A year of oblique sounding measurements over diverse paths in the Northern Hemisphere - lessons learned

A study of link and network availability has been carried out based upon oblique sounder observations over an extensive region in the Northern Hemisphere for approximately a year. The authors have applied the measured propagation conditions in an analysis of high frequency data link (HFDL) performance based upon a specific system design specification. The authors conclude that space and frequency diversity will enable the normally unsatisfactory ensemble of HF channels to be be utilized effectively to provide an HFDL service with long-term average availabilities approaching 100%. They observe that average availabilities decrease as the network clusters migrate to higher geomagnetic latitudes. Daily, and monthly variations are observed as well. There is also a striking diurnal influence on average availability, with very little limit on the performance for the netted HFDL service between 1400-0400 LMT at the clusterhead position. This result represents the very best that may be achieved under conditions for which fullband sounding is available to drive a dynamic nowcasting and forecasting subsystem for resource management. Frequency sharing and dynamic reallocation is a requisite condition, but it may not be sufficient. A full suite of frequencies populating all of the aeronautical-mobile bands is needed to exploit the dynamic forecasting capability. The study is of particular importance to the aeronautical community