ABSTRACT
Tropospheric
angle-of-arrival
were
made at X-band
were
made
arrival
(7.3 GHz)
using sources
ations of elevation
Over
a one-year
every
season,
scintillation
angle
slowly
period,
were
458 hours
below
fluctuations,
fluctuations
fluctuations
ranged from
at a i O” elevation
angle are expected
values
angles
1 to i 00 mdeg
angle.
at elevation
Comparable
for bias refraction
of the refractive
power
correction
The
..
..
spanning
show strong
angles
by a
deep fades,
signal.
angles
elevation
below
fluctuations
models
power).
characterized
The
below
angle
2” to less
in elevation
based upon the use
index.
iii
—-
(log
amassed
of the received
above iO”.
drifted
by the rms vari-
i to iO dB rms at elevation
than 0.1 dB at elevation
of
observations
The results
angles
angle
slowly
events that produce
and depolarization
than 5 mdeg
allowing
were
1 to 20 elevation
ranged from
The
as they
of received
conditions.
of multipath
The measurements
characterized
of observation
measurements
orhits.
irregularities
time of day, and weather
a@e-Of-aprival
of surface
changed
and the logarithm
number of random occurrences
log power
42-day
The fluctuations
occurrences
2- to less
with
caused by atmospheric
the ray path.
scintillation
and at UHF (0.4 GHz).
on satellites
of the ray path to a satellite
of fluctuations
across
and amplitude
—.a?=-e
CONTENTS
.
iii
I.
n.
m.
Iv.
v.
Abstract
List of Illustrations
v
INTRODUCTION
i
INSTRUMENTATION
5
A.
Haystack
5
B.
Millstone
8
OBSERVATIONS
A.
Amplitude
B.
Elevation
C.
Orthogonal
Fluctuations
Angle Fluctuations
Polarization
Fluctmtions
i9
ANALYSIS
A.
Statistical
B.
Comparison
49
Summary
with Scintillation
Theoq
25
3i
CONCLUSIONS
32
References
,,
iv
LIST
OF
ILLUSTRATIONS
Title
Figure
I-i
,
Elevation
weather,
andtraverse
cloudy.
n-i
X-band
receiver
11-2
X-band
tracker.
Page
angle fluctiuations;
i3-i5
September
i975;
system.
111-%
Received
signal levelsat
111-2
Received
eignal levels
111-3
RMS fluctuations
in log power
at X-band.
in log power
at UHF.
high elevation
III-4
RMS fluctuations
111-5
Apparent
elevation
angle at X-band,
111-6
Apparent
elevation
angle at UHF,
111-7
Normalized
elevation
angle error
angles.
high-angle
high-angle
Elevation
and traverse
111-9
Apparent
elevation
angle at X-band,
111-10
Apparent
elevation
angle at URF,
Ill-ii
Normalized
angle residuals,
angle error
high-angle
low-angle
data.
data.
low-angle
data.
voltages,
low -angle
Elevation
i5
111-i4
RMS fluctuations
in elevation
angle at X-band.
i6
IH-i5
RMS fluctuations
in traverse
angle at X-band.
16
111-i6
Received sigml fluctuations in the principal and orthogonal
polarization
sum channels and the elevation and traverse
difference
channels, low-angle data at X-band.
i7
111-i7
Received signal fluctuations in the principal and orthogonal
polarization
sum channe16, low-angle
data W UHF.
i8
2330 UT,
29 April
Satellite
IV-3
L-band radar observations
of a rise
sphere (LCS-4,
Object No. 5398).
IV-4
continued,
data.
20
i975.
Iv-2
rise
low -angle
data.
Comparkon
of received
signal level and quadrature
elevation angle error voltage fluctuations,
low -angle
data.
rise,
residuals,
data.
111-12
Satellite
angle
high-angle
111-+3
Iv-i
and traverse
data.
data.
voltages,
111-8
elevation
angles.
at lowelemtion
0!00 UT,
30 April
2i
i975.
and set of a 1 -m2 calibration
22
Elevation angle and rms log cross section
sphere track depicted in Fig. IV-3.
values
for calibration
22
IV-5
Three
IV-6
RMS fluctuations
in log power
at X-band.
IV-7
RMS fluctuations
in log power
at X-band,
spring
IV-8
RMS fluchratiom
in log power
at X-band,
summer
IV-9
RMS fluctuations
in log power
at X-band.
fall season.
at X-band,
winter
satellite
rises
witbin
12 hours,
29 April
24
24
season.
season.
Iv-io
RMS fluctuations
in log power
Iv-ii
RMS fluctuations
in elevation
angle at X-band,
spring
Iv-iz
RMS fluctuations
in elevation
angle at X-band,
summer
v
23
i975,
24
24
26
season.
season.
season.
26
26
Page
TiUe
Figure
Iv-i3
RMS fluctuations
in elevation
angle at X-band.
faU seas On.
26
IV-14
RMS fluctuations
in elevation
angle at X-band,
winter
27
Iv-i5
RMS fluctuations
in log power,
IV-46
RMS fluctuations
in elevation
IV-47
RMS fluctuations
in log power at X-band
v-i
Median rms fluctuations
27
fu33 year.
angle,
in elevation
27
full year.
and UHF,
i
[
d“
/
~,{
..,.,
‘....._
,!:,
29-30 April
angle by season.
\
I
season.
i975.
29
31
LOW
ELEVATION
ANGLE
AN
MEASU~~NTS
ANALYSIS
OF
MADE
1.
AT
IMPOSED
SCINTILLATION
HAYSTACK
BY THE
TROPOSP~RE:
OBSERVATIONS
AND
MILLSTONE
INTRoDUCTION
Radar
spatial
systems
operating
and temporal
variations
cur at all elevation
Millstone
Propagation
on radar
study was sponsored
fense Agency
at Millstone
July 1973 time periwl
racy.
This report
for ABMDAto
effects
provide
stone Hill
refraction–elevation
correction
Study.
and on the random
(or correction)
The residual
errors
The bias errors
varying
during an observation
exist.
included
correspond
Unfortunately,
Residuals
ae scintillation
stationary
behavior
increasing
observation
in the correction
tion error
consider
time.
measurement
accu-
Hill Radar Facility
and range errors
–have
amount of data on the state
specifically
remain
of the refraction
after
for the Mill-
the model
errors
duration
errors
corresponds
between
correc
that occur
-
of the
during
correction
and scintillation
for short observation
This difficulty
occur
arises
about the
does not
periods
from
variances
maybe
the non-
increase
in the estimation
in the atmosphere
with
of bias errors
and to possible
inadequacies
can be made for the bias component
of the refrac -
A study of refraction
(scintiDation).
and scintilor slowly
to random fluctuations
and angle-o f-arrival
complications
variations
bias errors
that are constant
bias effects
intervals.
range
Additional
Ideally,
toti?=o classes:
to be bias values
but not for the random component
effects
must
both components.
futiher,
of a radar operating
here was devised.
Program
[IDCSP)
at low elevation
Northeast
were
multiple
passes
angles,
transmissions
satellites.
stone Hill Radar Facility6
residuals
and to establish
In this etudyangle-of-arrival
0.4 and 7.3 GHzbyobserving
bythe
De-
i969 to
depends upon the sophistication
refraction
separation
errors:
(large-scale)
mafel.
errors
as belonging
scintillation
considered
for longer
To s+mdy this problem
curacy
period;
of refraction
due both to long-term
Missile
can he found in handbooks. 2>3>4 These
residuals
fluctuations
to residual
a clear
that maybe
refraction
Laboratory
pericd.
are often modeled
lation.
on radar
based upon a limited
of these
of the propaga-
Ballistic
at the Millstone
by Crane 4$5 was generated
Residual
The magnitude
ocThe
during the February
angle errors
models
errors
The model described
procedure
bias values.
correction
of refraction
Radar Propagation
an observation
conducted
of tropospheric
andrefraction”
the effects
errors
5 to 10”.
and Bell Telephone
of the ionosphere
program
caused hy
propagation
to investigate
Command
errors
angles below
through the Advanced
System
of the troposphere.
tions have been app3ied.
Tropospheric
Laboratory
the effects
an estimate
of the atmosphere.
Lincoln
the effects
a follow-m
measurement
only at elevation
by the U.S. Army
to investigate
describes
been studied in the past,
models
A joint
and the SAFEGUARD
investigate
The gross
concern
Studyi was undertaken
measurements.
(ABM.DA)
experience
in the index of ref~actiim.
angles but are of major
Hill Radar
tion medium
within the troposphere
Radio Observatory
observed
of i-,
for each of the spheres
and O.I-mz
foruseaa
the program
of propagation
the fnterim
a 0.4-GHz
beacon
radar
sphere
calibration
position
references
scintillation
were
spheres.
studies
were
.s~.
at the Mill-
MadditiOn,
Best fit orbits
forobservations
were
at
atellite
Observatory,
Radar observations
ac -
reported
observed
beacon tracker
at the Haystack
tracks.
on the metric
DefenseC ommunicationS
monoptdse
tracker
CorWration(NEROC),
using L-band
0.2-,
it imposes
andamplihlde
from
For reception,
and a 7.3-GHz
the limitations
operated
bias errOr
were
made of
constmcted
atlowelevation
=gles
,..
Bias error
on each of tie passes.
accuracy
to separate
sphere.
