autocorrelation functions, cross correlation functions for the spaced antennas, and appropriate spectral density functions. Results show estimates of the statistics of the ground diffraction pattern to gain insight into gross ionospheric irregularity size, and irregularity velocity in the antenna planes.

Scintillation Monitoring Using Asymmetry Index

NASA Astrophysics Data System (ADS)

Shaikh, Muhammad Mubasshir; Mahrous, Ayman; Abdallah, Amr; Notarpietro, Riccardo

Variation in electron density can have significant effect on GNSS signals in terms of propagation delay. Ionospheric scintillation can be caused by rapid change of such delay, specifically, when they last for a longer period of time. Ionospheric irregularities that account for scintillation may vary significantly in spatial range and drift with the background plasma at speeds of 45 to 130 m/sec. These patchy irregularities may occur several times during night, e.g. in equatorial region, with the patches move through the ray paths of the GNSS satellite signals. These irregularities are often characterized as either ‘large scale’ (which can be as large as several hundred km in East-West direction and many times that in the North-South direction) or ‘small scale’ (which can be as small as 1m). These small scale irregularities are regarded as the main cause of scintillation [1,2]. In normal solar activity conditions, the mid-latitude ionosphere is not much disturbed. However, during severe magnetic storms, the aurora oval extends towards the equator and the equator anomaly region may stretched towards poles extending the scintillation phenomena more typically associated with those regions into mid-latitudes. In such stormy conditions, the predicted TEC may deviate largely from the true value of the TEC both at low and mid-latitudes due to which GNSS applications may be strongly degraded. This work is an attempt to analyze ionospheric scintillation (S4 index) using ionospheric asymmetry index [3]. The asymmetry index is based on trans-ionospheric propagation between GPS and LEO satellites in a radio occultation (RO) scenario, using background ionospheric data provided by MIDAS [4]. We attempted to simulate one of the recent geomagnetic storms (NOAA scale G4) occurred over low/mid-latitudes. The storm started on 26 September 2011 at UT 18:00 and lasted until early hours of 27 September 2011. The scintillation data for the storm was taken from an ionospheric

HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations

NASA Technical Reports Server (NTRS)

Frey, A.; Gordon, W. E.

1982-01-01

Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended to include antenna filtering. This type of filtering is important for UHF radio star scintillations since the antenna usually has a narrow beamwidth. HF power densities of less than 37 microwatts/sq m incident on the ionosphere give rise to electron density irregularities larger than 13% of the ambient density (at 260 km) having scale sizes of approximately 510 m perpendicular to the geomagnetic field. The irregularities are found to form within 20-25 s after the HF power is turned on. The drift velocities of the irregularities can be estimated from the observed power spectra.

Temporal and Spatial Characterization of GPS Fading From Ionospheric Irregularities Under Low latitude

NASA Astrophysics Data System (ADS)

De Paula, E. R.; Moraes, A. D. O.; Vani, B. C.; Sobral, J. H. A.; Abdu, M. A.; Galera Monico, J. F.

2017-12-01

The ionosphere over the peak of the anomaly represents a treat for navigation systems based on GNSS. Brazilian territory is mostly under this harsh layer for satellite communication in general and in particular for navigation, like GPS users, where their receivers tracking performance are damaged under scintillation conditions. Ionospheric scintillation is responsible for significant degradation in the accuracy of navigation and positioning. Phase shifts accompanied by amplitude fades significantly degrades the signal-to-noise ratio of the received signal disrupting the channel and loosing navigation performance. The stronger the scintillations are, more difficulty will be for the GNSS receiver tracking loops to recover the phase and code replicas. These phenomena under specific geophysical conditions may severely affect the system availability and positioning. In this work the temporal characteristics of amplitude scintillation will be analyzed at the three available GPS frequencies, L1, L2C and L5. Aspect like fading duration and depth will be evaluated and compared among the three available frequencies for the current solar cycle. This work will use GPS scintillation data recorded during six months of data during 2014 to 2015 at three stations under Brazilian territory located near the southern crest of the equatorial ionization anomaly. The analysis will be performed focusing on the fading profile of the three frequencies comparing how the fading of those signals behave statistically between them. Aspects like loss of lock, spatial orientation between the signal across the ionospheric irregularity will also be discussed showing how much more susceptible the new frequencies might be in comparison to the widely used and studied L1 frequency.

Band-Gap and Band-Edge Engineering of Multicomponent Garnet Scintillators from First Principles

NASA Astrophysics Data System (ADS)

Yadav, Satyesh K.; Uberuaga, Blas P.; Nikl, Martin; Jiang, Chao; Stanek, Christopher R.

2015-11-01

Complex doping schemes in R3 Al5 O12 (where R is the rare-earth element) garnet compounds have recently led to pronounced improvements in scintillator performance. Specifically, by admixing lutetium and yttrium aluminate garnets with gallium and gadolinium, the band gap is altered in a manner that facilitates the removal of deleterious electron trapping associated with cation antisite defects. Here, we expand upon this initial work to systematically investigate the effect of substitutional admixing on the energy levels of band edges. Density-functional theory and hybrid density-functional theory (HDFT) are used to survey potential admixing candidates that modify either the conduction-band minimum (CBM) or valence-band maximum (VBM). We consider two sets of compositions based on Lu3 B5O12 where B is Al, Ga, In, As, and Sb, and R3Al5 O12 , where R is Lu, Gd, Dy, and Er. We find that admixing with various R cations does not appreciably affect the band gap or band edges. In contrast, substituting Al with cations of dissimilar ionic radii has a profound impact on the band structure. We further show that certain dopants can be used to selectively modify only the CBM or the VBM. Specifically, Ga and In decrease the band gap by lowering the CBM, while As and Sb decrease the band gap by raising the VBM, the relative change in band gap is quantitatively validated by HDFT. These results demonstrate a powerful approach to quickly screen the impact of dopants on the electronic structure of scintillator compounds, identifying those dopants which alter the band edges in very specific ways to eliminate both electron and hole traps responsible for performance limitations. This approach should be broadly applicable for the optimization of electronic and optical performance for a wide range of compounds by tuning the VBM and CBM.

The Equatorial Scintillations and Space Weather Effects on its Generation during Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Biktash, Lilia

Great diversity of the ionospheric phenomena leads to a variety of irregularity types with spatial size from many thousands of kilometers to few centimeters and lifetimes from days to fractions of second. Since the ionosphere strongly influences the propagation of radio waves, signal distortions caused by these irregularities affect short-wave transmissions on Earth, transiono-spheric satellite communications and navigation. In this work the solar wind and the equatorial ionosphere parameters, Kp, Dst, AU, AL indices characterized contribution of different mag-netospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the space weather effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict scintil-lations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of elec-tron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind -magnetosphere -ionosphere during magnetic storms have progressed greatly. We have examined scintillation relation to magnetospheric and ionospheric currents and show that the factor, which presents during magnetic storms to fully inhibit scin-tillation, is the positive Bz-component of the IMF. During the positive Bz IMF F layer cannot raise altitude where scintillations are formed. The auroral indices and Kp do better for the prediction of the ionospheric scintillations at the equator. The interplanetary magnetic field data and models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere cur-rents and

A comparison of TEC fluctuations and scintillations at Ascension Island

NASA Astrophysics Data System (ADS)

Basu, S.; Groves, K. M.; Quinn, J. M.; Doherty, P.

1999-11-01

With increasing reliance on space-based platforms for global navigation and communication, concerns about the impact of ionospheric scintillation on these systems have become a high priority. Recently, the Air Force Research Laboratory (AFRL) performed amplitude scintillation measurements of L1 (1.575 MHz) signals from GPS satellites at Ascension Island (14.45° W, 7.95° S; magnetic latitude 16° S) during February-April, 1998, to compare amplitude scintillations with fluctuations of the total electron content (TEC). Ascension Island is located in the South Atlantic under the southern crest of the equatorial anomaly of F2 ionization where scintillations will be much enhanced during the upcoming solar maximum period. Ascension Island is included in the global network of the International GPS Service (IGS) and the GPS receivers in this network report the carrier to noise (C/N) ratio, the dual frequency carrier phase and pseudorange data at 30-s intervals. Such data with a sampling interval of 30 s were analyzed to determine TEC, the rate of change of TEC (ROT) and also ROTI, defined as the standard deviation of ROT. The spatial scale of ROTI, sampled at 30 s interval, will correspond to 6 km when the vector sum of the ionospheric projection of the satellite velocity and the irregularity drift orthogonal to the propagation path is of the order of 100 m/s. On the other hand, the scale-length of the amplitude scintillation index corresponds to the Fresnel dimension which is about 400 m for the GPS L1 frequency and an ionospheric height of 400 km. It is shown that, in view of the co-existence of large and small scale irregularities in equatorial irregularity structures, during the early evening hours, and small magnitude of irregularity drifts, ROTI measurements can be used to predict the presence of scintillation causing irregularities. The quantitative relationship between ROTI and S4, however, varies considerably due to variations of the ionospheric projection of the

Measurement and Mitigation of the Ionosphere in L-Band Interferometric SAR Data

NASA Technical Reports Server (NTRS)

Rosen, Paul A.; Hensley, Scott; Chen, Curtis

2010-01-01

Satellite-based repeat-pass Interferometric Synthetic Aperture Radar (InSAR) provides a synoptic high spatial resolution perspective of Earth's changing surface, permitting one to view large areas quickly and efficiently. By measuring relative phase change from one observation to the next on a pixel-by-pixel basis, maps of deformation and change can be derived. Variability of the atmosphere and the ionosphere leads to phase/time delays that are present in the data that can mask many of the subtle deformation signatures of interest, so methods for mitigation of these effects are important. Many of these effects have been observed in existing ALOS PALSAR data, and studies are underway to characterize and mitigate the ionosphere using these data. Since the ionosphere is a dispersive medium, it is possible in principle distinguish the ionospheric signatures from the non-dispersive effects of deformation and the atmosphere. In this paper, we describe a method for mapping the ionosphere in InSAR data based on a multi-frequency split-spectrum processing technique.

Understanding Transient Forcing with Plasma Instability Model, Ionospheric Propagation Model and GNSS Observations

NASA Astrophysics Data System (ADS)

Deshpande, K.; Zettergren, M. D.; Datta-Barua, S.

2017-12-01

Fluctuations in the Global Navigation Satellite Systems (GNSS) signals observed as amplitude and phase scintillations are produced by plasma density structures in the ionosphere. Phase scintillation events in particular occur due to structures at Fresnel scales, typically about 250 meters at ionospheric heights and GNSS frequency. Likely processes contributing to small-scale density structuring in auroral and polar regions include ionospheric gradient-drift instability (GDI) and Kelvin-Helmholtz instability (KHI), which result, generally, from magnetosphere-ionosphere interactions (e.g. reconnection) associated with cusp and auroral zone regions. Scintillation signals, ostensibly from either GDI or KHI, are frequently observed in the high latitude ionosphere and are potentially useful diagnostics of how energy from the transient forcing in the cusp or polar cap region cascades, via instabilities, to small scales. However, extracting quantitative details of instabilities leading to scintillation using GNSS data drastically benefits from both a model of the irregularities and a model of GNSS signal propagation through irregular media. This work uses a physics-based model of the generation of plasma density irregularities (GEMINI - Geospace Environment Model of Ion-Neutral Interactions) coupled to an ionospheric radio wave propagation model (SIGMA - Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere) to explore the cascade of density structures from medium to small (sub-kilometer) scales. Specifically, GEMINI-SIGMA is used to simulate expected scintillation from different instabilities during various stages of evolution to determine features of the scintillation that may be useful to studying ionospheric density structures. Furthermore we relate the instabilities producing GNSS scintillations to the transient space and time-dependent magnetospheric phenomena and further predict characteristics of scintillation in different geophysical

Band-gap and band-edge engineering of multicomponent garnet scintillators from first principles

DOE PAGES

Yadav, Satyesh K.; Uberuaga, Blas P.; Nikl, Martin; ...

2015-11-24

Complex doping schemes in R 3Al 5O 12 (where R is the rare-earth element) garnet compounds have recently led to pronounced improvements in scintillator performance. Specifically, by admixing lutetium and yttrium aluminate garnets with gallium and gadolinium, the band gap is altered in a manner that facilitates the removal of deleterious electron trapping associated with cation antisite defects. Here, we expand upon this initial work to systematically investigate the effect of substitutional admixing on the energy levels of band edges. Density-functional theory and hybrid density-functional theory (HDFT) are used to survey potential admixing candidates that modify either the conduction-band minimummore » (CBM) or valence-band maximum (VBM). We consider two sets of compositions based on Lu 3B 5O 12 where B is Al, Ga, In, As, and Sb, and R 3Al 5O 12, where R is Lu, Gd, Dy, and Er. We find that admixing with various R cations does not appreciably affect the band gap or band edges. In contrast, substituting Al with cations of dissimilar ionic radii has a profound impact on the band structure. We further show that certain dopants can be used to selectively modify only the CBM or the VBM. Specifically, Ga and In decrease the band gap by lowering the CBM, while As and Sb decrease the band gap by raising the VBM, the relative change in band gap is quantitatively validated by HDFT. These results demonstrate a powerful approach to quickly screen the impact of dopants on the electronic structure of scintillator compounds, identifying those dopants which alter the band edges in very specific ways to eliminate both electron and hole traps responsible for performance limitations. Furthermore, this approach should be broadly applicable for the optimization of electronic and optical performance for a wide range of compounds by tuning the VBM and CBM.« less

Comparison of NAVSTAR satellite L band ionospheric calibrations with Faraday rotation measurements

NASA Technical Reports Server (NTRS)

Royden, H. N.; Miller, R. B.; Buennagel, L. A.

1984-01-01

It is pointed out that interplanetary navigation at the Jet Propulsion Laboratory (JPL) is performed by analyzing measurements derived from the radio link between spacecraft and earth and, near the target, onboard optical measurements. For precise navigation, corrections for ionospheric effects must be applied, because the earth's ionosphere degrades the accuracy of the radiometric data. These corrections are based on ionospheric total electron content (TEC) determinations. The determinations are based on the measurement of the Faraday rotation of linearly polarized VHF signals from geostationary satellites. Problems arise in connection with the steadily declining number of satellites which are suitable for Faraday rotation measurements. For this reason, alternate methods of determining ionospheric electron content are being explored. One promising method involves the use of satellites of the NAVSTAR Global Positioning System (GPS). The results of a comparative study regarding this method are encouraging.

Effects of transionospheric signal decorrelation on Global Navigation Satellite Systems (GNSS) performance studied from irregularity dynamics around the northern crest of the EIA

NASA Astrophysics Data System (ADS)

Das, T.; Roy, B.; Paul, A.

2014-10-01

Transionospheric satellite navigation links operate primarily at L band and are frequently subject to severe degradation of performances arising out of ionospheric irregularities. Various characteristic features of equatorial ionospheric irregularity bubbles like the drift velocity, characteristic velocity, decorrelation time, and decorrelation distance can be determined using spaced aerial measurements at VHF. These parameters measured at VHF from a station Calcutta situated near the northern crest of the Equatorial Ionization Anomaly (EIA) in the geophysically sensitive Indian longitude sector have been correlated with L band scintillation indices and GPS position accuracy parameters for identifying possible proxies to L band scintillations. Good correspondences have been observed between decorrelation times and distances at VHF with GPS S4 and Position Dilution of Precision during periods of GPS scintillations (S4 > 0.3) for February-April 2011, August-October 2011, and February-April 2012. A functional relation has been developed between irregularity drift velocity measured at VHF and S4 at L band during February-April 2011, and validation of measured S4 and predicted values performed during August-October 2011 and February-April 2012. Significant improvement in L band scintillation prediction and consequent navigational accuracy will result using such relations derived from VHF irregularity measurements which are much simpler and inexpensive.

On the occurrence and strength of multi-frequency multi-GNSS Ionospheric Scintillations in Indian sector during declining phase of solar cycle 24

NASA Astrophysics Data System (ADS)

Srinivasu, V. K. D.; Dashora, N.; Prasad, D. S. V. V. D.; Niranjan, K.; Gopi Krishna, S.

2018-04-01

This study presents unique perspectives of occurrence and strength of low latitude ionospheric scintillations on multiple signals of Global Navigation Satellite System (GNSS) and its frequency dependence using continuous observation records of 780 nights. A robust comparative analysis is performed using scintillation index, S4 and its variation during pre-midnight and post-midnight duration from a GNSS receiver located at Waltair (17.7°N, 83.3°E), India, covering period from July 2014 to August 2016. The results, generally exhibit the impact of declining phase of solar cycle 24 on occurrence and strength of scintillations, which, however, is evidently different over different frequencies transmitted from different GNSS systems. A deeper quantitative analysis uniquely reveals that apart from the solar cycle and seasonal effects, the number of visible satellites of a selected GNSS markedly affect the occurrence and also the strength. Processing scheme of adopting 6 hourly time windows of pre-midnight and post-midnight brought a novel result that the strength and occurrence of strong scintillations decrease with declining solar activity during pre-midnight hours but remarkably increase for moderate and weak scintillations during post-midnight. The physical processes that dominate the post-midnight equatorial ionosphere are invoked to explain such variations that are special during declining solar activity. Finally, inter-GNSS signal analysis in terms of the effect of strong, moderate and weak scintillations is presented with due consideration of number of satellite passes affected and frequency dependence of mean S4. The quantitative results of this study emphasize for the first time effect of low latitude scintillation on GNSS signals in Indian zone under changing background solar and seasonal conditions.

Ionospheric scintillation by a random phase screen Spectral approach

NASA Technical Reports Server (NTRS)

Rufenach, C. L.

1975-01-01

The theory developed by Briggs and Parkin, given in terms of an anisotropic gaussian correlation function, is extended to a spectral description specified as a continuous function of spatial wavenumber with an intrinsic outer scale as would be expected from a turbulent medium. Two spectral forms were selected for comparison: (1) a power-law variation in wavenumber with a constant three-dimensional index equal to 4, and (2) Gaussian spectral variation. The results are applied to the F-region ionosphere with an outer-scale wavenumber of 2 per km (approximately equal to the Fresnel wavenumber) for the power-law variation, and 0.2 per km for the Gaussian spectral variation. The power-law form with a small outer-scale wavenumber is consistent with recent F-region in-situ measurements, whereas the gaussian form is mathematically convenient and, hence, mostly used in the previous developments before the recent in-situ measurements. Some comparison with microwave scintillation in equatorial areas is made.

Toward the Probabilistic Forecasting of High-latitude GPS Phase Scintillation

NASA Technical Reports Server (NTRS)

Prikryl, P.; Jayachandran, P.T.; Mushini, S. C.; Richardson, I. G.

2012-01-01

The phase scintillation index was obtained from L1 GPS data collected with the Canadian High Arctic Ionospheric Network (CHAIN) during years of extended solar minimum 2008-2010. Phase scintillation occurs predominantly on the dayside in the cusp and in the nightside auroral oval. We set forth a probabilistic forecast method of phase scintillation in the cusp based on the arrival time of either solar wind corotating interaction regions (CIRs) or interplanetary coronal mass ejections (ICMEs). CIRs on the leading edge of high-speed streams (HSS) from coronal holes are known to cause recurrent geomagnetic and ionospheric disturbances that can be forecast one or several solar rotations in advance. Superposed epoch analysis of phase scintillation occurrence showed a sharp increase in scintillation occurrence just after the arrival of high-speed solar wind and a peak associated with weak to moderate CMEs during the solar minimum. Cumulative probability distribution functions for the phase scintillation occurrence in the cusp are obtained from statistical data for days before and after CIR and ICME arrivals. The probability curves are also specified for low and high (below and above median) values of various solar wind plasma parameters. The initial results are used to demonstrate a forecasting technique on two example periods of CIRs and ICMEs.

Monitoring of ionospheric irregularities with multi-GNSS observations: a new ionosphere activity index and product services

NASA Astrophysics Data System (ADS)

Wang, Ningbo; Li, Zishen; Yuan, Yunbin; Yuan, Hong

2017-04-01

Key words: Ionospheric irregularity, Rate of TEC (ROT), Rate of ROT index (RROT), GPS and GLONASS The ionospheric irregularities have a strong impact on many applications of Global Navigation Satellite Systems (GNSS) and other space-based radio systems. The rate of ionospheric total electron content (TEC) change index (ROTI, TECu/min), defined as the standard deviation of rate of TEC change (ROT) within a short time (e.g. 5 minutes), has been developed to describe the ionospheric irregularities and associated scintillations. However, ROT parameter may still contain the trend term of ionospheric TEC in spite of small-scale fluctuations. On the basis of single-differenced ROT (dROT) values, we develop a new ionosphere activity index, rate of ROT change index (RROT, TECu/min), to characterize the irregularity degree of the ionosphere. To illustrate the use of the index, we investigated the consistency between ROTI and RROT indexes, through the analysis of GPS data and S4 observations collected at two high-latitude stations of the northern hemisphere. It is confirmed that the correlation coefficients between RROT and S4 are higher than those between ROTI and S4 for the test period, meaning that the proposed RROT index is applicable to monitor the ionospheric irregularities and associated scintillations. RROT index can be easily calculated from dual-frequency GNSS signals (like GPS L1 and L2 carrier phase measurements). On the basis of GPS and GLONASS data provided by the IGS, ARGN, EPN and USCORS tracking networks (more than 1500 stations per day), absolute ROT (AROT), gradient of TEC index (GOTI), ROTI and RROT maps are generated to reflect the ionospheric irregularity activities. These maps are provided in an IONEX-like format on a global scale with a temporal resolution of 15 minutes and a spatial resolution of 5 and 2.5 degrees in longitude and latitude, respectively, and the maps with high spatial resolution (2x2 degrees) are also generated for European, Australia

Space-based Scintillation Nowcasting with the Communications/Navigation Outage Forecast System

NASA Astrophysics Data System (ADS)

Groves, K.; Starks, M.; Beach, T.; Basu, S.

2008-12-01

The Air Force Research Laboratory's Communication/Navigation Outage Forecast System (C/NOFS) fuses ground- and space-based data in a near real-time physics-based model aimed at forecasting and nowcasting equatorial scintillations and their impacts on satellite communications and navigation. A key component of the system is the C/NOFS satellite that was launched into a low-inclination (13°) elliptical orbit (400 km x 850 km) in April 2008. The satellite contains six sensors to measure space environment parameters including electron density and temperature, ion density and drift, electric and magnetic fields and neutral wind, as well as a tri-band radio beacon transmitting at 150 MHz, 400 MHz and 1067 MHz. Scintillation nowcasts are derived from measuring the one-dimensional in situ electron density fluctuations and subsequently modeling the propagation environment for satellite-to-ground radio links. The modeling process requires a number of simplifying assumptions regarding the three-dimensional structure of the ionosphere and the results are readily validated by comparisons with ground-based measurements of the satellite's tri-band beacon signals. In mid-September 2008 a campaign to perform detailed analyses of space-based scintillation nowcasts with numerous ground observations was conducted in the vicinity of Kwajalein Atoll, Marshall Islands. To maximize the collection of ground-truth data, the ALTAIR radar was employed to obtain detailed information on the spatial structure of the ionosphere during the campaign and to aid the improvement of space-based nowcasting algorithms. A comparison of these results will be presented; it appears that detailed information on the electron density structure is a limiting factor in modeling the scintillation environment from in situ observations.

Modeling and prediction of ionospheric scintillation

NASA Technical Reports Server (NTRS)

Fremouw, E. J.

1974-01-01

Scintillation modeling performed thus far is based on the theory of diffraction by a weakly modulating phase screen developed by Briggs and Parkin (1963). Shortcomings of the existing empirical model for the scintillation index are discussed together with questions of channel modeling, giving attention to the needs of the communication engineers. It is pointed out that much improved scintillation index models may be available in a matter of a year or so.

Analytical study of nighttime scintillations using GPS at low latitude station Bhopal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maski, Kalpana, E-mail: k-maski@rediffmail.com; Vijay, S. K.

2015-07-31

Sporadically structured ionosphere (i.e. in-homogeneities in refractive index) can cause fluctuations (due to refraction effects) on the radio signal that is passing through it. These fluctuations are called ionospheric scintillations. Low latitude region is suitable for studying these scintillations. The influence of the ionosphere on the propagation of the radio wave becomes very marked with reference to communication or navigational radio system at very low frequency (VLF) to a high frequency (HF), which operate over the distances of 1000 km or more. Radio wave communication at different frequencies depends on structure of the ionosphere. With the advent of the artificialmore » satellites, they are used as a prime mode of radio wave communication. Some natural perturbation termed as irregularities, are present in the form of electron density of the ionosphere that cause disruption in the radio and satellite communications. Therefore the study of the ionospheric irregularities is of practical importance, if one wishes to understand the upper atmosphere completely. In order to make these communications uninterrupted the knowledge of irregularities, which are present in the ionosphere are very important. These irregularities can be located and estimated with the help of Ionospheric TEC and Scintillation. Scintillation is generally confined to nighttime hours, particularly around equatorial and low latitudes.« less

Comparison of multifrequency equatorial scintillation - American and Pacific sectors

NASA Astrophysics Data System (ADS)

Livingston, R. C.

1980-08-01

In this paper we examine the severity of radio wave amplitude scintillation measured at two stations near the equator but far separated in longitude: Kwajelein, Marshall Islands (167 E), and Ancon, Peru (-77 E). The data used are long-term observations of the Defense Nuclear Agency (DNA) Wideband satellite signal intensity at VHF, UHF, and L band frequencies. The seasonal behavior of the scintillation at the two stations is similar; each shows a broad 8- to 9-month disturbed season centered about local summer. There is short-term variability in the scintillation occurrence statistics but no clear equinoctial maxima. Little difference is observed in the occurrence or severity of L band scintillation at the two stations, although a systematic difference in the frequency dependence of the scintillation produces significantly stronger VHF and UHF scintillation at Ancon. The VHF and UHF latitudinal distributions of scintillation are asymmetric about the geomagnetic equator at both stations.

Update on the Commensal VLA Low-band Ionospheric and Transient Experiment (VLITE)

NASA Astrophysics Data System (ADS)

Kassim, Namir E.; Clarke, Tracy E.; Ray, Paul S.; Polisensky, Emil; Peters, Wendy M.; Giacintucci, Simona; Helmboldt, Joseph F.; Hyman, Scott D.; Brisken, Walter; Hicks, Brian; Deneva, Julia S.

2017-01-01

The JVLA Low-band Ionospheric and Transient Experiment (VLITE) is a commensal observing system on the NRAO JVLA. The separate optical path of the prime-focus sub-GHz dipole feeds and the Cassegrain-focus GHz feeds provided an opportunity to expand the simultaneous frequency operation of the JVLA through joint observations across both systems. The low-band receivers on 10 JVLA antennas are outfitted with dedicated samplers and use spare fibers to transport the 320-384 MHz band to the VLITE correlator. The initial phase of VLITE uses a custom-designed real-time DiFX software correlator to produce autocorrelations, as well as parallel and cross-hand cross-correlations from the linear dipole feeds. NRL and NRAO have worked together to explore the scientific potential of the commensal low frequency system for ionospheric remote sensing, astrophysics and transients. VLITE operates at nearly 70% wall time with roughly 6200 hours of JVLA time recorded each year.VLITE data are used in real-time for ionospheric research and are transferred daily to NRL for processing in the astrophysics and transient pipelines. These pipelines provide automated radio frequency interference excision, calibration, imaging and self-calibration of data.We will review early scientific results from VLITE across all three science focus areas, including the ionosphere, slow (> 1 sec) transients, and astrophysics. We also discuss the future of the project, that includes its planned expansion to eVLITE including the addition of more antennas, and a parallel capability to search for fast (< 1 sec), dispersed transients, such as Fast Radio Bursts and Rotating Radio Transients. We will also present early results of commissioning tests to utilize VLITE data products to complement NRAO’s 3 GHz VLA Sky Survey (VLASS). Revised pipelines are under development for operation during the on-the-fly operation mode of the sky survey.

Response of the EIA ionosphere to the 7-8 May 2005 geomagnetic storm

NASA Astrophysics Data System (ADS)

Aggarwal, Malini; Joshi, H. P.; Iyer, K. N.; Kwak, Y. S.

2013-08-01

In this paper, response of low latitude ionosphere to a moderate geomagnetic storm of 7-8 May 2005 (SSC: 1920 UT on 7 May with Sym-H minimum, ∼-112 nT around 1600 UT on 8 May) has been investigated using the GPS measurements from a near EIA crest region, Rajkot (Geog. 22.29°N, 70.74°E, Geomag.14°), India. We found a decrease in total electron content (TEC) in 12 h after the onset of the storm, an increase during and after 6 h of Sym-H deep minimum with a decrease below its usual-day level on the second day during the recovery phase of the storm. On 8 May, an increase of TEC is observed after sunset and during post-midnight hours (maximum up to 170%) with the formation of ionospheric plasma bubbles followed by a nearly simultaneous onset of scintillations at L-band frequencies following the time of rapid decrease in Sym-H index (-30 nT/h around 1300 UT).

Ionospheric irregularity characteristics from quasiperiodic structure in the radio wave scintillation

NASA Astrophysics Data System (ADS)

Chen, K. Y.; Su, S. Y.; Liu, C. H.; Basu, S.

2005-06-01

Quasiperiodic (QP) diffraction pattern in scintillation patches has been known to highly correlate with the edge structures of a plasma bubble (Franke et al., 1984). A new time-frequency analysis method of Hilbert-Huang transform (HHT) has been applied to analyze the scintillation data taken at Ascension Island to understand the characteristics of corresponding ionosphere irregularities. The HHT method enables us to extract the quasiperiodic diffraction signals embedded inside the scintillation data and to obtain the characteristics of such diffraction signals. The cross correlation of the two sets of diffraction signals received by two stations at each end of Ascension Island indicates that the density irregularity pattern that causes the diffraction pattern should have an eastward drift velocity of ˜130 m/s. The HHT analysis of the instantaneous frequency in the QP diffraction patterns also reveals some frequency shifts in their peak frequencies. For the QP diffraction pattern caused by the leading edge of the large density gradient at the east wall of a structured bubble, an ascending note in the peak frequency is observed, and for the trailing edge a descending note is observed. The linear change in the transient of the peak frequency in the QP diffraction pattern is consistent with the theory and the simulation result of Franke et al. Estimate of the slope in the transient frequency provides us the information that allows us to identify the locations of plasma walls, and the east-west scale of the irregularity can be estimated. In our case we obtain about 24 km in the east-west scale. Furthermore, the height location of density irregularities that cause the diffraction pattern is estimated to be between 310 and 330 km, that is, around the F peak during observation.

Ionosphere VHF scintillations over Vaddeswaram (Geographic Latitude 16.31°N, Geographic Longitude 80.30°E, Dip 18°N), a latitude Indian station - A case study

NASA Astrophysics Data System (ADS)

Brahmanandam, P. S.; Uma, G.; Pant, T. K.

2017-10-01

This research reports the 250 MHz amplitude ionosphere scintillations recorded at Vaddeswaram (Geographic Latitude 16.31°N, Geographic Longitude 80.30°E, Dip 18°N), a low-latitude station in India. Though amplitude scintillations were recorded for four continuous days (05-08 November 2011), the presence of intense and long-duration scintillations on 06 November 2011 instigated us to verify the ionosphere background conditions. This research, therefore, is also used important databases including, diurnal variations of h‧F (virtual height of the F-layer) and the vertical drifts as measured by an advanced digital ionosonde radar located at an Indian equatorial station i.e. Trivandrum (Geographic Latitude 8.5°N, Geographic Longitude 77°E, Dip 0.5°N), equatorial Electrojet (EEJ) ground strength measured using magnetometers and the total electron content (TEC) maps provided by the International GPS Service (IGS) to study the background ionosphere conditions. The interesting observations are higher E × B drifts, the occurrence of long-duration range-type spread F signatures at Trivandrum and, thereafter, intense scintillations over Vaddeswaram. It was found a secondary peak at around 1600 LT in EEJ strength followed by a higher upward drift velocity (more than 60 m/s) with a significant raise of the F region up to 470 km over the magnetic equator on 06 November 2011. The possible physical mechanisms of these important observational results are discussed in the light of available literature.

Discrete Electronic Bands in Semiconductors and Insulators: Potential High-Light-Yield Scintillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Hongliang; Du, Mao-Hua

Bulk semiconductors and insulators typically have continuous valence and conduction bands. In this paper, we show that valence and conduction bands of a multinary semiconductor or insulator can be split to narrow discrete bands separated by large energy gaps. This unique electronic structure is demonstrated by first-principles calculations in several quaternary elpasolite compounds, i.e., Cs 2NaInBr 6, Cs 2NaBiCl 6, and Tl 2NaBiCl 6. The narrow discrete band structure in these quaternary elpasolites is due to the large electronegativity difference among cations and the large nearest-neighbor distances in cation sublattices. We further use Cs 2NaInBr 6 as an example tomore » show that the narrow bands can stabilize self-trapped and dopant-bound excitons (in which both the electron and the hole are strongly localized in static positions on adjacent sites) and promote strong exciton emission at room temperature. The discrete band structure should further suppress thermalization of hot carriers and may lead to enhanced impact ionization, which is usually considered inefficient in bulk semiconductors and insulators. Finally, these characteristics can enable efficient room-temperature light emission in low-gap scintillators and may overcome the light-yield bottleneck in current scintillator research.« less

Discrete Electronic Bands in Semiconductors and Insulators: Potential High-Light-Yield Scintillators

DOE PAGES

Shi, Hongliang; Du, Mao-Hua

2015-05-12

Bulk semiconductors and insulators typically have continuous valence and conduction bands. In this paper, we show that valence and conduction bands of a multinary semiconductor or insulator can be split to narrow discrete bands separated by large energy gaps. This unique electronic structure is demonstrated by first-principles calculations in several quaternary elpasolite compounds, i.e., Cs 2NaInBr 6, Cs 2NaBiCl 6, and Tl 2NaBiCl 6. The narrow discrete band structure in these quaternary elpasolites is due to the large electronegativity difference among cations and the large nearest-neighbor distances in cation sublattices. We further use Cs 2NaInBr 6 as an example tomore » show that the narrow bands can stabilize self-trapped and dopant-bound excitons (in which both the electron and the hole are strongly localized in static positions on adjacent sites) and promote strong exciton emission at room temperature. The discrete band structure should further suppress thermalization of hot carriers and may lead to enhanced impact ionization, which is usually considered inefficient in bulk semiconductors and insulators. Finally, these characteristics can enable efficient room-temperature light emission in low-gap scintillators and may overcome the light-yield bottleneck in current scintillator research.« less

High Resolution Reconstruction of the Ionosphere for SAR Applications

NASA Astrophysics Data System (ADS)

Minkwitz, David; Gerzen, Tatjana; Hoque, Mainul

2014-05-01

Caused by ionosphere's strong impact on radio signal propagation, high resolution and highly accurate reconstructions of the ionosphere's electron density distribution are demanded for a large number of applications, e.g. to contribute to the mitigation of ionospheric effects on Synthetic Aperture Radar (SAR) measurements. As a new generation of remote sensing satellites the TanDEM-L radar mission is planned to improve the understanding and modelling ability of global environmental processes and ecosystem change. TanDEM-L will operate in L-band with a wavelength of approximately 24 cm enabling a stronger penetration capability compared to X-band (3 cm) or C-band (5 cm). But accompanied by the lower frequency of the TanDEM-L signals the influence of the ionosphere will increase. In particular small scale irregularities of the ionosphere might lead to electron density variations within the synthetic aperture length of the TanDEM-L satellite and in turn might result into blurring and azimuth pixel shifts. Hence the quality of the radar image worsens if the ionospheric effects are not mitigated. The Helmholtz Alliance project "Remote Sensing and Earth System Dynamics" (EDA) aims in the preparation of the HGF centres and the science community for the utilisation and integration of the TanDEM-L products into the study of the Earth's system. One significant point thereby is to cope with the mentioned ionospheric effects. Therefore different strategies towards achieving this objective are pursued: the mitigation of the ionospheric effects based on the radar data itself, the mitigation based on external information like global Total Electron Content (TEC) maps or reconstructions of the ionosphere and the combination of external information and radar data. In this presentation we describe the geostatistical approach chosen to analyse the behaviour of the ionosphere and to provide a high resolution 3D electron density reconstruction. As first step the horizontal structure of

Ionosphere/microwave beam interaction study

NASA Technical Reports Server (NTRS)

Gordon, W. E.; Duncan, L. M.

1978-01-01

The microwave beam of the Solar Power Satellite (SPS) is predicted to interact with the ionosphere producing thermal runaway up to an altitude of about 100 kilometers at a power density threshold of 12 mW/cm sq (within a factor of two). The operation of the SPS at two frequencies, 2450 and 5800 MHz, is compared. The ionosphere interaction is less at the higher frequency, but the tropospheric problem scattering from heavy rain and hail is worse at the higher frequency. Microwave signals from communication satellites were observed to scintillate, but there is some concern that the uplink pilot signal may be distorted by the SPS heated ionosphere. The microwave scintillations are only observed in the tropics in the early evenings near the equinoxes. Results indicate that large phase errors in the uplink pilot signal can be reduced.

Spacecraft Radio Scintillation and Solar System Exploration

NASA Technical Reports Server (NTRS)

Woo, Richard

1993-01-01

When a wave propagates through a turbulent medium, scattering by the random refractive index inhomogeneities can lead to a wide variety of phenomena that have been the subject of extensive study. The observed scattering effects include amplitude or intensity scintillation, phase scintillation, angular broadening, and spectral broadening, among others. In this paper, I will refer to these scattering effects collectively as scintillation. Although the most familiar example is probably the twinkling of stars (light wave intensity scintillation by turbulence in the Earth's atmosphere), scintillation has been encountered and investigated in such diverse fields as ionospheric physics, oceanography, radio astronomy, and radio and optical communications. Ever since planetary spacecraft began exploring the solar system, scintillation has appeared during the propagation of spacecraft radio signals through planetary atmospheres, planetary ionospheres, and the solar wind. Early studies of these phenomena were motivated by the potential adverse effects on communications and navigation, and on experiments that use the radio link to conduct scientific investigations. Examples of the latter are radio occultation measurements (described below) of planetary atmospheres to deduce temperature profiles, and the search for gravitational waves. However,these concerns soon gave way to the emergence of spacecraft radio scintillation as a new scientific tool for exploring small-scale dynamics in planetary atmospheres and structure in the solar wind, complementing in situ and other remote sensing spacecraft measurements, as well as scintillation measurements using natural (celestial) radio sources. The purpose of this paper is to briefly describe and review the solar system spacecraft radio scintillation observations, to summarize the salient features of wave propagation analyses employed in interpreting them, to underscore the unique remote sensing capabilities and scientific relevance of

Climatology of ionospheric scintillation over the Vietnam low-latitude region for the period 2006-2014

NASA Astrophysics Data System (ADS)

Tran, Thi Lan; Le, Huy Minh; Amory-Mazaudier, C.; Fleury, R.

2017-10-01

This paper presents the characteristics of the occurrence of ionospheric scintillations at low-latitude, over Vietnam, by using continuous data of three GSV4004 receivers located at PHUT/Hanoï (105.9°E, 21.0°N; magnetic latitude 14.4°N), HUES/Hue (107.6°E, 16.5°N; magnetic latitude 9.5°N) and HOCM/Ho Chi Minh city (106.6°E, 10.8°N; magnetic latitude 3.3°N) for the period 2006-2014. The results show that the scintillation activity is maximum during equinox months for all the years and depends on solar activity as expected. The correlations between the monthly percentage scintillation occurrence and the F10.7 flux are of 0.40, 0.52 and 0.67 for PHUT, HUES and HOCM respectively. The distribution of scintillation occurrences is dominant in the pre-midnight sector and around the northern crest of the equatorial ionization anomaly (EIA), from the 15°N to 20°N geographic latitude with a maximum at 16°N. The results obtained from the directional analysis show higher distributions of scintillations in the southern sky of PHUT and in the northern sky of HUES and HOCM, and in the elevation angles smaller than 40°. The correlation between ROTI and S4 is low and rather good at PHUT (under EIA) than HOCM (near equator). We found better correlation in the post-midnight hours and less correlation in the pre-midnight hours for all stations. When all satellites are considered during the period of 2009-2011, the range of variation of the ration between ROTI and S4 is from 1 to 7 for PHUT, from 0.3 to 6 for HUES and from 0.7 to 6 for HOCM.

Reconstruction of the ionospheric electron density by geostatistical inversion

NASA Astrophysics Data System (ADS)

Minkwitz, David; van den Boogaart, Karl Gerald; Hoque, Mainul; Gerzen, Tatjana

2015-04-01

The ionosphere is the upper part of the atmosphere where sufficient free electrons exist to affect the propagation of radio waves. Typically, the ionosphere extends from about 50 - 1000 km and its morphology is mainly driven by solar radiation, particle precipitation and charge exchange. Due to the strong ionospheric impact on many applications dealing with trans-ionospheric signals such as Global Navigation Satellite Systems (GNSS) positioning, navigation and remote sensing, the demand for a highly accurate reconstruction of the electron density is ever increasing. Within the Helmholtz Alliance project "Remote Sensing and Earth System Dynamics" (EDA) the utilization of the upcoming radar mission TanDEM-L and its related products are prepared. The TanDEM-L mission will operate in L-band with a wavelength of approximately 24 cm and aims at an improved understanding of environmental processes and ecosystem change, e.g. earthquakes, volcanos, glaciers, soil moisture and carbon cycle. Since its lower frequency compared to the X-band (3 cm) and C-band (5 cm) radar missions, the influence of the ionosphere will increase and might lead to a significant degradation of the radar image quality if no correction is applied. Consequently, our interest is the reconstruction of the ionospheric electron density in order to mitigate the ionospheric delay. Following the ionosphere's behaviour we establish a non-stationary and anisotropic spatial covariance model of the electron density separated into a vertical and horizontal component. In order to estimate the model's parameters we chose a maximum likelihood approach. This approach incorporates GNSS total electron content measurements, representing integral measurements of the electron density between satellite to receiver ray paths, and the NeQuick model as a non-stationary trend. Based on a multivariate normal distribution the spatial covariance model parameters are optimized and afterwards the 3D electron density can be

Atmosphere and ionosphere of venus from the mariner v s-band radio occultation measurement.

PubMed

Kliore, A; Levy, G S; Cain, D L; Fjeldbo, G; Rasool, S I

1967-12-29

Measurements of the frequency, phase, and amplitude of the S-band radio signal of Mariner V as it passed behind Venus were used to obtain the effects of refraction in its atmosphere and ionosphere. Profiles of refractivity, temperature, pressure, and density in the neutral atmosphere, as well as electron density in the daytime ionosphere, are presented. A constant scale height was observed above the tropopause, and the temperature increased with an approximately linear lapse rate below the tropopause to the level at which signal was lost, presumably because heavy defocusing attenuation occurred as critical refraction was approached. An ionosphere having at least two maxima was observed at only 85 kilometers above the tropopause.

Study the gradient characteristics of the ionosphere at equatorial latitude during the latest cycle of solar activity

NASA Astrophysics Data System (ADS)

Nguyen Thai, Chinh; Temitope Seun, Oluwadare; Le Thi, Nhung; Schuh, Harald

2017-04-01

The sun has its own seasons with an average duration of about 11 years. In this time, the sun enters a period of increased activity called the solar maximum and a period of decreased activity called the solar minimum. Cycles span from one minimum to the next. The current solar cycle is 24, which began on January 4, 2008 and is expected to be ended in 2019. During this period, the ionosphere changes its thickness and its characteristics as well. The change is most complicated and unpredictable at the equatorial latitudes in a band around 150 northward and 150 southward from the equator. Thailand is located in these regions is known as one of the countries most affected by the ionosphere change. Ionospheric information such as the vertical total electron content (VTEC) and scintillation indices can be extracted from the measurements of GNSS dual-frequency receivers. In this study, a Matlab tool is programmed to calculate some ionosphere parameters from the normal RINEX observation file including VTEC value, amplitude scintillation S4 index and others. The value of VTEC at one IGS station in Thailand (13.740N, 100.530E) is computed for almost one full solar cycle, that is 8 years, from 2009 to 2016. From these results, we are able to derive the rules of TEC variation over time and its dependence on solar activity in the equatorial regions. The change of VTEC is estimated in diurnal, seasonal and annual variation for the latest solar cycle. The solar cycle can be represented in several ways, in this paper we use the sunspot number and the F10.7 cm radio flux to describe the solar activity. The correlation coefficients between these solar indices and the monthly maximum of VTEC value are around 0.87, this indicates a high dependence of the ionosphere on solar activity. Besides, a scintillation map derived from GNSS data is displayed to indicate the intensity of scintillation activity.

Characterizing Daytime GHZ Scintillation at Equatorial Regions Using Gnss Radio Occultation Measurements

NASA Astrophysics Data System (ADS)

Seif, A.; Zhang, K.; Tsunoda, R. T.; Abdullah, M.; Carter, B. A.; Norman, R.; Wu, S.

2015-12-01

Ionospheric scintillation of radio waves can behave differently at different locations with a strong diurnal dependence; particularly in the equatorial regions. Ionospheric scintillations at gigahertz (GHz) frequencies have been observed during both daytime and nighttime. It is believed that daytime scintillation is associated with blanketing sporadic E (Esb), whereas nighttime scintillation is attributed to F layer irregularities. Scintillation events associated with Esbduring daytime are of our primary interest. Recent studies show that in the ionosphere, electron density profiles from Global Navigation Satellite System (GNSS) Radio Occultation (RO) provide valuable information to help better understand the physics of the ionosphere. In particular, GNSS RO observations of GHz scintillation in the proximity of the E-layer have been interpreted as being caused by sporadic E. In this paper the characteristics of daytime scintillations at 1.5 GHz recorded simultaneously from two stations (i) Universiti Kebangsaan Malaysia (UKM) (2.55°N, 101.461°E; dip latitude 5.78°S), and (ii) Langkawi (6.19°N, 99.51°E; dip latitude 1.90°S) during November and December 2010 are analyzed. The characteristics of daytime GHz scintillation and its relationship with E region irregularities at equatorial regions are investigated. Ground-based scintillation and Total Electron Content (TEC) data recorded by the GSV4004 receivers were utilized in combination with the amplitude scintillation measurements in terms of GPS C/A code SNR fluctuations during a ground-based GPS and space-borne GNSS RO experiment at the two equatorial stations. Scintillation activity was found to be more prominent at UKM. Moreover, strong scintillation with the S4 index exceeding 0.6 has only been observed at UKM, while at Langkawi the scintillation intensity (S4 index) did not exceed 0.3. Signal-to-noise measurements obtained from GNSS RO indicate that daytime scintillations are very likely caused by Esb. Our

Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith

NASA Astrophysics Data System (ADS)

Leyser, Thomas B.; James, H. Gordon; Gustavsson, Björn; Rietveld, Michael T.

2018-02-01

The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O) conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect.

Dual-band beacon experiment over Southeast Asia for ionospheric irregularity analysis

NASA Astrophysics Data System (ADS)

Watthanasangmechai, K.; Yamamoto, M.; Saito, A.; Saito, S.; Maruyama, T.; Tsugawa, T.; Nishioka, M.

