Ml Bureau of Standards

library, N.W. Bldg

APR 4 1961

ZDoulder laboratories

PB161589

^o. 88

PROLONGED SPACE-WAVE FADEOUTS

IN TROPOSPHERIC PROPAGATION

BY

A. P. BARSIS AND MARY ELLEN JOHNSON

U. S. DEPARTMENT OF COMMERCE

NATIONAL 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 services 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 pro\ ides

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 ^tote

88

February 8, 1961

PROLONGED SPACE-WAVE FADEOUTS

IN TROPOSPHERIC PROPAGATION

by

A. P. Barsis and Mary Ellen Johnson

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 $2.00

TABLE OF CONTENTS

Page No.

Abstract

1. Introduction

2. Eastern Colorado Data

2. 1 General

2.2 Continuous Recordings 1952-1953

2. 3 Vertical Diversity Studies

3. Southern California Data (Navy Electronics Laboratory)

4. Southern California Data (Point Mugu)

4. 1 General

4. 2 Classification of Refractive Index Profiles

4. 3 Dependence of Fadeout Characteristics on

Profile Types 19

4.4 Dependence of Fadeout Characteristics on

Carrier Frequency and Grazing Angle 23

5. Fadeouts on a Knife-Edge Diffraction Path 29

6. Comparison of the Results for the Various Paths and

Conclusions 34

7. Acknowledgements 38

8. References 39

1

5

56

8

12

14

14

15
ABSTRACT

This paper contains the results of studies performed during the

last several years on the short-term variability of tropospheric signals

received over within- the-horizon paths. Signal variations of this type

have been termed "prolonged space-wave fadeouts, " as they are mainly

characterized by reductions in signal level to many decibels below presumably constant values determined from geometrical optics methods.

The data described here were obtained from measurements over propagation paths in the Pacific Coast region of Southern California, and the

continental region of Eastern Colorado. Fadeouts are analyzed as a

function of carrier frequency, path characteristics, and meteorological

parameters. The study also includes an evaluation of fadeouts observed

over a path using a mountain peak as a diffracting knife-edge like obstacle

between transmitter and receiver.
PROLONGED SPACE-WAVE FADEOUTS

IN TROPOSPHERIC PROPAGATION

by

A. P. Barsis and M. E. Johnson

1. INTRODUCTION

The short-term variability of long-distance beyond-the-horizon

signals in the very-high and ultra-high frequency bands can easily be

described statistically. It has been postulated by scattering theories

and verified experimentally that the short-term variations of such signals

are Rayleigh-distributed. Short-term as used here means periods of

up to one hour. However, this relatively simple statistical description

does not apply to within-the-horizon, or diffraction paths. Inspection

of field strength recordings shows that short-term signal variations

over such paths consist of "fadeouts, " i.e. reductions in signal level

to values below a long-term average or median, which may last from

minutes to a good part of the hour. The term "space-wave fadeout" was

chosen because the phonomenon was first observed over within-thehorizon paths at ultra-high frequencies, where the space-wave (presumably constant for a standard atmosphere) is the principal mode of propagation.

A description and evaluation of the initial National Bureau of

Standards fadeout studies is given in a paper by Bean [ 1954], where a relation between the occurrence of ground based layers and fadeouts

was first extablished. Recently the same phenomenon was observed

over a "knife-edge diffraction" path, which uses a mountain as the

diffracting obstacle between the path terminals.
-2-

The following data are included in this study:

1. Data obtained over the 113 km path in Eastern Colorado

which already have been discussed by Bean in his

original paper [1954], The experiments were performed

by the National Bureau of Standards in 1952 and 1953,

using a frequency of 1046 Mc. The path profile is

shown in Fig. 1.

2. Data obtained from the Navy Electronics Laboratory.

The experiments were performed over a 185 km path

in Southern California during 1950 and 1951, using

frequencies of 138 and 12 50 Mc. The path profile is

shown in Fig. 2.

3. Data obtained from a joint program by the National

Bureau of Standards and the Naval Air Missile Test

Center (Pt. Mugu, California). A 104 km over-water

path in Southern California was used during the period

November 1955 to July 1959, with frequencies in the

100, 250, and 400 Mc range. The path profile is shown

in Fig. 3. Some results have been presented in an

earlier paper by Barsis and Capps [1957] .

4. Data obtained from a 223 km path in Colorado, using

Pikes Peak as a diffracting knife-edge. The experiments were performed by the National Bureau of

Standards in 1959 and I960, using a frequency of 751 Mc.

The path profile is shown in Fig. 4.

Pertinent data for all paths are shown on Table I, below. They

include the terminal elevation, grazing angles, and other characteristics.

The grazing angles are given for an effective earth radius of 9000 km.

This value corresponds approximately to the 4/3 effective earth radius
-3-

factor commonly used. For the exponential model of atmospheric radio

refractivity [Bean and Thayer, 1959a], the corresponding value of

surface refractivity is approximately 316 N-units.

TABLE I Characteristics of Paths Used for Fadeout Studies

Grazing Angle

Length Terminal Heights, Meters for N = 316

Path km above ground above m. s. 1. milliradians

Cheyenne Mountain 113 * 2670 3. 6, 3. 7 &4.

- Karval 1.5, 4.3 & 13 1545, 1547 &

1555

Mt. Wilson 185

- Pt. Loma

San Nicolas Island 104

- Laguna Peak

Beulah 223

- Table Mesa

* 1712 3.8

* 30

6 264 2.0 &3.6

* 2 54&427

7 1912 4292m**

8&15 1674&1681

* Not pertinent, because on mountain top or above steep slope. ** Height of obstacle above mean sea level.

Carrier Frequency Period of

Path Used, Mc Polarization Operation

Cheyenne Mountain 1046 Horizontal 1952-53

- Karval

Mt. Wilson 138, 1250 Not known 1950-51

- Pt. Loma

San Nicolas Island 98.6, 100, 244 Vertical 1955-59

- Laguna Peak 249, 394

Beulah 751 Horizontal 1959-60

- Table Mesa
-4-

In order to provide a unique definition for the phenomenon to be

studied, it is necessary to emphasize the distinction between the term

"fading" as commonly employed, and the term "prolonged space -wave

fadeout" as used here. "Fading" usually refers to the rapid amplitude

variations of a radio signal transmitted over relatively long distances

through the troposphere or the ionosphere. In the case of long-distance

tropospheric scatter propagation, the rapid fading is presumably caused

by the vector addition of a large number of field components arriving at

the receiving location with random phase. The amplitude distribution

of such a signal tends to have the form of a Rayleigh distribution, and

the fading rate with reference to a short-term average or median value

varies with carrier frequency, atmospheric conditions, and path length

approximately within the limits of 0. 1 to 10 cycles per second.

The term "prolonged space-wave fadeout, " however, is restricted to paths where the geometric-optics space-wave is predominant

and to knife-edge diffraction paths. The fading rate here is extremely

slow, and the amplitude distribution of the received signal cannot be

represented by a Rayleigh, or any other simple distribution function.

Fadeouts of this type may be caused by vector addition of a few specular

components caused by reflection from layers, or similar phenomena,

and tend to shift with the variable refractive index structure of the lower

atmosphere, thus causing the variations in signal level. Possible small

contributions to the received field due to scatter are neglected in this

analysis. Fig. 5 shows a typical space-wave fadeout. The depth D of

the fadeout is measured with reference to an arbitrary signal level,

which may be an hourly median value, or a long-term median of hourly

median values. The same reference level is R decibels above the RMS

receiver noise level. The quantity

RD

= R - D (1)
-5-

is then the instantaneous carrier envelope signal to RMS noise ratio,

and can be used to calculate quantities like teleprinter error rate for

signals of this character.

The definition of space-wave fadeouts was restricted to those

fadeouts which extend to at least 5 decibels below the reference level.

In earlier analyses (Cheyenne Mountain - Karval, Mt. Wilson - Point

Loraa, and some of the Point Mugu data) fadeouts of a duration less

than one minute at the 5 db level were neglected due to the time- scale

of the records analyzed. This restriction was removed in later

analyses, where it was possible to measure fadeouts of shorter durations.

Fadeout statistics to be discussed in this paper include the fadeout incidence, which is the number of fadeouts observed in a given time

period, the diurnal and seasonal variation in fadeout incidence and

other characteristics, and the distribution of fadeout durations at various

levels. In all cases, distributions of fadeout durations were obtained by

setting up convenient time intervals (like 1-2 minutes, 2-3 minutes, etc.),

counting the number of fadeouts whose duration fell into each interval,

and calculating a cumulative distribution in percent of the total number

of fadeouts. For the Pt. Mugu data, extensive meteorological observations are available, which permit an analysis of fadeout characteristics

as functions of meteorological parameters. In most cases a comparison

of fadeout characteristics for various values of carrier frequency is

also included.

2. EASTERN COLORADO DATA

2. 1 General

Description of the tropospheric propagation paths extending eastward from Cheyenne Mountain is contained in a National Bureau of

Standards Circular [Barsis, et al, 1955] . Of the paths investigated,
the one to Karval was used for fadeout studies on 1046 Mc. The path

length is 113 kilometers and the path profile is shown on Fig. 1. Results

obtained in 1952 have already been reported by Bean [1954] . From his

analysis of fadeout dependence on meteorological characteristics he

concluded that fadeouts were more likely when a ground-modified refractive index profile was observed, than for a well-mixed atmosphere

with a linear profile.

Additional data were obtained during 1953, including simultaneous

measurements at Karval in December using three dipole antennas at

1. 5, 4. 3 and 13 meters above ground. This corresponds to spacings up

to approximately 30 wavelengths. Fig. 6 shows a sample of recording

charts for the three antenna heights at the time of a fadeout. It appears

that the fadeout characteristics are extremely well correlated in time.

The "transmitter-off" period in the record serves to emphasize the

time correlation of the fadeouts. The small, more rapid signal variations superimposed on the recording traces are probably due to a scatter component, and are not considered in the analvsis.

2.2 Continuous Recordings 1952-1953

An antenna 13 meters above ground was used for continuous recordings during both years. Fig. 7 shows the fadeout incidence (number

of occurrences of fadeouts) as a function of the time of the day for all

data and for both years. The values shown refer to the 5 db fadeouts,

and the abscissa scale is normalized to take into account times of

equipment outage. A very definite diurnal trend is evident: fadeouts

are much more numerous during the night and early morning hours.

