Wind Measuring Accuracy of L-band Radar-digital Radiosonde System Through the Intercomparison with GPS Data

GPS Sounding and Wind Measuring System(GSWMS)is a new generation of sounding system, which measures wind speed and wind direction by GPS technology. It will be the major developing trend of sounding because of positioning accuracy and characteristic of weather independent. L-band Radar and Electrical Radiosonde System(LRERS)has been employed widely at eighty stations. The data acquisition rate, accuracy, reliability, and automation have improved significantly. But the accuracy of LRERS measuring wind, the differences between its precision of measuring wind and GSWMS, and the potential of this system still needs further analysis. LRERS has designed experiments to compare 59-701 radar system with Vaisala RS-80 system. But the results are not accurate enough because of frequency interference, clock synchronization, different data processing methods and so on. In order to handle this problem, a new radiosonde with GPS function has been developed, the data of which, such as temperature, pressure, humidity, latitude, longitude and height, are received by GPS receiver through L-band radar. Real-time position and wind data are received and processed by means of L-band radar with just measuring wind at the same time. Then the wind and height data can be obtained by a strict dynamic intercomparison, due to precise time synchronization and consistent calculating methods. Thus the basic differences between these two wind profiles and comparability in the practical sounding application can be obtained.23 electrical radiosondes with GPS function model has been set free which are traced by L-band radar in Shanghai and Nanjing from the last ten days of May to the first ten days of June. The analyzed result of 23 intercomparison data demonstrates that the accuracy indicators for GSWMS relative positioning is attained to meter grade, which can show the pendulum details of wind caused by radiosonde's spiral rise. The accuracy of LRERS can not reach meter grade, but it can also show the pendulum trend after handled by 3-points smoothing. Generally, after 30-point suitable smoothing to eliminate the pendulum phenomenon, two fine upper-air wind profiles from the two independent systems of LRERS and GSWMS are quite consistent when the elevation of radar is not too low and the radiosonde is near to the station. It reveals that the wind-finding accuracy of the LRERS may reach that of the GSWMS. However, when the balloon ascends to the high layer of low wind speed and is far away from the station, the wind measuring accuracy of the LRERS is not as good as that of GSWMS and much more smoothing is required for the original raw data from the radar. The intercomparison analysis shows that the operation of LRERS at the sounding network has much potential to be mined. Original location data should be explored sufficiently to provide upper air wind data approaching GPS position.