NBS

knicai ^iote

>oulaer laboratories

9k. 37

AN ATLAS OF OBLIQUE-INCIDENCE

IONOGRAMS

" VAUGHN AGY, KENNETH DAVIES

AND ROGER SALAMAN

S. DEPARTMENT OF COMMERCE

flONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and

properties of materials: the development of methods and instruments for testing materials, devices,

and structures; advisory ser\ices to government agencies on scientific and technical problems: in- vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and applied research,

development, engineering, instrumentation, testing, evaluation, calibration services, and various

consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is required. The scope of activities is suggested by the listing of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

of professional and scientific societies. The Bureau itself publishes three periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the

National Bureau of Standards ($1.25) and its Supplement ($1.50), available from the Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

technical ^Ttote

31

November 1959

AN ATLAS OF OBLIQUE- INCIDENCE IONOGRAMS

by

Vaughn Agy, Kenneth Davie

s

and Roger Salaman

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C.

Price$ 2.25

AN ATLAS OF OBLIQUE- INCIDENCE IONOGRAMS

by

Vaughn Agy, Kenneth Davie

s

and Roger Salaman

INTRODUCTION

This atlas is intended to serve a twofold purpose : first, to

provide a compilation of records, of a type becoming standard in the

field of ionospheric research, for those workers who are not now

familiar with them, and second, to present records which are characteristic of the specific paths used by the National Bureau of Standards

for consideration by those using other paths.

To date, NBS sweep-frequency experiments have been carried out over two approximately east-west paths: Sterling, Va. - St. Louis, Mo.

(about 1150 km), and Sterling, Va. - Boulder, Colo, (about 2370 km).

The experimental data on these paths were taken under the supervision of

R. Silberstein and P. G. Sulzer. For each path a midpoint verticalincidence station was established within about one mile of the geographical midpoint of the great circle path. For the Sterling - St. Louis

path the midpoint station was near Batavia, Ohio and for the Sterling - Boulder path it was near Carthage, Illinois. The shorter path was used

from August 1951 to December 1952 when the St. Louis equipment was moved

west to Boulder. From September 1953 to May 1955; routine records were

made over the Sterling-Boulder path, after which time various minor

equipment changes were made to improve the time-delay records and to

obtain records giving more propagation information for the path.

The data concerning the end-point stations are tabulated below:

Equipment Power Time

Sweep Pulse Pulse

Frequency Length Rep Rate Antennas

C-3 10 kw

(modified)

12 min 2-25 Mc 50 us

** 25/sec Horizontal

Rhombic

^Changed in 1955 to 7J minutes.

**Unless otherwise noted in the body of the atlas.
- 2 -

For the Sterling- St. Louis path the time at which each record was made (indicated below and to the left of each record shown) is 75 ° West

Meridian Time. For the Sterling-Boulder path, 90° West Meridian Time

was used. The time given for each obli que -incidence ionogram is that

at which the frequency passed upward through 23 Mc (changed to 2k Mc

during the first months of 1958).

The relatively slow sweep time allowed for manual adjustment, when

necessary, to synchronize the two equipments. The midpoint verticalincidence equipment operated in normal fashion, sweeping from 1 Mc to

25 Mc in 15 seconds once every 6 minutes and later once every 3 minutes.

The 3 minute spacing between sweeps allowed selection of the verticalincidence ionogram made within !§ minutes of the time the slower

oblique-incidence sweep passed through the frequency of interest, e.g.,

the MUF.

The oblique -incidence ionograms are plots of time-delay against

frequency (on a linear scale). The ordinate (time-delay) scale, however, just as for vertical- incidence ionograms, is calibrated in terms

of the apparent virtual half-path. In order to determine the absolute

time delay (or virtual half-path) between the two stations at a given

frequency, it is necessary to take the arithmetic mean of the ordinates

on the two end-point records. For given virtual heights* of reflection,

the virtual half-paths are plotted in Figure 1 for the Sterling-St.

Louis path and in Figure 2 for the Sterling-Boulder path. In addition

to the 1-, 2-, 3-hop modes, the M and N modes are presented involving

both F- layer reflections and E-layer reflections (with the E-layer

virtual height assumed to be 100 km).

The ionograms for the shorter path usually show vertical- incidence

as well as oblique-incidence traces; for the longer path, however, in

order to avoid undue compression of the virtual half-path scale, the

first 1000 km of half-path are not recorded. On some of the later

records, one or both scales are expanded in order to allow examination

of some of the detailed structure of the recorded traces.