Considerable
Using multipass
the errors
effort
orbit fits,
of better
L-band
radar
sphere tracks
the position
tracking
sessions
fluctuations
were
cross
tracked
to provide
has not been performed.
radar
Scintillation
i975.
The durations
observations
accurate
of the observations
was amassed
of received
calculated
power
over
Observations
were
position
for examples
satellites
interval
only scintillation
the correlation
of the rereference
is considered
between
for tropospheric
scintillation.
scintillation
to account for the differences
of refraction.
analysis
(rms)
curves
when the results
larger
to
than the correlaobservations
at both frequencies
doppler,
are
but are useful
of the frequency
(log power),
depen-
and angle of
theory ( Rytov approxi-
given in Refs. 8, 9. and i O are
dependence
power
squares
has been made to
The antennas used for these
Tbe simultaneous
power
theory
was
in the
The rms values
No attempt
The same weak scintillation
in wavelength
angles
program
fluctuations
fitted by least
significantly
the fluctuations
Weak scintillation
at elevation
in this report.
frequency.
of received
and a total of 458 hours
will be reported.
the mean trend.
of 0.7 km, i.e.,
and Millstone
and i i December.
observed
An extensive
at O.4 and 7.3 GHZ.
at either
in the logarithm
caused by ionospheric
number yields
for
estimation.
further
27 January
were
about quadratic
to remove
made simultaneously
dence of rms fluctuations
(3-d)
and phase
an analysis
made at Haystack
for examining the frequency dependence of the rms fluctuation values.
~rane8, 9, i O
has reported a theoretical
amlysis
and observations
dimensional
most
have been generated
6 to 40 hours,
and angle of arrival
by a distance
not useful for studying
were
made between
conditions.
fluctuations
indices
i 973
sessions
scintillation
of scintillation,
of funding only root mean square
and f -hr intervals
errors:
were
were
under all weather
for amplitude
spheric
At first,
esti’rnates for bias error
The satellites
are separated
modified
effects.
State vectors
within a set ranged from
tion distance
arrival
i October
also made during the last four
(amplitide)
data.
during the year.
observations
mation) is valid
between
of funding for this program,
Except
(log power)
5-rein.
tbe data within an observation
study the angle b%
sessions
angle propagation
on cross-section
using the IDCSP
but due to the termination
logarithm
were
angles below 10”
but during the last four tracking
measurement
sets of measurements
43” down to the horizon
planned,
facility.7
data will not be made in this report.
Nineteen
of observations
caused by the atmo-
of the Millstone
than 4 mdeg at elevation
data recordings
due to a sudden termination
sidual errors
from
objects,
information
to the L-band
during
the errors
measurement
at any instant within the time used for the
of better
Coherent
emphasized.
to provide
each of the objects
from
made during 16 tracking
section
in addition to the position
Unfortunately,
of a sphere
accuracy
position
than 70 pad).
of large
were
target
for the calibration
i 974 for the study of low elevation
were
extreme
caused by the instrument
observations
and 30 September
observations
requires
has been expended
orbit fit is known with an angular
(an accuracy
estimation
between
ionospheric
and tropo. ‘* ’13 three-
coupled with an assumed
spectral density for tropospheric
-7/12
an estimated A
wavelength dependence
refractivity
fluctuations
for rms variations
( K = wave-
in log power
(ox).
The wavelength dependence for angle-of-arrival
and Doppler fluctuations is given by 1° and
~-i.
respectively.
The last results do not depend upon the exponent of tbe assumed refractive
index spectrum.
wavelength
The Haystack
dependence
and Millstone
observations
for Cx fm. measurements
are in agreement
at low elevaticm
2
angles.
with tbe predicted
co -
I
I
-u@m
.
-
:!:R:E;::*z:%?l::RFAcE
\“
.
.
.
RMs RESIDUALS ABOUT SURFACE
REFRACTIVITY
CORRECTION MADE
WITH 3 N UNIT RM5 REFRACTIVITY
MEAWREMEN7
ERROR
\
4
,0 L“”\
:x\
t.
\
-
Ice
:
\“””
Y’
.
3
@
TX*”
‘
‘
-.x
x
?R.%
e
“a
5mi”
I hr
ELEVA7WN :
.
0
TRAVERSE,
x
a
‘1
I
I
‘\’;~
\
.,..[”,”
“-’““L
.-..,
‘-BAND
. .
ii’k
‘“
&
NOISE UMIT
~~
APPARENT
ELEVATION
Fig. 1-!.
Elevation and traverse
i975; weather,
cloudy.
The angle -of -arrival
creasing
observation
traverse
[azimuth
Figure
I-i
cumulus clouds and clear
for elevation
angles
mation.
tion.
refractivity
scintillations
The results
suggesting
Bias error
Figure
sky.
I-i
ray tracing
These
estimates
rms fluctuations
the expected
bias errors
for the surface
and
of
of less than 50 prad
rms residual
generated
in-
errors
for Millstone.5
fluctuations
The
in hiss em-m. esti-
of those obtained on each observation
represents
are expected
in elevation
sets made under conditions
of two of the expected
model
in the rms value with
data show rms errors
also displays
due to the natural
analysis
13-$5 September
increase
the observed
on Fig. 1-i are typical
correction
the rms fluctuations
from
displays
model for estimating
displayed
correction
angle fluctuations;
show the expected
are within a factor
that the surface
and because
expected
above i O”.
ldeo
1 for one of the observation
fair-weather
observed
I
time.
X cos (elevation)
about the surface
)
observations
ANGLE
a practical
limit for refraction
to apply for periods
set
correc
-
of an hour or mm-e,
variability
of the atmosphere
correction
model,
better
exceed
thosez
bias estimates
are
not warranted.
This
I
report
describes
the X-band
instrumentation
Crom the configuration
ple observations
and rrns fluctuation
observations
are presented
and the predictions
in Section V.
I
instrumentation
reported
used at Haystack,
the changes
by GhiIoni,6 and the processing
data are presented
of weak scintillation
in Section
theory
f.ff.
programs.
A comparison
is given in Section
in the U ED?
IV.
Sam-
between
Conclusions
,. _.. . .
IL
1NSTRUMENTATION
Haystack
A.
The goal of the measurement
scintillation
over the widest
dependence
angular
was required
measurement
also desired
program
possible
precision
tions in angle of arrival
(oe)
with instrumental
in angle
a very
narrow
noise contributions
To achieve
frequency
position
due to theinstrmnent
The 36.6-m
feed.
Four identical
sum (zLH),
difference
tically
stages
receiver
principal
(AAZ),
channels
in Fig. 11-l.
of frequency
level.
i2, i3
were
elevation
provided:
and IF amplification.
rections
from
orbital
was provided
on the
computer
were
Computer-aided
within 0.5 Hz of the apparent
variations
4-horn
polarization
principal
monopulse
(left-hand
polarization
circular)
traverse
channels are
to the A/D converters
First-stage
schema-
after
four
amplifiers
with an
i2
feed in the radiometer
box.
Doppler cor-
provided
The frequency
local
This interchanged
for DC offsets
The quadrature
was performed
the role
signals
mixer
at the second IF stage.
tracking
of the twophase
for the long-term
loop was closed
Manual fre-
drift
of the os-
through the CDC-3300
pointing
Elevation
and azimuth
commands
differential
sampled
the final
autotrace
as well
error
pointing
at a 200-Hz
commands
Coherent
corrections
from the difference
(demand offset).
using orbital
was used to positicm the antenna.
by the CDC-3300
and azimuth
normalized
plex error
error
signals
and used to generate
signals
values
together
were
with thecmnplex
recorded
at a 10 sample
pointing
5
ephemeris
smoothed
Antenna position
polarization
commands
sum channel signals,
per second
were
for use in post-test
i“ phase with the principal
the differential
processing
oscillator
data.
and used
The sum of the U490 calculated
and the demand offset
elevation
computer
of the local
‘me u490 comput.e~. provided
channels
values)
computer
of the quadrature
filter.
in Fig.11-2.
position
sampled
fifth A/D
a means to compensate
components
encoder
were
90” every
andprovided
rate.
predetection
is depicted
as the Doppler
data obtained
detectors
with the 90” phase advance
40-Hz
system
signal was advanced
the sine and cosine
synchronized
to synthesize
the initial
reference
between
were
data samples
The computer-aided
to generate
oscillator
and nonorthogonality
of 20 successive
1
beacons,
at the fourth stage.
sample.
encoder
ii).
and 0.4 mdeg rms
less than O.i-dB
The rezeiver
at the third stage to compensate
satellites,
IDCSP
The phase oftbe2-MHz
video.
calculations
(AEL),
was provided
mounted behind the tracking
cillators
5“(Ref.
7299.5-MHz
with a conventional
sum (ZRH).
video
were
obtained
to track
principal
difference
polarization
Quadrature
conversion
above
was designed.
to maintain
was fitted
8-dB noise figure
quency control
,
was required
antenna
polarization
angles
fluctua-
set to obtain measurements
and the lDCSP
and to tune the receiver
signal
andorthogonal
described
elevation
system
5“ were
observations
was used to keep the antenna pointed within 4 mdeg of
This precision
in received
receiver
above
Earlier
angle
a specified
than 0.2 dBa.ndrms
goals were
using Haystack
tracking
(i ZO-ft) Haystack
on elevation
angles
frequencies.
than 2 mdegfor
and amplitude
angle for achieving
of less than 0.05 dB rms in log power
tracking
of the source
Information
(ox) should be less
design
angle
at elevation
at higher
angles,
these goals
bandwidth monopulse
of the mu-cc.
