Ionospheric tomography algorithms

Raymund, T. D.

doi:10.1002/ima.1850050204

Cited by 57 publications

(47 citation statements)

References 45 publications

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“…Reconstruction algorithms suitable for the application have also been developed, several of which are discussed by Raymund (1995). The European Incoherent Scatter radar facility (EISCAT) has played a crucial role in the development of ionospheric tomography, in providing independent veri®cation of tomographic images.…”

Section: Introductionmentioning

confidence: 99%

The spatial structure of the dayside ionospheric trough

Pryse¹,

Kersley²,

Williams³

et al. 1998

Ann Geophysicae

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Abstract. Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar con®rm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.

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Section: Introductionmentioning

confidence: 99%

The spatial structure of the dayside ionospheric trough

Pryse¹,

Kersley²,

Williams³

et al. 1998

Ann Geophysicae

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“…CIT processing of the recorded relative TEC data from multiple receivers along the trajectory of the satellite produces high-accuracy TEC data [Leitinger et al, 1975;Raymund, 1995]. These were compared with TEC data from coincident TOPEX dual-frequency altimeter passes over the Caribbean.…”

Section: Caribbean Total Electron Contentmentioning

confidence: 99%

Verification of ionospheric sensors

Coker¹,

Kronschnabl²,

Coco³

et al. 2001

Radio Science

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Abstract. Ionospheric products from sensors and models were compared to investigate strengths and limitations of each. Total electron content data from computerized ionospheric tomography (CIT) and TOPEX sensors in the Caribbean region in 1997 were compared to estimates produced by models Parameterized Ionospheric Model (PIM) and Raytrace/ICEDBent-Gallagher (RIBG) and global maps from GPS. A 5 total electron content unit (TECU) bias was observed in TOPEX. CIT and TOPEX confirmed the location and structure of the equatorial anomaly. A GPS map confirmed the location of the anomaly but did not reproduce structure less than 1000 km in latitude and 1500 km in longitude and underestimated TEC by at least 11 TECU or 25%. PIM positioned the anomaly 13 ø equatorward of its observed location and greatly underestimated (-50%) the rise in content over 5ø-25øN range. RIBG overestimated the latitudinal extent of the anomaly and underestimated TEC at the peak by 40%. Additional comparisons were made using CIT and ionosonde sensors at midlatitude during the summer of 1998. Fourteen days of TEC, hmF2, NmF2, and half-thickness comparisons showed reasonable agreement between CIT and ionosonde for TEC and NmF2. The hmF2 and half-thickness comparisons were contaminated by noise, which accounted for a significant portion of the ionospheric variation. Daytime cases where CIT overestimated maximum density were attributed to underestimating layer thickness. Finally, TOPEX and multiple GPS sensors were compared to verify regional ionospheric conditions associated with occurrence of nighttime ionospheric depletions in the Caribbean during Combined Ionospheric Campaigns in June of 1998. From 0300 to 0800 UT on June 26, GPS and TOPEX showed elevated nighttime content over the entire Caribbean region. Vertical TEC approached 25 TECU in some places with interspersed depletions, which in some cases evacuated nearly the entire ionospheric content.

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“…Before we discuss our own tests, we mention the results of a study that compared the performance of different reconstruction algorithms on a set of trial data [Raymund, 1995] Figure 4 we see that the algorithm is indeed capable of differentiating between purely stratified ionospheres at different altitudes. Surely, an error of 90 km in peak height is significant.…”

Section: Testsmentioning

confidence: 99%

A model‐independent algorithm for ionospheric tomography: 1. Theory and tests

Fehmers¹,

Kamp²,

Sluijter³

et al. 1998

Radio Science

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Abstract. This paper presents a model-independent algorithm for tomography of the ionosphere. Prior knowledge consists of the following pieces of information: electron density cannot be negative, the ionosphere is basically smooth and stratified, and electron density is low at high (•>700 km) and low (•<100 km) altitudes. Tests based on simulated measurements show that the method recovers the latitudinal structure well, whereas the vertical structure is recovered with moderate success: the estimated height of the layer of maximum electron density may be as much as 90 km in error. Because of the imposed smoothness the method tends to underestimate the peak in electron density by as much as one third in unfavorable cases. IntroductionSince its conception in 1986 [Austen et al., 1986], radiotomography of the ionosphere has grown into a relatively inexpensive technique to image the electron density distribution in vertical cross sections of the ionosphere. In general, tomography is a method to reconstruct a distribution from its line integrals. In ionospheric tomography the line integrals of electron density (called total electron content (TEC)) are measured by the differential Doppler technique, where a receiver registers the differential Doppler shift of an orbiting beacon satellite [Leitinger et al., 1984]. An array of receivers placed parallel to the satellite's ground path should yield enough data to make the tomographic inversion from the measurements into an image of electron density. The surface of reconstruction is defined by the lines of sight (or rather phase paths) between satellite and receivers (see Figure 1).The first studies in ionospheric tomography were based on simulated TEC measurements using model ionospheres. Later, real experimental data were used on the basis of phase shift measurements from either the U.S. Navy Navigation Satellite System (NNSS) or A literature study reveals that every research group has its own reconstruction algorithm. Why should this paper add one more to the stack? Here we argue why our algorithm is a valuable contribution to the field.The main problem in ionospheric tomography is the absence of (near-)horizontal line integrals in the data set [Yeh and Raymund, 1991]. This absence is the result of a geometry where the lines of integration correspond to lines of sight between an orbiting satellite and ground-based receivers (Figure 1). Consequently, there are no lines of sight that remain at an approximately constant altitude. A set of such lines would contain the vertical profile of ionospheric electron density. This information is virtually missing from the data set, and tomography cannot be expected to provide a reconstruction where the vertical profile is rendered truthfully. A mathematician would say that the inverse problem is ill posed. In this jargon the inverse problem is the reconstruction of the "cause" from the "effect," the cause being the ionospheric electron density distribution and the effect being the result of the experiment (the TEC data). The problem ...

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Ionospheric tomography algorithms

Cited by 57 publications

References 45 publications

The spatial structure of the dayside ionospheric trough

The spatial structure of the dayside ionospheric trough

Verification of ionospheric sensors

A model‐independent algorithm for ionospheric tomography: 1. Theory and tests

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