共查询到20条相似文献，搜索用时 31 毫秒
1.
Angela Aragon-Angel Manuel Hernandez-Pajares J. Miguel Juan Zornoza Jaume Sanz Subirana 《GPS Solutions》2010,14(1):23-33
The FORMOSAT-3/COSMIC satellite constellation has become an important tool toward providing global remote sensing data for
sounding of the atmosphere of the earth and the ionosphere in particular. In this study, the electron density profiles are
derived using the Abel transform inversion. Some drawbacks of this transform in LEO GPS sounding can be overcome by considering
the separability concept: horizontal gradients of vertical total electron content (VTEC) information are incorporated by the
inversion method, providing more accurate electron density determinations. The novelty presented in this paper with respect
to previous works is the use of the phase change between the GPS transmitter and the LEO receiver as the main observable instead
of the ionospheric combination of carrier phase observables for the implementation of separability in the inversion process.
Some of the characteristics of the method when applied to the excess phase are discussed. The results obtained show the equivalence
of both approaches but the method exposed in this work has the potentiality to be applied to the neutral atmosphere. Recent
FORMOSAT-3/COSMIC data have been processed with both the classical Abel inversion and the separability approach and evaluated
versus colocated ionosonde data. 相似文献
2.
Experimental analysis was performed using multiplicative algebraic reconstruction technique (MART) to map the ionosphere over Brazil. Code and phase observations from the global navigation satellite system (GNSS) together with the international reference ionosphere (IRI) enabled the estimation of ionospheric profiles and total electron content (TEC) over the entire region. Twenty-four days of data collected from existing ground-based GNSS receivers during the recent solar maximum period were used to analyze the performance of the MART algorithm. The results were compared with four ionosondes. It was demonstrated that MART estimated the electron density peak with the same degree of accuracy as the IRI model in regions with appropriate geometrical coverage by GNSS receivers for tomographic reconstruction. In addition, the slant TEC, as estimated with MART, presented lower root-mean-square error than the TEC calculated by ionospheric maps available from the International GNSS Service (IGS). Furthermore, the daily variations of the ionosphere were better represented with the algebraic techniques, compared to the IRI model and IGS maps, enabling a correlation of the elevation of the ionosphere at higher altitudes with the equatorial ionization anomaly intensification. The tomographic representations also enabled the detection of high vertical gradients at the same instants in which ionospheric irregularities were evident. 相似文献
3.
Application of the TaiWan Ionospheric Model to single-frequency ionospheric delay corrections for GPS positioning 总被引：2，自引：2，他引：0
The performance of a three-dimensional ionospheric electron density model derived from FormoSat3/COSMIC GPS Radio Occultation measurements, called the TaiWan Ionosphere Model (TWIM), in removing the ionospheric delays in single-frequency pseudorange observations is presented. Positioning results using TWIM have been compared with positioning results using other ionospheric models, such as the Klobuchar (KLOB) and the global ionospheric model (GIM). C/A code pseudoranges have been observed at three International GPS Service reference stations that are representative of mid-latitude (BOR1 and IRKJ) and low-latitude (TWTF) regions of the ionosphere. The observations took place during 27 geomagnetically quiet days from April 2010 to October 2011. We perform separate solutions using the TWIM, KLOB, GIM ionospheric models and carry out a solution applying no ionospheric correction at all. We compute the daily mean horizontal errors (DMEAN) and the daily RMS (DRMS) for these solutions with respect to the published reference station coordinates. It has demonstrated that TEC maps generate using the TWIM exhibit a detailed structure of the ionosphere, particularly at low-latitude region, whereas the Klobuchar and the GIM only provide the basic diurnal and geographic features of the ionosphere. Also, it is shown that even for lower satellite elevations, the TWIM provides better positioning than the Klobuchar and GIM models. Specifically, using TWIM, the difference of the uncorrected solution (no ionospheric correction), and the other solutions, relative to the uncorrected solution, is 45 % for the mean horizontal error (DMEAN) and 42 % for the horizontal root-mean-square error (DRMS). Using Klobuchar and GIM, the percent for DMEAN only reaches to about 12 % and 3 %, while the values for the DRMS are only 12 and 4 %, respectively. In the vertical direction, all models have a percentage of about 99 and 70 % for the mean vertical error (VMEAN) and vertical root-mean-square error (VRMS), respectively. These percentages show the greater impact of TWIM on the ionospheric correction compared to the other models. In at least 40 % of the observed days and across all stations, TWIM has the smallest DMEAN, VMEAN, DRMS, and VRMS daily values. These values reach 100 % at station TWTF. This shows the overall performance of TWIM is better than the Klobuchar and GIM. 相似文献
4.
