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This work presents the geomagnetic characterization of the municipality of Macae, Brazil. Data from IGRF12 (twelfth edition of International Geomag-netic Reference Field) were used. Through the data collected in a regular grid of 0.1 degrees of the components, north, east and vertical were generated maps of components, inclination, declination, horizontal component and geomagnetic total field. The results showed important relative variations of these magnitudes, such as the magnetic declination that varied around 0.2 degrees along the area of the municipality, which is a considerable value and capable of causing significant changes in directions by compass in the studied region.

Summary In 2012-2015, on the Norwegian shelf, a marine electromagnetic sounding surveys were carried out using the differential-normalized electro prospecting method (DNME) with length of several thousand kilometers. The effectiveness of the method is confirmed in reference fields such as Troll. More than 20 wells were drilled, a significant part of forecasts was confirmed. However, new deposits were later discovered at the survey sites, which anomalies had not previously distinguished according to the inversion data. The fact of lack of anomalous effects made us look at the results of the shooting of those years in a new way. For one of the survey lines crossing the reference field, the following results are presented: a multivariate statistical analysis applied to the reprocessed data; one-dimensional inversion of transients simultaneously with the apparent resistivity curve with a more detailed step; inversion within the 2.5D model. The research carried out shows that at the first stage, it is advisable to highlight the area of most significant interest based on the result of multivariate statistical analysis. The results of the multivariate statistical analysis do not contradict the results of 2D modeling.

A one arc-minute resolution gravimetric quasigeoid model has been computed for New Zealand, covering the region $$25^{\circ }\hbox {S}$$ – $$60^{\circ }\hbox {S}$$ and $$160^{\circ }\hbox {E}$$ – $$170^{\circ }\hbox {W}$$ . It was calculated by Wong and Gore modified Stokes integration using the remove–compute–restore technique with the EIGEN-6C4 global gravity model as the reference field. The gridded gravity data used for the computation consisted of 40,677 land gravity observations, satellite altimetry-derived marine gravity anomalies, historical shipborne marine gravity observations and, importantly, approximately one million new airborne gravity observations. The airborne data were collected with the specific intention of reinforcing the shortcomings of the existing data in areas of rough topography inaccessible to land gravimetry and in coastal areas where shipborne gravimetry cannot be collected and altimeter-derived gravity anomalies are generally poor. The new quasigeoid has a nominal precision of $$\pm \,48\,\hbox {mm}$$ on comparison with GPS-levelling data, which is approximately $$14\,\hbox {mm}$$ less than its predecessor NZGeoid09.

Mapping geophysics research was conducted by geomagnetic method to know anomaly pattern of magnetic pole and to know distribution location and depth of temple gate composing stone in Losari Temple Site by using magnetic data. Data collection used Proton Precessions Magnetometer (PPM) G-856AX by area width of 88 km x 40 km and measurement space of 3 meter used looping method. Field data was corrected by daily variation and IGRF (International Geomagnetics Reference Field) correction and then reduction to pole. The slice modeling was conducted on local anomaly map on height of 6 meter. The result of the local magnetic field anomalies incision then interpolated to get an idea of the spread and depth of rocks making up the fence Losari temple. Local anomaly map shows that anomaly position lies in southwest, southeast, and northeast from main temple. Based from interpolated distribution of magnetic pole anomaly is dominated in depth of 2 meter to 4 meter.

En los relevamientos magnéticos realizados sobre la superficie de la Tierra se utiliza el Campo Geomagnético Internacional de Referencia (IGRF) para sustraer la contribución del campo principal de la Tierra. Cada cinco años se publica un nuevo modelo de IGRF y la variación secular del período previo debe ser actualizada, generándose el denominado modelo DGRF. Una vez que el DGRF es publicado, las anomalías magnéticas calculadas previamente deben ser recalculadas. La actualización de las anomalías podría ser particularmente importante para relevamientos magnéticos regionales o para compilaciones de datos magnéticos adquiridos en diferentes épocas. En este trabajo se muestra la importancia de esta corrección, particularmente para el periodo 1995-2000, en el cual la diferencia DGRF-IGRF es llamativamente apreciable. Se documenta la validez de la corrección utilizando datos del Observatorio Geomagnético Permanente de Trelew, Argentina.