2013-12-01

An experiment of dual-band beacon over Southeast Asia was started in March 2012 in order to capture and analyze ionospheric irregularities in equatorial region. Five GNU Radio Beacon Receivers (GRBRs) were aligned along 100 degree geographic longitude. The distances between the stations reach more than 500 km. The field of view of this observational network covers +/- 20 degree geomagnetic latitude including the geomagnetic equator. To capture ionospheric irregularities, the absolute TEC estimation technique was developed. The two-station method (Leitinger et al., 1975) is generally accepted as a suitable method to estimate TEC offsets of dual-band beacon experiment. However, the distances between the stations directly affect on the robustness of the technique. In Southeast Asia, the observational network is too sparse to attain a benefit of the classic two-station method. Moreover, the least-squares approch used in the two-station method tries too much to adjust the small scales of the TEC distribution which are the local minima. We thus propose a new technique to estimate the TEC offsets with the supporting data from absolute GPS-TEC from local GPS receivers and the ionospheric height from local ionosondes. The key of the proposed technique is to utilize the brute-force technique with weighting function to find the TEC offset set that yields a global minimum of RMSE in whole parameter space. The weight is not necessary when the TEC distribution is smooth, while it significantly improves the TEC estimation during the ESF events. As a result, the latitudinal TEC shows double-hump distribution because of the Equatorial Ionization Anomaly (EIA). In additions, the 100km-scale fluctuations from an Equatorial Spread F (ESF) are captured at night time in equinox seasons. The plausible linkage of the meridional wind with triggering of ESF is under invatigating and will be presented. The proposed method is successful to estimate the latitudinal TEC distribution from dual-band

The CERTO Beacon on CASSIOPE/e-POP and Experiments Using High-Power HF Ionospheric Heaters

NASA Astrophysics Data System (ADS)

Siefring, Carl L.; Bernhardt, Paul A.; James, H. Gordon; Parris, Richard Todd

2015-06-01

A new Coherent Electromagnetic Radio Tomography (CERTO) beacon is on the CASSIOPE satellite and part of the enhanced-Polar Outflow Probe (e-POP) suite of scientific instruments. CERTO signals can be used to measure ionospheric Total Electron Content (TEC) and radio scintillations along propagation paths between CERTO and receivers. The combination of CERTO and the array of e-POP in-situ diagnostics form a powerful tool for studying ionospheric plasma processes that have not been previously possible. Of note, the combination CERTO and the Radio Receiver Instrument (RRI), a modern digital receiver, which measures between 10 Hz to 18 MHz in selectable bands allows for innovative High Frequency (HF) radio propagation experiments. The use of high-power HF ionospheric heating facilities for such experiments further allows for repeatable studies of a number of important plasma processes. The new CERTO beacon transmits un-modulated, phase-coherent waves at 150, 400, and 1067 MHz with either right-hand-circular or linear polarization and TEC is measured using either differential phase and/or Faraday rotation. With a linear array of CERTO receivers, TEC data can be used for tomographic imaging of the ionosphere yielding two-dimensional maps of the plasma below the satellite orbit. In addition, the three CERTO frequencies cover a wide range for determination of radio scintillation effects caused by diffraction from propagation through ionospheric irregularities. We will describe the CERTO beacon and several potential innovative experiments using HF heating facilities in conjunction with CERTO, the RRI and other e-POP instruments.

Investigating the effect of geomagnetic storm and equatorial electrojet on equatorial ionospheric irregularity over East African sector

NASA Astrophysics Data System (ADS)

Seba, Ephrem Beshir; Nigussie, Melessew

2016-11-01

The variability of the equatorial ionosphere is still a big challenge for ionospheric dependent radio wave technology users. To mitigate the effect of equatorial ionospheric irregularity on trans-ionospheric radio waves considerable efforts are being done to understand and model the equatorial electrodynamics and its connection to the creation of ionospheric irregularity. However, the effect of the East-African ionospheric electrodynamics on ionospheric irregularity is not yet well studied due to lack of multiple ground based instruments. But, as a result of International Heliophysical Year (IHY) initiative, which was launched in 2007, some facilities are being deployed in Africa since then. Therefore, recently deployed instruments, in the Ethiopian sector, such as SCINDA-GPS receiver (2.64°N dip angle) for TEC and amplitude scintillation index (S4) data and two magnetometers, which are deployed on and off the magnetic equator, data collected in the March equinoctial months of the years 2011, 2012, and 2015 have been used for this study in conjunction with geomagnetic storm data obtained from high resolution OMNI WEB data center. We have investigated the triggering and inhibition mechanisms for ionospheric irregularities using, scintillation index (S4), equatorial electrojet (EEJ), interplanetary electric field (IEFy), symH index, AE index and interplanetary magnetic field (IMF) Bz on five selected storm and two storm free days. We have found that when the eastward EEJ fluctuates in magnitude due to storm time induced electric fields at around noontime, the post-sunset scintillation is inhibited. All observed post-sunset scintillations in equinox season are resulted when the daytime EEJ is non fluctuating. The strength of noontime EEJ magnitude has shown direct relation with the strength of the post-sunset scintillations. This indicates that non-fluctuating EEJ stronger than 20 nT, can be precursor for the occurrence of the evening time ionospheric irregularities

Analysis of strong scintillation events by using GPS data at low latitudes

NASA Astrophysics Data System (ADS)

Forte, Biagio; Jakowski, Norbert; Wilken, Volker

2010-05-01

Drifting structures charaterised by inhomogeneities in the spatial electron density distribution at ionospheric heights originate scintillation of radio waves propagating through. The fractional electron density fluctuations and the corresponding scintillation levels may reach extreme values at low latitudes during high solar activity. Strong scintillation events have disruptive effects on a number of technological applications. In particular, operations and services based on GPS signals and receivers may experience severe disruption due to a significant degradation of the signal-to-noise ratio, eventually leading to signal loss of lock. Experimental scintillation data collected in the Asian sector at low latitudes by means of a GPS dual frequency receiver under moderate solar activity (2006) have been analysed. The GPS receiver is particularly modified in firmware in order to record power estimates on the C/A code as well as on the carriers L1 and L2. Strong scintillation activity is recorded in the post-sunset period (saturating S4 and SI as high as 20 dB). An overview of these events is presented, by taking into account scintillation impact on the signal intensity, phase, and dynamics. In particular, the interpretation of these events based on a refined scattering theory is provided with possible consequences for standard scintillation models.

A method for scintillation characterization using geodetic receivers operating at 1 Hz

NASA Astrophysics Data System (ADS)

Juan, J. M.; Aragon-Angel, A.; Sanz, J.; González-Casado, G.; Rovira-Garcia, A.

2017-11-01

Ionospheric scintillation produces strong disruptive effects on global navigation satellite system (GNSS) signals, ranging from degrading performances to rendering these signals useless for accurate navigation. The current paper presents a novel approach to detect scintillation on the GNSS signals based on its effect on the ionospheric-free combination of carrier phases, i.e. the standard combination of measurements used in precise point positioning (PPP). The method is implemented using actual data, thereby having both its feasibility and its usefulness assessed at the same time. The results identify the main effects of scintillation, which consist of an increased level of noise in the ionospheric-free combination of measurements and the introduction of cycle-slips into the signals. Also discussed is how mis-detected cycle-slips contaminate the rate of change of the total electron content index (ROTI) values, which is especially important for low-latitude receivers. By considering the effect of single jumps in the individual frequencies, the proposed method is able to isolate, over the combined signal, the frequency experiencing the cycle-slip. Moreover, because of the use of the ionospheric-free combination, the method captures the diffractive nature of the scintillation phenomena that, in the end, is the relevant effect on PPP. Finally, a new scintillation index is introduced that is associated with the degradation of the performance in navigation.

Dual-frequency radio soundings of planetary ionospheres avoid misinterpretations of ionospheric features

NASA Astrophysics Data System (ADS)

Paetzold, M.; Andert, T.; Bird, M. K.; Häusler, B.; Hinson, D. P.; Peter, K.; Tellmann, S.

2017-12-01

Planetary ionospheres are usually sounded at single frequency, e.g. S-band or X-band, or at dual-frequencies, e.g. simultaneous S-band and X-band frequencies. The differential Doppler is computed from the received dual-frequency sounding and it has the advantage that any residual motion by the spaceraft body is compensated. The electron density profile is derived from the propagation of the two radio signals through the ionospheric plasma. Vibrational motion of small amplitude by the spacecraft body may still be contained in the single frequency residuals and may be translated into electron densities. Examples from Mars Express and Venus Express shall be presented. Cases from other missions shall be presented where wave-like structures in the upper ionosphere may be a misinterpretation.

Geophysical analysis of coherent satellite scintillation data

NASA Astrophysics Data System (ADS)

Fremouw, E. J.; Lansinger, J. M.; Miller, D. A.

1981-11-01

In May of 1976, Air Force Satellite P76-5 was launched with the Defense Nuclear Agency's Wideband beacon, DNA-002, as its sole payload. Several researchers have employed the resulting data in studies of ionospheric structure and its effect on transionospheric radio communications. In the present work, recordings of amplitude and phase scintillation imposed on Wideband's VHF and UHF signals by the ionosphere have been used to study medium-scale structures in the auroral-zone F layer. Results include quantitative identification of a very close relationship between scintillation and solar/geomagnetic activity, together with lack of a seasonal variation in scintillation activity in the Alaskan sector. A surprisingly high correlation (90%) was found between monthly means of phase-scintillation index, on the one hand, and sunspot number and 10-cm solar radio flux, on the other. The high-latitude scintillation boundary was found to be very similar to the soft-electron precipitation boundary, including similarity in expansion rates with increasing magnetic activity. Interestingly, it is systematically shifted poleward of the precipitation boundary on the day side of the earth and equatorward on the night side. Taken together, the results of this research disclose a rather direct relationship between scintillation and soft-electron precipitation, with plasma convection likely playing an important role in generation of the scintillation-producing irregularities.

Intermediate scale plasma density irregularities in the polar ionosphere inferred from radio occultation

NASA Astrophysics Data System (ADS)

Shume, E. B.; Komjathy, A.; Langley, R. B.; Verkhoglyadova, O. P.; Butala, M.; Mannucci, A. J.

2014-12-01

In this research, we report intermediate scale plasma density irregularities in the high-latitude ionosphere inferred from high-resolution radio occultation (RO) measurements in the CASSIOPE (CAScade Smallsat and IOnospheric Polar Explorer) - GPS (Global Positioning System) satellites radio link. The high inclination of the CASSIOPE satellite and high rate of signal receptionby the occultation antenna of the GPS Attitude, Positioning and Profiling (GAP) instrument on the Enhanced Polar Outflow Probe platform on CASSIOPE enable a high temporal and spatial resolution investigation of the dynamics of the polar ionosphere, magnetosphere-ionospherecoupling, solar wind effects, etc. with unprecedented details compared to that possible in the past. We have carried out high spatial resolution analysis in altitude and geomagnetic latitude of scintillation-producing plasma density irregularities in the polar ionosphere. Intermediate scale, scintillation-producing plasma density irregularities, which corresponds to 2 to 40 km spatial scales were inferred by applying multi-scale spectral analysis on the RO phase delay measurements. Using our multi-scale spectral analysis approach and Polar Operational Environmental Satellites (POES) and Defense Meteorological Satellite Program (DMSP) observations, we infer that the irregularity scales and phase scintillations have distinct features in the auroral oval and polar cap regions. In specific terms, we found that large length scales and and more intense phase scintillations are prevalent in the auroral oval compared to the polar cap region. Hence, the irregularity scales and phase scintillation characteristics are a function of the solar wind and the magnetospheric forcing. Multi-scale analysis may become a powerful diagnostic tool for characterizing how the ionosphere is dynamically driven by these factors.

Canadian High Arctic Ionospheric Network (CHAIN)

NASA Astrophysics Data System (ADS)

Jayachandran, P. T.; Langley, R. B.; MacDougall, J. W.; Mushini, S. C.; Pokhotelov, D.; Hamza, A. M.; Mann, I. R.; Milling, D. K.; Kale, Z. C.; Chadwick, R.; Kelly, T.; Danskin, D. W.; Carrano, C. S.

2009-02-01

Polar cap ionospheric measurements are important for the complete understanding of the various processes in the solar wind-magnetosphere-ionosphere system as well as for space weather applications. Currently, the polar cap region is lacking high temporal and spatial resolution ionospheric measurements because of the orbit limitations of space-based measurements and the sparse network providing ground-based measurements. Canada has a unique advantage in remedying this shortcoming because it has the most accessible landmass in the high Arctic regions, and the Canadian High Arctic Ionospheric Network (CHAIN) is designed to take advantage of Canadian geographic vantage points for a better understanding of the Sun-Earth system. CHAIN is a distributed array of ground-based radio instruments in the Canadian high Arctic. The instrument components of CHAIN are 10 high data rate Global Positioning System ionospheric scintillation and total electron content monitors and six Canadian Advanced Digital Ionosondes. Most of these instruments have been sited within the polar cap region except for two GPS reference stations at lower latitudes. This paper briefly overviews the scientific capabilities, instrument components, and deployment status of CHAIN. This paper also reports a GPS signal scintillation episode associated with a magnetospheric impulse event. More details of the CHAIN project and data can be found at http://chain.physics.unb.ca/chain.

CARINA Satellite Mission to Investigate the Upper Atmosphere below the F-Layer Ionosphere

NASA Astrophysics Data System (ADS)

Siefring, C. L.; Bernhardt, P. A.; Briczinski, S. J., Jr.; Huba, J.; Montgomery, J. A., Jr.

2017-12-01

A new satellite design permits broad science measurements from the ocean to the ionosphere by flying below the F-Layer. The satellite called CARINA for Coastal-Ocean, Assimilation, Radio, Ionosphere, Neutral-Drag, and Atmospherics. The unique system capabilities are long duration orbits below the ionosphere and a HF receiver to measure broadband signals. The CARINA science products include recording the ocean surface properties, data for assimilation into global ionosphere models, radio wave propagation measurements, in-situ observations of ionospheric structures, validating neutral drag models and theory, and broadband atmospheric lightning characterization. CARINA will also measure nonlinear wave-generation using ionospheric modification sites in Alaska, Norway, Puerto Rico, and Russia and collaborate with geophysics HF radars (such as Super-DARN) for system calibration. CARINA is a linear 6-U CubeSat with a long antenna extended in the wake direction. The CARINA science mission is supported by three instruments. First, the Electric Field Instrument (EFI) is a radio receiver covering the 2 to 18 MHz range. The receiver can capture both narrow and wide bandwidths for up to 10 minutes. EFI is designed to provide HF signal strength and phase, radar Doppler shift and group delay, and electron plasma density from photoelectron excited plasma waves. Second a Ram Langmuir Probe (RLP) measures high-resolution ion currents at a 10 kHz rate. These measurements yield electron and ion density at the spacecraft. Finally, the Orbiting GPS Receiver (OGR) provides dual frequency GPS position with ionosphere correction. OGR also measures total electron content above the spacecraft and L-Band scintillations. CARINA will be the lowest satellite in orbit at 250 km altitude, <0.01 eccentricity, and up to 4-month lifetime. The design supports unique capabilities with broad applications to the geosciences. Remote sensing of the ocean will sample the HF signals scattered from the rough

Performance of ionospheric maps in support of long baseline GNSS kinematic positioning at low latitudes

NASA Astrophysics Data System (ADS)

Park, J.; Sreeja, V.; Aquino, M.; Cesaroni, C.; Spogli, L.; Dodson, A.; De Franceschi, G.

2016-05-01

Ionospheric scintillation occurs mainly at high and low latitude regions of the Earth and may impose serious degradation on GNSS (Global Navigation Satellite System) functionality. The Brazilian territory sits on one of the most affected areas of the globe, where the ionosphere behaves very unpredictably, with strong scintillation frequently occurring in the local postsunset hours. The correlation between scintillation occurrence and sharp variations in the ionospheric total electron content (TEC) in Brazil is demonstrated in Spogli et al. (2013). The compounded effect of these associated ionospheric disturbances on long baseline GNSS kinematic positioning is studied in this paper, in particular when ionospheric maps are used to aid the positioning solution. The experiments have been conducted using data from GNSS reference stations in Brazil. The use of a regional TEC map generated under the CALIBRA (Countering GNSS high-Accuracy applications Limitations due to Ionospheric disturbances in BRAzil) project, referred to as CALIBRA TEC map (CTM), was compared to the use of the Global Ionosphere Map (GIM), provided by the International GNSS Service (IGS). Results show that the use of the CTM greatly improves the kinematic positioning solution as compared with that using the GIM, especially under disturbed ionospheric conditions. Additionally, different hypotheses were tested regarding the precision of the TEC values obtained from ionospheric maps, and its effect on the long baseline kinematic solution evaluated. Finally, this study compares two interpolation methods for ionospheric maps, namely, the Inverse Distance Weight and the Natural Neighbor.

The VLA Low-band Ionosphere and Transient Experiment (VLITE)

NASA Astrophysics Data System (ADS)

Clarke, Tracy; Peters, Wendy; Brisken, Walter; Giacintucci, Simona; Kassim, Namir; Polisensky, Emil; Helmboldt, Joseph; Richards, Emily E.; Erickson, Alan; Ray, Paul S.; Kerr, Matthew T.; Deneva, Julia; Coburn, William; Huber, Robert; Long, Jeff

2018-01-01

The VLA Low-band Ionosphere and Transient Experiment (VLITE, http://vlite.nrao.edu/ ) is a commensal low-frequency observing system that has been operational on the National Radio Astronomy Observatory's Karl G. Jansky Very Large Array (VLA) since late 2014. The separate optical paths of the prime-focus sub-GHz dipole feeds and the Cassegrain-focus 1-50 GHz feeds allow both systems to operate simultaneously with independent correlators. The initial 2.5 years of VLITE operation provided real-time correlation of 10 antennas across the 320-384 MHz band with a total observing time approaching 12,000 hours. During the summer of 2017, VLITE was upgraded to a total of 16 antennas (more than doubling the number of baselines) with enhanced correlator capabilities to enable correlation of the on-the-fly observing mode being used for the new NRAO VLA Sky Survey (VLASS).We present an overview of the VLITE system, including highlights of the complexities of a commensal observing program, sparse-array challenges, and scientific capabilities from our science-ready data pipeline. In the longer term, we seek a path to broadband expansion across all VLA antennas to develop a powerful new LOw Band Observatory (LOBO).

A Campaign to Study Equatorial Ionospheric Phenomena over Guam

NASA Astrophysics Data System (ADS)

Habash Krause, L.; Balthazor, R.; Dearborn, M.; Enloe, L.; Lawrence, T.; McHarg, M.; Petrash, D.; Reinisch, B. W.; Stuart, T.

2007-05-01

With the development of a series of ground-based and space-based experiments, the United States Air Force Academy (USAFA) is in the process of planning a campaign to investigate the relationship between equatorial ionospheric plasma dynamics and a variety of space weather effects, including: 1) ionospheric plasma turbulence in the F region, and 2) scintillation of radio signals at low latitudes. A Digisonde Portable Sounder DPS-4 will operate from the island of Guam (with a magnetic latitude of 5.6° N) and will provide measurements of ionospheric total electron content (TEC), vertical drifts of the bulk ionospheric plasma, and electron density profiles. Additionally, a dual-frequency GPS TEC/scintillation monitor will be located along the Guam magnetic meridian at a magnetic latitude of approximately 15° N. In campaign mode, we will combine these ground-based observations with those collected from space during USAFA's FalconSAT-3 and FalconSAT-5 low-earth orbit satellite missions, the first of which is scheduled to be active over a period of several months beginning in the 2007 calendar year. The satellite experiments are designed to characterize in situ irregularities in plasma density, and include measurements of bulk ion density and temperature, minority-to- majority ion mixing ratios, small scale (10 cm to 1 m) plasma turbulence, and ion distribution spectra in energy with sufficient resolution for observations of non-thermalized distributions that may be associated with velocity- space instabilities. Specific targets of investigation include: a) a comparison of plasma turbulence observed on- orbit with spread F on ionograms as measured with the Digisonde, b) a correlation between the vertical lifting of the ionospheric layer over Guam and the onset of radio scintillation activity along the Guam meridian at 15° N magnetic latitude, and c) a correlation between on-orbit turbulence and ionospheric scintillation at 15° N magnetic latitude. These relationships

Topside and ground ionosonde observations of a mid-latitude scintillation region

NASA Astrophysics Data System (ADS)

Hajkowicz, L. A.

1982-02-01

Ionospheric amplitude scintillations of transmissions in the VHF range from orbiting satellites were compared with topside and ground (bottomside) ionograms of an inhomogeneous region in southern mid-latitudes. It is evident that, for the event considered, there is a good spatial correlation between intense topside and bottomside spread-F and scintillations. The ionospheric disturbance pattern appears to agree with a quasi-sinusoidal model of frontal disturbances (derived from the angle-of-arrival experiments) in the F-region at these geographic latitudes.

The Mesoscale Ionospheric Simulation Testbed (MIST) Regional Data Assimilation Model (Invited)

NASA Astrophysics Data System (ADS)

Comberiate, J.; Kelly, M. A.; Miller, E.; Paxton, L.

2013-12-01

The Mesoscale Ionospheric Simulation Testbed (MIST) provides a regional nowcast and forecast of electron density values and has sufficient resolution to include equatorial plasma bubbles. The SSUSI instrument on the DMSP F18 satellite has high-resolution nightly observations of plasma bubbles at 8 PM local time throughout the current solar maximum. MIST can assimilate SSUSI UV observations, GPS TEC measurements, and SCINDA S4 readings simultaneously into a single scintillation map over a region of interest. MIST also models ionospheric physics to provide a short-term UHF scintillation forecast based on assimilated data. We will present examples of electron density and scintillation maps from MIST. We will also discuss the potential to predict scintillation occurrence up to 6 hours in advance using observations of the equatorial arcs from SSUSI observations at 5:30 PM local time on the DMSP F17 satellite.

Intermediate-scale plasma irregularities in the polar ionosphere inferred from GPS radio occultation

NASA Astrophysics Data System (ADS)

Shume, E. B.; Komjathy, A.; Langley, R. B.; Verkhoglyadova, O.; Butala, M. D.; Mannucci, A. J.

2015-02-01

We report intermediate-scale plasma irregularities in the polar ionosphere inferred from high-resolution radio occultation (RO) measurements using GPS (Global Positioning System) to CASSIOPE (CAScade Smallsat and IOnospheric Polar Explorer) satellite radio links. The high inclination of CASSIOPE and the high rate of signal reception by the GPS Attitude, Positioning, and Profiling RO receiver on CASSIOPE enable a high-resolution investigation of the dynamics of the polar ionosphere with unprecedented detail. Intermediate-scale, scintillation-producing irregularities, which correspond to 1 to 40 km scales, were inferred by applying multiscale spectral analysis on the RO phase measurements. Using our multiscale spectral analysis approach and satellite data (Polar Operational Environmental Satellites and Defense Meteorological Satellite Program), we discovered that the irregularity scales and phase scintillations have distinct features in the auroral oval and polar cap. We found that large length scales and more intense phase scintillations are prevalent in the auroral oval compared to the polar cap implying that the irregularity scales and phase scintillation characteristics are a function of the solar wind and magnetospheric forcings.

Amplitude Scintillation due to Atmospheric Turbulence for the Deep Space Network Ka-Band Downlink

NASA Technical Reports Server (NTRS)

Ho, C.; Wheelon, A.

2004-01-01

Fast amplitude variations due to atmospheric scintillation are the main concerns for the Deep Space Network (DSN) Ka-band downlink under clear weather conditions. A theoretical study of the amplitude scintillation variances for a finite aperture antenna is presented. Amplitude variances for weak scattering scenarios are examined using turbulence theory to describe atmospheric irregularities. We first apply the Kolmogorov turbulent spectrum to a point receiver for three different turbulent profile models, especially for an exponential model varying with altitude. These analytic solutions then are extended to a receiver with a finite aperture antenna for the three profile models. Smoothing effects of antenna aperture are expressed by gain factors. A group of scaling factor relations is derived to show the dependences of amplitude variances on signal wavelength, antenna size, and elevation angle. Finally, we use these analytic solutions to estimate the scintillation intensity for a DSN Goldstone 34-m receiving station. We find that the (rms) amplitude fluctuation is 0.13 dB at 20-deg elevation angle for an exponential model, while the fluctuation is 0.05 dB at 90 deg. These results will aid us in telecommunication system design and signal-fading prediction. They also provide a theoretical basis for further comparison with other measurements at Ka-band.

An ionospheric index suitable for estimating the degree of ionospheric perturbations

NASA Astrophysics Data System (ADS)

Wilken, Volker; Kriegel, Martin; Jakowski, Norbert; Berdermann, Jens

2018-03-01

Space weather can strongly affect trans-ionospheric radio signals depending on the used frequency. In order to assess the strength of a space weather event from its origin at the sun towards its impact on the ionosphere a number of physical quantities need to be derived from scientific measurements. These are for example the Wolf number sunspot index, the solar flux density F10.7, measurements of the interplanetary magnetic field, the proton density, the solar wind speed, the dynamical pressure, the geomagnetic indices Auroral Electrojet, Kp, Ap and Dst as well as the Total Electron Content (TEC), the Rate of TEC, the scintillation indices S4 and σ(ϕ) and the Along-Arc TEC Rate index index. All these quantities provide in combination with an additional classification an orientation in a physical complex environment. Hence, they are used for brief communication of a simplified but appropriate space situation awareness. However, space weather driven ionospheric phenomena can affect many customers in the communication and navigation domain, which are still served inadequately by the existing indices. We present a new robust index, that is able to properly characterize temporal and spatial ionospheric variations of small to medium scales. The proposed ionospheric disturbance index can overcome several drawbacks of other ionospheric measures and might be suitable as potential driver for an ionospheric space weather scale.

Limitations to Dual Frequency Ionosphere Corrections for Frequency Switched K-Q-Band Observations with the VLBA

NASA Technical Reports Server (NTRS)

Lanyi, Gabor; Gordon, David; Sovers, Ojars J.

2004-01-01

A series of VLBA experiments were carried out at K and Q bands for astrometry and imaging within the KQ VLBI Survey Collaboration. The paired K and Q observations of each source are separated by approximately 3 minutes of time. We investigate the delay effect of the ionosphere between K and Q bands involving the interscan separation. This differential delay effect is intermixed with the differential fluctuation effect of the troposphere.

Ionospheric Specifications for SAR Interferometry (ISSI)

NASA Technical Reports Server (NTRS)

Pi, Xiaoqing; Chapman, Bruce D; Freeman, Anthony; Szeliga, Walter; Buckley, Sean M.; Rosen, Paul A.; Lavalle, Marco

2013-01-01

The ISSI software package is designed to image the ionosphere from space by calibrating and processing polarimetric synthetic aperture radar (PolSAR) data collected from low Earth orbit satellites. Signals transmitted and received by a PolSAR are subject to the Faraday rotation effect as they traverse the magnetized ionosphere. The ISSI algorithms combine the horizontally and vertically polarized (with respect to the radar system) SAR signals to estimate Faraday rotation and ionospheric total electron content (TEC) with spatial resolutions of sub-kilometers to kilometers, and to derive radar system calibration parameters. The ISSI software package has been designed and developed to integrate the algorithms, process PolSAR data, and image as well as visualize the ionospheric measurements. A number of tests have been conducted using ISSI with PolSAR data collected from various latitude regions using the phase array-type L-band synthetic aperture radar (PALSAR) onboard Japan Aerospace Exploration Agency's Advanced Land Observing Satellite mission, and also with Global Positioning System data. These tests have demonstrated and validated SAR-derived ionospheric images and data correction algorithms.

Cubesat-Based Dtv Receiver Constellation for Ionospheric Tomography

NASA Astrophysics Data System (ADS)

Bahcivan, H.; Leveque, K.; Doe, R. A.

2013-12-01

The Radio Aurora Explorer mission, funded by NSF's Space Weather and Atmospheric Research program, has demonstrated the utility of CubeSat-based radio receiver payloads for ionospheric research. RAX has primarily been an investigation of microphysics of meter-scale ionospheric structures; however, the data products are also suitable for research on ionospheric effects on radio propagation. To date, the spacecraft has acquired (1) ground-based UHF radar signals that are backscattered from meter-scale ionospheric irregularities, which have been used to measure the dispersion properties of meter-scale plasma waves and (2) ground-based signals, directly on the transmitter-spacecraft path, which have been used to measure radio propagation disturbances (scintillations). Herein we describe the application of a CubeSat constellation of UHF receivers to expand the latter research topic for global-scale ionospheric tomography. The enabling factor for this expansion is the worldwide availability of ground-based digital television (DTV) broadcast signals whose characteristics are optimal for scintillation analysis. A significant part of the populated world have transitioned, or soon to be transitioned, to DTV. The DTV signal has a standard format that contains a highly phase-stable pilot carrier that can be readily adapted for propagation diagnostics. A multi-frequency software-defined radar receiver, similar to the RAX payload, can measure these signals at a large number of pilot carrier frequencies to make radio ray and diffraction tomographic measurements of the ionosphere and the irregularities contained in it. A constellation of CubeSats, launched simultaneously, or in sequence over years, similar to DMSPs, can listen to the DTV stations, providing a vast and dense probing of the ionosphere. Each spacecraft can establish links to a preprogrammed list of DTV stations and cycle through them using time-division frequency multiplexing (TDFM) method. An on board program can

Satellite Constellations for Space Weather and Ionospheric Studies: Overview of the COSMIC and COSMIC-2 Missions

NASA Astrophysics Data System (ADS)

Schreiner, W. S.; Pedatella, N. M.; Weiss, J.

2016-12-01

Measurements from constellations of low Earth orbiting (LEO) satellites are proving highly useful for ionospheric science and space weather studies. The Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC), a joint US/Taiwan mission launched in April 2006, is a six micro-satellite constellation carrying Global Positioning System (GPS) radio occultation (RO) receivers. COSMIC has collected a large amount of useful data from these scientific payloads and is still currently collecting up to 1,000 RO measurement events per day on average. The GPS RO dual-frequency L-band phase and amplitude measurements can be used to observe absolute Total Electron Content (TEC) and scintillation on lines of sight between the LEO and GPS satellites, and electron density profiles via the RO method. The large number and complete global and local time coverage of COSMIC data are allowing scientists to observe ionospheric and plasmaspheric phenomena that are difficult to see with other instruments. The success of COSMIC has prompted U.S. agencies and Taiwan to execute a COSMIC follow-on mission (called COSMIC-2) that will put twelve satellites with GNSS (Global Navigation Satellite System) RO payloads into orbit on two launches in the 2017-20 time frame. The first launch in 2017 will place six satellites in a 520-km altitude 24 deg inclination orbit, which is ideal for low latitude ionospheric research and space weather forecasting. The planned second launch (not currently funded) places six additional satellites in a 750 km 72 deg inclination orbit to provide global coverage and increased sampling density. COSMIC-2 will make use of an advanced radio occultation receiver with an innovative beam-forming antenna design, and is expected to produce at least 10,000 high-quality atmospheric and ionospheric profiles per day from GPS and GLONASS signals to support operational weather prediction, climate monitoring, and space weather forecasting. Each COSMIC-2 spacecraft

Global Scale Observations of Ionospheric Instabilities from GPS in Low Earth Orbit

NASA Technical Reports Server (NTRS)

Kramer, Leonard; Goodman, John L.

2003-01-01

The GPS receiver used for navigation on the Space Shuttle exhibits range rate noise which appears to result from scintillation of the satellite signals by irregularities in ionospheric plasma. The noise events cluster in geographic regions previously identified as susceptible to instability and disturbed ionospheric conditions. These mechanisms are reviewed in the context of the GPS observations. Range rate data continuously monitored during the free orbiting phase of several space shuttle missions reveals global scale distribution of ionospheric irregularities. Equatorial events cluster +/- 20 degrees about the magnetic equator and polar events exhibit hemispheric asymmetry suggesting influence of off axis geomagnetic polar oval system. The diurnal, seasonal and geographic distribution is compared to previous work concerning equatorial spread F, Appleton anomaly and polar oval. The observations provide a succinct demonstration of the utility of space based ionospheric monitoring using GPS. The susceptability of GPS receivers to scintillation represents 'an unanticipated technical risk not factored into the selection of receivers for the United States space program.

On the relation between GNSS phase scintillation and auroral brightness around satellite's IPP

NASA Astrophysics Data System (ADS)

Spanswick, E.; Mushini, S. C.; Skone, S.; Donovan, E.

2017-12-01

Aurora occurs in different well-known morphologies, or types, including arcs and patchy-pulsating aurora (PPA). Previous observational studies have demonstrated that global navigation satellite system (GNSS) signals transiting the ionosphere in regions of aurora can contain varying levels of scintillation. These scintillations are often attributed to the ionospheric disturbances associated with auroral precipitation, which in extreme cases can affect the accuracy of these systems. One question that remains unanswered is whether a satellite's line of sight transmission through the aurora is a sufficient condition for signal scintillation. Previous studies have used "level" or "strength" of auroral emission as a proxy indicator for scintillation using limited datasets. In general, these results are mixed and inconclusive. In this study, we use a large data set (700 Auroral arc events) to statistically study the relationship between aurora and scintillation of GPS signals. This is one of the largest datasets used in this type of studies. We utilize the THEMIS (Time History of Events and Macroscale Interactions during Substorms) All-Sky Imagers (ASIs) located at Fort Smith (59.9 N, 248.1 E geog.) and Gillam (56.5 N, 265.4 E geog.), Canada. Corresponding GPS data were obtained from CHAIN (Canadian High Arctic Ionospheric Network) GPS receivers collocated with the ASIs. These GPS receivers are custom made receivers capable of providing high rate GPS signal power and phase observations as well as scintillation indices. To obtain information how aurora is affecting the signal, brightness around satellite's Ionospheric Pierce Point (IPP) was calculated and correlated with sigma phi from the satellite's signal. A very low correlation of 0.003 was observed between them. Correlation between the rate of change of brightness around the satellite's IPP and sigma phi was also calculated and a correlation coefficient of 0.7 was observed between them. These results indicate that GPS

A review of ionospheric effects on Earth-space propagation

NASA Technical Reports Server (NTRS)

Klobuchar, J. A.

1984-01-01

A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

Effects of the Ionosphere on Passive Microwave Remote Sensing of Ocean Salinity from Space

NASA Technical Reports Server (NTRS)

LeVine, D. M.; Abaham, Saji; Hildebrand, Peter H. (Technical Monitor)

2001-01-01

Among the remote sensing applications currently being considered from space is the measurement of sea surface salinity. The salinity of the open ocean is important for understanding ocean circulation and for modeling energy exchange with the atmosphere. Passive microwave remote sensors operating near 1.4 GHz (L-band) could provide data needed to fill the gap in current coverage and to complement in situ arrays being planned to provide subsurface profiles in the future. However, the dynamic range of the salinity signal in the open ocean is relatively small and propagation effects along the path from surface to sensor must be taken into account. In particular, Faraday rotation and even attenuation/emission in the ionosphere can be important sources of error. The purpose or this work is to estimate the magnitude of these effects in the context of a future remote sensing system in space to measure salinity in L-band. Data will be presented as a function of time location and solar activity using IRI-95 to model the ionosphere. The ionosphere presents two potential sources of error for the measurement of salinity: Rotation of the polarization vector (Faraday rotation) and attenuation/emission. Estimates of the effect of these two phenomena on passive remote sensing over the oceans at L-band (1.4 GHz) are presented.

Equatorial scintillation and systems support

NASA Astrophysics Data System (ADS)

Groves, K. M.; Basu, S.; Weber, E. J.; Smitham, M.; Kuenzler, H.; Valladares, C. E.; Sheehan, R.; MacKenzie, E.; Secan, J. A.; Ning, P.; McNeill, W. J.; Moonan, D. W.; Kendra, M. J.

1997-09-01

The need to nowcast and forecast scintillation for the support of operational systems has been recently identified by the interagency National Space Weather Program. This issue is addressed in the present paper in the context of nighttime irregularities in the equatorial ionosphere that cause intense amplitude and phase scintillations of satellite signals in the VHF/UHF range of frequencies and impact satellite communication, Global Positioning System navigation, and radar systems. Multistation and multifrequency satellite scintillation observations have been used to show that even though equatorial scintillations vary in accordance with the solar cycle, the extreme day-to-day variability of unknown origin modulates the scintillation occurrence during all phases of the solar cycle. It is shown that although equatorial scintillation events often show correlation with magnetic activity, the major component of scintillation is observed during magnetically quiet periods. In view of the day-to-day variability of the occurrence and intensity of scintillating regions, their latitude extent, and their zonal motion, a regional specification and short-term forecast system based on real-time measurements has been developed. This system, named the Scintillation Network Decision Aid, consists of two latitudinally dispersed stations, each of which uses spaced antenna scintillation receiving systems to monitor 250-MHz transmissions from two longitudinally separated geostationary satellites. The scintillation index and zonal irregularity drift are processed on-line and are retrieved by a remote operator on the Internet. At the operator terminal the data are combined with an empirical plasma bubble model to generate three-dimensional maps of irregularity structures and two-dimensional outage maps for the region.

Ionospheric Correction in Using ALOS PALSAR InSAR Data for Monitoring Permafrost Subsidence associated with an Arctic Tundra Fire

NASA Astrophysics Data System (ADS)

Liao, H.; Meyer, F. J.; Liu, L.

2017-12-01

Tundra fires have important ecological impacts on vegetation succession, carbon cycling, and permafrost dynamics. Recent research has demonstrated that SAR Interferometry (InSAR) is a useful tool for quantifying surface subsidence caused by permafrost degradation and tundra fires. Many of these studies have relied on L-band SAR data due to its ability to remain relatively high coherence in the changing Arctic environment. L-band SAR data, however, are susceptive to ionospheric effects. Traditionally, permafrost-related InSAR studies dealt with ionospheric artifacts by either throwing away ionosphere-contaminated data or by fitting and removing low-order polynomial surfaces from affected images. Discarding data samples is always luxurious and risky, as the number of SAR images is limited and the incurred reduction of temporal sampling might hinder the retrieval of important short-term dynamics in active layer and permafrost. Baseline fitting relies on the assumption that ionospheric signals large spatial scales, an assumption that is often violated in polar regions. To improve upon this situation, we propose the integration of the split-spectrum ionospheric correction technique into permafrost-related InSAR processing workflows. We demonstrate its performance for correcting L-band SAR data in permafrost zones. For the Anaktuvuk River fire area, Alaska, 6 out of 15 ALOS-1 PALSAR scenes used by Liu et al. 2014 were found to be contaminated by ionospheric signals. We extracted the ionospheric phase screens for all contaminated data. We derive their power spectra and provide information on the typical magnitudes and spatial structures of identified phase screens. With the ionosphere corrected data we revisit a model that was developed by Liu et.al (2014) to estimate pre-fire and post-fire thaw-season subsidence for the Anaktuvuk River fire region. We will demonstrate that for our area of interest ionospheric correction leads to improvements of the InSAR-based permafrost

Ionospheric effects during severe space weather events seen in ionospheric service data products

NASA Astrophysics Data System (ADS)

Jakowski, Norbert; Danielides, Michael; Mayer, Christoph; Borries, Claudia

Space weather effects are closely related to complex perturbation processes in the magnetosphere-ionosphere-thermosphere systems, initiated by enhanced solar energy input. To understand and model complex space weather processes, different views on the same subject are helpful. One of the ionosphere key parameters is the Total Electron Content (TEC) which provides a first or-der approximation of the ionospheric range error in Global Navigation Satellite System (GNSS) applications. Additionally, horizontal gradients and time rate of change of TEC are important for estimating the perturbation degree of the ionosphere. TEC maps can effectively be gener-ated using ground based GNSS measurements from global receiver networks. Whereas ground based GNSS measurements provide good horizontal resolution, space based radio occultation measurements can complete the view by providing information on the vertical plasma density distribution. The combination of ground based TEC and vertical sounding measurements pro-vide essential information on the shape of the vertical electron density profile by computing the equivalent slab thickness at the ionosonde station site. Since radio beacon measurements at 150/400 MHz are well suited to trace the horizontal structure of Travelling Ionospheric Dis-turbances (TIDs), these data products essentially complete GNSS based TEC mapping results. Radio scintillation data products, characterising small scale irregularities in the ionosphere, are useful to estimate the continuity and availability of transionospheric radio signals. The different data products are addressed while discussing severe space weather events in the ionosphere e.g. events in October/November 2003. The complementary view of different near real time service data products is helpful to better understand the complex dynamics of ionospheric perturbation processes and to forecast the development of parameters customers are interested in.

Magnetic field orientations in Saturn's upper ionosphere inferred from Voyager radio occultations

NASA Technical Reports Server (NTRS)

Hinson, D. P.

1984-01-01

The radio scintillations observed during occultations of Voyagers 1 and 2 by Saturn are analyzed to determine the morphology of plasma irregularities and hence the magnetic field orientation in Saturn's upper atmosphere. The measurement techniques, the weak scattering theory, and the method used to relate the observed radio scintillations to physical properties of the ionospheric irregularities are briefly described. Results on the spatial characteristics of the irregularities are presented, and the magnetic field orientation in Saturn's ionosphere is inferred. Although the occultation measurements generally confirm the accuracy of the Saturnian magnetic field model of Connerney et al. (1982), it is found that a small adjustment of the coefficients in that model's zonal harmonic expansion would remove the discrepancy between the model predictions and the measurements. A strategy for obtaining improved measurements of Saturn's magnetic field from radio occultation observations of scintillations and Faraday rotation using an orbiting spacecraft is briefly discussed.

Study of Sun-Earth interactions using equatorial VHF scintillation in the Indian region

NASA Astrophysics Data System (ADS)

Banola, Sridhar

Plasma density irregularities in the ionosphere (associated with ESF, plasma bubbles and Spo-radic E layers) cause scintillations in various frequency ranges. VHF radio wave scintillation technique is extensively used to study plasma density irregularities of sub-kilometre size . Ef-fects of magnetic and solar activity on ionospheric irregularities are studied so as to ascertain their role in the space weather of the near earth environment in space. Indian Institute of Ge-omagnetism operated a ground network of 13 stations monitoring amplitude scintillations on 244/251 MHz (FLEETSAT 73° E) signals in placecountry-regionIndia for more than a decade under AICPITS. At present VHF scintillation is being recorded at Mumbai by monitoring 251 MHz signal transmitted by geostationary satellite UFO2(71.2 E). sampling at 20 Hz. During CAWSES campaign (March-April 2006, low sunspot period) occurrence of daytime scintilla-tions was observed higher than the nighttime scintillations. This could be due to the fact that during low sunspot years occurrence of spread-F is limited to a narrow latitude region near the dip equator. To study solar cycle association of scintillations, long series of simultaneous amplitude scintillation data for period Jan 1989 to Dec 2000 at Indian low-latitude stations Tirunelveli/Trivandrum, close to dip equator, Pondicherry/Karur, located at the fringe of elec-trojet, Mumbai (dip lat. 13.5o N), a temperate station and Ujjain (dip lat. 18.6o N), close to anomaly crest region are utilized. Nighttime scintillation occurrence is solar activity dependent. Equatorial scintillations are inhibited with increase in geomagnetic activity.

Ppp Analisys with GPS and Glonass Integration in Periods Under Ionospheric Scintillation Effects

NASA Astrophysics Data System (ADS)

Marques, H. A. S.

2015-12-01

The GNSS is widely used nowadays either for geodetic positioning or scientific purposes. The GNSS currently includes GPS, GLONASS, Galileo among other emerging systems. The GPS and GLONASS are currently operational with a full satellite constellation. The GPS is still the most used nowadays and both GPS and GLONASS are under a modernization process. The geodetic positioning by using data from multi-constellation can provide better accuracy in positioning and also more reliability. The PPP is benefited once the satellite geometry is crucial in this method, mainly for kinematic scenarios. The satellite geometry can change suddenly for data collected in urban areas or in conditions of strong atmospheric effects such as Ionospheric Scintillation (IS) that causes weakening of signals with cycle slips and even loss of lock. The IS is caused by small irregularities in the ionosphere layer and is characterized by rapid change in amplitude and phase of the signal being stronger in equatorial and high latitudes regions. In this work the PPP is evaluated with GPS and GLONASS data collected by monitoring receivers from Brazilian CIGALA/CALIBRA network under IS conditions. The PPP processing was accomplished by using the GPSPPP software provided by Natural Resources Canadian (NRCAN). The IS effects were analyzed taking account the S4 and PHI60 indices. Considering periods with moderate IS effects, the use of only GPS data in the PPP presented several peaks in the coordinate time series due to cycle slips and loos of lock. In cycle slip conditions the ambiguity parameter are reinitialized by GPSPPP and considering loss of lock few satellites can be available in some epochs affecting the positioning geometry and consequently decreasing accuracy. In such situations, the PPP using GPS and GLONASS data presented improvements in positioning accuracy of the order to 70% in height component when compared with PPP using only GPS data. Analyses of GDOP and ambiguities parameters were

Ionospheric Irregularities and Acoustic/Gravity Wave Activity Above Low-Latitude Thunderstorms

NASA Astrophysics Data System (ADS)

Lay, Erin H.

2018-01-01

Ionospheric irregularities due to plasma bubbles, scintillation, and acoustic/gravity waves are studied in the low-latitude ionosphere in relation to thunderstorm activity. Ionospheric total electron content (TEC) measurements from the Low Latitude Ionospheric Sensor Network and lightning measurements from the World-Wide Lightning Location Network are compared during two summer months and two winter months in 2013. Large amplitude fluctuations in TEC are found to have a strongly peaked diurnal pattern in the late evening and nighttime summer ionosphere. The maximum magnitude and coverage area of these fluctuations increases as thunderstorm area increases. Summertime midamplitude fluctuations do not exhibit the same diurnal variation but do increase in magnitude and coverage area as thunderstorm area increases. Wintertime ionospheric fluctuations do not appear to be related to thunderstorm activity. These findings show that thunderstorms have an observable effect on magnitude and coverage area of ionospheric fluctuations.

950 keV X-Band Linac For Material Recognition Using Two-Fold Scintillator Detector As A Concept Of Dual-Energy X-Ray System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Kiwoo; Natsui, Takuya; Hirai, Shunsuke

2011-06-01

One of the advantages of applying X-band linear accelerator (Linac) is the compact size of the whole system. That shows us the possibility of on-site system such as the custom inspection system in an airport. As X-ray source, we have developed X-band Linac and achieved maximum X-ray energy 950 keV using the low power magnetron (250 kW) in 2 {mu}s pulse length. The whole size of the Linac system is 1x1x1 m{sup 3}. That is realized by introducing X-band system. In addition, we have designed two-fold scintillator detector in dual energy X-ray concept. Monte carlo N-particle transport (MCNP) code wasmore » used to make up sensor part of the design with two scintillators, CsI and CdWO4. The custom inspection system is composed of two equipments: 950 keV X-band Linac and two-fold scintillator and they are operated simulating real situation such as baggage check in an airport. We will show you the results of experiment which was performed with metal samples: iron and lead as targets in several conditions.« less

Velocity Noise in Space Shuttle and ISS GPS from the Ionosphere

NASA Technical Reports Server (NTRS)

Kramer, Leonard

2004-01-01

A viewgraph presentation on the noise velocity effects on the Space Shuttle and International Space Station (ISS) Global Positioning System (GPS) from the ionosphere is shown. The topics include: Scintillation in MAGR/S GPS used for Shuttle; 2) Geographic Distribution of Scintillation; 3) Diurnal Variability; 4) Feynman's interpretation of interference; 5) Angle between line of sight and S/C velocity; and 6) Space Station GPS

Evaluation of Inversion Methods Applied to Ionospheric ro Observations

NASA Astrophysics Data System (ADS)

Rios Caceres, Arq. Estela Alejandra; Rios, Victor Hugo; Guyot, Elia

The new technique of radio-occultation can be used to study the Earth's ionosphere. The retrieval processes of ionospheric profiling from radio occultation observations usually assume spherical symmetry of electron density distribution at the locality of occultation and use the Abel integral transform to invert the measured total electron content (TEC) values. This pa-per presents a set of ionospheric profiles obtained from SAC-C satellite with the Abel inversion technique. The effects of the ionosphere on the GPS signal during occultation, such as bending and scintillation, are examined. Electron density profiles are obtained using the Abel inversion technique. Ionospheric radio occultations are validated using vertical profiles of electron con-centration from inverted ionograms , obtained from ionosonde sounding in the vicinity of the occultation. Results indicate that the Abel transform works well in the mid-latitudes during the daytime, but is less accurate during the night-time.

