Frequency dependence of VHF ionospheric scattering.

Abstract

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C.. and Boulder. Colorado, is suggested in the following listing of the divisions and sections engaged in technical work. In general, each section carries out specialized research, development, and engineering in the field indicated by its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front cover.

Relation of turbulence theory to ionospheric forward scatter propagation experiments

“…The steeper slope approach ing the diss ipation range and the smaller inertial slope seem.ed to ex plain the data rather nicely [16]. However, tlw newer data [10] indicates that s uch a dichotomy does noL exist, and that the exponent is constant over t he wavenumber range employed at any g iven hour-even though the slope itself shows diurnal and seasonal variaL ions.…”

“…This expression reduces to the R ayleigh distribu t ion if the component correlation p is assumed to b e zero. However, this assumption is probably not justifi ed for electromagnetic scattering-as it is for electrical s hot noise-and the more gener al expression (2.2) may explain interesting anomalies in the experimental envelope distribution data [10]. The data generally seem to emphasize larger values of R (relative to the mean) more than the Rayleigh distribution predicts, with corresponding redu ctions in the occurrence of small values.…”

“…To avoid confus ion on how the seco nd effect is accounted for , it is convenienL Lo compare received power on two different frequen cies for scaled antennas, viz, equal Gil fa ctors. The definiLive experiments by the NBS group [10] on frequency dependence actually used car efully scaled rhombic antennas, so as Lo insure identical illumination of the scaLtering layers and similar antenna r esponse. With this convention, t he frequency variation is that due to the spectrum plus a ;\2 factor wh ich represents tb e physical scaling of the receiving aerial size.…”

“…With this convention, t he frequency variation is that due to the spectrum plus a ;\2 factor wh ich represents tb e physical scaling of the receiving aerial size. If the spectrum is expressible as a simple inverse power (n) of wavenumber in tile rclevan t turbulen t range , one would predict a (scaled antenna) frequency scalin g law [30], const P n = 1"+2 ' (7.1 ) The most r ece nt experimen Lal daLa is LhaL reported by Blail' [10], u ing 30,40, 50, 74 , and 10 ~I c . H e finds that the ex ponent n in eq (7 .1) is variable, ranging from 7 to 10.…”

On the forward scattering of radio waves in the lower ionosphere

“…In the first type of these experiments the transmission lo ss was measured on scaled aerials at several frequencies between 30 and 108 Mc/s, Blair [1959] and Blair, Davis, and Kirby [1961 ]. Th e genen.l conclusion to b c dntwn from these experi-1 ments is that the scattering exponent is in the range 6 to 7 rather than 9 as found in the present work.…”