不同GPS掩星电离层剖面产品相关性分析

将在一定时空限定范围内的不同低轨卫星COSMIC、GRACE、CHAMP、FY3C的电离层掩星电子密度剖面定义为一个掩星对来对比分析不同类型掩星电离层产品。结果表明：COSMIC掩星对之间的电子密度剖面整体轮廓符合得很好,电子密度剖面主要在250 km以下和500 km以上存在较大的偏差,250~500 km的电子密度整体偏差较小,统计得到的COSMIC掩星对的电子密度参量NmF2和hmF2的相关系数能分别达到0.99和0.97,具有高度相关性,不同COSMIC卫星之间没有明显的系统误差;COSMIC、GRACE、CHAMP和FY3C不同低轨卫星间的电子密度剖面略有差异,通过统计电子密度参量NmF2和hmF2之间的相关系数,COSMIC和CHAMP的相关系数分别为0.95和0.86,COSMIC和GRACE的相关系数分别为0.98和0.94,COSMIC和FY3C的相关系数分别为0.96和0.92,不同掩星类型之间的电子密度参量之间也具有高度相关性,验证了不同卫星任务GPS掩星电离层剖面的一致性。     

GPS电离层掩星数据分析汶川大地震电离层响应

利用COSMIC和CHAMP掩星的电离层掩星资料研究汶川大地震引起的电离层响应。选取了2008年4月30日到5月18日共19天的北纬20°到40°,东经80°到120°的共309个掩星数据进行分析。采用人工神经网络插值技术,分析震中附近上空电离层F2区的临界频率的日变化。结果表明：震前6天电离层F2区的临界频率和电子密度的峰值高度开始明显下降,在震前的三天内其值达到最小。震后他它们的值开始逐步回升。     

日本九州岛地震震前电离层TEC异常

采用IGS发布的GIM数据,提出了一种结合滑动时窗法和临近格网点电离层TEC相关性分析法的联合分析方法,研究了震前电离层异常变化与地震的关系。通过分析震区附近5个格网点TEC的异常变化情况,发现震前电离层TEC发生明显异常变化,且格网点之间的TEC序列相关性受地震显著影响;通过分析二维电离层图的TEC异常空间分布,发现震前三天震中附近分别出现6h、12h和6h的异常。最后利用电离层层析的方法,对电离层异常时刻进行了电子密度的反演,进一步分析了电子密度在电离层异常时刻的分布情况。     

基于空间电离层环境层析成像测量仪的地震电离层扰动监测系统设计

为了更好地开展地震电离层扰动监测和异常信息提取研究,基于空间电离层环境层析成像测量仪研制了地震电离层扰动监测系统,包括小区域监测站网和监测软件系统.?该监测系统产出空间分辨率1°×1°的电离层总电子含量(TEC)、F2层最大电子密度(NmF2)和F2层峰值电子密度对应高度(hmF2)二维分布图,对扰动异常超过10％的事...     

利用掩星和地基GPS研究日食电离层效应

21世纪最长的一次日全食于2009-07-22发生,从亚洲东部一直延伸到太平洋地区,同时,日食后期开始伴随着一次中等强度的磁暴。本文利用COSMIC掩星GPS数据反演了食甚时刻电子密度变化情况,利用武汉CORS地基GPS数据反演了局部TEC时序变化情况,并分析了日食电离层效应的物理机制。     

利用掩星技术研究南极地区顶部电离层特性

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。     

电离层异常原因分析与建模

分析了地震、磁暴、太阳耀斑等自然现象引发电离层异常的物理机制,并总结了电离层异常的特点。针对电离层中电子分布受地磁、太阳热辐射和地壳变动等影响较大,基于抛物层和赤道双峰模型建立了电子密度呈高斯型分布的电离层异常模型,为进一步研究电离层异常的耦合机制提供了依据。     

地基GPS与掩星联合的电离层层析成像方法研究

由于有限视角、稀疏布站等原因,地基G PS电离层层析成像存在垂直分辨率不高的问题,联合掩星进行电离层层析成像是一个重要的解决途径。一方面地基G PS观测能保证电离层层析成像的时间连续性和区域覆盖性;另一方面由于掩星信号能够提供地基G PS没有的水平射线信息,提升了电离层层析成像的垂直分辨率水平。利用地基GPS站与COSMIC卫星的掩星观测进行的仿真结果表明：与仅利用地基G PS相比,联合掩星进行电离层层析成像,不仅在电离层电子密度反演精度方面有明显提升,而且在电离层F2层峰值高度（hm F2）和电离层总电子含量（T EC ）的精度方面同样有明显提高。     

