First results from a combined riometer and oblique sounder campaign in the auroral region

A quantitative comparison between measured D-layer absorption and variations of received signal strength of an obliquely propagating HF signal has never been conducted before using independent, co-located instruments. Initial results and analysis is presented here from a combined observational campaign using the Imaging Riometer for Ionospheric Studies (IRIS) at Kilpisjarvi in Northern Finland, and a oblique HF sounder spanning the same region of the ionosphere. These experimental observations form the basis for validating the predictions in the changes in absorption based on the predictions of the Lancaster-Sodankyla ion chemistry model combined with the ray path calculations of the RaTS numerical ray tracing program. The observations, combined with the modelling, represent progress towards being able to include ionospheric absorption in HF channel simulations.