Recently available D-region profiles are used to determine a model in which direct D-region reflection is assumed to be the dominant daylight mode in the 2- to 5-MHz region. This model is applied to the calculation of daylight absorption as a function of frequency and path length at oblique incidence. Good agreement with measurement is found, in contrast to early absorption calculation techniques, which show discrepancies of up to 50 decibels in this frequency range. Evidence suggesting direct D-region reflection higher in the HF band is presented.
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