The minimum number of fadeouts was observed around noon and in the

early afternoon. The possible cause for this diurnal behavior and the
correlation of fadeouts with ground modifications of the refractive index

profile has been discussed by Bean [1954] . An interesting example of this correlation is shown on Fig. 8.

Here, the refractivity profiles observed in the same area have been

plotted versus the time of the day together with the observed fadeout

incidence. The data shown are for December 13, 1953. Refractivity

profiles were obtained along the 500-ft tower at Haswell, some 38 km

to the southeast of the Karval site. For this day, fadeouts were observed

only during the early morning hours, when the refractivity profile showed

a marked ground modification. Coincidentally, the surface refractivity

during these hours was near its daily minimum, as also shown on Fig. 8.

Seasonal variations of fadeout incidence at Karval are shown on

Figs. 9 and 10. Fig. 9 is a bar graph similar to Fig. 7, but showing

the normalized 5 db fadeout incidence for the months from February

1952 to August 19 53. Fig. 10 shows the seasonal variations of total

fadeout time at the 5 db and 10 db levels relative to the monthly transmission loss median for the same time period. This is the total time

per month during which the signal remained at or below these levels,

expressed as a fraction of the total recording time. Both graphs demonstrate that fadeouts are much more numerous in summer than in winter,

as the summer maximum exists for both years.

Thus the results of the diurnal and seasonal variation analysis

shows that for the relatively dry continental climate of Eastern Colorado,

fadeouts tend to be more numerous in summer than in winter, and more

numerous at night time than during daylight hours.

A somewhat different analysis of fadeout characteristics for this

path is presented in the next two figures. Fig. 11 shows the cumulative

distribution of fadeout durations at three levels with reference to the

monthly median. Data for the entire period of recording during 1952
-8-

and 1953 were included in this study. From Fig. 11 it is seen that the

median fadeout duration is 6. 2 minutes at the 5 db level, 5. minutes

at the 10 db level, and 3. 1 minutes at the 1 5 db level below the monthlymedian transmission loss value. It also is seen, as an example, that

2% of all 10 db fadeouts are at least one hour (60 minutes) long. The

importance of such statistics in the design of communication, navigation,

or positioning systems is evident.

The data from Fig. 11 are replotted in a different fashion on

Fig. 12. Here each curve represents a fixed percentage of all fadeouts

observed, and thus shows the level distribution during individual fadeouts. The 50% curve on Fig. 12, as an example, represents the distributions of levels for the "median" fadeout. These curves have been

extrapolated in order to obtain estimates for the duration of deep fades

in excess of 15 db. The graph shows, as an example, that almost all

fadeouts (as represented by the curve labelled 99%) have a duration of

0. 43 minutes at a level of 2 5 db below the monthly median.

Curves of this type (Fig. 12) will be used for system performance

calculations in a companion paper.

2. 3 Vertical Diversity Studies

As mentioned above, simultaneous measurements using three

receiving antenna heights were made at Karval during December, 1953.

The receiving antennas were at 1. 5, 4. 3, and 14 meters above ground,

and were connected to separate 1046 Mc receivers and recorders.

During this period a total number of 322 hours were recorded simultaneously on all three receivers. The following table summarizes the

5 db and 10 db fadeout statistics for these hours.
-CI- TABLE II

Fadeout Statistics, Eastern Colorado Path

1046 Mc, December 1953

Fadeout Incidence

5 db 10 db

Antenna Height

above ground, meters

Total Number

of Fadeouts

Fadeouts

per hour

Total Number

of Fadeouts

Fadeouts

per hour

1.5 36 0. 112 7 0.0217

4.3 30 0.093 5 0.0155

14.0 75 0.233 14 0.0435

It is seen that there are about twice as many fadeouts on the

higher antenna than on the lower ones. For the purpose of estimating

the effectiveness of vertical diversity, a study was made of the number

of instances when 5 db and 10 db fadeouts occurred simultaneously on

pairs of antennas or on all three of them. Simultaneous fadeouts mean

that any portion of the fadeouts observed on the antennas considered

coincided in time. Results are given in Table III, below.

TABLE III

Statistics of Simultaneous Fadeouts for December 1953

Number of Fadeouts Observed Simultaneously

Antenna Combinations 5 db 10 db

1. 5 and 4. 3 m

1. 5 and 14 m

4. 3 and 14 m

all antennas

25 5

27 6

24 5

19 5
-10-

The numbers in Table III may be expressed as percentages of

the total number of fadeouts observed on either one of the pair or triplet

compared. This is done in Table IV S which follows. Here the designations "higher, " "middle, " and "lower" refer to the comparison of the

combinations listed in the first column.

TABLE IV

Percentages of Fadeouts Observed Simultaneously

on Two or More Antennas

Percentages of Total Number of Fadeouts

Observed on Antenna

Antenna Combinations Higher Middle Lower

5 db Fadeouts

69.4

36.0

32.0

63.3 52.8

10 db Fadeouts

1. 5 and 4. 3 m 83. 3

1. 5 and 14 m 75.0

4. 3 and 14 m 80.0

all antennas 25. 3

1.5 and 4. 3 m 100.0 - 71.4

1. 5 and 14 m 42. 9 - 85. 7

4. 3 and 14 m 35.7 - 100.0

all antennas 35.7 100.0 71.4

This analysis permits at least a qualitative estimate on the

effectiveness of vertical space diversity. Table IV shows that for installations of this type there is at least a 0. 357 probability that 10 db

fadeouts occur simultaneously on three vertically spaced antennas.

There are substantially more fadeouts on a high antenna while there is
-11-

more correlation between fadeouts occuring simultaneously on the two

lower antennas.

These figures are operationally important, as a 10 db fadeout

necessitates that much margin in available transmitter power for oneway (communications) application. In a radar application, a 10 db

fadeout means a 20 db reduction in signal level, as the signal travels

both ways. A corresponding increase in transmitter power is necessary.

Although the percentage of total time or total hours during which

fadeouts occur is small, it should be kept in mind that such fadeouts

are relatively long, and may impair the usefulness of a communications

or navigation system for minutes at a time. Fig. 13 shows the cumulative distribution of the durations of 5 db and 10 db fadeouts for all

three antenna heights, using all data available for December, 1953.

(The previous comparative analysis was restricted to those hours where

data were available for all three antennas.) Table V, below, shows the

median fadeout duration, and the duration of 10% of all fadeouts, taken

from Fig. 13.

TABLE V

Fadeout Durations for December 1953

Cheyenne Mountain- Karval Path, 1046 Mc

Duration in Minutes Greater than

Median Fadeout

Antenna Height, Mete rs 5 db

10.6

10 db

1.5 3. 5

4.3 10.4 5.7

14.0 6.1 5.0

10% of all Fadeouts

5 db 10 db

39 20.5

45 18.5

60 56.0
-12-

This table shows that the median fadeout tends to be shorter for

the higher antenna, but that a small number of fadeouts observed on the

high antenna (10% of the total) tend to be quite long (about one hour).

The statement holds approximately for both levels investigated, although

the median 10 db fadeout observed on the lowest antenna is relatively

short.

Finally, Fig. 14 shows the cumulative distribution of the maximum measured depth of all fadeouts. There does not appear to be any

marked distinction between the three antenna heights.

3. SOUTHERN CALIFORNIA DATA

(NAVY ELECTRONICS LABORATORY)

The profile for this 185 km long path was shown on Fig. 2. The

terminals were located on Mt. Wilson and on Point Loma, 1712 and 30

meters above mean sea level, respectively. Data on 138 Mc and 1250

Mc, obtained by the U. S. Navy Electronics Laboratory, were made

available to the National Bureau of Standards for analysis. Several

months of continuous transmission loss measurements between May,

1950, and February, 1951, were used in this study. Fadeouts were

defined and analyzed in the same way as for the Colorado data, namely

at several levels (5, 10, and 15 db) below the monthly median of hourly

medians of basic transmission loss.

For this path, one of the more interesting results was the existence of a substantial number of fadeouts on a frequency as low as 138

Mc. This is in contrast to the data of Eastern Colorado, where very

few pronounced fadeouts were observed on frequencies around 100 and

200 Mc.
-13-

The frequency dependence of the fadeouts, and the fadeout dependence on meteorological parameters will be further discussed in

connection with the Point Mugu data. Here it should be kept in mind

that the climate for Southern California is radically different from the

one for continental areas, and may even be termed unique in the sense

that a very pronounced stratification of the refractive index structure

is almost always present.

The diurnal and seasonal variations of 5 db fadeouts for this

path are shown on Figs. 15 and 16. In contrast to the Eastern Colorado

path, fadeouts occur here around the clock, with a rather pronounced

afternoon maximum on 1250 Mc, and the suggestion of a minimum in

mid-morning. The seasonal variations as far as analyzed, are characterized by a minimum in November. Especially striking is the sharp

reduction in the number of 1250 Mc fadeouts from October to November,

1950. However, there are not enough data available to make a concise

definition of the seasonal trend.

The cumulative distribution of the durations of individual fadeouts is shown on Fig. 17 for both frequencies. It is seen from this

figure as well as from Table VI, below, that the fadeouts tend to be

longer at the lower frequency. However, the fadeout incidence (number

of fadeouts in a given time period) is greater for the higher frequency,

as shown on Fig. 16. The distributions have been replotted for both

frequencies on Fig. 18 similar to the representation shown on Fig. 12

for the Cheyenne Mountain- Karval path.

Table VI, below, summarizes some of the results of the analysis

of the N. E.L. data. No correlation studies between fadeout occurrence

on the two frequencies were performed. A comparison of fadeout characteristics for the Colorado and the California paths will be presented

in a later section of this paper.
-14-

TABLE VI

Fadeout Durations for N. E.L. Path, Southern California

Fadeout Durations in Minutes (greater than)

138 Mc 1250 Mc

for median fadeout

to 5 db 6.6 2.6

to 10 db 5.7 1.7

to 1 5 db 3.9 1. 1

for 10% of all fadeouts

to 5 db 39. 1 10.0

to 10 db 37. 1 7. 1

to 15 db 18.8 4.2

4. SOUTHERN CALIFORNIA DATA (POINT MUGU)

4. 1 General

The joint propagation study conducted by the Naval Air Missile

Test Center, Point Mugu, California, and the National Bureau of

Standards was originally designed to compare within-the-horizon and

beyond-the-horizon over water paths of approximately the same length.

Meteorological data to support the transmission loss measurements

were supplied by the U. S. Naval Air Station at Point Mugu. The profiles for the within-the-horizon paths are shown on Fig. 3.