In some cases (e.g. Section I-3) the midpoint vertical- incidence

records are included for comparison. Although not always labeled, these

records are easily identified by the logarithmic frequency scale. The

end-point records, unless otherwise noted, were those made at the

western terminus of the path, i.e. St. Louis for the shorter path and

Boulder for the longer path. The primary reason for this choice is the

fact that these records usually are freer of interference than those

made at Sterling.

^Virtual height in this sense, for the 1-hop mode, is the height above

a spherical earth of the apex of an isosceles triangle whose base is the

chord between the two stations and whose legs are equal in length to the

absolute virtual half-path between the stations.
100

1000

900

< 800

700

600

500

3 HOP

2 H DP -/ \

/ M" (2 F-E)

1 n"(cj. c \ /

1/

1 HOF

STFRI INIfi — ST 1 niJIS 1 IPSO Km

100 200 300 400

VIRTUAL HEIGHT OF REFLECTION IN Km, h' FIGURE I

500
1700

1600

TM 1500

Q.

e"

< 1400

3

I-K

>

<

1300

1200

100

3 HOP

V

V

*\

2 HOP

// "M"(2F-E)

l "n"(f + E) .*

J_ HOP

STERLING- ROUI DER ?37n k m

100 200 300 400

VIRTUAL HEIGHT OF REFLECTION IN Km, h" 500

FIGURE 2
- 3

-

The body of the atlas is divided into three parts, giving examples

of records made: (l) over the Sterling-St. Louis (1150 km) path, (2) over the Sterling-Boulder (2370 km) path during the routine phase of

this part of the experiment, and (3) over the Sterling-Boulder path during the more recent phase of the experiment in which equipment changes

were made to increase the observable detail in the ionograms and to make

measurements of recorded pulse amplitudes. Some sequences of ionograms

are included to show the variations during a day, or during shorter

periods when the development of a specific phenomenon can be seen. Other single records are included simply to show the occurrence rather

than the development of a particular phenomenon. Many of the records

for which interpretations are not readily evident are included because

of the interest they may arouse. However, it is not the purpose of the

atlas to give detailed interpretations of the ionograms shown.

For the most part, the analysis of the records has consisted of a comparison of the MUF determined directly from the oblique -incidence

records with that obtained by applying the appropriate Smith transmission curves (see references) to the midpoint vertical- incidence ionograms. It is worth noting that although, on" the average, the scaling

of MUF from the vertical-incidence midpoint records agrees well with the

observed MUF, there are frequent discrepancies in detail. For an even- tual understanding of oblique -incidence propagation, the discrepancies

are just as important as the cases of close agreement.

The use of various descriptive terms has developed to aid in the

description of certain aspects of the oblique-incidence ionograms. One

of these terms is "nose", which is suggested by the shape of the trace on an oblique- incidence ionogram indicating the merging of a high-angle

and a low-angle ray. It has become customary occasionally to speak of

the "junction frequency" or simply the "nose frequency" for a particular

layer when referring to the classical MUF for that layer, but when com- plications arise, as shown in Sections II-3 and III-3, "nose" may also

be used to refer to a junction frequency different from the MUF.

REFERENCES

(NBS work of special interest)

1. Ionospheric Radio Propagation, Chap. 6, NBS Circular W>2 (1948).

2. P. G. Sulzer and E. E. Ferguson, Proc . I.R.E. kO, 1124 (1952).

3. B. Wieder, J. Geophys. Research, 60, 395 (1955)-

k. P. G. Sulzer, J. Geophys. Research, 60, 411 (1955)*

5. V. Agy and K. Davie s, J. Research NBS, 63D, No. 2 (Sept-Oct. 1959).
- 1+ -

INDEX OF SELECTIONS

I. Sterling-St. Louis - 1150 km

1. Diurnal Variations

2. Post Sunrise Development of the F Layers

3. Spread Echo

k. MUF Extensions

5. Equipment Sensitivity

6. Importance of the High-Angle Ray

7. Sporadic E

8. Moving Irregularities

9. Unusual and Complex Traces

II. Sterling-Boulder - 237O km

(Routine)

1. Diurnal Variations

2. Post Sunrise Development

3. Miscellaneous Sequences

Apparent Stratifications

Complex Traces

MUF Extension

Sporadic E

k. Miscellaneous Ionograms

Multi-hop Traces

Fl MUF

E2 Trace

0-X Frequency Separation

III. Sterling-Boulder - 2370 km

(Exper imental

)

1. Magnetic Storm

A. 3-day Sequence

B. Detailed Sequence During Storm

2. Morning and Afternoon Sequences

3. Inner and Outer "Nose"

k. "Disturbed F2 Nose"

