本文提出了一个高频返回散射传播最小时延P_0所对应的地面大圆距离D_0计算的新方法,用此法作P_0对D_0的换算可仅仅用单站的P～f电离图完成。此法的计算结果与求解射线积分方程的方法的结果相当一致,在D_0>1000公里时,两者相差小于1%。标定实验表明,从单站P～f图推出的应答机地面距离与其实际距离的偏差在3%之内。 In this paper, we propose a new method for calculating the large circular distance D_0 corresponding to the minimum propagation delay of radio-frequency backscatter P_0. By using this method, the conversion of P_0 to D_0 can be done using only the single-station P ~ f ionization pattern. The result of this method is quite consistent with the method of solving the ray integral equation. When D_0> 1000 km, the difference between them is less than 1%. The calibration experiment shows that the deviation of the transponder ground distance from the single station P ~ f diagram and its actual distance is within 3%.