Transequatorial propagation of very low frequency radiowaves
Abstract
This study reports on observations of dawn/dusk transition fading of very low frequency radiowaves on a long, transequatorial northeasterly propagation path. A mode conversion model is developed and numerical modeling results are presented for transition fading on long transequatorial paths, both northeasterly and southwesterly. From these results the following general conclusions are drawn: (a) Anomalous transequatorial transition fading is not observed for the northeasterly propagation path. The transition fading data support completely the mode conversion model of transition fading developed by Crombie. (b) The transequatorial sunrise transition reported in the literature as anomalous is completely explained by correctly allowing for variations of the geomagnetic field along the path. The geomagnetic field influences the nighttime modal parameters to such an extent for the southwesterly path considered that the approximate WKB method of mode summation cannot be employed. (c) Careful application of model techniques appears to be capable of describing all LF and VLF propagation in the earth-ionosphere waveguide, provided the effect of the earth's magnetic field is properly included at night. However, an improved model of the ionosphere at altitudes below 100 km is desired.
- Publication:
-
Final Report Naval Ocean Systems Center
- Pub Date:
- April 1981
- Bibcode:
- 1981nosc.reptQ....S
- Keywords:
-
- Radio Waves;
- Transequatorial Propagation;
- Very Low Frequencies;
- Earth (Planet);
- Geomagnetism;
- Ionospheric Propagation;
- Mathematical Models;
- Communications and Radar