10 research outputs found
Final report under Contract No. AF (604) - 1089
The main body of this report is divided into eight sections, corresponding
to the eight aspects of Arctic radio wave propagation listed
in Section I, Purposes of the Contract, In cases where the work has already
been fully described in Interim Scientific Report No. 1 (AFCRC-TN-
55-579, here in after referred to as R(l)), brief summaries only are given.
The progress in these eight fields is summarized as follows:
Task No. 1 Sweep-Frequency Ionospheric Backscatter
Because of lack of equipment, no progress was made on this task.
Task No. 2 Auroral and Meteor Echoes
Three frequencies were used in this work:
(a) At 50 me
A low“power9 50 me radar equipments specially designed
and built for auroral radar research, was operated with a steerable antenna
to monitor both auroral and meteor activity,, The results showed
that the diurnal distribution of meteor activity is similar at College
to that observed elsewhere, and that the meteor echo rates observed on
this equipment are not affected by the presence of aurora.
(b) At 106 me
The 106 me SCR 270 DA radar was used for two main experiments,
as described in R(l). First, the aspect sensitivity of the
auroral echoes was investigated. The results showed clearly that the
auroral ionization giving rise to VHF auroral radar echoes is aligned
along the earth's magnetic lines of force3 in that the auroral radar
echoes are strongest when the radio waves are traveling perpendicularly
to the magnetic lines of force through the aurora. Second, the relationship
between visual and radar aurora was investigated; this work showed
that the auroral radar echoes are often closely associated in range and
azimuth with visual aurora, although the strength of the echoes is not
proportional to the visual brightness of the auroral forms„
(c) At 210 me
The 210 me SA-2 radar was installed in a trailer and
tested without modification, It was then modified by the building of a
steerable 16-Yagi array, by increasing the pulse length, and by reducing
the receiver bandwidth„ Simultaneous operation of the 50 me and the
improved 210 me equipment resulted in the detection of many auroral echoes
at the lower frequency; no auroral (or meteor) echoes were obtained on
the 210 me equipment during the contract period although good mountain *
echoes were obtained at ranges up to 250 km„
Task No„ 3 Investigation of Microwave Link
As explained in R(l), the experimental observations carried out on
this link showed the absence of significant tropospheric refraction effects,
and the work was terminated at the end of the first year of the contract.
Task No. 4 Prediction of Auroral and Ionospheric Storms
Several types of work were undertaken in order to improve our understanding
of auroral and ionospheric storms; these storms are two aspects
of the bombardment of the upper atmosphere by particles from the sun, In
particular, a solar radio interferometer was set up to monitor the solar
radio emissions at 65 me As described in R(l), an all sky camera and a
photoelectric photometer were developed for the monitoring of the visual
auroral activity.
An investigation of earth potentials has shown that they provide a
simple method of monitoring magnetic activity; some tests were also made
using a rapid-response electronic magnetometer. Some of the results obtained
with these equipments are discussed in the report.
A study of the form of the front surface of a neutral corpuscular
stream advancing into a magnetic field similar to the earth's magnetic
field is presented. This study shows the presence of equatorial and polar
forbidden zones and the fact that only the particles arriving near
the border between these forbidden zones can reach the earth's upper atmosphere.
An equatorial motion of the zone of bombardment could be produced
by an increase either in particle density or in particle velocity.
Task No. 5 Whistlers
A new type of whistler has been discovered that has simultaneous
rising and descending components.
Analysis of data obtained during the contract period indicates a
diurnal variation in the rate of occurrence of whistlers that appears to
be correlated with ionospheric heights. A correlation between the day-to-
day occurrence of the dawn chorus and the daily K-index sums is also
found.
Task No. 6 Diffraction and Scatter of Radio Waves by Mountains
(a) Diffraction
The diffraction of VHF radio waves by mountains has been investigated
over three diffraction paths. The results show that the experimentally
observed signal strengths are in fair agreement with the
values calculated theoretically using knife-edge approximations. One
important observation, which has not been reported previously, is the
variability of the diffracted signal strength from point to point across
the ground. Also, although diffracted signals are normally described as
being very constant in amplitude, slow fades lasting some hours and occurring
over a relatively narrow frequency band were observed over one 200-
mile path.
(b) Mountain scatter
Observations of mountain scatter were made using the SCR-270
DA radar and a mobile receiving equipment. The results imply that detectable
scattered signals can be obtained over a very wide range of azimuths
(greater than + 135°) relative to the line joining the transmitter
and the mountain. It was found that the scattered signals were considerably
broadened in pulse length.Task No. 7 Ionospheric Absorption
The work done in connection with ionospheric absorption under this
contract has been described previously in R(l). Undertaken at the request
of the 58th Weather Reconnaissance Squadron, USAF, this study demonstrated
convincingly that their communication failures were caused by ionospheric
absorption phenomena, rather than by equipment or personnel failures.
Task No. 8 Assistance to the Alaska Air Command on Problems of Radio
Propagation As described in R(l), an investigation of a VHF radio link was made
at the request of the Alaska Air Command. Continuous records of received
signal strength at each end of the link revealed that the communication
failures were caused by tropospheric refraction effects. A low-noise
preamplifier, built and operated in parallel with a normal equipment, was
found to reduce the number of fade-outs.
A one-day symposium on Arctic radio wave propagation was held at the
Geophysical Institute on January 26, 1956, for the benefit of communications
personnel in the territory,, Approximately fifty visitors attended
these meetings. The Geophysical Institute has also assisted the Alaska
Air Command by the loan of electronic equipment and pen recorders as well
as by supplying specialists who have acted in an advisory capacity on
problems of radio wave propagation.The research reported in this document has been sponsored by the Air Force Cambridge Research Center, Air Research and Development CommandoList of Illustrations – Section I Purpose of Contract – Section II Abstract – Section III Experimental Work : Sweep-frequency ionospheric backscatter ; Auroral and meteor echoes ; Microwave propagation ; Prediction of auroral and ionospheric storms ; “Whistlers” ; Mountain scatter and diffraction at VHF ; Ionospheric absorption ; Assistance to Alaska Air Command – Section IV Recommendations – Section V PersonnelYe