Observations
in log power
elevation
angle and frequency
the apparent
error).
angles.
useful elevation
scintillation
should be less
at higher
of arrivaL
automatic
minimum
(rms
amplitude
had shown that the rms fluctuations
To make observations
was to observe
range of elevation
to de finetbe
for modeling
at Haystack
data (i9-bit
analysis.
sum sigmd
(demand offset).
time,
The
were
The Com-
and antenna position
rate for post processing.
The angle
-EmEL.
ANTENNA
,,;
t
,,
‘2MHz+
S0-++
t
2C0- H,
LflL;~SS
11
d
A/O
WWFRTER
1
,Fig. II-i.
X-band
receiver
6
m-m
UW:ss
A(D
MRTER
1
system.
HI,YSTLCK
ANTE MA
--EE1
-El
-@El
Fig.11-Z.
X-bared tracker.
)i
j,
,!
,,
4
,,
I
7
..—-,..-.-.
encoder
values
. . .-.
were
ing the pointing
sampled
at the ZOO-HZ rate and averaged
The recorded
complex
signal
in a subsequent
post-detection
averaging,
noise ranged
between
rose
or set,
of signal
and as a result
level
receivers
was available
radio
stars
were
switched
for this radiometer
B.
system
the satellite
angles
However,
only one instance
encoder
values
polarization
●
obtained from the
to analysis.
correction
The monopulse
0.005” in traverse.
was also used during the measurement
was on axis and no pointing
A
and was used to observe
corrections
prior
path.
sum channel.
calibration.
and +0.005
receiver
precision.
used with the X-band
changes,
The pointing
position
The X-band
along the observation
was used with the orthogonal
plane.
The receiver
measurement
were
and re-
ae the satellite
These
A t 5-GHz,
500-MHz -
program.
Tbe feed
was required.
Millstone
by the IDCSP
The receiver
system
Data obtained
from
computer
at Millstone
satellites.
Because
hand circular
were
complex
equal amplitude
polarization
were
in active
intersite
link.
progressed,
Radar
available
The elevation
At first,
orthogonal
the telemetry
observations.
Propagation
Study!
to the CDC-3300
system
polarization
level
was modsignal,
and
at UHF had highly elliptical
on the principal
and traverse
signal trans-
only the AGC
the data transfer
complex
use,
for scintillation
Millstone
The IDCSP transmission
signals
channels.
telemetry
at a i O-Hz rate and transferred
channel signals,
values.
source
for the earlier
sampled
As the experiment
difference
the 40i -MHz
are no longer
an adequate
via the Millstone/Haystack
antenna encoder
Nearly
and orthogonal
the satellites
was used as configured
and recorded.
to provide
the Millstone
was used to track
and provided
the receiver
at Haystack
was sampled
izations.
Observatory
about the atmosphere
—0.075 * 0.005” in elevation
signal was stable in amplitude
ified
between
the desired
40 to
during the i975 season,
O.Z to ~.4 mdeg rms.
achieved
at the Haystack
mdiometer
The UHF beacon tracker
mitted
ranged from
from
due to receiver
within this range due
at low elevation
A and Cygnus for antenna pointing
added to the reported
bandwidth Dicke
varied
usage on the satellites.
off axis in the elevation
were
ranged
operating
in the distance
for use on any channel by cable
Cassiopeia
star observations
still
absorption
processing
radiometer
satellites
scintilla-
and i O-sample
in log power
ratio
that were
system
use was noted during the observations.
information
total power X-band
feed was mounted
offsets
available
additional
This radiometer
radio
of transponder
on angle measurement
to provide
the bright
The signal-to-noise
satellites
change due to transponder
Radiometer
20-MHz
and to generat-
and used to generate
rms fluctuations
caused by variations
post-detection
averaged,
for the IDCSP
detectable
the eight IDCSP
plus i O-sample
system
to recording
Using this tracking
and in tbe mmmnt of atmospheric
noise limitations
system
minimum
i“ signal level
station
detected,
program.
0,04 and 0.06 dB.
between
due to changes
ceiver
data were
analysis
the signal-to-noise-ratio
The corresponding
to differences
prior
..
commands.
tion statistics
45 dB.
.
.,
(right-hand
difference
polar-
circular)
channels were
right-
polarization.
8
—..
- . .. . . .
III.
OBSERVATIONS
Amplitude
A.
The lDCSP
satellites
synch ronoue orbits
each satellite
stack,
Fluctuations
were
moving
tracked
slowly
was approximately
the apparent
slow angle tracking
the atmosphere
as they rose
with respect
or set.
The satellites
to a ground station.
i 2 days with each satellite
visible
only two beamwidths
rate,
station geometry
the satellite
across
-to -ground
in near-
for about 5 days.
angular motion was typically
drifted
were
The orhit aI period
for
At Hay-
in five minutes.
was essentially
At this
fixed while
the path.
‘“
~
X- 8AN0
z
3
“ .. .
:
s
z
~
;
J
:
~
.x
30 —
.0,05569
m
3
g
,0 .
;
.
signal levels
at high
1
!
0
Fig. III- i. Received
elevation angles.
1
1
!
,0
““,
G
:
: .0—
:
2
,. - .x .0.0.9d,
d
>
5
: m—
“
z
g ,0_
;
.
0
!
I
m
m
TIME
35.25. APPARENT
ELWATION ANGLE
,Examples
of observed
high and low elevation
between
\
ellite,
35.25 and 34.20’
at X-band
the signal-to
were
higher
noise
Slight changes
exceeded
and display
fluctuations
The high-angle
fluctuations
than the values
modulation
increased
spi%
expected
in the minimum
received
detectable
signal
(ml.)
6
,4.X
in Figs.
III-i
data are for elevation
noise limit.
The meamred
due to thermal
the satellites
1
5.
and -2 for
angles
For this sat-
was 42 dB in a 1-Hz band; at UHF (O.4 GHz)
were
at the spin rate was usually
the X-band
are given
near the thermal
ratio
ratio was 39 dB in a i -H. band.
caused by satellite
peak-to-peak
thermal
eignal level
respectively.
(7.3 GHz) the signal-to-noise
-noise
slightly
fluctuations
received
angles,
t
40
1
so
WYvalue were
noise because
of small
spinning at i 50 rpm,
evident.
level
rms fluctuations
The combined
fluctuations
observed
at X-band
additimaal
‘and O.i to 0.2 dB
effect
of spin and
to the O.06-dB level.
but the minimum
value never
O.07 dB.
9
—...——_
.,.
..%W-,=,,.,
-
Fig. 111-2. Received
elevationlmgles.
“
——
..
,0
signal levels
at low
<
0.0
‘0 Tm!m.
#
“..
.
.
..
.
.
:;
,.
..-
. .
“.
“%.
.
.
.
08 SERV’ITIOM
IN,,,
0.,
”,,
1
).
1
Fig. III-3.
at X-band,
I
.
.... .
. ..r.
...”
.. . ...+
+-
O8SERVATION
INTERVAL
. 5.,”.
.,”,
W,A.ENT
.
.
ELEVATION
,,
.
5.,”.
b
Ihr
..o~
RMS fluctuations
in log power
,,
W.RENT
ANGLE (d!, )
Fig. DI-4.
at UHF.
ELEVAT (ON ANGLE
RMS fluctuations
14<,1
in log power
The signal-to-noise
combined
effect
ratio for the UHF (O. 4-GHz)
of satellite
nel (right -hand circular)
rotation
ox values
nel output was reconstructed
IO-HZ predetection
a coherent
signals
and December.
onal channel had a minimum
slightly
The signal level
fluctuations
increased
the i-see-averaged
was at – 0.22” in the direction
40 min.
before
figure,
i.e.,
At UHF,
X-band
disappearing
due to interfering
behavior
quadratic
remove
rms values
occurring
curve least
were
on the hour.
square
intervals
occurring
uncertainty
absorption.
A similar
observed
that would be associated
with a single
appear
similar
caused by the ground.
were
fixed
(in dB) ahout
with the start of the
calculated
relative
The quad rat ic curve
observing
station geom
for successive
intervals
to a
was used to
in satellite-to-ground
fitting procedure
5-rein.
are
at X-band
rms fluctuations
also calculated
curve
over
atmosphere.
5 -min.
was also used for the
were
expected
to represent
geomet W (no change in ele -
angle).
Examples
of tbe 5 -min.
-2 amd observations
and 4 -hr rms fluctuation
-4.
The data are for 3 IDCSP
at 26o” azimuth
elevation
(A.),
observation
satellites,
i975.
The i-hr
much longer
period
fluctuations.
rms values
the i -hr sample.
B.
remo”es
for tbe data given
Az,
ax values
periods
spanning
3 to 4“ elevation
The data were
figures.
obtained
Tbe quasi-periodic
(curve-fitting)
process
due to the long-period
between
and a highbetween
0900
for Figs. 111-1 and -2 and an additional
while the ground reflection
The det rending
a difference
observation
in Figs. fU -f and
in Figs. 111-3 and
spanning 5“ to 0“ El at 100” A.,
most of the wmirmce
This causes
the 5-min.