5. Disturbed Conditions

6. Rarely Observed Ionograms

7. Equipment Effects

8. Fixed Frequency vs. Sweep Frequency

9. Field Strength Variations near the MUF
I. Sterling- St. Louis - 115 km

1-1

Sterling- St. Louis

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Winter Day

January 9-10, 1952

ZK = 28 ° P

Equinoctial Day (Spring)

March 5-6, 1952

ZK = 1*7 o P

Equinoctial Day (Spring)

April 2, 1952

ZK = P

1*8-

Summer Day

May 28,, 1952

ZK = P

38+

Summer Day

June 25-26, 1952

ZK = P

30

Equinoctial Day (Fall)

September 18-19, 1952

ZK = 8-

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1-2

Sterling-St. Louis

Sequences Shoving Development of the F Layers

After Sunrise

April 2k, 1952

The Fl trace is seen to develop out of the low angle F2

trace and the night F layer is continuous with the day F2 layer.

May 15, 1952

Here the F2-layer trace develops out of the Pedersen ray

trace of the night F layer. The night F layer is continuous with

the day Fl layer.
APRIL 24, 1952

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Sterling-St. Louis

Ionograms Showing Spread Echo

May 1, 1952

The midpoint vertical- incidence record is not only spread

but weak, indicating high absorption. The oblique -incidence

record is somewhat spread but appears to be relatively strong.

May 29, 1952

On these records spread echoes are evident at vertical

incidence but the oblique- incidence traces are relatively sharp.

May 29, 1952

Moderate spread on the oblique- incidence records accompanies

severe spread seen at vertical incidence.

The great amount of spread apparent on the midpoint verticalincidence ionograms represents a complicated ionospheric structure

which shows itself in the complex traces seen on the obliqueincidence ionograms.

July 25, October 21, 1952

The July 25 ionograms show more spread at oblique incidence

than at vertical incidence; the October 21 records show comparable

spread

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Ionograms Showing MUF Extensions

September 11, 1952 j October 3, September 3, 1951; September 12,

July 18, September 26, 1952

Note the following:

(1) The echoes at frequencies above that which the highangle and low-angle rays merge. This has been named

the MUF extension.

(2) On July 18, September 12 and September 26, it is

difficult to separate the 2 -hop E echo from the 1-hop

Fl echo.

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perhaps because of the presence of the underlying Fl

layer

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Sterling-St. Louis

Ionograms Showing Effects of Equipment

Sensitivity

May 28, July l8, September 5, 1952

(1) Note in the May 28 records the relative strength

of the high-angle Fl ray.

(2) In the ionograms for July 18 the number of multiples

is markedly reduced as the gain is reduced.

(3) In the September 5 records the disappearance of the

Es trace is to he noted.
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Sterling-St. Louis

Ionograms Showing Relative Importance of High-Angle Ray

May Ik, 1952

The one-hop low-angle ray is cut off by sporadic E which

is evident on the oblique-incidence record (19*1-5) but not on

the vertical- incidence ionogram (19^-2). The high-angle ray may,

therefore, be relatively important (note the presence of M and

N-type echoes).

May 15, 1952

Here again the low-angle ray has been cut off by intense

sporadic E.

October 3j November 18, December 2, 1952

The high-angle ray here is relatively unimportant. This is

especially typical of winter day conditions.

February 13, July 17, August 28, September 11, 1952

An example showing the relatively rare high-angle E-layer ray.
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1-7

Sterling- St. Louis

Ionograms Showing Sporadic E Reflections

May 15, July 17, 1952

On "both records Es extends out past 20 Mc and the record

for May 15 shows blanketing of the F-layer echoes. The record

for July 17 gives an example of complex echo structure.
MAY 15, 1952

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Sterling- St. Louis

Sequences Showing Moving Irregularities

April 30, 1952

Moving irregularity seen on oblique-incidence ionograms

not apparent on the vertical- incidence records.

May 28, 1952

Apparent downward motion of irregularity indicated.
APRIL 30, 1952

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1-9

Sterling- St. Louis

Ionograms Showing Unusual and Complex Traces

February 6, March 19, December 3, 1952

Apparent stratifications and complex traces.

May 22, 1952

Here the complexities show up in the 2-hop echo trace.

