地球磁场观测与模型的历史进展

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"Geomagnetic Observations and Models" 是 IAGA（国际地磁学与大气电学协会）特别索普龙系列书籍中的第五卷，由 Bengt Hultqvist 担任系列编辑，瑞典空间物理研究所，基律纳，瑞典出版。这本书反映了地球磁场这一古老地球属性的研究进展，自16世纪以来，随着人类对磁性现象的好奇心和导航技术的发展，特别是指南针的使用，磁场观测逐渐系统化并不断提高。该书的核心内容关注地球磁场的测量，包括磁偏角（最早被测量的磁场分量）的发现，随后是磁倾角的测量，最终发展到全面的磁场矢量分析。这些观测对于理解地球内部结构、太阳系内各天体以及它们与星际介质之间的相互作用具有重要意义。IAGA 的使命在于推动全球范围内的磁学和大气电学研究，促进各国、机构和个人在这些领域的研究，鼓励国际合作，并通过国际平台进行讨论和发布研究成果。此外，书中还涵盖了地球磁场内部结构的研究，由多位作者如 E. Petrovský、D. Ivers、T. Harinarayana 和 E. Herrero-Berver 联合编纂，他们共同探讨了地球磁场的起源、演化及其与地质过程的关系。这些模型不仅提供了对地球磁场动态的理解，也为探索其他行星的磁场特征提供借鉴。通过对磁观测数据的标准化程序、数据获取系统、数据分析方法和成果发布进行规范，本书对于提升地磁学研究的精度和一致性起到了关键作用。通过阅读这本书，读者可以深入了解地球磁场的历史演变、现代测量技术以及未来研究的方向，对于那些对地球物理学、空间科学和导航技术感兴趣的读者来说，这是一本不可或缺的参考资料。

2 J.L. Rasson et al.

• The observations proper: better instruments, staff,

accuracy, lower instrument noise in time and ampli-

tude, continuity of data

• The storage and forwarding of data: data centers,

availability of data

Our paper will deal with the scientiﬁc contribu-

tions presented at the Sopron IAGA 2009 Assembly

regarding this observatory network. But principally we

will deal with the improvements as explained above.

We will ﬁrst review the INDIGO project, a collabo-

ration between the British Geological Survey, Institut

Royal Météorologique de Belgique and agencies in

all the continents to improve existing observatories

and help create new ones. Next, the China Earthquake

Administration’s (CEA) centralized effort to upgrade

about 30 magnetic observatories will be presented as a

case study. Finally the problem of covering the ocean

regions on Earth with observatories is addressed in

“Filling the Gaps”.

1.1.2 Highlights from the Sopron IAGA

Assembly in 2009

The Assembly presented a rich programme deal-

ing with magnetic observatories in the world net-

work. During the Assembly lectures, Dr. C. Reeves

pointed out in “Geomagnetism and the Exploration of

Global Geology” that “a programme lasting decades

needs also to eliminate s ecular variation from its

results so that adjacent survey blocks may be stitched

together objectively. It is a singular success for IAGA

that the International Geomagnetic Reference Field

(IGRF) has been adopted almost universally by mag-

netic anomaly surveyors to achieve this”. On another

note, the Assembly lecture by Dr A Rodger “The

Mesosphere as a Link in Sun-Climate Relationships”

revealed to us the possibility to measure the mag-

netic ﬁeld in the mesosphere (altitude 50–100 km)

from an Earth based station, using a laser to inspect

the sodium atoms there [Moussaoui et al., 2009]. Do

we witness a new observation method in the making

here?

During presentations and discussions, it turned out

that the geomagnetic observatory data user community

requested increasing data and products from magnetic

observatories, leading to new tasks for them:

• Proposal for a new observatory data product: quasi-

deﬁnitive data

• Towards a metadata standard for geomagnetic

observatory data

• 1-second INTERMAGNET standard magnetometry

The “Quasi Deﬁnitive Data” is required in order

to speed-up the delivery of good quality data to users

unable or unwilling to wait until the beginning of the

next year when observatories traditionally release their

deﬁnitive data. With this new product, quasi deﬁni-

tive data should be available after a few months only.

Data users also realize that the phasing out of year-

books, with the advent of exclusive digital databases,

leaves them in the dark about many events and changes

occurring in geomagnetic observatories. Therefore a

metadata standard would come in handy to show the

way as to how to replace or complement the obser-

vatory yearbooks. A growing number of observatories

collect data at a 1 Hz sampling rate, because there is a

demand for higher time resolutions from the user com-

munity. INTERMAGNET is in the process of deﬁning

a standard for this 1 Hz variometric data, and manufac-

turers are now proposing instruments able to comply

with its 0.01 s timing accuracy and 0.01 nT noise limit

[Korepanov et al., 2007].

Also the widespread network and good availability

of geomagnetic observatory data resulted in it being

used as proxies in the following cases:

• Expected trends in the geomagnetic sq ﬁeld due

to secular changes in the earth’s magnetic ﬁeld

allow monitoring of the long term changes in the

ionosphere

• Ionospheric reﬂection of the magnetic activity

described by the new index η: Ionospheric data are

sparse in time and in space in opposition to the

magnetic data

• Geomagnetic activity (Ap index) and polar surface

air temperature variability

1.1.3 The Network

The network is presented in Fig. 1.1, with a dis-

tinction made for the observatories having attained

INTERMAGNET certiﬁcation (more details at

www.intermagnet.org). As is to be expected, a non

1 The Global Geomagnetic Observatory Network 3

Fig. 1.1 The global network of active geomagnetic observa-

tories as it exists beginning 2010 (Mollweide projection). The

names and IAGA codes of these observatories can be found

on http://www.meteo.be/IAGA_WG_V.1/ along with the sta-

tion details like latitude and longitude, elevation and operation

years

uniform distribution of the observatories on the globe

is clearly seen.

