An examination of observatory biases during the Magsat and Ørsted missions

Macmillan, Susan; Thomson, Alan

doi:10.1016/s0031-9201(02)00209-1

Cited by 8 publications

(4 citation statements)

References 7 publications

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“…The remanent magnetization component of the crustal field can be considered constant in the decadal time scale considered in this study. It is a common assumption in global magnetic field modeling that the crustal field is static (Macmillan and Thomson, 2003).…”

Section: Introductionmentioning

confidence: 99%

Crustal geomagnetic field and secular variation by regional and global models for Austria

Peqini

Duka

Egli

et al. 2018

Austrian Journal of Earth Sciences

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Using 12-year-long series of data (2001-2012) from geomagnetic observatories and repeat stations in Austria and its neighboring countries, a regional spatial-temporal (ST) model is developed based on the polynomial expansion consisting of latitude, longitude, and time of the geomagnetic field components and total magnetic field F. Additionally, we have used three different global models (CHAOS-5, POMME-9, and EMM2015), which are built on spherical harmonics up to a maximum degree Lmax and give the core field and crustal field separately. The normal field provided by the ST model and its “model bias”, which comprise the residuals of the differences between measured and predicted values, are calculated and the respective maps are shown. The residuals are considered an estimate of the local crustal field. In the case of global models, we have applied for each of these three methods to calculate the “model bias”: residuals of the differences between observed values and predicted values of the model, residuals of the differences between observed values and core field values of the model, and the average bias for the period 2001-2012. The normal field of the region of Austria provided by each global model is also calculated. Generally, the regional and global models yield relatively similar crustal fields for the Austrian region, especially when the first method is used. The normal fields calculated by them are in good agreement with each other. Each of the global models directly provides the crustal field, and they are compared with the aeromagnetic data provided by aeromagnetic surveys over the Austrian region. The ST model is in better agreement with aeromagnetic data. We have also analyzed the secular variation over the region, which is calculated from the rate of change of normal field given by the ST and global models.

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Section: Introductionmentioning

confidence: 99%

Crustal geomagnetic field and secular variation by regional and global models for Austria

Peqini

Duka

Egli

et al. 2018

Austrian Journal of Earth Sciences

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“…Most of these studies suggest the existence of induced time-varying anomalies, but none of them is conclusive in terms of their exact dimension and origin. Investigations of only geomagnetic observatory data indicate significant induced magnetization components, but the distances between the observatories are too large to allow for inferences on crustal structure [Alldredge 1983, Lesur and Gubbins 2000, Macmillan and Thomson 2003, Verbanac et al 2007]. Thébault et al [2009] estimated rates of change of induced lithospheric anomalies based on a vertically integrated susceptibility grid of the Earth's crust [Hemant and Maus 2005] for anomalies of wavelengths between 440 and 2700 km.…”

Section: Introductionmentioning

confidence: 99%

Repeat station data compared to a global geomagnetic field model

Korte

Lesur

2013

Annals of Geophysics

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<p>Geomagnetic repeat station surveys with local variometers for improved data reductions have been carried out in Germany for about ten years. For nearly the same time interval the satellites Ørsted and CHAMP have provided a good magnetic field data coverage of the whole globe. Recent global field models based on these satellite data together with geomagnetic observatory data provide an improved description of the core field and secular variation. We use the latest version of the GFZ Reference Internal Magnetic Model to compare the magnetic field evolution predicted by that model between 2001 and 2010 to the independent repeat station data collected over the same time interval in Germany. Estimates of crustal bias at the repeat station locations are obtained as averages of the residuals, and the scatter or trend around each average provides information about influences in the data from field sources not (fully) described by the global model. We find that external magnetic field signal in the order of several nT, including long-term trends, remains both in processed annual mean and quiet night time repeat station data. We conclude that the geomagnetic core field secular variation in this area is described to high accuracy (better than 1 nT/yr) by the global model. Weak long-term trends in the residuals between repeat station data and the model might indicate induced lithospheric anomalies, but more data are necessary for a robust analysis of such signals characterized by very unfavorable signal-to-noise ratio.</p>

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“…This will affect the long-term record of secular variation. Such problems can be identified by determining changes in observatory biases through careful comparison of ground station and satellite data (Mandea and Langlais 2002;Macmillan and Thomson 2003). The absolute hut is equipped with a DI-flux, a GSM-90 Overhauser magnetometer, and the loggers and other electronic equipment in 5 to 6 m distance from the sensors.…”

Section: Oceanic Islandsmentioning

confidence: 99%

Geomagnetic Observations for Main Field Studies: From Ground to Space

et al. 2010

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Direct measurements of the geomagnetic field have been made for more than 400 years, beginning with individual determinations of the angle between geographic and magnetic North. This was followed by the start of continuous time series of full vector measurements at geomagnetic observatories and the beginning of geomagnetic repeat stations surveys in the 19th century. In the second half of the 20th century, true global coverage with geomagnetic field measurements was accomplished by magnetometer payloads on lowEarth-orbiting satellites. This article describes the procedures and instruments for magnetic field measurements on ground and in space and covers geomagnetic observatories, repeat J. Matzka ( )

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An examination of observatory biases during the Magsat and Ørsted missions

Cited by 8 publications

References 7 publications

Crustal geomagnetic field and secular variation by regional and global models for Austria

Crustal geomagnetic field and secular variation by regional and global models for Austria

Repeat station data compared to a global geomagnetic field model

Geomagnetic Observations for Main Field Studies: From Ground to Space

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