Elevation
Angle
at UHF have
used to generate
fluctuations
and i -br variance
the
evident
values,
the recorded
averaged
were
produced
encoder
for each of the ten/second
values
ii
and averaged
data samples
inphase error
voltages.
in
which
Fluctuations
estimates
! -hr
fluctuations
effects
for the UHF data.
Angle -of -arrival
combining
one ‘1rise”
within the data set are shown in these
shown on Fig. 111-2 have 2- to 4 -min.
is largest
viz,
one “ set” observation
spanning 37 to 33° El at i90”
and 2iO0 UT i December
time period
values
made within i2 hours of each of these data sets are given
(El)
5-min.
were
for the data in this
with a roughly
for each hour of data,
caused by the changes
The fluctuations
beam of the Haystack
The fluctuations
that hour.
The
20 and 60 min. (time)
fluctuations
fl”ct”ations
III-2
1.5 and 0“.
caused by tbe lower
between
The rms fluctuations
RIMS values
within the hour.
intervals,
calculated
Figure
for an additional
is negligible
are calculated
fit to the data over
slow changes in signal level
et ry and atmospheric
5-rein.
from the ground.
duration
and orthogonal
angles.
For the 73-mdeg
At UHF much smaller
given on each of the figures
for the Orthog-
for the principal
was tracked
in Fig. HI-2 are entirely
reflections
made with
ion bandwidth
sets and iO HZ for measurethe ox values
angles between
diffraction
is 2. 5“ and the fluctuations
behavior.
These
one -hour interval
vation
depicted
chan-
an effective
at UHF were
at low elevation
and the satellite
and horizon
appear to ride the longer
The rms values
tbe mean trend.
significantly
of set,
polarization
with
changed.
below the radio horizom
tbe fluctuations
to have a quasi-periodic
temporal
values
and UHF data for elevation
of ground multipath
the antenna beamwidth
primarily
The minimum
and the
chan-
The predetect
With the i O-Hz filters,
of 0.07 dB.
depicts
the effect
measurements
channel receiver.
as the .t ransm itted polarization
horizon
antenna,
(AGC ) voltage
lower,
polarization
.The principal
of 0.07 dB.
polarization
was slightly
the principal
was 250 Hz for most of the observation
ments made in November
varied
limited
gain control
phase locked to the principal
for the quadrature
channels
to a mf~mum
Orthogonal
observations
noise
from an automatic
bandwidth.
receiver
and thermal
by
A
3’”’1
-EEL
t
3*D
o
I
I
m
I
40
I
I
20
I
,0
-
T!~E3k
Fig. III-5.
Apparent elevation
X-bred,
high-angle data.
Fig. III-6.
Apparent elevation
UHF, high-angle data.
angle at
angle at
~ ‘: .g
q:
Q
I
t?l~
.
0.
‘5
: .m_
<
.-4.sQ
5C4- -0.0.6mm
~.
w_
“’ -, m
I
I
I
I
!
i:~
Fig. UI-7.
Normalized
elevation angle
error voltages,
high-angle data.
Fig. III-8.
residuals,
Elevation
high-angle
and traverse
data.
~gle
predetermined
calibration
channel voltage
voltage)
constant was used to convert
inphase with the sum charnel
into an angle deviation
calibration
curves
were
(The calibration
were very
program
UHF system
was manually
required
determined
bration
adjusted prior
after initial
data processing
values
ceive r noise limit.
this defect
suffered
sampling
by detecting
for data reported
level
set at UHF.
to the sum channel
only once during
disturbed.)
the
The
and new calibration
curves
could only be
of data reduction,
the available
rather than the correct
one second are depicted
cali -
reported
readings
“glitches.”
The observed
the expected
detrend
the data (estimate
due to receiver
random errors
positions
in the computer
expected
error
The theoretical
using only a nominal
to the angle-of-arrival
fluctuation
The autotrack
rms fluctuation
are displayed
time constant.
larger
were
data are also displayed
A small non-zero
exhibited
in Fig. fI1-7.
quadrature
in part caused
in the figure.
error
voltage
small non-zero
used to
limitation
estimate
voltage
These
of
for the data pre sented in
voltages
causing the observed
and corresponding
computer-aided
system
data were
is apparent
oscillation.
t racker
had a
and
The quadrature
not used in real time for tracking.
in these data.
fluctuations
is
cent ribut ion
was used to cent rol the antenna position,
by tracker
long-period
The difference
value.
The closed-loop
voltage
to
is less
Due to the requirement
than i see,
angle error
error
measurement
the error
predicted
and
averaged
fitting procedure
unclere stimated
constant
elevaticm
The inphase error
fluctuations
The quadrature
that depended
voltages
upon the polarization
transmission.
The residual
elevation
are shown in Fig. f31-8.
both angle encoder
angle errors
The tracker
data and error
any antenna positioning
from the quadratic
the bias errors.
has a time
inphase and quadrature
angular deviations
of the satellite
was significantly
system
difficult,
The theoretical
curve,
value to be less than the theoretically
The X-band
beam.
to remedy
was to cause an additional
angle-of-arrival
calibration
proved
was 0.6 mdeg.
ratio and a i-33z bandwidtb.
em-or voltage -to-angle
Efforts
rms measurement
is due to the curve
noise was 20 mdeg for the 2. 5“ Millstone
ratio achieved
The angle encoder
per second were
of the “glitches!’
The combined
angle
near the re -
or ‘Iglitche s“ within each
malfunction.
taken at 200 values
rms errors
biases).
were
is 0, 3 mdeg (Ref. 2).
system
i -hr rms measurement
and observed
based upon a 39-dB signal-to-noise
the observed
limit
The net effect
than 0.4 mdeg.
between
for the high elevation
fluctuations
beam and the 42-dB signal-to-noise
due to an encoder
the improper
of these
The signal level
one to two 5- to 10-mdeg
interval
of less than 0.3 mdeg.
Fig. Ifl-6.
over
Haystack
rms fluctuation
removes
voltage-to-angle
feed were
the calibration
using a nominal
angle measurement
here the encoder
reduce the effect
generally
relative
had to be modified
and, at the current
averaged
For the 73 -mdeg
at Haystack
tenth of a second
error
of the sum channel
Error
to each set of observations,
(Fig. III- 1) in Figs. 111-5 and -6.
in a i -Hz band, the theoretical
,! ,
(error
and during each observation
to the X-band
Unfortunately,
had to be generated
angle estimates
observations
7-see
constants
voltage
curves.
Elevation
system
value.
channels
connections
error
by the magnitude
encoder
at X-band
The calibration
for each data set.
UEF angle-of-arrival
divided
and phases of the difference
after the wavegufde
curves
were
signal
to the position
obtained occasionally
constants
stable at X-band.
observation
relative
the normalized
curve
Traverse
that remained
oscillation
voltage
data in constmcting
uncertaintiess.
which are cawed
angle residual
after
curve
is not evident
The residual
fitting
angle -of -arri”al
error
are also displayed
equation
in Fig. U1-8.
$3
——...
estimates
data show slow deviations
by using only a second-order.
errors
to one hour of data
in these data since the use of
-----————’-—-.--—..---—-
to represent
‘“”l -i!mmL
\
o
1
m
I
30
I
*O
TIME
Fig. III- 9.
d X-band,
Apparent
low-angle
..
5.
o
I
!
m
TcME
(.(”)
elevat iOn angle
data.
1
3.
1
20
0
,0
5.
[.!”1
Fig. 111-’10. Apparent elevation
at UHF, low-angle
data.
lii~
!
,
4.
angle
20
m’%.)
Fig. III- i 2. Elevation and traverse
residuals,
low-angle
data.
angle
‘1
J
At low elevation
angles,
fluctuations
in Fig. 111-9 and fluctuations
X-band
inphase
vation
displayed
decreases;
40 min.
error
angle residuals
angle fluctuations
errors
due to the ground were
and quadrature
tion and traverse
the traverse
high above the horizon
voltages
are displayed
angles below
to exclude
ground
(Fig. ID-i 1) are all less than i O mdeg.
the signal ievel
fluctuations
by the apparent
angle-of-arrival
successfully
maintained
may have occurred
component
fluctuations
Fig. UI-2.
A close
comparison
complex
signal level
combine
to produce
$”, i.e.,
more
the horizon
this effect.
level
caused
system
changes
that
voltage
shows relatively
fluctuations
large
quasi-
displayed
shows that the quasi-periodic
in
fluctua-
Both UHF and X-band
quarter-period
displacement
This relationship
is characteristic
!4
At
X-band
the characteristic
to rnult ipath.
in the figure
Two signals
Since the elevation
for times
between
$0 and 20 min.
with a i 2-dB difference
angle for this multipath
above the horizon,
than 40 dB below tbe mainlobe
a ground reflection
to antenna gain changes
curves.
response
is evident
change is 4 dB.
than ‘t6 beamwidths
is more
from
system
4 mdeg,
negligible.
3, and both show this apparent
response
Sufficiently
show that the X-band
as shown in Fig, III-13.
error
fitt~g
angle
exceed
signal level
the two curves
ele -
noise for only the last
are at angles
and that any signal
error
The
The inphase angle deviations
were
to the received
of a period
receiver
system
scintillation
reveal
and cuwe
the angle deviations
observations
deviations
signal and quadrature
monopulse
monopulse
The peak-to-peak
originated
in Fig. III-i
the received
of a complex
severe
between
hy a quarter
data are displayed
effects.
