New Approach to Omega PPCs (Propagation Corrections).

摘要

The currently available propagation correction (PPC) model algorithm maintained by the U.S. Coast Guard Omega Navigation System Center was developed in 1980. Although an improvement over the earlier 1974 algorithm, the 1980 PCC model exhibits a number of deficiencies. To correct these deficiencies, a new approach to modeling PPCs is presented. This model incorporates semi-empirical forms directly into the time-dependent portions of the model, thus insuring that the PPC predictions are directly data-driven and data collected during path transition conditions may be used for model calibration. A geomagnetic conductivity sub-model is described which provides effective phase velocity and excitation factor phase functional forms for day or night path segments with given geomagnetic bearing, geomagnetic latitude, and ground conductivity. This sub-model describes all space-dependent quantities (on which phase depends) except for the spatially anomalous ionospheres of the auroral and polar regions. A diurnal sub-model is described in which the diurnal phase behavior on a propagation path is treated as a sum of discrete phase changes on path segments having ionospheric reflection heights determined from classical Chapman photoionization models. In addition, onset and recovery times for sunrise and sunset are characterized by several parameters which can be adjusted to fit observed data. (rrh)