Important results of this program have been reported previously

by Bar sis and Capps [1957] . Additional data evaluated since are presented here. The following data form the basis for a study of spacewave fadeouts, and their dependence on path and meteorological

parameters.
-15-

(a) Evaluation of two years radio data on 394 Mc, including

correlation of the observed fadeout phenomena with

refractive index profile types.

(b) Comparison of fadeout data on the three frequencies

(approximately 100, 2 50, and 400 Mc) for typical winter

and summer months.

(c) Comparison of fadeout data for two widely spaced (vertically) receiving sites within the radio horizon.

4. 2 Classification of Refractive Index Profiles

It will be appropriate to discuss first the evaluation of the meteorological data, and the classification of the refractive index profiles.

The data supplied by the Point Mugu Naval Air Station included pseudoadiabatic charts from radiosonde ascents at San Nicolas Island and at

Point Mugu, and surface observations of temperature, barometric

pressure, and relative humidity. From these data the refractivity as

a function of height was computed and plotted in the form of curves of a modified refractive index as a function of height defined by Bean, et

al [1959b] . Values of the surface refractivity were determined as well.

The modified refractive index A(h) at a height h above the surface

is given by

A(h) = N(h) + 313 [1 - exp(-0. I44h)] (2)

where N(h) is the refractivity at the height h above the surface (in kilometers). The constants used in this formula are derived from observations within the United States, as explained by Bean, et al [1959b]. The

"standard exponential atmosphere" would be a vertical straight line,

if plotted in terms of A- units.
-16-

This representation has been used in order to make the distinction between various types of refractive index profiles more evident.

Previous radio meteorological studies have shown that within the Pacific

Coast region refractive index profiles characterized by a constant

gradient are much less frequent than the occurrence of either elevated

or ground-based layers. Consequently, the calculation of transmission

loss as a function of refractive index gradient is not often expected to

give results comparable to the measured values. Actual transmission

loss calculations taking into account existing layers may be performed

by analytical or by ray-tracing methods as suggested by Doherty [1952].

However, the procedure tends to become quite involved. It has been

found more convenient to investigate the transmission loss and other

characteristics of the received field empirically as a function of various

properties of the refractive index profiles. The first step in an analysis

of this kind is to define characteristic parameters of the refractive

index profiles, and to classify the profiles into easily recognizable

types.

Fig. 19 illustrates the five basic profile types used, plotted as

A-curves. Classification is made in accordance with the height above

ground h of the base of the lowest super-refractive layer, the thickness

h of the layer, the refractive index gradient AN, existing below the

layer, and the refractive index gradient AN, within the layer. A superrefractive layer is somewhat arbitrarily defined to exist if its refractive

index gradient is greater than 60 N-units per kilometer.* The classifications shown on Fig. 19 are tabulated and explained below:

* In this and the following analyses the expressions "greater than, " "less

than, " "in excess of, " ect. , are based on the use of absolute values of

refractive index gradients. It is understood that refractivity generally

decreases with height, and that the refractive index gradient is almost

always negative.
17-

Type of Profile

Linear

High Elevated HE

Layer

Medium Ele- ME

vated Layer

Low Elevated LE

Layer

Ground Based GB

Layer

Refractive index gradient less than 60 Nunits per kilometer for the entire profile.

Base of layer higher than one kilometer

above the surface with AN, less than, and

AN? in excess of 60 N-units per kilometer.

Like HE, but base of layer between 0. 5

kilometers and 1.0 kilometer above the

surface.

Like HE, but base of layer less than 0. 5

kilometers above the surface.

Surface based layer, with AN in excess of

60 N-units per kilometer.

As an illustration of the effect of the refractive index profiles

on the character of the received signal, consider Fig. 20, which contains two chart samples of the Laguna Peak record representing the

within-the-horizon path. The upper record, taken at a time when a

linear refractive index was observed at Pt. Mugu, shows a virtually

constant signal over a period of several hours. The lower record corresponds to a time when ground-based layers were observed at Pt.

Mugu, and shows very substantial space -wave fadeouts.

Table VII, below, shows the relative frequency of occurrence

of the various profile types at both sounding locations during the period

November 1955 to October 1957. It is not possible to distinguish between

"ground-based" (GB) and "low elevated" (LE) layers for profiles observed

at San Nicolas Island, as the radiosonde measurements were conducted

from an airstrip located about 170 meters above sea level, but close

enough to the coast so that sea level is the actual reference.

i
-18-

TABLE VII

Occurrence of Various Profile Types

November 1955 to October 1957

Number of Times Percentage of Total

Profile Type &

lumber

Observed Obse rvations

Total IS Pt,. Mugu San Nicolas Pt. Mugu Sian Nicolas

Observed Island Island

L 93 66 27 21.9 7.5

HE 55 28 27 9.3 7. 5

ME - 117 62 55 20.6 15. 3

LE1 . GB [ 395

52

93 [-2 50

17. 3

30.9 1

» 69.7

Totals:

660 301 359

It is quite evident that profiles characterized by layers below

1000 meters predominate. More than half of all observations indicate

layers below the 500-meter level. Both path terminals for the propagation studies were located below this elevation. The effect of the layer

height on the propagation characteristics will be discussed below. In

this study, profiles observed at both sounding locations will be used.

Of all observations there were only 96 radiosonde ascents taken approximately simultaneously at both locations (within about one and one-half

hours). 62 profiles out of these 96, or somewhat more than one-half,

showed the same profile type in accordance with the classification used.

Although this conclusion does not fully support the assumption of complete equivalence of the profiles obtained at the two locations, it does

not preclude the use of all profiles regardless of their origin for

further analysis.
-19-

4. 3 Dependence of Fadeout Characteristics on Profile Types

For this study, the 394 Mc data for the path San Nicolas Island - Laguna Peak Summit were used (see Fig. 3), covering the period

November 1955 to October 1957. Within this period approximately

14, 000 hours of good data were obtained. However, in the study of

fadeout dependence on refractive index profile types, only those data

were used which fell within the three-hour period centered on the time

of the radiosonde ascent. Soundings were usually taken around 8 a. m.

local time; in some instances additional soundings were taken between

noon and 4 p. m.

In this analysis a fadeout was defined as a reduction in signal

level to at least five or ten decibels below the monthly median lasting

at least one minute. The terms "fadeout incidence" and "fadeout time"

are used. Fadeout incidence is the number of times fadeouts are

observed concurrently with a specific type of refractive index profile,

expressed in percent. Fadeout time is the total time the signal re- mained at least 5 or 10 db below the monthly median. It is also expressed

in percent relative to the three-hour period centered on the radiosonde

ascent. As an example, 32. 3% 5 db fadeout incidence for linear profiles

means that out of the total number of linear refractive index profiles

observed, 32. 3% have one or more prolonged 5 db space-wave fadeouts

associated with them which occurred within the three-hour period centered

on the meteorological observation. As an example of 5 db fadeout time,

19.9% for ground-based layers means that during 19.9% of three hour

time interval centered on the meteorological observation (35.8 minutes)

the signal remained at least 5 db below the monthly median. Results of

the analysis are given in Table VIII, below.
-20-

TABLE VIII

Fadeout Characteristics Versus Refractive Index Profile Types

San Nicolas Island to Laguna Peak (Summit)

394 Mc, November 1955 to October 1957

Percentage of Percentage of

Total Number of Fadeout Incidence Fadeout Time

Profile Type Ob served Profiles 5 db 10 db 5 db 10 db

Linear (L) 93 32. 3 18. 3 10. 7 2.7

High Elevated

Layer (HE) 55 16.4 7. 3 5.3 1.4

Medium Elevated

Layer (ME) 117 30. 1 18.8 6.9 2. 3

Low Elevated

Layer (LE) 302 70.2 50.0 20.9 7.7

Ground- Based

Layer (GB) 93 66.7 51.6 19.9 8.6

L + HE 148 26.4 14.2 8.7 2.4

ME + LE + GB 512 60.6 43.2 17. 5 7.0

L + HE + ME 265 28. 3 16.2 7.9 2.4

LE + GB 395 69.4 50.4 20.6 8.3

All Profiles 660 52. 9 36.7 15. 5 5.9

It is seen that fadeout incidence and fadeout time are both functions of the profile type. Substantially more fadeouts and more fadeout

time were observed at the 5 and the 10 db level for the low elevated and

ground-based layers than for the other types. The various combinations

of profile types used in Table VIII show that the effect of medium-height

elevated layers (between 500 and 1000 meters above the surface) may

be included in either of the two groups (L and HE, or LE and GB) without any substantial change. The figures for the combination of all
-21-

profile types show that for this path the overall fadeout incidence is

36. 7%, and the overall fadeout percentage is 5. 9%, both for the

operationally important 10 db fadeouts.

Fig. 21 shows the dependence of fadeout time, as defined above

for 5 db fadeouts, on the refractive index profile parameters h , h, +h , and AN • h is the elevation of the base of the layer above the surface

(in this case, mean sea level), h + h is the elevation of the top of the

layer with h indicating the thickness of the layer, and AN- the refractive index gradient within the layer. The same data were used in' this

study, as before (for Table VIII), except that only 5 db fadeouts were

considered. The graphs were obtained by an averaging procedure

described below, resulting in mean percentage fadeout time, and the

standard deviations of the individual mean values indicated by the vertical

"wings" about the points shown.

The abscissa scale on Fig. 21(a) represents the height h of the

layer base. For the purpose of averaging, the heights h. were divided

into intervals of 0.2 kilometers up to a value of 1.4 kilometers. Values

of percentage fadeout time corresponding to each height interval were

averaged, and the resulting mean values plotted on Fig. 21(a) as ordinates at the abscissa values corresponding to the mean height within

the interval. As an example, the point plotted at h = 0.49 kilometers,

and 9.6% fadeout time is the mean value of percentage fadeout time

observed for all hours when the layer height, h , was between 0.4 and

0. 6 kilometers. To illustrate some special cases, the point plotted at

h = corresponds to the mean value of percent fadeout time for all

occurrences of a ground-based layer. The value plotted at h = 1. 82

kilometers represents the average for all layer heights in excess of

1. 4 kilometers, and the value corresponding to linear profiles is plotted

at the far right of the graph, as it may be considered a limiting value

with h approaching infinity.
-22-

In a similar way the percentage fadeout time has been plotted

versus the elevation of the top of the layer (h + h ) on Fig. 21(b).