Application of GPS Measurements for Ionospheric and Tropospheric Modelling

NASA Astrophysics Data System (ADS)

Rajendra Prasad, P.; Abdu, M. A.; Furlan, Benedito. M. P.; Koiti Kuga, Hélio

military navigation. The DOD's primary purposes were to use the system in precision weapon delivery and providing a capability that would help reverse the proliferation of navigation systems in military. Subsequently, it was very quickly realized that civil use and scientific utility would far outstrip military use. A variety of scientific applications are uniquely suited to precise positioning capabilities. The relatively high precision, low cost, mobility and convenience of GPS receivers make positioning attractive. The other applications being precise time measurement, surveying and geodesy purposes apart from orbit and attitude determination along with many user services. The system operates by transmitting radio waves from satellites to receivers on the ground, aircraft, or other satellites. These signals are used to calculate location very accurately. Standard Positioning Services (SPS) which restricts access to Coarse/Access (C/A) code and carrier signals on the L1 frequency only. The accuracy thus provided by SPS fall short of most of the accuracy requirements of users. The upper atmosphere is ionized by the ultra violet radiation from the sun. The significant errors in positioning can result when the signals are refracted and slowed by ionospheric conditions, the parameter of the ionosphere that produces most effects on GPS signals is the total number of electrons in the ionospheric propagation path. This integrated number of electrons, called Total Electron Content (TEC) varies, not only from day to night, time of the year and solar flux cycle, but also with geomagnetic latitude and longitude. Being plasma the ionosphere affects the radio waves propagating through it. Effects of scintillation on GPS satellite navigation systems operating at L1 (1.5754 GHz), L2 (1.2276 GHz) frequencies have not been estimated accurately. It is generally recognized that GPS navigation systems are vulnerable in the polar and especially in the equatorial region during the

Exploring the Cigala/calibra Network Data Base for Ionosphere Monitoring Over Brazil

NASA Astrophysics Data System (ADS)

Vani, B. C.; Galera Monico, J. F.; Shimabukuro, M. H.; Pereira, V. A.; Aquino, M. H.

2013-12-01

The ionosphere in Brazil is strongly influenced by the equatorial anomaly, therefore GNSS based applications are widely affected by ionospheric disturbances. A network for continuous monitoring of the ionosphere has been deployed over its territory since February/2011, as part of the CIGALA and CALIBRA projects. Through CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America), which was funded by European Commission (EC) in the framework of the FP7-GALILEO-2009-GSA (European GNSS Agency), the first stations were deployed at Presidente Prudente, São Paulo state, in February 2011. CIGALA was finalized in February 2012 with eight stations distributed over the Brazilian territory. Through CALIBRA (Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil), which is also funded by the European Commission now in the framework of the FP7-GALILEO-2011-GSA, new stations are being deployed. Some of the stations are being specifically placed according to geomagnetic considerations aiming to support the development of a local scintillation and TEC model. CALIBRA started in November 2012 and will have two years of duration, focusing on the development of improved and new algorithms that can be applied to high accuracy GNSS techniques in order to tackle the effects of ionospheric disturbances. PolarRxS-PRO receivers, manufactured by Septentrio, have been deployed at all stations This multi-GNSS receiver can collect data at rates of up to 100 Hz, providing ionospheric TEC, scintillation parameters like S4 and Sigma-Phi, and other signal metrics like locktime for all satellites and frequencies tracked. All collected data (raw and ionosphere monitoring records) is stored at a central facility located at the Faculdade de Ciências e Tecnologia da Universidade Estadual Paulista (FCT/UNESP) in Presidente Prudente. To deal with the large amount of data, an analysis infrastructure has also been established

Large ionospheric disturbances produced by the HAARP HF facility

NASA Astrophysics Data System (ADS)

Bernhardt, Paul A.; Siefring, Carl L.; Briczinski, Stanley J.; McCarrick, Mike; Michell, Robert G.

2016-07-01

The enormous transmitter power, fully programmable antenna array, and agile frequency generation of the High Frequency Active Auroral Research Program (HAARP) facility in Alaska have allowed the production of unprecedented disturbances in the ionosphere. Using both pencil beams and conical (or twisted) beam transmissions, artificial ionization clouds have been generated near the second, third, fourth, and sixth harmonics of the electron gyrofrequency. The conical beam has been used to sustain these clouds for up to 5 h as opposed to less than 30 min durations produced using pencil beams. The largest density plasma clouds have been produced at the highest harmonic transmissions. Satellite radio transmissions at 253 MHz from the National Research Laboratory TACSat4 communications experiment have been severely disturbed by propagating through artificial plasma regions. The scintillation levels for UHF waves passing through artificial ionization clouds from HAARP are typically 16 dB. This is much larger than previously reported scintillations at other HF facilities which have been limited to 3 dB or less. The goals of future HAARP experiments should be to build on these discoveries to sustain plasma densities larger than that of the background ionosphere for use as ionospheric reflectors of radio signals.

Study of the activities of MSTIDs, FAIs, and scintillations in middle latitudes

NASA Astrophysics Data System (ADS)

Oh, S. J.; Kil, H.; Kwak, Y. S.; Tae-yong, Y.

2017-12-01

We investigate the role of medium-scale traveling ionospheric disturbances (MSTIDs) in the creation of field-aligned irregularities (FAIs) and scintillations in middle latitudes. The occurrences of MSTIDs, FAIs, and scintillations are monitored using the total electron content perturbation maps over Japan, observations of VHF radar at Daejeon in South Korea, and observations of scintillation monitors over South Korea, respectively. The observations of the electron density by Swarm satellites are used for the investigation of the conjugate property in MSTIDs and FAIs.

Obtaining Networked Scintillation and Total Electron Content Data Across Africa and Asia: Partnering with the IHY/UNBSSI Developing Nations Program

NASA Astrophysics Data System (ADS)

Groves, K. M.; Basu, S.; Erickson, T.; Sunanda, B.; David, B.

2005-12-01

Under the Scintillation Network Decision Aid (SCINDA) project, scientists at the Air Force Research Laboratory (AFRL) have developed a sensor network for the purpose of monitoring low-latitude ionospheric total electron content (TEC) and scintillations associated with equatorial Spread F. In addition to monitoring GPS scintillations, TEC and VHF scintillations, the sensor package measures ionospheric drifts when irregularities are present providing important data on vertical electric fields in the F-region .The network currently consists of twelve stations distributed around the globe and the data have been used to conduct numerous studies on the characteristics and climatology of equatorial scintillation, including the impacts of magnetic storms on the equatorial ionosphere. Notably absent from the existing network are observing sites in Africa where both satellite observations and limited historical data sets suggest significant scintillation activity, though the detailed behavior and longitudinal variations across the continent are largely unknown. The latter aspect, in particular, is of great interest because of substantial changes in the orientation of the geomagnetic field in extreme West Africa that transition to a more uniform field geometry spanning the rest of the continent. Understanding the effects of these changes on scintillation climatology will provide new insights into the processes that trigger equatorial Spread F and assist researchers in developing improved forecasts of such activity. AFRL aims to establish 5-8 monitoring sites across equatorial Africa in collaboration with host nations participating in the United Nations Basic Space Science Initiative during the IHY period. In addition to expanding scientific opportunities, it is hoped that these sites will lead to greater awareness of the significant space weather issues impacting Africa and result in enhanced international collaboration between both African and non-African scientists

Ionospheric irregularities and acoustic/gravity wave activity above low-latitude thunderstorms

DOE PAGES

Lay, Erin H.

2017-12-18

Ionospheric irregularities due to plasma bubbles, scintillation, and acoustic/gravity waves are studied in the low-latitude ionosphere in relation to thunderstorm activity. Ionospheric total electron content (TEC) measurements from the Low Latitude Ionospheric Sensor Network (LISN) and lightning measurements from the World-Wide Lightning Location Network (WWLLN) are compared during two summer months and two winter months in 2013. Large amplitude fluctuations in TEC are found to have a strongly-peaked diurnal pattern in the late evening and nighttime summer ionosphere. The maximum magnitude and coverage area of these fluctuations increases as thunderstorm area increases. Summertime mid-amplitude fluctuations do not exhibit the samemore » diurnal variation, but do increase in magnitude and coverage area as thunderstorm area increases. Wintertime ionospheric fluctuations do not appear to be related to thunderstorm activity. Lastly, these findings show that thunderstorms have an observable effect on magnitude and coverage area of ionospheric fluctuations.« less

Ionospheric irregularities and acoustic/gravity wave activity above low-latitude thunderstorms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lay, Erin H.

Ionospheric irregularities due to plasma bubbles, scintillation, and acoustic/gravity waves are studied in the low-latitude ionosphere in relation to thunderstorm activity. Ionospheric total electron content (TEC) measurements from the Low Latitude Ionospheric Sensor Network (LISN) and lightning measurements from the World-Wide Lightning Location Network (WWLLN) are compared during two summer months and two winter months in 2013. Large amplitude fluctuations in TEC are found to have a strongly-peaked diurnal pattern in the late evening and nighttime summer ionosphere. The maximum magnitude and coverage area of these fluctuations increases as thunderstorm area increases. Summertime mid-amplitude fluctuations do not exhibit the samemore » diurnal variation, but do increase in magnitude and coverage area as thunderstorm area increases. Wintertime ionospheric fluctuations do not appear to be related to thunderstorm activity. Lastly, these findings show that thunderstorms have an observable effect on magnitude and coverage area of ionospheric fluctuations.« less

High Latitude Scintillation Monitoring at UHF with the COMMX Experiment on TACSat4

NASA Astrophysics Data System (ADS)

Bernhardt, P. A.; Siefring, C. L.; Akins, K.; Nurnberger, M.

2013-12-01

UHF Beacon Transmissions at 253 MHz have provided high latitude scintillation monitoring from Gakona Alaska using the COMMX instrument on TACSat4. TACSat4 was constructed by the Naval Research Laboratory and was launched in September 2011 as an experimental communications satellite. Ground UHF transmissions are uplinked to TACSat4 using the 4 meter diameter antenna deployed to view the earth. These signals are coherently translated to other UHF frequency to be rebroadcast to the ground. Scintillation monitoring is achieved by taking the 401.25 MHz signals from ground DORIS beacons located in Cold Bay, Alaska; Yellowknife, Canada; Kauai, Hawaii; and Soccoro Island, Mexico. These signals are translated to 253 MHz and broadcast with the 4 meter antenna pointed to the UHF receiver located at Gakona, Alaska. The satellite antenna gain is 18 dB in this UHF band and the transmitter power is 2 Watts. The satellite is in an elliptical orbit with an inclination of 63 degrees and a perigee of 12,000 km. Doppler frequency shifts allow separation of each uplink from the ground DORIS beacons. This new scintillation monitoring system has been used to detect natural and artificial field aligned irregularity effects on the amplitude and phase of UHF carriers where typical scintillation amplitudes are 2dB or less. Using the HAARP transmitter in Alaska, TACSat4 was used to discover the artificial ionization clouds produce scintillation with as much as 16 dB and amplitude indices S4 greater than unity. This is the first demonstration of significant effects on radio scintillations using high power HF radio waves to disturb the ionosphere.

Formation of ionospheric irregularities over Southeast Asia during the 2015 St. Patrick's Day storm

NASA Astrophysics Data System (ADS)

Spogli, Luca; Cesaroni, Claudio; Di Mauro, Domenico; Pezzopane, Michael; Alfonsi, Lucilla; Musicò, Elvira; Povero, Gabriella; Pini, Marco; Dovis, Fabio; Romero, Rodrigo; Linty, Nicola; Abadi, Prayitno; Nuraeni, Fitri; Husin, Asnawi; Le Huy, Minh; Lan, Tran Thi; La, The Vinh; Pillat, Valdir Gil; Floury, Nicolas

2016-12-01

We investigate the geospace response to the 2015 St. Patrick's Day storm leveraging on instruments spread over Southeast Asia (SEA), covering a wide longitudinal sector of the low-latitude ionosphere. A regional characterization of the storm is provided, identifying the peculiarities of ionospheric irregularity formation. The novelties of this work are the characterization in a broad longitudinal range and the methodology relying on the integration of data acquired by Global Navigation Satellite System (GNSS) receivers, magnetometers, ionosondes, and Swarm satellites. This work is a legacy of the project EquatoRial Ionosphere Characterization in Asia (ERICA). ERICA aimed to capture the features of both crests of the equatorial ionospheric anomaly (EIA) and trough (EIT) by means of a dedicated measurement campaign. The campaign lasted from March to October 2015 and was able to observe the ionospheric variability causing effects on radio systems, GNSS in particular. The multiinstrumental and multiparametric observations of the region enabled an in-depth investigation of the response to the largest geomagnetic storm of the current solar cycle in a region scarcely reported in literature. Our work discusses the comparison between northern and southern crests of the EIA in the SEA region. The observations recorded positive and negative ionospheric storms, spread F conditions, scintillation enhancement and inhibition, and total electron content variability. The ancillary information on the local magnetic field highlights the variety of ionospheric perturbations during the different storm phases. The combined use of ionospheric bottomside, topside, and integrated information points out how the storm affects the F layer altitude and the consequent enhancement/suppression of scintillations.

Dispersive Phase in the L-band InSAR Image Associated with Heavy Rain Episodes

NASA Astrophysics Data System (ADS)

Furuya, M.; Kinoshita, Y.

2017-12-01

Interferometric synthetic aperture radar (InSAR) is a powerful geodetic technique that allows us to detect ground displacements with unprecedented spatial resolution, and has been used to detect displacements due to earthquakes, volcanic eruptions, and glacier motion. In the meantime, due to the microwave propagation through ionosphere and troposphere, we often encounter non-negligible phase anomaly in InSAR data. Correcting for the ionsphere and troposphere is therefore a long-standing issue for high-precision geodetic measurements. However, if ground displacements are negligible, InSAR image can tell us the details of the atmosphere.Kinoshita and Furuya (2017, SOLA) detected phase anomaly in ALOS/PALSAR InSAR data associated with heavy rain over Niigata area, Japan, and performed numerical weathr model simulation to reproduce the anomaly; ALOS/PALSAR is a satellite-based L-band SAR sensor launched by JAXA in 2006 and terminated in 2011. The phase anomaly could be largely reproduced, using the output data from the weather model. However, we should note that numerical weather model outputs can only account for the non-dispersive effect in the phase anomaly. In case of severe weather event, we may expect dispersive effect that could be caused by the presence of free-electrons.In Global Navigation Satellite System (GNSS) positioning, dual frequency measurements allow us to separate the ionospheric dispersive component from tropospheric non-dispersive components. In contrast, SAR imaging is based on a single carrier frequency, and thus no operational ionospheric corrections have been performed in InSAR data analyses. Recently, Gomba et al (2016) detailed the processing strategy of split spectrum method (SSM) for InSAR, which splits the finite bandwidth of the range spectrum and virtually allows for dual-frequency measurements.We apply the L-band InSAR SSM to the heavy rain episodes, in which more than 50 mm/hour precipitations were reported. We report the presence of

Low-Latitude Ionospheric Density Irregularities and Associated Scintillations Investigated by Combining COSMIC RO and Ground-Based Global Positioning System Observations Over a Solar Active Period

NASA Astrophysics Data System (ADS)

Yang, Zhe; Liu, Zhizhao

2018-05-01

This study for the first time presents a locally integrated analysis of occurrences of ionospheric E and F region irregularities/scintillations in southeast China, by employing radio occultation (RO) profile data retrieved from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites and observations from a ground-based Global Navigation Satellite System receiver over a solar active period from 2014 to 2015. Their occurrences in both nighttime and daytime were examined by using both amplitude scintillation index (S4) and the rate of change of total electron content index. It is found that (1) F region irregularities occurred predominantly during 20-03 local time (LT) and exhibited maximum (minimum) during equinoxes (solstices) and equinoctial (solstice) asymmetry. Their geographic mapping reveals the maximum occurrence in the westward tilted structure of equatorial plasma bubbles. In addition, the altitude-time variations indicate that their occurrences at higher altitudes were prevailing at 20-22 LT. (2) The E region irregularities were found prominently during 15-00 LT at altitudes of 90-110 km with an even geographic distribution. Their occurrences with maximum in summer (May-August) were distinctly detected by RO observations but insignificantly by ground-based observations. (3) By examining simultaneous observations of E and F region irregularities, it is found that they appeared absent during 21-00 LT and predominant after midnight. This could be related to the weakening/disruption of sporadic E (Es) layers during the development of equatorial plasma bubbles. A sign of coupling of E and F regions during nighttime is likely revealed from RO profile data.

The Canadian High Arctic Ionospheric Network (CHAIN)

NASA Astrophysics Data System (ADS)

Jayachandran, P. T.; Langley, R. B.; MacDougall, J. W.; Mushini, S. C.; Pokhotelov, D.; Chadwick, R.; Kelly, T.

2009-05-01

Polar cap ionospheric measurements are important for the complete understanding of the various processes in the solar wind - magnetosphere - ionosphere (SW-M-I) system as well as for space weather applications. Currently the polar cap region is lacking high temporal and spatial resolution ionospheric measurements because of the orbit limitations of space-based measurements and the sparse network providing ground- based measurements. Canada has a unique advantage in remedying this shortcoming because it has the most accessible landmass in the high Arctic regions and the Canadian High Arctic Ionospheric Network (CHAIN) is designed to take advantage of Canadian geographic vantage points for a better understanding of the Sun-Earth system. CHAIN is a distributed array of ground-based radio instruments in the Canadian high Arctic. The instruments components of CHAIN are ten high data-rate Global Positioning System ionospheric scintillation and total electron content monitors and six Canadian Advanced Digital Ionosondes. Most of these instruments have been sited within the polar cap region except for two GPS reference stations at lower latitudes. This paper briefly overviews the scientific capabilities, instrument components, and deployment status of CHAIN.

Ionospheric effects on DInSAR measurements of interseismic deformation in China

NASA Astrophysics Data System (ADS)

Gong, W.; Shan, X.; Song, X.; Liao, H.; Meyer, F. J.

2017-12-01

Interseismic deformation signals are small ground displacement that is critical to monitor the strain accumulates of major faults to foresee the potential seismic hazard. Accurate measurements of surface deformation could help recognize and interpret even subtle displacement and to give a better understanding of active fault behavior. However, the value and applicability of InSAR for inter-seismic monitoring problems is limited by the influence of temporal decorrelation and electromagnetic path delay variations (atmospheric disturbance), both reducing the sensitivity and accuracy of the technique. Ionospheric signal, a major part of atmospheric disturbance in InSAR, is related to the density of free electrons along the ray path, thus, that is dependent on the SAR signal frequency. Ionosphere induced phase distortions can lead to azimuth/range defocusing, geometry distortions and interferometric phase distortions. Some ionosphere phenomenon have been reported more severe at equatorial region and polar zones, e.g., ionosphere irregularity, while for middle latitude regions like West China it has not been thoroughly analyzed. Thus, this study is focus on the evaluation of ionosphere impacts in middle latitude zone, and its impacts in monitoring interseismic deformation in West China. The outcome would be useful to provide an empiric prior error condition of ionosphere disturbance, which can further benefit InSAR result interpretation and geophysical inversion, as well as the SAR data arrangement in future operational-(cloud) InSAR processing system. The study focus on two parts: 1. We will analyze the temporal-spatial variation of ionosphere and its magnitude at middle latitude zone, and investigate its impacts to current satellite SAR (C-band (Sentinel-1) and L-band (ALOS2) dataset) in earthquake-related deformation studies, especially inter-seismic study. 2. Ionosphere phase patterns at mid latitudes is typically small and the structure is compatibly smooth. This

Longitudinal Variations of Low-Latitude Ionospheric Irregularities during the 2015 St. Patrick's Day Storm

NASA Astrophysics Data System (ADS)

Pi, X.; Vergados, P.

2017-12-01

GPS data from more than 2000 globally distributed ground-based stations are processed to generate Global Map of Ionospheric Irregularities and Scintillation (GMIIS) at 5-minite cadence for the 2015 St. Patrick's Day Storm. The time sequence of GMIIS provides global snapshots of evolving ionospheric irregularities that are helpful in investigations of small-scale ionospheric perturbations globally. Such data from selected stations at longitudes distributed around the globe are also analyzed to investigate longitudinal variations of low-latitude ionospheric irregularities (LLII) during the storm. Prior to the storm day, The GPS data show typical seasonal (March equinox) activities of LLII during evening hours in different longitude regions, i.e., active in American through Asian longitudes but relatively inactive in the Pacific sector. The data also reveal dramatic changes in LLII during the storm main phase (17 March 2015) and recovery phase (18-19 March 2015). While remaining inactive in the Pacific region, LLII have gone through complicated variations in the longitude regions of high scintillation season. The variations include active, weakened or suppressed, or post-midnight triggering during the storm main phase and recovery phase depending on specific longitude. To understand possible responsible causes of these variations in different longitudes, the Global Assimilative Ionospheric Model (GAIM) is used to reproduce ambient ionospheric state and its disturbances. For this storm study, GAIM assimilates GPS data from about 650 globally distributed stations and from spaceborne receivers onboard the COSMIC satellites. The global assimilative modeling enables us to investigate the changes of the equatorial ionospheric anomaly (EIA) and corresponding ionospheric dynamical processes in the concerned longitudes. This presentation will combine pictures of small- and large-scale ionospheric perturbations and attempt to obtain insight into mechanisms that drive LLII

GNSS Active Network of West of Sao Paulo State Applied to Ionosphere Monitoring

NASA Astrophysics Data System (ADS)

Aguiar, C. R.; Camargo, P. D.

2008-12-01

In Brazil, a research project of atmospheric studies from reference stations equipped with dual frequency GNSS receivers is in initial phase. These stations have composed the GNSS Active Network of West Sao Paulo State (Network-GNSS-SP) and have been broadcasting GNSS data in real time. Network-GNSS-SP is in tests phase and it's the first Brazilian network to provide GNSS measurements in real time. In Spatial Geodesy Study Brazilian Group (GEGE) has been researched the ionosphere effects on L band signal, as well as the GPS potential on ionosphere dynamic monitoring and, consequently, the application of this one to spatial geophysics study, besides dynamic ionosphere modeling. An algorithm based on Kalman filter has been developed for ionosphere modeling at low latitude regions and estimation of ionospheric parameters as absolute vertical TEC (VTEC) for the monitoring of ionosphere behavior. The approach used in this study is to apply a model for the ionospheric vertical delay. In the algorithm, the ionospheric vertical delay is modeled and expanded by Fourier series. In this paper has been realized on-line processing of the Network-GNSS-SP data and the initial results reached with the algorithm can already be analyzed. The results show the ionospheric maps created from real time TEC estimates.

Assessment of scintillation proxy maps for a scintillation study during geomagnetically quiet and disturbed conditions over Uganda

NASA Astrophysics Data System (ADS)

Amabayo, Emirant B.; Jurua, Edward; Cilliers, Pierre J.

2017-02-01

The objective of this paper is demonstrate the validity and usefulness of scintillation proxies derived from IGS data, through its comparison with data from dedicated scintillation monitors and its application to GNSS scintillation patterns. The paper presents scintillation patterns developed by using data from the dedicated scintillation monitors of the scintillation network decision aid (SCINDA) network, and proxy maps derived from IGS GPS data for 2011 and 2012 over low latitude stations in Uganda. The amplitude and phase scintillation indicies (S4 and σΦ) were obtained from the Novatel GSV4004B ionospheric scintillation and total electron content (TEC) monitor managed by SCINDA at Makerere (0.340N, 32.570E). The corresponding IGS GPS proxy data were obtained from the receivers at Entebbe (0.040N, 32.440E) and Mbarara (0.600S, 30.740E). The derived amplitude (S4p) and phase (sDPR) scintillation proxy maps were compared with maps of S4 and σΦ during geomagnetic storms (moderate and strong) and geomagnetically quiet conditions. The scintillation patterns using S4 and σΦ and their respective proxies revealed similar diurnal and seasonal patterns of strong scintillation occurrence. The peaks of scintillation occurrence with mean values in the range 0.3 < (S4p , sDPR) ≤ 0.6 were observed during nighttime (17:00-22:00 UT) and in the months of March-April and September-October. The results also indicate that high level scintillations occur during geomagnetically disturbed (moderate and strong) and quiet conditions over the Ugandan region. The results show that SCINDA and IGS based scintillation patterns reveal the same nighttime and seasonal occurrence of irregularities over Uganda irrespective of the geomagnetic conditions. Therefore, the amplitude and phase scintillation proxies presented here can be used to fill gaps in low-latitude data where there are no data available from dedicated scintillation receivers, irrespective of the geomagnetic conditions.

Excitation of earth-ionosphere waveguide in the ELF and lower VLF bands by modulated ionospheric current. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Field, E.C.; Bloom, R.M.

1993-05-21

In this report the authors use the principal of reciprocity in conjunction with a full-wave propagation code to calculate ground-level fields excited by ionospheric currents modulated at frequencies between 50 and 100 Hz with HF heaters. Their results show the dependence on source orientation, altitude, and dimension and therefore pertain to experiments using the HIPAS or HAARP ionospheric heaters. In the end-fire mode, the waveguide excitation efficiency of an ELF HED in the ionosphere is up to 20 dB greater than for a ground-based antenna, provided its altitude does not exceed 80-to-90 km. The highest efficiency occurs for a sourcemore » altitude of around 70 km; if that altitude is raised to 100 km, the efficiency drops by about 20 dB in the day and 10 dB at night. That efficiency does not account for the greater conductivity modulation that might be achieved at altitudes greater than 70 km, however. The trade-off between the altitude dependencies of the excitation efficiency and maximum achievable modulation depends on the ERP of the HF heater, the optimum altitude increasing with increasing ERP. For HIPAS the best modulation altitude is around 70 km, whereas for HAARP there might be marginal value in modulating at attitudes as high as 100 Km. Ionospheric modification, Ionospheric currents, Ionospheric heating.« less

Assessment of Ionospheric Spatial Decorrelation for CAT I GBAS in Equatorial Region at Nominal days: Data Selection and Bias Removal

NASA Astrophysics Data System (ADS)

Chang, H.; Lee, J.

2017-12-01

Ground-based augmentations of global positioning system (GBAS) provide the user with the integrity parameter, standard deviation of vertical ionospheric gradient (σvig), to ensure integrity. σvig value currently available in CAT I GBAS is derived from the data collected from the reference stations located on the US mainland and have a value of 4 mm/km. However, since the equatorial region near the geomagnetic equator is relatively more active in the ionosphere than the mid-latitude region, there is a limit to applying σvig used in the mid-latitude region on the equatorial region. Also, since the ionospheric phenomena of daytime and nighttime in the equatorial region are significantly different, it is necessary to apply σvig whilst distinguishing the time zone. This study presents a method for obtaining standard deviation of vertical ionospheric gradient in the equatorial region at nominal days considering the equatorial ionosphere environment. We used the data collected from the Brazilian region near the geomagnetic equator in the nominal days. One of the distinguishing features of the equatorial ionosphere environment from the mid-latitude ionosphere environment is that the scintillation event occurs frequently. Therefore, the days used for the analysis were selected not only by geomagnetic indexes Kp (Planetary K index) and Dst (Disturbance storm index), but also by S4 (Scintillation index) which indicates scintillation event. In addition, unlike the ionospheric delay bias elimination method used in the mid-latitude region, the `Long-term ionospheric anomaly monitor (LTIAM)' used in this study utilized the bias removal method that applies different bias removal standards according to IPP (Ionospheric pierce point) distance in consideration of ionospheric activity. As a result, σvig values which are conservative enough to bound ionosphere spatial decorrelation for the equatorial region in nominal days are 8 mm/km for daytime and 19 mm/km for nighttime

Handling cycle slips in GPS data during ionospheric plasma bubble events

NASA Astrophysics Data System (ADS)

Banville, S.; Langley, R. B.; Saito, S.; Yoshihara, T.

2010-12-01

During disturbed ionospheric conditions such as the occurrence of plasma bubbles, the phase and amplitude of the electromagnetic waves transmitted by GPS satellites undergo rapid fluctuations called scintillation. When this phenomenon is observed, GPS receivers are more prone to signal tracking interruptions, which prevent continuous measurement of the total electron content (TEC) between a satellite and the receiver. In order to improve TEC monitoring, a study was conducted with the goal of reducing the effects of signal tracking interruptions by correcting for "cycle slips," an integer number of carrier wavelengths not measured by the receiver during a loss of signal lock. In this paper, we review existing cycle-slip correction methods, showing that the characteristics associated with ionospheric plasma bubbles (rapid ionospheric delay fluctuations, data gaps, increased noise, etc.) prevent reliable correction of cycle slips. Then, a reformulation of the "geometry-free" model conventionally used for ionospheric studies with GPS is presented. Geometric information is used to obtain single-frequency estimates of TEC variations during momentary L2 signal interruptions, which also provides instantaneous cycle-slip correction capabilities. The performance of this approach is assessed using data collected on Okinawa Island in Japan during a plasma bubble event that occurred on 23 March 2004. While an improvement in the continuity of TEC time series is obtained, we question the reliability of any cycle-slip correction technique when discontinuities on both GPS legacy frequencies occur simultaneously for more than a few seconds.

Ionospheric Variability as Observed by the CTECS and CORISS Sensors

NASA Astrophysics Data System (ADS)

Bishop, R. L.; Redding, M.; Straus, P. R.

2013-12-01

The Compact Total Electron Content Sensor (CTECS) is a GPS radio occultation instrument designed for cubesat platforms that utilizes a COTS receiver, modified firmware, and a custom designed antenna. CTECS was placed on the Pico Satellite Solar Cell Testbed 2 (PSSC2) nanosat that was installed on the Space Shuttle Atlantis (STS-135). PSSC2 was successfully released from the shuttle on 20 July 2011 near 380 km altitude. Because of attitude control and power issues, only 13.5 hours of data was collected during its approximately 5-month mission life. The C/NOFS Occultation Receiver for Ionospheric Sensing and Specification (CORISS) GPS radio occultation sensor on the C/NOFS satellite has collected data nearly continuously from May 2008 to June 2013. Both CTECS and CORISS obtain Total Electron Content and scintillation data. In this presentation the CTECS data is first validated against CORISS and available ground-based observations. Then combining the CTECS and CORISS data, low and mid latitude ionospheric variability including scintillation events is presented.

Exploiting LF/MF signals of opportunity for lower ionospheric remote sensing

NASA Astrophysics Data System (ADS)

Higginson-Rollins, Marc A.; Cohen, Morris B.

2017-08-01

We introduce a method to diagnose and track the D region ionosphere (60-100 km). This region is important for long-distance terrestrial communication and is impacted by a variety of geophysical phenomena, but it is traditionally very difficult to detect. Modern remote sensing methods used to study the D region are predominately near the very low frequency (VLF, 3-30 kHz) band, with some work also done in the high-frequency and very high frequency bands (HF/VHF, 3-300 MHz). However, the frequency band between VLF and HF has been largely ignored as a diagnostic tool for the ionosphere. In this paper, we evaluate the use of 300 kHz radio reflections as a diagnostic tool for characterizing the D region of the ionosphere. We present radio receiver data, analyze diurnal trends in the signal from these transmitters, and identify ionospheric disturbances impacting LF/MF propagation. We find that 300 kHz remote sensing may allow a unique method for D region diagnostics compared to both the VLF and HF/VHF frequency bands, due to a more direct ionospheric reflection coefficient calculation method with high temporal resolution without the use of forward modeling.

Real-time Scintillation Monitoring in Alaska from a Longitudinal Chain of ASTRA's SM-211 GPS TEC and Scintillation Receivers

NASA Astrophysics Data System (ADS)

Crowley, G.; Azeem, S. I.; Reynolds, A.; Santana, J.; Hampton, D. L.

2013-12-01

Amplitude and phase scintillation can cause serious difficulties for GPS receivers. Intense scintillation can cause loss of lock. High latitude studies generally show that phase scintillation can be severe, but the amplitude scintillation tends to be small. The reason for this is not yet understood. Furthermore, the actual causes of the ionospheric irregularities that produce high latitude scintillation are not well understood. While the gradient drift instability is thought to be important in the F-region, there may be other structures present in either the E- or F-regions. The role of particle precipitation is also not well understood. Four of ASTRA's CASES GPS receivers were deployed in Alaska to demonstrate our ability to map scintillation in realtime, to provide space weather services to GPS users, and to initiate a detailed investigation of these effects. These dual-frequency GPS receivers measure total electron content (TEC) and scintillation. The scintillation monitors were deployed in a longitudinal chain at sites in Kaktovic, Fort Yukon, Poker Flat, and Gakona. Scintillation statistics show phase scintillations to be largest at Kaktovic and smallest at Gakona. We present GPS phase scintillation and auroral emission results from the Alaska chain to characterize the correspondence between scintillation and auroral features, and to investigate the role of high latitude auroral features in driving the phase scintillations. We will also present data showing how phase scintillation can cause other GPS receivers to lose lock. The data and results are particularly valuable because they illustrate some of the challenges of using GPS systems for positioning and navigation in an auroral region like Alaska. These challenges for snowplough drivers were recently highlighted, along with the CASES SM-211 space weather monitor, in a special video in which ASTRA and three other small businesses were presented with an entrepreneurial award from William Shatner (http://youtu.be/bIVKEQH_YPk).

Research of Ionospheric Scintillation in Asia (RISA)

DTIC Science & Technology

2014-03-01

5a. CONTRACT NUMBER FA2386-11-1-4087 5b. GRANT NUMBER Grant AOARD-114087 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Dr Nitin...11-1-4087 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Nitin Kumar Tripathi 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK...anomaly, as these locations experience the strongest global levels of scintillation (Groves et al., 1997). As a result, large quantities of data sets

Using GPS TEC measurements to probe ionospheric spatial spectra at mid-latitudes

NASA Astrophysics Data System (ADS)

Lay, E. H.; Parker, P. A.; Light, M. E.; Carrano, C. S.; Debchoudhury, S.; Haaser, R. A.

2017-12-01

The physics of how random ionospheric structure causes signal degradation is well understood as weak forward scattering through an effective diffraction grating created by plasma irregularities in the ionosphere. However, the spatial scale spectrum of those irregularities required for input into scintillation models and models of traveling ionospheric disturbances is poorly characterized, particularly at the kilometer to tens of kilometer scale lengths important for very-high-frequency (VHF) scintillation prediction. Furthermore, the majority of characterization studies have been performed in low-latitude or high-latitude regions where geomagnetic activity dominates the physical processes. At mid-latitudes, tropospheric and geomagnetic phenomena compete in disturbing the ionosphere, and it is not well understood how these multiple sources affect the drivers that influence the spatial spectrum. In this study, we are interested in mid-latitude electron density irregularities on the order of 10s of kilometers that would affect VHF signals. Data from the GPS networks Japan GEONET and the Plate Boundary Observatory (PBO, UNAVCO) in the western United States were analyzed for this study. Japan GEONET is a dense network of GPS receivers (station spacing of tens of km), with fairly evenly spaced positions over all of Japan. The PBO, on the other hand, has several pockets of extremely dense coverage (station spacing within a few km), but is less dense on average. We analyze a day with a large solar storm (2015/03/17, St. Patrick's Day Storm) to allow high scintillation potential at mid-latitudes, a day with low geomagnetic activity and low thunderstorm activity (2016/01/31), and a day with low geomagnetic activity and high thunderstorm activity (2015/08/02). We then perform two-dimensional spatial analyses on the TEC data from these two networks on scale lengths of 20 to 200 km to infer the spatial scale spectra.

An Initial Investigation of Ionospheric Gradients for Detection of Ionospheric Disturbances over Turkey

NASA Astrophysics Data System (ADS)

Koroglu, Meltem; Arikan, Feza; Koroglu, Ozan

2015-04-01

Ionosphere is an ionized layer of earth's atmosphere which affect the propagation of radio signals due to highly varying electron density structure. Total Electron Content (TEC) and Slant Total Electron Content (STEC) are convenient measures of total electron density along a ray path. STEC model is given by the line integral of the electron density between the receiver and GPS satellite. TEC and STEC can be estimated by observing the difference between the two GPS signal time delays that have different frequencies L1 (1575 MHz) and L2 (1227 MHz). During extreme ionospheric storms ionospheric gradients becomes larger than those of quiet days since time delays of the radio signals becomes anomalous. Ionosphere gradients can be modeled as a linear semi-infinite wave front with constant propagation speed. One way of computing the ionospheric gradients is to compare the STEC values estimated between two neighbouring GPS stations. In this so-called station-pair method, ionospheric gradients are defined by dividing the difference of the time delays of two receivers, that see the same satellite at the same time period. In this study, ionospheric gradients over Turkey are computed using the Turkish National Permanent GPS Network (TNPGN-Active) between May 2009 and September 2012. The GPS receivers are paired in east-west and north-south directions with distances less than 150 km. GPS-STEC for each station are calculated using IONOLAB-TEC and IONOLAB-BIAS softwares (www.ionolab.org). Ionospheric delays are calculated for each paired station for both L1 and L2 frequencies and for each satellite in view with 30 s time resolution. During the investigation period, different types of geomagnetic storms, Travelling Ionospheric Disturbances (TID), Sudden Ionospheric Disturbances (SID) and various earthquakes with magnitudes between 3 to 7.4 have occured. Significant variations in the structure of station-pair gradients have been observed depending on location of station-pairs, the

An assessment of the application of in situ ion-density data from DMSP to modeling of transionospheric scintillation

NASA Astrophysics Data System (ADS)

Secan, James A.; Reinleitner, Lee A.; Bussey, Robert M.

1990-03-01

Modern military communication, navigation, and surveillance systems depend on reliable, noise-free transionospheric radio frequency channels. They can be severely impacted by small scale electron-density irregularities in the ionosphere, which cause both phase and amplitude scintillation. Basic tools used in planning and mitigation schemes are climatological in nature and thus may greatly over- and under-estimate the effects of scintillation in a given scenario. The results are summarized of a 3 year investigation into the feasibility of using in-situ observations of the ionosphere from the USAF DMSP satellite to calculate estimates of irregularity parameters that could be used to update scintillation models in near real time. Estimates for the level of intensity and phase scintillation on a transionospheric UHF radio link in the early evening auroral zone were calculated from DMSP Scintillation Meter (SM) data and compared to the levels actually observed. The intensity scintillation levels predicted and observed compared quite well, but the comparison with the phase scintillation data was complicated by low-frequency phase noise on the UHF radio link. Results are presented from analysis of DMSP SSIES data collected near Kwajalein Island in conjunction with a propagation-effects experiment. Preliminary conclusions to the assessment study are: (1) the DMSP SM data can be used to make quantitative estimates of the level of scintillation at auroral latitudes, and (2) it may be possible to use the data as a qualitative indicator of scintillation activity levels at equatorial latitudes.

Total Electron Content Retrieved From L-Band Radiometers and Potential Improvements to the IGS Model

NASA Astrophysics Data System (ADS)

Soldo, Yan; Hong, Liang; El-Nimri, Salem; Le Vine, David M.

2018-04-01

In recent years, several L-band microwave instruments have been launched into Earth's orbit to measure soil moisture and ocean salinity (e.g., Soil Moisture and Ocean Salinity [SMOS], Aquarius, and Soil Moisture Active/Passive [SMAP]). As the microwave signal travels through the ionosphere, the polarization vector rotates (Faraday rotation) and it is possible to estimate the total electron content (TEC) along the path by measuring this change. A comparison is presented of the TEC retrieved from Aquarius and SMAP over the ocean with the values provided by the IGS (International Global Navigation Satellite System Service (GNSS)). The TEC retrieved from Aquarius and SMAP measurements show good agreement with each other and, on a global scale, are in agreement with the TEC provided by the IGS. However, there are cases in which the TEC from the two satellite sensors are in good agreement with each other but differ significantly from the IGS TEC. The comparison suggests that the L-band instruments are a reliable source of TEC over the ocean and could be a valuable supplementary source of TEC values that could be assimilated in the IGS models, especially over the ocean, where GNSS ground stations are sparse.

GPS and GLONASS 1 Hz phase rate observations to study high latitudes ionospheric irregularities

NASA Astrophysics Data System (ADS)

Ghoddousi-Fard, R.; Prikryl, P.; Jacobsen, K. S.; Lahaye, F.

2016-12-01

It has been shown that dual frequency 1 Hz GPS phase rate observations can serve as a promising proxy for phase scintillation over high latitudes (see e.g. Ghoddousi-Fard et al., 2013, 2015). However signals from other GNSS constellations including GLONASS have been available and widely used for positioning applications. Usage of additional GNSS constellations should allow improved sampling of the ionosphere, a critical advantage to study small scale ionospheric irregularities over high latitudes. Migration of global GPS networks to multi-GNSS are now underway such as International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) and other national, public and private sector networks. In this presentation, GPS and GLONASS observations from high latitude MGEX stations as well as a dense regional network over Norway are used to map high latitude ionospheric irregularities by means of standard deviation of phase rate variations. Occurrence of GPS phase irregularities as a function of magnetic latitude and local time are compared with those from both GPS and GLONASS. By including 1 Hz GLONASS measurements at about 185 stations over Norway during geomagnetic storm of March 17-18, 2015, this study complements a recently submitted paper that examined the GPS phase scintillation occurrence in the context of solar wind coupling to the magnetosphere-ionosphere system and auroral electrojet currents (Prikryl et al., 2016). Ghoddousi-Fard et al. (2013). GPS phase difference variation statistics: A comparison between phase scintillation index and proxy indices. Adv. Space Res., 52, 1397-1405, doi: 10.1016/j.asr.2013.06.035. Ghoddousi-Fard et al. (2015). Analysis of GPS phase rate variations in response to geomagnetic field perturbations over the Canadian auroral region. Adv. Space Res., 55, 1372-1381, doi: 10.1016/j.asr.2014.12.021. Prikryl et al. (2016). GPS phase scintillation at high latitudes during the geomagnetic storm of March 17-18, 2015, submitted to J. Geophys. Res

Application of the nudged elastic band method to the point-to-point radio wave ray tracing in IRI modeled ionosphere

NASA Astrophysics Data System (ADS)

Nosikov, I. A.; Klimenko, M. V.; Bessarab, P. F.; Zhbankov, G. A.

2017-07-01

Point-to-point ray tracing is an important problem in many fields of science. While direct variational methods where some trajectory is transformed to an optimal one are routinely used in calculations of pathways of seismic waves, chemical reactions, diffusion processes, etc., this approach is not widely known in ionospheric point-to-point ray tracing. We apply the Nudged Elastic Band (NEB) method to a radio wave propagation problem. In the NEB method, a chain of points which gives a discrete representation of the radio wave ray is adjusted iteratively to an optimal configuration satisfying the Fermat's principle, while the endpoints of the trajectory are kept fixed according to the boundary conditions. Transverse displacements define the radio ray trajectory, while springs between the points control their distribution along the ray. The method is applied to a study of point-to-point ionospheric ray tracing, where the propagation medium is obtained with the International Reference Ionosphere model taking into account traveling ionospheric disturbances. A 2-dimensional representation of the optical path functional is developed and used to gain insight into the fundamental difference between high and low rays. We conclude that high and low rays are minima and saddle points of the optical path functional, respectively.

High Latitude Scintillations during the ICI-4 Rocket Campaign.

NASA Astrophysics Data System (ADS)

Patra, S.; Moen, J.

2015-12-01

We present the first results from the Norwegian ICI-4 sounding rocket campaign in February 2015. The ICI-4 was launched into F-region auroral blobs from the Andøya Space Center. The multi needle langmuir probe (m-NLP) on board the rocket sampled the ionospheric density structures at a sub-meter spatial resolution. A multi-phase screen model has been developed to estimate the scintillations from the density measurements acquired on-board spacecrafts. The phase screen model is validated and the comparison of the estimated values with scintillations measured by ground receivers during the campaign will be presented. A combination of scintillation receivers in Svalbard and surrounding areas as well as all sky imagers at Ny Ålesund, Longyerbyen, and Skibotn are used to improve the performance of the model.

Radar detection during scintillation. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knepp, D.L.; Reinking, J.T.

1990-04-01

Electromagnetic signals that propagate through a disturbed region of the ionosphere can experience scattering which can cause fluctuations in the received amplitude, phase, and angle-of-arrival. This report considers the performance of a radar that must operate through a disturbed propagation environment such as might occur during strong equatorial scintillation, during a barium release experiment or after a high altitude nuclear detonation. The severity of the channel disturbance is taken to range from weak scattering where the signal quadrature components are uncorrelated Gaussian variates. The detection performance of noncoherent combining is compared to that of double threshold (M out of N)more » combining under various levels of scintillation disturbance. Results are given for detection sensitivity as a function of the scintillation index and the ratio of the radar hopping bandwidth to the channel bandwidth. It is shown that both types of combining can provide mitigation of fading, and that noncoherent combining generally enjoys an advantage in detection sensitivity of about 2 dB. This work serves as a quantitative guideline to the advantages and disadvantages of certain types of detection strategies during scintillation and is, therefore, useful in the radar design process. However, a detailed simulation of the radar detection algorithms is necessary to evaluate a radar design strategy to predict performance under scintillation conditions.« less

Study of equatorial plasma bubbles using all sky imager and scintillation technique from Kolhapur station: a case study

NASA Astrophysics Data System (ADS)

Sharma, A. K.; Gurav, O. B.; Gaikwad, H. P.; Chavan, G. A.; Nade, D. P.; Nikte, S. S.; Ghodpage, R. N.; Patil, P. T.

2018-04-01

The nightglow observations of OI 630.0 nm emission carried out from low latitude station Kolhapur using All Sky Imager (ASI) with 140° field of view (FOV) for the month of April 2011 are used. The images were processed to study the field aligned irregularities often called as equatorial plasma bubbles (EPBs). The present study focuses on the occurrence of scintillation during the traversal of EPBs over ionospheric pierce point (IPP). Here we dealt with the depletion level (depth) of the EPB structures and its effect on VHF signals. We compared VHF scintillation data with airglow intensities at Ionospheric pierce point (IPP) from the same location and found that the largely depleted EPBs make stronger scintillation. From previous literature, it is believed that the small scale structures are present near the steeper walls of EPBs which often degrades the communication, the analysis presented in this paper confirms this belief.

Modelling the probability of ionospheric irregularity occurrence over African low latitude region

NASA Astrophysics Data System (ADS)

Mungufeni, Patrick; Jurua, Edward; Bosco Habarulema, John; Anguma Katrini, Simon

2015-06-01

This study presents models of geomagnetically quiet time probability of occurrence of ionospheric irregularities over the African low latitude region. GNSS-derived ionospheric total electron content data from Mbarara, Uganda (0.60°S, 30.74°E, geographic, 10.22°S, magnetic) and Libreville, Gabon (0.35°N, 9.68°E, geographic, 8.05°S, magnetic) during the period 2001-2012 were used. First, we established the rate of change of total electron content index (ROTI) value associated with background ionospheric irregularity over the region. This was done by analysing GNSS carrier-phases at L-band frequencies L1 and L2 with the aim of identifying cycle slip events associated with ionospheric irregularities. We identified at both stations a total of 699 events of cycle slips. The corresponding median ROTI value at the epochs of the cycle slip events was 0.54 TECU/min. The probability of occurrence of ionospheric irregularities associated with ROTI ≥ 0.5 TECU / min was then modelled by fitting cubic B-splines to the data. The aspects the model captured included diurnal, seasonal, and solar flux dependence patterns of the probability of occurrence of ionospheric irregularities. The model developed over Mbarara was validated with data over Mt. Baker, Uganda (0.35°N, 29.90°E, geographic, 9.25°S, magnetic), Kigali, Rwanda (1.94°S, 30.09°E, geographic, 11.62°S, magnetic), and Kampala, Uganda (0.34°N, 32.60°E, geographic, 9.29°S, magnetic). For the period validated at Mt. Baker (approximately, 137.64 km, north west), Kigali (approximately, 162.42 km, south west), and Kampala (approximately, 237.61 km, north east) the percentages of the number of errors (difference between the observed and the modelled probability of occurrence of ionospheric irregularity) less than 0.05 are 97.3, 89.4, and 81.3, respectively.

