V—2 ROCKETS—KRAUSE 
phase shifts, intensities and numbers of 
modes, direction of arrival of wave 
fronts, ducting, multipath phenomena, 
and the actual rapidity of variations 
of these quantities. 
The method we are using for meas- 
uring the index of refraction consists 
of the transmission of two or more 
harmonically related crystal-controlled 
continuous-wave radio-frequency sig- 
nals from the rocket to special receiv- 
ing and recording equipment at 
suitable locations on the ground. 
These frequencies of transmission are 
so chosen that one is sufficiently high 
that its velocity of propagation is 
essentially unaffected by the iono- 
sphere; that is, in the above equation, 
the index of refraction remains essen- 
tially unity. The other frequency is 
chosen to be slightly above the maxi- 
mum critical frequency predicted for 
the regions which the rocket will 
penetrate. For the latter frequency, 
as may be seen from the equation, the 
index of refraction will approach zero, 
and as a result the velocity of propa- 
gation will be greatly affected. If 
one considers the phase relation be- 
tween the two radio-frequency signals 
as received on the ground, it may be 
shown that for transmission from any 
point in the ionosphere, the rate of 
change of phase between the two sig- 
nals as received on the ground is a 
function of the missile velocity and the 
index of refraction for the particular 
frequency at that point (40). This 
allows the determination of the index 
of refraction for the low frequency as 
a function of altitude, with a suitable 
choice of the higher frequency. 
The phase beat frequency experi- 
ment has successfully recorded con- 
tinuous data up to an altitude of 
approximately 110 km. and at several 
points above that up to 128 km. (41). 
Although the analysis of these data is 
very complex and although only a 
preliminary analysis has been made, 
I would like to point out a few of the 
interesting results of this experiment. 
Figure 9 shows a series of curves of the 
received signal strength on the ground 
203 
at one of the receiver stations versus 
the altitude of the missile. A similar 
set of curves was obtained at a second 
receiving station located about 30 
miles from the first. The theoretical 
free-space signal strength at the re- 
ceiver station should be a continuously 
decreasing function with altitude. 
The fluctuations in the curves are 
primarily due to ionospheric attenu- 
ation and the missile antenna patterns. 
The latter are being obtained from 
models, and the curves will be cor- 
rected accordingly. ‘There is some 
reason to believe at this time that the 
sudden drop at 65 km. is due to the 
presence of the D layer. 
Figure 10 shows representative sec- 
tions of the continuous-film records 
obtained at one receiving station, and 
illustrates very clearly the different 
types of complex beats obtained. ‘The 
phase beat frequency first became ap- 
parent at about 43-km. altitude and 
remained at a low value up to about 
84 km. This would imply that ifa D 
layer exists in this region its effect on 
the 4.274-me. signal was small below 
84 km. The phase beat frequency in- 
creased rapidly at 84km. At 111 km. 
the beat frequency is lost owing to 
loss of the 4.274-me. signal. Intensive 
analysis of the phase beat frequency 
data is continuing and it is hoped that 
a more definite report will be available 
in about 6 months. 
Many experimental problems associ- 
ated with the ionosphere work have 
been encountered and solved, and a 
great deal of invaluable experience as 
to a suitable instrumentation for 
rocket investigation has been acquired. 
It was soon found that the problem of 
developing suitable antennas for trans- 
mitting at low frequencies from the 
rocket was a major problem. Con- 
siderable theoretical and laboratory 
research has been carried out to 
establish a fundamental basis for the 
direct measurement of the electron 
and ion densities as a function of alti- 
tude. An experiment is virtually com- 
plete for inclusion in a July flight, 
which involves primarily a determin- 