These
as shown
as the elevation
measurement
at times
of the normalized
that are similar
tions are displaced
between
track during
“glitc h,”
increase
than can be attributed
deviation.
at X-band
observations
than the noise.
to exceed
reflection
are far larger
These
The X-band observations
Although
due to angle-of-arrival
The quadrature
periodic
appear
evident
in Fig. J31-i %, and the X-hand eleva-
angle residuals
0.25”.
were
at UHF as shown in Fig. III-f O.
in Fig. III-12.
greater
The elevation
angle residuals
evident
are displayed
that are significantly
in Fig. III-8,
or for elevation
due to the atmosphere
can
event is CIOse to
and the antenna gain in the direction
peak,
the multipath
but must have been generated
FKCEIVED
of
signal could not have
within the atmosphere.
-mm
—
in level
At
.-
BAND
SIGNAL
LEVEL
. NORMAL\ZEO O“ADRb7URE
ERROR vOLTAGE
Fig. L31-13. Comparison
of received
signal
level and quadrature elevation
angle error
voltage fhctuations,
low-angle data.
I
$
1
1
1
I
I
UHF
..
I — RECEIVED
I
o
SIGNAL
,
m
I
LEVEL
1
3.
20
11.6
[.1”1
I
40
,
50
II
.,
the antenna gafn toward
UHF,
tion angles
source
below
the horizon
i o which correspond
of the multipath
in Fig. 111-40 were
was less than 3 dB below the mainlobe
to times
between
at UHF is ground reflection.
generated
and hence the apparent
using only the nominal
fluctuations
peak at eleva-
i5 and 60 min.
Thus the most likely
The UHF elevation
angle data displayed
error
due to this multipath
voltage-to-angle
calibration
curve
could be exaggerated.
-
I
. .
.
.
..
,.6
“. . .
.
. .
F,”,,..
.e
,
l“.
1
“.
8.
.
-i=
A,h,
APPARENT
ELEVATION
ANGLE [,,91
Fig. III- i 4. RMS fluctuations
angle at X-band.
The 5-min.
corresponding
at elevation
“.
.
.
.o%-:.&
“>
.*
fluctuations.
Polarization
;,,,,,.,,
~
polarization
recorded
at both frequencies.
the end of the year,
ly of tbe same level
signals
in received
were
with the values
10”.
angle
due to “glitches”
and
are significantly
The i -hr rms fluctuations
due to longer
are roughly
coherently
Quadrature
The orthogonally
an order
period
(large-
of magnitude
larger
i”.
filters
i“ level
at X-band
data were
received
implying
signal
ranged
from
was slow depending
being observed.
to the principal
only from July to
at Millstone
at Millstone
a linearly
satellite
for receiver
obtained
only installed
signal
and in phase relative
expected
and UHF using the
video data with a i O-Hz bandwidth were
were
signal,
polarization
The variation
detected
video
polarized
polarized
and the particular
power
The traverse
angle fluctuations
values
angles below
The UHF quadrature
the orthogonal
signal.
ground station geometry
fluctuations
at elevation
as the principally
At X-band,
angles below
in traverse
in Fig. If I -14, and the
instrument al errors
angle fluctuations
and the i O-Hz predetection
polarization
are given
Tbe elevation
the 5 -min.
signal as reference.
observations.
ANGLE [d., )
Fluctuations
polarization
principal
the source.
Z and 3 times
The elevation
The orthogonal
O.5”.
noise at elevation
angle fluctuations
0rthogona3
the November
above
ELEVATION
are given in Fig. 13-i 5.
above the expected
angles
angle are between
than the traverse
identical
angle fluctuations
than the instrumental
in elevation
principal
.
Fig. 111-i5. RMS fluctuations
angle at X-band.
in elevation
are not significantly
noise
c.
.
.
&PP&RENT
and i -hr rms ele”at ion angle fluctuations
rms traverse
fluctuations
scale)
A
.
.
~,~
~,,~
greater
A
.
OBSERVATION
,NTERV.L
. 5 ml”,
receiver
A,h,
.. “.
. .
I
1“.
OBSERVATION
INTERVAL
,0
polarized
prior
to
was roughsignal
at
i5 to 25 dB below the
upon the satellite-to-
At high angles,
polarization
the rms
signal were
noise.
16
.—-.
.—.__
. . . .._-
“1-ImEL
pRtNCIPAL
,
sum
ORT”CIGONAL-PRINCIPAL
o
I
!
1
1
I
!
1
1
I
1
1
I
!
1
1
1
1
I
1
,0
I
,0
-w
..
“..
Q-EL
o —
.. . -
I
l-TR
o
-0.2
.2
O-7R
-0.2
o
I
,0
TIME
I
40
I
,.
m
(ml. )
Fig. 221-i6.
Received signal fluctuations in the principal and orthogonal polarization
scan
channels and the elevation and traverse
difference
channels, low-angle data at X-band.
The orthogonal
at low elevation
polarization
signal
indicate
the antenna.
differences
variation
large
signal-level
excursions
event that occurred
variations
different
em-or voltages
multipath
at
52
deviations.
between
could,
ICI
and
however,
components
min.
to the principal
Figure
polarization
are also displayed
are
in the figure
and which variations
accompanied
polarization
211-46 displays
signals.
path at the two polarizations
are due to antenna deviations
due to angle-of-arrival
and -i 7.
to principal
in the propagation
The complex
ratio
These
with respect
angles as shown in Figs. III-96
and phase of the ratio of the orthogonal
ratio
varied
by ratio
20
min.
are
@
correlated
that combine
to provide
the logarithm
Fluctuations
in the
or variations
due to
to help identify
which
are due to propagation
The
changes that appear
On the other hand, the ratio variations
a composite
antema
to be
dm-ing the mult ipath
with angle-of-arrival
be caused by the cross-polarized
signal
response
deviations.
to the
signal which the antenna
‘0
-i!EE!L
ORTHOGONAL
,.
I
POLARIZATION
—
I
o
I
I
!
r
I
20
PRINCIPAL
POLARIZATION
,.
I
,50 —
!ta
—
w —
.0 —
m —
,~
T,ME
Fig. III - i7.
Received
signal fluctuations
channels, low-angle data at UHF.
tracks.
At UHF (Fig. III-17)
ences between
the logarithm
the large
[ml.)
in the principal
phase variations
of the orthogonal
observed,
and principal
reflections.
18
and orthogonal
power
combined
variations,
polarization
with larger
sum
differ-
are due to ground
IV.
ANALYSIS
A.
Statistical
The
fluctuation
-35”,
and low,
observations
Summary
<i.5-,
were
conditions.
time
histories
elevation
angles
Roughly
equal numbers
near the horizon
a random
taining
cess
of a single
a physical
Figs.
IV-3,
These
-4,
-44,
problems
to very
satellite
understanding
ful only if the process
times
small
rise
is stationary.
The 5-rein.
significantly
will be examined
made during each season.
that were
large
hy iOS elevation
a time history
process.
at elevation
angle.
The data
that is a single
A quantitative
of fhe process.
and i.hr
measure
in ob-
of the pro-
in turn are use-
values
that the process
with a limited
sample
is “sef”l
These
rms fluctuation
suggesting
in tum starting
458 hours Of
meteorological
number of time histories
moments
and -i 5 differed
were
values
or set provide
the statistical
series,
at high,
with time of day.
of a limited
of the fluctuation
from
measurement
of the day under different
fluctuations
and a variation
An examination
can only be acquired
two hours of observations
of hours of observations
dependence
process.
for
During, the entire
angle and signal-level
and decreased
seasonal
Observations
from
angles.
above are
made on 37 days at different
The data all showed ele”aticm.
showed a slight
depicted
depicted
in
is not stationary.
rmmber of time-history
exam-
ples.
A dependence
angle is evident
and displayed
level,
from
the time
in Figs. IV-1
elevation
elevation
of the magnitude
angle,
angles.
changing from
pIotted
in Figs.
nificant
more
level
Iv-3
and - f4.
fluctuations
le”el
component
observed
under clear
fluct”atiom
of the ele”ation
decrease
from
The elevation
a“d elewt
The elewation
with increasing
error
typical
rise
data show large
fl”ctwdions
voltage
of two-ray
variations
angle error
angle variations
are evident
angle quadrature
occur
which correspond
error
at 2° El.
do not decrease
voltage
only in combination
at t to 2-
(p-p)
is evident
error
signal
voltage
The difference
ion angle fluctuations
No significant
sky conditions
11 dB peak-to-peak
as
in the eleva-
in the rms values
fluctuations
elewat ion angle than do the s igrml le”el
mult ipath.
on elevation
in the X-band
40 mdeg p-p at 2“ El to iO mdeg p-p at 5“ El.
of signal
rapidly
quadrature
fluctuations
and quadrature
a“d angle -of arrival
of a satellite
These
and i.5 dB p-p at 5° El.
tion angle dependence
to decay
history
and -Z.
level
The signal -lem?l variations
to 3 dB p-p at 3“ El,
rapidly,
of signal
appear
fhctu at ions.
Sig-
with the quasi-periodic
voltage
fluctuations
or signal
with the i O- to 2O-mdeg point ing angle var iat ions
abcme 40.
