1、BSI Standards PublicationBS ISO 16695:2014Space environment (naturaland artificial) Geomagneticreference modelsCopyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO
2、16695:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 16695:2014.The UK participation in its preparation was entrusted to TechnicalCommittee ACE/68/-/4, Space systems and operations - Spaceenvironment (natural and artificial).A list of organizations repres
3、ented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 73
4、121 1ICS 49.140Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 28 February 2014.Amendments issued since publicationDate Text affectedCopyright British Standards In
5、stitution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO 16695:2014 ISO 2014Space environment (natural and artificial) Geomagnetic reference modelsEnvironnement spatial (naturel et artificiel) Modle
6、s de rfrence du champ magntique terrestreINTERNATIONAL STANDARDISO16695First edition2014-02-15Reference numberISO 16695:2014(E)Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from
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9、ail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandCopyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO 16695:2014ISO 16695:2014(E) ISO 2014 All rights rese
10、rved iiiContents PageForeword ivIntroduction v1 Scope . 12 Reference frames . 12.1 General . 12.2 Geocentric reference frame 22.3 Geodetic reference frame . 22.4 Geodetic to geocentric coordinate transform . 33 Specification of the geomagnetic field vector . 33.1 General . 33.2 Magnetic vector compo
11、nents in the geocentric frame . 43.3 Magnetic elements in the geodetic reference frame . 43.4 Transform of magnetic vector components from geocentric to geodetic frame 64 Specification of the geomagnetic reference model . 64.1 Potential of the magnetic field . 64.2 Geomagnetic reference radius . 84.
12、3 Epoch of a sub-model 84.4 Validity of a sub-model 84.5 Time-dependence of Gauss coefficients 84.6 Calculation of magnetic vector components in the geocentric reference frame 94.7 Spatial wavelength 104.8 Root-mean-square difference between two model fields .105 Examples of the use of geomagnetic r
13、eference models.115.1 Compute reference magnetic elements near the Earths surface .115.2 Compute reference magnetic vector in near-Earth space 115.3 Compute reference magnetic vector in magnetosphere 12Annex A (informative) Available geomagnetic reference models .13Bibliography .18Copyright British
14、Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO 16695:2014ISO 16695:2014(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national
15、 standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. Internationa
16、l organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended fo
17、r its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.or
18、g/directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be
19、in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions r
20、elated to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 20, Aircraft and space vehicles, Subcommittee S
21、C 14, Space systems and operations.iv ISO 2014 All rights reservedCopyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO 16695:2014ISO 16695:2014(E)IntroductionFor ce
22、nturies, geomagnetic reference models have been used to describe the vector field (for example, by its direction and strength) as a function of position and date. Such models are widely used in upper-atmospheric, ionospheric, and magnetospheric research, and in characterizing the near-Earth space en
23、vironment. They further provide an essential reference for navigation, heading, and attitude determination and control subsystems of spacecraft and ground-based systems.Earths magnetic field is represented in such models as a spherical harmonic expansion of the equivalent scalar magnetic potential.
24、This representation was proposed by Karl Friedrich Gauss (1777-1855) and has been used ever since to describe the geomagnetic field. The spherical harmonic coefficients of the geomagnetic field are commonly called Gauss coefficients. In 1969, the International Association for Geomagnetism and Aerono
25、my (IAGA) introduced the International Geomagnetic Reference Field (IGRF), which uses the Gauss representation to describe Earths magnetic field. This International Standard closely mirrors the established specification of such models, including formulae and computational procedure.There are several
26、 internal and external sources contributing to the observed magnetic field. All of these sources affect a scientific or navigational instrument, but only some of them are represented in geomagnetic reference models. The strongest contribution, by far, is the magnetic field produced by motions in the
27、 Earths liquid-iron outer core, which is called the core field. This core field changes perceptibly from year to year. When extrapolating the temporal evolution of the field into the future, a linear extrapolation of the Gauss coefficients is used. Geomagnetic reference models specify the Gauss coef
28、ficients for a start date (epoch) and provide their linear change over time as a set of so-called secular variation (SV) coefficients. Due to unpredictable nonlinear changes in the core field, predictive geomagnetic reference models are valid only for a limited period, and users subsequently have to
29、 update to a newer version.Other sources also contribute to the magnetic field. Magnetic minerals in the crust and upper mantle give rise to magnetic anomalies which can be significant locally. Electric currents induced by the flow of conducting sea water through the ambient magnetic field make a fu