Pigeons were released at four release sites within the Gernsheim anomaly, a magnetic 'hill' with a peak 199 nT above the regional reference field and gentle 'slopes' to all sides, situated 44 km south of the Frankfurt loft. Local magnetic conditions at the sites differed in total intensity and in direction and steepness of the intensity gradient. At all sites, the pigeons were well oriented, showing counterclockwise deviations from the home directions that were most pronounced in the western part of the anomaly. There was no systematic difference in orientation behavior or homing performance between the sites within the anomaly and a control site outside. No effect of the local gradient direction was found, nor did the difference in intensity between home loft and the release site affect behavior. This argues against the use of magnetic navigational factors. However, pigeons released for the first time within the anomaly tended to have longer mean vectors with increasingly steeper gradients, which could mean that the birds might somehow have realized the anomalous nature of the local magnetic conditions and ignored them, relying on non-magnetic cues instead.

In the frame work of the Austrian Geoid 2000 project, the accuracy of the geoid has to be enhanced. One of the possibilities is to use an adapted reference field. The traditional remove/restore technique has the disadvantage of removing a part of the effect of the topography and its compensation twice. In order to avoid this double consideration the effect of the topographic-isostatic masses for the used fixed data window has been subtracted from the reference field yielding an adapted reference field. This adapted reference field has been used for the remove/restore technique. The paper shows a comparison between the geoid computed by the adapted technique using the enhanced reference field, the geoid computed by the traditional remove/restore technique and the geoid based on the RTM-method for the remove/restore process. All the models are checked against a geoid derived by GPS and levelling points. The geoid based on the adapted remove/restore technique shows the best results.

The area of the Ionian sea, between Albania and the Southern Italian Peninsula, has been taken into account for the production of geomagnetic component maps. Data from the national Albanian and Italian magnetic repeat station networks have been merged, and normal reference fields in latitude and longitude, have been computed. Data processing, reduction procedures and comparisons with IGRF are presented.

We present the methods used to derive mathematical models of global secular variation of the main geomagnetic field for the period 1985 to 2000. These secular-variation models are used in the construction of the candidate US/UK models for the Definitive Geomagnetic Reference Field at 1990, the International Geomagnetic Reference Field for 1995 to 2000, and the World Magnetic Model for 1995 to 2000 (see paper II, Quinn et al., 1997). The main sources of data for the secular-variation models are geomagnetic observatories and repeat stations. Over the areas devoid of these data secular-variation information is extracted from aeromagnetic and satellite data. We describe how secular variation is predicted up to the year 2000 at the observatories and repeat stations, how the aeromagnetic and satellite data are used, and how all the data are combined to produce the required models.

The magnetic survey in China carried out in resent years is briefly introduced. On the basis of the magnetic data at 119 repeat stations, 39 permanent observatories and 20 grid values of the IGRF 2000, the magnetic charts and models of China for 2000, called China Geomagnetic Reference Field 2000 (or ChinaGRF 2000) have been compiled.

This work focuses on some currently used high‐degree geopotential models that represent the gravity field in Spain. Six test areas of different topographic structures that cover the greatest part of the territory are selected to get information on the gravity field. A number of 27,691 free‐air gravity anomalies and three geopotential models are considered in this work. Comparisons of free‐air and geopotential models‐implied anomalies are studied in the test areas and in all of Spain. The results show that the model IFE88E2 is the most suitable for use as a reference field in the region of Spain.

A preliminary assessment of the IGRF-1990 in Mexico is carried out by comparing geomagnetic elements measured throughout Mexico and IGRF derived geomagnetic values. Mean differences of 10.6 nT, 24.4 nT, and −0.6′ are obtained for total intensity, horizontal component, and declination (RMS deviations of 206 nT, 116 nT, and 18.7′, respectively). The differences correlate with MAGSAT derived magnetic anomalies, e.g. they are associated with crustal sources. We conclude that the IGRF provides a satisfactory geomagnetic reference field for Mexico.