Here the linear profile may be considered a limiting case if h + h

approaches zero as well as infinity. On this graph the subdivision of

the heights into 0.2 kilometer intervals was carried on to 2.0 kilometers,

with all greater heights lumped together to give a single average value.

On Fig. 21(c) the abscissa scale represents the refractive index

gradient &1NL within the layer. This scale was divided into intervals of

20 N-units for the averaging process. This graph does not include

values corresponding to linear profiles, because by definition of the

profile types a linear profile does not have a value of AN? associated

with it. On all graphs the vertical wings about each mean represent an

estimate of the standard deviation of the mean, which is actually the

standard deviation of the individual means about their overall mean,

The extent of the wings relative to the variations of the mean values

themselves serve as a rough estimate of the existence of a trend in the

data.

The graphs of Fig. 21 provide additional information on the dependence of fadeout time on layer characteristics, whereas the results

shown in Table VIII apply to a more general classification of the layers.

Fig. 21(a) shows quite clearly that the percentage fadeout time is greatest for ground-based and very low layers (below 200 meters above the

surface). The dependence on the height of the top of the layer shown in

Fig. 21(b) indicates maximum fadeout time for heights h. + h below

* The standard deviation of the mean, s , is obtained from the standard m

deviation s of the individual values by dividing by \l n , where n is the

number of values averaged, s therefore includes the effect of the

number of measurements in any particular group.
-23-

800 meters. Both terminals are well below this height, suggesting

that a well-defined discontinuity in the refractive index profile structure

favors the occurrence of fadeouts, if the ray paths penetrate the discontinuity. The second maximum on Fig. 21(b) appears to be less

significant due to the wide spread of the data.

Fadeout time dependence on the refractive index gradient AN

within the layer is not significant, as shown by Fig. 21(c).

Summarizing the results of this particular study, it appears

that fadeout incidence and fadeout time are strongly dependent on the

existence of refractive index profile discontinuities, and are a function

of layer height above the surface. Layers which start at elevations

substantially above the path terminals do not seem to produce as many

fadeouts as the ones which are at elevations comparable to the height

of the ray paths.

i 4. 4 Dependence of Fadeout Characteristics on Carrier

Frequency and Grazing Angle

In addition to the 394 Mc data obtained since November, 1955,

on the path San Nicolas Island - Laguna Peak Summit, some data are

available on other frequencies during two short periods. From November, 1957, until January, 1958, transmissions on 100 Mc, 244 Mc, and

the original 394 Mc frequency were recorded over the same path. From

April to the beginning of August, 1959, 98. 3, 249, and 394 Mc were

used. Furthermore, an additional receiving site, called the "Van"

location was established on Laguna Peak at an elevation of 254 meters

above mean sea level, which is still within the radio horizon of the

transmitting antenna location. This site was also in use between April

and August of 1959. A 394 Mc receiver was installed there, permitting
-24-

comparison of the signal characteristics at the same frequency, but

for different grazing angles (2.0 and 3.6 milliradians, respectively).

For all frequencies, vertical polarization with corner-reflector

antennas were used.

Very little meteorological data could be obtained for these two

recording periods, so that the evaluation of the data will be restricted

to studies of the carrier frequency and antenna height (or grazing angle)

dependence of the fadeouts without any correlation with meteorological

data.

Fadeout incidence (here the number of fadeouts in a 90-day

period) for the winter and summer measurement period mentioned

above are shown on Fig. 22 as a function of carrier frequency. For

this study, fadeouts have been defined relative to the hourly median

signal level as well as relative to the median of all hourly medians

within a month as previously used. The graphs show points for 10 and

20 db fadeouts at the three frequencies, arbitrarily connected by straight

lines. Data for the "Van" location have also been included. It is seen

that there is a strong frequency dependence, especially for the winter

period. The grazing angle dependence is more pronounced for the

fadeouts measured relative to the monthly medians, as the "Van" points

are more separated from the solid line which denotes the "Summit"

data. It should also be noted that there are more than one hundred 20

db fadeouts in a 90-day summer period on 394 Mc, which would correspond to more than one such fadeout per day if evenly distributed.

The operational importance of this frequency of occurrence cannot be

overemphasized.

Examples of the diurnal variations of the space-wave fadeouts

observed on the three frequencies are shown on Figs. 23 and 24. Here

the summer data are used (April - August, I960), and the data are
-25-

separated into four time blocks as defined by Norton, et al [1955] , corresponding to early-morning, mid-morning, afternoon, and evening

hours. On Fig. 23, the ordinate values show the number of fadeouts

per hour, and the data are grouped by frequency (for both, the "Van"

and the "Summit" locations), time blocks, and depth of fadeouts relative

to the hourly medians. It is seen that there are generally more fadeouts

at the "Summit" location (which corresponds to a larger grazing angle)

than at the "Van. " A slight diurnal trend is discernible with the fadeout

incidence greatest for the afternoon hours, except for the 5 db fadeouts,

on 394 Mc which occur most frequently in the early evening hours. A

similar trend is noted for the 249 Mc and the 100 Mc data, although

there may not be enough of the latter to draw any valid conclusions.

On Fig. 24, the ordinate is in percent fadeout time, and only

10 db fadeouts below the monthly medians are used. Percent fadeout

time is then the percentage of total time the signal remained at least

10 db below the monthly median. This percentage is also higher for

the "Summit" data than for the "Van" data. As there are also more

fadeouts at the "Summit" (see Fig. ZZ) , the duration of the individual

fadeouts may be expected to be approximately equal at both locations.

This will be further discussed below.

Fig. 24 also shows that fadeout times on 394 and 98. 3 Mc are

comparable. Referring again to Fig. 22, it is seen that there are less

fadeouts on 98. 3 Mc than on 394 Mc. This leads to the conclusion that

the individual fadeouts tend to be longer on the lower frequency. A

comparison of the N. E.L. data on 138 Mc and 12 50 Mc lead to the same

results (see Table VI in Section 3, above).

The diurnal trend of the percentage fadeout time is similar to

the trend in the number of fadeouts shown on Fig. 23. This also agrees

with the results for the N. E.L. path (see Fig. 15).
-26-

Some of the basic data used to prepare Figs. 22 and 24 are

shown in Table IX below. The table contains fadeout data with reference to the monthly medians. Data with respect to the hourly medians

were shown on Fig. 23.

TABLE IX

Fadeout Statistics for San Nicolas Island - Laguna

Peak Path, April - July, 1959, 10 db Fadeouts

Relative to Monthly Median Level

Number of Average

Total No. Fadeo uts Observed Percentage Fadeout

Frequency of Hours No rmalized Fadeout Duration,

Mc of Data

2648

Total

957

to 90 Days

781

Time Minutes

394 (Summit) 4.0 7 6.8

394 (Van) 1751 408 50 3 2.80 7.2

249 2288 256 242 3. 18 17.0

98.3 1015 108 230 4. 30 24.2

An example of a more complete analysis of fadeout duration is

shown on Fig. 25 which depicts cumulative distributions of the duration

of 10 db fadeouts for both periods relative to monthly and hourly medians,

Here the minimum measured duration of fadeouts relative to the hourly

median was approximately 0.4 minutes. The curves are labelled with

the total number of the 10 db fadeouts observed in each case, and are

coded to denote the different frequencies and paths. As an example,

the dotted curve on the lower left-hand graph for 249 Mc shows that for

the summer period 50% of all fadeouts observed on this frequency to at

least 10 db below the monthly median had a duration of 7 minutes, or longer; 10% of these fadeouts were as long as 27 minutes, and 90% of

them, 1.8 minutes.
-27-

Comparing the 50% (median) values from the lower left-hand

graph with the corresponding average fadeout duration values for the

same period from Table IX it appears that the median fadeout duration

is substantially less than the average fadeout duration. This may be

explained by the fact that there are many more relatively short fadeouts

than very long ones, and in calculations of averages the long fadeouts

have more weight. The appearance of Fig. 25 suggests a log-normal

distribution of fadeout durations, as they are plotted using a logarithmic

ordinate scale.

Comparison of the four graphs of Fig. 2 5 shows additional

results which are summarized in Table X below.

TABLE X

Median Fadeout Duration at the 10 db Level

Fadeout Duration in Minutes

Nominal Relative to WinterMonthly Median

Summer

Relative to Ho urly Median

Frequency Winter Summer

400 Mc (Summit) 5.4 3. 5 2.2 1. 70

400 Mc (Van) No Data 3.4 No Data 1.60

2 50 Mc 6.6 7.0 1.80 1.95

100 Mc 14.0 9. 1 9.0 3.0

It is seen that:

(a) Fadeouts are longer and more frequent if measured relative

to the monthly transmission loss medians than relative to the hourly

transmission loss medians. This results from the substantial variations in the hourly median levels over the period of one month.

(b) Fadeouts are generally shorter, but more frequent in summer,
-28-

(c) The frequency dependence of fadeout duration is more pronounced if fadeouts are measured relative to the monthly median than

if measured relative to the hourly median. (The 100 Mc curve on the

upper right-hand graph of Fig. 10 is based on only three data points,

and therefore may not be reliable.) On the basis of Table X, one may

also conclude that there is little frequency dependence of fadeout duration measured relative to the hourly median in the 2 50-400 Mc range,

whereas the frequency dependence in this range is much more apparent

if fadeout durations are measured relative to the monthly medians.

(d) The curves for the "Summit" and the "Van" locations, both

for 394 Mc, are almost coincident. It is concluded that no effects of

the grazing angle on fadeout duration has been found in the data analyzed

here.

Distribution curves of fadeout durations for 394 Mc have been

replotted on Fig. 26 in the same form as Figs. 12 and 18, in order to

facilitate their application to reliability studies of communication

circuits. On Fig. 26 the fadeout duration distributions are compared

for the "Summit" and the "Van" locations, with the fadeouts measured

relative to the hourly median. The median fadeouts (the curves

labelled "50%") taken from Fig. 26 have durations at the various levels as shown on Table XI, below. The values at the 10 db level do not

agree exactly with the values shown previously in Table X, because

the curves of Fig. 26 have been smoothed.
29-

TABLE XI

Duration of Median Fadeouts at Various Levels

Relative to the Hourly Median, 394 Mc

San Nicolas Island - Laguna Peak Path

Duration, Minutes

Summit

3. 5

2.

