Further comments on quasi-periodic scintillations in radio-satellite transmissions

Journal of Atmospheric

and Terrestrial

Physics,

vol.38,

pp. 443 to 445.

Pergsmon Press, 1970.Printed inNorthern Ireland

Further comments on quasi-periodic scintillations in radio-satellite transmissions FREDERICKSLACK Tmus-Ionospheric PropagationBranch,IonosphericPhysicsLaboratory,Air Force Cambridge ResearchLaboratories,HanscomAir ForceBase, MA, U.S.A. and L. A. HAJKOWICZ Departmentof Physics,Universityof Queensland,Saint Lucia, Brisbane,4067 Australia (Received 23 .Jum 1975)

It has been recently reported (HAJXOWICZ,1974) that regular quasi-periodic (QP) amplitude scintillations in radio-satellite transmissions could be of a non-ionosphericorigin. Namely, it was found that on a number of occasions QP scintillations (here with referred to as &PA) w%r% recorded whenever there were two satellites tra~~tti~g at an identical frequency within the beamwidth of the receiving antenna. In addition it was suggested that some &PA could be associated with an interferenceeffect between satellite and ground radio transmissions. It was concluded that the qu~i-p%~o~c nature of QPA was due to doppler frequency shift of satellita transmitted radio signals. The reporting of these &PA scintillations that are amenable to straight forward analysis may tend to obscure,or deny the existence of a second class of more elusive QP sc~t~latio~ probably associated with ionosphericinhomogeneitiesin the F-region. These QP scintillations (herewith referred to as QPB) were reported by ELKINS and SLACK(1969), and SLACK(1972). To reinforce the validity of their existence, it seems appropriate to elaborate on them at this time with emphasis on examples that preclude the possibility of QPB being &PA. A cursory comparison betwaen pen recordings produced by &PA and QPB indicate similarity, however closer inspection rev%& that the interfering doppler related radio frequency signals ar% developed in s%oonds, where as the ionospheric related QP are developed in minutes, consistent with ionospheric drift rates. These records could not be the result of an orbiting satellite signal interfering with the 136 MHz geostationary satdlite signal being monitored, because of the 150’ antenna that was used with a 3” beam width that produced the Sagamore Hill record. Thus an orbiting satellite travelling at approximately 7 hm/ s%c would traverse the beam in approximately

10 see, much too short a tim% to allow the QP pattern to develop. Further avidence that the QP previously reported on are ionosphericallyrelated is illustrated in Fig. 1 which shows Pen recordings from four stations monitoring the same geostationa~ satellite 136 MHz RF signal. Note the difference in time when the anomalies appear, the maximum being approximately three minutes between Sagamore Hill and North Ipswich, a distance of 10 km. If this were the beat not% between the satellite signal and a ground transmitter signal, it would appear simultaneously at all stations. If it were the beat between the monitored satellite signal and an orbiting satellite signal, the greatest time separation would be approximately

20oJoLY I%?

Fig. I. Qua&periodicscintillationsappearingat four sites on AT&5 Geostationarysatellite136 MI& trammissions. Time separationsare in accordancewith ionospheria wind drifts.

443

F. SLACKand L. A. HAJKOWICZ

444

2 seo and would not be discernible on this record. In a year’s monitoring of the geostationary satellite signal 90 QP events, with similar time displacements were selected for analysis yielding ionospheric wind velocities consistent with other types of measurements. In several cases the time displacements were the same as more normal scintillation appearing just before or after the quasiperiodic scintillations. Fig. 2 is an example of this. VEL. *$ 123 rnfMt.

Recent data showing the QP to be ionosphericrtlly related is illustrated in Figs. 3 and 4. These pen recordings show the anomalies simultaneously on 5 different frequencies from geostationary satellite ATS-6 using the 150’ radio telescope at the receiving site with its beam width becoming progressively narrower at each frequency, approximately 1.0’ at 360 MHz. The final illustration Fig. 5, shows a portion of a very active day for QP when the anomalies

CANARY BlRo

21 JULY

1967

Fig. 2. Quasi periodic scintillations 8ppe8ring at two sites with 10 km separation. Spacing is the same as normal scintillation and is in accordance with ionospheric wind drift.

NOVEMBER 28, 1974,

Fig 3.

2210 UT

NOVEMBER 25,

1974,

0050

UT

Fig 4.

Figs. 3 and 4. Recent recordings of ATS-6 geostetionery satellite on five frequencies. Signals were detected on 150’ radio telescope at Hamilton, MA.

Further comments on quasi-periodic scintillations in radio-satellite transmissions appeared

on transmissions

from

each with a different bearing.

445

three

ATS-3

satellites

was trans-

AT&S was transmitting on 136 MHz at an azimuth of 226’ and LES-6 was transmitting on 228 MHz at mitting on 136 MHz at an azimuth of 180’.

an azimuth of 120’. It is clear from all of the illustrations

ATS 5'Nl

multifrequency IL ATSIII v' ._ 0820UT

observation

of the Quasi-Periodic Scintillations eliminate interfering satellite transmissions as the source of these scinti.Us;tions.However, it should not be general practice to associate all QP scintillations with various ionospheric phenomena (HAJKOWICZ, 1974). This approach could lead to erroneous conclusions unless sticient data is available to differentiate between QPA and QPB events. duration

it300 v

Fig. 5. Quasi-periodic scintillations detected on AT&6, 136 MHz at four sites with time separation in accordance with ionospheric wind drift. ATS-3, 136 MHz and LES-5,228 mz were detected at different bearings at another site on Sagamore Hill, Hamilton, MA.

REFERENCES L. A. ELKINST. and SLACKF.

1974

SLACK

1972

HAJOWICZ

F.

that the

and the relative long

1969

J. atmos. tew. Phy8. 36, 1689. J. atmos. tew. Phy8. 31, 421. J. atmoa. tern. Phys. 84, 927.