Regional models of the geomagnetic field offer higher resolution than can be achieved with global models. However, for any particular application, the choice of geomagnetic reference field, global or regional, depends on the accuracy requirements and whether information at crustal wavelengths is needed. The most stringent demands of directional drilling may be beyond the accuracy limits of even the best regional models, whereas a good global model may be adequate to meet many navigational requirements. Accurate regional data, particularly estimates of secular variation from observatories and repeat stations, provide the foundations for global as well as regional field models, and need to be made available to the world community.

Candidate models for the Definitive Geomagnetic Reference Field 1985 (DGRF-85) and the 1990 International Geomagnetic Reference Field (IGRF-90) have been produced jointly by the British Geological Survey and the United States Naval Oceanographic Office as part of their respective World Magnetic Modeling and Charting programs which are sponsored by the British Hydrographic Office and by the United States Defense Mapping Agency. These models are based on spherical harmonic expansions of the geomagnetic field to degree 10 (120 coefficients) for the main field and degree 8 (80 coefficients) for the secular variation. They are presented here along with a discussion of the data and modeling techniques that were used to produce them.

The DGRF/IGRF candidate models have been compared to the Canadian Geomagnetic Reference Field 1990 (CGRF90) over the approximate area of Canada. It is found that all candidate models for 1985 are of equal quality when compared to the CGRF90. For 1990, the BGS/NOAA and IZMIRAN models more closely agree with the CGRF. The BGS/NOAA secular variation model differs from the CGRF90 by up to 30nT/yr in the vertical component.

A compilation of aeromagnetic data for Europe is in progress to produce a map showing crustal anomalies of total intensity for the epoch 1980.0 and the altitude 3000m above m.s.l. and to interpret it in terms of large-scale features in the crust. A report is given of our experience with secular variation and with the reference field which has to be subtracted from the total intensity values to obtain crustal anomalies.When aeromagnetic surveys are compiled, data from observatories and repeat stations are necessary in order to estimate secular variation with sufficient precision. Data from repeat stations are more detailed and realistic than computed values from global reference field models. The secular variations computed from three different reference field models differ considerably.The influence of the reference field and its truncation level on the shape of anomalies is examined by calculating differences between the reference fields. The decision to use the DGRF 1980 model for publishing a map showing European crustal anomalies for 1980.0 is based on the fact that this model gives a better approximation of observed values at observatories and repeat stations in Central Europe than two other models. These differences between observed and computed values are partly caused by inhomogeneous input data used for the calculation of reference fields. The input data is inhomogeneous because each observatory publishes their annual mean values based on its own observatory standard and not on the International Magnetic Standard.

In the past five years, considerable progress has been made in improving the accuracy of scalar gravimetry by integrated INS/DGPS sys- tems, both of the strapdown and the stable platform system type. Less attention has been given to vec- tor gravimetry and the results that have been pub- lished are much poorer in comparison. If the attitude components of the gravity disturbance vector could be determined with the same accuracy as its magni- tude, deflections of the vertical could be estimated with a standard deviation of about 0.3 arc seconds for a mimimum half-wavelength resolution of 1.5–2.0 km. This is not be possible at the moment. In this paper the reasons for the accuracy difference have been studied by analysing airborne gravity data taken over a well-determined reference field in the Canadian Rocky Mountains. Two different methods have been applied to determine the horizontal components of the gravity disturbance vector, i.e. the deflections of the vertical. In the first one, the standard method-direct deflection determination along individual profiles — has been used. In the second one, deflections have been estimated from gravity disturbances at flight level, using a modified Vening-Meinesz approach. The differences in results between the two methods clearly point to the large influence of gyro drifts in the direct deflection determination method.

The latest release of International Geomagnetic Reference Field (IGRF-11) was published online at the end of 2009. IGRF is a standard reference model of Earth's internal magnetic field. The reference field is typically updated every 5 years by an international team of geomagnetic field modelers working under the auspices of the International Association of Geomagnetism and Aeronomy and in collaboration with institutions collecting and disseminating magnetic field measurements from satellites and a worldwide network of ground-based observatories. As with earlier versions of the reference field, IGRF-11 provides a global picture of the past and present geomagnetic field as well as a linear prediction of field changes over the upcoming 5 years. IGRF is widely used in navigation and heading systems, geophysical surveying, and space weather modeling and prediction.

