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[en] Complete text of publication follows. In this paper we introduced a methodology, measurements, and results obtained from two campaigns conducted on December 2008 and February 2009, making a total of 16 of the 52 repeat magnetic network stations existing in Mexico, for Mexico Magnetic Chart Epoch 2010.0. The last magnetic chart in Mexico was issued in the 90's by Magnetic Survey of Geophysics Institute-UNAM. We took over the recuperation of lost measurements that had been left over at lack of money and human resources. In 2009 the Magnetic Survey was included inside SIBA (Environmental and Biodiversity Informatics System) project. Founds were approved and then we could start getting to work for magnetic chart survey with at least two complete magnetic network reoccupations. At the fist 16 stations (that had been all ready made up till now) we got a lot of problems. But the main one was the lost or destroyed over of original marks measured in 90's and it was hard too finding a new good place for replacing these sites. Observed measurements in these sites shown satisfactory records inside the expected rate. In 2009 we will be able to carry out three more campaigns to measure 24 more stations having a total of 40 by the end year. During 2010 and 2011 we will complete the survey to finish the whole magnetic chart for epoch 2010.0.
[en] Complete text of publication follows. Scientists across Europe and around the world mounted the first sustained and organized effort to measure geomagnetism in the early and the mid-19th century. The participants ultimately numbered in the hundreds and dozens of observatories collaborated. This massive enterprise did not appear out of no where, but rather, it emerged largely because of the interest and influence of Alexander von Humboldt. This paper examines the several roles that Humboldt played in launching one of the first global scientific collaborations.
[en] Complete text of publication follows. Pakistan (23-40degN, 60-80degE) is spread over 800,000 square km. The country consists of a variety of terrains with flat Indus plain to the east, mountains to the north and northwest Balochistan plateau to the west. The geomagnetic observatory at Karachi (24.95degN, 167.14degE) was established in 1983. Due to development of infrastructure and vehicular movement near the observatory, quality of the data became poor. This observatory has now been shifted to Sonmiani, 48 km north of Karachi. The site was selected after performing a magnetic survey and selecting the cleanest and lowest magnetic gradient parts. Additionally, being part of a huge government property in rural surroundings, the Sonmiani site offers long-term protection from cultural noise. The Observatory has been named after Pakistani Physicists Nobel Prize Abdus Salaam, who was Scientific Director at Sonmiani in the 1960's. Our activity: site selection, operation of Sonmiani observatory and the data from both observatories is compared and is presented. The work was carried out with collaboration of IRM, Belgium.
[en] Complete text of publication follows. Space-based geomagnetic observations are usually made on board low altitude near polar orbiting satellites. These satellites sweep all longitude sectors and provide quasi regular and homogenous global scale dataset. Especially, for the study of the equatorial electrojet (EEJ) features including its longitude dependence, only satellite magnetic measurements are capable of providing such global coverage. However, the orbit along-track methods of extracting the EEJ signature from satellite observations do not allow an accurate estimate of its peak current density in certain longitude sectors. By comparing ground-based and satellite observations, we show that satellite orbit along-track methods fit well the latitude profiles of the EEJ magnetic effect when the satellite paths are perpendicular to the dip-equator, as in most part of the longitude sectors of Asia and Africa. Otherwise, the EEJ latitude profiles are biased, which leads to poor estimate of the EEJ features (magnetic signature, peak-current density, position of the EEJ center, etc.), as in the Atlantic Ocean and most of South American sectors, where the dip-equator is strongly tilted from the East-West direction.
[en] Complete text of publication follows. A simple procedure for calculation of piezomagnetic fields due to uniform regional stresses in the heterogeneously magnetized crust is proposed. There is a prominent similarity between spatial distributions of anomalies in the geomagnetic total force values due to magnetization structures in the Earth's crust and those due to the piezomagnetic signals arisen from there. This similarity enables us to compute the piezomagnetic field due to uniform regional stress without determination of explicit structure of the magnetization intensities in the crust. The situation is quite similar to that of 'reduction to the pole', which is often use for interpretation of magnetic survey data. We give an explicit formula that gives the 2-D spectrum of the piezomagnetic field from that of local magnetic anomalies, and applied the formula to a synthesized data. Obtained values are compared with the exact solution of the piezomagnetic field in order to check the efficacy of the novel method, and it is verified that the calculation by using the formula gives values precise enough for practical use.
[en] Complete text of publication follows. Alexander von Humboldt was a major figure in the worldwide establishment of magnetic observatories. His influence was felt in the early geomagnetic programmes of European nations, for example in Germany, Britain and its then colonies, as well as in Russia and beyond. In this paper we will review von Humboldt's role in the 'Gottingen Magnetic Union' and in the 'Magnetic Crusade' and we will examine his relationship with such figures as Edward Sabine in Britain and with Carl Friedrich Gauss and Wilhelm Weber in Germany. We will review the sequence of historical events that led to the establishment of magnetic observatories and their operating procedures in the mid 1800s. We will also reflect on the concurrent scientific and technical developments at the time and the wider cultural aspects of the 1800s that contributed to the development of the science of Geomagnetism. Ultimately, von Humboldt's vision was of a global network of magnetic observatories. Much of what was established in the mid 1800s, through his encouragement, can be seen to persist through to the modern day.
