| Summary: | The riometry technique is limited by its inability to directly determine the altitude of the principal ionospheric absorption layer during periods of enhanced Cosmic Noise Absorption (CNA). We describe here a technique based on the simple vertical parallax principle, enabling direct measurements of this altitude. The technique utilizes the overlapping beams of two closely spaced imaging riometers in Antarctica. Descriptive statistics on peak absorption heights are presented. The altitude determination of a D-region absorption event and an event that occurred in the F-region near 200 km altitude are presented in more detail. The identification of an F-region event using the parallax technique confirms earlier findings that radiowave absorption in the F-region is a potentially significant contributor to CNA. This technique enables a simple and repeatable ground-based measurement of the altitude of the CNA layer peak, and can be extended to estimating precipitation spectra based on peak absorption heights.
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