Ionospheric Irregularities Predictions and Plumes Characterization for Satellite Data Validation and Calibration

DTIC Science & Technology

2014-01-17

at São José dos Campos, São Paulo - Brazil Good S4 agreement for the 6 receivers and for moderate scintillations – no strong scintillations tested...Space Research - INPE Fundação de Ciências, Aplicações e Tecnologia Espaciais, Av. Dr. João Guilhermino, 429/11 – São José dos Campos, São Paulo ...The ionospheric plumes were characterized for 3 longitudinal sectors (east of Brazil , Peruvian coast and pacific zone)using VHF radars and algorithms

Ionospheric Anomalies of the 2011 Tohoku Earthquake with Multiple Observations during Magnetic Storm Phase

NASA Astrophysics Data System (ADS)

Liu, Yang

2017-04-01

days. Associated with geomagnetic storm at similar time, radio occultation data provided by COSMIC were deeply investigated within the whole month. It's quite different that the storm or earthquake didn't trigger scintillation burst. This is probably due to the storm occurrence local time was in noon sector, which has little impact on ionospheric irregularities increase, but help to enhance the effect of westward electricity, which on the other hand diminishes scintillation bubbles (Li et al 2008). A small geomagnetic disturbance was also found almost a week prior to the earthquake, the relationship of this event to the major earthquake is worth further discussion. Similar analysis of GNSS TECs have been done, the results indicated that it can be also referred as precursor to the major earthquake. Li G, Ning B, Zhao B, et al. Effects of geomagnetic storm on GPS ionospheric scintillations at Sanya[J]. Journal of Atmospheric and Solar-Terrestrial Physics, 2008, 70(7):1034-1045. Liu J Y, Chen Y I, Chuo Y J, et al. A statistical investigation of pre-earthquake ionospheric anomaly[J]. Journal of Geophysical Research Atmospheres, 2006, 111(A5). Liu J Y, Sun Y Y. Seismo-traveling ionospheric disturbances of ionograms observed during the 2011 Mw 9.0 Tohoku Earthquake[J]. Earth, Planets and Space, 2011, 63(7):897-902. Zhao B, Wang M, Yu T, et al. Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake?[J]. Journal of Geophysical Research Atmospheres, 2008, 113(A11):A11304. Pulinets S A. Seismic activity as a source of the ionospheric variability [J]. Advances in Space Research, 1998, 22(6):903-906.

Scintillation Effects on Space Shuttle GPS Data

NASA Technical Reports Server (NTRS)

Goodman, John L.; Kramer, Leonard

2001-01-01

Irregularities in ionospheric electron density result in variation in amplitude and phase of Global Positioning System (GPS) signals, or scintillation. GPS receivers tracking scintillated signals may lose carrier phase or frequency lock in the case of phase sc intillation. Amplitude scintillation can cause "enhancement" or "fading" of GPS signals and result in loss of lock. Scintillation can occur over the equatorial and polar regions and is a function of location, time of day, season, and solar and geomagnetic activity. Mid latitude regions are affected only very rarely, resulting from highly disturbed auroral events. In the spring of 1998, due to increasing concern about scintillation of GPS signals during the upcoming solar maximum, the Space Shuttle Program began to assess the impact of scintillation on Collins Miniaturized Airborne GPS Receiver (MAGR) units that are to replace Tactical Air Control and Navigation (TACAN) units on the Space Shuttle orbiters. The Shuttle Program must determine if scintillation effects pose a threat to safety of flight and mission success or require procedural and flight rule changes. Flight controllers in Mission Control must understand scintillation effects on GPS to properly diagnose "off nominal" GPS receiver performance. GPS data from recent Space Shuttle missions indicate that the signals tracked by the Shuttle MAGR manifest scintillation. Scintillation is observed as anomalous noise in velocity measurements lasting for up to 20 minutes on Shuttle orbit passes and are not accounted for in the error budget of the MAGR accuracy parameters. These events are typically coincident with latitude and local time occurrence of previously identified equatorial spread F within about 20 degrees of the magnetic equator. The geographic and seasonal history of these events from ground-based observations and a simple theoretical model, which have potential for predicting events for operational purposes, are reviewed.

High Sensitive Scintillation Observations At Very Low Frequencies

NASA Astrophysics Data System (ADS)

Konovalenko, A. A.; Falkovich, I. S.; Kalinichenko, N. N.; Olyak, M. R.; Lecacheux, A.; Rosolen, C.; Bougeret, J.-L.; Rucker, H. O.; Tokarev, Yu.

The observation of interplanetary scintillations of compact radio sources is powerful method of solar wind diagnostics. This method is developed mainly at decimeter- meter wavelengths. New possibilities are opened at extremely low frequencies (decameter waves) especially at large elongations. Now this approach is being actively developed using high effective decameter antennas UTR-2, URAN and Nancay Decameter Array. New class of back-end facility like high dynamic range, high resolution digital spectral processors, as well as dynamic spectra determination ideology give us new opportunities for distinguishing of the ionospheric and interplanetary scintillations and for observations of large number of radio sources, whith different angular sizes and elongations, even for the cases of rather weak objects.

Spatial irregularities in Jupiter's upper ionosphere observed by Voyager radio occultations

NASA Technical Reports Server (NTRS)

Hinson, D. P.; Tyler, G. L.

1982-01-01

Radio scintillations (at 3.6 and 13 cm) produced by scattering from ionospheric irregularities during the Voyager occultations are interpreted using a weak-scattering theory. Least squares solutions for ionospheric parameters derived from the observed fluctuation spectra yield estimates of (1) the axial ratio, (2) angular orientation of the anisotropic irregularities, (3) the power law exponent of the spatial spectrum of irregularities, and (4) the magnitude of the spatial variations in electron density. It is shown that the measured angular orientation of the anisotropic irregularities indicates magnetic field direction and may provide a basis for refining Jovian magnetic field models.

Precipitation Estimation Using L-Band and C-Band Soil Moisture Retrievals

NASA Technical Reports Server (NTRS)

Koster, Randal D.; Brocca, Luca; Crow, Wade T.; Burgin, Mariko S.; De Lannoy, Gabrielle J. M.

2016-01-01

An established methodology for estimating precipitation amounts from satellite-based soil moisture retrievals is applied to L-band products from the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) satellite missions and to a C-band product from the Advanced Scatterometer (ASCAT) mission. The precipitation estimates so obtained are evaluated against in situ (gauge-based) precipitation observations from across the globe. The precipitation estimation skill achieved using the L-band SMAP and SMOS data sets is higher than that obtained with the C-band product, as might be expected given that L-band is sensitive to a thicker layer of soil and thereby provides more information on the response of soil moisture to precipitation. The square of the correlation coefficient between the SMAP-based precipitation estimates and the observations (for aggregations to approximately100 km and 5 days) is on average about 0.6 in areas of high rain gauge density. Satellite missions specifically designed to monitor soil moisture thus do provide significant information on precipitation variability, information that could contribute to efforts in global precipitation estimation.

Seasonal variations of reflexibility and transmissibility of ULF waves propagating through the ionosphere of geomagnetic mid-latitudes

NASA Astrophysics Data System (ADS)

Prikner, K.

Using reference models of the daytime and night ionosphere of geomagnetic mid-latitudes in a quiescent period in summer, autumn and winter, the seasonal variation of ULF frequency characteristics of amplitude and energy correction factors of the ionosphere - vertical reflexibility, transmissibility, are studied. The existence of two frequency bands within the ULF range with different properties of ionospheric wave filtration is pointed out: (1) continuous band f 0.1-0.2 Hz with the mirror effect of the ionosphere with respect to the incident wave, but with small ionospheric absorption of wave energy; (2) the f 0.2 Hz band with resonance frequency windows and wave emissions with a sharply defined frequency structure. The seasonal variation from summer to winter indicates a decrease in wave energy absorption in the ionosphere and a slight displacement of the resonances towards higher frequencies.

TIMED/GUVI Observations of Aurora, Ionosphere, Thermosphere and Solar EUV Variations

NASA Astrophysics Data System (ADS)

Zhang, Y.; Paxton, L. J.; Schaefer, R. K.

2017-12-01

The FUV (100-200 nm) emissions from the ionosphere and thermosphere carry rich information of the density and composition of the IT system, aurora and solar EUV flux. The key emissions include atomic hydrogen line (121.6nm), atomic oxygen lines (e.g. 130.4, 135.6, 164.1 nm), atomic nitrogen lines (e.g. 120.0, 149.3, 174.3 nm), molecular nitrogen bands (LBH and VK bands) and nitric oxide ɛ bands. TIMED/GUVI data cover the nearly full FUV range and generate many space weather products (ionosphere, thermosphere, aurora and solar EUV) that extend the products from other missions (such as NASA GOLD and ICON) and help to solve some of MIT (Magnetosphere-Ionosphere-Thermosphere) science problems and serve as validation data sources for models.

Study of a coincident observation between the ROCSAT-1 density irregularity and Ascension Island scintillation

NASA Astrophysics Data System (ADS)

Liu, Y. H.; Chao, C. K.; Su, S.-Y.; Liu, C. H.

2012-10-01

A coincident observation that occurred on 24 March 2000 between the irregularity structure measured by ROCSAT-1 and the scintillation experiment at the Ascension Island has been studied. The study of scintillation statistics is carried out first, and the results show that the Nakagami distribution can portray the normalized intensity of the L-band scintillation at various S4 values, up to S4 equal to 1.4. Moreover, the departure of frequency dependence on S4 predicted by the weak scintillation is noticed due to multiple forward scattering effects. The coincident feature between the characteristics of irregularity structure and the scintillation variation are then studied. The causal relationship between the fluctuation of ion density and the scintillation variation is obtained. A numerical simulation using the parabolic wave equation has been carried out with the ROCSAT-1 data in space to compare with the ground scintillation observation. The results show the reasonable scintillation level at the coincident time to indicate a direct relationship between the irregularity structure and the scintillation in both temporal and amplitudinal variations. Finally, some assumptions and limitations of the simulation model are discussed.

St. Patrick's Day 2015 geomagnetic storm analysis based on Real Time Ionosphere Monitoring

NASA Astrophysics Data System (ADS)

García-Rigo, Alberto

2017-04-01

Alberto García-Rigo (1), David Roma-Dollase (2), Manuel Hernández-Pajares (1), Zishen Li (3), Michael Terkildsen (4), German Olivares (4), Reza Ghoddousi-Fard (5), Denise Dettmering (6), Eren Erdogan (6), Haris Haralambous (7), Yannick Béniguel (8), Jens Berdermann (9), Martin Kriegel (9), Anna Krypiak-Gregorczyk (10), Tamara Gulyaeva (11), Attila Komjathy (12), Panagiotis Vergados (12), Joachim Feltens (13,19), René Zandbergen (13), Tim Fuller-Rowell (14), David Altadill (15), Nicolas Bergeot (16), Andrzej Krankowski (17), Loukis Agrotis (18), Ivan Galkin (20), Raul Orus-Perez (21) 1. UPC-IonSAT research group, Technical University of Catalonia, Spain 2. Department of Engineering: Electronics, University of Barcelona (UB), Spain 3. Academy of Opto-Electronics, Chinese Academy of Sciences (CAS), China 4. Bureau of Meteorology, Space Weather Services, Australia 5. Canadian Geodetic Survey, Natural Resources Canada (NRCan) / Government of Canada, Canada 6. Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM), Germany 7. Frederick University Cyprus, Cyprus 8. IEEA, France 9. Institute of Communications and Navigation, DLR, Germany 10. Institute of Geodesy, UWM, Poland 11. Institute of Terrestrial Magnetism, ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Russia 12. NASA - Jet Propulsion Laboratory (JPL), California Institute of Technology, USA 13. Navigation Support Office, ESA-ESOC, Germany 14. NOAA affiliate, USA 15. Observatori de l'Ebre (OE), CSIC - Universitat Ramon Llull, 43520 Roquetes, Spain 16. Planetology and Reference Systems, Royal Observatory of Belgium (ROB), Belgium 17. Space Radio-Diagnostics Research Centre, UWM (SRRC/UWM), Poland 18. SYMBAN Limited, ESA-ESOC, Germany 19. Telespazio VEGA Deutschland GmbH c/o ESA-ESOC, Germany 20. University of Massachusetts Lowell, Space Science Lab, USA 21. Wave Interaction and Propagation Section (TEC-EEP), ESA-ESTEC, The Netherlands IAG's Real Time

First evidence of anisotropy of GPS phase slips caused by the mid-latitude field-aligned ionospheric irregularities

NASA Astrophysics Data System (ADS)

Afraimovich, E. L.; Ishin, A. B.; Tinin, M. V.; Yasyukevich, Yu. V.; Jin, S. G.

2011-05-01

The mid-latitude field-aligned irregularity (FAI) along the magnetic field line is a common phenomenon in the ionosphere. However, few data reveal the field-aligned ionospheric irregularities. They are insufficient to identify FAIs effects so far, particularly effect on global positioning system (GPS) signals. In this paper, the mid-latitude FAIs by line-of-sight angular scanning relative to the local magnetic field vector are investigated using the denser GPS network observations in Japan. It has been the first found that total GPS L2 phase slips over Japan, during the recovery phase of the 12 Feb 2000 geomagnetic storm were caused by GPS signal scattering on FAIs both for the lines-of-sight aligned to the magnetic field line (the field of aligned scattering, FALS) and across the magnetic field line (the field of across scattering, FACS). The FALS results are also in a good agreement with the data of the magnetic field orientation control of GPS occultation observations of equatorial scintillation during thorough low earth orbit (LEO) satellites measurements, e.g. Challenging Minisatellite Payload (CHAMP) and Satellite de Aplicaciones Cientificas-C (SAC-C). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors.

Seasonal variations of reflexibility and transmissibility of ULF waves propagating through the ionosphere of geomagnetic mid-latitudes

NASA Astrophysics Data System (ADS)

Prikner, K.

Using reference models of the daytime and night ionosphere of geomagnetic mid-latitudes in a quiescent period in summer, autumn and winter, the seasonal variation of ULF frequency characteristics of amplitude and energy correction factors of the ionosphere - vertical reflexibility, transmissibility and absorption, are studied. The existence of two frequency bands within the ULF range with different properties of ionospheric wave filtration is pointed out: (a) continuous band f of less than 0.1 to 0.2 Hz with the mirror effect of the ionosphere with respect to the incident wave, but with small ionospheric absorption of wave energy; and (b) a Hz band of greater than 0.2 Hz with resonance frequency windows and wave emissions with a sharply defined frequency structure. The seasonal variation from summer to winter indicates a decrease in wave energy absorption in the ionosphere and a slight displacement of the resonances towards higher frequencies.

High energy resolution plastic scintillator

NASA Astrophysics Data System (ADS)

van Loef, Edgar V.; Feng, Patrick; Markosyan, Gary; Shirwadkar, Urmila; Doty, Patrick; Shah, Kanai S.

2016-09-01

In this paper we present results on a novel tin-loaded plastic scintillator. We will show that this particular plastic scintillator has a light output similar to that of BGO, a fast scintillation decay (< 10 ns), exhibits good neutron/gamma PSD with a Figure-of-Merit of 1.3 at 2.5 MeVee cut-off energy, and excellent energy resolution of about 12% (FWHM) at 662 keV. Under X-ray excitation, the radioluminescence spectrum exhibits a broad band between 350 and 500 nm peaking at 420 nm which is well-matched to bialkali photomultiplier tubes and UV-enhanced photodiodes.

Impact of multiconstellation satellite signal reception on performance of satellite-based navigation under adverse ionospheric conditions

NASA Astrophysics Data System (ADS)

Paul, Ashik; Paul, Krishnendu Sekhar; Das, Aditi

2017-03-01

Application of multiconstellation satellites to address the issue of satellite signal outages during periods of equatorial ionospheric scintillations could prove to be an effective tool for maintaining the performance of satellite-based communication and navigation without compromise in accuracy and integrity. A receiver capable of tracking GPS, Global Navigation Satellite System (GLONASS), and Galileo satellites is operational at the Institute of Radio Physics and Electronics, University of Calcutta, Calcutta, India, located near the northern crest of the equatorial ionization anomaly in the Indian longitude sector. The present paper shows increased availability of satellites combining GPS, GLONASS, and Galileo constellations from Calcutta compared to GPS-only scenario and estimates intense scintillation-free (S4 < 0.6) satellite vehicle look angles at different hours of the postsunset period 19:00-01:00 LT during March 2014. A representative case of 1 March 2014 is highlighted in the paper and overall statistics for March 2014 presented to indicate quantitative advantages in terms of scintillation-free satellite vehicle look angles that may be utilized for planning communication and navigation channel spatial distribution under adverse ionospheric conditions. The number of satellites tracked and receiver position deviations has been found to show a good correspondence with the occurrence of intense scintillations and poor user receiver-satellite link geometry. The ground projection of the 350 km subionospheric points corresponding to multiconstellation shows extended spatial coverage during periods of scintillations (0.2 < S4 < 0.6) compared to GPS.

Investigation of ionospheric effects on SAR Interferometry (InSAR): A case study of Hong Kong

NASA Astrophysics Data System (ADS)

Zhu, Wu; Ding, Xiao-Li; Jung, Hyung-Sup; Zhang, Qin; Zhang, Bo-Chen; Qu, Wei

2016-08-01

Synthetic Aperture Radar Interferometry (InSAR) has demonstrated its potential for high-density spatial mapping of ground displacement associated with earthquakes, volcanoes, and other geologic processes. However, this technique may be affected by the ionosphere, which can result in the distortions of Synthetic Aperture Radar (SAR) images, phases, and polarization. Moreover, ionospheric effect has become and is becoming further significant with the increasing interest in low-frequency SAR systems, limiting the further development of InSAR technique. Although some research has been carried out, thorough analysis of ionospheric influence on true SAR imagery is still limited. Based on this background, this study performs a thorough investigation of ionospheric effect on InSAR through processing L-band ALOS-1/PALSAR-1 images and dual-frequency Global Positioning System (GPS) data over Hong Kong, where the phenomenon of ionospheric irregularities often occurs. The result shows that the small-scale ionospheric irregularities can cause the azimuth pixel shifts and phase advance errors on interferograms. Meanwhile, it is found that these two effects result in the stripe-shaped features in InSAR images. The direction of the stripe-shaped effects keep approximately constant in space for our InSAR dataset. Moreover, the GPS-derived rate of total electron content change index (ROTI), an index to reflect the level of ionospheric disturbances, may be a useful indicator for predicting the ionospheric effect for SAR images. This finding can help us evaluate the quality of SAR images when considering the ionospheric effect.

Simultaneous Global Positioning System observations of equatorial scintillations and total electron content fluctuations

NASA Astrophysics Data System (ADS)

Beach, Theodore L.; Kintner, Paul M.

1999-10-01

One aspect of the Global Positioning System (GPS) is the potential to conduct geophysical research, and worldwide networks of GPS receivers have been established to exploit this potential. Several research groups have begun using this global GPS data to study ionospheric total electron content (TEC) variations, also referred to as GPS phase fluctuations, as surrogates for ionospheric scintillations. This paper investigates the relationship between GPS amplitude scintillations and TEC variations for the same line of sight using observations from Ancón, Peru. These observations were taken under equatorial spread F conditions for three nights in April 1997. As expected, only when the spectrum of TEC fluctuations includes significant power at the Fresnel scale do scintillations appear. We also find that when the TEC fluctuation spectrum includes the Fresnel scale, the S4 scintillation index is roughly proportional to measures of TEC fluctuation for the weak scintillations observed. The proportionality constant varies from night to night, however, casting doubt on the ability to predict GPS S4 successfully from TEC fluctuation data alone. We also present a simple theoretical phase screen model and show that if a relationship between TEC fluctuation measures and S4 exists, that relationship depends on the power spectrum of phase variations at the screen. Unfortunately, the available TEC data, at 30 s per sample (with some aliasing apparently permitted), offer limited spectral information. A preliminary comparison of 1 s/sample data with the same data decimated to a 30 s/sample interval suggests, however, that the level of successful S4 prediction, based on TEC fluctuation measures alone, is comparable at either sample rate.

Improvement of the Scintillation-Irregularity Model in WBMOD

DTIC Science & Technology

1983-02-28

satellite over e small s.ction of its orbit . 2-4 IMPLEMENTATION AT AFGWC One of the tasks carried out was to modify the most recent version of WaMOD...influence scintillation strength OSRTN Sets up integral to calculate phase variance, for finite outer scale ROMINT Modified Romberg quadrature integration... orbit calculation, and implc-Nentation of Ln irregularity drift routine based on a recently published model of ionospheric convection st high latitudes

The ionospheric response to the Saint Patrick storm over South East Asia

NASA Astrophysics Data System (ADS)

Spogli, L.; Alfonsi, L.; Di Mauro, D.; Pezzopane, M.; Cesaroni, C.; Povero, G., Sr.; Pini, M., Sr.; Dovis, F., Sr.; Romero, R.; Linty, N.; Abadi, P.; Nuraeni, F.; Husin, A.; Huy Le, M.; La The, V.; Pillat, V. G.; Floury, N.

2015-12-01

ERICA, a project funded by the European Space Agency, aims at characterizing the ionospheric variability of the Equatorial Ionospheric Anomaly in the South East Asia. In particular, ERICA focuses on the variation of the plasma electron density in the southern and northern crests of the anomaly and over the dip equator identified by the Equatorial Ionospheric Trough. To achieve this goal, an ad hoc measurements campaign is on-going with ground-based instruments located in the footprints of the Equatorial Ionospheric Anomaly and of the Equatorial Ionospheric Trough in Vietnam and Indonesia.The campaign started on the 1st of March 2015, timing to monitor the Saint Patrick storm effects on the ionosphere by means of ionosondes, double frequency hardware and software defined radio GNSS receivers, ground based and spaceborne magnetometers and Langmuir probe. Such multi-instrumental and multi-parametric observations of the region enables an in-depth investigation of the ionospheric response to the largest geomagnetic storm of the current solar cycle. The observations record positive and negative ionospheric storms, sporadic E layer and spread F conditions, scintillations enhancement and inhibition, TEC gradients. The ancillary information on the local magnetic field allows to highlight the variety of ionospheric perturbations happened during the main and the long recovery phase of the storm.The paper presents the outcomes of the investigation evidencing the peculiarities of a region not yet extensively reported in the open literature.

Scintillation measurements at Bahir Dar during the high solar activity phase of solar cycle 24

NASA Astrophysics Data System (ADS)

Kriegel, Martin; Jakowski, Norbert; Berdermann, Jens; Sato, Hiroatsu; Wassaie Mersha, Mogese

2017-01-01

Small-scale ionospheric disturbances may cause severe radio scintillations of signals transmitted from global navigation satellite systems (GNSSs). Consequently, small-scale plasma irregularities may heavily degrade the performance of current GNSSs such as GPS, GLONASS or Galileo. This paper presents analysis results obtained primarily from two high-rate GNSS receiver stations designed and operated by the German Aerospace Center (DLR) in cooperation with Bahir Dar University (BDU) at 11.6° N, 37.4° E. Both receivers collect raw data sampled at up to 50 Hz, from which characteristic scintillation parameters such as the S4 index are deduced. This paper gives a first overview of the measurement set-up and the observed scintillation events over Bahir Dar in 2015. Both stations are located close to one another and aligned in an east-west, direction which allows us to estimate the zonal drift velocity and spatial dimension of equatorial ionospheric plasma irregularities. Therefore, the lag times of moving electron density irregularities and scintillation patterns are derived by applying cross-correlation analysis to high-rate measurements of the slant total electron content (sTEC) along radio links between a GPS satellite and both receivers and to the associated signal power, respectively. Finally, the drift velocity is derived from the estimated lag time, taking into account the geometric constellation of both receiving antennas and the observed GPS satellites.

Excitation of Earth-ionosphere waveguide in the ELF and lower VLF bands by modulated ionospheric current

NASA Astrophysics Data System (ADS)

Field, E. C.; Bloom, R. M.

1993-05-01

In this report, the principal of reciprocity is used in conjunction with a full-wave propagation code to calculate ground-level fields excited by ionospheric currents modulated at frequencies between 50 and 100 Hz with HF heaters. Results show the dependence on source orientation, altitude, and dimension and therefore pertain to experiments using the HIPAS or HAARP ionospheric heaters. In the end-fire mode, the waveguide excitation efficiency of an ELF HED in the ionosphere is up to 20 dB greater than for a ground-based antenna, provided its altitude does not exceed 80 to 90 km. The highest efficiency occurs for a source altitude of around 70 km; if that altitude is raised to 100 km, the efficiency drops by about 20 dB in the day and 10 dB at night. That efficiency does not account for the greater conductivity modulation that might be achieved at altitudes greater than 70 km, however. The trade-off between the altitude dependencies of the excitation efficiency and maximum achievable modulation depends on the ERP of the HF heater, the optimum altitude increasing with increasing ERP. For HIPAS the best modulation altitude is around 70 km, whereas for HAARP there might be marginal value in modulating at attitudes as high as 100 km.

Decorrelation of L-band and C-band interferometry to volcanic risk prevention

NASA Astrophysics Data System (ADS)

Malinverni, E. S.; Sandwell, D.; Tassetti, A. N.; Cappelletti, L.

2013-10-01

SAR has several strong key features: fine spatial resolution/precision and high temporal pass frequency. Moreover, the InSAR technique allows the accurate detection of ground deformations. This high potential technology can be invaluable to study volcanoes: it provides important information on pre-eruption surface deformation, improving the understanding of volcanic processes and the ability to predict eruptions. As a downside, SAR measurements are influenced by artifacts such as atmospheric effects or bad topographic data. Correlation gives a measure of these interferences, quantifying the similarity of the phase of two SAR images. Different approaches exists to reduce these errors but the main concern remain the possibility to correlate images with different acquisition times: snow-covered or heavily-vegetated areas produce seasonal changes on the surface. Minimizing the time between passes partly limits decorrelation. Though, images with a short temporal baseline aren't always available and some artifacts affecting correlation are timeindependent. This work studies correlation of pairs of SAR images focusing on the influence of surface and climate conditions, especially snow coverage and temperature. Furthermore, the effects of the acquisition band on correlation are taken into account, comparing L-band and C-band images. All the chosen images cover most of the Yellowstone caldera (USA) over a span of 4 years, sampling all the seasons. Interferograms and correlation maps are generated. To isolate temporal decorrelation, pairs of images with the shortest baseline are chosen. Correlation maps are analyzed in relation to snow depth and temperature. Results obtained with ENVISAT and ERS satellites (C-band) are compared with the ones from ALOS (L-band). Results show a good performance during winter and a bad attitude towards wet snow (spring and fall). During summer both L-band and C-band maintain a good coherence with L-band performing better over vegetation.

Equatorial Scintillation Study at Ilorin and Nsukka, Nigeria during Year 2011-2012

NASA Astrophysics Data System (ADS)

Akala, A.

2017-12-01

This study presents GNSS scintillations over Ilorin (8.48 oN, 4.54 oE, and mag lat: 1.83oS) and Nsukka (6.84 oN, 7.37 oE, and mag lat: 2.94oS), Nigeria during year 2011-2012. The two stations are located within the inner flank of the equatorial ionization anomaly. Firstly, we investigated the climatology of equatorial scintillations at the two stations. We suppressed multipath effects on the data by imposing a 300 elevation masking on the data. In addition, we investigated scintillation occurrences at the two locations on a satellite-by-satellite basis at varying elevation angles. The source of scintillation records at low-elevation angle is attributed to multipath, while that at high-elevation angle is attributed to ionospheric irregularities. Seasonally, scintillations recorded highest occurrences during March equinox, and the least during June solstice. The trend of scintillations, at both low- and high-elevation angles at the two stations were almost the same. EGNOS satellites signals scintillated at the two locations during the time intervals when GPS satellites signals experienced scintillations. These results could support the development of scintillation models for equatorial Africa, and could also be of benefit to GPS and EGNOS service providers and designers, with a view to providing robust services for GNSS user community in Africa.

Atmosphere-Ionosphere Electrodynamic Coupling

NASA Astrophysics Data System (ADS)

Sorokin, V. M.; Chmyrev, V. M.

Numerous phenomena that occur in the mesosphere, ionosphere, and the magnetosphere of the Earth are caused by the sources located in the lower atmosphere and on the ground. We describe the effects produced by lightning activity and by ground-based transmitters operated in high frequency (HF) and very low frequency (VLF) ranges. Among these phenomena are the ionosphere heating and the formation of plasma density inhomogeneities, the excitation of gamma ray bursts and atmospheric emissions in different spectral bands, the generation of ULF/ELF/VLF electromagnetic waves and plasma turbulence in the ionosphere, the stimulation of radiation belt electron precipitations and the acceleration of ions in the upper ionosphere. The most interesting results of experimental and theoretical studies of these phenomena are discussed below. The ionosphere is subject to the action of the conductive electric current flowing in the atmosphere-ionosphere circuit. We present a physical model of DC electric field and current formation in this circuit. The key element of this model is an external current, which is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization and change of electrical conductivity. Variation of conductivity and external current in the lower atmosphere leads to perturbation of the electric current flowing in the global atmosphere-ionosphere circuit and to the associated DC electric field perturbation both on the Earth's surface and in the ionosphere. Description of these processes and some results of the electric field and current calculations are presented below. The seismic-induced electric field perturbations produce noticeable effects in the ionosphere by generating the electromagnetic field and plasma disturbances. We describe the generation mechanisms of such experimentally

DFT Studies of Semiconductor and Scintillator Detection Materials

NASA Astrophysics Data System (ADS)

Biswas, Koushik

2013-03-01

Efficient radiation detection technology is dependent upon the development of new semiconductor and scintillator materials with advanced capabilities. First-principles based approaches can provide vital information about the structural, electrical, optical and defect properties that will help develop new materials. In addition to the predictive power of modern density functional methods, these techniques can be used to establish trends in properties that may lead to identifying new materials with optimum properties. We will discuss the properties of materials that are of current interest both in the field of scintillators and room temperature semiconductor detectors. In case of semiconductors, binary compounds such as TlBr, InI, CdTe and recently developed ternary chalcohalide Tl6SeI4 will be discussed. Tl6SeI4 mixes a halide (TlI) with a chalcogenide (Tl2Se), which results in an intermediate band gap (1.86 eV) between that of TlI (2.75 eV) and Tl2Se (0.6 eV). For scintillators, we will discuss the case of the elpasolite compounds whose rich chemical compositions should enable the fine-tuning of the band gap and band edges to achieve high light yield and fast scintillation response.

IAR signatures in the ionosphere: Modeling and observations at the Chibis-M microsatellite

NASA Astrophysics Data System (ADS)

Pilipenko, V.; Dudkin, D.; Fedorov, E.; Korepanov, V.; Klimov, S.

2017-02-01

A peculiar feature of geomagnetic variations at middle/low latitudes in the ULF band, just below the fundamental tone of the Schumann resonance, is the occurrence of a multi-band spectral resonant structure, observed by high-sensitivity induction magnetometers during nighttime. The occurrence of such spectral structure was commonly attributed to the Ionospheric Alfvén Resonator (IAR) in the upper ionosphere. Rather surprisingly, while ground observations of the IAR are ubiquitous, there are practically no reports on the IAR signatures from space missions. According to the new paradigm, the multi-band spectral structure excited by a lightning discharge is in fact produced by a regular sequence of an original pulse from a stroke and echo-pulses reflected from the IAR upper boundary. Upon the interaction of initial lightning-generated pulse with the anisotropic lower ionosphere, it partially penetrates into the ionosphere, travels up the ionosphere as an Alfvén pulse, and reflects back from the upper IAR boundary. The superposition of the initial pulse and echo-pulses produces spectra with multiple spectral peaks. Our modeling of Alfvénic pulse propagation in a system with the altitude profile of Alfven velocity modeling the realistic ionosphere has shown that IAR spectral signatures are to be evident only on the ground and above the IAR. Inside the IAR, the superposition of upward and downward propagating pulses produces a more complicated spectral pattern and the IAR spectral signatures deteriorate. We have used electric field data from the low-orbit Chibis-M microsatellite to search for IAR signatures in the ionosphere. We found evidence that the multi-band structure revealed by spectral analysis in the frequency range of interest is indeed the result of a sequence of lightning-produced pulses. According to the proposed conception it seems possible to comprehend why the IAR signatures are less evident in the ionosphere than on the ground.

Precipitation estimation using L-Band and C-Band soil moisture retrievals

USDA-ARS?s Scientific Manuscript database

An established methodology for estimating precipitation amounts from satellite-based soil moisture retrievals is applied to L-band products from the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) satellite missions and to a C-band product from the Advanced Scatterome...

L Band Service Compatibility Part I: Optimum OOBE Compatibility

DOT National Transportation Integrated Search

2014-12-04

Discussion: -- Two Parts - Today we focus on optimum L Band ABC Out of Band Emission into GPS L1, OOBE. - Next ABC meeting will examine GPS-side mitigation of Adjacent Band Interference, ABI. -- Greater Compatibility: OOBE and ABI are distinct but pa...

Advanced Ionospheric Sensing using GROUP-C and LITES aboard the ISS

NASA Astrophysics Data System (ADS)

Budzien, S. A.; Stephan, A. W.; Chakrabarti, S.; Finn, S. C.; Cook, T.; Powell, S. P.; O'Hanlon, B.; Bishop, R. L.

2015-12-01

The GPS Radio Occultation and Ultraviolet Photometer Co-located (GROUP-C) and Limb-imaging Ionospheric and Thermospheric Extreme-ultraviolet Spectrograph (LITES) experiments are manifested for flight aboard the International Space Station (ISS) in 2016 as part of the Space Test Program Houston #5 payload. The two experiments provide technical development and risk-reduction for future DoD space weather sensors suitable for ionospheric specification, space situational awareness, and data products for global ionosphere assimilative models. In addition, the combined instrument complement of these two experiments offers a unique opportunity to study structures of the nighttime ionosphere. GROUP-C includes an advanced GPS receiver providing ionospheric electron density profiles and scintillation measurements and a high-sensitivity far-ultraviolet photometer measuring horizontal ionospheric gradients. LITES is an imaging spectrograph that spans 60-140 nm and will obtain high-cadence limb profiles of the ionosphere and thermosphere from 150-350 km altitude. In the nighttime ionosphere, recombination of O+ and electrons produces optically thin emissions at 91.1 and 135.6 nm that can be used to tomographically reconstruct the two-dimensional plasma distribution in the orbital plane below ISS altitudes. Ionospheric irregularities, such as plasma bubbles and blobs, are transient features of the low and middle latitude ionosphere with important implications for operational systems. Irregularity structures have been studied primarily using ground-based systems, though some spaced-based remote and in-situ sensing has been performed. An ionospheric observatory aboard the ISS would provide new capability to study low- and mid-latitude ionospheric structures on a global scale. By combining for the first time high-sensitivity in-track photometry, vertical ionospheric airglow spectrographic imagery, and recent advancements in UV tomography, high-fidelity tomographic reconstruction of

Relation of decorrelated transionospheric GPS signal fluctuations from two stations in the northern anomaly crest region with equatorial ionospheric dynamics

NASA Astrophysics Data System (ADS)

Paul, K. S.; Paul, A.

2017-05-01

The ionosphere around the northern crest of the equatorial ionization anomaly (EIA) and beyond exhibits rapid temporal as well as spatial development of ionization density irregularities during postsunset hours. A GPS campaign was conducted during September 2012 and April 2013 from the Institute of Radio Physics and Electronics, Calcutta (22.58°N, 88.38°E geographic; magnetic dip: 32°N), and North Bengal University (NBU), Siliguri (26.72°N, 88.39°E geographic, magnetic dip: 39.49°N) in India in order to assess and quantify differences, if any, in the nature of carrier to noise ratio (C/N0) fluctuations observed on the same satellite link around the same time interval from these stations. Significant decorrelation of the received signals was found when tracking the same satellite vehicle (SV) link from these stations during periods of scintillations. Low values of correlation coefficient of C/N0 at L1 frequency recorded on the same SV link at these two stations were found to correspond with high irregularity characteristic velocities. North-south spatial displacement rates of the impact of ionospheric irregularities were calculated based on coordinated GPS observations which followed an increasing trend with irregularity characteristic velocities measured at VHF. Values of characteristic velocities in excess of 36 m/s were also found to result in large receiver position deviations 3.5-4.0 m during periods of scintillations. Information related to time lag associated with occurrence of scintillations on the same SV link observed from two stations could be useful for improving performance of transionospheric satellite-based position determination techniques.

A study on ionospheric scintillation near the EIA crest in relation to equatorial electrodynamics

NASA Astrophysics Data System (ADS)

Chatterjee, S.; Chakraborty, S. K.; Veenadhari, B.; Banola, S.

2014-02-01

Equatorial electrojet (EEJ) data, which are considered as a proxy index of equatorial electric field, are analyzed in conjunction with equatorial ionosonde, total electron content (TEC) and scintillation data near the equatorial ionization anomaly (EIA) crest for the equinoctial months of high solar activity years (2011-2012) to identify any precursor index of postsunset evolution of equatorial electron density irregularities and subsequent occurrence of scintillation near the northern EIA crest. Only geomagnetically quiet and normal electrojet days are considered. The diurnal profiles of EEJ on the scintillation days exhibit a secondary enhancement in the afternoon to presunset hours following diurnal peaks. A series of electrodynamical processes conducive for generation of irregularities emerge following secondary enhancement of EEJ. Latitudinal profile of TEC exhibits resurgence in EIA structure around the postsunset period. Diurnal TEC profile near the EIA crest resembles postsunset secondary enhancement on the days with afternoon enhancement in EEJ. Occurrence of equatorial spread F and postsunset scintillation near the EIA crest seems to follow the secondary enhancement events in EEJ. Both the magnitude and duration of enhanced EEJ are found to be important for postsunset intensification of EIA structure and subsequent occurrence of equatorial irregularities. A critical value combining the two may be considered an important precursor for postsunset occurrence of scintillation near the EIA crest. The results are validated using archived data for the years 1989-1990 and explained in terms of modulation effects of enhanced equatorial fountain.

Ionospheric TEC Weather Map Over South America

NASA Astrophysics Data System (ADS)

Takahashi, H.; Wrasse, C. M.; Denardini, C. M.; Pádua, M. B.; de Paula, E. R.; Costa, S. M. A.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. Galera; Ivo, A.; Sant'Anna, N.

2016-11-01

Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total 140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m-2 (TECU) <10) to the crest region (TECU > 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

Effect of geomagnetic storms on VHF scintillations observed at low latitude

NASA Astrophysics Data System (ADS)

Singh, S. B.; Patel, Kalpana; Singh, A. K.

2018-06-01

A geomagnetic storm affects the dynamics and composition of the ionosphere and also offers an excellent opportunity to study the plasma dynamics. In the present study, we have used the VHF scintillations data recorded at low latitude Indian station Varanasi (Geomag. latitude = 14^{°}55^' }N, long. = 154^{°}E) which is radiated at 250 MHz from geostationary satellite UFO-02 during the period 2011-2012 to investigate the effects of geomagnetic storms on VHF scintillation. Various geomagnetic and solar indices such as Dst index, Kp index, IMF Bz and solar wind velocity (Vx) are used to describe the geomagnetic field variation observed during geomagnetic storm periods. These indices are very helpful to find out the proper investigation and possible interrelation between geomagnetic storms and observed VHF scintillation. The pre-midnight scintillation is sometimes observed when the main phase of geomagnetic storm corresponds to the pre-midnight period. It is observed that for geomagnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time and extends to early morning hours.

GNSS monitoring of the ionosphere for Space Weather services

NASA Astrophysics Data System (ADS)

Krankowski, A.; Sieradzki, R.; Zakharenkova, I. E.; Cherniak, I. V.

2012-04-01

The International GNSS Service (IGS) Ionosphere Working Group routinely provides the users global ionosphere maps (GIMs) of vertical total electron content (vTEC). The IGS GIMs are provided with spatial resolution of 5.0 degrees x 2.5 degrees in longitude and latitude, respectively. The current temporal resolution is 2 hours, however, 1-hour maps are delivered as a pilot project. There are three types IGS GIMs: the final, rapid and predicted. The latencies of the IGS ionospheric final and rapid products are 10 days and 1 day, respectively. The predicted GIMs are generated for 1 and 2 days in advance. There are four IGS Associate Analysis Centres (IAACs) that provide ionosphere maps computed with independent methodologies using GNSS data. These maps are uploaded to the IGS Ionosphere Combination and Validation Center at the GRL/UWM (Geodynamics Research Laboratory of the University of Warmia and Mazury in Olsztyn, Poland) that produces the IGS official ionospheric products, which are published online via ftp and www. On the other hand, the increasing number of permanently tracking GNSS stations near the North Geomagnetic Pole allow for using satellite observations to detect the ionospheric disturbances at high latitudes with even higher spatial resolution. In the space weather service developed at GRL/UWM, the data from the Arctic stations belonging to IGS/EPN/POLENET networks were used to study TEC fluctuations and scintillations. Since the beginning of 2011, a near real-time service presenting the conditions in the ionosphere have been operational at GRL/UWM www site. The rate of TEC index (ROTI) expressed in TECU/min is used as a measure of TEC fluctuations. The service provides 2-hour maps of the TEC variability. In addition, for each day the daily map of the ionospheric fluctuations as a function geomagnetic local time is also created. This presentation shows the architecture, algorithms, performance and future developments of the IGS GIMs and this new space

Reconfigurable L-Band Radar

NASA Technical Reports Server (NTRS)

Rincon, Rafael F.

2008-01-01

The reconfigurable L-Band radar is an ongoing development at NASA/GSFC that exploits the capability inherently in phased array radar systems with a state-of-the-art data acquisition and real-time processor in order to enable multi-mode measurement techniques in a single radar architecture. The development leverages on the L-Band Imaging Scatterometer, a radar system designed for the development and testing of new radar techniques; and the custom-built DBSAR processor, a highly reconfigurable, high speed data acquisition and processing system. The radar modes currently implemented include scatterometer, synthetic aperture radar, and altimetry; and plans to add new modes such as radiometry and bi-static GNSS signals are being formulated. This development is aimed at enhancing the radar remote sensing capabilities for airborne and spaceborne applications in support of Earth Science and planetary exploration This paper describes the design of the radar and processor systems, explains the operational modes, and discusses preliminary measurements and future plans.

Earth Studies Using L-band Synthetic Aperture Radar

NASA Technical Reports Server (NTRS)

Rosen, Paul A.

1999-01-01

L-band SAR has played an important role in studies of the Earth by revealing the nature of the larger-scale (decimeter) surface features. JERS-1, by supplying multi-seasonal coverage of the much of the earth, has demonstrated the importance of L-band SARs. Future L-band SARs such as ALOS and LightSAR will pave the way for science missions that use SAR instruments. As technology develops to enable lower cost SAR instruments, missions will evolve to each have a unique science focus. International coordination of multi-parameter constellations and campaigns will maximize science return.

Infrasonic troposphere-ionosphere coupling in Hawaii

NASA Astrophysics Data System (ADS)

Garces, M. A.

2011-12-01

The propagation of infrasonic waves in the ionospheric layers has been considered since the 1960's. It is known that space weather can alter infrasonic propagation below the E layer (~120 km altitude), but it was thought that acoustic attenuation was too severe above this layer to sustain long-range propagation. Although volcanoes, earthquakes and tsunamis (all surface sources) appear to routinely excite perturbations in the ionospheric F layer by the propagation of acoustic and acoustic-gravity waves through the atmosphere, there are few reports of the inverse pathway. This paper discusses some of the routine ground-based infrasonic array observations of ionospheric returns from surface sources. These thermospheric returns generally point back towards the source, with an azimuth deviation that can be corrected using the wind velocity profiles in the mesosphere and lower thermosphere. However, the seismic excitation in the North Pacific by the Tohoku earthquake ensonified the coupled lithosphere-atmosphere-ionosphere waveguide in the 0.01 - 0.1 Hz frequency band, producing anomalous signals observed by infrasound arrays in Hawaii. These infrasonic signals propagated at curiously high velocities, suggesting that some assumptions on ionospheric sound generation and propagation could be revisited.

Ionospheric Remote Sensing using GPS Radio Occultation and Ultraviolet Photometry aboard the ISS

NASA Astrophysics Data System (ADS)

Budzien, S. A.; Powell, S. P.; O'Hanlon, B.; Humphreys, T.; Bishop, R. L.; Stephan, A. W.; Gross, J.; Chakrabarti, S.

2017-12-01

The GPS Radio Occultation and Ultraviolet Photometer Co-located (GROUP-C) experiment launched to the International Space Station (ISS) on February 19, 2017 as part of the Space Test Program Houston #5 payload (STP-H5). After early orbit testing, GROUP-C began routine science operations in late April. GROUP-C includes a high-sensitivity far-ultraviolet photometer measuring horizontal nighttime ionospheric gradients and an advanced software-defined GPS receiver providing ionospheric electron density profiles, scintillation measurements, and lower atmosphere profiles. GROUP-C and a companion experiment, the Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph (LITES), offer a unique capability to study spatial and temporal variability of the thermosphere and ionosphere using multi-sensor approaches, including ionospheric tomography. Data are collected continuously across low- and mid-latitudes as the ISS orbit precesses through all local times every 60 days. The GROUP-C GPS sensor routinely collects dual-frequency GPS occultations, makes targeted raw signal captures of GPS and Galileo occultations, and includes multiple antennas to characterize multipath in the ISS environment. The UV photometer measures the 135.6 nm ionospheric recombination airglow emision along the nightside orbital track. We present the first analysis of ionospheric observations, discuss the challenges and opportunities of remote sensing from the ISS platform, and explore how these new data help address questions regarding the complex and dynamic features of the low and middle latitude ionosphere-thermosphere relevant to the upcoming GOLD and ICON missions.

Studies of Ionospheric Plasma Structuring at Low Latitudes from Space and Ground, Their Modeling and Relationship to Scintillations

DTIC Science & Technology

2009-01-01

1 DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited. Studies of Ionospheric Plasma Structuring at Low...program combines observations and modeling of the nighttime ionosphere to come to a better physical understanding of the factors that contribute to...the day-to-day variability of the development of ionospheric irregularities. The scope encompasses irregularities developing at equatorial and mid

Generation of Artificial Ionospheric Irregularities in the Midlatitude Ionosphere Modified by High-Power High-Frequency X-Mode Radio Waves

NASA Astrophysics Data System (ADS)

Frolov, V. L.; Bolotin, I. A.; Komrakov, G. P.; Pershin, A. V.; Vertogradov, G. G.; Vertogradov, V. G.; Vertogradova, E. G.; Kunitsyn, V. E.; Padokhin, A. M.; Kurbatov, G. A.; Akchurin, A. D.; Zykov, E. Yu.

2014-11-01

We consider the properties of the artificial ionospheric irregularities excited in the ionospheric F 2 region modified by high-power high-frequency X-mode radio waves. It is shown that small-scale (decameter) irregularities are not generated in the midlatitude ionosphere. The intensity of irregularities with the scales l ⊥ ≈50 m to 3 km is severalfold weaker compared with the case where the irregularities are excited by high-power O-mode radio waves. The intensity of the larger-scale irregularities is even stronger attenuated. It is found that the generation of large-scale ( l ⊥ ≈5-10 km) artificial ionospheric irregularities is enhanced at the edge of the directivity pattern of a beam of high-power radio waves.

Studies of Ionospheric Plasma Structuring at Low Latitudes from Space and Ground, their Modeling and Relationship to Scintillations

DTIC Science & Technology

2008-09-30

2006JA011646, 2006. [published, refereed] Lee, J. K., F. Kamalabadi, and J. J. Makela, Three-dimensional tomography of ionospheric variability using a...Studies of Ionospheric Plasma Structuring at Low Latitudes from Space and Ground, their Modeling and...illinois.edu Award Number: N00173-05-1-G904 LONG-TERM GOALS This program combines observations and modeling of the nighttime ionosphere to come to a

Considering the potential of IAR emissions for ionospheric sounding

NASA Astrophysics Data System (ADS)

Potapov, A. S.; Polyushkina, T. N.; Tsegmed, B.; Oinats, A. V.; Pashinin, A. Yu.; Edemskiy, I. K.; Mylnikova, A. A.; Ratovsky, K. G.