1. 4

1. 06

0. 87

0. 75

0. 66

3. 5

1. 6

0. 96

0. 65

0. 49

0. 38

0. 31

Level, db Summit Van

5

10

15

20

25

30

35

Some of the larger db values were obtained by extrapolation of

the curves. The curves on Fig. 26 and the data in Table XI show that

the fadeout durations tend to be shorter for the Van location, which

corresponds to a smaller grazing angle. This trend was not apparent

in the average fadeout duration values listed in Table DC.

5. FADEOUTS ON A KNIFE-EDGE DIFFRACTION PATH

During the past year, transmission loss measurements were

made over a 223 km path in Colorado, using continuous -wave signals

on 751 Mc. Fig. 4 shows the path profile. The top of Pikes Peak,

4292 meters above mean sea level, forms the diffracting knife-edge.

The transmitting installation is located near Beulah (southwest of

Pueblo), and the receiving installation is on Table Mesa, north of

Boulder. A complete description of the equipment used and the
-30-

measurements performed are contained in a separate paper [Barsis

and Kirby, 1961] . The data discussed here are concerned with prolonged space-wave fadeouts observed on this path on two receiving

antennas, spaced vertically by approximately 20 wavelengths.

Although this path is not "optical" (terminals within each other's

radio horizon), the fading characteristics may be compared with the

ones previously described, because the received field may be considered as the vector sum of up to four rays, each of which is modified

in magnitude and phase by the diffracting knife edge [Dickson, et al,

1953] . Fig. 27 shows a typical sample of field strength records obtained simultaneously from the two receiving antennas. The fadeouts

in this case appear to be extremely well correlated, just as in the case

of the Cheyenne Mountain - Karval path (Fig. 6). Here, too, the small,

superimposed more rapid signal variations have not been considered

in the analysis. Fig. 27 suggests that fadeout phenomena on this

obstacle gain path are similar to the ones observed on the within-thehorizon paths, and that vertical space diversity would be of little use

due to the apparent correlation of the fadeouts observed on the two

antennas.

An analysis of fadeouts was made of the data recorded using the

two spaced receiving antennas. The lower of the two was a 3 meter

(10 ft) parabolic reflector, 3 meters above ground, and the upper one

a corner reflector 15 meters above ground.* The transmitting antenna

was a 4. 5 meter (14 ft) parabolic reflector mounted 7 meters above

ground level. Horizontal polarization was used for all tests. Continuous recordings were available during 8 five-day periods between May

and September, I960.

* During two of the five-day recording periods (in June), the corner

reflector was at an elevation of 23 meters above ground. No material

difference in the characteristics of the fadeouts at the two elevations

was found.
-31-

The diurnal trend in the number of fadeouts observed at various

levels below the hourly median is shown on Fig. 28. In order to provide a better comparison of fadeout incidence for the various time

blocks, the number of fadeouts per hour is shown for each time block„

Several facts stand out in a study of this graph. First, the 5 db fadeouts are much more frequent than expected from a comparison with

the other levels, especially for the higher antenna (the corner reflector)

Then, the diurnal trend for the 5 db fadeouts is different from the

others, showing a maximum for Time Blocks 4 or 5 (0600 to 1300 and

1300 to 1800 local time). For all other levels, maximum fadeout incidence is observed during Time Block 7, the early morning hours

(midnight to 0600 local time). It is also noted that the minimum fadeout incidence is less pronounced for the 5 db level than for the other

levels. This minimum occurs in Time Block 5, the afternoon hours

(1300 to 1800 local time). There are also substantially more 5 db

fadeouts on the higher antenna during daylight hours (Time Blocks 4

and 5).

All this suggests the existence of two separate propagation

mechanisms, with one producing only 5 db fadeouts, and the other one

responsible for the deeper fadeouts. The latter mechanism might be

similar to the one responsible for the fadeouts on the within- the -horizon

paths.

The cumulative distributions of fadeout durations for this path

are shown on Fig. 29 for both antennas. Here, fadeout durations as short as 0. 1 minutes could be measured. It is quite apparent here,

especially for the corner reflector, that the 5 db fadeouts have different

characteristics than the others. The cross-over of the 5 db curve

implies again that there are many of these 5 db fadeouts which do not

extend to deeper levels, and might be due to a different phenomenon.
-32-

Table XII, below, is a tabulation of median fadeout durations taken

from Fig. 29.

TABLE XII

Median Fadeout Durations at Levels Below the Hourly Median

Colorado Obstacle Gain Path, 751 Mc, Summer I960

Level, db below Median Fadeo ut D ura.ti<Dn, Minutes

Hourly Median Corner Reflec:tor 3 Meter Dish

5 0. 72 0.66

10 0.81 0.62

15 0.66 0.44

20 0. 50 0.27

It is seen that the median fadeout at all levels is longer on the

corner reflector antenna. The different behavior of the 5 db fadeouts

is again apparent by their median duration, which is actually less for

the corner reflector than the median duration of the 10 db fadeout.

For the 3 meter dish the median durations at these two levels are

comparable.

The data from Fig. 29 have been replotted on Fig. 30 in order

to show the level distributions for individual fadeouts. This is the

same type of presentation which was used on Figs. 12, 18, and 25 for

the other paths. Due to the possibility of a different mechanism being

responsible for 5 db fadeouts, the curves were based on the 10, 15,

20, and 25 db levels read from Fig. 29, and extrapolated to lower and

higher levels. The curves shown on Fig. 30 were smoothed by the

"firm-grip-on-the-pencil" method, just as the equivalent ones for the

other paths. These types of curves, as mentioned before, will be
-33-

used as a basis for system performance or circuit reliability estimates

in a companion paper.

The effectiveness of vertical space diversity for this path may

also be evaluated by the number of fadeouts occurring simultaneously

on both antennas as a percentage of the total number of observed fadeouts. This is the same evaluation as was done for the three vertically

spaced antennas at Karval (see Section 2. 3), except that the fadeouts

were measured with respect to the hourly median over the Pikes Peak

obstacle gain path. The results are given in Table XIII, below, using

5 db and 10 db fadeouts. For this study summer data with the corner

reflector antenna at the 23 meter elevation were excluded, so that only

those data were used for which the antenna separation was 7 meters

(17.5 wavelength at 751 Mc). Fadeouts were classified as simultaneous

when any portion of them coincided in time.

TABLE XIII

Statistics of Simultaneous Fadeouts, Pikes Peak

Obstacle Gain Path, Summer I960, 751 Mc

Receiving Antenna

3-Meter Dish Corner Reflector

at 8 Meters at 15 Meters

5 db Fadeouts

Total Number Observed 464 631

Number of Simultaneous Fadeouts 175 175

Percentage of Simultaneous

Fadeouts 37.7% 25.7%

10 db Fadeouts

Total Number Observed 120 151

Number of Simultaneous Fadeouts 32 32

Percentage of Simultaneous

Fadeouts 30.0% 21.2%
-34-

The total number of fadeouts shown on Table XIII is different

from the corresponding data on Fig. 29 because of the exclusion of the

two-week period when the corner reflector antenna was at a higher

elevation. Comparison with the Karval data in Section 2. 3 shows again

a greater number of fadeouts for the higher antenna. The percentage

of simultaneous fadeouts appears to be smaller: this might be due to

the fact that it was not possible to synchronize the time scales exactly

when the recording charts were analyzed. As a great number of the

fadeouts were shorter than one minute, a small shift in the time scale

may change the apparent relative time of occurrence of some short

fadeouts. Even so, the results given in Table XIII show that there is a probability of 0.212 that 10 db fadeouts (relative to the hourly median

of transmission loss) occur simultaneously on the two spaced antennas.

This may be compared with the 0. 357 probability from Table IV, as

obtained for the Cheyenne Mountain - Karval path.

If the two-week period mentioned is included in the studies, the

fadeout percentages shown in Table XIII decrease slightly. It is difficult to say whether this constitutes a true effect of antenna height, or

is caused by the inclusion of an additional time period; height gain

effects can be properly evaluated only when simultaneous measurements

are available. The two weeks of data in question have been included in

the study of distributions of fadeout durations without any significant

change in the results, as mentioned above.

6. COMPARISON OF THE RESULTS FOR THE

VARIOUS PATHS AND CONCLUSIONS

The results discussed in Sections 2 through 5 above permit

various comparative evaluations of fadeout characteristics. The climatic

effects may be studied by comparing results obtained in Colorado with
-35-

those obtained at the Pacific Coast„ Frequency effects are available

from the Pacific Coast measurements, and space diversity studies

from the Colorado measurements. A detailed study of the effect of

refractivity profiles on fadeout characteristics was only performed

for the Point Mugu data, and has been discussed in Section 4. 3, above.

General climatic effects are summarized in the following table

by comparing diurnal and seasonal variations of the fadeout characteristics.

TABLE XIV

Comparison of Diurnal and Annual Variations

of Fadeout Characteristics

Eastern Colorado Pacific Coast

Obstacle Gain Mt. Wilson Point Mugu

Karval Path Path Path Path

Seasonal Trend

of Fadeout

Incidence

Diurnal Trend

of Fadeout

Incidence

Median Fadeout

Duration for

1000 Mc Range,

10 db Fadeouts

Summer

Maximum

Nighttime

Maximum

5. Minutes

Not Not Not

Investigated Pronounced Pronounced

Morning Afternoon Afternoon

Maximum Minimum Minimum

5. 7 Minutes

* Not investigated for fadeouts relative to the monthly median.

Outstanding effects are the very definite lack of fadeouts during

daytime hours for the Karval path, and the absence of any pronounced

seasonal variations for Pacific Coast data, as far as investigated. It

is also noted that maximum fadeout incidence for the Karval path is at
-36-

night, whereas it is shifted to the morning hours for the Pikes Peak

obstacle gain path. Median fadeout durations at 1000 Mc at the 10 db

level relative to the monthly median are comparable for both areas.

Diurnal and seasonal trends in the occurrence of fadeouts

similar to the ones observed at Karval were reported from measurements at 1300 Mc over a 82 km overland path within the radio horizon,

located in East Germany [Kuehn, 1957] . Despite the difference in the

general climatology, the low-level modifications of the refractive

index structure which are most likely to produce fadeouts appear to

have similar diurnal and seasonal trends in both regions. Knehn'

s

data, like the ones obtained at Karval, show a minimum occurrence

of fadeouts around the noon hour, strong maxima at night, and also

substantially more fadeouts during the summer months.

