Comparison of Three Wind Measuring Systems for Flight Test

A preliminary field test of wind accuracy obtained using Global Positioning Satellite (GPS) tracked radio sounding balloons (rawinsondes) is presented. Recently, the Edwards AFB Weather Flight began converting to GPS rawinsondes their Radio Automatic Theodolite Sounder (RATS) system, which utilizes ground-based phased array tracking. During the fall of 1999 wind comparisons were conducted using the GPS and RATS rawinsondes and a RIR-716 RADAR tracked reflector. Wind speed differences between the GPS rawinsondes and the RADAR were significantly less than between the RATS and the RADAR. Differences are influenced by data reporting objectives and data processing techniques, as well as by the inherent tracking accuracy of the systems. This paper also illustrates temperature measurement differences experienced during Reduced Vertical Separation Mandate (RVSM) calibration flight test days with the DC-8 airplane. GPS sondes, synoptic weather analysis and DC-8 airplane data indicate a warm temperature bias for the RATS system data. (Subsequent system improvements will be illustrated subject to data availability.) This brief field test indicates that the GPS sounding system tracking data is more precise than the radio theodolite system and can reduce the burden on range RADAR scheduling when high resolution data are needed.