Spherical cap harmonic modelling of high latitude magnetic activity and equivalent sources with sparse observations

Walker, J. K.

doi:10.1016/0021-9169(89)90106-2

Cited by 29 publications

(15 citation statements)

References 24 publications

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“…By visual inspection of magnetograms from the year 1976 a number of quiet or slightly unsettled days were chosen. Data for the same day from the neighbouring observatories were used to correct the component values at the "repeat station" using each of the following six methods: 5) In this method, the external and induced disturbance field for each component is modelled over Canada for each hour of the day using spherical cap harmonic analysis (HAINES, 1988;WALKER, 1989). The harmonic expansion index for the model was 11 and the F level of significance for the coefficients was 3.0.…”

Section: Correcting High Latitude Repeat Station Data For Magnetic Acmentioning

confidence: 99%

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Removing magnetic activity from high latitude magnetic repeat station observations.

Newitt

Walker

1990

J. geomagn. geoelec

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The temporal magnetic disturbances which occur during magnetic repeat station surveys cause errors in the determination of the main field secular variation. However, their effects can be significantly reduced by optimizing the survey period and by modelling and subtracting the disturbance field. An analysis of data from five Canadian observatories, which form a meridional line from midlatitudes (Victoria) across the auroral zone to the polar cap (Resolute), shows that simple linear techniques for correcting the observations at a repeat station were generally unsuccessful. However, the subtraction of perturbations obtained by modelling data from 19 North American observatories using the new method of spherical cap harmonic analysis removed most of the temporal variations. After the removal of such fields, 80% of the errors at auroral zone locations were generally less than 10 nT. If repeat station surveys in high latitude regions are extended to several days, in order to increase the probability of observing a quiet or unsettled interval, and the disturbance field is modelled and removed from the observations, the errors in the secular variation are comparable to those obtained using observatory data.

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Section: Correcting High Latitude Repeat Station Data For Magnetic Acmentioning

confidence: 99%

“…We then look at high latitude magnetic activity with a view to optimizing the time at which repeat station surveys are conducted. Finally, we examine simple correction techniques and the promising technique of spherical cap harmonic modelling (WALKER, 1989) which might be used to reduce observations to the undisturbed magnetic field level.…”

Section: Introductionmentioning

confidence: 99%

Removing magnetic activity from high latitude magnetic repeat station observations.

Newitt

Walker

1990

J. geomagn. geoelec

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“…The former modeling techniques are based on the least squares estimation of a functional model for certain types of observables derived from the GPS carrier phase and code measurements. Polynomials and spherical harmonics are some of the base functions that are commonly in use (Walker 1989;Komjathy 1997;Schaer 1999;Coster et al 2003). In grid based modeling, the spherical shell of free electrons is developed into a grid of rectangular elements, then special reconstruction algorithms are used for estimating the electron density within the every element of the shell (El-Arini et al 1993Gao et al 1994;Skone 1998;Liao 2000;Liao and Gao 2001).…”

Section: Introductionmentioning

confidence: 99%

Development and analysis of 3D ionosphere modeling using base functions and GPS data over Iran

Razin

2015

Acta Geod Geophys

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In this study, a 3D-model of the electron density has been performed using the global positing system (GPS) measurements over Iran. 2D spherical harmonic functions and empirical orthogonal functions are used as base functions to model the horizontal and the vertical content of the electron density, respectively. The ionosonde data in Tehran (u = 35.7382°, k = 51.3851°) has been used for choosing an optimum value for the regularization parameter. To apply the method for constructing a 3D-image of the electron density, GPS measurements of the Iranian permanent GPS network (at 3-day in 2007) have been used. The instability of solution has been numerically analyzed and the Tikhonov method has been used for regularizing the solution. To come up with an optimum regularization parameter, the relative error in electron density profile computed from ionosonde measurements and their 3D model are minimized. The modeling region is between 24°to 40°N and 44°to 64°W. The result of 3D-Model has been compared to that of the international reference ionosphere model 2012 (IRI-2012). The data analysis shows that the latitudinal section of ionosphere electron density from 3D technique supports the expected time and height variations in ionosphere electron density. Moreover, these findings show that the height of maximum electron density is changed during the day and night and confirms the efficiency of multi-layer models in comparison to single-layer models. This method could recover 64-99 % of the ionosphere electron density.

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“…To date, all proposed ionospheric models could be classified into two different categories: grid-based and function-based. The early modeling methods are mostly based on the function fitting techniques such as the broadcast ionosphere model from the GPS satellites (Klobuchar, 1987), the polynomial functions (Coster et al, 1992;Komjathy, 1997) and the spherical harmonics (Schaer, 1999;Walker, 1989). On the other hand, the grid-based method, first proposed by the MITRE Corporation and the Air Force Phillips Laboratory (El-Arini et al, 1994 and1995), has demonstrated its capability for higher modeling accuracy when compared to the function-based algorithms.…”

Section: Introductionmentioning

confidence: 99%

Precise Ionosphere Modeling Using Regional GPS Network Data

Gao

Liu²

2002

J. of GPS

114

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Abstract. The ionosphere affects the electromagnetic waves that pass through it by inducing an additional transmission time delay. The ionosphere influence has now become the largest error source in GPS positioning and navigation after the turn-off of the Selective Availability (SA). In this paper, methods of 2D gridbased and 3D tomography-based ionospheric modeling are developed based on regional GPS reference networks. Performance analysis was conducted using data from two different regional GPS reference networks. The modeling accuracy of the vertical TEC (VTEC) is at the level of several TECU for 2D ionospheric modeling and about one TECU for 3D tomographic modeling after a comparison to independent ionospheric map data or directly measured ionospsheric TEC values. The data analysis has indicated that the modeling accuracy based on the 3D tomography method is much higher than the 2D grid-based approach.

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Spherical cap harmonic modelling of high latitude magnetic activity and equivalent sources with sparse observations

Cited by 29 publications

References 24 publications

Removing magnetic activity from high latitude magnetic repeat station observations.

Removing magnetic activity from high latitude magnetic repeat station observations.

Development and analysis of 3D ionosphere modeling using base functions and GPS data over Iran

Precise Ionosphere Modeling Using Regional GPS Network Data

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