Abstract : Precision low elevation angle radar observations of orbiting spheres were used to evaluate the utility of surface based refraction techniques. Elevation angle error measurements were obtained from differences between the precision radar measurements and the true or absolute position of the orbiting sphere obtained from a multiple pass orbit determination using data from the same radar system. The results of the refraction effects study show that the average observed elevation angle error caused by refraction is identical with the average calculated elevation angle error obtained from ray tracings using radiosonde data to within the measurement accuracy of the radar system. The results also reveal a relatively large uncorrectable component of the elevation angle error caused by small scale refractive index gradients. This uncorrectable component is of the order of 30 millidegrees (mdeg) at a true elevation angle of 1 degree and 4 mdeg at 10 degrees.