Almost no fadeouts at all were observed on lower frequencies

over the Colorado Paths. The frequencies used concurrently with

1046 Mc were 100 and 192. 8 Mc for Cheyenne Mountain - Karval, and

100*Mc for the Pikes Peak obstacle gain path. In contrast thereto, a

sufficient number of fadeouts for evaluation was observed on 138 Mc

for the Mt. Wilson path, and on 100 Mc for the Point Mugu path. This

again may be an indication of the radical climatic differences between

a continental and a maritime area.

The effects of vertical space diversity have been discussed for

both Colorado paths in Sections 2. 3 and 5. It appears that fadeouts are

reasonably well correlated at antenna spacings which might be practical for diversity arrangements, and thus impair the effectiveness of

vertical space diversity for line-of-sight paths as well as the obstacle

gain paths. It already has been mentioned that during two of the re- cording periods in June the vertical spacing was increased to 1 5 meters

between the two antennas. No significant change in the apparent signal

characteristics was observed.
-37-

The two antennas on Laguna Peak are too far apart to consider

such an arrangement a practical diversity system. The experiment

was designed in this case to study the effect of the grazing angle on

fadeouts. Although results are not very pronounced, there is a tendency

for more fadeouts on the summit of Laguna Peak, representing a greater

elevation and a greater grazing angle (see Fig. 22). This result is

also somewhat supported by the Colorado height-gain studies, where

substantially more fadeouts were observed at the higher antennas.

(See Table II in Section 2. 3 and Table XIII in Section 5.)

In conclusion, it is recognized that space-wave fadeouts constitute an important phenomenon in line-of- sight or related propagation

characteristics, especially on frequencies above 400 Mc . The phenomenon is observed regardless of climatic conditions, although the structure

of the refractive index profile affects its frequency of occurrence.

Space-wave fadeouts have to be taken into account in the design of

communication systems, because of the relatively long and large drops

in signal level. The studies performed so far show that vertical space

diversity is not effective in compensating for all fadeouts because of

the observed degree of correlation. Experiments on correlation using

horizontally spaced antennas or frequency diversity are yet to be

performed.

Fadeout statistics as developed in this paper will be used in a companion paper to estimate the performance of communication circuits

over paths of this nature. The analysis will be based primarily on

fadeout incidence and the distributions of fadeout durations as shown

on Figs. 12, 18, 26, and 30.
-38-

7. ACKNOWLEDGEMENTS

In dealing with an extensive measurement program of this type

it is not possible to acknowledge the contributions of individuals. Data

collection and evaluation was performed by the Cheyenne Mountain

Field Station (partially with the support of the Air Navigation Development Board), the Tropospheric Measurement Section, and the Propagation-Terrain Effects Section of the National Bureau of Standards.

We also wish to acknowledge the assistance of the Navy Electronics

Laboratory, San Diego, California, and of the Naval Air Missile Test

Center, Point Mugu, California, in obtaining data, supplying equipment, and doing analysis work.

The authors wish to thank Messrs. B. R. Bean and R. S. Kirby

for their review and suggestions. Drafting work was done by J. C.

Harman and his group, and the manuscript was typed by Mrs. D. J.

Hunt.
-39-

8. REFERENCES

Barsis, A. P., J. W. Herbstreit, and K. O. Hornberg, Cheyenne

Mountain tropospheric propagation experiments, National

Bureau of Standards Circular 554 (Jan,, 1955).

Barsis, A. P. , and F. M. Capps, Effect of super-refractive layers

on tropospheric signa,l characteristics in the Pacific coast region,

IRE 1957 WESCON Convention Record, Part 1, 116-133 (1957),

Barsis, A. P., and R. S. Kirby, VHF and UHF signal characteristics

observed on a long knife-edge diffraction path, paper to be submitted for inclusion in the 1961 IRE International Convention

Record.

Bean, B. R, , Prolonged space-wave fadeouts at 1046 Mc observed in

Cheyenne Mountain propagation program, Proc. IRE 42, No. 5,

848-853 (May 1954).

Bean, B. R. , L. P. Riggs, and J. D. Horn, Synoptic study of the

vertical distribution of the radio refractive index, J. Research

NBS 63D, (Radio Prop.), No. 2, 249- 254 (Sept. -Oct. 1959).

Bean, B. R. , and G. D. Thayer, Central Radio Propagation Laboratory exponential reference atmosphere, J. Research NBS 63D,

(Radio Prop.), No. 3, 31 5- 3 1 7 (Nov. -Dec. 1959).

Doherty, L. H. , Geometrical optics and the. field at a caustic with

application to radio wave propagation between aircraft, Cornell

University School of Electrical Engineering Research Report

EE 138 (Sept. 1952).

Dickson, F. H. , J. J. Egli, J. W. Herbstreit, and G. S. Wickizer,

Large reductions of VHF transmission loss and fading by the

presence of a mountain obstacle in beyond-line-of- sight paths,

Proc. IRE 4l_, No. 8, 967-969 (Aug. 1953). A discussion of

this paper is given by J. H. Crysdale in Proc. IRE 43, No. 5,

627 (May 1955).

Kuehn, U. , Ein Beitrag zur Kentniss der Ausbreitungsbedingungen bei

1. 3 GHz nach Messungen an einer Uebertragungsstrecke mit

optischer Sicht, Technische Mitteilungen (B.R.F.) 1. No. 1. 4-10 (Oct. 1957), Berlin - Adlershof (East Germany).
-40-

Norton, K. A. , P. L. Rice, and L. E. Vogler, The use of angular

distance in estimating transmission loss and fading range for

propagation through a turbulent atmosphere over irregular

terrain, Proc. IRE 43, No. 10, 1488-1526 (Oct. 1955).
Sd313W Nl N0I1VA333

<

>

en<

Z>

COH ,

^ u

o

UJ <

2 cr 2 o

Ul i >- o

UJ o

X —

.

CJ

UJO

or

<

or

ui

cr

cJ- c-JSd313W Nl N0I1VA333

UJ

UJ

>-

UJX

o
Sd313W N0I1VA313

<

O

Q.

I z.o

in —

_J <

^§

Hi ^

=! o

o

<r

<

cr

cr

<

o

CO

Sd313lAI Nl N0I1VA333
SH313W Nl N0I1VA313

— <o

S2

CO

i u_oI LU? 00

_l X

hh- <

CO CL <

81

2-8

co

o

CL

Sd313lAI Nl N0I1VA313
SH3131AI Nl N0I1VA313

<

Q_

<

O

Ld

_l

o

COm

o

o

<

CCo

_J

o

o

o

LjJ _Ju_o

(T

Q_

<

q:

SH3131AI Nl N0I1VA313
TYPICAL PROLONGED SPACE -WAVE FADEOUT

HOURLY MEDIAN CARRIER LEVEL

MINUTES

Figure 5
RECORDING CHART SAMPLE FOR CHEYENNE MOUNTAIN -KARVAL

WITHIN-THE- HORIZON PATH

1046 MC

T3

h-h-<5

Ld

OQ

DECEMBER 9, 1953

Figure 6
CO

COMPARISON OF THE DIURNAL DISTRIBUTIONS

OF PROLONGED SPACE-WAVE FADEOUTS

THAT OCCURRED AT 1046 MC AT KARVAL, COLORADO

FOR 1952 AND 1953

1953

IDo

LUO

50 <r

ii 40 _Q

~TD

if) 30 Ll

o

?i) CO

LUO

2 10 LU

LTrr

Z)CJCJ fiO CJ

Ll. O 50 crhi

DD 40 ;>-

)

Z 30 Q

LU 20 N

_l

< 10 ^

LTO

1952

> V

. V

x V

, y ."

<XXXX>

14 16 18 20 22 M 2 4 6 8 10 HOUR OF THE DAY

Figure 7
OQ<

cro

_joC ) oQ _J < <r

cr > Q cr

_ioo <^ h-

_l < „ _l

U) in (.n

=?OFII_E HASW

hZ>oUJQ rO ^ £ 2j

ACTIVITY TOWER

III >11 UJ

rO

crUJ

DO cr cr o ;> U_ UJ CO

UJ UJ |-

cr lli o

UJ

u_ ^ o o Q

UJ

CD2

CD ^ ^

8«5

y E m o Q

<t 2 LL 2„i LL ^ x U_ o ^ o 2 UJ o CJ2 Q UJ

UJ cr 2 cr < 3

h=

O

CD CJ O oX

ICO

OO

CO -I<>

or<

CO

hCNJ O

UJQ

UJ = ><1 LU

<=5 ~~

U<

Q_COQ

-z. o_lo

or CO Q_ |I1

;\\\//1\\//

>-<

LlO

croI

LO CZ> LO r— r— co CNJ CNJ CNJ

S1IND

N Nl A1IAI10VUJ3U

SH313IAI Nl 3DVJanS 3H1 3A09V 1H0I3H
NORMALIZED NUMBER OF OCCURRENCES

OF 5db PROLONGED SPACE-WAVE FADEOUTS THAT OCCURRED

AT 1046 MC AT KARVAL, COLORADO DURING 1952-1953

o

CD

CD -Q

T3

CDN

J J A S 1952

Month of the Year

A M J J A 1953

Figure 9
o

_l

ujoO

LlI X <Q

LU^ ro

>-

m

_J 05

UJX

<\] in

01CD

cr < ^ ~>

_L UJ

n \- CD CO X -Q h1— O ~> ^ O O UJ ^ Q XO < £ < .Q UJ

LU TJ >

cre

iij

lO <1 <

UJ S

UJ

_i

g

h- h- (f) _l < Q < en UJ H

~~ (0 P 7*

VQ Li. < _l O cr O

UJ<

LlI 3

_r

LLQ_O

UJ

O

cr

rr

Z>Q

UJ

a. <

!5 \\ s * \\1 I s \\ /

,' 11 // / 1 /// .a

IT)

JOO

m

in

in

3IAII1 9NIQd0D3d 1V101 30 39VlN3Dd3d
CUMULATIVE DISTRIBUTIONS OF THE PROLONGED SPACE-WAVE FADEOUTS

THAT ARE AT LEAST 5, 10, AND 15 db BELOW THE MONTHLY MEDIAN FIELD

AT 1046 MC AT KARVAL, COLORADO, 1952 AND 1953

2J

CO

LJ

CO

Q

<

<

Q

>

O

CO

-z. o

\-

<

Q

,uuu

000

700

500

300

200

100

TO

50

30

20

10

7

5

3

2

1

N = NIW BER rf rAD EC UTS

5d

N=

b128 3

^-10

\

N

db

= 449

^15

N

db

= 167

0.05 0.10.2 0.5 I 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.5 99.8 999

PERCENT OF OBSERVATIONS THAT EXCEED THE ORDINATE VALUE

Figure 1

1
UJ

o

<

ccO

h-=>O

LUO

2

300

200

70

50

30

20

0.7

0.5

03

DISTRIBUTION OF FADEOUT DURATIONS FOR

VARIOUS LEVELS BELOW THE MONTHLY MEDIANS

1046 Mc, CHEYENNE MOUNTAIN - KARVAL PATH

FEBRUARY 1952 - AUGUST 1953

1 %

2 %

5 %

10%

20 %

30 %

^"^"J

'""""-^-.^^^

""

, 50 % ' —-— .