The data displayed
in Figs. IV- I and -2 can be interpreted
tuations that depend only on the initial
i
time.
ff, as is usuaIIy assumed
bias errors
i
,
arise
L-band
radar
The observations
i6 min.
for different
observations
were
The cross-section
through the atmosphere,
observations.
For the l-m2
for the i -see averages
tion resulting
from
tion between
2 and 30 elevation
receiver
bias error
station)
fluc-
and not on
due to refraction,
the fluct”atiom
tbe
d“e to the stratifi-
azimuth directions.
section
represent
are larger
calibration
displayed
of bias errors
index,
of a calibration
the south then north a“d were
fluctuations
hence,
analysis
of refractive
of the cross
made toward
as representing
angle (satellite-to-ground
for ray-tracing
from the stratification
cation should be identical
ele”ation
signal
level
sphere,
LCS-4,
angle steering
set
in time by less than
for the one-way
the signal-to-noise
The error
noise was less than 0.2 dB.
are shown in Fig. IV-3.
changes for the two-way
than the fluctuations
i“ this figure.
sphere
separated
in measuring
The peak-to-peak
exceeded
20 dB.
satellite
ratio
the rms
beacon
exceeded
log cross
cross-section
The detailed
path
30 dB
secvaria-
fluctuation
60
m
.
b~
SIQNALLEVEL
.
.NGLE-OF-.
. .
s.
ERRORS
ELEVATION
-------
TRAVERSE
0.6
6
QUADRATURE
ERROR
—
ELEV,ir(ON
------
TRAVERSE
:
~o
g
:
~
.
R -0.6
VOLTAGE
-
,0
:
.
g
~
-!0
I
!
.000
2,3,
00,0
uNivERSL
TIME [h,,
APPARENT
Fig. IV-I.
Satellite
1
,,.
ELEVaTIO.
rise,
I
20
—
0!0,
min., ur 1
1
2,0
I
,..
I
RR, VAL
—
ANGLE
(dog)
233o UT,
29 April
i975.
:
0
m
X-BAND
-EEm_
..
SIGNAL
LEVEL
$0
t
..~
,0
0
ANGLE-OF-ARRIVAL
:
<
ERROR
ELEVATION
—
Y
TRAVERSE
-40
0.6
QUADRATURE
—
ERROR VOLTAGE
ELEvATION
-
m
TRAVERSE
j
:
0
!=
.,.
I
0,,.
0.6
.!0.
I
0,0,
uNwERs#L
,
!
TIME (w,
m;..,
I
,.0
I
..0
Fig. IV-2.
Satellite
02,0
.7)
1
s .0
APP&RENT
ELEVATION
ANGLE
rise
continued,
(W)
OiOO UT,
30 April
21
..-—-–—-———.,.s
1975.
:
a
,.
o
I
. II
I *
A
A
vwrv”v~
R!SE 1130uT
170-de,
AZIMUTH
-,0 -
.20
I
IIW11144.
1
1
1
!
1
1
1
I
!
1
.
-m
.20
Fig. IV-3.
L-band radar observations
sphere (LCS-4,
Object No. 5398).
of a rise
and set of a %-mz calibration
.
,.
:,,
,,,,.
0 SOUTH
L ‘:
.
NORTH
”
.<.
“t
...
.:
,.. , o<w
g
.i
“.0
,0.
.. . .
MVAT;ON
y.
2:.. ,
. .:....J.-......~. :
., .. ~. .. .. +..
. .+
.“:“ . :..”.
”
.“.
. ..
..
.
.
.
:!
IN STRUMEN
LIMIT
1
1
,468,012
TIME
TIME
(ml.)
Elevation angle and rms
Fig. IV-4.
sphere track depicted in Fig. IV-3.
1
I
I
log cross
22
section
values
(rein)
1
,
t~ls
for calibration
,
TA
$,
time
~“
histOries
values
fOr observations
These
differ.
Figure
fluctuations.
f
valuee
IV-4 displays
The rms values
detrending
process
t ion angles
below
above.
i O” encompassing
mate of the variance
of the fluctuation
elevation
Because
vals will have larger
tervals,
~
,,;
i
however,
A time-of-day
data are
for
the variance
variances
three
mtellite
in Fig. Iv-4
depends
angle.
rises
observed
six
a useful
identical
larger
provide
at the same
observation
Smaller
esti-
vs elevation
The rms values
in the rms values
used in computing
in the fluctuations
using the same
to provide
they are reasonably
spread
angles
shows the rms values
due to the change in elevation
a larger
for the
section
for elevation
intervals
the north and south.
because
peak
spanned less than 0.6” at eleva-
angle,
(samples)
dependence
for 8. 5-see
interval
on elevation
would also produce
the number of fluctuations
toward
process
is evident
number of fluctuations
The insert
angle and these are found to be identical
a good description
angles.
calculated
Each 8.5-see
a sufficient
of the process.
Even the peak-to
alone is not responsible
elevation” angle and rms cross
The 0.2 -dB noise limit
in this plot were
as described
are different.
stratification
both the apparent
for the same pass of LCS-4.
above 45”.
E,
tO the nOrth and wuth
data show that large-scale
observation
due to a decrease
interinin
the value.
is also evident
hours apart
a8 shown in Fig. IV-5.
on the same
day (same
-,.
g
These
day as for
~1
q60
--
l.,Jv-lJw
,-
.
:s,0
1
I
1
!
(
I
T,ME
,
m
(“,
I
[
,
)
1
I
m
1
1
I
IV-5.
Three
satellite
rises
1
,
(,.”1
!
.NGLE
1
%0
I
.NGLE
ELEVATION
FM.
I
!
)
,
ELEvATION
I
I
,,03
,,1”
1
w
(d*O)
I
within i2 hours.
1
1
29 ADril
1
1
i975.
23
—.--.—.—
-
-imma-
..
.. . .
...
Tixm
.,.. :
. ,, . .
i.; ““.
‘$
,8-,9
NovEMBER
‘
:,.
.
~:’?
W. THER:
1975
IV-6.
at X-band.
R
Fig.
CLEAR
I
,0
I
ELEVATION
. .
00!
L
o,
‘
0.,
~~
0.40.6
ANGLE (4.,1
MS fluctuations
I
APPARENT
Fig. IV-7.
at x-band,
in log power
‘
z
4
ELEVATION
6s10
‘0
J
““’m
.NGLECdeQ)
RMS fluctuations
spring season.
in log power
1’-----’:--’...
,
‘
....;
,
.’<...
, ,:.:,
_::-:~’
.
0.1
I.
:,
‘waHit--
SUMMER
JUNE- d“LY-AuwsT
CLMR
.
I . C1.ouo
0.07
0.,
0,2
RA4N
0.4
06
1
1
APPARENT
Fig. IV-8.
at X-band,
.
I
2
+
ELEVATION
6 .10
,.
II
0.01
,0
0.!
~o so j~
M-mm,
ANGLE (d.ql
RMS fluctuations
summer season.
Fig.
in log power
at
24
IV-9.
X-band,
R MS
fall
ELEvbT (ON ANGLE
fluctuations
season.
in
ld.gl
log
power
Figs.
IV-4
and -2).
the morning,
afternoon,
The character
low-frequency
larger
component.
fluctuations
fn the evening,
had disappeared.
at a given
elevation
obtained
-i4,
elevation
in the rms values
The seasonal
(scattered
Days with showery
countered
weather
cluded thin scattered
,,
:(”
!.
,,
were
included
through
as !Irain.l!
data set
lv-i5
overcast),
A single
encountered.
as clear
If rain occurred
weather
as shown in
for a given
the ex-
days with clear
observation
observations
clear
skies,
and days with rain.
get often enmay have in-
sky and cloudy conditions
at any time within an observation
on weather
fluctuations
groups
and -16 summarize
including
dependence
lower
eleva-
1 and 100.
Data sets that encompassed
No clear
data
at a given
in rms values
all the observations
rain were
below
these
from two sets of observa-
cumulus to complete
Sets displayed
clouds.
showed
between
dB range
angles
Although
in rms values
variation
Figures
-i4.
angles
in the ‘Iclo”d *1cat egory.
was classified
the ‘*cloud”
cirrus
a significant
component
narrow
at elevation
within four hours.
the spread
In
By
on them a high-frequency
but the high-frequency
angle data are obtained
display
encompass
types.
are evident.
The data displayed
all obtained
fair-weather
and widespread
several
for each rise.
the data often fall into two different
season
for elevation
summaries
days with clouds
large
near i 00- and 260-,
angle as shown in Figs. IV-7
tremes
remained
When the low elevation
Data for an entire
different
variations
at a given time of day span a relatively
by more than six hours,
Fig. IV-6.
peak-to-peak
which have superimposed
and -i 5 were
at azimuth angles
tion angle is small.
tions spaced
are evident
angle as shown in Fig. IV-4.
-4,
is markedly
with small
the fluctuations
The rms variations
iO” in Figs. IV-3,
were
of the fluctuations
fluctuations
type was ohserved.
than for clear
sky;
set it
In the spring
in the fall
the reverse
:
occurred.
In general,
seasons
were
rms “alues
roughly
i ‘,
rms signal
and were
the measurement
elevation
the same.
angles
error
The elevation-angle
at elevation
level
variations
angles
able above the receiver
tion model
as shown in Fig. IV-i 6.
in traverse
ment measurement
B.
