The effect of turbulence on atmospheric gradient parameters estimated from ground‐based radiometric and space geodetic measurements

Spatial and temporal fluctuations in the refractive index of air affect estimates of atmospheric parameters determined from data obtained from radio signals which have propagated through the atmosphere. These effects will become increasingly important as we continue to improve the accuracy of microwave space geodetic techniques. Using a straightforward expression for the covariance of a general vector of atmospheric parameters, I calculate the effects on estimates of spatial gradients for a frozen Kolmogorov turbulence field moving over a site at constant velocity. Numerical calculations are performed to investigate the implications for three techniques: ground‐based microwave radiometry, geodesy with the Global Positioning System, and Very Long Baseline Interferometry. The results indicate that a prevailing wind with no true static gradients may give rise to apparent azimuthal asymmetries when gradient parameters are estimated. Moreover, care must be taken in comparing gradient parameters determined using data from these different techniques, because these techniques sample the atmosphere on different spatial and temporal scales.