Low-frequency propagation paths in arctic areas

The vcry low.ground c?,:ductiv it!ese nc.o untercd in arctic :Lrcas, [lnd t he particular ]o11ospl1(' l'I c condltlO ll s prevall lllg at hIgh latlt e's, c,w lea d to ),fLtller unusual radiation :L nd propagation cond itions.In order to deter min e the magnitude of these effects fi eld intensities from tra ns mitter s located in the Lahrador and Grce n land a reas were m e~su red both on t he surface of t he earth and during se vera l aircraft flights over thi s arefL.T he many factors invol ved in If propagation are co nsid e red and calclJi alcd fi eld intensities co mpare ~ with experime nta.1 values.U nder conditions where tIle initial portion of the propagatIOn path I S acr?ss lCecap or permafrost, the atte nU fLt ion obser ved is very great, and when the propagatIOn path extends out over sea water, the fi eld intensity recover v taking place after t he coas tli ne is crossed is ver y m arked.Estimates of s kywave field inte nsity appear to agree with t he obse rved results provided the ra diated fie ld pattern is sui.tably mod i fi~d by the a nte nna cutba ck f~ctol' which accou n ts for the p r ese nce of a fil1ltely conductIng c urved earth.These vertIcal pattern s based on work by a long wi th th e fi eld in tensity flight data, i ndicate t hat t he siting of low-frequency stations ~eveml miles or m ore inland in ar ctic regions may ca se a grcat increase in total transmission path loss.