August 8, May 8, 1952

The Pedersen ray ordinary and extraordinary traces are differently shaped.
FEBRUARY 6, 1952 MARCH 19, 1952

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MARCH 19, 1952 DECEMBER 3, 1952

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II. Sterling-Boulder - 2370 km

(Routine

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II-l

Sterl ing-Boulder

(Routine)

Sequences Showing Diurnal Variation

Winter DayFebruary 3-k , 195^

XK = 18-

P

Winter Day

February 10-11, 1951*- ZK = 18+

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Equinoctial Day

March 31-Aprll 1, 195^

ZK = 15-

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Summer Day

May 11-12, 195*4- ZK = 15-

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August k-5, 1951*-

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Sterling-Boulder

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Sequences Showing Morning Bifurcation of the F layer

April 1, 195*4-

"Splitting at the bottom" : Fl layer develops under

the nighttime F layer.

August 11, 1951*-

Continuity "between nighttime F layer and daytime Fl layer.

April 1^, 195^

"Splitting at the top": Nighttime F layer is continuous

with the daytime Fl layer.
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0810 0834
II-3

Sterling-Boulder

(Routine)

Miscellaneous Sequences

November 5, 1953

Oblique -incidence records showing development of apparent

stratifications, possibly produced by "off-path" reflections.

Some ionospheric roughness indicated by slight spread and presence

of Z- trace on vertical- incidence records.

November 12, 195

3

Complexities in oblique -incidence records, perhaps associated

with "oblique" reflection and forked trace evident on the midpoint

vertical- incidence ionograms shown.

June 23, 195^

Sporadic E reflections out to 2k- Mc; pronounced MUF extension.

July 21, 195^

Complex nose structure; Es reflections.

August 25, 195^

Es evident from traces between those for 1XF and 2XF. Complex

nose structure.

November 12, 1953

Apparent stratification and inner "nose". (See footnote in

Section III-3)
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NOVEMBER 12, 1953

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Sterling-Boulder

(Routine

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Miscellaneous Ionograms

January 7, 195^

Five F-layer modes present

July 22 , 1954

The record indicates the difficulty encountered in specifying exactly the Fl MUF for this path.

August 25, 195^

E2, Fl, and F2 traces evident.

April 5, 1955

The Pedersen ray gives a clear indication of the increase in

0-X frequency separation as the angle of incidence increases.
JANUARY 7, 1954

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5 0934

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AUGUST 25, 1954

1059

APRIL 5. 1955

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III. Sterling-Boulder - 2370 km

(Experimental

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(All ionograms with expanded frequency scales

were made using 20 \ib pulses)

III-1A

Sterling-Boulder

(Exper imental

)

June 28-29, I958 Magnetic Storm

Ionogram Series from Quiet Day before Storm

to Quiet Day after Storm

Date

6/27/59

6/28/59

6/29/59

Midpoint

Time K

P

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1059 1+

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1959 2+

2259 3+

0159 I4.0 CA59 k0759 3o

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2259 80

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01*29 70

Date

6/29/59

6/30/59

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Detailed Sequence During Magnetic Storm

June 28-29, 1958
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III-2

Sterling-Boulder

(Exper imental

)

Morning and Afternoon Sequences

June 20, 1958

Unusual morning sequence showing the development of an Fl layer and then an F2 layer.

June 9r 1958

Normal afternoon sequence. The trace of a possible offpath signal may be seen from l8l3 to I835 GST.

August 6, 1958

Normal afternoon sequence. A disturbance in the F2 layer

can be seen on the oblique- and vertical- incidence ionograms at

lK5k CST.
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CARTHAGE AUGUST 6,1957

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III-3

Sterling-Boulder

(Experimental

)

"inner"* and "Outer" Nose

August 9, 1957

August 23, 1957

Sequences showing development of "inner" nose on obliqueincidence ionograms and simultaneous midpoint vertical- incidence

disturbances.

June 19, 1958

Sequence showing development of "outer" nose on obliqueincidence ionograms and blanketing by Es on end-point verticalincidence ionograms.

Occasionally, as shown in the following records, in addition

to the well defined "nose" representing the classical F2 MUF,

a second nose appears at frequencies below (or above) the

classical MQF. The additional nose, for the sake of brevity,

is referred to as an "inner" (or "outer") nose.
STERLING

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Sterling-Boulder

(Experimental

)

"Disturbed F2 Nose"

April 30, 1957

Some spread can be seen on midpoint vertical- incidence

ionograms at time of "disturbed nose" on oblique- incidence

ionograms

.

April 20, 1958

May 12, 1958

Sequences of "disturbed-nose" oblique- incidence ionograms,

June 2k, 1958

Spread nose on oblique- incidence ionogram and spread F on end-point vertical- incidence ionograms.
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WASHINGTON

0210

BOULDER

0330

III-5

Sterling-Boulder

(Experimental

)

Disturbed Conditions

February 5, 1957

Sequence showing traveling disturbance in oblique- and

vertical- incidence ionograms.

