The sensitivity of D-region partial reflections to irregularity composition

D-region electron-density profiles derived from differential-absorption partial-reflection measurements may be inaccurate at heights below about 70 km, because the data analysis depends critically on the assumed composition of the scattering irregularities, which is at present uncertain. Simulated measurements show the sensitivity of the profiles to variations in the relative roles of fluctuations in electron density and electron-neutral collision frequency. Measuring differential phase in addition to amplitude may help remove the ambiguity.