Effect of Spread-F on A1 Absorption Measurements

Abstract

An implicit assumption of the Al or pulse reflection method of measuring ionospheric radio wave absorption is that a single echo is returned from the ionosphere at any one time. This assumption breaks down during spread-F conditions because a number of echoes are then observed to overlap, leading to an overestimation of the A1 system calibration constant. The difference between the normal- and spread-F calibration constants depends on the number and fading characteristics of the echoes and the degree to which the various echoes interfere with each other. A simple model is invoked to simulate the A1 amplitude observations during spread-F conditions.