GPS/LEO掩星技术中超折射效应的修正

Corrections to the Superrefraction Effects in GPS/LEO Occultation Technique

在GPS掩星探测地球大气技术中,Abel积分变换要求大气折射指数n是折射半径a的单值函数.当大气折射率的垂直梯度达到小于一个极限值d N／dr≈-0.16N-unit m-1,上述单值性不成立,称其为超折射,此时Abel积分变换不再适用。如果还是在形式上应用经典的Abel变换,在反演结果中就会产生负大气折射率偏差.描述了低对流层中超折射现象的物理特性和数学表示;在广义Abel积分变换的基础上,讨论了超折射层内和超折射层下的大气剖面反演算法;选择丁一个简单的采样间隔内等大气折射率垂直梯度假设,对英国高分辨率无线电探空观测资料进行模拟计算,验证了负超折射与大气折射率偏差的关系,并提出的广义Abel变换的合理性.

Abel inversion in GPS/LEO occultation technique requires the atmospheric index n to be a single-valued function of the refractional radius a. This condition is broken when the vertical refractivity gradient is below a critical value dN/dr - -0.16 N-units m-1, that is called superrefraction. Abel inversion is no longer valid under this condition, and, if classical Abel inversion is still formally applied, negative refractivity bias occurs in results. The physical characteristic and mathematical expression of superrefraction layer in lower troposphere are illustrated. In the frame of a general Abel inversion, inversion algorithm of refractivity in and below superrefraction layer is discussed. Under a simple assumption of constant vertical gradient of refractivity in sampling intervals, simulation process is carried out for UK High Resolution Radiosonde Data. The computational results have proved the relationship among the negative refractivity bias and superrefraction, and the validity of the general Abel inversion method proposed.