[en] Complete text of publication follows. While high-degree global models of the gravity field have been produced for decades, the break-through for magnetic models has only been achieved in the last few years. This is primarily due to three reasons: (1) Long wavelength control for a global model requires highly accurate satellite measurements at low orbital altitudes. These have only recently become available with the ongoing CHAMP mission. (2) Due to the secular change of the Earth's core field, marine and airborne magnetic surveys have unknown offsets which make it difficult to integrate 60 years of surveys into a common global field model. (3) The geopotential can conveniently be inferred from measurements of the gravity acceleration by direct integration. In contrast, the magnetic potential is not completely determined by measurements of the anomaly of the total intensity, and it has to be estimated in an iterative scheme. Here, we present our modeling approach starting with the determination of the long-wavelength lithospheric field from CHAMP data then merging the marine and aeromagnetic data into the EMAG2 global magnetic anomaly grid which then provides the basis for the estimation of the NGDC-720 model (http://geomag.org).
[en] Complete text of publication follows. Recent technological advances suggest that we are on the threshold of a new era in applied magnetic surveys, where acquisition of magnetic gradient tensor data will become routine. In the meantime, modern ultrahigh resolution conventional magnetic data can be used to calculate gradient tensor elements from TMI or TMI gradient surveys. Until the present, not a great deal of attention has been paid to processing and interpretation of gradient tensor data. New methods for inverting gradient tensor surveys to obtain source parameters have been developed for a number of elementary, but useful, models. These include point pole, line of poles, point dipole (sphere), line of dipoles (horizontal cylinder), thin and thick dipping sheets and sloping step models. A key simplification is the use of eigenvalues and associated eigenvectors of the tensor. Rotational invariants can be expressed as combinations of eigenvalues. The scaled source strength (e.g. p/r3 for a point pole, m/r4 for a point dipole) is a particularly useful quantity that can be calculated from the eigenvalues. Gradient tensor data collected over the Tallawang magnetite skarn deposit in New South Wales will be presented to illustrate the methods. A number of methods have been proposed for locating dipole-like sources from spot measurements or isolated profiles of magnetic gradient tensor data. In particular, there is an inherent four-fold ambiguity in obtaining solutions for dipole location and orientation of its moment from point-by-point analysis of gradient tensors. This paper presents a new, simple and efficient method for uniquely determining the location and magnetic moment of a dipole source from a short segment of gradient tensor data that is relatively free of contamination from background gradients. A separate algorithm, which deconvolves gradient tensor data along a profile by separating scalar and vector aspects of the dipole inversion problem, will be described. This enables contamination from background gradients to be estimated and removed, thereby improving estimation of dipole parameters. Besides the geological applications, these algorithms are readily applicable to the detection, location and classification (DLC) of magnetic objects, such as naval mines, UXO, shipwrecks, archaeological artefacts and buried drums.
[en] Complete text of publication follows. Narmada-Son-lineament (NSL) is an important geomorphic feature of Central India. It is trending in the ENE-WSW direction, traversing the Indian shield from the west coast to Jabalpur region. All the geological and geophysical studies of this mega lineament conducted so far in the Jabalpur-Mandala region do not reflect tectonics and subsurface geology, because of extension and thickness of the trap below the alluvial and the sources of magma eruptions leading to Deccan traps volcanism. For a better evaluation of the trap thickness, location of intrusives and understanding tectonics of the region, a ground magnetic survey was carried out using a proton precession magnetometer with a sensitivity of 0.1 nT. The observations have been taken along all accessible roads at intervals of 2 to 5 km. The total field contour anomaly map was prepared on a scale of 1: 600,000 with 100 nT contour interval. The area under study extends over 10,000 km2 bounded by latitude 22deg22' to 23deg30'N and longitude 79deg30' to 81deg18'E. The magnetic anomaly brings out several prominent anomalies observed over alluvial covered areas to the north of Jabalpur region indicating the extension of Deccan traps below the alluvial as well as the presence of several intrusive at depth. Magnetic interpretation as work out in the present study, predicts an average thickness of 0.6 km for the Deccan traps, besides bringing out shallow and deeper intrusive bodies at 1.5 and 4.5 km, respectively. The map reveals complex magnetic contours with several interesting anomalies attributable to dyke- and sheet-like bodies and Deccan traps. The anomalies are generally closed and aligned in the E-W to NE-SW direction. The studies reveal a strong magnetization contrast between trap and crystalline basement that varies from 600 to 900 x 10-5 emu suggesting that the intrusives are basic in composition.