Scintillation
arrival
a“d relate
refractive
scribe
theory
attempts
because
a wider
NO variations
and satellite
values
of the
range
of
elevation
were
evident
ranged
significantly
angle fluctuation
“p to 40”.
fluctuations
above
spin were
than
at
between
1 and
higher than for
observed
data were
fluctuations
fluctuations
using a surface
of the orthogonal-to-principal
all be-
w ere measur-
The elevation-angle
expected
angles
larger
as high as 2 mdeg were
they did not show significant
correc-
polarization
increases
above instru-
i o.
Theory
to describe
the random
the spectrum
along the ray path.
only for weak scintillation
f O”.
The elevation-angle
angles
angles
the rms valw%’ to either
the dependence
displayed
angle fluctuations
RMS values
i 0-.
hiss-error
with Scintillation
index fluctuations
model exists
above
noise at elevation
Comparison
noise
angle and in the ratio
further
the rest
0.5 and i 4 dB at elevation
above
elevation
i ~.
noise for elevation
to the predicted
between
angles
The clear-sky
identical
are not discussed
fluctuations
The summer
below
angles
are nearly
signals
rms
i”.
angles
as high as 30”.
low % mdeg rms for elevation
Fluctuations
ranged
by the receiver
The 5-min.
angles below
at elevation
fluctuations;
variations.
introduced
above i 50.
seasons
the largest
less than O.2 dB at elevation
i 00 mdeg for elevation
the other
data showed
than did the signal-level
The 5-rein.’
below
the summer
fluctuations
or correlation
At the present
when ax < 5 dB [(Ref.
of the rms fl”ct”ation
values
time,
9)1.
m frequency,
in signal level
and angle
function describing
an adequate
The theOw
propagation
of
the
theoretical
cm be used tO degeometry,
and on
. ... .
. ..
.
. . ..
.
.
CLEAR
. CLOUD
.
RAIN
APPARENT
Fig. IV-IO.
at x-band,
ELEVATION
RMS fluctuations
winter season.
0>
1
,0
I
ANGLE
1;.
APPAFSNT ELEVATION
(d*Q)
ANBLE wag)
Fig. IV-i i.
R MS fluctuations in elevatiOn
angle at X-band, spring season.
in log Wwer
-D@m_
ELEVAT,ON
ANGLE
.-
I
,,
,,.
.
,,
0.,
1 ...’..’
APPb..&
ELEvATI..AN;LE
,
RAIN
.
o
x
APPA.&
(e+ol
ELEVATION
bNGLE
RMS fluctuations
Fig. IV-43.
angle at X-band, fall season.
RMS fluctuations in elevation
Fig. IV-12.
angle at X-band, summer season.
@+U
)
in elevation
,i
4
$
.;:
26
;:,f
,,..,,
,,,
; ?,...
!
,:.!
>,?-
.
Fig. IV- 44. RMS fluctuations in elevation
angle at X-band, winter season.
,. ; :-.
:
“..
.
&
.,”,
..
OECEM#?EER-~A#ARY ,,.
::j
. CLEAR
—
. CLOUD
. RAIN
1.
J
01
APPARENT ELEVATION
AN:LC
i~d
,m
1,
I
A,,ARENT
ELEVATION
Fig. IV-i 5.
full year.
ANGLE
RMS fluctuations
,
1
!
0,,
,0
!,
(@l
AF.PA.
EN,ELEVATION
Fig. IV-i6.
RMS fluctuations
angle, full year.
in log power.
27
,0
m
ANGLE
(’44’9)
in elevation
the intensity
of either
index fluctuations.
the turbulence
Following
Crane
or gravity (buoyancy) waves responsible
for the refractive
8,9,+0
and noting that the results for tropospheric
scintil-
lation
can be obtained from the expreasicms
cation
by k2/(2rr e), then UX in decibels
developed
for icmotipheric
scintillation
hy multipli-
becomes:
(i)
\
where
Z.
= 2u/f.o,
u
p . expnent
= outer scale of turbulence
of power
fluctuations
u . axial ratio
spectrum
(or gravity
of refractive
waves)
index
*N(:)
for the refractive
index spectrum
$ = zenith angle of tangent to ray at p
k . 2T/A, A . wavelength
re = classical
electron
2
- variance
‘N -
of the refractive
Z = P(L - p)/L,
= –r(z+)
b
P
radims9
index fluctuations
L = length of ray path, p . position
Cos (+2
.1 2’P-4)’2
2<p<6
;
;
p/4
p=4
I . x/2
G(@,4)=
along ray
(i + cosz~
;
+ az sinz~)
(cosz * + az sinz *)(p-1)/2
and the power
spectrum
for refractive
index fluctuations
U;(P)
aL:r(p/2)
*N(P> ~) =
z~r(3/2)
K =
=wemrnber
S h, Sv = ~rimntal
For
isotropic
reduced
I
turbulence
r(~)
i +
[()
L2
~
and vertical
22
1
P12
(K;
= 2 T/d, d = scale
(CT. i ) with p . 1i/.3and
by Tatarski i5
to the equation given
is given by:
+c!
.“)
size
wavenumberif.
Lo
and L very
large,
this expression
can be
.3; =(*)2
where
c;
replaces
u:
A reasonable
&56k’qLc’(p,p’/6
*
N
0
as a measure
expression
of the intensitY
For
ionospheric
across
Of turbulence.
for the angle-of-arrival
of tbe values to be used in describing
scintillation,
the power
Lo exceeds
the path during a measurement
(2)
varimce
spectrum
requires
a better
understanding
for the refractive-index
fluctuations.
any scale, size associated
with atmospheric
drift
10
In that case, a reasonably simple approxi -
interval.
mate expression
for u: ban be generated.
From analyses of tropospheric
scintillation
data re by Tatarsla, i 5 it is e~dent that L is larger than the Fresnel zone sizes typical Of mi 0
crowave and optical propagation through the lower atmosphere.
For tropospheric
turbulence
i6
Anisotropy
(a <1 ) occurs at scale
at scale sizes smaller than Lo, the spectrum is isotropic.
ported
sizes
larger
greatly
exceed
than Lo.
Since,
the traverse-angle
ciated with atmospheric
inal 10-m/eec
for
the Haystack
fluctuations,
and are only valid
for weak scintillation.9
the weak-scintillati~n
frequency
fluctuations
than tbe scale sizes
observation
period.
and (2) were
The X-band
dependence
at kcdb frequencies
given
derived
and UHF observations
by Eq. (2 ).
are plotted
using the Rytov
Five-minute
in Fig. IV-17.
approximation
were
used to check
ox observations
TWO curves
separated
7,3 6!!,
0,4
EXPECTED
OEPENOENCE
LAYER
AT
0,0,
~,,
RMS fluctuations
G14Z
ELEVillON
ANGLE
OF A TURBULENT
l-km
HEIGHT
I
AP;RENT
Fig. lV-i7.
as so -
For a nom-
Lo << 3 km.
for ax given in Eq. (i)
made simultaneously
the elevation-angle
drift by the line of sight and a 5-rein.
drift by the line of sight.
The expressions
measures,
Lo must be smaller
1
20.0
ELEVATION
in log power
ANGLE
at X-band
,@.!
(t+q)
and URF.
29-30 April
i975.
by
A -7/i2
were
plotted on this figure
curves
were
generated
be interpreted
The X-band
as being in reasonable
This discrepancy
by averaging
Tatarski?3
weighted
~.
over
producing
similar
lar-ge.g
For large
randomly
As a result,
the elevation
theory
fluctuations
events.
results
index perturbations
of the spectrum
spectrum
waves
for scintillation
spectrum.
geometrical
at large
scale
frequencies,
ture size,
The angle -of -arrival
data have an elevation
between
angle
fluctuations
reveal
become
a number of
of strong
model is not available.
derived
using a power
spectrum for the
i4
The beturbulence.
for atmospheric
of importance
cause.
fluctu-
attenuated by
-4, and -i4).
appear to be characteristic
used to derive
a distinction
fluctuations
scale
sizes,
(ray tracing ).
sizes),
~.
to angle-of-arrival
(t) only assumed
The fluctuations
is usually
the two phenomena
fluctuations
the existence
of a
could be due to gravity
drawn between
waves
are not important;
the signal-level
v , however,
are dominated
by the large
the propagation
phenomena
In the limit
tbe angle-of-arrival
fluctuations,
decreases
for axfixed aperture
beamwidth
sizes
angle in-
and turbulence,
the shape of the
is of importance.
At large
optics
scale
zone
below the value required
the time histories
e“ents
above were
hut not its
Although
The angle-of-arrival
perturbations.
gi”en
analysis
shape,
the differences
however,
These
that is often observed
The theoretical
m- to tm-bulence.
Figs. IV-3,
Fresnel
as the elevation
data.
by
for a uniformly
which are not severely
angle-of-arrival
strong scintillation
at the larger
and its general
decreases
fluctuations
was discussed
by 20 percent
for the X-band
d >> ~Z,
or strong scintillation,
multipath
a viable
is not known.
sizes,
in the X-band
effect
of the size of the first
of the aperture
dependence.
in ox as the elevation
model is not valid when the signal-level
Currently,
havior
slope
scale
The weak-scintillation
refractive
Again
steeper
to that for the UHF data (see
occmring
scintillation.
are reduced
is one-half
and the antenna rapidly
by the large
The weak scintillation
This latter
antenna aperture.
