The intrinsic high accuracy of modern HF direction finders cannot be realized in practice due to the perturbations and tilts which exist in the ionosphere. Particular attention is given in this dissertation to the effect of Travelling Ionospheric Disturbances (TIDs) since their occurrence is difficult to predict and the magnitude of the induced bearing error extremely variable.\ud\udTID activity is quantified by monitoring simultaneously the bearings of a number of transmitters whose locations and frequencies are well known. This information is then employed to determine the expected bearing error on a target transmission reflected in the same area of the ionosphere. The major limitations of this correction scheme are investigated.\ud\udThe large-scale temporal and spatial variations of the quiet ionosphere (Systematic Ionospheric Tilts, SITs) produce bearing errors of similar magnitude to those due to TIDs. Rapid calculation of these errors for various path geometries and ionospheric conditions is possible by raytracing through 3-D ionospheric models. The limitations of a correction scheme which employs a 3-D model based on ionospheric predictions are examined.\ud\udVariance is a particularly useful statistic in assessing the 'reliability' of bearings made on a particular HF circuit. A scheme is proposed in which the bearings of a network of reference transmitters are monitored continuously allowing a variance to be assigned to any target transmission, even if it is only present for a very short time. These variance values are of considerable value in practical DF applications.\ud\udWhenever possible the experimental observations are related to the underlying physical processes in the ionosphere which generate these DF errors.
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机译:由于存在于电离层中的扰动和倾斜,实际上无法实现现代HF测向仪固有的高精度。本文特别注意了行进电离层扰动(TID)的影响,因为它们的发生很难预测,并且所引起的轴承误差的幅度也非常可变。\ ud \ udTID活动通过同时监视多个轴承来量化位置和频率众所周知的发射机。然后,该信息将用于确定在电离层同一区域中反射的目标传输的预期方位误差。研究了这种校正方案的主要局限性。\ ud \ ud安静电离层的大规模时空变化(系统性电离层倾斜,SIT)产生的方位误差与由于TID引起的误差相似。通过3-D电离层模型进行射线追踪,可以针对各种路径几何形状和电离层条件快速计算这些误差。检验了使用基于电离层预测的3-D模型的校正方案的局限性。\ ud \ ud方差是评估特定HF电路上轴承的“可靠性”时特别有用的统计信息。提出了一种方案,其中连续监视参考发射机网络的方位,从而允许将方差分配给任何目标变速器,即使方差仅在很短的时间内出现。这些方差值在实际的DF应用中具有相当大的价值。\ ud \ ud只要有可能,实验观察都与电离层中潜在的物理过程相关,这些物理过程会产生这些DF误差。
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