Use of GPS to Adjust Radisondes: Validation using AIRS

Larry McMillin



Results from a study comparing water vapor measurements from radiosondes, GPS, and AIRS are reported. The focus of this talk is the use of the GPS total water vapor to adjust the radiosonde total water vapor and the effect of the adjustment on the layer water vapor amounts. This adjustment is necessary because radiosondes have instrument to instrument biases while the GPS is relatively unbiased. Once the adjustment factor is obtained based on the total water vapor, the adjustment is applied to the layer precipitable water values for each observation. The layer values are then compared to AIRS retrievals. The results show a significant increase in the accuracy of the lower level precipitable water when compared to AIRS values. The adjustment is applied to all the U.S. radiosonde types and shows improvement for all types. The results indicate that, particularly with a mixed system like the U.S. has, the GPS can play a valuable role in normalizing the various instrument types. Given the minimal cost of the ground stations, it is feasible to place all radiosonde locations. It is also possible to provide GPS soundings on a time scale that would allow them to be used for operational adjustments of the radiosonde data. The results show that these steps would produce a significant increase in the accuracy of the observations if they were to be implemented.