Results show that the current 4/ 3 effective earth's radius model has the lowest accuracy and can be used only below the height of 1 kilometer over the surface to guarantee sounding accuracy while the modified effective earth's radius model has the greatest accuracy. 计算结果表明:目前使用的4/3地球半径模式精度较差,只能在离地面1km高度以下使用,才能保证精度;改进等效地球半径模式的精度最高;