2017-11-01

Knowledge of the ionospheric state allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. At present, probing of the ionosphere is produced by radio sounding with ground ionosondes, as well as by raying signals from satellites. We want to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called ionospheric Alfvén resonator (IAR). To do this, we present observations of the IAR emission made simultaneously for the first time at three stations using identical induction magnetometers. The stations are within one-hour difference of local time, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare frequency and frequency difference between adjacent harmonics of the observed multi-band emission with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a stable correlation between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation is high; it varies at different stations, but is observed distinctly along the whole meridian. However, coefficients of a regression equation that connects the ionosphere critical frequency with DSB frequency vary significantly from day to day at all stations. The reason for such a big spread of the regression parameters is not clear and needs further investigation before we are able to

East-west asymmetric of scintillation occurrence in Indonesia using GPS and GLONASS observations

NASA Astrophysics Data System (ADS)

Abadi, P.; Otsuka, Y.; Shiokawa, K.; Saito, S.; Husin, A.; Dear, V.; Anggarani, S.

2015-12-01

By using GNSS (Global Navigation Satellite Systems) receiver to collect amplitude scintillation at L1 frequency from GPS and GLONASS, we investigated ionospheric scintillation occurrence at equator anomaly in Indonesia from July 2014 to June 2015. The receiver is installed at Bandung (6.9 deg S, 107.6 deg E; 9.9 deg S mag. latitude), Indonesia. In this study, we grouped our analysis into two groups based on duration of observation, (1) July-December 2014 (monthly F10.7 ranged from 124.7-158.7) which is named autumn equinox and (2) January-June 2015 (monthly F10.7 ranged from 120.1-141.7) which is named spring equinox. Our preliminary results can be summarized as follows; (1) the intensity of scintillations at spring equinox is higher than at autumn equinox although solar activity at autumn equinox is higher than at spring equinox, see Figure 1 and (2) as shown in Figure 2, the directional distribution of scintillation occurrences at spring equinox mostly concentrate in the western sky, so we see east-west asymmetric, but the distribution at autumn equinox doesn't show clearly east-west asymmetric. Previous studies have reported that occurrence rate of the scintillation at spring equinox season is higher than at autumn equinox. Our results suggest that equinoctial asymmetry of scintillation occurrence can be also as an asymmetric of scintillation intensity and east-west asymmetric of scintillation occurrence between spring and autumn equinox. In general, plasma bubble is tilted westward as it vertically develop due to vertical shear in the eastward plasma drift in F region, and consequently, it will be tilted westward as it extends in latitude. Scintillation intensity will be stronger when signal propagation tend to be parallel with structure of the plasma bubble. Figure 2 also imply that the latitudinal extension of plasma bubble is higher at spring equinox than at autumn equinox. More the bubble extends in latitude, more the bubble structure exists in the western

Study of ionospheric irregularities from Kolhapur (16.4°N, 74.2°E)

NASA Astrophysics Data System (ADS)

Sharma, A. K.; Chavan, G. A.; Gaikwad, H. P.; Gurav, O. B.; Nade, D. P.; Nikte, S. S.; Ghodpage, R. N.; Patil, P. T.

2018-04-01

The paper reports night time observations of ionospheric irregularities made through amplitude scintillation of 251 MHz signal at Kolhapur (16.4°N, 74.2°E), an equatorial Appleton anomaly region using spaced antenna system. Monthly and night time percentage of occurrence of scintillations, during increasing solar cycle from January 2011 to August 2015, is discussed. The parameters such as-maximum cross-correlation function (CI), Fade Rate are also studied. The percentage occurrence is observed to be higher in post sunset period and during equinoctial months than in winter and summer months. Scintillation occurrence is observed to be suppressed during increasing solar activity. CI shows seasonal changes. Percentage of occurrence of CI ≥ 0.5 decreases with increase in solar activity and fade rate also shows solar activity dependence.

A computer model for high-latitude phase scintillation based on wideband satellite data from Poker Flat

NASA Astrophysics Data System (ADS)

Fremouw, E. J.; Lansinger, J. M.

1981-02-01

A mathematical model has been developed for describing plasma-density irregularities responsible for radiowave scintillation produced in the auroral ionosphere, and the model has been committed to an applications-oriented computer code, WBMOD. The model characterizes the three-dimensional configuration, gradient sharpness, and height-integrated strength of irregularities represented by a power-law spatial spectrum as functions of geomagnetic latitude, time of day, sunspot number, and planetary geomagnetic activity index. Program WBMOD permits calculation of the power-law index and spectral strength (at a fluctuation frequency of 1 Hz) of phase scintillation, together with scintillation indices (variances) for phase and intensity, using a phase-screen scattering theory. The model has been calibrated and iteratively tested against phase-scintillation data from the DNA Wideband Satellite Experiment, collected at Poker Flat, Alaska. It does not account for seasonal variations in high-latitude scintillation observed in other longitude sectors. The program contains a model for middle-latitude and equatorial irregularities as well as for auroral latitudes, but only the latter has been tested extensively against high-quality scintillation data.

Electrodynamics of ionospheric weather over low latitudes

NASA Astrophysics Data System (ADS)

Abdu, Mangalathayil Ali

2016-12-01

The dynamic state of the ionosphere at low latitudes is largely controlled by electric fields originating from dynamo actions by atmospheric waves propagating from below and the solar wind-magnetosphere interaction from above. These electric fields cause structuring of the ionosphere in wide ranging spatial and temporal scales that impact on space-based communication and navigation systems constituting an important segment of our technology-based day-to-day lives. The largest of the ionosphere structures, the equatorial ionization anomaly, with global maximum of plasma densities can cause propagation delays on the GNSS signals. The sunset electrodynamics is responsible for the generation of plasma bubble wide spectrum irregularities that can cause scintillation or even disruptions of satellite communication/navigation signals. Driven basically by upward propagating tides, these electric fields can suffer significant modulations from perturbation winds due to gravity waves, planetary/Kelvin waves, and non-migrating tides, as recent observational and modeling results have demonstrated. The changing state of the plasma distribution arising from these highly variable electric fields constitutes an important component of the ionospheric weather disturbances. Another, often dominating, component arises from solar disturbances when coronal mass ejection (CME) interaction with the earth's magnetosphere results in energy transport to low latitudes in the form of storm time prompt penetration electric fields and thermospheric disturbance winds. As a result, drastic modifications can occur in the form of layer restructuring (Es-, F3 layers etc.), large total electron content (TEC) enhancements, equatorial ionization anomaly (EIA) latitudinal expansion/contraction, anomalous polarization electric fields/vertical drifts, enhanced growth/suppression of plasma structuring, etc. A brief review of our current understanding of the ionospheric weather variations and the

Measurement of tritium with high efficiency by using liquid scintillation counter with plastic scintillator.

PubMed

Furuta, Etsuko; Ohyama, Ryu-ichiro; Yokota, Shigeaki; Nakajo, Toshiya; Yamada, Yuka; Kawano, Takao; Uda, Tatsuhiko; Watanabe, Yasuo

2014-11-01

The detection efficiencies of tritium samples by using liquid scintillation counter with hydrophilic plastic scintillator (PS) was approximately 48% when the sample of 20 μL was held between 2 PS sheets treated by plasma. The activity and count rates showed a good relationship between 400 Bq to 410 KBq mL(-1). The calculated detection limit of 2 min measurement by the PS was 13 Bq mL(-1) when a confidence was 95%. The plasma method for PS produces no radioactive waste. Copyright © 2014 Elsevier Ltd. All rights reserved.

Intercepted signals for ionospheric science

NASA Astrophysics Data System (ADS)

Lind, F. D.; Erickson, P. J.; Coster, A. J.; Foster, J. C.; Marchese, J. R.; Berkowitz, Z.; Sahr, J. D.

2013-05-01

The ISIS array (Intercepted Signals for Ionospheric Science) is a distributed, coherent software radio array designed for the study of geospace phenomena by observing the scatter of ambient radio frequency (RF) signals. ISIS data acquisition and analysis is performed using the MIDAS-M platform (Millstone Data Acquisition System - Mobile). Observations of RF signals can be performed between HF and L-band using the Array nodes and appropriate antennas. The deployment of the Array focuses on observations of the plasmasphere boundary layer. We discuss the concept of the coherent software radio array, describe the ISIS hardware, and give examples of data from the system for selected applications. In particular, we include the first observations of E region irregularities using the Array. We also present single-site passive radar observations of both meteor trails and E region irregularities using adaptive filtering techniques.

Cherenkov and scintillation light separation in organic liquid scintillators

NASA Astrophysics Data System (ADS)

Caravaca, J.; Descamps, F. B.; Land, B. J.; Yeh, M.; Orebi Gann, G. D.

2017-12-01

The CHErenkov/Scintillation Separation experiment (CHESS) has been used to demonstrate the separation of Cherenkov and scintillation light in both linear alkylbenzene (LAB) and LAB with 2 g/L of PPO as a fluor (LAB/PPO). This is the first successful demonstration of Cherenkov light detection from the more challenging LAB/PPO cocktail and improves on previous results for LAB. A time resolution of 338± 12 ps FWHM results in an efficiency for identifying Cherenkov photons in LAB/PPO of 70 ± 3 % and 63± 8% for time- and charge-based separation, respectively, with scintillation contamination of 36± 5% and 38± 4%. LAB/PPO data is consistent with a rise time of τ _r=0.72± 0.33 ns.

A case study of lightning, whistlers, and associated ionospheric effects during a substorm particle injection event

NASA Technical Reports Server (NTRS)

Rodriguez, J. V.; Inan, U. S.; Li, Y. Q.; Holzworth, R. H.; Smith, A. J.; Orville, R. E.; Rosenberg, T. J.

1992-01-01

The relationships among cloud-to-ground (CG) lightning, sferics, whistlers, VLF amplitude perturbations, and other ionospheric phenomena occurring during substorm events were investigated using data from simultaneous ground-based observations of narrow-band and broad-band VLF radio waves and of CG lightning made during the 1987 Wave-Induced Particle Precipitation campaign conducted from Wallops Island (Virginia). Results suggest that the data collected on ionospheric phenomena during this event may represent new evidence of direct coupling of lightning energy to the lower ionosphere, either in conjunction with or in the absence of gyroresonant interactions between whistler mode waves and electrons in the magnetosphere.

The Scintillation Prediction Observations Research Task (SPORT) Mission

NASA Astrophysics Data System (ADS)

Spann, J. F.; Swenson, C.; Durão, O.; Loures, L.; Heelis, R. A.; Bishop, R. L.; Le, G.; Abdu, M. A.; Habash Krause, L.; De Nardin, C. M.; Fonseca, E.

2015-12-01

Structure in the charged particle number density in the equatorial ionosphere can have a profound impact on the fidelity of HF, VHF and UHF radio signals that are used for ground-to-ground and space-to-ground communication and navigation. The degree to which such systems can be compromised depends in large part on the spatial distribution of the structured regions in the ionosphere and the background plasma density in which they are embedded. In order to address these challenges it is necessary to accurately distinguish the background ionospheric conditions that favor the generation of irregularities from those that do not. Additionally we must relate the evolution of those conditions to the subsequent evolution of the irregular plasma regions themselves. The background ionospheric conditions are conveniently described by latitudinal profiles of the plasma density at nearly constant altitude, which describe the effects of ExB drifts and neutral winds, while the appearance and growth of plasma structure requires committed observations from the ground from at least one fixed longitude. This talk will present an international collaborative CubeSat mission called SPORT that stands for Scintillation Prediction Observations Research Task. This mission that will advance our understanding of the nature and evolution of ionospheric structures around sunset to improve predictions of disturbances that affect radio propagation and telecommunication signals. The science goals will be accomplished by a unique combination of satellite observations from a nearly circular middle inclination orbit and the extensive operation of ground based observations from South America near the magnetic equator. This approach promises Explorer class science at a CubeSat price.

The Scintillation Prediction Observations Research Task (SPORT) Mission

NASA Astrophysics Data System (ADS)

Spann, James; Le, Guan; Swenson, Charles; Denardini, Clezio Marcos; Bishop, Rebecca L.; Abdu, Mangalathayil A.; Cupertino Durao, Otavio S.; Heelis, Roderick; Loures, Luis; Krause, Linda; Fonseca, Eloi

2016-07-01

Structure in the charged particle number density in the equatorial ionosphere can have a profound impact on the fidelity of HF, VHF and UHF radio signals that are used for ground-to-ground and space-to-ground communication and navigation. The degree to which such systems can be compromised depends in large part on the spatial distribution of the structured regions in the ionosphere and the background plasma density in which they are embedded. In order to address these challenges it is necessary to accurately distinguish the background ionospheric conditions that favor the generation of irregularities from those that do not. Additionally we must relate the evolution of those conditions to the subsequent evolution of the irregular plasma regions themselves. The background ionospheric conditions are conveniently described by latitudinal profiles of the plasma density at nearly constant altitude, which describe the effects of ExB drifts and neutral winds, while the appearance and growth of plasma structure requires committed observations from the ground from at least one fixed longitude. This talk will present an international collaborative CubeSat mission called SPORT that stands for the Scintillation Prediction Observations Research Task. This mission will advance our understanding of the nature and evolution of ionospheric structures around sunset to improve predictions of disturbances that affect radio propagation and telecommunication signals. The science goals will be accomplished by a unique combination of satellite observations from a nearly circular middle inclination orbit and the extensive operation of ground based observations from South America near the magnetic equator. This approach promises Explorer class science at a CubeSat price.

The Scintillation Prediction Observations Research Task (SPORT) Mission

NASA Astrophysics Data System (ADS)

Spann, James; Swenson, Charles; Durão, Otavio; Loures, Luis; Heelis, Rod; Bishop, Rebecca; Le, Guan; Abdu, Mangalathayil; Krause, Linda; Nardin, Clezio; Fonseca, Eloi

2016-04-01

Structure in the charged particle number density in the equatorial ionosphere can have a profound impact on the fidelity of HF, VHF and UHF radio signals that are used for ground-to-ground and space-to-ground communication and navigation. The degree to which such systems can be compromised depends in large part on the spatial distribution of the structured regions in the ionosphere and the background plasma density in which they are embedded. In order to address these challenges it is necessary to accurately distinguish the background ionospheric conditions that favor the generation of irregularities from those that do not. Additionally we must relate the evolution of those conditions to the subsequent evolution of the irregular plasma regions themselves. The background ionospheric conditions are conveniently described by latitudinal profiles of the plasma density at nearly constant altitude, which describe the effects of ExB drifts and neutral winds, while the appearance and growth of plasma structure requires committed observations from the ground from at least one fixed longitude. This talk will present an international collaborative CubeSat mission called SPORT that stands for the Scintillation Prediction Observations Research Task. This mission will advance our understanding of the nature and evolution of ionospheric structures around sunset to improve predictions of disturbances that affect radio propagation and telecommunication signals. The science goals will be accomplished by a unique combination of satellite observations from a nearly circular middle inclination orbit and the extensive operation of ground based observations from South America near the magnetic equator. This approach promises Explorer class science at a CubeSat price.

LITES and GROUP-C Mission Update: Ionosphere and Thermosphere Sensing from the ISS

NASA Astrophysics Data System (ADS)

Stephan, A. W.; Budzien, S. A.; Chakrabarti, S.; Hysell, D. L.; Powell, S. P.; Finn, S. C.; Cook, T.; Bishop, R. L.

2016-12-01

The Limb-imaging Ionospheric and Thermospheric Extreme-ultraviolet Spectrograph (LITES) and GPS Radio Occultation and Ultraviolet Photometer Co-located (GROUP-C) experiments are scheduled for launch to the International Space Station (ISS) in November 2016 as part of the Space Test Program Houston #5 payload (STP-H5). The two experiments provide technical development and risk-reduction for future space weather sensors suitable for ionospheric specification, space situational awareness, and data products for global ionosphere assimilative models. The combined instrument suite of these experiments offers a unique capability to study spatial and temporal variability of the thermosphere and ionosphere using multi-sensor and tomographic approaches. LITES is an imaging spectrograph that spans 60-140 nm and continuously acquires limb profiles of the ionosphere and thermosphere from 150-350 km altitude. GROUP-C includes a high-sensitivity far-ultraviolet photometer measuring horizontal ionospheric gradients and an advanced GPS receiver providing ionospheric electron density profiles and scintillation measurements. High-cadence limb images and nadir photometry from GROUP-C/LITES are combined to tomographically reconstruct high-fidelity two-dimensional volume emission rates within the ISS orbital plane. The GPS occultation receiver provides independent measurements to calibrate and validate advanced daytime ionospheric algorithms and nighttime tomography. The vantage from the ISS on the lower portion of the thermosphere and ionosphere will yield measurements complementary to the NASA GOLD and ICON missions which are expected to fly during the STP-H5 mission. We present a mission status update and available early orbit observations, and the opportunities for using these new data to help address questions regarding the complex and dynamic features of the low and middle latitude ionosphere-thermosphere system that have important implications for operational systems.

Feasibility of precise navigation in high and low latitude regions under scintillation conditions

NASA Astrophysics Data System (ADS)

Juan, José Miguel; Sanz, Jaume; González-Casado, Guillermo; Rovira-Garcia, Adrià; Camps, Adriano; Riba, Jaume; Barbosa, José; Blanch, Estefania; Altadill, David; Orus, Raul

2018-02-01

Scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation. This phenomenon appears when the radio signal passes through ionospheric irregularities. These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips. In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudes. For low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by σϕ) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal. With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditions. For high-latitude receivers the situation differs. In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s). Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large σϕ), but with a moderate fade in the amplitude (moderate S4). Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions.

Characteristics and climatology of mid-latitude F-region ionospheric irregularities observed by COSMIC radio occultation measurements

NASA Astrophysics Data System (ADS)

Watson, C.; Pedatella, N. M.

2017-12-01

Small-medium scale ( 1-50 km) ionospheric plasma irregularities are a ubiquitous feature of the earth's F region ionosphere. COSMIC radio occultation measurements provide a valuable opportunity to improve upon the incomplete global observational picture of irregularity occurrence and characteristics. A climatological database of ionospheric irregularities and their characteristics (e.g. magnitude, scale size, gradient, and associated scintillation) has been developed through detection of total electron content (TEC) perturbations by COSMIC precise orbit determination (POD) antennas and associated receivers. Vertical scale sizes ranging from 1 to 50 km were resolved from 1 Hz TEC measurements stored in podTec files. Amplitude scintillation index (S4) of ScnLv1 files was used as a proxy for the occurrence of smaller scale (<1 km) scintillation producing structures. Four years of processed data (2007-2008 and 2012-2013) has revealed interesting climatological features of irregularity occurrence and characteristics. The presentation will focus on the results at mid-latitudes. One interesting mid-latitude feature is a high occurrence of irregularities in regions corresponding to the solar terminator. Perturbations larger than 0.1 TEC units (TECU) were observed 50%-80% of the time in terminator regions, with higher occurrence and more intense perturbations around sunset and during years of high solar activity. Altitude of peak occurrence of terminator irregularities was about 150 km, with a sharp upper-altitude cut-off of 250 km. The occurrence and characteristics of these irregularities are modified according to proximity to solar terminator location. A possible link to thermospheric neutral density perturbations also associated with the solar terminator will be discussed. The climatology of non-terminator mid-latitude irregularities is consistent with previous observations of mid-latitude field-aligned irregularities (FAIs), including a local-time dependent altitude

Improved model for correcting the ionospheric impact on bending angle in radio occultation measurements

NASA Astrophysics Data System (ADS)

Angling, Matthew J.; Elvidge, Sean; Healy, Sean B.

2018-04-01

The standard approach to remove the effects of the ionosphere from neutral atmosphere GPS radio occultation measurements is to estimate a corrected bending angle from a combination of the L1 and L2 bending angles. This approach is known to result in systematic errors and an extension has been proposed to the standard ionospheric correction that is dependent on the squared L1 / L2 bending angle difference and a scaling term (κ). The variation of κ with height, time, season, location and solar activity (i.e. the F10.7 flux) has been investigated by applying a 1-D bending angle operator to electron density profiles provided by a monthly median ionospheric climatology model. As expected, the residual bending angle is well correlated (negatively) with the vertical total electron content (TEC). κ is more strongly dependent on the solar zenith angle, indicating that the TEC-dependent component of the residual error is effectively modelled by the squared L1 / L2 bending angle difference term in the correction. The residual error from the ionospheric correction is likely to be a major contributor to the overall error budget of neutral atmosphere retrievals between 40 and 80 km. Over this height range κ is approximately linear with height. A simple κ model has also been developed. It is independent of ionospheric measurements, but incorporates geophysical dependencies (i.e. solar zenith angle, solar flux, altitude). The global mean error (i.e. bias) and the standard deviation of the residual errors are reduced from -1.3×10-8 and 2.2×10-8 for the uncorrected case to -2.2×10-10 rad and 2.0×10-9 rad, respectively, for the corrections using the κ model. Although a fixed scalar κ also reduces bias for the global average, the selected value of κ (14 rad-1) is only appropriate for a small band of locations around the solar terminator. In the daytime, the scalar κ is consistently too high and this results in an overcorrection of the bending angles and a positive bending

Cherenkov and scintillation light separation in organic liquid scintillators

DOE PAGES

Caravaca, J.; Descamps, F. B.; Land, B. J.; ...

2017-11-29

The CHErenkov/Scintillation Separation experiment (CHESS) has been used to demonstrate the separation of Cherenkov and scintillation light in both linear alkylbenzene (LAB) and LAB with 2 g/L of PPO as a fluor (LAB/PPO). This is the first successful demonstration of Cherenkov light detection from the more challenging LAB/PPO cocktail and improves on previous results for LAB. A time resolution of 338 ± 12 ps FWHM results in an efficiency for identifying Cherenkov photons in LAB/PPO of 70 ± 3 % and 63 ± 8 % for time- and charge-based separation, respectively, with scintillation contamination of 36 ± 5 % andmore » 38 ± 4 %. LAB/PPO data is consistent with a rise time of τ r = 0.72 ± 0.33 ns.« less

Cherenkov and scintillation light separation in organic liquid scintillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caravaca, J.; Descamps, F. B.; Land, B. J.

The CHErenkov/Scintillation Separation experiment (CHESS) has been used to demonstrate the separation of Cherenkov and scintillation light in both linear alkylbenzene (LAB) and LAB with 2 g/L of PPO as a fluor (LAB/PPO). This is the first successful demonstration of Cherenkov light detection from the more challenging LAB/PPO cocktail and improves on previous results for LAB. A time resolution of 338 ± 12 ps FWHM results in an efficiency for identifying Cherenkov photons in LAB/PPO of 70 ± 3 % and 63 ± 8 % for time- and charge-based separation, respectively, with scintillation contamination of 36 ± 5 % andmore » 38 ± 4 %. LAB/PPO data is consistent with a rise time of τ r = 0.72 ± 0.33 ns.« less

Plasma Instability Growth Rates in the F-Region Cusp Ionosphere

NASA Astrophysics Data System (ADS)

Moen, J. I.; Daabakk, Y.; Oksavik, K.; Clausen, L.; Bekkeng, T. A.; Abe, T.; Saito, Y.; Baddeley, L. J.; Lorentzen, D. A.; Sigernes, F.; Yeoman, T. K.

2014-12-01

There are at least two different micro-instability processes that applies to the F-region cusp/polar cap ionosphere. These are the Gradient Drift Instability (GDI) and the Kelvin Helmholtz Instability (KHI). Due to space weather effects on radio communication and satellite signals it is of practical interest to assess the relative importance of these two instability modes and to quantify their growth rates. The Investigation of Cusp Irregularities (ICI) rocket program has been developed to investigate these plasma instabilities and formation scintillation irregularities. High resolution measurements are critical to get realistic quantities on the growth rates. The results achieved so far demonstrates that cusp ionosphere precipitation can give rise to km scale plasma structures on which grow rates are down to a few tens of seconds compared to earlier measures of ten minutes based on ground observations. This has to do with the spatial resolution required for these measurements. Growth rates for the KHI instability is found to be of the same order, which is consistent with growth rates calculated from the EISCAT Svalbard Radar. I.e. both instability modes can be highly efficient in the cusp ionosphere.

Study of transionospheric signal scintillation: Quasi- particle approach

NASA Astrophysics Data System (ADS)

Lyle, Ruthie D.

1998-07-01

A quasi-particle approach is applied to study amplitude scintillation of transionospheric signals caused by Bottomside Sinusoidal (BSS) irregularities. The quasi- particle method exploits wave-particle duality, viewing the wave as a distribution of quasi-particles. This is accomplished by transforming the autocorrelation of the wave function into a Wigner distribution function, which serves as a distribution of quasi-particles in the (/vec r,/ /vec k) phase space. The quasi-particle distribution at any instant of time represents the instantaneous state of the wave. Scattering of the signal by the ionospheric irregularities is equivalent to the evolution of the quasi-particle distribution, due to the collision of the quasi-particles with objects arising from the presence of the BSS irregularities. Subsequently, the perturbed quasi-particle distribution facilitates the computation of average space time propagation properties of the wave. Thus, the scintillation index S4 is determined. Incorporation of essential BSS features in the analysis is accomplished by analytically modeling the power spectrum of the BSS irregularities measured in-situ by the low orbiting Atmosphere-E (AE - E) Satellite. The effect of BSS irregularities on transionospheric signals has been studied. The numerical results agree well with multi-satellite scintillation observations made at Huancayo Peru in close time correspondence with BSS irregularities observed by the AE - E satellite over a few nights (December 8-11, 1979). During this period, the severity of the scintillation varied from moderate to intense, S4 = 0.1-0.8.

Power Spectrum of Atmospheric Scintillation for the Deep Space Network Goldstone Ka-Band Downlink

NASA Technical Reports Server (NTRS)

Ho, C.; Wheelon, A.

2004-01-01

Dynamic signal fluctuations due to atmospheric scintillations may impair the Ka-band (around 32-GHz) link sensitivities for a low-margin Deep Space Network (DSN) receiving system. The ranges of frequency and power of the fast fluctuating signals (time scale less than 1 min) are theoretically investigated using the spatial covariance and turbulence theory. Scintillation power spectrum solutions are derived for both a point receiver and a finite-aperture receiver. The aperture-smoothing frequency ((omega(sub s)), corner frequency ((omega(sub c)), and damping rate are introduced to define the shape of the spectrum for a finite-aperture antenna. The emphasis is put on quantitatively describing the aperture-smoothing effects and graphically estimating the corner frequency for a large aperture receiver. Power spectral shapes are analyzed parametrically in detail through both low- and high-frequency approximations. It is found that aperture-averaging effects become significant when the transverse correlation length of the scintillation is smaller than the antenna radius. The upper frequency or corner frequency for a finite-aperture receiver is controlled by both the Fresnel frequency and aperture-smoothing frequency. Above the aperture-smoothing frequency, the spectrum rolls off at a much faster rate of exp (-omega(sup 2)/omega(sup 2, sub s), rather than omega(sup -8/3), which is customary for a point receiver. However, a relatively higher receiver noise level can mask the fast falling-off shape and make it hard to be identified. We also predict that when the effective antenna radius a(sub r) less than or = 6 m, the corner frequency of its power spectrum becomes the same as that for a point receiver. The aperture-smoothing effects are not obvious. We have applied these solutions to the scenario of a DSN Goldstone 34-m-diameter antenna and predicted the power spectrum shape for the receiving station. The maximum corner frequency for the receiver (with omega(sub s) = 0

Preface: C/NOFS Results and Equatorial Ionospheric Dynamics

NASA Technical Reports Server (NTRS)

Klenzing, J.; de La Beaujardiere, O.; Gentile, L. C.; Retterer, J.; Rodrigues, F. S.; Stoneback, R. A.

2014-01-01

The Communication/Navigation Outage Forecasting System (C/NOFS) satellite was launched into orbit in April 2008 as part of an ongoing effort to understand and identify plasma irregularities that adversely impact the propagation of radio waves in the upper atmosphere. Combined with recent improvements in radar, airglow, and ground-based studies, as well as state-of-the-art modeling techniques, the C/NOFS mission has led to new insights into equatorial ionospheric electrodynamics. In order to document these advances, the C/NOFS Results and Equatorial Dynamics Technical Interchange Meeting was held in Albuquerque, New Mexico from 12 to 14 March 2013. The meeting was a great success with 55 talks and 22 posters, and covered topics including the numerical simulations of plasma irregularities, the effects of atmospheric tides, stratospheric phenomena, and magnetic storms on the upper atmosphere, causes and predictions of scintillation-causing ionospheric irregularities, current and future instrumentation efforts in the equatorial region. The talks were broken into the following three topical sessions: A. Ambient Ionosphere and Thermosphere B. Transient Phenomena in the Low-Latitude Ionosphere C. New Missions, New Sensors, New Science and Engineering Issues. The following special issue was planned as a follow-up to the meeting. We would like to thank Mike Pinnock, the editors and staff of Copernicus, and our reviewers for their work in bringing this special issue to the scientific community. Our thanks also go to Patricia Doherty and the meeting organizing committee for arranging the C/NOFS Technical Interchange Meeting.

EMI survey for maritime satellite, L-band, shipboard terminal

NASA Technical Reports Server (NTRS)

Taylor, R. E.; Brandel, D. L.; Hill, J. S.

1975-01-01

The paper presents results of an onboard EMI survey of an L-band shipboard terminal for operation with two geostationary maritime satellites. Significant EMC results include: (1) antenna noise temperature measurements indicate a maximum of 70 K steady background component at 1.6 GHz at sea for elevation angles of 5 degrees and higher; (2) field intensity measurements from 1-10 GHz show that a L-band terminal can operate simultaneously with onboard S-band and X-band navigation radar; (3) radar transmitter case emissions, below deck, in-band from 1535-1660 MHz, at 1 m distance from the cabinet, are equivalent, or greater than above-deck emissions in the same frequency range; and (4) conducted-emission tests of a ship's power lines to both radars show both narrow band and broad band emissions are 15 dB to 50 dB higher than equivalent U.S. commercial power lines from 150 kHz to 32 MHz.

Ionospheric Correction of InSAR for Accurate Ice Motion Mapping at High Latitudes

NASA Astrophysics Data System (ADS)

Liao, H.; Meyer, F. J.

2016-12-01

Monitoring the motion of the large ice sheets is of great importance for determining ice mass balance and its contribution to sea level rise. Recently the first comprehensive ice motion of the Greenland and the Antarctica have been generated with InSAR. However, these studies have indicated that the performance of InSAR-based ice motion mapping is limited by the presence of the ionosphere. This is particularly true at high latitudes and for low-frequency SAR data. Filter-based and empirical methods (e.g., removing polynomials), which have often been used to mitigate ionospheric effects, are often ineffective in these areas due to the typically strong spatial variability of ionospheric phase delay in high latitudes and due to the risk of removing true deformation signals from the observations. In this study, we will first present an outline of our split-spectrum InSAR-based ionospheric correction approach and particularly highlight how our method improves upon published techniques, such as the multiple sub-band approach to boost estimation accuracy as well as advanced error correction and filtering algorithms. We applied our work flow to a large number of ionosphere-affected dataset over the large ice sheets to estimate the benefit of ionospheric correction on ice motion mapping accuracy. Appropriate test sites over Greenland and the Antarctic have been chosen through cooperation with authors (UW, Ian Joughin) of previous ice motion studies. To demonstrate the magnitude of ionospheric noise and to showcase the performance of ionospheric correction, we will show examples of ionospheric-affected InSAR data and our ionosphere corrected result for comparison in visual. We also compared the corrected phase data to known ice velocity fields quantitatively for the analyzed areas from experts in ice velocity mapping. From our studies we found that ionospheric correction significantly reduces biases in ice velocity estimates and boosts accuracy by a factor that depends on a

Low-latitude Ionospheric Research using the CIRCE Mission

NASA Astrophysics Data System (ADS)

Dymond, K.; Nicholas, A. C.; Budzien, S. A.; Stephan, A. W.

2016-12-01

The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) is a dual-satellite mission consisting of two 6U CubeSats actively maintaining a lead-follow configuration in the same orbit with a launch planned for the 2018-2019 time frame. These nano-satellites will each feature two 1U ultraviolet photometers, observing the 135.6 nm emission of atomic oxygen at nighttime. The primary objective is to characterize the two-dimensional distribution of electrons in the Equatorial Ionization Anomaly (EIA). The methodology used to reconstruct the nighttime ionosphere employs continuous UV photometry from four distinct viewing angles in combination with an additional data source, such as in situ plasma density measurements or a wide-band beacon data, with advanced image space reconstruction algorithm tomography techniques. The COSMIC/FORMOSAT-3 (CF3) constellation featured six Tiny Ionospheric Photometers, a compact UV sensor design which served as the pathfinder for the CIRCE instruments. The TIP instruments on the CF3 satellites demonstrated detection of ionospheric bubbles before they had penetrated the peak of the F-region ionosphere. We present our mission concept, simulations illustrating the imaging capability of the sensor suite, and a range of science questions addressable using such a system.

Radio Sounding of the Martian and Venusian Ionospheres

NASA Astrophysics Data System (ADS)

Paetzold, M.; Haeusler, B.; Bird, M. K.; Peter, K.; Tellmann, S.; Tyler, G. L.; Withers, P.

2011-12-01

The Mars Express Radio Science Experiment MaRS and the radio science experiment Vera on Venus Express sound the ionospheres of Mars and Venus, respectively, at two frequencies in the microwave band and cover altitudes from the base of the ionosphere at 80 km (100 km at Venus) to the ionopause at altitudes between 300 km and 600 km. In general, both ionospheres consists of a lower layer M1 (V1 at Venus) at about 110 km (115 km), and the main layer M2 (V2) at about 135 km (145 km) altitude, both formed mainly by solar radiation at X-ray and EUV, respectively. The specific derivation and interpretation of the vertical electron density profiles at two radio frequencies from radio sounding is demonstrated in detail. Cases of quiet and disturbed ionospheric electron density profiles and cases of potential misinterpretations are presented. The behavior of the peak densities and peak altitudes of both ionospheres as a function of solar zenith angle and phase of the solar cycle as seen with Mars Express and Venus Express will be compared with past observations, models and conclusions.

Ionospheric very low frequency transmitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuo, Spencer P.

2015-02-15

The theme of this paper is to establish a reliable ionospheric very low frequency (VLF) transmitter, which is also broad band. Two approaches are studied that generate VLF waves in the ionosphere. The first, classic approach employs a ground-based HF heater to directly modulate the high latitude ionospheric, or auroral electrojet. In the classic approach, the intensity-modulated HF heater induces an alternating current in the electrojet, which serves as a virtual antenna to transmit VLF waves. The spatial and temporal variations of the electrojet impact the reliability of the classic approach. The second, beat-wave approach also employs a ground-based HFmore » heater; however, in this approach, the heater operates in a continuous wave mode at two HF frequencies separated by the desired VLF frequency. Theories for both approaches are formulated, calculations performed with numerical model simulations, and the calculations are compared to experimental results. Theory for the classic approach shows that an HF heater wave, intensity-modulated at VLF, modulates the electron temperature dependent electrical conductivity of the ionospheric electrojet, which, in turn, induces an ac electrojet current. Thus, the electrojet becomes a virtual VLF antenna. The numerical results show that the radiation intensity of the modulated electrojet decreases with an increase in VLF radiation frequency. Theory for the beat wave approach shows that the VLF radiation intensity depends upon the HF heater intensity rather than the electrojet strength, and yet this approach can also modulate the electrojet when present. HF heater experiments were conducted for both the intensity modulated and beat wave approaches. VLF radiations were generated and the experimental results confirm the numerical simulations. Theory and experimental results both show that in the absence of the electrojet, VLF radiation from the F-region is generated via the beat wave approach. Additionally, the beat wave

Effects of tropospheric and ionospheric refraction errors in the utilization of GEOS-C altimeter data

NASA Technical Reports Server (NTRS)

Goad, C. C.

1977-01-01

The effects of tropospheric and ionospheric refraction errors are analyzed for the GEOS-C altimeter project in terms of their resultant effects on C-band orbits and the altimeter measurement itself. Operational procedures using surface meteorological measurements at ground stations and monthly means for ocean surface conditions are assumed, with no corrections made for ionospheric effects. Effects on the orbit height due to tropospheric errors are approximately 15 cm for single pass short arcs (such as for calibration) and 10 cm for global orbits of one revolution. Orbit height errors due to neglect of the ionosphere have an amplitude of approximately 40 cm when the orbits are determined from C-band range data with predominantly daylight tracking. Altimeter measurement errors are approximately 10 cm due to residual tropospheric refraction correction errors. Ionospheric effects on the altimeter range measurement are also on the order of 10 cm during the GEOS-C launch and early operation period.

Radio science electron density profiles of lunar ionosphere based on the service module of circumlunar return and reentry spacecraft

NASA Astrophysics Data System (ADS)

Wang, M.; Han, S.; Ping, J.; Tang, G.; Zhang, Q.

2017-09-01

The existence of lunar ionosphere has been under debate for a long time. Radio occultation experiments had been performed by both Luna 19/22 and SELENE missions and electron column density of lunar ionosphere was provided. The Apollo 14 mission also acquired the electron density with in situ measurements. But the results of these missions don't well-matched. In order to explore the lunar ionosphere, radio occultation with the service module of Chinese circumlunar return and reentry spacecraft has been performing. One coherent S-band and X-band radio signals were recorded by China deep space stations, and local correlation was adopted to compute carrier phases of both signals. Based on the above work, the electron density profiles of lunar ionosphere was obtained and analyzed.

Interstellar scintillations of PSR B1919+21: space-ground interferometry

NASA Astrophysics Data System (ADS)

Shishov, V. I.; Smirnova, T. V.; Gwinn, C. R.; Andrianov, A. S.; Popov, M. V.; Rudnitskiy, A. G.; Soglasnov, V. A.

2017-07-01

We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radio telescope, together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60 000 km. We show that interstellar scintillation of this pulsar consists of two components: diffractive scintillations from inhomogeneities in a layer of turbulent plasma at a distance z1 = 440 pc from the observer or homogeneously distributed scattering material to the pulsar; and weak scintillations from a screen located near the observer at z2 = 0.14 ± 0.05 pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift in observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded a scattering angle in the observer plane of θscat = 0.7 mas. An analysis of the time-frequency correlation function for weak scintillations yielded an angle of refraction in the direction to the pulsar θref, 0 = 110 ms and a distance to the prism zprism ≤ 2 pc.

EMP-002a Phase Shift through the Ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soltz, R.; Simons, D.; Fenimore, E.

2015-10-20

In this note we review the derivation and use of the Ionospheric Transfer Function (ITF) in the DIO- RAMA model to calculate the propagation of a broad band ElectroMagnetic Pulse (EMP) through the Ionosphere in the limit of geometric optics. This note is intended to resolve a misunderstanding between the NDS VVA and EMP modeling teams regarding the appropriate use of the phase and group velocities in DIORAMA. The di erent approaches are documented in EMP-002 note, \\Phase vs. Group" [1], generated by the LLNL DIORAMA VVA team, and the subsequent response from the DIORAMA EMP modeling team' [2].

Production of Ionospheric Perturbations by Cloud-to-Ground Lightning and the Recovery of the Lower Ionosphere

NASA Astrophysics Data System (ADS)

Liu, Ningyu; Dwyer, Joseph; Rassoul, Hamid

2013-04-01

The fact that lightning/thunderstorm activities can directly modify the lower ionosphere has long been established by observations of the perturbations of very low frequency (VLF) signals propagating in the earth-ionosphere waveguide. These perturbations are known as early VLF events [Inan et al., 2010, JGR, 115, A00E36, 2010]. More recently discovered transient luminous events caused by the lightning/thunderstorm activities only last ~1-100 ms, but studies of the early VLF events show that the lightning ionospheric effects can persist much longer, >10s min [Cotts and Inan, GRL, 34, L14809, 2007; Haldoupis et al., JGR, 39, L16801, 2012; Salut et al., JGR, 117, A08311, 2012]. It has been suggested that the long recovery is caused by long-lasting conductivity perturbations in the lower ionosphere, which can be created by sprites/sprite halos which in turn are triggered by cloud-to-ground (CG) lightning [Moore et al., JGR, 108, 1363, 2003; Haldoupis et al., 2012]. We recently developed a two-dimensional fluid model with simplified ionospheric chemistry for studying the quasi-electrostatic effects of lightning in the lower ionosphere [Liu, JGR, 117, A03308, 2012]. The model chemistry captures major ion species and reactions in the lower ionosphere. Additional important features of the model include self-consistent background ion density profiles and full description of electron and ion transport. In this talk, we present the simulation results on the dynamics of sprite halos caused by negative CG lightning. The modeling results indicate that electron density around 60 km altitude can be enhanced in a region as wide as 80 km. The enhancement reaches its full extent in ~1 s and recovers in 1-10 s, which are on the same orders as the durations of slow onset and post-onset peaks of some VLF events, respectively. In addition, long-lasting electron and ion density perturbations can occur around 80 km altitude due to negative halos as well as positive halos, which can explain

Rapid-run ionosonde observations of traveling ionospheric disturbances in the auroral ionosphere

NASA Astrophysics Data System (ADS)

Kozlovsky, Alexander; Turunen, Tauno; Ulich, Thomas

2013-08-01

2007, the Sodankylä Geophysical Observatory routinely performs vertical ionosphere soundings once per minute, using a frequency-modulated continuous-wave chirp at the rate of 500 kHz/s from 500 kHz to 16 MHz. We used these data to study traveling ionospheric disturbances (TIDs) during 10-16 local time. The observations were made between April 2007 and June 2012, mostly during low solar activity. The TIDs were studied in five bands of periods corresponding to the following: infrasonic (acoustic) waves and the buoyancy cutoff (periods from 5 to 10 min); small-scale gravity waves (GWs; 10-15 min); medium-scale (MS; 15-30 min) GWs; medium-large scale (MS-LS; 30-60 min) GWs; and large-scale (LS; 60-120 min) GWs. Relative contribution (with respect to LS TIDs) of the short-period (5-15 min) and MS (15-30 min) TIDs shows minima in winter and maxima in summer. These annual variations anticorrelate with variations of true height, namely, the largest relative amplitudes occur in summer, when TIDs were observed at minimal heights. We suggest that the summer increase of shorter-period TIDs is due to lowering reflection to the height where the Brunt-Väisälä period is smaller and, hence, shorter-period gravity waves exist. The summer maxima were most prominent during the 3 years of minimal solar activity (2008-2010). In 2011, when solar activity increased, the annual variation seems less prominent. Annual variations of the longer-period (30-120 min) TIDs are essentially less significant. For all TIDs, no obvious dependences on the AE and Ap indices of magnetic activity were found.

Codoped direct-gap semiconductor scintillators

DOEpatents

Derenzo, Stephen Edward [Pinole, CA; Bourret-Courchesne, Edith [Berkeley, CA; Weber, Marvin J [Danville, CA; Klintenberg, Mattias K [Berkeley, CA

2008-07-29

Fast, bright inorganic scintillators at room temperature are based on radiative electron-hole recombination in direct-gap semiconductors, e.g. CdS and ZnO. The direct-gap semiconductor is codoped with two different impurity atoms to convert the semiconductor to a fast, high luminosity scintillator. The codopant scheme is based on dopant band to dopant trap recombination. One dopant provides a significant concentration of carriers of one type (electrons or holes) and the other dopant traps carriers of the other type. Examples include CdS:In,Te; CdS:In,Ag; CdS:In,Na; ZnO:Ga,P; ZnO:Ga,N; ZnO:Ga,S; and GaN:Ge,Mg.

Codoped direct-gap semiconductor scintillators

DOEpatents

Derenzo, Stephen E.; Bourret-Courchesne, Edith; Weber, Marvin J.; Klintenberg, Mattias K.

2006-05-23

Fast, bright inorganic scintillators at room temperature are based on radiative electron-hole recombination in direct-gap semiconductors, e.g. CdS and ZnO. The direct-gap semiconductor is codoped with two different impurity atoms to convert the semiconductor to a fast, high luminosity scintillator. The codopant scheme is based on dopant band to dopant trap recombination. One dopant provides a significant concentration of carriers of one type (electrons or holes) and the other dopant traps carriers of the other type. Examples include CdS:In,Te; CdS:In,Ag; CdS:In,Na; ZnO:Ga,P; ZnO:Ga,N; ZnO:Ga,S; and GaN:Ge,Mg.

Microwave time delays for the dual L-C-band feed system

NASA Technical Reports Server (NTRS)

Chen, J.

1989-01-01

A new dual-frequency feed system at Goldstone is designed to receive the Phobos spacecraft signal at L-band (1668 + or - 40 MHz) and transmit to the spacecraft at C-band (5008.75 + or - 5.00 MHz) simultaneously. Hence, calculations of the time delay from the C-band range calibration coupler to the phase center of the L-C dual feed and back to the L-band range calibration coupler are required to correct the range measurements. Time delays of the elements in the dual-frequency feed system are obtained mostly from computer calculations and partly from experimental measurements. The method used and results obtained are described.

A technique for inferring zonal irregularity drift from single-station GNSS measurements of intensity (S4) and phase (σφ) scintillations

NASA Astrophysics Data System (ADS)

Carrano, Charles S.; Groves, Keith M.; Rino, Charles L.; Doherty, Patricia H.

2016-08-01

The zonal drift of ionospheric irregularities at low latitudes is most commonly measured by cross-correlating observations of a scintillating satellite signal made with a pair of closely spaced antennas. The Air Force Research Laboratory-Scintillation Network Decision Aid (AFRL-SCINDA) network operates a small number of very high frequency (VHF) spaced-receiver systems at low latitudes for this purpose. A far greater number of Global Navigation Satellite System (GNSS) scintillation monitors are operated by the AFRL-SCINDA network (25-30) and the Low-Latitude Ionospheric Sensor Network (35-50), but the receivers are too widely separated from each other for cross-correlation techniques to be effective. In this paper, we present an alternative approach that leverages the weak scatter scintillation theory to infer the zonal irregularity drift from single-station GNSS measurements of S4, σφ, and the propagation geometry. Unlike the spaced-receiver technique, this approach requires assumptions regarding the height of the scattering layer (which introduces a bias in the drift estimates) and the spectral index of the irregularities (which affects the spread of the drift estimates about the mean). Nevertheless, theory and experiment suggest that the ratio of σφ to S4 is less sensitive to these parameters than it is to the zonal drift. We validate the technique using VHF spaced-receiver measurements of zonal irregularity drift obtained from the AFRL-SCINDA network. While the spaced-receiver technique remains the preferred way to monitor the drift when closely spaced antenna pairs are available, our technique provides a new opportunity to monitor zonal irregularity drift using regional or global networks of widely separated GNSS scintillation monitors.

Comparison of the calibration of ionospheric delay in VLBI data by the methods of dual frequency and Faraday rotation

NASA Technical Reports Server (NTRS)

Scheid, J. A.

1985-01-01

When both S-band and X-band data are recorded for a signal which has passed through the ionosphere, it is possible to calculate the ionospheric contribution to signal delay. In Very Long Baseline Interferometry (VLBI) this method is used to calibrate the ionosphere. In the absence of dual frequency data, the ionospheric content measured by Faraday rotation, using a signal from a geostationary satellite, is mapped to the VLBI observing direction. The purpose here is to compare the ionospheric delay obtained by these two methods. The principal conclusions are: (1) the correlation between delays obtained by these two methods is weak; (2) in mapping Faraday rotation measurements to the VLBI observing direction, a simple mapping algorithm which accounts only for changes in hour angle and elevation angle is better than a more elaborate algorithm which includes solar and geomagnetic effects; (3) fluctuations in the difference in total electron content as seen by two antennas defining a baseline limit the application of Faraday rotation data to VLBI.

Description of a Ground Facility for Conducting Ionospheric Scintillation Measurements with the ATS-5 Spacecraft

DOT National Transportation Integrated Search

1974-07-01

Some of the capabilities of the DOT/TSC Westford Propagation Facility located in Westford Massachusetts as they relate to ionospheric measurements will be described. A detailed bibliography of over 400 references is supplied.