COSMIC掩星观测数据反演电离层电子密度廓线

利用COSMIC掩星观测数据,将Abel积分方法和"洋葱分层"反演方法反演得到的电子密度廓线与传统电离层观测方法的观测结果进行了对比。结果表明,通过两种反演方法计算得到的电子密度廓线与垂测仪的结果在整体趋势和结构上符合得较好,反演计算得到的foF2与垂测仪的观测结果有较高的一致性,但hmax仍存在较大的误差。     

基于深度学习构建的全球电离层NmF2模型

采用递归神经网络对空基COSMIC和地基垂测站数据建立了全球电离层峰值电子密度模型,模型均方根误差达到1.3×10~5 el/cm~3。在春夏秋冬4个季节内,人工神经网络ANN模型预测精度比IRI模型分别提高了25.7%、19.7%、33.3%和21.8%。另外,ANN模型不仅能够有效地模拟全球电离层时空变化特征,也能够成功地模拟电离层的诸多区域物理变化特性,如赤道电离异常、威德尔海异常、中纬度夜间异常和冬季异常。ANN模型可以为改正单频接收机的电离层延迟发挥一定的作用。     

Ionospheric electron density observed by FORMOSAT-3/COSMIC over the European region and validated by ionosonde data

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.     

FORMOSAT-3/COSMIC observations of the ionospheric auroral oval development

The ionospheric radiance and electron density observed by the tiny ionospheric photometer (TIP) and GPS occultation experiment (GOX) payloads on FORMOSAT-3/COSMIC satellites are applied to determine the boundaries of the auroral oval and its width in the winter nighttime ionosphere for both hemispheres. The TIP collects ionospheric emission at 135.6 nm due to electron impact excitation, while the GOX offers ionospheric electron density profiles with radio occultation (RO) technique. Comparison between them shows similar patterns of the plasma structure in the polar caps. The mean width of the auroral bands ranges between about 2 and 11° latitude in the winter nighttime and it varies with longitudes. The comparison by month suggests that the mean radius of the auroral ovals varies with the intensity of the auroral radiance.     

Analysis of ionospheric electron parameters versus geomagnetic index Dst from RO data of FORMOSAT-3/COSMIC

The FORMOSAT-3/COSMIC mission has provided ample ionospheric electron density profiles retrieved from the global positioning system radio occultation technique. Currently, there can be more than 2,000 electron density profiles acquired per day covering the global ionosphere from altitude 90 to 800 km. Utilizing the advantage of such a complete coverage, we statistically analyze how the ionospheric electron parameters NmF2, hmF2, and TEC respond to the geomagnetic index Dst for different magnetic latitudes and magnetic local time (MLT) and on quiet and storm times. A data set of 24 months is used for this study, in which most of the results focus on the low-latitude dayside regions. The results indicate that, in general, NmF2, hmF2, and TEC decrease as Dst increases at all seasons. Only during the sudden commencement phase (SSC) of storm events, NmF2 and TEC appear to increase as Dst increases.     

Seismo-ionospheric precursor of the 2008 Mw7.9 Wenchuan earthquake observed by FORMOSAT-3/COSMIC

The seismo-ionospheric precursor prior to the Mw7.9 earthquake near Wenchuan, China, on 12 May 2008 was observed by the FORMOSAT-3/COSMIC satellite constellation. By binning radio occultation observations, the three-dimensional ionospheric structure can be obtained to monitor the ionospheric electron density variation prior to the earthquake. It has been determined that near the epicenter the F2-peak height, hmF2, descends about 25 km and the F2-peak electron density, NmF2, decreases about 2 × 10⁵ el/cm³ around noon within 5 days prior to the earthquake. The integrated electron content decreases more than 2 TECU between 250 and 300 km altitude.     

Improving the Abel transform inversion using bending angles from FORMOSAT-3/COSMIC

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.     

Estimation and analysis of GPS satellite DCB based on LEO observations

The Global Positioning System (GPS) satellite differential code bias (DCB) should be precisely calibrated when obtaining ionospheric slant total electron content (TEC). So far, it is ground-based GPS observations that have been used to estimate GPS satellite DCB. With the increased Low Earth Orbit (LEO) missions in the near future, the real-time satellite DCB estimation is a crucial factor in real-time LEO GPS data applications. One alternative way is estimating GPS DCB based on the LEO observations themselves, instead of using ground observations. We propose an approach to estimate the satellite DCB based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and Challenging Minisatellite Payload (CHAMP) GPS observations during the years 2002–2012. The results have been validated through comparisons with those issued by Center for Orbit Determination in Europe (CODE). The evaluations indicate that: The approach can estimate satellite DCB in a reasonable way; the DCB estimated based on CHAMP observations is much better than those on COSMIC observations; the accuracy and precision of DCB show a possible dependency on the ionospheric ionization level. This method is significance for the real-time processing of LEO-based GNSS TEC data from the perspective of real-time applications.