June 9, 1958

Disturbed oblique -incidence and vertical- incidence night

ionograms. Kp remained between 5+ and 5- • (See also the June 9*

1958 example of Morning and Afternoon Sequences in Section III-2)
CARTHAGE FEBRUARY 5, 1957

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III-6

Sterling-Boulder

(Experimental

)

Earely Observed Ionograms

May 5, 1958

The appearance of the extraordinary component as a nose

extension.

April 9, 1957

The rounded F2 nose may be attributed to the similarity

between the vertical- incidence ionogram and the transmission

curve.

August 2, 1956

August 30, 1957

The high-angle ray of the E mode is seldom seen on the

2^00 km path.
MAY 5, 1958

«AMiAl llll I* I
BOULDER APRIL 9, 1957

2109

OBLIQUE

CARTHAGE

!00 Km

2109

VERTICAL
BOULDER AUGUST 2,1956

100 Km

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III-7

Sterling-Boulder

(Exper imental

)

Equipment Effects

The June 2k, 1958, 0659 and O707 CST ionograms were

received using 100 and 20 \is transmitted pulses respectively.

The June 26, 1958, ±9kk CST ionogram was received with every

10th transmitter pulse changed to 100 or 20 u.s. The loss of

detail with the longer pulse can be seen.

The top records on August 1, 1958 are those ordinarily

received. The bottom records were taken simultaneously with

large differentiation in the receiving system.

The I323 CST ionogram of July 23, 1957 illustrates the

effect of transmitter double pulsing. The parallel traces on the March 12, 1957 an<i April 23, 1957 ionograms may also be

attributed to a deformed transmitter pulse.
BOULDER JUNE 24, 1958

0659

0707

JUNE 26, 1958

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III-8

Sterling-Boulder

(Experimental

)

Fixed Frequency vs. Sweep Frequency

May 7, 1958

The first ionogram shows the pulse received on 20.08^1 Mc,

from 1920 to 2100 CST. The following sweep-frequency ionograms

were obtained during the same period. Both transmitters used a

25 us pulse at a 25 pps repetition rate. The output of the

fixed-frequency transmitter was about 200 kw.

The hesitation of the F2 MUF at about 20 Mc appears as a nose extension on the fixed-frequency record.
BOULDER MAY 7, 1958

1930 20.084 Mc

2000 CST

2030 2100

1941

Iiwt25 1956

2011
BOULDER MAY 7,1958

2026

2041

2056

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III-9

Sterling-Boulder

(Experimental

)

A Sequence of A- scan Records Shoving Field Strength

Variations Near the MUF

In addition to the time-delay studies, some attention

has been given to received field strengths. Here is shown a series of A-scan records made at Boulder and the corresponding

oblique-incidence ionograms. The frequency at which the

A-scan records were made increases upward in each column and

from left to right. These were made at the rate of 2.\ per

second (or every . 025 Mc ) . On each record, time delay

increases toward the right. The pulse amplitudes — the scale

is approximately linear — vary somewhat due to normal fading.

At frequencies greater than 1^.8 Mc (near the top of the

first column) the Pedersen ray first makes its appearance. At

about 15.1 Mc (at the top of the second column) it shows two

component pulses, the ordinary and the extraordinary modes. At

about 15.3 Mc (near the top of the third column) similar slight

separation of the and X modes in the low-angle ray can be

seen. Following the progression upward in the fourth column,

as the low-angle and high-angle rays begin to overlap (just

above 15.^- Mc) the pulse structure becomes complex; at 15-V75

Mc the ordinary rays have combined and at 15^55 Mc only the

extraordinary ray pulses are left. These have combined at about

15.625 Mc and have disappeared at 15-7 Mc.
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.i , —g- i ...

fi> Hjvd snons

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Asiin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington. D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front

cover. WASHINGTON, D.C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Photographic Technology. Length. Engineering

Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Poly- mer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Physics.

Mineral Products.

crostructure.

Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Mi

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and W all Coverings. Codes and Safety Standards. Heat Transfer. Concreting Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earth Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engineering. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High Frequency Impedance Standards. Electronic Calibration Center. Microwaye Physics. Microwave Circuit Standards.

Radio Communication and Systems. Loyv Frequency and Very Low- Frequency Research. High fre- quency and Very High Frequency Research. Ultra High Frequency and Super High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis. Field Operations.