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Space Environment and Disturbance Torques
Published in Yaguang Yang, Spacecraft Modeling, Attitude Determination, and Control Quaternion-based Approach, 2019
where a = 6378km, is the equatorial radius of the Earth, Pnm(θ) are Schmidt semi-normalized Legendre polynomials of degree n and order m (the input to these polynomials are actually in cos (θ), rather than θ, but this has been dropped for brevity), gnm and hnm are Gauss coefficients in unit nanotesla (nT). The set of Gaussian coefficients used in the analytical models are called the International Geomagnetic Reference Field (IGRF). These coefficients are updated every five years by a group of scientists from the International Association of Geomagnetism and Aeronomy (IAGA). The recent one, which takes advantage of a comprehensive set of observation data, including satellite measurements from the CHAMP, Orsted and SAC-C missions, was published in 2015 [75, 199]. This version of IGRF remains valid until 2020.
The Content of the Site Plan
Published in Robert M. Sanford, Environmental Site Plans and Development Review, 2017
True and magnetic north arrows are commonly shown on site plans. By convention, north arrow points are placed to the right or top of the plan. In some cases, there is an assumed north placed straight up on the site plan regardless of the real north direction. A compass normally does not point to true north. It points to magnetic north. The angle between magnetic north and the true north direction is called the magnetic declination. This declination changes over time, thus making it necessary to adjust the orientation on older maps and also reiterate why the date of the map is important. Magnetic north is close to 15 degrees west of true north. A third north that may be on a site plan is called “grid north,” referring to the grid lines, usually Universal Transverse Mercator (UTM) on a map. Magnetic fields fluctuate over the Earth and every five years a new International Geomagnetic Reference Field (IGRF) is generated to produce accurate calculations of angles of declination.
Attitude Sensor Measurement Models
Published in Chingiz Hajiyev, Halil Ersin Soken, Fault Tolerant Attitude Estimation for Small Satellites, 2020
Chingiz Hajiyev, Halil Ersin Soken
One of the well-known models for obtaining the Earth magnetic field vector components in the reference frame is the International Geomagnetic Reference Field (IGRF) model. Inputs to the IGRF model are the radial distance from the center of the Earth (r), geocentric colatitude (θ – in degree), the east longitude (ϕ – in degree) and time t. Eq. (4.5) returns the magnetic field vector in spherical polar coordinates using Gauss coefficients (gnm, hnm) , which are functions of time and given in units of nT. Brθϕt=−∇a∑n=1N∑m=0narn+1gnmtcosmϕ+hnmtsinmϕPnmcosθ.
Advances in geodynamo modelling
Published in Geophysical & Astrophysical Fluid Dynamics, 2019
Johannes Wicht, Sabrina Sanchez
Predictions of the geomagnetic field have several practical applications. They are particularly important because of the role the geomagnetic field plays for space weather, which can heavily impact Earth-orbiting satellites and space missions (Mandea and Purucker 2018). Every five years, different groups from the geomagnetism community make a joint effort to update the International Geomagnetic Reference Field (IGRF, Thébault et al.2015)2 . They provide model coefficients for the large scale internal magnetic field and its secular variation based on different methodologies and data selections. Based on an intricate weighted averaging, the models are combined to generate the reference field and its secular variation (see Thébault et al.2015a for details on the calculation of the last IGRF). Assuming a linear time dependence of the coefficients, the IGRF also provides a magnetic field prediction for the next five years. Despite the simple method, the level of accuracy is more than adequate for the short term horizon (e.g. Bärenzung et al.2018). On time scales longer than a decade, however, the linear extrapolation becomes increasingly less reliable and more involved models accounting for the flow dynamics begin to pay off (Aubert 2015).
Multi-disciplinary ore deposit exploration in Sonqor, northwest Iran
Published in Australian Journal of Earth Sciences, 2021
S. Niroomand, D. Poreh, A. Kananian
For each point on the Earth, magnetic field intensity is derived from magnetic structures, geological assemblage/structures and International Geomagnetic Reference Fields (IGRF). IGRF is subtracted from the field measured data, the remainder being the magnetic field of the anomalies of the study area. With respect to the deviation of magnetic angles of the Earth, the sources of the captured anomalies are not exactly located beneath the latter, whose shapes also might have slightly deteriorated. In the study area, where different data-acquisition lines produce different magnetic dipoles, filters were derived to minimise these effects, improving the likelihood of shapes of structures being realistic.