70%

90 %

95 %

98 %

'

99 % ,

15 20 LEVEL, db

Figure 12

25 30 35
DISTRIBUTION OF PROLONGED SPACE WAVE FADEOUTS

CHEYENNE MOUNTAIN - KARVAL PATH

1046 Mc, DECEMBER, 1953

200

70

50

30

20

CO 10

L±J H 7 z>2 5 >

CO 3 hZ>O 2 Ula

<rLl

1 _l<3Q 300 >

Q 200

U_O

CO 100 2

o TO h-< 50

Lt

Z)Q 30

20

10

5 db BEL NT

•. uw ML iLY ML Ul MINI

---.•^

****.•-TV ANTENNA HEIGHTS

•._ 1.5 m. \

1.3 m.

4 m.

•. ^^*

\

\

\ V

v.

••.. ""^

•••...

10 d LO\m i\ /IPiM THL/ i\/ii D be V l\ 'IUN i IVItIDIAN

'•••

., ANTENNA HEIGHTS

"•••

.... 1.5 m. "\ 4.3 m. 4 m.

\

^^"^*-

'-» \V

\

V V V

>*

•*h.

2 3 5 10 20 30 40 50 60 70 80 90 95 97 98 99 PERCENT OF OBSERVATIONS EXCEEDING THE ORDINATE VALUE

Figure 13
MAXIMUM DEPTH OF FADEOUTS IN DECIBELS

BELOW THE MONTHLY MEDIAN FIELD FOR KARVAL, COLORADO

AT ANTENNA HEIGHTS 1.5, 4.3 AND 14 METERS, DECEMBER, 1953

a>O

Q

o

0) o

o

>

C

Q

22

20

4

i

N = Niimber of Fa deo jfs

14

,

' m

^8

-4.3 m

*6

1.5 r inn

0.1 0.2 0.5 I 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.8 99.9

Percent of Observations That Exceed the Ordinate Value

Figure 14
o

o

goLl) -Z. cr <

o° oo W ro (/)

Ll_ — 3

O 2! o

UJ (/) Q CD h J ^ 3 UJ §^ S£Q ^ £

J ^ L±J ^ U. >

o < o ^ H

Q

iuj

o §£

3

DQ 0-^ jd

E w £

H Q

CO LU H

Q C3 ^

crQ

O

crQ_

x>

If) u.o

o

crUJ

DO

UJ>

o

cr

UJ

QD

o

h-o

o

>

<

o

m

0}

uj en

uj cr > < ^ cr -GO

I- UJ

co Li_ CD Q

31

>-<

(J

00

rO

l^M

;$$$&li§§§§

>-<Q

UJX

o

cr

Z)O

X

LO

CD

sino3avd qpe jo S30N3ddnooo do dda^nN
NORMALIZED NUMBER OF OCCURRENCES OF 5 db SPACE-WAVE FADEOUTS

MT. WILSON- PT LOMA, 138 AND 1250 Mc PROPAGATION PATHS

138 1250 Mc

CO

h-o

LUQ

LlO

co

LdO

LTCCU

O

o

o

LTLU

GO

Q

LUM

_l<

cro

1,400

400

200

MAY AUGUST NOVEMBER FEBRUARY

1950 1950 1950 1951

MAY

1950

OCTOBER

1950

NOVEMBER

1950

Figure 16
CUMULATIVE DISTRIBUTIONS OF PROLONGED SPACE-WAVE FADEOUTS

FOR THE MT WILSON - POINT LOMA PROPAGATION PATH

2,000

1,000

TOO

500

300

200

70

50

30

20

10

7

5

MAY, AUGUST, NOVEMBER, 1950 AND FEBRUARY, 1951

FADEOUT LEVELS RELATIVE TO MONTHLY MEDIAN

\

\

V - I38 Mc

\

\

\

- I250MC

\

\

\

V \

",-»-Jk x

v>

\ \

v\\

\

\ \\

> \

N w

\ \

VN

\

^i\

\ \ S. Vs \k >

V V

\ \\ 5db \ \ \ 5db

N=2554

i

> ^N = II27 \

\

\^

v \\

10 db __-

\

\1

v; V lOdb

N=I252

v ^ N = 223

\ \

> \

I5db

^ N> I5db

N=347 ^tr N=7I

> x^

s„ \^.

, \ ^

\\.^

>

0.0 1 0.05 OJ 0.2 0.5 I 2 5 10 20 30 40 50 60 TO 80 90 95 98 99 99.5 99.899.9 99.99

PERCENT OF OBSERVATIONS THAT EXCEED THE ORDINATE VALUE

Figure 17
CO

-z. <o

l±J

>3X

bJX

UJ

CDCO

_J

LlI >

UJ

eno

CO

z.g

q:

Z)O

hZ>o

L±J Q<O

COzg

h-Z>

DO

tr

h-coQ <

CL<oO <£

°- I I o

-,m

COo

/• 111 i

/// 1 ' 1 I / '// 1 IIi / / ' r^ 1 / / >' 11 /// ii / / 1 I / / 1 / i ' / ' 1 / / / i / ! / / 1 / / / / / / / / i / / / / / 1 

/

250

MC / i i il / r i 1 , 1l / / i ll / I / / // // /// / / / /

// / / i 1 / / / / / / / / l / / / ' if / / / / / /1 1 1 / / / / / / / 1 1 / / / / / / / // I

S? N? ^ -5 ^°

CJ* 0^ 0> CJ* cT* CT" O^ CJ~

— CM IT)

O

O

O

O

— CM rO in 1 1 O

OO KCD (Ti1 Q

_l

UJ>

UJ

CO

/// / / / / j // / / / // / / 1 / // / 1 1 1 / 1 / - 1 1 1 / 1 / 1 j / 1 I 1 / / 1 1 / / / / / / / 1 / / // / ' / ' / // o / /

// / / / / / / / / / / / / / / /

cxi ft / / / / i / / K> / / / / / / / / / 1 / / > ' / / / / / ' / J 7 / / / / / 1 / /' / / / / ; / / / / / / 1 / / / / / / // j / / / // / / / / / / / / / 1 / // //// // /

o^! o-° 5* cr- CT" c>" 55 0- O^ (T" O^

CVJ LO o o o — oo ro 1 Om

O

QO IT)

n ro en

m I

X3

L±J >

LU

<T3

CVJ LO

CD

CNJ

S3XDNIIAI ni Nonvyna
o

BASE (GB)

ROUND

LAYER o

CO

UJo

or

Q_X

UJQ

UJ>

I-o

<

oru_

ui

or

CO

uio_

o

CO

ceUJ

c_> <

or<

x

o

Q

EVATE (LE)

DW

EL

LAYER

_j

""* -C *"

VAT

ED

/IE)

M

ELE

rER

(H

=> < o -J

UJ5

CO

I <

UJ>

cr

Q

UJ —

.

1- UJ < -r > 5 UJ-UJ

15

X

LINEAF (L)

Bovdans 3Aoav sh3±3iaio~ii>i
X

h-<

LLZON

CHOX1 < Ld III X Q_

h- < z

-z. 3 T O

\- <. ^

_l P Q<

in "5

Q

_J

CO o

XJ cro CO D o <r >

UJ _i -P en o 5> o o CD ^ z O

sl- P" tn O < O

r^ co

CO<

co oo

Q. eno

CDo

c5

cc3

qp'uDipa|/\j AmiuoiAi M0|3g qp'uopaiAl A|i_|4U0|/\| M0|3g
PERCENT FADEOUT TIME AS A FUNCTION

OF PROFILE CHARACTERISTICS

SAN NICOLAS ISLAND-LAGUNA PEAK (SUMMIT)

PERIOD NOVEMBER 1955-OCTOBER 1957

394 Mc LU

3

a

o

IS

LUO

dc

UJ

Q_

25

20

10 H (a)

\V\ T T »-X r"T-4

VT L-^.x—

X f—T -

LIMITING VALUES

FOR L PROFILES

L±J 30

0.2 0.4 0.6 0.8 1.0 1.2 1.4

h, (KILOMETERS)

1.8 2.0

S

o

LUO

DC

LU

Q_

25

20

15

10

5

i

LU

h

o

LUQ

<

LUO

DC

LU

Q_

T (b) T

11

1

X ST T I Kk -i- X

1 w/IITINC )R L 15 VAI UF9

1

..//x -«

1x^ T I I

/\ FC PROFILES -

«~x

- LIMITING VALUES

FOR L PROFILES

SxI

-X

\]>

f X \I

--

X

1 T

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 h.+ h, (KILOMETERS)

35

30

25

20

15

10

5

i, m

2

(c) -

x

3 :\ i

x^

t T

T y

n\

\T

1

8 :""

1 Y i NL4

1

i

60 -80 -100 -120 -140 -160 -180 -200 -220 -240 -260 -280 -300 -320 -340

AN? (N-UNITS/KILOMETER)

Figure 21
<

o

UJ^ > -J o cr ^ 3

III o

Z> J_

o n

LU V h-

<

LU

Ld

Q_

li_ hO <

<L

_J

•z. z Ld

o z> Q_

o

2

<

_l

1 3 1 U_

7*

< <

<

_l

CD

li 1 if)

c

•) <

z.

ll 1 _lO <

or o LJ

LU _) ^ ^ o

o 7* V

o <

C/)

_J

X

3 ^L

o O

UJ ^ n

IS

o

h-LU>

_lLU

cr

^

, <

V (? +

\

\

. < CL rw- V > V > \ Sft

\ \ ^t

\\ \ *2 <£. \\ \ cn £

\N 1 \

\

1 \

1 x/i \

\

\

\ \ \ TJ \

O \ o \ CM \

\

\ \ \ V \ \

„—

\

X) Vv \ "**—"' V N s

"s s

s

\

V

V V >

\ s

\ \. s

\

l S N N

\

\

\*

-V

X

\

N

\

\

\ <

>

®2

\ > giS 1 l\

\ \ It

\ 3s

\ 1 \ > 1

\ o\

i X2 \

-° \

"O

\

7:3 \ O O N 00 V

\ \

X

s o

> s

V X

V X

X

\

\

X X

s X

v

\

\

N

\ x

X

X

X

>\ V v

CO

CO

r-O

O

>-

Z>O

UJ

a:

o

Z>O

UJ

cc

CM

CM

C7>

Ll_

Soo

eo co co <o co co co eo o co co co c— lo i-ooj C—> r— lo ro cnj —

CO i— lo ro CNJ

SAVQ 06/Sin03QVJ JO d39NnN
s^<

LlI Q_<Z

z>o<

_l1 QZ

<r

_j 0)m

CO 0} CO h- < co i 3 o o o —I< z 1 z

_l <T tr CO LL<

DCO

U_

UJ(Jz

LlI Qo

IDO

LUQ<

Stcr> *en I • -• • • \

FS o ^

Iwwww o- :-./-:

U3oo

_JCD

O

<MI O

CO * 8 o o o eg

UJ o ^ ro O CQ m o

Lug s o

1^-

(J o o IDO

CD I O

UJ3 Q s o i l, ' J.*A.u,.' . ' - ' . ' )''.'n| Tt , .;•;-;-:::;•:•: In..,,,,,,..