Real-time estimation of ionospheric delay using GPS measurements

NASA Astrophysics Data System (ADS)

Lin, Lao-Sheng

1997-12-01

When radio waves such as the GPS signals propagate through the ionosphere, they experience an extra time delay. The ionospheric delay can be eliminated (to the first order) through a linear combination of L1 and L2 observations from dual-frequency GPS receivers. Taking advantage of this dispersive principle, one or more dual- frequency GPS receivers can be used to determine a model of the ionospheric delay across a region of interest and, if implemented in real-time, can support single-frequency GPS positioning and navigation applications. The research objectives of this thesis were: (1) to develop algorithms to obtain accurate absolute Total Electron Content (TEC) estimates from dual-frequency GPS observables, and (2) to develop an algorithm to improve the accuracy of real-time ionosphere modelling. In order to fulfil these objectives, four algorithms have been proposed in this thesis. A 'multi-day multipath template technique' is proposed to mitigate the pseudo-range multipath effects at static GPS reference stations. This technique is based on the assumption that the multipath disturbance at a static station will be constant if the physical environment remains unchanged from day to day. The multipath template, either single-day or multi-day, can be generated from the previous days' GPS data. A 'real-time failure detection and repair algorithm' is proposed to detect and repair the GPS carrier phase 'failures', such as the occurrence of cycle slips. The proposed algorithm uses two procedures: (1) application of a statistical test on the state difference estimated from robust and conventional Kalman filters in order to detect and identify the carrier phase failure, and (2) application of a Kalman filter algorithm to repair the 'identified carrier phase failure'. A 'L1/L2 differential delay estimation algorithm' is proposed to estimate GPS satellite transmitter and receiver L1/L2 differential delays. This algorithm, based on the single-site modelling technique, is

Optimizing ZnS/6LiF scintillators for wavelength-shifting-fiber neutron detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crow, Lowell; Funk, Loren L; Hannan, Bruce W

2016-01-01

In this paper we compare the performance of grooved and flat ZnS/6LiF scintillators in a wavelength shifting-fiber (WLSF) detector. Flat ZnS/6LiF scintillators with the thickness L=0.2-0.8 mm were characterized using photon counting and pulse-height analysis and compared to a grooved scintillator of approximately 0.8 mm thick. While a grooved scintillator considerably increases the apparent thickness of the scintillator to neutrons for a given coating thickness, we find that the flat scintillators perform better than the grooved scintillators in terms of both light yield and neutron detection efficiency. The flat 0.8-mm-thick scintillator has the highest light output, and it is 52%more » higher compared with a grooved scintillator of same thickness. The lower light output of the grooved scintillator as compared to the flat scintillator is consistent with the greater scintillator-WLSF separation and the much larger average emission angle of the grooved scintillator. We also find that the average light cone width, or photon travel-length as measured using time-of-flight powder diffraction of diamond and vanadium, decreases with increasing L in the range of L=0.6-0.8 mm. This result contrasts with the traditional Swank diffusion model for micro-composite scintillators, and could be explained by a decrease in photon diffusion-coefficient or an increase in micro-particle content in the flat scintillator matrix for the thicker scintillators.« less

On the origin of the ionosphere at Moon : a study using results from Chandrayaan-I S-band radio occultation experiment and a photochemical model

NASA Astrophysics Data System (ADS)

Kailasam Madathil, Ambili; Bhardwaj, Anil; Choudhary, Raj Kumar

2016-07-01

Using Chandrayaan-1 communication link between orbiter and ground (S-band frequency), the presence of ionosphere at Moon has been explored using Radio Occultation technique. Results obtained from the observations conducted between July 30 and August 14, 2009 show evidence for a possible existence of the Ionosphere at Moon. A few seconds before the occultation of Chandrayaan-1 radio signals, extra fluctuation in the rate of change of difference between the theoretically estimated Doppler and observed Doppler was observed. The fluctuation was more pronounced when the probing radio waves were crossing through the day-night terminator. Using standard onion-peeling technique to invert the phase changes in radio signals to the refractivity of the medium, we estimated the bending angle and hence the electron density profiles for the Lunar medium. The estimated electron density near the Lunar surface was of the order of 400 - 1000 cm ^{-3} which decreased monotonically with increasing altitude till about 40 km above the surface where it became negligible. The observed electron density was compared with the results from a model which was developed based on CHACE measurements abroad Moon Impact Probe of Chandrayaan-I. The model included the photo chemical reactions and solar wind interactions of the lunar plasma. We propose that the ionosphere over Moon could have molecular origin with H _{2}O ^{+},CO_{2} ^{+} and H_{3}O ^{+} as dominant ions.

Ionospheric Electron Density Measurements Using COSMIC

NASA Astrophysics Data System (ADS)

Dymond, K. F.; Budzien, S. A.; Bernhardt, P. A.; Rocken, C.; Syndergaard, S.

2007-12-01

At 0140 UTC on April 15, 2006, the joint Taiwan-U.S. COSMIC/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate and Formosa Satellite mission #3; hereafter COSMIC) mission, a constellation of six micro-satellites, was launched into a 512-km orbit from Vandenberg Air Force Base in California. Using on-board propulsion these satellites have been deployed to their final orbits at 800 km with 30 degrees of separation. This process has taken about 17 months following the launch. There are three instruments aboard each COSMIC satellite: the GPS Occultation Experiment (GOX), the Tri-Band Beacon (TBB), and the Tiny Ionospheric Photometer (TIP). These three instruments constitute a unique suite of instruments for studying the Earth's ionosphere. The GOX instrument operates by inferring the slant total electron content (the integral of the electron density along the line-of-sight) between the COSMIC satellites and the GPS satellites as a function of tangent height above the Earth's limb. These data can be inverted to produce electron density profiles in the E and F regions of the ionosphere. The TBB is a three frequency radio beacon that radiates coherently at 150, 400, and 1067 MHz. When the relative phases of the signals are measured between the COSMIC satellites and ground-based or space-based receivers, the total electron content along the line-of-sight can be determined. By making the measurements from a set of receivers, the two-dimensional distribution of electrons beneath the satellite can be determined using tomographic techniques. The TIP instrument measures the optical signature of the natural decay of the ionosphere produced via ecombination of the O+ ions and electrons. The TIP measurements can be used to characterize the morphology and dynamics of the global ionosphere. Additionally, the TIP measurements can be inverted in conjunction with the GPS occultation measurements, using tomographic techniques, to produce the two

The climatology of low latitude ionospheric currents derived from CHAMP observations

NASA Astrophysics Data System (ADS)

Stolle, Claudia; Alken, Patrik

2010-05-01

The multi-year data base of magnetic field and ionospheric measurements from the CHAMP satellite contain enormous potential to investigate the behaviour and the origin of currents in the E and F region ionosphere. Special advantage is drawn from the satellite's near polar orbit and the full data coverage over all longitudes and local times. This paper will present findings about two prominent features of the low latitude ionosphere: equatorial plasma irregularities and the equatorial electrojet (EEJ). Equatorial plasma irregularities (commonly known as "bubbles") severely disturb the post sunset F region ionosphere and cause the strongest radio wave scintillations globally during solar maximum years. Using CHAMP vector magnetic field data, it was possible for the first time to show on a long term basis that equatorial plasma irregularities have signatures in all components of the magnetic field. The first ever global climatology of the occurrence rate of these magnetic signatures has been compiled. Such a data base of disturbed orbits is especially useful for core and crustal magnetic field modellers. The magnetic field observations of CHAMP, Ørsted, and SAC-C were employed to develop a climatological model of the EEJ. Measurements of the EEJ and empirical values from electron density and thermospheric density and winds have in addition enabled the development of a climatological model of the equatorial electric field. These results provide excellent opportunity to investigate the seasonal/longitudinal characteristics of the EEJ and the influence of atmospheric waves on E region dynamics.

Space Weather Effects on the Dynamics of Equatorial F Region Irregularities

NASA Astrophysics Data System (ADS)

Bhattacharyya, A.; Basu, S.; Groves, K.; Valladares, C.; Sheehan, R.

Space weather effects on transionospheric radio waves used for navigation and communication may be divided into two categories depending on the spatial scale size of the ionospheric perturbation produced by such effects. For large-scale (> 10 km) perturbations in the ionospheric plasma density, there are changes in the excess time delay for a radio wave signal, which propagates through the ionosphere, while small scale (< 1 m) structures or irregularities in the ionosphere may give rise tok amplitude and phase scintillations on UHF/L-band radio waves, resulting in loss of data, cycle slips and loss of phase lock for signals used in communication/navigation systems. In the equatorial region, where such effects may be severe, space weather effects on the dynamics of equatorial spread F (ESF) irregularities are studied from two different angles. The first one deals with the effect of magnetic activity on the generation of ESF irregularities by helping or hindering the growth of the Rayleigh Taylor (R-T) instability in the post-sunset equatorial F region. For this purpose, spaced receiver observations of scintillations on a UHF signal transmitted from a geostationary satellite and recorded near the dip equator, are used to establish the `age' of the irregularities. This is necessary because the occurrence of scintillations, particularly in the post midnight period, may also be due to irregularities which drift into the path of the radio wave signal, after having been generated more than 3 hours before the actual observation of scintillations. In order to associate the generation of irregularities with major changes in space weather, a parameter that is a measure of random variations in irregularity drift speed is computed from spaced receiver scintillation data. A large value of this parameter is usually a signature of random variations in irregularity drift due to polarization electric fields associated with freshly generated irregularities. Once these electric fields

Simultaneous Observations of Lower Band Chorus Emissions at the Equator and Microburst Precipitating Electrons in the Ionosphere

NASA Astrophysics Data System (ADS)

Mozer, F. S.; Agapitov, O. V.; Blake, J. B.; Vasko, I. Y.

2018-01-01

On 11 December 2016 at 00:12:30 UT, Van Allen Probe-B, at the equator and near midnight, and AC6-B, in the ionosphere, were on magnetic field lines whose 100 km altitude foot points were separated by 600 km. Van Allen Probe-B observed a 30 s burst of lower band chorus waves (with maximum amplitudes >1 nT) at the same time that AC6-B observed intense microburst electrons in the loss cone. One second averaged variations of the chorus intensity and the microburst electron flux were well correlated. The low-altitude electron flux expected from quasi-linear diffusion of the equatorial electrons by the equatorial chorus is in excellent agreement with the observed, 1 s averaged, low-altitude electron flux. However, the large-amplitude, <0.5 s duration, low-altitude electron pulses require nonlinear processes for their explanation.

Method and apparatus for calibrating the ionosphere and application to surveillance of geophysical events

NASA Technical Reports Server (NTRS)

Macdoran, P. F. (Inventor)

1984-01-01

The columnar electron content of the ionosphere between a spacecraft and a receiver is measured in realtime by cross correlating two coherently modulated signals transmitted at different frequencies (L1,L2) from the spacecraft to the receiver using a cross correlator. The time difference of arrival of the modulated signals is proportional to electron content of the ionosphere. A variable delay is adjusted relative to a fixed delay in the respective channels (L1,L2) to produce a maximum at the cross correlator output. The difference in delay required to produce this maximum is a measure of the columnar electron content of the ionosphere. A plurality of monitoring stations and spacecraft (Global Positioning System satellites) are employed to locate any terrestrial event that produces an ionospheric disturbance.

Magnetosphere-Ionosphere Coupling During a Geomagnetic Substorm on March 1, 2017

NASA Astrophysics Data System (ADS)

Coster, A. J.; Hampton, D. L.; Sazykin, S. Y.; Wolf, R.; Huba, J.; Varney, R. H.; Reimer, A.; Lynch, K. A.; Samara, M.; Michell, R.

2017-12-01

On March 1, 2017, at approximately 10 UT, magnetometers at Ft Yukon and Poker Flat in Alaska measured the classic signature of an auroral substorm: a rapid decrease in the northward component of the magnetic field. Nearby, a camera at Venetie Alaska captured intensive visual brightening of multiple auroral arcs at approximately the same time. Our data and model analysis focuses on this time period. We are taking advantage of the extensive instrumentation that was in place in Northern Alaska on this date due to the ISINGLASS rocket campaign. Although no rockets were flown on March 1, 2017, this substorm was monitored at Poker by the three-filter all-sky survey and at Venetie by three all-sky cameras running simultaneously with each filtered for a different wavelength. Our analysis includes co-incidental high precision GNSS receiver data providing total electron content (TEC) measurements during the overhead auroral arcs. The receiver at Venetie also monitored L-band scintillation. In addition, the Poker Flat Incoherent Scatter radar captured the rapid ionization enhancement in the 100-200 km region across multiple beams looking to the north of Poker. The timing of these events between the multiple sites is closely monitored, and inferences of the propagation of this event are described. The available SuperDARN data from this time period indicates this substorm happened at about the same time within the Harang discontinuity. This event presented an unprecedented opportunity to observe occurrence and development of a substorm with a combination of ground-based remote sensing instruments. To support our interpretation of the data, we present first simulations of the magnetosphere-ionosphere coupled system during a substorm with the self-consistently coupled SAMI/RCM code.

Multi-Scale Ionospheric Responses to the St. Patrick's Day Storm (2015) Studied Using a Multimodel Ensemble Prediction System and GPS Data

NASA Astrophysics Data System (ADS)

Pi, X.; Butala, M.; Vergados, P.; Mannucci, A. J.; Komjathy, A.; Wang, C.; Rosen, G.; Schunk, R. W.; Scherliess, L.; Eccles, V.; Gardner, L. C.; Sojka, J. J.; Zhu, L.

2015-12-01

Under the U.S. NASA and NSF collaborative space weather modeling initiative, a Multimodel Ensemble Prediction System (MEPS) for ionosphere-thermosphere-electrodynamics is being developed. The system includes several Global Assimilative Ionospheric Models (GAIMs) developed by the investigators from Utah State University, Jet Propulsion Laboratory, and University of Southern California. In this study, four GAIMs are applied to a study of ionospheric response to the 17 March 2015 St. Patrick's Day storm. It is the most severe geomagnetic storm in the current solar cycle so far. The daily planetary magnetic Ap index and magnetic Kp, Dst, as well as AE indices reached their very high values, i.e., 108, 8, -202 nT, and 2269 nT, respectively. In the assimilative modeling, GPS data from hundreds of globally-distributed ground stations and a number of COSMIC satellites are assimilated into GAIMs to reproduce ionospheric 3-D volume densities and 2-D total electron content (TEC) during the severe storm. Evolution of strong, latitudinally-dependent, and hemispherically asymmetric ionospheric disturbances is revealed through the assimilative modeling. Using the same GPS data, Global Maps of Ionospheric Irregularities and Scintillation (GMIIS) have also been produced. Comparisons of the modeled large-scale ionospheric disturbances and measured small-scale ionospheric irregularities offer additional insight into the M-I-T coupling processes in different regions during varying storm phases. This presentation will provide a picture of distinguished multi-scale ionospheric response to the coronal mass ejection (CME) event during the major geomagnetic storm.

Analysis of rocket beacon transmissions for computerized reconstruction of ionospheric densities

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.; Huba, J. D.; Chaturvedi, P. K.; Fulford, J. A.; Forsyth, P. A.; Anderson, D. N.; Zalesak, S. T.

1993-01-01

Three methods are described to obtain ionospheric electron densities from transionospheric, rocket-beacon TEC data. First, when the line-of-sight from a ground receiver to the rocket beacon is tangent to the flight trajectory, the electron concentration can be obtained by differentiating the TEC with respect to the distance to the rocket. A similar method may be used to obtain the electron-density profile if the layer is horizontally stratified. Second, TEC data obtained during chemical release experiments may be interpreted with the aid of physical models of the disturbed ionosphere to yield spatial maps of the modified regions. Third, computerized tomography (CT) can be used to analyze TEC data obtained along a chain of ground-based receivers aligned along the plane of the rocket trajectory. CT analysis of TEC data is used to reconstruct a 2D image of a simulated equatorial plume. TEC data is computed for a linear chain of nine receivers with adjacent spacings of either 100 or 200 km. The simulation data are analyzed to provide an F region reconstruction on a grid with 15 x 15 km pixels. Ionospheric rocket tomography may also be applied to rocket-assisted measurements of amplitude and phase scintillations and airglow intensities.

Slant path L- and S-Band tree shadowing measurements

NASA Technical Reports Server (NTRS)

Vogel, Wolfhard J.; Torrence, Geoffrey W.

1994-01-01

This contribution presents selected results from simultaneous L- and S-Band slant-path fade measurements through a pecan, a cottonwood, and a pine tree employing a tower-mounted transmitter and dual-frequency receiver. A single, circularly-polarized antenna was used at each end of the link. The objective was to provide information for personal communications satellite design on the correlation of tree shadowing between frequencies near 1620 and 2500 MHz. Fades were measured along 10 m lateral distance with 5 cm spacing. Instantaneous fade differences between L- and S-Band exhibited normal distribution with means usually near 0 dB and standard deviations from 5.2 to 7.5 dB. The cottonwood tree was an exception, with 5.4 dB higher average fading at S- than at L-Band. The spatial autocorrelation reduced to near zero with lags of about 10 lambda. The fade slope in dB/MHz is normally distributed with zero mean and standard deviation increasing with fade level.

Slant path L- and S-Band tree shadowing measurements

NASA Astrophysics Data System (ADS)

Vogel, Wolfhard J.; Torrence, Geoffrey W.

1994-08-01

This contribution presents selected results from simultaneous L- and S-Band slant-path fade measurements through a pecan, a cottonwood, and a pine tree employing a tower-mounted transmitter and dual-frequency receiver. A single, circularly-polarized antenna was used at each end of the link. The objective was to provide information for personal communications satellite design on the correlation of tree shadowing between frequencies near 1620 and 2500 MHz. Fades were measured along 10 m lateral distance with 5 cm spacing. Instantaneous fade differences between L- and S-Band exhibited normal distribution with means usually near 0 dB and standard deviations from 5.2 to 7.5 dB. The cottonwood tree was an exception, with 5.4 dB higher average fading at S- than at L-Band. The spatial autocorrelation reduced to near zero with lags of about 10 lambda. The fade slope in dB/MHz is normally distributed with zero mean and standard deviation increasing with fade level.

Super Resolution Imaging of the Bottomside Ionosphere with the LWA

NASA Astrophysics Data System (ADS)

Obenberger, K.; Parris, R. T.; Taylor, G. B.; Dowell, J.; Malins, J. B.; Pedersen, T.

2017-12-01

Standard ionospheric sounding instruments typically only utilize a handful HF antennas to receive their transmitted signal, and therefore are limited in their ability to image reflections from the bottomside ionosphere. This limitation is primarily due to the low signal to noise ratio of only a few receiving elements. However, recent advancements in digital processing have ushered in a new era of many-element radio telescopes, capable of sub degree all-sky imaging in the HF band. The Long Wavelength Array station at Sevilleta National Wildlife Refuge, New Mexico (LWA-SV), which was specifically designed with improved HF performance for imaging bottomside propagation, began observations this year. I will discuss the new capabilities and imaging techniques of LWA-SV, and show some preliminary measurements of small scale ionospheric structure.

Passive Microwave Measurements Over Conifer Forests at L-Band and C-Band

NASA Technical Reports Server (NTRS)

LeVine, D. M.; Lang, R.; Chauhan, N.; Kim, E.; Bidwell, S.; Goodberlet, M.; Haken, M.; deMatthaeis, P.

2000-01-01

Measurements have been made at L-band and C-band over conifer forests in Virginia to study the response of passive microwave instruments to biomass and soil moisture. A series of aircraft measurements were made in July, August and November, 1999 over relatively homogenous conifer forests of varying biomass. Three radiometers participated in these measurements. These were: 1) the L-band radiometer ESTAR, a horizontally polarized synthetic aperture radiometer which has been used extensively in past measurements of soil moisture; 2) the L-band radiometer SLFMR, a vertically polarized cross-track scanner which has been used successfully in the past for mapping sea surface salinity; and 3) The ACMR, a new C-band radiometer which operates at V- and H-polarization and in the configuration for these experiments did not scan. All three radiometers were flown on the NASA P-3 aircraft based at the Goddard Space Flight Center's Wallops Flight Facility. The ESTAR and SLFMR were mounted in the bomb bay of the P-3 and imaged across track whereas the ACMR was mounted to look aft at 54 degrees up from nadir. Data was collected at altitudes of 915 meters and 457 meters. The forests consisted of relatively homogeneous "managed" stands of conifer located near Waverly, Virginia. This is a relatively flat area about 30 miles southeast of Richmond, VA with numerous stands of trees being grown for the forestry industry. The stands selected for study consisted of areas of regrowth and mature stands of pine. In addition, a small stand of very large trees was observed. Soil moisture sampling was done in each stand during the aircraft over flights. Data was collected on July 7, August 27, November 15 and November 30, 1999. Measurements were made with ESTAR on all days. The ACMR flew on the summer missions and the SLFMR was present only on the August 27 flight. Soil moisture varied from quite dry on July 7 to quite moist on November 30 (which was shortly after a period of rain). The microwave

Ionospheric "Volcanology": Ionospheric Detection of Volcano Eruptions

NASA Astrophysics Data System (ADS)

Astafyeva, E.; Shults, K.; Lognonne, P. H.; Rakoto, V.

2016-12-01

It is known that volcano eruptions and explosions can generate acoustic and gravity waves. These neutral waves further propagate into the atmosphere and ionosphere, where they are detectable by atmospheric and ionospheric sounding tools. So far, the features of co-volcanic ionospheric perturbations are not well understood yet. The development of the global and regional networks of ground-based GPS/GNSS receivers has opened a new era in the ionospheric detection of natural hazard events, including volcano eruptions. It is now known that eruptions with the volcanic explosivity index (VEI) of more than 2 can be detected in the ionosphere, especially in regions with dense GPS/GNSS-receiver coverage. The co-volcanic ionospheric disturbances are usually characterized as quasi-periodic oscillations. The Calbuco volcano, located in southern Chile, awoke in April 2015 after 43 years of inactivity. The first eruption began at 21:04UT on 22 April 2015, preceded by only an hour-long period of volcano-tectonic activity. This first eruption lasted 90 minutes and generated a sub-Plinian (i.e. medium to large explosive event), gray ash plume that rose 15 km above the main crater. A larger second event on 23 April began at 04:00UT (01:00LT), it lasted six hours, and also generated a sub-Plinian ash plume that rose higher than 15 km. The VEI was estimated to be 4 to 5 for these two events. In this work, we first study ionospheric TEC response to the Calbuco volcano eruptions of April 2015 by using ground-based GNSS-receivers located around the volcano. We analyze the spectral characteristics of the observed TEC variations and we estimate the propagation speed of the co-volcanic ionospheric perturbations. We further proceed with the normal mode summation technique based modeling of the ionospheric TEC variations due to the Calbuco volcano eruptions. Finally, we attempt to localize the position of the volcano from the ionospheric measurements, and we also estimate the time of the

Coronal Mass Ejections in September 2017 from Monitoring of Interplanetary Scintillations with the Large Phased Array of the Lebedev Institute of Physics

NASA Astrophysics Data System (ADS)

Chashei, I. V.; Tyul'bashev, S. A.; Shishov, V. I.; Subaev, I. A.

2018-05-01

Results of monitoring of interplanetary scintillations with the Large Phased Array of the Pushchino Radio AstronomyObservatory at 111 MHz during a period of flare activity of the Sun in the first ten days of September 2017 are presented. Enhancements of scintillations associated with interplanetary coronal mass ejections propagating after limb flares have been recorded. The propagation velocities are estimated to be about 2000 km/s for an ejection on September 7 and about 1000 km/s for an ejection on September 6. It is shown that, during the propagation from the Sun, the lateral part of the ejections decelerates faster than its leading part. Night-time enhancements of second-timescale scintillations during periods of high geomagnetic activity have an ionospheric origin.

Ionospheric Signature of Surface Mine Blasts from Global Positioning System Measurements

NASA Technical Reports Server (NTRS)

Calais, Eric; Minster, J. Bernard; Hofton, Michelle A.; Hedlin, Michael A. H.

1998-01-01

Sources such as atmospheric or buried explosions and shallow earthquakes are known to produce infrasonic pressure waves in the atmosphere. Because of the coupling between neutral particles and electrons at ionospheric altitudes, these acoustic and gravity waves induce variations of the ionospheric electron density. The Global Positioning System (GPS) provides a way of directly measuring the total electron content in the ionosphere and, therefore, of detecting such perturbations in the upper atmosphere. In July and August 1996, three large surface mine blasts (1.5 Kt each) were detonated at the Black Thunder coal mine in eastern Wyoming. As part of a seismic and acoustic monitoring- experiment, we deployed five dual-frequency GPS receivers at distances ranging from 50 to 200 km from the mine and were able to detect the ionospheric perturbation caused by the blasts. The perturbation starts 10 to 15 min after the blast, lasts for about 30 min, and propagates with an apparent horizontal velocity of 1200 meters per second. Its amplitude reaches 3 x 10 (exp 14) el per square meters in the 7-3 min period band, a value close to the ionospheric perturbation caused by the M = 6.7 Northridge earthquake. The small signal-to-noise ratio of the perturbation can be improved by slant-stacking the electron content time-series recorded by the different GPS receivers taking into account the horizontal propagation of the perturbation. The energy of the perturbation is concentrated in the 200 to 300 second period band, a result consistent with previous observations and numerical model predictions. The 300 second band probably corresponds to gravity modes and shorter periods to acoustic modes, respectively. Using a 1-D stratified velocity model of the atmosphere we show that linear acoustic ray tracing fits arrival times at all GPS receivers. We interpret the perturbation as a direct acoustic wave caused by the explosion itself. This study shows that even relatively small subsurface

Application of Geostationary GNSS and SBAS Satellites for Studying Ionospheric TEC Disturbances of Geomagnetic and Meteorological Origin

NASA Astrophysics Data System (ADS)

Padokhin, A. M.; Kurbatov, G. A.; Yasyukevich, Y.; Yasyukevich, A.

2017-12-01

With the development of GNSS and SBAS constellations, the coherent multi-frequency L band transmissions are now available from a number of geostationary satellites. These signals can be used for ionospheric TEC estimations in the same way as widely used GPS/GLONASS signals. In this work, we compare noise patterns in TEC estimations based on different geostationary satellites data: augmentation systems (Indian GAGAN, European EGNOS and American WAAS), and Chinese COMPASS/Beidou navigation system. We show that noise level in geostationary COMPASS/Beidou TEC estimations is times smaller than noise in SBAS TEC estimation and corresponds to those of GPS/GLONASS at the same elevation angles. We discuss the capabilities of geostationary TEC data for studying ionospheric variability driven by space weather and meteorological sources at different time scales. Analyzing data from IGS/MGEX receivers we present geostationary TEC response on X-class Solar flares of current cycle, moderate and strong geomagnetic storms, including G4 St. Patrick's day Storm 2015 and recent G3 storm of the end of May 2017. We also discuss geostationary TEC disturbances in near equatorial ionosphere caused by two SSW events (minor and major final warming of 2015-2016 winter season) as well as geostationary TEC response on typhoons activity near Taiwan in autumn 2016. Our results show large potential of geostationary TEC estimations with GNSS and SBAS signals for continuous ionospheric monitoring.

Inorganic scintillating materials and scintillation detectors

PubMed Central

YANAGIDA, Takayuki

2018-01-01

Scintillation materials and detectors that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspection, are reviewed. The fundamental physics understood today is explained, and common scintillators and scintillation detectors are introduced. The properties explained here are light yield, energy non-proportionality, emission wavelength, energy resolution, decay time, effective atomic number and timing resolution. For further understanding, the emission mechanisms of scintillator materials are also introduced. Furthermore, unresolved problems in scintillation phenomenon are considered, and my recent interpretations are discussed. These topics include positive hysteresis, the co-doping of non-luminescent ions, the introduction of an aimed impurity phase, the excitation density effect and the complementary relationship between scintillators and storage phosphors. PMID:29434081

Rapid method for determination of 90Sr in seawater by liquid scintillation counting with an extractive scintillator.

PubMed

Uesugi, Masaki; Watanabe, Ryosuke; Sakai, Hiroaki; Yokoyama, Akihiko

2018-02-01

A rapid determination method of 90 Sr is developed for the monitoring of seawater around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Three ideas of chemical separation and measurements to accelerate 90 Sr analysis are investigated. Strontium is co-precipitated in a two-step procedure with hydroxyapatite after the removal of magnesium phosphate in the presence of citric acid. The purification process of strontium is in combination with solid phase extraction disks. One or two sheets of Sr Rad disk and cyclic operations are examined to eliminate interfering substances and secure the exchange capacity. The suitable conditions of adsorption and stripping are determined with a 85 Sr tracer. Seawater samples up to 1L can be analyzed within 4h. Additionally, the appropriate pH conditions to extract strontium to the scintillator are studied, and the 90 Sr activity is assessed via liquid scintillation counting using an extractive scintillator based on the di-(2-etyl hexyl)-phosphoric acid (HDEHP) extraction method. The new scintillation counting method involves a small quenching effect and a low background compared to the conventional emulsion scintillator method. The minimum detectable activity (MDA) is 35mBq/L of 90 Sr in 180min of counting. The proposed method provides analytical results within a day after receipt of the samples. Copyright © 2017 Elsevier B.V. All rights reserved.

Mapping Greenland's Firn Aquifer using L-band Microwave Radiometry

NASA Astrophysics Data System (ADS)

Miller, J.; Bringer, A.; Jezek, K. C.; Johnson, J. T.; Scambos, T. A.; Long, D. G.

2016-12-01

Greenland's recently discovered firn aquifer is one of the most interesting, yet still mysterious, components of the ice sheet system. Many open questions remain regarding timescales of refreezing and/or englacial drainage of liquid meltwater, and the connections of firn aquifers to the subglacial hydrological system. If liquid meltwater production at the surface of the Greenland ice sheet continues to increase, subsequent increases in the volume of mobile liquid meltwater retained within Greenland's firn aquifer may increase the possibility of crevasse-deepening via hydrofracture. Hydrofracture is an important component of supraglacial lake drainage leading to at least temporary accelerated flow velocities and ice sheet mass balance changes. Firn aquifers may also support hydrofracture-induced drainage and thus are potentially capable of significantly influencing ice sheet mass balance and sea level rise. Spaceborne L-band microwave radiometers provide an innovative tool for ice-sheet wide mapping of the spatiotemporal variability of Greenland's firn aquifer. Both refreezing and englacial drainage may be observable given the sensitivity of the microwave response to the upper surface of liquid meltwater retained within snow and firn pore space as well as the ability of L band instruments to probe the ice sheet from the surface to the firn-ice transition at pore close-off depth. Here we combine L-band (1.4 GHz) brightness temperature observations from multiple sources to demonstrate the potential of mapping firn aquifers on ice sheets using L-band microwave radiometry. Data sources include the interferometric MIRAS instrument aboard ESA's Soil Moisture and Ocean Salinity (SMOS) satellite mission and the radiometer aboard NASA's Soil Moisture Active Passive (SMAP) satellite mission. We will also present mulit-frequency L-band brightness temperature data (0.5-2 GHz) that will be collected over several firn aquifer areas on the Greenland ice sheet by the Ohio State

Generation of Artificial Ionospheric Irregularities by the Modification of the Earth's Middle-Latitude Ionosphere by X-Mode Powerful HF Radio Waves

NASA Astrophysics Data System (ADS)

Frolov, Vladimir; Padokhin, Artem; Kunitsyn, Viacheslav; Akchurin, Adel; Bolotin, Ilya; Zykov, Evgeniy; Vertogradov, Gennadiy

Basing on experimental data obtained at the SURA heating facility by modification of the Earth’s middle-latitude ionosphere, we consider in the report some peculiarities of the generation of artificial plasma density irregularities when X-mode powerful waves (PW) are used for ionosphere pumping [1]. Experiments were carried out during 2008 - 2012 under quite ionospheric conditions (Sigma K_p = 10 - 30). Analysis of obtained experimental data has shown that: 1) In our measurements the generation of small-scale irregularities with l{_⊥} {≃} 10 - 20 m is not observed in contrast to analogous measurements conducted at the EISCAT-heater [2,3]. 2) The generation of irregularities with l{_⊥} {≃} 50 m - 3 km is mainly observed in evening and night hours. In these conditions their intensity is by 3 to 4 times below in comparison with the O-mode pumping. During day hours these irregularities are not detected due to both strong PW energy absorption in the lower ionosphere and forming a defocusing lens at altitudes of 130 - 150 km [4]. 3) The generation of irregularities with l{_⊥} {≥} 5 - 10 km is only observed in evening and night hours. In these conditions their intensity is by 10 times below in comparison with the O-mode pumping. 4) The generation of the irregularities with l{_⊥} {≥} 50 m is observed only when the PW reflects in the ionospheric F _{2} region. 5) Under day-time conditions the defocusing lens is forming at altitudes of about of 130 - 150 km when the ionosphere is pumping both X- and O- mode powerful waves [4]. Its horizontal size is determined by the HF beam. In our experiments [1] it was revealed that the stronger generation of irregularities with scale-lengths l{_⊥} {≃} 5 - 10 km is observed at the HF beam edge where the effective radiated power is of about 0.1 P _{max}. Such a “beam-edge” effect is also observed when the ionosphere is modified by O-mode PW. The enhancement of irregularity generation at the HF beam edge was

Radio Tomography of Ionospheric Structures (probably) due to Underground-Surface-Atmosphere-Ionosphere Coupling

NASA Astrophysics Data System (ADS)

Kunitsyn, V.; Nesterov, I.; Andreeva, E.; Rekenthaler, D. A.

2012-12-01

. The single-point measurements (by ionosondes or by isolated receivers) are not amenable to unambiguous interpretation; based on these data, it is impossible to distinguish the contribution of USAI coupling from the ionospheric effects induced by the "ordinary" impacts (the Sun, the solar wind, geomagnetic perturbations, galactic cosmic rays, etc.). In order to localize sources of the ionospheric disturbances, the geophysicist needs information on the spatial structure and dynamics of the ionospheric perturbations. This information (2D-4D RT images) is optimally provided by RT methods. We present examples of the ionospheric disturbances caused by EQs as well as the ionospheric precursors of these EQs in the form of specific ionospheric irregularities: AGW- and soliton-like wave disturbances, which we identified using RT methods. Based on the results of the RT studies in the Alaska and Taiwan regions, we have detected several dozen AGW-related precursors of EQs. These data allow us to attempt to locate the source of these perturbations. We discuss the possibilities and prospects of further research aimed at identifying and analyzing precursors of EQs and establishing the mechanisms of USAI coupling. We are grateful to Northwest Research Associates, Inc., and Dr. L.-C.Tsai for providing raw RT data for Alaska and Taiwan.

Ionospheric response to the 17-18 March 2015 geomagnetic storm as seen from multiple TEC and NmF2 measurements along 100°E

NASA Astrophysics Data System (ADS)

Bhuyan, Pradip; Yokoyama, Tatsuhiro; Kalita, Bitap Raj; Seemala, G. K.; Hazarika, Rumajyoti; Komolmis, Tharadol; Yatini, Clara; Chakrabarty, Dibyendu; Supnithi, Pornchai

2016-07-01

The response of the ionosphere along 100°E to the strong geomagnetic storm of 17-18 March 2015 has been investigated combining TEC and NmF2 data from multiple stations spanning low latitudes in the northern and southern hemispheres to the equator. The GPS TEC data measured over Dibrugarh (27.4°N, 95°E), Kohima (25.6°N, 94.1°E) and Ahmedabad (23.0°N, 72.5°E) and NmF2 measured along a chain of ionosonde stations Dibrugarh (27.5°N, 95°E), Chiang Mai (18.76ºN, 98.93ºE), Chumphon (10.72ºN,99.37ºE), Kototabang (0.2ºS,100.32ºE) and Cocos Island (12.2ºS,96.8ºE ) were used to examine the signature of the storm around the low-mid latitude ionosphere in this sector. Nearly similar TEC variation has been observed over Dibrugarh and Kohima located at the northern edge of the EIA. The maximum TEC on 18 March over Dibrugarh and Kohima was reduced by more than ~80 TECU compared to that on the geomagnetically quiet day of 16 March 2015. In contrast to the substantial reduction in TEC over ~100°E TEC from the ~75°E longitude station Ahmedabad showed insignificant variations on the same day. Strong reduction in NmF2 at the crest of the anomaly in both northern and southern hemisphere (Dibrugarh, Ching Mai and Cocos Island) and enhancement near the equator (Cumphon and Kototbang) has been observed. The O/N2 ratio as obtained from the TIMED/GUVI reduced substantially along 100°E on 18 March compared to other longitude sectors. Equatorward meridional winds depleted the ionization at the crest region and enhanced the same near the equator. No L band scintillation was observed in the evening of 17 March at Dibrugarh and Kohima indicating absence of F region irregularity along this longitude while strong scintillations were observed at 75°E. The reversal of the IMF Bz from southward to northward direction in the dusk to evening sector inhibited the growth of the irregularity due to reversal of the PPEF at 100°E while the PPEF favoured generation and growth of Spread F

An Ionospheric Index Model based on Linear Regression and Neural Network Approaches

NASA Astrophysics Data System (ADS)

Tshisaphungo, Mpho; McKinnell, Lee-Anne; Bosco Habarulema, John

2017-04-01

The ionosphere is well known to reflect radio wave signals in the high frequency (HF) band due to the present of electron and ions within the region. To optimise the use of long distance HF communications, it is important to understand the drivers of ionospheric storms and accurately predict the propagation conditions especially during disturbed days. This paper presents the development of an ionospheric storm-time index over the South African region for the application of HF communication users. The model will result into a valuable tool to measure the complex ionospheric behaviour in an operational space weather monitoring and forecasting environment. The development of an ionospheric storm-time index is based on a single ionosonde station data over Grahamstown (33.3°S,26.5°E), South Africa. Critical frequency of the F2 layer (foF2) measurements for a period 1996-2014 were considered for this study. The model was developed based on linear regression and neural network approaches. In this talk validation results for low, medium and high solar activity periods will be discussed to demonstrate model's performance.

Morphology of auroral zone radio wave scintillation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rino, C.L.; Matthews, S.J.

1980-08-01

This paper describes the morphology of midnight sector and morning sector auroral zone scintillation observations made over a two-year period using the Wideband satelite, which is in a sun-synchronous, low-altitude orbit. No definitive seasonal variation was found. The nighttime data showed the highest scintillation ocurrence levels, but significant amounts of morning scintillation were observed. For the most part the scintillation activity followed the general pattern of local magnetic activity. The most prominent feature in the nightime data is a localized amplitude and phase scintillation enhancement at the point where the propagation vector lies within an L shell. A geometrical effectmore » due to a dynamic slab of sheetlike structures in the F region is hypothesized as the source of his enhancement. The data have been sorted by magnetic activity, proximity to local midnight, and season. The general features of the data are in agreement with the accepted morphology of auroral zone scintillation.« less

U.S. Aeronautical L-Band Satellite Technology Test Program : Interim Tests Results

DOT National Transportation Integrated Search

1975-06-01

The U.S. Aeronautical L-Band satellite test program was performed between September 1974 and April 1975 as part of an international ATS-6 L-Band satellite test program. The U.S. program consisted of both technology and ATC communications demonstratio...

Impact of heliogeophysical disturbances on ionospheric HF channels

NASA Astrophysics Data System (ADS)

Uryadov, V. P.; Vybornov, F. I.; Kolchev, A. A.; Vertogradov, G. G.; Sklyarevsky, M. S.; Egoshin, I. A.; Shumaev, V. V.; Chernov, A. G.

2018-04-01

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ∼50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (∼100 m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero - Yoshkar-Ola and Cyprus - Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus - Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval.

The SNO+ Scintillator Purification Plant and Projected Sensitivity to Solar Neutrinos in the Pure Scintillator Phase

NASA Astrophysics Data System (ADS)

Pershing, Teal; SNO+ Collaboration

2016-03-01

The SNO+ detector is a neutrino and neutrinoless double-beta decay experiment utilizing the renovated SNO detector. In the second phase of operation, the SNO+ detector will contain 780 tons of organic liquid scintillator composed of 2 g/L 2,5-diphenyloxazole (PPO) in linear alkylbenzene (LAB). In this phase, SNO+ will strive to detect solar neutrinos in the sub-MeV range, including CNO production neutrinos and pp production neutrinos. To achieve the necessary detector sensitivity, a four-part scintillator purification plant has been constructed in SNOLAB for the removal of ionic and radioactive impurities. We present an overview of the SNO+ scintillator purification plant stages, including distillation, water extraction, gas stripping, and metal scavenger columns. We also give the projected SNO+ sensitivities to various solar-produced neutrinos based on the scintillator plant's projected purification efficiency.

Strong Ionospheric Disturbances Observed by a Dense GPS Array After Large Earthquakes: Case Study of the 2003 Tokachi-oki Earthquake and its Geophysical Mechanism

NASA Astrophysics Data System (ADS)

Heki, K.; Ping, J.

2004-12-01

Ionospheric disturbances have been detected after, e.g. Northridge (Calais and Minster, 1995) and Denali (Ducic et al., 2003) earthquakes. Similar signals observed after the 2003 Tokachi-Oki Earthquake, the largest earthquake in Japan after the completion of GEONET, a nationwide array composed of over 1000 CGPS stations. We followed a standard procedure: applying a band-pass filter for the ionospheric combination of the L1 and L2 phase signals and calculating subioonospheric points (SIP) assuming thin ionosphere at the height of 350 km. Owing to the high density of SIP, many interesting features are observed and several important parameters were constrained, e.g. (1) apparent propagation speed, (2) directivity of disturbance signals, (3) decay during propagation, etc. As for (1), the observed speed of about 1 km/sec is significantly smaller than the Rayleigh Wave velocity, significantly faster than Travelling Ionospheric Disturbances (TID), but is consistent with the sound velocity at the ionospheric heights. The acoustic wave generated by sudden vertical movement of the Earth's surface first propagate upward. Then it will be refracted by height-dependent velocity structure resulting in horizontally propagating wave through the ionosphere. The observed TEC variation, with a wavelength of a few hundred km, may reflect electron density oscillation caused by the passage of such an acoustic wave. Regarding (2), there was a clear indication that the wave does not propagate northward. As first suggested by Calais et al. (1998), such a blocking is considered to be due to interaction between the geomagnetic field and the movement of charged particles comprising the ionosphere associated with the acoustic wave propagation. The model predicts that there will be no southward propagation of ionospheric disturbances caused by earthquakes in southern hemisphere mid-latitudes, which needs be confirmed by future earthquakes. The point (3) enabled the authors to define the

A Technique for Real-Time Ionospheric Ranging Error Correction Based On Radar Dual-Frequency Detection

NASA Astrophysics Data System (ADS)

Lyu, Jiang-Tao; Zhou, Chen

2017-12-01

Ionospheric refraction is one of the principal error sources for limiting the accuracy of radar systems for space target detection. High-accuracy measurement of the ionospheric electron density along the propagation path of radar wave is the most important procedure for the ionospheric refraction correction. Traditionally, the ionospheric model and the ionospheric detection instruments, like ionosonde or GPS receivers, are employed for obtaining the electron density. However, both methods are not capable of satisfying the requirements of correction accuracy for the advanced space target radar system. In this study, we propose a novel technique for ionospheric refraction correction based on radar dual-frequency detection. Radar target range measurements at two adjacent frequencies are utilized for calculating the electron density integral exactly along the propagation path of the radar wave, which can generate accurate ionospheric range correction. The implementation of radar dual-frequency detection is validated by a P band radar located in midlatitude China. The experimental results present that the accuracy of this novel technique is more accurate than the traditional ionospheric model correction. The technique proposed in this study is very promising for the high-accuracy radar detection and tracking of objects in geospace.

Large Scale Assessment of Radio Frequency Interference Signatures in L-band SAR Data

NASA Astrophysics Data System (ADS)

Meyer, F. J.; Nicoll, J.

2011-12-01

Imagery of L-band Synthetic Aperture Radar (SAR) systems such as the PALSAR sensor on board the Advanced Land Observing Satellite (ALOS) has proven to be a valuable tool for observing environmental changes around the globe. Besides offering 24/7 operability, the L-band frequency provides improved interferometric coherence, and L-band polarimetric data has shown great potential for vegetation monitoring, sea ice classification, and the observation of glaciers and ice sheets. To maximize the benefit of missions such as ALOS PALSAR for environmental monitoring, data consistency and calibration are vital. Unfortunately, radio frequency interference (RFI) signatures from ground-based radar systems regularly impair L-band SAR data quality and consistency. With this study we present a large-scale analysis of typical RFI signatures that are regularly observed in L-band SAR data over the Americas. Through a study of the vast archive of L-band SAR data in the US Government Research Consortium (USGRC) data pool at the Alaska Satellite Facility (ASF) we were able to address the following research goals: 1. Assessment of RFI Signatures in L-band SAR data and their Effects on SAR Data Quality: An analysis of time-frequency properties of RFI signatures in L-band SAR data of the USGRC data pool is presented. It is shown that RFI-filtering algorithms implemented in the operational ALOS PALSAR processor are not sufficient to remove all RFI-related artifacts. In examples, the deleterious effects of RFI on SAR image quality, polarimetric signature, SAR phase, and interferometric coherence are presented. 2. Large-Scale Assessment of Severity, Spatial Distribution, and Temporal Variation of RFI Signatures in L-band SAR data: L-band SAR data in the USGRC data pool were screened for RFI using a custom algorithm. Per SAR frame, the algorithm creates geocoded frame bounding boxes that are color-coded according to RFI intensity and converted to KML files for analysis in Google Earth. From

Comparative study of nondoped and Eu-doped SrI2 scintillator

NASA Astrophysics Data System (ADS)

Yanagida, Takayuki; Koshimizu, Masanori; Okada, Go; Kojima, Takahiro; Osada, Junya; Kawaguchi, Noriaki

2016-11-01

Optical and scintillation properties of nondoped and Eu 3% doped SrI2 crystals grown by the Vertical Bridgman method were investigated. Eu-doped crystal showed an intense single band emission at 430 nm due to the Eu2+ 5d-4f transitions in both photoluminescence and scintillation while the nondoped crystal had a complex spectral shape. The latter emission consists of mainly four bands: 360 nm, 540 nm, 410 nm and 430 nm. The origins of 360 nm and 540 nm were self-trapped exciton and unexpected impurity, respectively. The origins of 410 and 430 nm lines were ascribed to F center in different I sites. Under 137Cs γ-ray irradiations, both crystals showed a clear photoabsorption peak. The scintillation light yields of the nondoped and Eu-doped SrI2 resulted 33,000 ph/MeV and 82,000 ph/MeV, respectively. The energy resolution at 662 keV of Eu-doped was 4% while that of the non-doped SrI2 was 8%.

Design of dual band FSS by using quadruple L-slot technique

NASA Astrophysics Data System (ADS)

Fauzi, Noor Azamiah Md; Aziz, Mohamad Zoinol Abidin Abd.; Said, Maizatul Alice Meor; Othman, Mohd Azlishah; Ahmad, Badrul Hisham; Malek, Mohd Fareq Abd

2015-05-01

This paper presents a new design of dual band frequency selective surface (FSS) for band pass microwave transmission application. FSS can be used on energy saving glass to improve the transmission of wireless communication signals through the glass. The microwave signal will be attenuate when propagate throughout the different structure such as building. Therefore, some of the wireless communication system cannot be used in the optimum performance. The aim of this paper is designed, simulated and analyzed the new dual band FSS structure for microwave transmission. This design is based on a quadruple L slot combined with cross slot to produce pass band at 900 MHz and 2.4 GHz. The vertical of pair inverse L slot is used as the band pass for the frequency of 2.4GHz. While, the horizontal of pair inverse L slot is used as the band pass at frequency 900MHz. This design is simulated and analyzed by using Computer Simulation Technology (CST) Microwave Studio (MWS) software. The characteristics of the transmission (S21) and reflection (S11) of the dual band FSS were simulater and analyzed. The bandwidth of the first band is 118.91MHz which covered the frequency range from 833.4MHz until 952.31MHz. Meanwhile, the bandwidth for the second band is 358.84MHz which covered the frequency range from 2.1475GHz until 2.5063GHz. The resonance/center frequency of this design is obtained at 900MHz with a 26.902dB return loss and 2.37GHz with 28.506dB a return loss. This FSS is suitable as microwave filter for GSM900 and WLAN 2.4GHz application.

