The source of this stunning GPS-RO power appears to be a combination of extremely high precision and vertical resolution, the true absoluteness of the measurements (lack of any significant bias), and all-weather operation — observing where other sensors can't. Noting that no bias corrections are applied to GPS profiles, Healy and Thépaut (2006) of ECMWF observe: "GPSRO appears to be particularly good at identifying and partially correcting model biases in the upper troposphere and lower stratosphere…. This suggests that assimilating GPSRO observations may help to separate model and observation biases and therefore indirectly assist in the bias correction of other satellite measurements."  In other words, the addition of high-accuracy GPSRO data enhances the effectiveness of data from conventional sensors.