This is a summary of two papers, “Reformulation of Stokes’s Theory for Higher than Second-Degree Reference Field and Modification of Integration Kernels,” and “The Modification of Stokes’s Formula for Higher Degree Reference Field Considering Errors in Truncation, Harmonic Coefficients, and Terrestrial Data,” submitted to the Journal of Geophysical Research by the authors.

The paper describes the theoretical aspects of the gravimetric geoid. Stokes’ integral convolution approach reformulated for the higher-order reference field, OSU86F in this case, is used. In addition to the theoretical aspects, an example of the actual solution for Taiwan area is shown.

There is now an increasing body of evidence which suggests that the onset of a substorm expansive phase is triggered in the near-Earth tail region, inside X ∼ −12 RE [Samson et al., 1992]. For this reason, it is necessary to characterize the magnetic field in the near-Earth region, particularly the quiet time reference field. We have therefore carried out a detailed study of the magnetic field at geostationary orbit, using data acquired during quiet times from the GOES 5 and GOES 6 satellites which operated simultaneously during 1986. Diurnal and seasonal variations of the total field, and the perturbation magnetic field with the IGRF removed, have been identified and attributed to variations in the position of the neutral sheet with respect to the satellite. We have processed the data to remove seasonal effects by using the semiempirical expression developed by Lopez [1990] to express the displacement of the neutral sheet with respect to the magnetic equatorial plane. We then use our magnetic field model, recently developed by Donovan [1993a], to model the observed quiet time magnetic field at geostationary orbit, and also determine the quiet time current configuration.

Comparisons of proposed and adopted geomagnetic reference field models are made against North American test data for the period 1965 to 1985. These test data (X, Y, Z, and F) include Canadian map and aeromagnetic data and USGS land-based data. Model values are also tested against predicted component values for 1982 and 1984 derived from 27 magnetic observatories on or near the North American continent.These tests indicate that all candidate models provide an excellent fit to North American test data at epochs 1965, 1970, and 1975. Only the USGS and NASA models fit these data satisfactorily at 1980. The best secular variation models for 1980-1985 appear to be the IGS and USGS models.Finally, our tests indicate that the recently adopted series of reference field models provides a reasonable and satisfactory fit to North American test data.

When compiling magnetic data that have been collected over several decades, the accuracy of the magnetic reference fields that are used to reduce the data to a common datum-level becomes an important factor. Definitive magnetic reference fields have been defined at 5-year intervals. In this study we evaluated these reference fields by applying them to marine magnetic data that have been collected off the Canadian east coast in the period 1963–1984. For 35–50° N, the anomalies for the period 1970–1975 were found to be ∼ 50 nT higher than those obtained in other periods. A cross-over analysis performed on the whole data set yielded ∼ 60 000 cross points and confirmed these results. As the source of the anomalies are unvarying, we conclude from these observations that the magnetic reference fields in this part of the world do not accurately correct for the time-varying component of the magnetic field. This has serious consequences for magnetic data compilations; when not treated in a generally accepted fashion, these inaccuracies could lead to user-defined corrections to the reference fields, which would be a step in the wrong direction.

Geomagnetic measurements from land, marine and aerial surveys conducted in the years 1945–1964 were used to test the 14 models proposed as additions, for that period, to the series of definitive geomagnetic reference field (DGRF) models. Overall, NASA's ‘SFAS’ models and the BGS (British Geological Survey) models agree best with these data. Comparisons of the two proposed definitive main-field models for 1980.0, with each other and with the existing IGRF 1980 main-field model, show mostly close agreement, with the greatest absolute differences (several tens of nanotesla) occurring in the region of Antarctica. Comparison of the the three proposed forecast secular-variation models for 1985–1990 with estimates of recent rates of change at 148 magnetic observatories shows that the IZMIRAN (U.S.S.R.) and USGS models are in closest agreement with these data.

