An investigation of the equatorial scintillation of satellite signals at 257.55 and 1541.5 MHz for about 10 ø and 50 ø elevation angles is reported. Diurnal and seasonal variations are shown for the two frequencies and the two elevation angles. A periodicity in the occurrence of the scintillation was observed and is attributed to the gravitational field of the moon. It is proposed that the moon's gravity may affect the occurrence and intensity of equatorial scintillation by modulating the velocity of the zonal winds at ionospheric heights. An additional possible contribution to the periodic variation in the scintillation is a periodic variation which occurred in the geomagnetic activity during the first half of the year. PAULSON ...-,.
The technique of inverting a single-ended lidar return to obtain range-dependent atmospheric extinction coefficients requires an assumption concerning the relationship between the volumetric backscatter and extinction coefficients. By comparing the powers returned from a volume common to each of two lidars located at opposite ends of a propagation path the need for this relationship can be eliminated, and the extinction coefficient is determined as a function of position between the two lidars. If the lidars are calibrated, the backscatter coefficients and their relationship to extinction can then be determined as a function of position. We present measurements obtained with two lidars which were operated reciprocally over a slant path of ~1 km during reduced visibility conditions. The measured extinction and backscatter coefficients determined by this method provide the boundary value inputs to both the forward and reverse integration algorithms for inverting the single-ended lidar returns. The accuracies by which both singleended integration schemes can reproduce the double-ended measurements are examined by allowing the ratio of backscatter to extinction coefficients to be either constant or varying with position between the two lidars as measured.
D ata are prese nted from a ncar vertical inciden ce cw VLF sounding sys tem whose transmitter is l ocatcd at Scntin el, Arizona. The configuration of the transmitting ante nn a is such that the verti cally polarized g rounchl'ave patte rn h a s deep nu lls in which receivers may be located . The sma ll gro undwave a ll ows t he pola ri zation components of the downcomin g s k.vwave to be measured \\'ith co nsidera ble accuracy. The so undin g sy stem was operated at four frequencies i n the VLF range.The observations show certain st rikin g features. The record s of rece ivers pl aced to the ea st of the trans mi tter arc diffe rent in characte r from r eco rd s of receivers p laced in a co["-r e~pondin g posit ion to the west of t ile tra nsmitte r. Ch aracte ri stic record s of componpnts p olarized in the pla ne of in cid en ce are often very diffe rent fro m t h ose of co mpo nents p olarized normal to the pla ne of incide nce.R ap idly movin g fcatures ofte n pass over the t ri a ngle of receiving stations causin g 180 0 to 360 0 phase ch anges.A m odel is proposed which can expl ain the observation al feat ures of the data.
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