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MAGNETIC SURVEY DATA A'IAILABLE

PRIOR· TO " ,

THE WORLD MAGNET1C SURVEY EFFORT , . ~

.OF THE IQSY

OTS PRICE

XEROX $

111 CROF I LM $ __ ..-:::... __

PREPARED- BY- - - - - --

S. HENDRICKS

J. C. CAIN

------ GODDARD SPACE FLIGHT CENTER ----­GREENBELT, MD.

. ,

https://ntrs.nasa.gov/search.jsp?R=19630013144 2020-07-19T02:11:06+00:00Z

MAGNETIC SURVEY DATA AVAILABLE PRIOR TO THE

WORLD MAGNETIC SURVEY EFFORT OF THE IQSY

by

S. Hendricks and J. C. Cain

Goddard Space Flight Center

Greenbelt, Maryland

ABSTRACT

Given are the distributions of magnetic survey information

available from all sources since 1900. The data are tallied

according to distribution by area and decade, and according

to component measured. Recommendations are made on the basis

of these studies for specific surveys during the IQSY.

(1964.0 - 1966.0)

Contents

page

I. INTRODUCTION ...................... 1

II. SOURCES ........................ 1

III. DATA PENDING ...................... 3

IV. DISTRIBUTIONS OF DATA .................. 3

1° By component and area

2. By decade and area

3. By year

4. By altitude

V. DENSITIES OF DATA .................... 5

VI. RECOMMENDATIONS FOR FUTURE SURVEYS ........... 7

TABLES

i. Number of points per i0 ° block of latitude-longitude

a. Declination

b. Inclination

c. Horizontal Intensity

d. Vertical Intensity

e. Total Field

f. Total Observations

2. Number of observations per i0 ° block by decade

a. 1900-1909

b. 1910-1919

c. 1920-1929

d. 1930-1939

e. 1940-1949

f. 1950-1959

g. 1960-1961

3. Number of component observations per year

4. Number of component observations per kilometer of altitude

5. Area of latitude-longitude Blocks

,

2.

FIGURES

Number of observations per 105km 2 (data 1900-1961)

Number of observations per 105km 2 (data since 1955.0)

I. INTRODUCTION

In an attempt to obtain the most accurate reference field

possible for future use in reducing satellite data, all available

magnetic survey data are being collected for incorporation into a

computer program that produces a set of spherical harmonic

coefficients which fit the data. The purpose of this report is

to assess the data presently available and to make recommendations

for additional acquisitions.

II. SOURCES

The major portion of the present information has been supplied

by the U. S. Coast and Geodetic Survey which provided a punched

card copy of the data from which their 1955 charts were derived.

These are observations dating from 1900 which have been accrued

from approximately 500 sources. As with all data in this report,

an attempt was made to differentiate between originally observed

values and those which were computed, so that the basic data would

consist only of observed values. Due to the wide variety of

sources, this deletion was not always feasible but, on the basis

of the information available, some editing was done as follows:

(1) The horizontal and vertical intensity values were

eliminated from USCGS measurements,

(2) In addition, the vertical intensity value was dropped

from surface observations if a particular datum contained

values for inclination and horizontal intensity, and was

from a source other than a U. S. observatory.

- 2 -

Since analysis of these observations will also involve

studies of secular change, it was deemed desirable to delete

values which had been reduced to epoch. On the basis of this

premise some 21,300 observations from a Russian publication*

which had been reduced to epoch 1940 were removed from the main

block of data with the hope that it may be possible to replace

them with the original data.

Data were also received from the U. S. Oceanographic Office.

These 32,000 observations were the result of Project Magnet, an

airborne survey in which measurements of F, I, and D were averaged

over five minute intervals along track lines covering most of the

northern hemisphere other than the Soviet Union and China.

A third source of information was the Canadian Department of

Mines and Technical Surveys which, since 1953, has conducted an

airborne survey, mainly in that North American area, resulting in

nearly 12,000 H, Z, and D observations (5 minute averages).

The Geophysical and Polar Research Institute of the University

of Wisconsin has provided about 2400 observations of total field in

the area around the South Pole.

Compounded systematic catalog of magnetic determinations of the

general magnetic survey of the USSR, 1931-1942, Scientific

Research Institute of Terrestrial Magnetism, 1947.

- 3 -

The Southern and Indian Oceans, and the South China Sea were

surveyed by the Japanese Antarctic Research Expedition with a

ship-towed magnetometer. Their report (Nagata, et al, 1961)

supplied another 5000 observations of total field, approximately

half of which have been incorporated in this summary.

Total field measurements from the Vanguard III satellite

(1959 Eta) comprised the sixth major source of data. The 85 day

active life of the proton precession magnetometer provided 2797

observations over South America, Southern Africa, Australia,

California, and the east coast of the U. S. (Cain, et al, 1962).