The candidate models for the definitive geomagnetic reference field (DGRF) for the years 1945, 1950, 1955 and 1960—S45, 50, 55, 60, SFA45, 50, 55, 60, SFAS45, 50, 55, 60, and BGSMF50, 60—are evaluated using magnetic observatory data and observatory anomaly solutions given by the CSFC(9/80) and GSFC(12/83) models. The results indicate that the series of SFA models is the most successful series of models, and the BGSMF60 model is the best individual model, but the BGSMF50 model is less successful.

Comparisons of secular variations computed from geomagnetic reference field models were made against the data obtained at Mbour and Bangui observatories and at 24 magnetic repeat stations in West Africa. The obtained results were very similar between the observatory and the repeat station data, indicating that (1) the TGRF models provide an excellent fit to secular variation data, and (2) there are no significant anomalies in African secular variation.

Using cross-over analysis the reduction of total magnetic intensity values to magnetic anomalies was studied in an area with ship-tracks which have been made over a period of several years. Under these circumstances the secular variation becomes important. At first we used the old IGRF 1975. This reference field does not correct the secular variation accurately. In the period 1969–1980 the mean values of the differences of the magnetic anomalies at crossing rise to more than 150 nT. The recently adopted reference fields DGRF 1965, DGRF 1970, DGRF 1975 and PGRF 1975 correct the secular variation much better. The mean values now only rise to about 50 nT over the same period. A reduction using a regional determined by filtering along the track removes the secular variation completely. The latter reduction has the disadvantage that the standard deviations of the mean values at the intersections increase, because the regional depends on the orientation of the track line. Calculation of average secular variation in subareas of 4×4 degrees yields a decrease from the northeast to the southwest.

The magnetic field at the surface of the earth, when averaged over a sufficient interval of time to remove transient variations (nominally 1 year), consists principally of a contribution originatin...

In August 1985 the International Association of Geomagnetism and Aeronomy revised the International Geomagnetism Reference Field (IGRF). This is the third revision since the first IGRF was produced in 1968. The revised IGRF now consists of 10 spherical harmonic models of the main geomagnetic field and its secular variation and covers the interval 1945–1990. For the interval 1965–1980 the constituent models are definitive (DGRFs), in the sense that it is not intended to revise them in the future. A brief description of the derivation of the revised IGRF is given, together with a brief review of basic formulae and a set of world contour maps of the geomagnetic elements for 1985.

International audience; The International Geomagnetic Reference Field (IGRF) is an internationally agreed global spherical harmonic model of the Earth's magnetic field of internal origin. It is currently computed every five years in the form of a model describing this field up to degree 13 at a reference epoch, plus a secular variation model up to degree 8, best estimating the linear evolution of this field over the following five years. Such a simple description of the field evolution is thought to provide a good enough prediction of the field, both for navigational and internationally agreed reference purposes (the very purpose of IGRF models). In particular, it assumes that any change in the field described by spherical harmonic degrees between 9 and 13 may be neglected over five years, given the uncertainties already involved in the determination of all other coefficients, and the practical accuracy needed for most IGRF applications. Recent progress in global field modelling based on increasingly accurate and numerous satellite data however show that all field coefficients can now be computed with much higher accuracy than possible in the past, and that higher degree secular variation coefficients could therefore also be considered for inclusion in IGRF models. The present short note intends to investigate the potential benefit of extending the IGRF predictive secular variation model to degrees higher than 8, given our current knowledge of the way the field behaves over time periods of five years.

Two geomagnetic main-field models for epochs 1995.0 and 2000.0 were proposed as candidate models for DGRF 1995 and DGRF 2000. A main-field model was derived for epoch 2000.0, using the high-quality data provided by the Ørsted satellite around this epoch. Since no high-quality satellite vector measurements of the magnetic field were acquired between 1980 and 1999, our approach was to extrapolate this 2000.0 accurate model back to 1995. To do this we produced a secular-variation model for the time-span 1995-2000, from ground measurements. The models obtained were incorporated into DGRF 1995 and DGRF 2000 as part of the 9th generation of the IGRF in 2003.