CD

h-m* 9 <_> O o co

hCD

ro

dnOH ddd Sin03QVd dO ddaiAIDN
-z. LUO

q:

uj

Q_

LU

IIZ)

o

LUO

L?

8

DIURNAL VARIATION OF FADEOUT TIME

PERIOD APRIL- JULY, 1959

10 db FADEOUTS RELATIVE TO MONTHLY MEDIAN

394 VAN

394 SUMMIT

L^ 249

EH 98.3

0000-0600 0600-1300 I300H800

PACIFIC STANDARD TIME

1800-2400

Figure 24
SAN NICOLAS ISLAND- LAGUNA PEAK PATH

DISTRIBUTIONS OF 10 db FADEOUT DURATIONS

RELATIVE TO MONTHLY MEDIANS RELATIVE TO HOURLY MEDIANS

CO

LU

O

<

a:=>Q

500

300 ,11 1-

,

1 1 JWINTFRU -| WMN 1 th p \

394 Mc (SUMMIT)

244 Mc OR 249 Mc • ^ \

_ 98.3 Mc OR IOO Mc

'> \\

>-— ___ ~s _ --

V =£-

\

vv ^446a

; 34o^ [--..

66I-^>n; ^

r 185-"

CO

<

cr

500

1 1 1

1 1 1 -]summer|- III 1 ]summer|- 394 Mc (SUMMIT)

~~"n \

- 394 Mc VAN

. 9/1/1 l\/l,~ no O/IQM^

"v^ \ \

" 98.3 Mc OR IOO Mc ^N ^^-108

\\ 256a

VQ

\x > )

**"~-

~^~\

\ V

\? V% 408-^ •v ^ N *<--29 ^^ s ^ -v

t /

J60

\

\ 700-^ 5 >>

^**.

v. 39I-"IK ^

\ «a>

2 3 5 10 20 30 40 50 60 70 80 90 95 97! PERCENT OF FADEOUTS

2 3 5 10 20 30 40 50 60 70 80 90 959798 99 PERCENT OF FADEOUTS

Figure 25
CO < 2 LL

or < o Q ^

Ll_

ll 1 <l co ^ LUn 2O S <

(- cc ^

<L ~~> _>

rr o o ~> T <L 0~) n _J U) UJ i 01 h- T O 3 1- 2 O < 1 UJ ^ _l ~~> LJ n CO ~3

Si _j

hi CO 1 _l 1 

DQ < IT o CO

_lo

0_

<r T' _l u O UJ ^

1- >

Z>m

UJ

_l <

CO

cr CO

h- _> - co o o Q or ^ £ <vT

T3

LU>

LU

CO

C\J

O)3

en Lu LOro

cr> r— lo '"O CXJ cz>

r

— lo ro cnj

s3inNi^ ni 'Nonvma inoaavj
RECORDING CHART SAMPLES FOR COLORADO

OBSTACLE GAIN PATH

751 MC

5

CD

T3

0345 0330 M.S.T. MARCH 24, I9600315

Figure 27
oo<

tro-J

x o h- o <

tr

°"< UJ o o2 UJ

LxJ _J Q O |h— CO

l_

m

fe ° oLjJ O< o&

DCUJ

CD

I0_

L±J CO3

"Om

in

O oC\J

-Q

T3m

tooo

_lCD

UJ

O

CMI Oo

03

O 52 tV o ( 1 o o |*J _J 1 m O

UJ o(0

;> o H

1^-

OooI o

UJ

O ± o oo_lOD

00

CvJ

dnoH d3d sinoaavd jo ddaiAinN
C/) crUl

CO<X

C/} CO n 1 III cr -> UJ UJ

_l

1—UJ

CO3

ro o X1

rr<> CO< o *L n CO <O

UJ

_l( ) O

rr

UJh

cr

en

cr

UJ

<r -> _> ^

hn o ~) u) _L (O

GO h- o -) Lu - n X

h- o o UJ ^ Q<

rr if s

L?5

c_> U. ll 1 _i O m o

c_> COo

QQ

cr

h-coQ

c/) cr

UlUl

en

crp

OS

o>

O^ // A / / /

CJ3

sf / / / /

co

m / / f / / o // / /

CO

in

J3

U j / /

LO o // 1

<=3~

CMCO

in yv ' I1 \ p

jD // 1 D

OJ \ /f 11

in

CM

V' // 1 1/

r~

s> // 1 aO

"CM /f /// o

Ul

cr

cr

croo

CO

h-O

UlQoo

cr / / / /

J//t

// / A

///

// / // / ' / /// / / /

// ' J ' /// / I /

CM t 

1 i <£ 1// /

^_ o /// /

CD

in /// i '

-Oa 11 O 1 „ —

CM

r^- 00 \l

XI //'/

J

in tr

id

/^ /

in

CM

/'

//

X) / / CM ' J 1 / /

<z> ZD r— o

Ul CD Q C£> <U

CDLO Ll_ O

CD 1—

«^t" s"U)

C3^ c ) rO

crUl CD CL

(S3inNiiAi) Nonvana
co

_iUJ>

LJ

CO

1-

or<> CO £

~z. < o ^ n to <

hi

U)

-z. o

h- >

en

ce

ii i _l( ) <

or i rr ^

<r

—

_) ^

hn CJ ->

{/>

X ro

m h- o -> LJ » o I CJ o UJ

1— ^ < o1 LO O Ll_ ll 1 _l o m CJ

c_> COzo

h-CD

orh-coQ

CO

cr

Ld

h-Ld

00<I

COQ

cc

Ld

h-LU

ro

CO

rroo

LU

cr

cr

croo /

//

t:

PI/ 1 I // 1/ j / / /// / I // 1 1 / J

//

7>i 7 1 1 

' 1111 f j 1 //// 1/ / j /' //t i / / //t 1 11 1 

' 11t 1 1I 1 1 ///

// / / ' / / // // / // 1/ 111 11 /f f 11 1 / i / / ' // . f / / /' / / / / / // / / / ' /, // / 1 1f 11 / i / // i / / / / / / i * ///f / // /

/' / f // ' ' 1 iii 2 3 O J

.Ja"

if

C? 3* ) OCM

5?O

5?Oif)

5?o o

en 5s

in01

C3 _Q ~ -o> 1 / // 111 1 1/ 11 // / // //// f /' // 1 , // 1 11 1 /// / i /

/// / / ' 111 / 11t 1 //// ' // / /1

ft//1 / i 111 1 , ' 1 / / /// 1 111 11 /' 1 f / / /( / //// / ' /1 11111 1 111r 1t ///// ft

// // / / // // 1 t // // / I 1 1// 1 i 1 / J1 11 // //f — CSJ If) o i< D O M ro Oif)

0^ o

CD

in

0)

c^

O3

LO

ro

iT >

S3inNi^\i ni Nouvdna inosavj
U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, 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, Colo., 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.

Electrochemistry. Electrical Instruments. Magnetic Measurements.

Photographic Research. Length. Engineering

Molecular Kinetics. Free

Radiological

WASHINGTON, D.C. ELECTRICITY. Resistance and Reactance.

Dielectrics. METROLOGY. Photometry and Colorimetry. Refractometry.

Metrology. Mass and Scale. Volumetry and Densimetry.

HEAT. Temperature Physics. Heat Measurements. Cryogenic Physics. Rheology.

Radicals Research. Equation of State. Statistical Physics. Molecular Spectroscopy.

RADIATION PHYSICS. X-Ray. Radioactivity. Radiation Theory. High Energy Radiation.

Equipment. Nucleonic Instrumentation. Neutron Physics.

CHEMISTRY. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances. MECHANICS. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Combustion Controls. ORGANIC AND FIBROUS MATERIALS. Rubber. Textiles. Paper. Leather. Testing and Specifications.

Polymer Structure. Plastics. Dental Research.

METALLURGY. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics.

MINERAL PRODUCTS. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and

Microstructure.

BUILDING RESEARCH. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. APPLIED MATHEMATICS. Numerical Analysis. Computation. Statistical Engineering. Mathematical

Physics.

DATA PROCESSING SYSTEMS. Components and Techniques. Digital Circuitry. Digital Systems. Analog

Systems. Applications Engineering.

ATOMIC PHYSICS. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics.

Atomic Physics.

INSTRUMENTATION. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical

Instruments. Basic Instrumentation.

Office of Weights and Measures. BOULDER, COLO.

CRYOGENIC ENGINEERING. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas

Liquefaction.

IONOSPHERE RESEARCH AND PROPAGATION. Low Frequency and Very Low Frequency Research. Ion- osphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. RADIO PROPAGATION ENGINEERING. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

RADIO STANDARDS. High frequency Electrical Standards. Radio Broadcast Service. Radio and Micx-owave

Materials. Atomic Frequency and Time Standards. Electronic Calibration Center. Millimeter-Wave Research. Microwave Circuit Standards.

RADIO SYSTEMS. High Frequency and Very High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Space Telecommunications.

UPPER ATMOSPHERE AND SPACE PHYSICS. Upper Atmosphere and Plasma Physics. Ionosphere and

Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

\JSCOtMi WS-8L