30、rther, albeit weak, contribution to the observed magnetic field. Time-varying electric currents in the upper atmosphere and near-Earth space generate an external magnetic field. The external field does not average to zero over time. Its steady contribution can therefore be included in a geomagnetic
31、reference model using external Gauss coefficients with linear secular variation. Time-varying external magnetic fields further induce electric currents in the Earth and oceans, producing secondary internal magnetic fields. Since there is no general consensus on how to separate these various internal
32、 and external sources, it is left to the producer of a geomagnetic reference model to specify which of these internal and external sources are included in their model, and any radial limitation to the validity of the external part of their model. ISO 2014 All rights reserved vCopyright British Stand
33、ards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO 16695:2014Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduc
34、tion or networking permitted without license from IHS-,-,-BS ISO 16695:2014Space environment (natural and artificial) Geomagnetic reference models1 ScopeThis International Standard defines reference models representing the geomagnetic field. It closely mirrors and clarifies specifications which have
35、 been in use for many decades.The approach is to represent the corresponding scalar magnetic potential by a spherical harmonic expansion having specified numerical coefficients, called Gauss coefficients. This International Standard covers models in which, at any one time, changes of the magnetic fi
36、eld are modelled by a linear time-dependence of each Gauss coefficient. A model might consist of a succession of sub-models, in each of which the coefficients change linearly with time. For such a step-wise linear model, the coefficients are continuous in time. This International Standard provides t
37、he formulae and a step-by-step computational procedure to evaluate a geomagnetic reference model for any desired location and date.This International Standard does not specify the interpretation of the geophysical content of a geomagnetic reference model. It is left to the producer of a model to spe
38、cify which internal and external magnetic sources are included in (or excluded from) their model.2 Reference frames2.1 GeneralFor positions remote from the Earth, it is customary to use a geocentric reference frame and to resolve the magnetic field vector into components based on this geocentric fra
39、me. For positions on and near the Earths surface, it is customary to use a geodetic reference frame, based on the standard World Geodetic System (WGS84) ellipsoid of rotation approximating the Earths surface, and to resolve the magnetic field vector into components based on this geodetic frame.The d
40、own axis in the geodetic frame is perpendicular to the surface of the WGS84 ellipsoid. Deflections of the vertical caused by local gravity anomalies have to be taken care of by the user and are not covered by this International Standard (see 5.1). Geocentric and geodetic coordinates are illustrated
41、in Figure 1.INTERNATIONAL STANDARD ISO 16695:2014(E) ISO 2014 All rights reserved 1Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-BS ISO 16695:2014ISO 16695:2014(E)N
42、OTE An axial cross-section through the point of interest P which is at longitude . This point P is specified in geocentric spherical polar coordinates by its distance r from the Earth centre O and the incidence angle of the OP line with the equatorial xy-plane. The same point P has geodetic coordina
43、tes given by its height h above the WGS84 reference ellipsoid and the incidence angle of its geodetic normal with the xy-plane.Figure 1 Geocentric and geodetic coordinates2.2 Geocentric reference frameA point location in geocentric Cartesian coordinates is given by the same (x, y, z), as used in geo
44、detic Cartesian coordinates (see 3.1.2 of ISO 19111, but note that it uses capital X, Y, and Z). Equivalently, coordinates can be specified as geocentric spherical polar (, , r), where is the longitude, is the geocentric latitude, and r is the distance from the Earth centre. The prime is used to dis
45、tinguish geocentric from geodetic terms where necessary.2.3 Geodetic reference frameThe geodetic reference frame is based on the WGS84 reference ellipsoid. This is an ellipsoid of rotation having a defined semi-major axis A (in the equatorial plane), and a flattening f. This leads to a semi-minor ax
46、is (essentially along the spin axis) of A(1f). Specifically,A = 6 378 137 m (1)1298 257223 563f= , (2)2 ISO 2014 All rights reservedCopyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy Not for ResaleNo reproduction or networking permitted without license
47、 from IHS-,-,-BS ISO 16695:2014ISO 16695:2014(E)e2= f (2 f) (3)wheree is the (first) eccentricity.A point location in geodetic coordinates is given by (, , h), where is the longitude, is the geodetic latitude, and h is the height (distance normal to the ellipsoid) above the WGS84 reference ellipsoid
48、. Geodetic and geocentric longitudes are identical. This nomenclature follows ISO 19111. A point location can also be specified by the Cartesian coordinates (x, y, z) in the WGS84 reference system, where the positive z and x axes point in the directions of the semi-minor axis and the prime meridian ( = 0) in the equatorial plane, respectively; this is the same as the geocentric Cartesian coordinate system. For the WGS84 ellipsoid we then have for c, the radius of curvature of the normal section at the geodetic latitude ,cAe=122sin(4
