An empirical model for average F-layer scintillation at VHF/UHF

An empirical approach to modeling the electron-density irregularities in the F layer that are primarily responsible for amplitude scintillation of VHF/UHF signals has been devised and tested. An irregularity model was postulated as a function of geomagnetic latitude, local time of day, season, and sunspot number. The primary parameters of the irregularities that were postulated were their strength and transverse scale-size. The irregularities were assumed to be aligned along the geomagnetic field, and their axial ratio was taken as constant, as were the height and thickness of the irregular layer. The model was tested by computing the fractional rms fluctuation in received power to be expected in a given situation, under the weak-scatter assumption, and comparing the results against values of this or related quantities reported in the literature. The model then was improved by iteration. The development made use of 12 data sets, and final testing employed those 12 plus an independent one. Lack of appropriate data precluded testing poleward of about 70° geomagnetic latitude. The model is offered as a tool for VHF/UHF communication-systems planning, to the extent that the average value of scintillation in a specified circumstance is of engineering value. Geophysical application should be limited to such uses as experiment planning, guiding of intuition, and serving as a basis for more refined modeling.