Low-latitude ionospheric research using the CIRCE Mission: instrumentation overview

NASA Astrophysics Data System (ADS)

Dymond, K. F.; Nicholas, A. C.; Budzien, S. A.; Stephan, A. W.; Marquis, P.; Brown, C. M.; Finne, T.; Wolfram, K. D.

2017-08-01

The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) is a dual-satellite mission consisting of two 6U CubeSats actively maintaining a lead-follow configuration in the same orbit with a launch planned for the 2018-2019 time-frame. These nanosatellites will each feature two 1U size ultraviolet photometers, observing the 135.6 nm emission of atomic oxygen at nighttime. The primary objective is to characterize the two-dimensional distribution of electrons in the orbital plane of the vehicles with special emphasis on studying the morphology of the Equatorial Ionization Anomaly (EIA). The methodology used to reconstruct the nighttime ionosphere employs continuous UV photometry from four distinct viewing angles in combination with an additional data source, such as in situ plasma density measurements or a wide-band beacon data, with advanced image space reconstruction algorithm tomography techniques. The COSMIC/FORMOSAT-3 (CF3) constellation featured six Tiny Ionospheric Photometers, compact UV sensors which served as the pathfinder for the CIRCE instruments. The TIP instruments on the CF3 satellites demonstrated detection of ionospheric bubbles before they had penetrated the peak of the F-region ionosphere, showed the temporal evolution of the EIA, and observed a Medium Scale Travelling Ionospheric Disturbance. We present our mission concept, some pertinent information regarding the instrument design, the results of simulations illustrating the imaging capability of the sensor suite, and a range of science questions addressable using such a system.

Challenges and Solutions for GNSS Receivers onboard LEO Satellites Traveling through the Ionosphere during Space Weather Events

NASA Astrophysics Data System (ADS)

Morton, Y.; Xu, D.; Yang, R.; Jiao, Y.; Rino, C.; Carrano, C. S.

2017-12-01

This presentation discusses challenges imposed on GNSS receiver carrier-tracking loop for receivers onboard LEO satellites traveling through ionosphere during space weather events and techniques that mitigate the effects. Recent studies show that the ESA's swarm satellites experienced a total loss of GPS signals in areas known for frequent occurrence of ionosphere plasma irregularities. The same phenomena have been observed in other satellite missions. More robust GNSS receiver technologies are needed to improve the navigation capabilities for future LEO satellite missions. A major challenge to characterize GNSS signals traversing ionospheric plasma structures to reach a LEO satellite is the lack of data. To overcome this challenge, we utilized a physics-based GNSS scintillation signal simulator to generate simulated data for analysis and algorithm development. The simulator relies on real scintillation data collected by ground-based receivers as the initializer to generate a realization of ionosphere irregularity structure statistical distribution. A user specifies desired satellite orbit, signal modulation scheme, receiver platform dynamics, and receiver front-end hardware design. These inputs are used to establish the signal propagation geometry to allow interception of the disturbed signal by a realistic GNSS receiver. The simulator results showed that plasma structures lead to strong disturbances on GNSS signals reaching a LEO platform. The disturbances are characterized by simultaneous deep amplitude fades and extremely rapid carrier phase fluctuations. The carrier phase rate is orders of magnitude higher than the ones experienced by receivers on the ground. Such high carrier dynamics far exceeds the range that can be tolerated by the bandwidth of a typical GNSS receiver. The deep amplitude fades further exacerbate the problem. Based on the simulator outputs, we established models of the disturbed signal parameters. These models are used in an adaptive

Detection of Ionospheric Alfven Resonator Signatures in the Equatorial Ionosphere

NASA Technical Reports Server (NTRS)

Simoes, Fernando; Klenzing, Jeffrey; Ivanov, Stoyan; Pfaff, Robert; Freudenreich, Henry; Bilitza, Dieter; Rowland, Douglas; Bromund, Kenneth; Liebrecht, Maria Carmen; Martin, Steven;

L-Band System Engineering - Concepts of Use, Systems Performance Requirements, and Architecture

NASA Technical Reports Server (NTRS)

Henriksen, Stephen; Zelkin, Natalie

2011-01-01

This document is being provided as part of ITT s NASA Glenn Research Center Aerospace Communication Systems Technical Support (ACSTS) contract NNC05CA85C, Task 7: New ATM Requirements-Future Communications, C-band and L-band Communications Standard Development. Task 7 was motivated by the five year technology assessment performed for the Federal Aviation Administration (FAA) under the joint FAA-EUROCONTROL cooperative research Action Plan (AP-17), also known as the Future Communications Study (FCS). It was based on direction provided by the FAA project-level agreement (PLA FY09_G1M.02-02v1) for "New ATM Requirements-Future Communications." Task 7 was separated into two distinct subtasks, each aligned with specific work elements and deliverable items. Subtask 7-1 addressed C-band airport surface data communications standards development, systems engineering, test bed development, and tests/demonstrations to establish operational capability for what is now referred to as the Aeronautical Mobile Airport Communications System (AeroMACS). Subtask 7-2, which is the subject of this report, focused on preliminary systems engineering and support of joint FAA/EUROCONTROL development and evaluation of a future L-band (960 to 1164 MHz) air/ground (A/G) communication system known as the L-band digital aeronautical communications system (L-DACS), which was defined during the FCS. The proposed L-DACS will be capable of providing ATM services in continental airspace in the 2020+ timeframe. Subtask 7-2 was performed in two phases. Phase I featured development of Concepts of Use, high level functional analyses, performance of initial L-band system safety and security risk assessments, and development of high level requirements and architectures. It also included the aforementioned support of joint L-DACS development and evaluation, including inputs to L-DACS design specifications. Phase II provided a refinement of the systems engineering activities performed during Phase I, along

Plastic fiber scintillator response to fast neutrons

NASA Astrophysics Data System (ADS)

Danly, C. R.; Sjue, S.; Wilde, C. H.; Merrill, F. E.; Haight, R. C.

2014-11-01

The Neutron Imaging System at NIF uses an array of plastic scintillator fibers in conjunction with a time-gated imaging system to form an image of the neutron emission from the imploded capsule. By gating on neutrons that have scattered from the 14.1 MeV DT energy to lower energy ranges, an image of the dense, cold fuel around the hotspot is also obtained. An unmoderated spallation neutron beamline at the Weapons Neutron Research facility at Los Alamos was used in conjunction with a time-gated imaging system to measure the yield of a scintillating fiber array over several energy bands ranging from 1 to 15 MeV. The results and comparison to simulation are presented.

Plastic fiber scintillator response to fast neutrons.

PubMed

Danly, C R; Sjue, S; Wilde, C H; Merrill, F E; Haight, R C

2014-11-01

The Neutron Imaging System at NIF uses an array of plastic scintillator fibers in conjunction with a time-gated imaging system to form an image of the neutron emission from the imploded capsule. By gating on neutrons that have scattered from the 14.1 MeV DT energy to lower energy ranges, an image of the dense, cold fuel around the hotspot is also obtained. An unmoderated spallation neutron beamline at the Weapons Neutron Research facility at Los Alamos was used in conjunction with a time-gated imaging system to measure the yield of a scintillating fiber array over several energy bands ranging from 1 to 15 MeV. The results and comparison to simulation are presented.

Quasi-Static Alfv{é}n Dynamics and Scale-Dependent Energy Deposition in Magnetosphere-Ionosphere Coupling

NASA Astrophysics Data System (ADS)

Lotko, W.; Lysak, R. L.; Streltsov, A. V.

2002-12-01

Alfv{é}n wave dynamics become quasi-static in the ionosphere and low-altitude magnetosphere in the ULF regime below 10 mHz and at altitudes less than a few RE when the following two conditions are met: ω L RE << vA (l) and ω l << 1 / μ 0 Σ P. L is the dipole shell parameter, ω is the wave frequency in radians, l represents field-aligned distance above the ionosphere, vA (l) is the local Alfv{é}n speed, and Σ P is the ionospheric Pedersen conductance. In this limit, reactive power stored in Alfv{é}nic fluctuations at high altitude flows quasi-statically into ionospheric Joule heating and low-altitude collisionless dissipation. The combined dissipative effects are described by the electrostatic model of Chiu-Cornwall-Lyons [1980] which captures the transverse wavelength dependence of low-altitude Alfv{é}nic energy deposition. The analysis and results described here 1) correspond to the low-altitude, low-frequency limit of theories for the interaction of an Alfv{é}n wave with the ionosphere [Knudsen et al., 1992], including effects of a low-altitude collisionless dissipation layer [Vogt and Haerendel, 1998], and field line eigenmodes with allowance for finite ionospheric conductivity and realistic parallel inhomogeneity [Allan and Knox, 1979]; 2) reconcile the interpretation of inverted-V precipitation regions as electrostatic potential structures with electromagnetic energy deposition via Alfv{é}n waves at frequencies below 10 mHz; 3) provide criteria for the validity of the Knight current-voltage relation in the ULF regime and its use in global MHD simulations; 4) relate low-altitude satellite measurements of both ``static'' and ULF electric and magnetic fields directly to the ionospheric Pedersen conductivity; and 5) offer a resolution to debates about high-altitude closure of auroral potential structures as O-, U-, or S-potential forms.

Kinesonde observations of ionosphere modification by intense electromagnetic fields from Platteville, Colorado.

NASA Technical Reports Server (NTRS)

Wright, J. W.

1973-01-01

Observations by the Kinesonde (a multifrequency, spaced antenna, digitized complex-amplitude radio sounding system) of ionospheric responses to excitation by the high-power transmitter at Platteville, Colo., are described. Increases of echo scintillation rate and intensity at frequencies reflected near and far from the excitation level are shown. Significant onset delays of these responses suggest disturbance propagation velocities of a few kilometers per second. Calculated echolocations show a time-dependent development toward the excitation region, again with a delayed response. Comments are offered regarding the relative utility of ionogram and Kinesonde observations for study of these phenomena.

Analysis of ionospheric refraction error corrections for GRARR systems

NASA Technical Reports Server (NTRS)

Mallinckrodt, A. J.; Parker, H. C.; Berbert, J. H.

1971-01-01

A determination is presented of the ionospheric refraction correction requirements for the Goddard range and range rate (GRARR) S-band, modified S-band, very high frequency (VHF), and modified VHF systems. The relation ships within these four systems are analyzed to show that the refraction corrections are the same for all four systems and to clarify the group and phase nature of these corrections. The analysis is simplified by recognizing that the range rate is equivalent to a carrier phase range change measurement. The equation for the range errors are given.

Preface: International Reference Ionosphere - Progress in Ionospheric Modelling

NASA Technical Reports Server (NTRS)

Bilitza Dieter; Reinisch, Bodo

2010-01-01

The international reference ionosphere (lRI) is the internationally recommended empirical model for the specification of ionospheric parameters supported by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) and recognized by the International Standardization Organization (ISO). IRI is being continually improved by a team of international experts as new data become available and better models are being developed. This issue chronicles the latest phase of model updates as reported during two IRI-related meetings. The first was a special session during the Scientific Assembly of the Committee of Space Research (COSPAR) in Montreal, Canada in July 2008 and the second was an IRI Task Force Activity at the US Air Force Academy in Colorado Springs in May 2009. This work led to several improvements and additions of the model which will be included in the next version, IRI-201O. The issue is divided into three sections focusing on the improvements made in the topside ionosphere, the F-peak, and the lower ionosphere, respectively. This issue would not have been possible without the reviewing efforts of many individuals. Each paper was reviewed by two referees. We thankfully acknowledge the contribution to this issue made by the following reviewers: Jacob Adeniyi, David Altadill, Eduardo Araujo, Feza Arikan, Dieter Bilitza, Jilijana Cander, Bela Fejer, Tamara Gulyaeva, Manuel Hermindez-Pajares, Ivan Kutiev, John MacDougal, Leo McNamara, Bruno Nava, Olivier Obrou, Elijah Oyeyemi, Vadym Paznukhov, Bodo Reinisch, John Retterer, Phil Richards, Gary Sales, J.H. Sastri, Ludger Scherliess, Iwona Stanislavska, Stamir Stankov, Shin-Yi Su, Manlian Zhang, Y ongliang Zhang, and Irina Zakharenkova. We are grateful to Peggy Ann Shea for her final review and guidance as the editor-in-chief for special issues of Advances in Space Research. We thank the authors for their timely submission and their quick response to the reviewer comments and humbly

Satellite-motion Compensation for Monitoring Travelling Ionospheric Disturbances (TIDs) Using GPS

NASA Astrophysics Data System (ADS)

Jackson-Booth, N.; Penney, R.

2016-12-01

The ionosphere exerts a strong influence over a wide range of modern communications and navigtion systems, but is subject to complex influences from both terrestrial and solar sources. Ionospheric disturbances can be triggered by lower-atmosphere phenomena such as hurricanes as well as geophysical events such as earthquakes, as well as being strongly influenced by cyclical and unpredictable solar behaviour. Dual-band GPS receivers provide a popular and convenient means of obtaining information about the ionosphere, and ionospheric disturbances. While GPS measurements can provide clues about the state of the ionosphere, there are many challenges in obtaining reliable information from them. For example, drop-outs and carrier-phase cycle slips may have little influence on using GPS for (medium-precision) navigation, but can lead to signal-processing artefacts that would cause false alarms in detecting ionospheric disturbances. If one is interested in measuring the motion of travelling ionospheric disturbances (TIDs) one must also be able to disentangle the effects of satellite motion from the TID motion. We discuss a novel approach to robustly separating TID waveforms from background trends within GPS time-series of total electron content (TEC), as well as innovative techniques for estimating TID velocities using ideas from Synthetic Aperture Radar (SAR). Underpinning these, we consider how to robustly pre-process GPS time-series to reduce the influence of drop-outs while also reducing data volumes. We present comparisons of our TID velocity estimates with more standard "cross-correlation" techniques, including cases where these standard techniques produce pathological results. We also show results from simulated GPS time-series derived from modelled ionospheric disturbances.

Daytime VHF amplitude scintillations recorded at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during 1997-2003

NASA Astrophysics Data System (ADS)

Uma, G.; Brahmanandam, P. S.; Srinivasu, V. K. D.; Prasad, D. S. V. V. D.; Rama Rao, P. V. S.

2018-04-01

In this research, it is presented the daytime amplitude scintillations recorded at VHF frequency (244 MHz) at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during seven continuous years (1997-2003). Contrary to the nighttime scintillation seasonal trends, the occurrence of daytime scintillations maximizes during summer followed by winter and the equinox seasons. The fade depths, scintillation indices and the patch durations of daytime scintillations are meager when compared with their nighttime counterparts. A co-located digital high frequency (HF) ionosonde radar confirms the presence of sporadic (Es) layers when daytime scintillations are observed. The presence of daytime scintillations is evident when the critical frequency of the Es-layer (foEs) is ≥4 MHz and Es-layers are characterized by a highly diffuse range spread Es echoes as can be seen on ionograms. It is surmised that the gradient drift instability (GDI) seems to be the possible mechanism for the generation of these daytime scintillations. It is quite likely that the spread Es-F-layer coupling is done through polarization electric fields (Ep) that develop inside the destabilized patches of sporadic E layers, which are mapped up to the F region along the field lines as to initiate the daytime scintillations through the GDI mechanism. Further, the presence of additional stratification of ionosphere F-layer, popularly known as the F3-layer, is observed on ionograms once the Es-layers and daytime scintillations are ceased.

Experimental evidence of electromagnetic pollution of ionosphere

NASA Astrophysics Data System (ADS)

Pronenko, Vira; Korepanov, Valery; Dudkin, Denis

multiple low orbiting satellites have confirmed a significant increase in their intensity over the populated areas of Europe and Asia. Recently, there are many experimental evidences of the existence of power line harmonic radiation (PLHR) in the ionosphere. Their spectra consist of succession of 50 (60) Hz harmonics which is accompanied by a set of lines separated by 50 (60) or 100 (120) Hz - the central frequency of which is shifted to high frequency. These lines cover rather wide band - according to the available experimental data, their central frequencies are observed from ~1.5 - 3 kHz up to 15 kHz, and recently the main mains frequencies are also observed. The examples of power line harmonic radiation, which were detected by “Sich-1M”, “Chibis-M” and “Demeter” satellites, have been presented and discussed. The available experimental data, as well as theoretical estimations, allow us with a high degree of certainty to say that the permanent satellite monitoring of the ionospheric and magnetospheric anthropogenic EM perturbations is necessary for: a) objective assessment and prediction of the space weather conditions; b) evaluation of the daily or seasonal changes in the level of energy consumption; c) construction of a map for estimation of near space EM pollution. This study is partially supported by SSAU contract N 4-03/13.

The domination of Saturn's low-latitude ionosphere by ring 'rain'.

PubMed

O'Donoghue, J; Stallard, T S; Melin, H; Jones, G H; Cowley, S W H; Miller, S; Baines, K H; Blake, J S D

2013-04-11

Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring 'rain' is important in modulating ionospheric emissions and suppressing electron densities.

Observing Tsunamis in the Ionosphere Using Ground Based GPS Measurements

NASA Technical Reports Server (NTRS)

Galvan, D. A.; Komjathy, A.; Song, Y. Tony; Stephens, P.; Hickey, M. P.; Foster, J.

2011-01-01

Ground-based Global Positioning System (GPS) measurements of ionospheric Total Electron Content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following recent seismic events, including the Tohoku tsunami of March 11, 2011. We observe fluctuations correlated in time, space, and wave properties with this tsunami in TEC estimates processed using JPL's Global Ionospheric Mapping Software. These TEC estimates were band-pass filtered to remove ionospheric TEC variations with periods outside the typical range of internal gravity waves caused by tsunamis. Observable variations in TEC appear correlated with the Tohoku tsunami near the epicenter, at Hawaii, and near the west coast of North America. Disturbance magnitudes are 1-10% of the background TEC value. Observations near the epicenter are compared to estimates of expected tsunami-driven TEC variations produced by Embry Riddle Aeronautical University's Spectral Full Wave Model, an atmosphere-ionosphere coupling model, and found to be in good agreement. The potential exists to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for future early warning systems.

Searching for MHz Transients with the VLA Low-band Ionosphere and Transient Experiment (VLITE)

NASA Astrophysics Data System (ADS)

Polisensky, Emil; Peters, Wendy; Giacintucci, Simona; Clarke, Tracy; Kassim, Namir E.; hyman, Scott D.; van der Horst, Alexander; Linford, Justin; Waldron, Zach; Frail, Dale

2018-01-01

NRL and NRAO have expanded the low frequency capabilities of the VLA through the VLA Low-band Ionosphere and Transient Experiment (VLITE, http://vlite.nrao.edu/ ), effectively making the instrument two telescopes in one. VLITE is a commensal observing system that harvests data from the prime focus in parallel with normal Cassegrain focus observing on a subset of VLA antennas. VLITE provides over 6000 observing hours per year in a > 5 square degree field-of-view using 64 MHz bandwidth centered on 352 MHz. By operating in parallel, VLITE offers invaluable low frequency data to targeted observations of transient sources detected at higher frequencies. With arcsec resolution and mJy sensitivity, VLITE additionally offers great potential for blind searches of rarer radio-selected transients. We use catalog matching software on the imaging products from the daily astrophysics pipeline and the LOFAR Transients Pipeline (TraP) on repeated observations of the same fields to search for coherent and incoherent astronomical transients on timescales of a few seconds to years. We present the current status of the VLITE transient science program from its initial deployment on 10 antennas in November 2014 through its expansion to 16 antennas in the summer of 2017. Transient limits from VLITE’s first year of operation (Polisensky et al. 2016) are updated per the most recent analysis.

Sounding rocket/ground-based observation campaign to study Medium-Scale Traveling Ionospheric Disturbances (MSTID)

NASA Astrophysics Data System (ADS)

Yamamoto, Mamoru; Otsuka, Yuichi; Abe, Takumi; Yokoyama, Tatsuhiro; Bernhardt, Paul; Watanabe, Shigeto; Yamamoto, Masa-yuki; Larsen, Miguel; Saito, Akinori; Pfaff, Robert; Ishisaka, Keigo

2012-07-01

An observation campaign is under preparation. It is to launch sounding rockets S-520-27 and S-310-42 from Uchinoura Space Center of JAXA, while ground-based instruments measure waves in the ionosphere. The main purpose of the study is to reveal seeding mechanism of Medium-Scale Traveling Ionospheric Disturbances (MSTID). The MSTID is enhanced in the summer nighttime of the mid-latitude ionosphere. The MSTID is not only a simple reflection of atmospheric waves to the ionosphere, but includes complicated processes including the electromagnetic coupling of the F- and E-regions, and inter-hemisphere coupling of the ionosphere. We will measure ionospheric parameters such as electron density and electric fields together with neutral winds in the E- and F-regions. TMA and Lithium release experiment will be conducted with S-310-42 and S-520-27 rockets, respectively. The observation campaign is planned in summer 2012 or 2013. In the presentation we will overview characteristics of MSTID, and show plan and current status of the project. We also touch results from the sounding rocket S-520-26 that was launched on January 12, 2012. We will show results of the rocket-ground dual-band beacon experiment.

Measurement of Scintillation and Ionization Yield and Scintillation Pulse Shape from Nuclear Recoils in Liquid Argon

DOE PAGES

Cao, H.

2015-05-26

We have measured the scintillation and ionization yield of recoiling nuclei in liquid argon as a function of applied electric field by exposing a dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy pulsed narrow band neutron beam produced at the Notre Dame Institute for Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged to detect and identify neutrons scattered in the TPC and to select the energy of the recoiling nuclei. We also report measurements of the scintillation yields for nuclear recoils with energies from 10.3 to 57.3 keV and for median applied electric fields from 0more » to 970 V/cm. For the ionization yields, we report measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to 486 V/cm. Furthermore, we report the observation of an anticorrelation between scintillation and ionization from nuclear recoils, which is similar to the anticorrelation between scintillation and ionization from electron recoils. Assuming that the energy loss partitions into excitons and ion pairs from 83mKr internal conversion electrons is comparable to that from 207Bi conversion electrons, we obtained the numbers of excitons (N ex) and ion pairs (N i) and their ratio (N ex/N i) produced by nuclear recoils from 16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in LAr-TPC signals due to columnar recombination, a comparison of the light and charge yield of recoils parallel and perpendicular to the applied electric field is presented for the first time.« less

Tropospheric and ionospheric media calibrations based on global navigation satellite system observation data

NASA Astrophysics Data System (ADS)

Feltens, Joachim; Bellei, Gabriele; Springer, Tim; Kints, Mark V.; Zandbergen, René; Budnik, Frank; Schönemann, Erik

2018-06-01

Context: Calibration of radiometric tracking data for effects in the Earth atmosphere is a crucial element in the field of deep-space orbit determination (OD). The troposphere can induce propagation delays in the order of several meters, the ionosphere up to the meter level for X-band signals and up to tens of meters, in extreme cases, for L-band ones. The use of media calibrations based on Global Navigation Satellite Systems (GNSS) measurement data can improve the accuracy of the radiometric observations modelling and, as a consequence, the quality of orbit determination solutions. Aims: ESOC Flight Dynamics employs ranging, Doppler and delta-DOR (Delta-Differential One-Way Ranging) data for the orbit determination of interplanetary spacecraft. Currently, the media calibrations for troposphere and ionosphere are either computed based on empirical models or, under mission specific agreements, provided by external parties such as the Jet Propulsion Laboratory (JPL) in Pasadena, California. In order to become independent from external models and sources, decision fell to establish a new in-house internal service to create these media calibrations based on GNSS measurements recorded at the ESA tracking sites and processed in-house by the ESOC Navigation Support Office with comparable accuracy and quality. Methods: For its concept, the new service was designed to be as much as possible depending on own data and resources and as less as possible depending on external models and data. Dedicated robust and simple algorithms, well suited for operational use, were worked out for that task. This paper describes the approach built up to realize this new in-house internal media calibration service. Results: Test results collected during three months of running the new media calibrations in quasi-operational mode indicate that GNSS-based tropospheric corrections can remove systematic signatures from the Doppler observations and biases from the range ones. For the ionosphere, a

RESEARCH PAPERS : Ionospheric signature of surface mine blasts from Global Positioning System measurements

NASA Astrophysics Data System (ADS)

Calais, Eric; Bernard Minster, J.; Hofton, Michelle; Hedlin, Michael

1998-01-01

Sources such as atmospheric or buried explosions and shallow earthquakes are known to produce infrasonic pressure waves in the atmosphere Because of the coupling between neutral particles and electrons at ionospheric altitudes, these acoustic and gravity waves induce variations of the ionospheric electron density. The Global Positioning System (GPS) provides a way of directly measuring the total electron content in the ionosphere and, therefore, of detecting such perturbations in the upper atmosphere. In July and August 1996, three large surface mine blasts (1.5 Kt each) were detonated at the Black Thunder coal mine in eastern Wyoming. As part of a seismic and acoustic monitoring experiment, we deployed five dual-frequency GPS receivers at distances ranging from 50 to 200 km from the mine and were able to detect the ionospheric perturbation caused by the blasts. The perturbation starts 10 to 15 min after the blast, lasts for about 30 min, and propagates with an apparent horizontal velocity of 1200 m s- 1. Its amplitude reaches 3 × 1014 el m- 2 in the 7-3 min period band, a value close to the ionospheric perturbation caused by the M=6.7 Northridge earthquake (Calais & Minster 1995). The small signal-to-noise ratio of the perturbation can be improved by slant-stacking the electron content time-series recorded by the different GPS receivers taking into account the horizontal propagation of the perturbation. The energy of the perturbation is concentrated in the 200 to 300 s period band, a result consistent with previous observations and numerical model predictions. The 300 s band probably corresponds to gravity modes and shorter periods to acoustic modes, respectively. Using a 1-D stratified velocity model of the atmosphere we show that linear acoustic ray tracing fits arrival times at all GPS receivers. We interpret the perturbation as a direct acoustic wave caused by the explosion itself. This study shows that even relatively small subsurface events can produce

Advanced solar irradiances applied to satellite and ionospheric operational systems

NASA Astrophysics Data System (ADS)

Tobiska, W. Kent; Schunk, Robert; Eccles, Vince; Bouwer, Dave

Satellite and ionospheric operational systems require solar irradiances in a variety of time scales and spectral formats. We describe the development of a system using operational grade solar irradiances that are applied to empirical thermospheric density models and physics-based ionospheric models used by operational systems that require a space weather characterization. The SOLAR2000 (S2K) and SOLARFLARE (SFLR) models developed by Space Environment Technologies (SET) provide solar irradiances from the soft X-rays (XUV) through the Far Ultraviolet (FUV) spectrum. The irradiances are provided as integrated indices for the JB2006 empirical atmosphere density models and as line/band spectral irradiances for the physics-based Ionosphere Forecast Model (IFM) developed by the Space Environment Corporation (SEC). We describe the integration of these irradiances in historical, current epoch, and forecast modes through the Communication Alert and Prediction System (CAPS). CAPS provides real-time and forecast HF radio availability for global and regional users and global total electron content (TEC) conditions.

A Passive Microwave L-Band Boreal Forest Freeze/Thaw and Vegetation Phenology Study

NASA Astrophysics Data System (ADS)

Roy, A.; Sonnentag, O.; Pappas, C.; Mavrovic, A.; Royer, A.; Berg, A. A.; Rowlandson, T. L.; Lemay, J.; Helgason, W.; Barr, A.; Black, T. A.; Derksen, C.; Toose, P.

2016-12-01

The boreal forest is the second largest land biome in the world and thus plays a major role in the global and regional climate systems. The extent, timing and duration of seasonal freeze/thaw (F/T) state influences vegetation developmental stages (phenology) and, consequently, constitute an important control on how boreal forest ecosystems exchange carbon, water and energy with the atmosphere. The effective retrieval of seasonal F/T state from L-Band radiometry was demonstrated using satellite mission. However, disentangling the seasonally differing contributions from forest overstory and understory vegetation, and the soil surface to the satellite signal remains challenging. Here we present initial results from a radiometer field campaign to improve our understanding of the L-Band derived boreal forest F/T signal and vegetation phenology. Two L-Band surface-based radiometers (SBR) are installed on a micrometeorological tower at the Southern Old Black Spruce site in central Saskatchewan over the 2016-2017 F/T season. One radiometer unit is installed on the flux tower so it views forest including all overstory and understory vegetation and the moss-covered ground surface. A second radiometer unit is installed within the boreal forest overstory, viewing the understory and the ground surface. The objectives of our study are (i) to disentangle the L-Band F/T signal contribution of boreal forest overstory from the understory and ground surface, (ii) to link the L-Band F/T signal to related boreal forest structural and functional characteristics, and (iii) to investigate the use of the L-Band signal to characterize boreal forest carbon, water and energy fluxes. The SBR observations above and within the forest canopy are used to retrieve the transmissivity (γ) and the scattering albedo (ω), two parameters that describe the emission of the forest canopy though the F/T season. These two forest parameters are compared with boreal forest structural and functional

C- and L-band space-borne SAR incidence angle normalization for efficient Arctic sea ice monitoring

NASA Astrophysics Data System (ADS)

Mahmud, M. S.; Geldsetzer, T.; Howell, S.; Yackel, J.; Nandan, V.

2017-12-01

C-band Synthetic Aperture Radar (SAR) has been widely used effectively for operational sea ice monitoring, owing to its greater seperability between snow-covered first-year (FYI) and multi-year (MYI) ice types, during winter. However, during the melt season, C-band SAR backscatter contrast reduces between FYI and MYI. To overcome the limitations of C-band, several studies have recommended utlizing L-band SAR, as it has the potential to significantly improve sea ice classification. Given its longer wavelength, L-band can efficiently separate FYI and MYI types, especially during melt season. Therefore, the combination of C- and L-band SAR is an optimal solution for efficient seasonal sea ice monitoring. As SAR acquires images over a range of incidence angles from near-range to far-range, SAR backscatter varies substantially. To compensate this variation in SAR backscatter, incidence angle dependency of C- and L-band SAR backscatter for different FYI and MYI types is crucial to quantify, which is the objective of this study. Time-series SAR imagery from C-band RADARSAT-2 and L-band ALOS PALSAR during winter months of 2010 across 60 sites over the Canadian Arctic was acquired. Utilizing 15 images for each sites during February-March for both C- and L-band SAR, incidence angle dependency was calculated. Our study reveals that L- and C-band backscatter from FYI and MYI decreases with increasing incidence angle. The mean incidence angle dependency for FYI and MYI were estimated to be -0.21 dB/1° and -0.30 dB/1° respectively from L-band SAR, and -0.22 dB/1° and -0.16 dB/1° from C-band SAR, respectively. While the incidence angle dependency for FYI was found to be similar in both frequencies, it doubled in case of MYI from L-band, compared to C-band. After applying the incidence angle normalization method to both C- and L-band SAR images, preliminary results indicate improved sea ice type seperability between FYI and MYI types, with substantially lower number of mixed

Medium-scale traveling ionospheric disturbances by three-dimensional ionospheric GPS tomography

NASA Astrophysics Data System (ADS)

Chen, C. H.; Saito, A.; Lin, C. H.; Yamamoto, M.; Suzuki, S.; Seemala, G. K.

2016-02-01

In this study, we develop a three-dimensional ionospheric tomography with the ground-based global position system (GPS) total electron content observations. Because of the geometric limitation of GPS observation path, it is difficult to solve the ill-posed inverse problem for the ionospheric electron density. Different from methods given by pervious studies, we consider an algorithm combining the least-square method with a constraint condition, in which the gradient of electron density tends to be smooth in the horizontal direction and steep in the vicinity of the ionospheric F2 peak. This algorithm is designed to be independent of any ionospheric or plasmaspheric electron density models as the initial condition. An observation system simulation experiment method is applied to evaluate the performance of the GPS ionospheric tomography in detecting ionospheric electron density perturbation at the scale size of around 200 km in wavelength, such as the medium-scale traveling ionospheric disturbances.

Color composite C-band and L-band image of Kilauea volcanoe on Hawaii

NASA Technical Reports Server (NTRS)

1994-01-01

This color composite C-band and L-band image of the Kilauea volcano on the Big Island of Hawaii was acuired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperature Radar (SIR-C/X-SAR) flying on the Space Shuttle Endeavour. The city of Hilo can be seen at the top. The image shows the different types of lava flows around the crater Pu'u O'o. Ash deposits which erupted in 1790 from the summit of Kilauea volcano show up as dark in this image, and fine details associated with lava flows which erupted in 1919 and 1974 can be seen to the south of the summit in an area called the Ka'u Desert. Other historic lava flows can also be seen. Highway 11 is the linear feature running from Hilo to the Kilauea volcano. The Jet Propulsion Laboratory alternative photo number is P-43918.

Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI

NASA Astrophysics Data System (ADS)

Liu, Jiang; Lyons, L. R.; Archer, W. E.; Gallardo-Lacourt, B.; Nishimura, Y.; Zou, Ying; Gabrielse, C.; Weygand, J. M.

2018-02-01

Omega bands are curved aurora forms that evolve from a quiet arc located along the poleward edge of a diffuse auroral band within the midnight to morningside auroral oval. They usually propagate eastward. Because omega bands are a significant contributor to an active magnetotail, knowledge about their generation is important for understanding tail dynamics. Previous studies have shown that auroral streamers, footprints of fast flows in the tail, can propagate into omega bands. Such events, however, are limited, and it is still unclear whether and how the flows trigger the bands. The ionospheric flows associated with omega bands may provide valuable information on the driving mechanisms of the bands. We examine these flows taking advantage of the conjunctions between the Swarm spacecraft and Time History of Events and Macroscale Interactions during Substorms all-sky imagers, which allow us to demonstrate the relative location of the flows to the omega bands' bright arcs for the first time. We find that a strong eastward ionospheric flow is consistently present immediately poleward of the omega band's bright arc, resulting in a sharp flow shear near the poleward boundary of the band. This ionospheric flow shear should correspond to a flow shear near the inner edge of the plasma sheet. This plasma sheet shear may drive a Kelvin-Helmholz instability which then distorts the quiet arc to form omega bands. It seems plausible that the strong eastward flows are driven by streamer-related fast flows or enhanced convection in the magnetotail.

Examples L-Band Interference will be Presented and Discussed, as well as the Importance of L-Band Soil Moisture Observations

NASA Technical Reports Server (NTRS)

Kim, Edward

2010-01-01

Examples of L-band interference will be presented and discussed, as well as the importance of L-band soil moisture observations, as part of this one-day GEOSS workshop XXXVII on "Data Quality and Radio Spectrum Allocation Impact on Earth Observations" will address the broad challenges of data quality and the impact of generating reliable information for decision makers who are Earth data users but not necessarily experts in the Earth observation field. GEO has initiated a data quality assessment task (DA-09-01a) and workshop users will review and debate the directions and challenges of this effort. Radio spectrum allocation is an element of data availability and data quality, and is also associated with a GEO task (AR-06-11). A recent U.S. National Research Council report on spectrum management will be addressed as part of the workshop. Key representatives from industry, academia, and government will provide invited talks on these and related issues that impact GEOSS implementation.

Evaluation of the impact of ionospheric disturbances on air navigation augmentation system using multi-point GPS receivers

NASA Astrophysics Data System (ADS)

Omatsu, N.; Otsuka, Y.; Shiokawa, K.; Saito, S.

2013-12-01

In recent years, GPS has been utilized for navigation system for airplanes. Propagation delays in the ionosphere due to total electron content (TEC) between GPS satellite and receiver cause large positioning errors. In precision measurement using GPS, the ionospheric delay correction is generally conducted using both GPS L1 and L2 frequencies. However, L2 frequency is not internationally accepted as air navigation band, so it is not available for positioning directly in air navigation. In air navigation, not only positioning accuracy but safety is important, so augmentation systems are required to ensure the safety. Augmentation systems such as the satellite-based augmentation system (SBAS) or the ground-based augmentation system (GBAS) are being developed and some of them are already in operation. GBAS is available in a relatively narrow area around airports. In general, it corrects for the combined effects of multiple sources of positioning errors simultaneously, including satellite clock and orbital information errors, ionospheric delay errors, and tropospheric delay errors, using the differential corrections broadcast by GBAS ground station. However, if the spatial ionospheric delay gradient exists in the area, correction errors remain even after correction by GBAS. It must be a threat to GBAS. In this study, we use the GPS data provided by the Geographical Survey Institute in Japan. From the GPS data, TEC is obtained every 30 seconds. We select 4 observation points from 24.4 to 35.6 degrees north latitude in Japan, and analyze TEC data of these points from 2001 to 2011. Then we reveal dependences of Rate of TEC change Index (ROTI) on latitude, season, and solar activity statistically. ROTI is the root-mean-square deviation of time subtraction of TEC within 5 minutes. In the result, it is the midnight of the spring and the summer of the solar maximum in the point of 26.4 degrees north latitude that the value of ROTI becomes the largest. We think it is caused by

Soil Moisture Limitations on Monitoring Boreal Forest Regrowth Using Spaceborne L-Band SAR Data

NASA Technical Reports Server (NTRS)

Kasischke, Eric S.; Tanase, Mihai A.; Bourgeau-Chavez, Laura L.; Borr, Matthew

2011-01-01

A study was carried out to investigate the utility of L-band SAR data for estimating aboveground biomass in sites with low levels of vegetation regrowth. Data to estimate biomass were collected from 59 sites located in fire-disturbed black spruce forests in interior Alaska. PALSAR L-band data (HH and HV polarizations) collected on two dates in the summer/fall of 2007 and one date in the summer of 2009 were used. Significant linear correlations were found between the log of aboveground biomass (range of 0.02 to 22.2 t ha-1) and (L-HH) and (L-HV) for the data collected on each of the three dates, with the highest correlation found using the LHV data collected when soil moisture was highest. Soil moisture, however, did change the correlations between L-band and aboveground biomass, and the analyses suggest that the influence of soil moisture is biomass dependent. The results indicate that to use L-band SAR data for mapping aboveground biomass and monitoring forest regrowth will require development of approaches to account for the influence that variations in soil moisture have on L-band microwave backscatter, which can be particularly strong when low levels of aboveground biomass occur

On the Longitudinal Morphology of Zonal Irregularity Drift Measured using Networks of GPS Scintillation Monitors

NASA Astrophysics Data System (ADS)

Carrano, C. S.; Groves, K. M.; Valladares, C. E.; Delay, S. H.

2014-12-01

A complete characterization of field-aligned ionospheric irregularities responsible for the scintillation of satellite signals includes not only their spectral properties (power spectral strength, spectral index, anisotropy ratio, and outer-scale) but also their horizontal drift velocity. From a system impacts perspective, the horizontal drift velocity is important in that it dictates the rate of signal fading and also, to an extent, the level of phase fluctuations encountered by the receiver. From a physics perspective, studying the longitudinal morphology of zonal irregularity may lead to an improved understanding of the F region dynamo and regional electrodynamics at low latitudes. The irregularity drift at low latitudes is predominantly zonal and is most commonly measured by cross-correlating observations of satellite signals made by a pair of closely-spaced antennas. The AFRL-SCINDA network operates a small number of VHF spaced-antenna systems at low latitude stations for this purpose. A far greater number of GPS scintillation monitors are operated by AFRL-SCINDA (25-30) and the Low Latitude Ionospheric Sensor Network (35-50), but the receivers are situated too far apart to monitor the drift using cross-correlation techniques. In this paper, we present an alternative approach that leverages the weak scatter scintillation theory (Rino, Radio Sci., 1979) to infer the zonal irregularity drift from single-station GPS measurements of S4, sigma-phi, and the propagation geometry alone. Unlike the spaced-receiver technique, this technique requires assumptions for the height of the scattering layer (which introduces a bias in the drift estimates) and the spectral index of the irregularities (which affects the spread of the drift estimates about the mean). Nevertheless, theory and experiment show that the ratio of sigma-phi to S4 is less sensitive to these parameters than it is to the zonal drift, and hence the zonal drift can be estimated with reasonable accuracy. In

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Yu; Cao Jinxiang; Wang Jian

2012-09-15

A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF{sub 6}, CCl{sub 2}F{sub 2}, and CO{sub 2} into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF{sub 6}{sup -}, CCl{sub 2}F{sub 2}{sup -}) intermediary species provide larger reduction of the electron density than the positive ionmore » (CO{sub 2}{sup +}) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF{sub 6} and CO{sub 2} releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere.« less

Limitations imposed by ionospheric turbulence on satellite-to-satellite Doppler measurement accuracy. [of earth gravity field

NASA Technical Reports Server (NTRS)

Grossi, M. D.

1982-01-01

For some time the possibility has been considered to perform an accurate survey from orbit of the earth gravity field by making use of low-low, satellite-to-satellite Doppler tracking with a radio link which operates in the frequency band in the range from 50 to 100 GHz. It is, therefore, of interest to discuss the upper bound in Doppler measurement accuracy imposed by the effects of ionospheric turbulence. The present investigation is concerned with the measurement error induced by ionospheric turbulence. The assumptin is made that the so-called ionospheric refractive 'bias' can be removed with one of the multifrequency methods of the current practice.

Studying Notable Debris Disks In L-band with the Vortex Coronagraph

NASA Astrophysics Data System (ADS)

Patel, Rahul; Beichman, Charles; Choquet, Elodie; Mawet, Dimitri; Meshkat, Tiffany; ygouf, marie

2018-01-01

Resolved images of circumstellar disks are integral to our understanding of planetary systems, as the micron sized dust grains that comprise the disk are born from the collisional grinding of planetesimals by larger planets in the system. Resolved images are essential to determining grain properties that might otherwise be degenerate from analyzing the star’s spectral energy distribution. Though the majority of scattered light images of disks are obtained at optical and near-IR wavelengths, only a few have been imaged in the thermal IR at L-band. Probing the spatial features of disks at L-band opens up the possibility of constraining additional grain properties, such as water/ice features.Here, we present the results of our effort to image the disks of a few notable systems at L-band using the NIRC2 imager at Keck, in conjunction with the newly commissioned vector vortex coronagraph. The vortex, along with the QACITS fine guiding program installed at Keck, enables us to probe the small ~lambda/D angular separations of these systems, and reach contrasts of 1/100,000. We will discuss the systems that have been imaged, and lessons learned while imaging in L-band. Our analysis of these disks reveal features previously unseen, and will lay the foundation for followup studies by missions such as JWST at similar wavelengths from space.

Ionospheric effects in uncalibrated phase delay estimation and ambiguity-fixed PPP based on raw observable model

NASA Astrophysics Data System (ADS)

Gu, Shengfeng; Shi, Chuang; Lou, Yidong; Liu, Jingnan

2015-05-01

Zero-difference (ZD) ambiguity resolution (AR) reveals the potential to further improve the performance of precise point positioning (PPP). Traditionally, PPP AR is achieved by Melbourne-Wübbena and ionosphere-free combinations in which the ionosphere effect are removed. To exploit the ionosphere characteristics, PPP AR with L1 and L2 raw observable has also been developed recently. In this study, we apply this new approach in uncalibrated phase delay (UPD) generation and ZD AR and compare it with the traditional model. The raw observable processing strategy treats each ionosphere delay as an unknown parameter. In this manner, both a priori ionosphere correction model and its spatio-temporal correlation can be employed as constraints to improve the ambiguity resolution. However, theoretical analysis indicates that for the wide-lane (WL) UPD retrieved from L1/L2 ambiguities to benefit from this raw observable approach, high precision ionosphere correction of better than 0.7 total electron content unit (TECU) is essential. This conclusion is then confirmed with over 1 year data collected at about 360 stations. Firstly, both global and regional ionosphere model were generated and evaluated, the results of which demonstrated that, for large-scale ionosphere modeling, only an accuracy of 3.9 TECU can be achieved on average for the vertical delays, and this accuracy can be improved to about 0.64 TECU when dense network is involved. Based on these ionosphere products, WL/narrow-lane (NL) UPDs are then extracted with the raw observable model. The NL ambiguity reveals a better stability and consistency compared to traditional approach. Nonetheless, the WL ambiguity can be hardly improved even constrained with the high spatio-temporal resolution ionospheric corrections. By applying both these approaches in PPP-RTK, it is interesting to find that the traditional model is more efficient in AR as evidenced by the shorter time to first fix, while the three

Simulation and mitigation of higher-order ionospheric errors in PPP

NASA Astrophysics Data System (ADS)

Zus, Florian; Deng, Zhiguo; Wickert, Jens

2017-04-01

We developed a rapid and precise algorithm to compute ionospheric phase advances in a realistic electron density field. The electron density field is derived from a plasmaspheric extension of the International Reference Ionosphere (Gulyaeva and Bilitza, 2012) and the magnetic field stems from the International Geomagnetic Reference Field. For specific station locations, elevation and azimuth angles the ionospheric phase advances are stored in a look-up table. The higher-order ionospheric residuals are computed by forming the standard linear combination of the ionospheric phase advances. In a simulation study we examine how the higher-order ionospheric residuals leak into estimated station coordinates, clocks, zenith delays and tropospheric gradients in precise point positioning. The simulation study includes a few hundred globally distributed stations and covers the time period 1990-2015. We take a close look on the estimated zenith delays and tropospheric gradients as they are considered a data source for meteorological and climate related research. We also show how the by product of this simulation study, the look-up tables, can be used to mitigate higher-order ionospheric errors in practise. Gulyaeva, T.L., and Bilitza, D. Towards ISO Standard Earth Ionosphere and Plasmasphere Model. In: New Developments in the Standard Model, edited by R.J. Larsen, pp. 1-39, NOVA, Hauppauge, New York, 2012, available at https://www.novapublishers.com/catalog/product_info.php?products_id=35812

Towards a Pan-European network for the mitigation of ionospheric threats (Invited)

NASA Astrophysics Data System (ADS)

Jakowski, N.; Hlubek, N.; Sato, H.; Berdermann, J.; Aquino, M. H.

2013-12-01

Measurements of signals from Global Navigation Satellite Systems (GNSS) offer the possibility to analyze the spatial and temporal characteristics of the electron density structure in the ionosphere and plasmasphere. Dual frequency ground based measurements are well suited to observe horizontal structures of the electron density and their dynamics whereas space based GNSS measurements can effectively contribute to explore the vertical structure of the ionosphere-plasmasphere ionization. The current data base, covering more than one solar cycle, enabled the development of empirical models of ionospheric key parameters such as the total electron content (TEC), the peak density NmF2 and the corresponding peak density height hmF2. TEC models can directly be used as correction in single frequency GNSS applications. Utilizing well established geodetic networks such as that of the International GNSS Service (IGS), it is discussed how ground based GNSS measurements are used to derive regional and global maps of the vertical TEC in near real time. Actual TEC maps are used for correcting ionospheric range errors in operational single frequency applications, e.g. in space based augmentation systems (SBAS) like WAAS in US and EGNOS in Europe. However, severe space weather conditions lead to perturbations of the ionospheric plasma which in turn can affect the performance of GNSS. These perturbations come at a wide range of spatial and temporal scales and are observed as large scale ionization fronts, medium scale travelling ionospheric disturbances, plasma bubbles and small scale irregularities causing radio scintillations at the receiver level. These disturbances can strongly degrade the accuracy, reliability, integrity and availability of the GNSS. This is especially detrimental for space and ground based augmentation systems which have specific accuracy and availability requirements. Therefore an important use of the measurements of GNSS signals is to assess the threat that

Ionospheric and magnetospheric plasmapauses'

NASA Technical Reports Server (NTRS)

Grebowsky, J. M.; Hoffman, J. H.; Maynard, N. C.

1977-01-01

During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of about 5.2 R sub e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2-5.4. The locations of the Explorer 45 plasmapause crossings during this month were compared to the latitudinal decreases of the H(+) density observed on ISIS 2 near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Vertical flows of the H(+) ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 kilometers/sec near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H(+) trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause.

Hypervelocity impact testing of L-band truss cable meteoroid shielding on Skylab

NASA Technical Reports Server (NTRS)

Jex, D. W.