Since 1995, the global positioning system (GPS) has been exploited by the means of the radio occultation (RO) method to obtain the vertical profiles of refractivity, temperature, pressure, and water vapor in the neutral atmosphere and electron density in the ionosphere. Applying the RO method to the study of the Earths atmosphere was demonstrated for the first time with the GPS/MET experiment. Since then, several satellites with GPS receivers, suitable for RO experiments, have been launched including Oersted, SUNSAT, CHAMP, SAC-C, and GRACE. Future RO investigations that are planned now include FORMOSAT3/COSMIC and Terra-SAR missions. New elements in the RO technology are required to meet the goals of improving the accuracy and broadening the potential of the RO method. In this paper, a methodological review of RO investigations is presented to emphasize new directions in applying the RO method: measuring the vertical gradients of the refractivity in the atmosphere and electron density in the lower ionosphere, determination of the temperature regime in the upper stratosphere, investigation of the internal wave activity in the atmosphere, and study of the ionospheric disturbances on a global scale. These new directions may be relevant for investigating the relationships between processes in the atmosphere and mesosphere, the study of thermal regimes in the intermediate heights of the upper stratosphere—lower mesosphere, and the analysis of the influence of the space weather phenomena on the lower ionosphere. 相似文献
5.
探讨了OpenMP多线程技术在全球电离层建模中的应用。在日固地磁参考系下采用15阶次的球谐展开建立全球电离层模型,并对1天解、3天解两种方案的结果与IGS电离层产品进行了对比,电离层图偏差的均方根约3~5 TECU,且3天解的方案首尾两组电离层图与IGS产品符合得更好;卫星差分码偏差和接收机差分码偏差与IGS的差异分别约为0.2 ns和2 ns,仅有少数几个接收机差分码偏差在少数几天与IGS差异较大,超过3~4 ns。实验中使用Dell服务器R730（配置:128 GB内存、2个CPU、8个核心和32个线程数）,采用OpenMP多线程并行计算能够明显提高全球电离层模型的建模效率,单天解算仅需约7 min,3天解算需约22 min,效率提升近8倍。使用3 d观测数据并采用OpenMP多线程并行计算来建立全球电离层模型可有效节省建模时间,同时还能提高首尾两组模型系数的精度以进一步提升全球电离层模型的精度,对建模算法的测试、电离层产品的快速发布以及模型后续检验和预测等带来了便利,也为后续实现利用多卫星导航系统观测数据快速建立全球电离层模型提供了参考。 相似文献
6.
7.
Current dual-frequency GPS measurements can only eliminate the first-order ionospheric term and may cause a higher-order range
bias of several centimeters. This research investigates the second-order ionospheric effect for GNSS users in Europe. In comparison
to previous studies, the electron density profiles of the ionosphere/plasmasphere are modeled as the sum of three Chapman
layers describing electron densities of the ionospheric F2, F1 and E layers and a superposed exponential decay function describing the plasmasphere. The International Geomagnetic Reference
Field model is used to calculate the geomagnetic field vectors at numerous points along the incoming ray paths. Based on extended
simulation studies, we derive a correction formula to compute the average value of the longitudinal component of the earth’s
magnetic field along the line-of-sight as a function of geographic latitude and longitude, and geometrical parameters such
as elevation and azimuth angles. Using our correction formula in conjunction with the total electron content (TEC) along the
line-of-sight, the second-order ionospheric term can be corrected to the millimeter level for a vertical TEC level of 1018 electrons/m2. 相似文献
8.