These
The UHF data can
elevation-angle
decrease
may be due in part to a reduction
the layer
the apparently
dependence.
at a t km height.
a significant
zone size to equal the diameter
averaging.
dependence
layer
freTJencY
with this expected
and exhibit
when the diameter
between
are dominated
aperture
turbulent
agreement
the 36.6-m
aperture
The distance
creases
the expected
He showed that the rms fluctuations
circular
for the firs t Fresnel
ations
for a hypothetical
data are not in agreemerit
angle increases.
caused
to represent
as the frequency
size,
of geometrical
fluctuations
a , increase
due to th~increase
the elevation-angle
increases
(increase
size
refractive
are adequately
optics
(the Rytov
index
described
by
approximation
are independent of frequency.
At high
7/f2
~a~
~
‘7/32).
For a fixed aperas f
in D/~Z
fluctuations
is linear
30
scale
where
D is aperture
increase
with frequency).
diameter.
as a percentageof the
v.
CONCLUSIONS
Observations
of tropospheric
angle fluctuations
angles
ranging
5-rein.
were
from
elevation
period
This result
to 43”.
made at Haystack
in Fig. V-i
uncertainties
Single-antenna
radar
is independent
of frequency.
using the surface
refractive
measurement
The median values
are displayed
angle measurement
calculated
were
evident above the instrumental
the horizon
observation
the troposphere.
scintillation
noise at initial
These
during a 5-rein.
will not achieve
The expected
correction
elevation
are nearly
within
a
data represent
observation
better
rms residuals
model
Elevation-
for the rms fluctuations
for each season.
expected
systems
and Millstone.
period
measurement
the
due to
accuracies.
for bias error
estimation
the same magnitude
as these
t
SUMMER
~. ,
SUMMER
FA. SPRING
0
FALL
.
wI mm
t
~
818,
1
t
0.1
APPARENT
Fig. V-i.
values.
utes,
Because
the median
parable
rate procedures
are therefore
possible,
designed
in elevation
in Fig. V-i
represent
model
estimate
longer
the minimum
provides
a reasonable
a better
angle by season.
apply for time intervals
cm.rection
it provides
to provide
scintillation
theory
aperture
not significantly
strong
displayed
!0
ANGLE (d.,)
errors
estimates
correction
than five
in providing
with errors
procedure.
of the hiss errors
min-
More
comelabo-
at one instant of time
not warranted.
The-tropospheric
multipath
tion was noted.
observations
for elevation
averaging
affect
scintillation
occurring
estimates
Since the sin-face
of weak scintillation
show severe
correction
rms values
to the minimum
ELEVATION
Median rms fluctuations
refraction
for bias refraction.
u
!0
angles
using tbe Haystack
the angle-of-arrival
occm-red.
events.
The strong
signals
i“ qualitative
2 to 30.
scintillation
was a result
diffe=ing
fluctuation
angles below
data
averaging
did
2 to 3”,
of a number of randomly
multipatb
is presumed
at slightly
with the predictions
The aperture
At elevation
scintillation
polarization
yeceived
agreement
The signal-level
36.6 -m antenna.
scintillation.
During the strong
The change in apparent
of the antenna to the multiple
were
above
events,
signal
depolariza-
to be caused by the response
angles
of arrival.
REFERENCES
*,
J. V. Evans, editor, ,,Millstone Hill Radar Propagation
Study: scientific
Results,
Parts I, 32, and 131j’ Technical Report 509, Lincoln Laboratory,
Nf.1.l’. (i3 November
i973), DDC Nos.:
Part 1, AD-78 ii79/7;
Part 11,
AD-782748/8;
Part 111, AtJ-7805<9/5.
2
D. K. Barton, Chapter 15 in Radar Svstem
Englewood Cliffs, N. J., i964).
3,
B. R. Bean, E. J. Dutton, and B. D. Warner,
Chapter 24, “Weather
on Radar:t in Radar Handbook, M. I. Skolnik, editor (McGraw-Hill,
New York, i970).
4,
crane,
SeC.
2.5,
,,Refraction
Methods of Experimental
Pby.&s,
demic Press,
New York, i 976).
5,
J. V. Evans, editor, ‘tMillstone Hill Radar Propagation
Study; Technical
Note i969-5i,
Lincoln Laboratory,
M.l. T. (26 September i969),
DDC AD-701939.
J, C, GbilOni, editor,
,,Millstone Hill Radar propagation
Study: InSt ru mentation;’ Technical Report 507, Lincoln Laboratory,
M. I.T. (20 Sepi40/7.
tember 1973), DDC AD-775
6.
Analy~
(Prentice
Hall,
Effects
Effects in th$ Neutral Atmosphere,”
in
Vol. 13B, M. L. Meeks, editOr (Aca-
EL K.
7,
J. V. EVanS, editor,
,1Millstone Hill Radar Propagation
Study: Calibra tion, “Technical
Report 508, Lincoln Laboratory,
M. I.T. (3 October f973, DDC AD-77968919.
8.
R. K. Crane, “Spectra
~,
204i (i976),
9.
R. K. Crane, 1’Ionospheric
publication,
i97 7).
of Ionospheric
Scintillation,
Scintillation!’
Proc.
IEEE
J. Geopbys.
(accepted
Res.
for
10.
and Doppler
R. K. Crane, ‘1Variance and Spectra of Angle-of-Arrival
Fluctuations Caused by Ionospheric
Scintillation;
J. Geopbys. Res. (submitted for publication,
t 976).
il.
R. K. Crane, “ Propagation
Phenomena Affecting Satellite Communication
Systems Operating in the Centimeter
and Millimeter
Wavelength Bands:’
Proc. IEEE ~9, 173 (i971), DDC AD-728i87.
of tbe Haystack Antenna and Radome,”
M. L. Meeks and J. Ruze, ,,Eval”atio”
IEEE Trans. Antennas and Propag. -9,
723 (i971),
DDC AD-737t66.
<2.
13.
H. G. Weiss,
11
The Haystack Microwave
Research FacilityU
IEEE Spec DDC
AD-6i4734.
tr”mz,
NO. 2, 50 (t965),
%4. s, ~. Sherman, ,,COmpIe X ~dica ted Angles Applied to Unre sO1ved Radar
Targets and Multipath:’ IEEE Trans. Aerospace
Electron.
Systems ~7,
i60 (i97i).
i5.
V. 1. Tatarskii,
Tbe Effects of the Turbulent Atmosphere
On Wave prOPAgan
(Nauka, Moscow,
t967j.
(Translation
available U. S. Depatiment
of Commerce,
National Technical Information Service,
Springhill,
Virginia,
i97i.)
16.
A. S. Monin and Y. M. Yaglom,
Statistical
Press,
Cambridge,
Mass., i975).
32
Fluid
Mechanics,
Vol. 2 (M. LT.
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Low Elevation Angle Measurement Limitations Imposed
by fhe Troposphere: An Analysis of Scintillation Observation!
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Technical Report
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NOTES
None
KEY
WORDS (Continue
on reverse
side
if naesmry
fmiex of refraction
tropospheric
(Continua
.?. wwr.
e ride
{daui/~
by blook
number)
x-band
UHF
muitipati
propagation
ampltmde scimflhion
ABSTRACT
md
if .SG.S.V
amd i&nti/~
by bkmk
bizw
errors
Miflstone radar
Haystack
radar
IDCSP satellites
wmb.r)
Tropospkrfc
.an$Je-of-arrfval axd amplitude mimflhdon measurements wem made at X-band
(7. 3 GHz) and at UHF (0.4 GNz). Tbe measurements were made using sources on safdlffes with
12-day O1bft.9. The ~le
of arrivat of tbe ray Path m a satellite changed slowly alfowing observations of flucmadons caused by atmospheric irregularities as they slowly drifted across tie ray
path ‘fbe fluctuations were cbaracterfzad by the rms variations of elevation angle and the logarfthm of received prover (fog power).
Over a one-yeax period, 458 twurs of obee-ation were amassed spanning every season,
time of day, and weather conditions. The leSIdtB show SUOW sclntflfation Occurrences below
DD, %3 1473 EDITION
OF
1 NOV 6S IS 00 S0i.EIE
UNCLASSIFIED
SECURITY CLAS$IFICAJ1ON OF THIS PAOE (When D.,ta .?”ler,d,
UNCLASSIFIED
SECURITY CLASSIFICATION
Q.
ABSTU
ACT
OF TtIIS PAGE @h..
Data
Entered)
(Con,lwd)
1 M 2“ elevation twgles cbaracferized by a number of random occurrexums of mtdtipaftt events that
produce deep fades, angle-of-arrival
flttctuationa, and depolarization of fk received s@tal.
The
log power fbtcmatlons ranged from 1 m 10 ds rms at elevation angles below 2° to less than 0.1 ds
at elevation angles shve 10°. The elevation angle fluctuations ranged from 1 to 100 mdeg at elevation angles below 2° to less than 5 ntdeg at a 10” elevation angle. Comparable fluctuations h
elevaUon angle are expected for bias refraction correction mcdels based upon tbe use of surface
values of the refractive in&x.
uNCLASSIFIED
5EcuR17Y cLAs$l FlcATlON OF nils
pAoe 6%.
Dote
E.teredl