III. DATA PENDING

In addition to the data covered by this report, a set of

total field readings obtained on cruises of the R/V Vema from

1959-62 and compiled by Lamont Geological Observatory are currently

being processed. This will add 3600 observations in southern ocean

areas.

Arrangements are being made in conjunction with the USCGS to

receive from the Geophysical and Polar Research Institute of the

University of Wisconsin a more recent series of total field

observations in the Arctic and Antarctic areas.

IV. DISTRIBUTIONS OF DATA

The above sources of data were converted to a standard format

and recorded on magnetic tape. Each of the 152,424 observations

was written with information regarding its position (latitude and

longitude in degrees, altitude in kilometers) and time (in Julian

- 4 -

days and fractions of a day since 1900), plus the measured values

for one or more components of the magnetic field. This tape was

scanned and the data were tabulated in the following ways:

(1) By component and area - Tables 1 (a) through 1 (e) show

the number of points in each 10° x 10° block of latitude

and longitude for observations of declination,

inclination, horizontal intensity, vertical intensity,

and total field. Longitude numbers refer to the eastern

boundary of the block (i.e. the longitude block labeled-

160 extends from 170°W to 160°W). The values from these

five tables were combined to give the totals which appear

in Table 1 (f).

(2) By decade and area - In order to determine how frequently

and how recently a particular region had been covered,

the data were divided into 10 year blocks and the

latitude - longitude distribution was compiled for each

decade. Table 2 (a through g) displays these figures

which, as with Table 1 (f), represent the sum of all

component measurements. Most of the polar data has

been accrued since 1950 and, although the total number

of points (57527) already accumulated in the present

decade is great in comparison with previous years,

there are vast regions over the ocean areas and over

the Soviet Union where no new data are available.

(3) By year - A more general breakdown in time is given

- 5 -

in Table 3 where the number of points for each

component is tallied for each year.

(4) By altitude - Although the preponderance of data

are surface observations, recent airborne surveys

have supplied considerable data up to 7 or 8

kilometers. This distribution is shown in Table 4.

Total field measurements taken by the Vanguard III

satellite provided data in the region from 510 to

3750 kin. altitude (Cain, et.al., 1962).

V. DENSITIES OF DATA

The large difference between the amount of surface area

covered by a 10 ° square at the equator and a similar square in

polar regions made it desirable to use another method for

illustrating distributions. The number of square kilometers in

each block was calculated using the formula:

jA - 360/_ in (@+Z_ _ ) - sin @

where R (earth's radius) was taken to be 6371.2 km, _ _ and

_ were i0 ° and _ was the latitude of the southernJ

boundary of the block. These areas are listed in Table 5.

Dividing the number of points in each block of Table 1 (f) by

the area A for that block gave the number of observations per

square kilometer. These figures were multiplied by a scale

factor of 105 to produce the results displayed in Figure i.

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- 6 -

Thus, for an equatorial block, where one degree equals 111 km,

a value of 1000 for a 10 ° block would represent data points at

an average of approximately 10 km intervals. It can be seen

from the figure that the density in areas near the magnetic

poles compares favorably with that over most of the larger land

masses. The numbers above 10 are rounded to the nearest

10 _bs/105 kin23 •

LATITUDE

TABLE 5

AREA (10 5 kin)

0°-i0 ° 12.3

10°-20 ° ii .9

200-30 ° ii .2

300-40 ° lO. 1

40o-50 ° 8.7

50 °- 60 ° 7.1

o60 - 70° 5.2

70 °- 80 ° 3.2

800-90 ° 1.1

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5 2 DENSITY OF MAGNETIC SURVEY OBSERVATIONS 1900-~961 (OBS PER 10 km ) FIGURE 1

- 7 -

VI. RECOMMENDATIONS FOR FUTURE SURVEYS

Vestine (1961) has suggested that data obtained since

1955.0 be considered as part of the World Magnetic Survey.

Figure 2 shows the density of data per 105 km 2 in 10 ° squares

since 1955, and hence, by Vestine's criterion, a tabulation of

the coverage already achieved by the WMS. In order to obtain

the desired accurate representation of the field at ionospheric

altitudes and above, a minimum grid spacing of i00 km should be

achieved. This would mean raising the numbers in each block of

Figure 2 to 12 or more. It can readily be seen from this figure

that there are large areas over the globe where this minimum

cr_erion is not yet met. Detailed recommendations for new

surveys must of course be made bearing in mind not only the

density of observations in a given area but also such considera-

tions as the usefulness of past observations, the existence of

data taken but not available, and known firm plans for surveys.

