民用飞机测距器试飞大气折射效应分析

Analysis of Atmospheric Refraction Effects in the Flight Testing of DME Installed on Civil Airplane

民用飞机测距器试飞中,大气折射误差是一种主要的试飞误差源。为降低其影响,需要采用精确的方法进行修正。等效地球半径法作为一种简单修正方法,适合于低高度条件下使用,如果高度增大、会使效果变差甚至失效,则难以满足试飞需要。文中基于射线跟踪法的原理,结合分段的大气折射率模型,提出了一种改进方法。推导出求解大气折射误差的数学公式,给出了一种数值算法。新方法具有计算精度高、使用范围大的特点,实际应用结果验证了其有效性。

Atmospheric refraction is a significant error source which must be properly treated in determining the performance of a developing DME by flight testing. To reduce atmospheric refraction effects, there is a need for an accurate refraction error correction scheme. The equivalent radius method which represents a simple approach to this problem can gives sufficiently accurate results for low-altitude application. However,when used for high-altitude application, inaccuracies and failures to produce results have been observed. As an efficient alternative, we develop an improved method for computing the refraction error based on ray-tracing tech- nique in given accurate subsection troposphere model. In this paper, the formulas for refraction error are derived and an algorithm which obains an approximate solution of the formulas is also presented. The introduced technique which results in high accuracy is readily applicable for a wide range of altitude . The efficacy of this technique has been verified by flight test results.