1973-01-01

A series of tests was performed to determine the protection provided by the L-band truss cable meteoroid shielding installed on Skylab space station at space environment temperatures of minus 180 F. The damage sustained when three test specimens were impacted by spherical projectiles at hypersonic speed was investigated. It is concluded that the L-band truss cable meteoroid shielding provides adequate protection at the indicated temperature.

Ionospheric research opportunity

NASA Astrophysics Data System (ADS)

Rickel, Dwight

1985-05-01

Ground-based explosions have been exploited successfully in the past as a relatively controlled source for producing ionospheric disturbances. On June 25, the Defense Nuclear Agency will conduct a high explosives test on the northern section of the White Sands Missile Range. Approximately 4,800 tons of ammonium nitrate and fuel oil (ANFO) will be detonated at ground level, producing an acoustic shock wave with a surface pressure change of approximately 20 mbar at a 6 km range. This shock front will have sufficient strength to propagate into the ionosphere with at least a 10% change in the ambient pressure across the disturbance front in the lower F region. Such an ionospheric perturbation will give ionospheric researchers an excellent opportunity to investigate acoustic propagation at ionospheric heights, shock dissipation effect, the ion-neutral coupling process, acoustic-gravity wave (traveling ionospheric disturbance) generation mechanisms, and associated RF phenomena.

Monitoring of sporadic plasma layers in the lower ionosphere in the communication link satellite-to-satellite

NASA Astrophysics Data System (ADS)

Pavelyev, Alexander; Matyugov, Stanislav; Wickert, Jens; Liou, Yuei An; Yakovlev, Oleg

Method of global monitoring of sporadic plasma layers in the lower ionosphere is developed. In-vestigations were carried out by use of analysis of the amplitude and phase components of radio holograms obtained during the radio occultation missions CHAMP, FORMOSAT-3. Sporadic amplitude scintillation observed in RO experiments contain important information concerning the seasonal, geographical, and temporal distributions of the ionospheric disturbances and de-pend on solar activity. The geographical and seasonal distributions of sporadic layers in the lower ionosphere as function of solar activity in the period 2002-2008 years is obtained. The general number of RO events with strong amplitude variations can be used as an indicator of the ionospheric activity. We found that during 2001-2008 the daily averaged S4 index measured during CHAllenging Minisatellite Payload (CHAMP) mission depends essentially on solar ac-tivity. The maximum occurred in January 2002, minimum has been observed in summer 2008. Different temporal behavior of S4 index has been detected for polar (with latitude greater than 55 degrees) and low latitude (moderate and equatorial) regions. For polar regions S4 index is slowly decreasing with solar activity. In the low latitude areas S4 index is sharply oscillat-ing, depending on the solar ultraviolet emission variations. The geographical distribution of S4 index variations indicates different origin of ionospheric plasma disturbances in polar and low latitude areas. Origin of the plasma disturbances in the polar areas may be connected with influence of solar wind, the ultraviolet emission of the Sun may be the main cause of the ionospheric irregularities in the low latitude zone. Analysis reveals global oscillations of S4 index with the periods of 5-7 months. Analysis of these oscillations may provide additional connection with solar activity. Therefore, the S4 index of RO signal is important radio physical indicator of solar activity.

ELBARA II, an L-band radiometer system for soil moisture research.

PubMed

Schwank, Mike; Wiesmann, Andreas; Werner, Charles; Mätzler, Christian; Weber, Daniel; Murk, Axel; Völksch, Ingo; Wegmüller, Urs

2010-01-01

L-band (1-2 GHz) microwave radiometry is a remote sensing technique that can be used to monitor soil moisture, and is deployed in the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency (ESA). Performing ground-based radiometer campaigns before launch, during the commissioning phase and during the operative SMOS mission is important for validating the satellite data and for the further improvement of the radiative transfer models used in the soil-moisture retrieval algorithms. To address these needs, three identical L-band radiometer systems were ordered by ESA. They rely on the proven architecture of the ETH L-Band radiometer for soil moisture research (ELBARA) with major improvements in the microwave electronics, the internal calibration sources, the data acquisition, the user interface, and the mechanics. The purpose of this paper is to describe the design of the instruments and the main characteristics that are relevant for the user.

ELBARA II, an L-Band Radiometer System for Soil Moisture Research

PubMed Central

Schwank, Mike; Wiesmann, Andreas; Werner, Charles; Mätzler, Christian; Weber, Daniel; Murk, Axel; Völksch, Ingo; Wegmüller, Urs

2010-01-01

L-band (1–2 GHz) microwave radiometry is a remote sensing technique that can be used to monitor soil moisture, and is deployed in the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency (ESA). Performing ground-based radiometer campaigns before launch, during the commissioning phase and during the operative SMOS mission is important for validating the satellite data and for the further improvement of the radiative transfer models used in the soil-moisture retrieval algorithms. To address these needs, three identical L-band radiometer systems were ordered by ESA. They rely on the proven architecture of the ETH L-Band radiometer for soil moisture research (ELBARA) with major improvements in the microwave electronics, the internal calibration sources, the data acquisition, the user interface, and the mechanics. The purpose of this paper is to describe the design of the instruments and the main characteristics that are relevant for the user. PMID:22315556

Tunable, Electrically Small, Inductively Coupled Antenna for Transportable Ionospheric Heating

NASA Astrophysics Data System (ADS)

Esser, Benedikt; Mauch, Daniel; Dickens, James; Mankowski, John; Neuber, Andreas

2018-04-01

An electrically small antenna is evaluated for use as the principle radiating element in a mobile ionospheric heating array. Consisting of a small loop antenna inductively coupled to a capacitively loaded loop, the electrically small antenna provides high efficiency with the capability of being tuned within the range of ionospheric heating. At a factor 60 smaller in area than a High-Frequency Active Auroral Research Program element, this antenna provides a compact, efficient radiating element for mobile ionospheric heating. A prototype antenna at 10 MHz was built to study large-scale feasibility and possible use with photoconductive semiconductor switch-based drivers. Based on the experimental study, the design has been extrapolated to a small 6 × 4 array of antennas. At a total power input of 16.1 MW this array is predicted to provide 3.6-GW effective radiated power typically required for ionospheric heating. Array cross talk is addressed, including effects upon individual antenna port parameters. Tuning within the range of ionospheric heating, 3-10 MHz, is made possible without the use of lossy dielectrics through a large capacitive area suited to tune the antenna. Considerations for high power operation across the band are provided including a method of driving the antenna with a simple switcher requiring no radio frequency cabling. Source matching may be improved via adjustment of the coupling between small loop antenna and capacitively loaded loop improving |S11| from -1 to -21 dB at 3 MHz.

Scintillation characterization of the pure Tl2LiGdBr6 single crystal

NASA Astrophysics Data System (ADS)

Jang, Jonghun; Rooh, Gul; Kim, Sunghwan; Kim, HongJoo

2018-05-01

A pure Tl2LiGdBr6 (TLGB) single crystal was developed. This scintillator was grown by the two-zone vertical Bridgman technique. Owing to the improvement in the crystal quality of TLGB, excellent scintillation properties were observed. The characterization of this scintillation material was carried out under X- and γ-ray excitations. In the X-ray excitation emission spectrum, the Tl+ ion emission band was observed between 390 and 550 nm and peaked at 435 nm. Under 662 keV γ-ray excitation, the energy resolution and light yield of the grown sample were measured to be 7.2% (FWHM) and 27,000 ± 2,700 ph/MeV, respectively. In addition, under the same γ-ray excitation, scintillation decay time was also measured at room temperature. Three decay time components were found to be 56 ns (24%), 105 ns (53%), and 1.5 µs (23%). Further improvements in scintillation properties are expected with the good quality crystal of this compound.

SNO+ Scintillator Purification and Assay

NASA Astrophysics Data System (ADS)

Ford, R.; Chen, M.; Chkvorets, O.; Hallman, D.; Vázquez-Jáuregui, E.

2011-04-01

We describe the R&D on the scintillator purification and assay methods and technology for the SNO+ neutrino and double-beta decay experiment. The SNO+ experiment is a replacement of the SNO heavy water with liquid scintillator comprised of 2 g/L PPO in linear alkylbenzene (LAB). During filling the LAB will be transported underground by rail car and purified by multi-stage distillation and steam stripping at a flow rate of 19 LPM. While the detector is operational the scintillator can be recirculated at 150 LPM (full detector volume in 4 days) to provide repurification as necessary by either water extraction (for Ra, K, Bi) or by functional metal scavenger columns (for Pb, Ra, Bi, Ac, Th) followed by steam stripping to remove noble gases and oxygen (Rn, O2, Kr, Ar). The metal scavenger columns also provide a method for scintillator assay for ex-situ measurement of the U and Th chain radioactivity. We have developed "natural" radioactive spikes of Pb and Ra in LAB and use these for purification testing. Lastly, we present the planned operating modes and purification strategies and the plant specifications and design.

Comparison of Measured Galactic Background Radiation at L-Band with Model

NASA Technical Reports Server (NTRS)

LeVine, David M.; Abraham, Saji; Kerr, Yann H.; Wilson, William J.; Skou, Niels; Sobjaerg, Sten

2004-01-01

Radiation from the celestial sky in the spectral window at 1.413 GHz is strong and an accurate accounting of this background radiation is needed for calibration and retrieval algorithms. Modern radio astronomy measurements in this window have been converted into a brightness temperature map of the celestial sky at L-band suitable for such applications. This paper presents a comparison of the background predicted by this map with the measurements of several modern L-band remote sensing radiometer Keywords-Galactic background, microwave radiometry; remote sensing;

Remote Sensing of the Ionosphere and Plasmasphere from Space Using Radiowaves

NASA Technical Reports Server (NTRS)

Mannucci, Anthony J.

2008-01-01

Topics include the scientific context, trans-ionospheric and sounding, small-scale structure, plasmasphere, fast and slow tomography, and pseudo-imaging. Individual slides focus on where geospace science stands today, variability in inner magnetosphere electric fields, Appleton-Hartree formula, phase and range ionospheric observables, examples of leveling, large ionization changes during storms, new mid-latitude phenomena, ionospheric sounding, COSMIC CERTO/Tri-band beacon, LEO-ground radio tomography, irregularity measurements, COSMIC, critical sensor data from COSMIC GPS limb sounding, occultation geometry, comparison of calibrated slant TEC measurements for 26 June 2006, historic examples of Abel electron density profiles, comparison of UCAR and JPL Able profiles of 26 June 2006, validating UCAR and JPL Abel profiles using Arecibo ISR measurements for 26 June 2006, E-region from GPS/MET 1995, Abel versus gradient assisted retrieval, 3000 profiles/day, plasmasphere, JASON TEC above satellite, GPS equatorial plasmasphere measurements, April 2002 geomagnetic storm, and space-based GPS tomography.

Aquarius Active-Passive RFI Environment at L-Band

NASA Technical Reports Server (NTRS)

Le Vine, David M.; De Matthaeis, Paolo

2014-01-01

Active/Passive instrument combinations (i.e., radiometer and radar) are being developed at L-band for remote sensing of sea surface salinity and soil moisture. Aquarius is already in orbit and SMAP is planned for launch in the Fall of 2014. Aquarius has provided for the first time a simultaneous look at the Radio Frequency Interference (RFI) environment from space for both active and passive instruments. The RFI environment for the radiometer observations is now reasonably well known and examples from Aquarius are presented in this manuscript that show that RFI is an important consideration for the scatterometer as well. In particular, extensive areas of the USA, Europe and Asia exhibit strong RFI in both the radiometer band at 1.41 GHz and in the band at 1.26 GHz employed by the Aquarius scatterometer. Furthermore, in areas such as the USA, where RFI at 1.4 GHz is relatively well controlled, RFI in the scatterometer band maybe the limiting consideration for the operation of combination active/passive instruments.

HF-enhanced 4278-Å airglow: evidence of accelerated ionosphere electrons?

NASA Astrophysics Data System (ADS)

Fallen, C. T.; Watkins, B. J.

2013-12-01

We report calculations from a one-dimensional physics-based self-consistent ionosphere model (SCIM) demonstrating that HF-heating of F-region electrons can produce 4278-Å airglow enhancements comparable in magnitude to those reported during ionosphere HF modification experiments at the High-frequency Active Auroral Research Program (HAARP) observatory in Alaska. These artificial 'blue-line' emissions, also observed at the EISCAT ionosphere heating facility in Norway, have been attributed to arise solely from additional production of N2+ ions through impact ionization of N2 molecules by HF-accelerated electrons. Each N2+ ion produced by impact ionization or photoionization has a probability of being created in the N2+(1N) excited state, resulting in a blue-line emission from the allowed transition to its ground state. The ionization potential of N2 exceeds 18 eV, so enhanced impact ionization of N2 implies that significant electron acceleration processes occur in the HF-modified ionosphere. Further, because of the fast N2+ emission time, measurements of 4278-Å intensity during ionosphere HF modification experiments at HAARP have also been used to estimate artificial ionization rates. To the best of our knowledge, all observations of HF-enhanced blue-line emissions have been made during twilight conditions when resonant scattering of sunlight by N2+ ions is a significant source of 4278-Å airglow. Our model calculations show that F-region electron heating by powerful O-mode HF waves transmitted from HAARP is sufficient to increase N2+ ion densities above the shadow height through temperature-enhanced ambipolar diffusion and temperature-suppressed ion recombination. Resonant scattering from the modified sunlit region can cause a 10-20 R increase in 4278-Å airglow intensity, comparable in magnitude to artificial emissions measured during ionosphere HF-modification experiments. This thermally-induced artificial 4278-Å aurora occurs independently of any artificial

Monte Carlo simulation of electron thermalization in scintillator materials: Implications for scintillator nonproportionality

DOE PAGES

Prange, Micah P.; Xie, YuLong; Campbell, Luke W.; ...

2017-12-20

The lack of reliable quantitative estimates of the length and time scales associated with hot electron thermalization after a gamma-ray induced energy cascade obscures the interplay of various microscopic processes controlling scintillator performance and hampers the search for improved detector materials. We apply a detailed microscopic kinetic Monte Carlo model of the creation and subsequent thermalization of hot electrons produced by gamma irradiation of six important scintillating crystals to determine the spatial extent of the cloud of excitations produced by gamma rays and the time required for the cloud to thermalize with the host lattice. The main ingredients of themore » model are ensembles of microscopic track structures produced upon gamma excitation (including the energy distribution of the excited carriers), numerical estimates of electron-phonon scattering rates, and a calculated particle dispersion to relate the speed and energy of excited carriers. All these ingredients are based on first-principles density functional theory calculations of the electronic and phonon band structures of the materials. The details of the Monte Carlo model are presented along with the results for thermalization time and distance distributions. Here, these results are discussed in light of previous work. It is found that among the studied materials, calculated thermalization distances are positively correlated with measured nonproportionality. In the important class of halide scintillators, the particle dispersion is found to be more influential than the largest phonon energy in determining the thermalization distance.« less

Monte Carlo simulation of electron thermalization in scintillator materials: Implications for scintillator nonproportionality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prange, Micah P.; Xie, YuLong; Campbell, Luke W.

2017-12-21

The lack of reliable quantitative estimates of the length and time scales associated with hot electron thermalization after a gamma-ray induced energy cascade obscures the interplay of various microscopic processes controlling scintillator performance and hampers the search for improved detector materials. We apply a detailed microscopic kinetic Monte Carlo model of the creation and subsequent thermalization of hot electrons produced by gamma irradiation of six important scintillating crystals to determine the spatial extent of the cloud of excitations produced by gamma rays and the time required for the cloud to thermalize with the host lattice. The main ingredients of themore » model are ensembles of microscopic track structures produced upon gamma excitation (including the energy distribution of the excited carriers), numerical estimates of electron-phonon scattering rates, and a calculated particle dispersion to relate the speed and energy of excited carriers. All these ingredients are based on first-principles density functional theory calculations of the electronic and phonon band structures of the materials. Details of the Monte Carlo model are presented along with results for thermalization time and distance distributions. These results are discussed in light of previous work. It is found that among the studied materials, calculated thermalization distances are positively correlated with measured nonproportionality. In the important class of halide scintillators, the particle dispersion is found to be more influential than the largest phonon energy in determining the thermalization distance.« less

An MF/HF radio array for radio and radar imaging of the ionosphere

NASA Astrophysics Data System (ADS)

Isham, Brett; Gustavsson, Bjorn; Belyey, Vasyl; Bullett, Terrence

2016-07-01

The Aguadilla Radio Array will be installed at the Interamerican University Aguadilla Campus, located in northwestern Puerto Rico. The array is intended for broad-band medium and high-frequency (MF/HF, roughly 2 to 25 MHz) radio and bistatic radar observations of the ionosphere. The main array consists of 20 antenna elements, arranged in a semi-random pattern providing a good distribution of baseline vectors, with 6-meter minimum spacing to eliminate spacial aliasing. A relocatable 6-element array is also being developed, in which each element consists of a crossed pair of active electric dipoles and all associated electronics for phase-coherent radio measurements. A primary scientific goal of the array is to create images of the region of ionospheric radio emissions stimulated by the new Arecibo Observatory high-power high-frequency radio transmitter. A second primary goal is the study of ionospheric structure and dynamics via coherent radar imaging of the ionosphere in collaboration with the University of Colorado / NOAA Versatile Interferometric Pulsed Ionospheric Radar (VIPIR), located at the USGS San Juan Observatory in Cayey, Puerto Rico. In addition to ionospheric research in collaboration with the Cayey and Arecibo Observatories, the goals of the project include the development of radio sounding, polarization, interferometry, and imaging techniques, and training of students at the university and high school levels.

Effect of Ionosphere on Geostationary Communication Satellite Signals

NASA Astrophysics Data System (ADS)

Erdem, Esra; Arikan, Feza; Gulgonul, Senol

2016-07-01

Geostationary orbit (GEO) communications satellites allow radio, television, and telephone transmissions to be sent live anywhere in the world. They are extremely important in daily life and also for military applications. Since, satellite communication is an expensive technology addressing crowd of people, it is critical to improve the performance of this technology. GEO satellites are at 35,786 kilometres from Earth's surface situated directly over the equator. A satellite in a geostationary orbit (GEO) appears to stand still in the sky, in a fixed position with respect to an observer on the earth, because the satellite's orbital period is the same as the rotation rate of the Earth. The advantage of this orbit is that ground antennas can be fixed to point towards to satellite without their having to track the satellite's motion. Radio frequency ranges used in satellite communications are C, X, Ku, Ka and even EHG and V-band. Satellite signals are disturbed by atmospheric effects on the path between the satellite and the receiver antenna. These effects are mostly rain, cloud and gaseous attenuation. It is expected that ionosphere has a minor effect on the satellite signals when the ionosphere is quiet. But there are anomalies and perturbations on the structure of ionosphere with respect to geomagnetic field and solar activity and these conditions may cause further affects on the satellite signals. In this study IONOLAB-RAY algorithm is adopted to examine the effect of ionosphere on satellite signals. IONOLAB-RAY is developed to calculate propagation path and characteristics of high frequency signals. The algorithm does not have any frequency limitation and models the plasmasphere up to 20,200 km altitude, so that propagation between a GEO satellite and antenna on Earth can be simulated. The algorithm models inhomogeneous, anisotropic and time dependent structure of the ionosphere with a 3-D spherical grid geometry and calculates physical parameters of the

Bright Eu2+-activated polycrystalline ceramic neutron scintillators

NASA Astrophysics Data System (ADS)

Wang, C. L.; Paranthaman, M. P.; Riedel, R. A.; Hodges, J. P.; Karlic, J. J.; Veatch, R. A.; Li, L.; Bridges, C. A.

2018-03-01

Scintillation properties of Eu2+-doped CaF2-AlF3-6LiF (Eu:CALF) polycrystalline ceramic thermal-neutron scintillators as a function of AlF3 concentration have been studied. The emission band peaked at a wavelength of 425-431 nm is due to the presence of Eu:CaF2 micro-crystallites. The highest light output from these samples is approximately 20,000 photons per thermal neutron, which is 3 times that of a GS20 6Li-glass scintillator. The pulse-decay lifetime and light output vs. AlF3 concentration may be understood using a radiation trapping model and the formation of a Li3AlF6 phase. At lower AlF3 concentration, Al3+ ions in Eu:CaF2 passivate the hole-trapping defects and enhance the light output; whereas at higher AlF3 concentration, Al3+ ions lead to the formation of electron trapping centers in Eu:CaF2 and the Li3AlF6 phase is formed, which reduces the light output. A neutron-gamma-discrimination (NGD) ratio of 9 × 108 was obtained from Principal Component Analysis (PCA) of digital waveforms, while Fisher Linear Discriminant Analysis (FLDA) can completely separate the thermal neutrons from 60Co gamma rays within the limit of gamma event statistics used in this work. Our results suggest that Eu:CALF scintillators can potentially replace the GS20 scintillator used for thermal and cold neutron detection systems.

Investigation of Ionospheric Turbulence and Whistler Wave Interactions with Space Plasmas

DTIC Science & Technology

2012-11-21

an oscillating LOS velocity with the same periodicity as the heating modulation pattern. A set of Fourier periodogram from the MUIR LOS velocity...scale ionospheric turbulence are discussed separately, viz., (a) anomalous heat source-induced acoustic gravity waves (AGW), and (b) HF radio wave...ionospheric ducts, acoustic gravity waves (AGWs), anomalous heat sources, inner and outer radiation belts, L parameter, whistler wave interactions

Modeling of N2 and O optical emissions for ionosphere HF powerful heating experiments

NASA Astrophysics Data System (ADS)

Sergienko, T.; Gustavsson, B.

Analyses of experiments of F region ionosphere modification by HF powerful radio waves show that optical observations are very useful tools for diagnosing of the interaction of the probing radio wave with the ionospheric plasma Hitherto the emissions usually measured in the heating experiment have been the 630 0 nm and the 557 7 nm lines of atomic oxygen Other emissions for instance O 844 8 nm and N2 427 8 nm have been measured episodically in only a few experiments although the very rich optical spectrum of molecular nitrogen potentially involves important information about ionospheric plasma in the heated region This study addresses the modeling of optical emissions from the O and the N2 triplet states first positive second positive Vegard-Kaplan infrared afterglow and Wu-Benesch band systems excited under a condition of the ionosphere heating experiment The auroral triplet state population distribution model was modified for the ionosphere heating conditions by using the different electron distribution functions suggested by Mishin et al 2000 2003 and Gustavsson at al 2004 2005 Modeling results are discussed from the point of view of efficiency of measurements of the N2 emissions in future experiments

Strontium and barium iodide high light yield scintillators

NASA Astrophysics Data System (ADS)

Cherepy, Nerine J.; Hull, Giulia; Drobshoff, Alexander D.; Payne, Stephen A.; van Loef, Edgar; Wilson, Cody M.; Shah, Kanai S.; Roy, Utpal N.; Burger, Arnold; Boatner, Lynn A.; Choong, Woon-Seng; Moses, William W.

2008-02-01

Europium-doped strontium and barium iodide are found to be readily growable by the Bridgman method and to produce high scintillation light yields. SrI2(Eu ) emits into the Eu2+ band, centered at 435nm, with a decay time of 1.2μs and a light yield of ˜90000photons/MeV. It offers energy resolution better than 4% full width at half maximum at 662keV, and exhibits excellent light yield proportionality. BaI2(Eu ) produces >30000photons/MeV into the Eu2+ band at 420nm (<1μs decay). An additional broad impurity-mediated recombination band is present at 550nm (>3μs decay), unless high-purity feedstock is used.

Scintillation Counters

NASA Astrophysics Data System (ADS)

Bell, Zane W.

Scintillators find wide use in radiation detection as the detecting medium for gamma/X-rays, and charged and neutral particles. Since the first notice in 1895 by Roentgen of the production of light by X-rays on a barium platinocyanide screen, and Thomas Edison's work over the following 2 years resulting in the discovery of calcium tungstate as a superior fluoroscopy screen, much research and experimentation have been undertaken to discover and elucidate the properties of new scintillators. Scintillators with high density and high atomic number are prized for the detection of gamma rays above 1 MeV; lower atomic number, lower-density materials find use for detecting beta particles and heavy charged particles; hydrogenous scintillators find use in fast-neutron detection; and boron-, lithium-, and gadolinium-containing scintillators are used for slow-neutron detection. This chapter provides the practitioner with an overview of the general characteristics of scintillators, including the variation of probability of interaction with density and atomic number, the characteristics of the light pulse, a list and characteristics of commonly available scintillators and their approximate cost, and recommendations regarding the choice of material for a few specific applications. This chapter does not pretend to present an exhaustive list of scintillators and applications.

Ionosphere Waves Service - A demonstration

NASA Astrophysics Data System (ADS)

Crespon, François

2013-04-01

In the frame of the FP7 POPDAT project the Ionosphere Waves Service was developed by ionosphere experts to answer several questions: How make the old ionosphere missions more valuable? How provide scientific community with a new insight on wave processes that take place in the ionosphere? The answer is a unique data mining service accessing a collection of topical catalogues that characterize a huge number of Atmospheric Gravity Waves, Travelling Ionosphere Disturbances and Whistlers events. The Ionosphere Waves Service regroups databases of specific events extracted by experts from a ten of ionosphere missions which end users can access by applying specific searches and by using statistical analysis modules for their domain of interest. The scientific applications covered by the IWS are relative to earthquake precursors, ionosphere climatology, geomagnetic storms, troposphere-ionosphere energy transfer, and trans-ionosphere link perturbations. In this presentation we propose to detail the service design, the hardware and software architecture, and the service functions. The service interface and capabilities will be the focus of a demonstration in order to help potential end-users for their first access to the Ionosphere Waves Service portal. This work is made with the support of FP7 grant # 263240.

Modeling Ionosphere Environments: Creating an ISS Electron Density Tool

NASA Technical Reports Server (NTRS)

Gurgew, Danielle N.; Minow, Joseph I.

2011-01-01

The International Space Station (ISS) maintains an altitude typically between 300 km and 400 km in low Earth orbit (LEO) which itself is situated in the Earth's ionosphere. The ionosphere is a region of partially ionized gas (plasma) formed by the photoionization of neutral atoms and molecules in the upper atmosphere of Earth. It is important to understand what electron density the spacecraft is/will be operating in because the ionized gas along the ISS orbit interacts with the electrical power system resulting in charging of the vehicle. One instrument that is already operational onboard the ISS with a goal of monitoring electron density, electron temperature, and ISS floating potential is the Floating Potential Measurement Unit (FPMU). Although this tool is a valuable addition to the ISS, there are limitations concerning the data collection periods. The FPMU uses the Ku band communication frequency to transmit data from orbit. Use of this band for FPMU data runs is often terminated due to necessary observation of higher priority Extravehicular Activities (EVAs) and other operations on ISS. Thus, large gaps are present in FPMU data. The purpose of this study is to solve the issue of missing environmental data by implementing a secondary electron density data source, derived from the COSMIC satellite constellation, to create a model of ISS orbital environments. Extrapolating data specific to ISS orbital altitudes, we model the ionospheric electron density along the ISS orbit track to supply a set of data when the FPMU is unavailable. This computer model also provides an additional new source of electron density data that is used to confirm FPMU is operating correctly and supplements the original environmental data taken by FPMU.

Physics-informed machine learning for inorganic scintillator discovery

NASA Astrophysics Data System (ADS)

Pilania, G.; McClellan, K. J.; Stanek, C. R.; Uberuaga, B. P.

2018-06-01

Applications of inorganic scintillators—activated with lanthanide dopants, such as Ce and Eu—are found in diverse fields. As a strict requirement to exhibit scintillation, the 4f ground state (with the electronic configuration of [Xe]4fn 5d0) and 5d1 lowest excited state (with the electronic configuration of [Xe]4fn-1 5d1) levels induced by the activator must lie within the host bandgap. Here we introduce a new machine learning (ML) based search strategy for high-throughput chemical space explorations to discover and design novel inorganic scintillators. Building upon well-known physics-based chemical trends for the host dependent electron binding energies within the 4f and 5d1 energy levels of lanthanide ions and available experimental data, the developed ML model—coupled with knowledge of the vacuum referred valence and conduction band edges computed from first principles—can rapidly and reliably estimate the relative positions of the activator's energy levels relative to the valence and conduction band edges of any given host chemistry. Using perovskite oxides and elpasolite halides as examples, the presented approach has been demonstrated to be able to (i) capture systematic chemical trends across host chemistries and (ii) effectively screen promising compounds in a high-throughput manner. While a number of other application-specific performance requirements need to be considered for a viable scintillator, the scheme developed here can be a practically useful tool to systematically down-select the most promising candidate materials in a first line of screening for a subsequent in-depth investigation.

Obituary: David L. Band (1957-2009)

NASA Astrophysics Data System (ADS)

Cominsky, Lynn

2011-12-01

David L. Band, of Potomac Maryland, died on March 16, 2009 succumbing to a long battle with spinal cord cancer. His death at the age of 52 came as a shock to his many friends and colleagues in the physics and astronomy community. Band showed an early interest and exceptional aptitude for physics, leading to his acceptance at the Massachusetts Institute of Technology as an undergraduate student in 1975. After graduating from MIT with an undergraduate degree in Physics, Band continued as a graduate student in Physics at Harvard University. His emerging interest in Astrophysics led him to the Astronomy Department at the Harvard Smithsonian Center for Astrophysics (CfA), where he did his dissertation work with Jonathan Grindlay. His dissertation (1985) entitled "Non-thermal Radiation Mechanisms and Processes in SS433 and Active Galactic Nuclei" was "pioneering work on the physics of jets arising from black holes and models for their emission, including self-absorption, which previewed much to come, and even David's own later work on Gamma-ray Bursts," according to Grindlay who remained a personal friend and colleague of Band's. Following graduate school, Band held postdoctoral positions at the Lawrence Livermore Laboratory, the University of California at Berkeley and the Center for Astronomy and Space Sciences at the University of California San Diego where he worked on the BATSE experiment that was part of the Compton Gamma Ray Observatory (CGRO), launched in 1991. BATSE had as its main objective the study of cosmic gamma-ray bursts (GRBs) and made significant advances in this area of research. Band became a world-renowned figure in the emerging field of GRB studies. He is best known for his widely-used analytic form of gamma-ray burst spectra known as the "Band Function." After the CGRO mission ended, Band moved to the Los Alamos National Laboratory where he worked mainly on classified research but continued to work on GRB energetics and spectra. When NASA planned

Ka-band and X-band observations of the solar corona acquired during the Cassini 2001 superior conjunction

NASA Technical Reports Server (NTRS)

Morabito, D. D.

2002-01-01

Simultaneous dual-frequency Ka-band (32 GHz) and X-band (8.4 GHz) carrier signal data have been acquired during the superior conjunction of the Cassini spacecraft June 2001, using the NASA Deep Space Network's facilities located in Goldstone, California. The solar elongation angle of the observations varied from -4.1 degrees (-16 solar radii) to -0.6 degrees (-2.3 solar radii). The observed coronal and solar effects on the signals include spectral broadening, amplitude scintillation, phase scintillation, and increased noise. The measurements were generally consistent with existing solar models, except during solar transient events when the signatures of the measurements were observed to increase significantly above the quiet background levels. This is the second solar conjunction of Cassini for which simultaneous X/Ka data were acquired. Both solar conjunctions, conducted in May 2000 and June 2001, occurred near the peak of the current 11 year solar cycle.

L-Band Orthogonal-Mode Crossed-Slot Antenna and VHF Crossed-Loop Antenna

DOT National Transportation Integrated Search

1972-01-01

A low-gain, circularly polarized, L-ban antenna; a low-gain, lineraly polarized, L-band antenna; and a low-gain, lineraly polarized, L-ban antenna; and a low-gain, circularly polarized, upper hemisphere, VHF satellite communications antenna intended ...

Direct EUV/X-Ray Modulation of the Ionosphere During the August 2017 Total Solar Eclipse

NASA Astrophysics Data System (ADS)

Mrak, Sebastijan; Semeter, Joshua; Drob, Douglas; Huba, J. D.

2018-05-01

The great American total solar eclipse of 21 August 2017 offered a fortuitous opportunity to study the response of the atmosphere and ionosphere using a myriad of ground instruments. We have used the network of U.S. Global Positioning System receivers to examine perturbations in maps of ionospheric total electron content (TEC). Coherent large-scale variations in TEC have been interpreted by others as gravity wave-induced traveling ionospheric disturbances. However, the solar disk had two active regions at that time, one near the center of the disk and one at the edge, which resulted in an irregular illumination pattern in the extreme ultraviolet (EUV)/X-ray bands. Using detailed EUV occultation maps calculated from the National Aeronautics and Space Administration Solar Dynamics Observatory Atmospheric Imaging Assembly images, we show excellent agreement between TEC perturbations and computed gradients in EUV illumination. The results strongly suggest that prominent large-scale TEC disturbances were consequences of direct EUV modulation, rather than gravity wave-induced traveling ionospheric disturbances.

Dayside Magnetosphere-Ionosphere Coupling and Prompt Response of Low-Latitude/Equatorial Ionosphere

NASA Astrophysics Data System (ADS)

Tu, J.; Song, P.

2017-12-01

We use a newly developed numerical simulation model of the ionosphere/thermosphere to investigate magnetosphere-ionosphere coupling and response of the low-latitude/equatorial ionosphere. The simulation model adapts an inductive-dynamic approach (including self-consistent solutions of Faraday's law and retaining inertia terms in ion momentum equations), that is, based on magnetic field B and plasma velocity v (B-v paradigm), in contrast to the conventional modeling based on electric field E and current j (E-j paradigm). The most distinct feature of this model is that the magnetic field in the ionosphere is not constant but self-consistently varies, e.g., with currents, in time. The model solves self-consistently time-dependent continuity, momentum, and energy equations for multiple species of ions and neutrals including photochemistry, and Maxwell's equations. The governing equations solved in the model are a set of multifluid-collisional-Hall MHD equations which are one of unique features of our ionosphere/thermosphere model. With such an inductive-dynamic approach, all possible MHD wave modes, each of which may refract and reflect depending on the local conditions, are retained in the solutions so that the dynamic coupling between the magnetosphere and ionosphere and among different regions of the ionosphere can be self-consistently investigated. In this presentation, we show that the disturbances propagate in the Alfven speed from the magnetosphere along the magnetic field lines down to the ionosphere/thermosphere and that they experience a mode conversion to compressional mode MHD waves (particularly fast mode) in the ionosphere. Because the fast modes can propagate perpendicular to the field, they propagate from the dayside high-latitude to the nightside as compressional waves and to the dayside low-latitude/equatorial ionosphere as rarefaction waves. The apparent prompt response of the low-latitude/equatorial ionosphere, manifesting as the sudden increase of

HF-induced airglow structure as a proxy for ionospheric irregularity detection

NASA Astrophysics Data System (ADS)

Kendall, E. A.

2013-12-01

The High Frequency Active Auroral Research Program (HAARP) heating facility allows scientists to test current theories of plasma physics to gain a better understanding of the underlying mechanisms at work in the lower ionosphere. One powerful technique for diagnosing radio frequency interactions in the ionosphere is to use ground-based optical instrumentation. High-frequency (HF), heater-induced artificial airglow observations can be used to diagnose electron energies and distributions in the heated region, illuminate natural and/or artificially induced ionospheric irregularities, determine ExB plasma drifts, and measure quenching rates by neutral species. Artificial airglow is caused by HF-accelerated electrons colliding with various atmospheric constituents, which in turn emit a photon. The most common emissions are 630.0 nm O(1D), 557.7 nm O(1S), and 427.8 nm N2+(1NG). Because more photons will be emitted in regions of higher electron energization, it may be possible to use airglow imaging to map artificial field-aligned irregularities at a particular altitude range in the ionosphere. Since fairly wide field-of-view imagers are typically deployed in airglow campaigns, it is not well-known what meter-scale features exist in the artificial airglow emissions. Rocket data show that heater-induced electron density variations, or irregularities, consist of bundles of ~10-m-wide magnetic field-aligned filaments with a mean depletion depth of 6% [Kelley et al., 1995]. These bundles themselves constitute small-scale structures with widths of 1.5 to 6 km. Telescopic imaging provides high resolution spatial coverage of ionospheric irregularities and goes hand in hand with other observing techniques such as GPS scintillation, radar, and ionosonde. Since airglow observations can presumably image ionospheric irregularities (electron density variations), they can be used to determine the spatial scale variation, the fill factor, and the lifetime characteristics of

Experiment to demonstrate separation of Cherenkov and scintillation signals

NASA Astrophysics Data System (ADS)

Caravaca, J.; Descamps, F. B.; Land, B. J.; Wallig, J.; Yeh, M.; Orebi Gann, G. D.

2017-05-01

The ability to separately identify the Cherenkov and scintillation light components produced in scintillating mediums holds the potential for a major breakthrough in neutrino detection technology, allowing development of a large, low-threshold, directional detector with a broad physics program. The CHESS (CHErenkov/Scintillation Separation) experiment employs an innovative detector design with an array of small, fast photomultiplier tubes and state-of-the-art electronics to demonstrate the reconstruction of a Cherenkov ring in a scintillating medium based on photon hit time and detected photoelectron density. This paper describes the physical properties and calibration of CHESS along with first results. The ability to reconstruct Cherenkov rings is demonstrated in a water target, and a time precision of 338 ±12 ps FWHM is achieved. Monte Carlo-based predictions for the ring imaging sensitivity with a liquid scintillator target predict an efficiency for identifying Cherenkov hits of 94 ±1 % and 81 ±1 % in pure linear alkyl benzene (LAB) and LAB loaded with 2 g/L of a fluor, PPO, respectively, with a scintillation contamination of 12 ±1 % and 26 ±1 % .

Positive hysteresis of Ce-doped GAGG scintillator

NASA Astrophysics Data System (ADS)

Yanagida, Takayuki; Fujimoto, Yutaka; Koshimizu, Masanori; Watanabe, Kenichi; Sato, Hiroki; Yagi, Hideki; Yanagitani, Takagimi

2014-10-01

Positive hysteresis and radiation tolerance to high-dose radiation exposure were investigated for Ce 1% and 3% doped Gd3(Al, Ga)5O12 (Ce:GAGG) crystal scintillator on comparison with other garnet scintillators such Ce:YAG, Ce:LuAG, Pr:LuAG, and ceramic Ce:GAGG. When they were irradiated by several Gy 60Co γ-rays, Ce 1% doped GAGG crystal exhibited ∼20% light yield enhancement (positive hysteresis). This is the first time to observe positive hysteresis in Ce doped GAGG. On the other hand, other garnet materials did not show the positive hysteresis and their light yields were stable after 800 Gy irradiation except Pr:LuAG. The light yield of Pr:LuAG decreased largely. When irradiated Ce:GAGG which showed positive hysteresis was evaluated in Synchrotron facility (UVSOR), new excitation band was created around 60 nm.

Liquid scintillators with near infrared emission based on organoboron conjugated polymers.

PubMed

Tanaka, Kazuo; Yanagida, Takayuki; Yamane, Honami; Hirose, Amane; Yoshii, Ryousuke; Chujo, Yoshiki

2015-11-15

The organic liquid scintillators based on the emissive polymers are reported. A series of conjugated polymers containing organoboron complexes which show the luminescence in the near infrared (NIR) region were synthesized. The polymers showed good solubility in common organic solvents. From the comparison of the luminescent properties of the synthesized polymers between optical and radiation excitation, similar emission bands were detected. In addition, less significant degradation was observed. These data propose that the organoboron conjugated polymers are attractive platforms to work as an organic liquid scintillator with the emission in the NIR region. Copyright © 2015 Elsevier Ltd. All rights reserved.

Ionospheric Modelling using GPS to Calibrate the MWA. II: Regional Ionospheric Modelling using GPS and GLONASS to Estimate Ionospheric Gradients

NASA Astrophysics Data System (ADS)

Arora, B. S.; Morgan, J.; Ord, S. M.; Tingay, S. J.; Bell, M.; Callingham, J. R.; Dwarakanath, K. S.; For, B.-Q.; Hancock, P.; Hindson, L.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kapińska, A. D.; Lenc, E.; McKinley, B.; Offringa, A. R.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, C.; Zheng, Q.

2016-07-01

We estimate spatial gradients in the ionosphere using the Global Positioning System and GLONASS (Russian global navigation system) observations, utilising data from multiple Global Positioning System stations in the vicinity of Murchison Radio-astronomy Observatory. In previous work, the ionosphere was characterised using a single-station to model the ionosphere as a single layer of fixed height and this was compared with ionospheric data derived from radio astronomy observations obtained from the Murchison Widefield Array. Having made improvements to our data quality (via cycle slip detection and repair) and incorporating data from the GLONASS system, we now present a multi-station approach. These two developments significantly improve our modelling of the ionosphere. We also explore the effects of a variable-height model. We conclude that modelling the small-scale features in the ionosphere that have been observed with the MWA will require a much denser network of Global Navigation Satellite System stations than is currently available at the Murchison Radio-astronomy Observatory.

Global Distributions of Ionospheric Electrostatic Potentials for Various Interplanetary Conditions

NASA Astrophysics Data System (ADS)

Kartalev, M.; Papitashvili, V.; Keremidarska, V.; Grigorov, K.; Romanov, D.

2001-12-01

We report on a study of the global ionospheric electrostatic potential distributions obtained from combining two algorithms used for the mapping of high-latitude and middle-latitude ionospheric electrodynamics; that is, the LiMIE (http://www.sprl.umich.edu/mist/) and IMEH (http://geospace.nat.bg) models, respectively. In this combination, the latter model utilizes the LiMIE high-latitude field-aligned current distributions for various IMF conditions and different seasons (summer, winter, equinox). The IMEH model is a mathematical tool, allowing us to study conjugacy (or non-conjugacy) of the ionospheric electric fields on a global scale, from the northern and southern polar regions to the middle- and low-latitudes. The proposed numerical scheme permits testing of different mechanisms of the interhemispheric coupling and mapping to the ionosphere through the appropriate current systems. The scheme is convenient for determining self-consistently the separatrices in both the northern and southern hemispheres. In this study we focus on the global ionospheric electrostatic field distributions neglecting other possible electric field sources. Considering some implications of the proposed technique for the space weather specification and forecasting, we developed a Web-based interface providing global distributions of the ionospheric electrostatic potentials in near-real time from the ACE upstream solar wind observations at L1.

Radio scintillations observed during atmospheric occultations of Voyager: Internal gravity waves at Titan and magnetic field orientations at Jupiter and Saturn. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hinson, D. P.

1983-01-01

The refractive index of planetary atmospheres at microwave frequencies is discussed. Physical models proposed for the refractive irregularities in the ionosphere and neutral atmosphere serve to characterize the atmospheric scattering structures, and are used subsequently to compute theoretical scintillation spectra for comparison with the Voyager occultation measurements. A technique for systematically analyzing and interpreting the signal fluctuations observed during planetary occultations is presented and applied to process the dual-wavelength data from the Voyager radio occultations by Jupiter, Saturn, and Titan. Results concerning the plasma irregularities in the upper ionospheres of Jupiter and Saturn are reported. The measured orientation of the irregularities is used to infer the magnetic field direction at several locations in the ionospheres of these two planets; the occultation measurements conflict with the predictions of Jovian magnetic field models, but generally confirm current models of Saturn's field. Wave parameters, including the vertical fluxes of energy and momentum, are estimated, and the source of the internal gravity waves discovered in Titan's upper atmosphere is considered.

Combined observations of Arctic sea ice with near-coincident colocated X-band, C-band, and L-band SAR satellite remote sensing and helicopter-borne measurements

NASA Astrophysics Data System (ADS)

Johansson, A. M.; King, J. A.; Doulgeris, A. P.; Gerland, S.; Singha, S.; Spreen, G.; Busche, T.

2017-01-01

In this study, we compare colocated near-coincident X-, C-, and L-band fully polarimetry SAR satellite images with helicopter-borne ice thickness measurements acquired during the Norwegian Young sea ICE 2015 (N-ICE2015) expedition in the region of the Arctic Ocean north of Svalbard in April 2015. The air-borne surveys provide near-coincident snow plus ice thickness, surface roughness data, and photographs. This unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies, but also to raise awareness of limitations. X-band and L-band satellite scenes were shown to be a useful complement to the standard SAR frequency for sea ice monitoring (C-band) for lead ice and newly formed sea ice identification. This may be in part be due to the frequency but also the high spatial resolution of these sensors. We found a relatively low correlation between snow plus ice thickness and surface roughness. Therefore, in our dataset ice thickness cannot directly be observed by SAR which has important implications for operational ice charting based on automatic segmentation.

Studies of the ionospheric turbulence excited by the fourth gyroharmonic at HAARP

NASA Astrophysics Data System (ADS)

Najmi, A.; Milikh, G.; Yampolski, Y. M.; Koloskov, A. V.; Sopin, A. A.; Zalizovski, A.; Bernhardt, P.; Briczinski, S.; Siefring, C.; Chiang, K.; Morton, Y.; Taylor, S.; Mahmoudian, A.; Bristow, W.; Ruohoniemi, M.; Papadopoulos, K.

2015-08-01

A study is presented of artificial ionospheric turbulence (AIT) induced by HF heating at High Frequency Active Auroral Research Program (HAARP) using frequencies close to the fourth electron gyroharmonic, in a broad range of radiated powers and using a number of different diagnostics. The diagnostics include GPS scintillations, ground-based stimulated electromagnetic emission (SEE), the HAARP ionosonde, Kodiak radar, and signals received at the Ukrainian Antarctic Station (UAS). The latter allowed analysis of waves scattered by the AIT into the ionospheric waveguide along Earth's terminator, 15.6 mm from the HAARP facility. For the first time, the amplitudes of two prominent SEE features, the downshifted maximum and broad upshifted maximum, were observed to saturate at ~50% of the maximum HAARP effective radiated power. Nonlinear effects in slant total electron content, SEE, and signals received at UAS at different transmitted frequencies and intensities of the pump wave were observed. The correlations between the data from different detectors demonstrate that the scattered waves reach UAS by the waveguide along the Earth's terminator, and that they were injected into the waveguide by scattering off of artificial striations produced by AIT above HAARP, rather than via direct injection from sidelobe radiation.

Tropospheric scintillation prediction models for a high elevation angle based on measured data from a tropical region

NASA Astrophysics Data System (ADS)

Abdul Rahim, Nadirah Binti; Islam, Md. Rafiqul; J. S., Mandeep; Dao, Hassan; Bashir, Saad Osman

2013-12-01

The recent rapid evolution of new satellite services, including VSAT for internet access, LAN interconnection and multimedia applications, has triggered an increasing demand for bandwidth usage by satellite communications. However, these systems are susceptible to propagation effects that become significant as the frequency increases. Scintillation is the rapid signal fluctuation of the amplitude and phase of a radio wave, which is significant in tropical climates. This paper presents the analysis of the tropospheric scintillation data for satellite to Earth links at the Ku-band. Twelve months of data (January-December 2011) were collected and analyzed to evaluate the effect of tropospheric scintillation. Statistics were then further analyzed to inspect the seasonal, worst-month, diurnal and rain-induced scintillation effects. By employing the measured scintillation data, a modification of the Karasawa model for scintillation fades and enhancements is proposed based on data measured in Malaysia.

A new tritiated water measurement method with plastic scintillator pellets.

PubMed

Furuta, Etsuko; Iwasaki, Noriko; Kato, Yuka; Tomozoe, Yusuke

2016-01-01

A new tritiated water measurement method with plastic scintillator pellets (PS-pellets) by using a conventional liquid scintillation counter was developed. The PS-pellets used were 3 mm in both diameter and length. A low potassium glass vial was filled full with the pellets, and tritiated water was applied to the vial from 5 to 100 μl. Then, the sample solution was scattered in the interstices of the pellets in a vial. This method needs no liquid scintillator, so no liquid organic waste fluid is generated. The counting efficiency with the pellets was approximately 48 % when a 5 μl solution was used, which was higher than that of conventional measurement using liquid scintillator. The relationship between count rate and activity showed good linearity. The pellets were able to be used repeatedly, so few solid wastes are generated with this method. The PS-pellets are useful for tritiated water measurement; however, it is necessary to develop a new device which can be applied to a larger volume and measure low level concentration like an environmental application.