Johannes Bouman 《Journal of Geodesy》2012,86(4):287-304
The vertical gradients of gravity anomaly and gravity disturbance can be related to horizontal first derivatives of deflection
of the vertical or second derivatives of geoidal undulations. These are simplified relations of which different variations
have found application in satellite altimetry with the implicit assumption that the neglected terms—using remove-restore—are
sufficiently small. In this paper, the different simplified relations are rigorously connected and the neglected terms are
made explicit. The main neglected terms are a curvilinear term that accounts for the difference between second derivatives
in a Cartesian system and on a spherical surface, and a small circle term that stems from the difference between second derivatives
on a great and small circle. The neglected terms were compared with the dynamic ocean topography (DOT) and the requirements
on the GOCE gravity gradients. In addition, the signal root-mean-square (RMS) of the neglected terms and vertical gravity
gradient were compared, and the effect of a remove-restore procedure was studied. These analyses show that both neglected
terms have the same order of magnitude as the DOT gradient signal and may be above the GOCE requirements, and should be accounted
for when combining altimetry derived and GOCE measured gradients. The signal RMS of both neglected terms is in general small
when compared with the signal RMS of the vertical gravity gradient, but they may introduce gradient errors above the spherical
approximation error. Remove-restore with gravity field models reduces the errors in the vertical gravity gradient, but it
appears that errors above the spherical approximation error cannot be avoided at individual locations. When computing the
vertical gradient of gravity anomaly from satellite altimeter data using deflections of the vertical, the small circle term
is readily available and can be included. The direct computation of the vertical gradient of gravity disturbance from satellite
altimeter data is more difficult than the computation of the vertical gradient of gravity anomaly because in the former case
the curvilinear term is needed, which is not readily available. 相似文献
9.
GPS observations of the ionospheric F2-layer behavior during the 20th November 2003 geomagnetic storm over South Korea 总被引：4，自引：1，他引：3
The ionospheric F2-layer peak density (NmF2) and its height (hmF2) are of great influence on the shape of the ionospheric
electron density profile Ne (h) and may be indicative of other physical processes within the ionosphere, especially those
due to geomagnetic storms. Such parameters are often estimated using models such as the semiempirical international reference
ionosphere (IRI) models or are measured using moderately priced to expensive instrumentation, such as ionosondes or incoherent
scatter radars. Global positioning system (GPS) observations have become a powerful tool for mapping high-resolution ionospheric
structures, which can be used to study the ionospheric response to geomagnetic storms. In this paper, we describe how 3-D
ionospheric electron density profiles were produced from data of the dense permanent Korean GPS network using the tomography
reconstruction technique. These profiles are verified by independent ionosonde data. The responses of GPS-derived parameters
at the ionospheric F2-layer to the 20th November 2003 geomagnetic storm over South Korea are investigated. A fairly large
increase in the electron density at the F2-layer peak (the NmF2) (positive storm) has been observed during this storm, which
is accompanied by a significant uplift in the height of the F2 layer peak (the hmF2). This is confirmed by independent ionosonde
observations. We suggest that the F2-layer peak height uplift and NmF2 increase are mainly associated with a strong eastward
electric field, and are not associated with the increase of the O/N2 ratio obtained from the GUVI instruments aboard the TIMED satellite. It is also inferred that the increase in NmF2 is not
caused by the changes in neutral composition, but is related to other nonchemical effects, such as dynamical changes of vertical
ion motions induced by winds and E × B drifts, tides and waves in the mesosphere/lower thermosphere region, which can be dynamically
coupled upward to generate ionospheric perturbations and oscillations. 相似文献
10.
Ionospheric electron density observed by FORMOSAT-3/COSMIC over the European region and validated by ionosonde data 总被引：4，自引：0，他引：4
Andrzej Krankowski Irina Zakharenkova Anna Krypiak-Gregorczyk Irk I. Shagimuratov Pawel Wielgosz 《Journal of Geodesy》2011,85(12):949-964
This research is motivated by the recent IGS Ionosphere Working Group recommendation issued at the IGS 2010 Workshop held
in Newcastle, UK. This recommendation encourages studies on the evaluation of the application of COSMIC radio occultation
profiles for additional IGS global ionosphere map (GIM) validation. This is because the reliability of GIMs is crucial to
many geodetic applications. On the other hand, radio occultation using GPS signals has been proven to be a promising technique
to retrieve accurate profiles of the ionospheric electron density with high vertical resolution on a global scale. However,
systematic validation work is still needed before using this powerful technique for sounding the ionosphere on a routine basis.
In this paper, we analyze the properties of the ionospheric electron density profiling retrieved from COSMIC radio occultation
measurements. A comparison of radio occultation data with ground-based measurements indicates that COSMIC profiles are usually
in good agreement with ionosonde profiles, both in the F2 layer peak electron density and the bottom side of the profiles.
For this comparison, ionograms recorded by European ionospheric stations (DIAS network) in 2008 were used. 相似文献
11.
