| The use of Digisonde measurements to study HF radiowave absorption in the ionosphere is examined. The capabilities of the Digisonde allow the separation of absorption losses from other sources of signal loss, such as transmitter and receiver characteristics, and spatial losses. Digisonde measurements are shown to have two major advantages over other techniques: (1) absorption is measured over a wide range of frequencies, and (2) these absorption measurements can be combined with the many other parameters simultaneously measured by the Digisonde. A simple model of ionospheric layers consistent with these results is developed, which shows that the E-layer is responsible for the larger part of the absorption in the 4 to 6 MHz range, with most of the absorption occurring in the lower part of the E-layer. |