There is a bias of more observatories on the emerged

lands and also in the northern hemisphere. It is note-

worthy to see that the Chinese network almost reaches

the density of stations that we witness in Europe. Our

Chapter 2 therefore looks into the centralized effort

China is deploying to build its high quality observa-

tories.

The interest for geomagnetic data from the South

Atlantic anomaly is growing and following the ren-

ovation of the Vassouras and Trelew observatory in

1993 [Rasson et al., 1996], many programs targeted

that region to install or upgrade observatories there,

including the difﬁcult to access St Helena and Tristan

da Cunha islands [Korte et al., 2009].

1.1.4 INDIGO: Better Geomagnetic

Observatories at the R ight Place

The INDIGO project aims to provide the means for

achieving quality observatories in a selected set of

places on the Earth. Equipment, software, training and

data processing, when missing on site, are given to

colleagues worldwide so that they might improve or

start their own geomagnetic observations.

Usually existing premises are used and/or reconﬁg-

ured to provide an adequate hosting of the INDIGO

equipment (Fig. 1.2). If necessary, local staff are

trained in observatory operations and observing

skills.

The installation of a successful observatory also

depends on the motivation of the local observatory

staff; with the help of the INDIGO project, most

common problems can be overcome.

A state-of-the-art magnetic observatory is an expen-

sive piece of infrastructure in equipment and in man-

power, since automatic observations are not possible at

the moment. Therefore the good ones tend to be clus-

tered in richer countries. INDIGO tries to provide help

where there are gaps in the observatory world map.

The INDIGO effort has therefore been directed

towards Asia, Africa and Latin-America (Fig. 1.3).

The original objective of the INDIGO project was to

make use of ﬁfteen EDA ﬂuxgate variometers donated

to the British Geological Survey (BGS), coupled with a

low power digitiser to make ﬁltered one-minute digital

daily recordings.

6 J.L. Rasson et al.

INTERMAGNET certiﬁcation. INDIGO observatories

have not yet reached the stage where the certiﬁcation

criteria can be met, but some are very close. The main

short term objective is training the observatory staff in

preparing their deﬁnitive data.

Several new observatories are actively involved in

becoming INDIGO’s: Quetta (Pakistan), Muntinlupa

(Philippines), Pilar and Orcadas-del-Sur (Argentina),

Tondano (Indonesia).

We foresee more observatories becoming involved,

particularly in Africa where difﬁcult conditions are

threatening the operation of some of the few exist-

ing observatories. Such observatories often beneﬁt

from lower cultural noise in comparison to established

Western observatories; they are far more sparsely dis-

tributed than Western observatories, and are located

close to regions of particular scientiﬁc interest such as

the dip equator or South-Atlantic anomaly.

New INDIGO equipment is constantly being pro-

jected and developed: full solar panel electrical sup-

plies, RF wireless transmission of data, MkIII data

logger.

INDIGO is the brainchild of retired but very active

colleague John C Riddick, C Turbitt and S Flower from

BGS together with one of us (JLR) [Ameen et al.,

2009].

1.2 Advances in a Newly Upgraded

Network: The China Earthquake

Administration (CEA) Effort

1.2.1 Observatories in China: Short

History Up to Twentieth Century

There were four major periods for the development of

the magnetic observatories in China’s mainland.

• Before the International Geophysical Year (IGY)

The ﬁrst magnetic observatory in China was con-

structed in Beijing in 1870 by Russia. It ceased

working in 1882. There were six other magnetic

observatories with different periods of operation but

all of them ceased working before 1944. One excep-

tion was Sheshan (SSH) Observatory which was

constructed in 1874 by the French missionary and

is still in operation now [Zongqi Chen, 1944].

• During the IGY

During the IGY, construction of seven magnetic

observatories including Beijing (BJI), Changchun

(CNH), Wuhan (WHN), Guangzhou (GZH),

Lanzhou (LZH), Lhasa (LSA) and Urumqi (WMQ)

observatories was initiated. Together with SSH,

these eight observatories became the backbone of

the Chinese magnetic network.

• From 1966 to 1979

The 1966 Xingtai Earthquakes triggered the

beginning of the Chinese research on earthquake

prediction. Various observation methods were uti-

lized including magnetic observation. More than

200 magnetic stations were set up around the coun-

try in the following years. These stations were

sponsored by different organizations and/or institu-

tions with a variety of observational procedures and

quality controls [Rongsheng Gao et al., 1999].

• After 1979

In 1979, all of the magnetic observatories and

stations were put under the administration of the

SSB (the State Seismological Bureau, now the

CEA). An organization (now the Geomagnetic

Network of China) in the Institute of Geophysics,

SSB (IGSSB, now IGCEA) was responsible for the

technical support and data management of the mag-

netic network. The network was readjusted several

times taking into account the distribution and the

observational environment of the stations [Anlong

Cheng et al., 1990]. Half of the stations ceased

working. Meanwhile, instrumentation at 29 of the

stations was improved to make them operate as

observatories. Seven observatories out of these 29

joined the existing 8 older observatories to form the

primary observatories. Data from these 15 observa-

tories have been being archived in the World Data

Center system ever since.

1.2.2 Planning the Major Upgrade:

Towards INTERMAGNET Standards

In the late 1990s, the CEA began to consider the

modernization of the geomagnetic network. Taking

into account the importance of continuous reliable

geomagnetic data, they started cautiously at the begin-

ning. Twenty one sets of the Chinese GM-3 type tri-

axial ﬂuxgate magnetometers were installed in twenty

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