电离层参量的提取是开展电离层研究的基础,而数据同化技术则是获取电离层参量的一种重要手段。以NeQuick模型的输出作为背景场,Kalman滤波作为同化算法,利用数据同化技术实现区域电离层TEC重构,结果表明,数据同化方法重构的倾斜总电子含量（TEC）和垂直TEC与实测值较为一致。相比NeQuick模型及全球电离层地图（GIM）数据,数据同化方法重构得到的TEC的平均误差和标准差均有明显的降低,实测数据验证了数据同化技术在区域TEC重构中的精度和可靠性。 相似文献
12.
N. Jakowski 《GPS Solutions》2005,9(2):88-95
The GPS radio occultation technique is a rather simple and inexpensive tool for getting information about the global characteristics of the vertical electron density distribution. No other ionospheric sounding technique (bottomside/topside vertical sounding, incoherent scatter) unifies vertical profiling through the entire ionosphere with global coverage. The paper addresses retrieval methods and algorithms applied for the generation of operational products including their limitations in accuracy and spatial resolution. Preliminary results of ionospheric radio occultation (IRO) measurements carried out onboard the German CHAMP satellite are reported. The achieved accuracy of the retrieved electron density profiles (EDPs) is estimated in particular by comparing the IRO results with independent vertical sounding data from European stations. It is concluded that CHAMP-IRO measurements have the potential to establish global data sets of EDPs, contribute to ionospheric research, develop and improve global ionospheric models and to provide operational space weather information. 相似文献
13.
A. G. Pavelyev J. Wickert Y. A. Liou Ch. Reigber T. Schmidt K. Igarashi A. A. Pavelyev S. S. Matyugov 《GPS Solutions》2005,9(2):96-104
A local mechanism for strong ionospheric effects on radio occultation (RO) global positioning satellite system (GPS) signals is described. Peculiar zones centered at the critical points (the tangent points) in the ionosphere, where the gradient of the electron density is perpendicular to the RO ray trajectory, strongly influence the amplitude and phase of RO signals. It follows from the analytical model of local ionospheric effects that the positions of the critical points depend on the RO geometry and the structure of the ionospheric disturbances. Centers of strong ionospheric influence on RO signals can exist, for example, in the sporadic E-layers, which are inclined by 3–6° relative to the local horizontal direction. Also, intense F2 layer irregularities can contribute to the RO signal variations. A classification of the ionospheric influence on the GPS RO signals is introduced using the amplitude data, which indicates different mechanisms (local, diffraction, etc.) for radio waves propagation. The existence of regular mechanisms (e.g., local mechanism) indicates a potential for separating the regular and random parts in the ionospheric influence on the RO signals. 相似文献
14.
掩星观测能够提供地面到低轨卫星轨道高度处的整个电离层电子密度剖面,对于顶部电离层的研究有重要的作用。本文利用COSMIC(constellation observing system for meteorology ionosphere and climate)掩星数据反演了电子密度剖面,提取了F2层峰值高度(hmF2)、F2层峰值密度(NmF2)、垂直标尺高(vertical scale height,VSH)等电离层参数,研究了南极地区的F2层在太阳活动周期内的变化、年际变化、周日变化等,并且重点分析了南极地区的顶部电离层的垂直结构特征,尤其是威德尔海异常在垂直方向上的变化。结果表明,整个南极的hmF2每日均值在250~300 km左右,NmF2每日均值在1~8×1011 el/m3之间,VSH每日均值在100~250 km,威德尔海异常主要表现在顶部电子密度的增强和底部电子密度的减少。 相似文献
15.
论电离层对GPS定位的影响 总被引：13，自引：2，他引：11
电离层是ＧＰＳ定位的主要误差源。本文论述电离层的特征和折射系数,以及电离层的下列影响：电离层码群延、电离层载波相位超前、电离层多普勒频移、振幅闪烁、电离层相位闪烁效应、磁暴对ＧＰＳ定位测量的影响、电离层对差分ＧＰＳ的影响和ＧＰＳ接收机的电离层改正。 相似文献
16.
