HF propagation assessment studies over paths in the Atlantic

In September, 1980, NRL utilized Barry AN/TRQ-35 oblique sounding equipment which was deployed on board a ship operating in the Atlantic Ocean in order to test a concept to provide a real-time model update with the oblique sounder as a data source. The purpose of this work was to show that very accurate HF channel assessment was possible over paths in the local vicinity of the sounded path. Presented are initial results of an exercise encompassing two short paths (less than 900 km) in the North Atlantic. These initial results indicate that by utilizing the oblique sounder to update the MINIMUF 3.5 model developed by NOSC, a significant increase in the accuracy of short term forecasting of the Maximum Usable Frequency (MUF) can be obtained. Over a 24-hr period, RMS errors from a model driven by the 5-day running average of 10.7 cm flux were approximately 4 MHz. Utilizing the oblique sounder as an update tool, this RMS error dropped to below 1 MHz. Further results are required, however, to validate the technique over longer periods of time, different geographies, and larger operational areas.