The usefulness of past observations is a complex subject

involving not only their accuracy and space-time distribution

but also the rates of secular change. The needs can thus best

be defined in relation to given areas. The purpose of this

report is to be a general guide and not to delve into these

questions in great detail.

The most striking gaps in Figure 2 appear in the southern

hemisphere. It points out that to equalize the distributions

it would be useful to concentrate the major efforts in these

135- 180-135' IBO' 165' ISO' 110' 105' 90' 75' 60' 45' 30' 90' 150· 165· IS' O' IS' 45' 75' 60' 30' 90-rmnmmmmmrrrrrmnmmmmmmmmnmmmmmnmrTTTlTTT1TTTTTTTrmnnmmmmmmTTTTlTTTTTTT1TlITTTmTT1TlTTTTTTTTTTT'!TT1TT!'TTT'lTTTTTTTTTT1TTTTmTTTTTTTTTITnrnTTrnTI'TTT~~~

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I I I I I I ~~-- I I I ~ t{ I I I I~-I I I I~- I I~- I I I I I I I 0 I I l!)r 3 45'1= -+- -+- -+- -r -r- -+- -r- -r- -t- -t- '- -r- -I- -+- -I- -+- -+- -+- -+- -+- 10 -+- -+- -+- -r- -+- -+- -j- -+- -t- 7 - 9 -I- 10 - I- 20 -I- 20 -+- ;'$"'30 -? 45'

I I I I I I 1 I J 1 ~ 11 I I I I I I I I I I I 1 1 J I I I I I I I I I I :

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180·

wi I I I I I I I 1 I I I 1 I I I I I I I I I I I I I I I I I I I I I I I ~ w

-;0+ I I _ I + I I I ~ I _~ 1 __ 1 _~ 1 o .. ;.1.~J _~ I +- I __ I+- I +- 1 +- 1 _ I __ 1 -0 Lf- '~ -V-: __ I _~ I -0 I -0 I -f-I _~I-'::I:--I--==--! ,H1, -- I __ JO -f- I ~

I I I I I ( 1 \ r-. lA _~ v+- ---r-."VV I I I I "- lIt"'-h J :: ~ I I I I __)-r ~'J) ~lJ'~ I 1'- - I I I I T"u :: ·~j·~~·.~.~Icff;'(T:-'I-~r~r-'rr~I --I-- I- ~-F~-v~t I +- I +- I+- 1-- 1 -0 1-- 1 +- I--I-~ I -0 I -0 1+ 1--1-0 1 + 1-0 rr-~~lt ~ ~

lIIJlJlIIIIIIIIIIIIIlIllItltltILltILI,I"ILIJl,l,ltIJ1tILIJ1,1,1 11,1, 1,1,,1.1, 11111,1,,1,1,l. IBO' 165' ISO' 135' 110' 105' 90' 75' 60' '5' 30' IS' O' .

-

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45' 60' 75' ,,;)- 30' 90' ISO' OS' 110' 135' 165'

DENSITY OF MAGNETIC SURVEY OBSERVATIONS 1955-1961 (OBS PER 10 5km2) FIGURE 2

- 8 -

areas, even if some of the high density areas were temporarily

neglected. A point worthy of mention in this connection is

that almost all of the data south of 30°S latitude is scalar B

as a result of proton magnetometer measurements by ship, air-

craft, and satellite. There is indication that the Zarya data

(Benkova and Tyurmina, 1961) will be helpful in filling in the

gap in the Indian Ocean and in some regions of the south Atlantic

down to about 40°S. The rest of the vast regions of the Pacific

and Antarctic need much further work.

The region of the Asian landmass is one where, hopefully,

it will be possible to obtain data already in existence but not

yet published.

There are also surprising gaps over other regions such as

South America, Africa, Australia and Greenland where one would

normally expect a better coverage. It is hoped that this

report will be useful in bringing forth existing data in these

and other areas.

REFERENCES

!

Benkova, N. P., and L. O. Tyurmina, Analytical representation

of the geomagnetic field over the territory of the Soviet

Union for the 1958 epoch, Geomagnetism and Aeronomy,

Vol. i, 81-96, 1961.

Cain, J. C., I. R. Shapiro, J. D. Stolarik, and J. P. Heppner,

Vanguard 3 magnetic field observations, J. Geophys.

Research_ 67, 5055-5069, 1962.

Nagata, T., T. Oguti, and S. Kakinuma, Results of geomagnetic

total force surveys over Southern Ocean, Indian Ocean and

South China Sea, National Antarctic Committee, Science

Council of Japan, March, 1961.

Vestine, E. H., Instruction manual on World Magnetic Survey,

Union Geodesique et Geophysique Internationale, N°ll,

August, 1961.