Improving the GNSS positioning stochastic model in the presence of ionospheric scintillation 总被引：1，自引：0，他引：1
M. Aquino J. F. G. Monico A. H. Dodson H. Marques G. De Franceschi L. Alfonsi V. Romano M. Andreotti 《Journal of Geodesy》2009,83(10):953-966
Ionospheric scintillations are caused by time- varying electron density irregularities in the ionosphere, occurring more often
at equatorial and high latitudes. This paper focuses exclusively on experiments undertaken in Europe, at geographic latitudes
between ~50°N and ~80°N, where a network of GPS receivers capable of monitoring Total Electron Content and ionospheric scintillation parameters was
deployed. The widely used ionospheric scintillation indices S4 and sj{\sigma_{\varphi}} represent a practical measure of the intensity of amplitude and phase scintillation affecting GNSS receivers. However, they
do not provide sufficient information regarding the actual tracking errors that degrade GNSS receiver performance. Suitable
receiver tracking models, sensitive to ionospheric scintillation, allow the computation of the variance of the output error
of the receiver PLL (Phase Locked Loop) and DLL (Delay Locked Loop), which expresses the quality of the range measurements
used by the receiver to calculate user position. The ability of such models of incorporating phase and amplitude scintillation
effects into the variance of these tracking errors underpins our proposed method of applying relative weights to measurements
from different satellites. That gives the least squares stochastic model used for position computation a more realistic representation,
vis-a-vis the otherwise ‘equal weights’ model. For pseudorange processing, relative weights were com- puted, so that a ‘scintillation-mitigated’
solution could be performed and compared to the (non-mitigated) ‘equal weights’ solution. An improvement between 17 and 38%
in height accuracy was achieved when an epoch by epoch differential solution was computed over baselines ranging from 1 to
750 km. The method was then compared with alternative approaches that can be used to improve the least squares stochastic
model such as weighting according to satellite elevation angle and by the inverse of the square of the standard deviation
of the code/carrier divergence (sigma CCDiv). The influence of multipath effects on the proposed mitigation approach is also
discussed. With the use of high rate scintillation data in addition to the scintillation indices a carrier phase based mitigated
solution was also implemented and compared with the conventional solution. During a period of occurrence of high phase scintillation
it was observed that problems related to ambiguity resolution can be reduced by the use of the proposed mitigated solution. 相似文献
17.
18.
Integral transformations of gravitational gradients onto a Gravity Recovery And Climate Experiment (GRACE) type of observable are derived in this article. The gravitational gradients represent components of the gravitational tensor in the local north-oriented frame. The GRACE type of observable corresponds to a difference between two gravitational vectors as projected onto the line of sight between the two GRACE satellites. In total, three integral transformations relating vertical–vertical, vertical–horizontal and horizontal–horizontal gravitational gradients with the GRACE type of observable are provided. Spectral and closed forms of corresponding isotropic kernels are derived for each transformation. Special cases show that the integral transformations are general and relate gravitational gradients to many other quantities of the gravitational field, such as the gravitational vector, and its radial and tangential components. Correctness of the mathematical derivations is validated in a closed-loop simulation using synthetic data. 相似文献
19.
Global Ionosphere Maps of VTEC from GNSS,satellite altimetry,and formosat-3/COSMIC data 总被引：1，自引：1，他引：0
For space geodetic techniques, operating in microwave band, ionosphere is a dispersive medium; thus signals traveling through
this medium are in the first approximation affected proportional to inverse of the square of their frequencies. This effect
allows gaining information about the parameters of the ionosphere in terms of Total Electron Content (TEC) or the electron
density (N
e
). TEC or electron density can then be expressed by means of spherical harmonic base functions to provide a Global Ionosphere
Map (GIM). The classical input data for development of GIMs are obtained from dual-frequency observations carried out at Global
Navigation Satellite Systems (GNSS) stations. However, GNSS stations are in-homogeneously distributed around the world, with
large gaps particularly over the oceans; this fact reduces the precision of the GIM over these areas. On the other hand, dual-frequency
satellite altimetry missions such as Jason-1 provide information about the ionosphere precisely above the oceans; and furthermore
Low Earth Orbiting (LEO) satellites, such as Formosat-3/COSMIC (F/C) provide well-distributed information of ionosphere globally.
This study investigates on global modeling of TEC through combining GNSS and satellite altimetry data with global TEC data
derived from the occultation measurements of the F/C mission. The combined GIMs of vertical TEC (VTEC) show a maximum difference
of 1.3–1.7 TEC units (TECU) with respect to the GNSS-only GIMs in the whole day. The root mean square error (RMS) maps of
combined solution show a reduction of about 0.1 TECU in the whole day. This decrease of RMS can reach up to 0.5 TECU in areas
where no or few GNSS observations are available, but high number of F/C measurement is carried out. This proves that the combined
GIMs provide a more homogeneous global coverage and higher reliability than results of each single method. All comparisons
and validations made within this study provide vital information regarding combination and integration of various observation
techniques in the Global Geodetic Observing System of the International Association of Geodesy. 相似文献