The radiosonde balloon sounding system at Serpong, Indonesia (6.36S, 106.65E, 50m MSL) measures the vertical profiles of pressure, temperature, humidity and horizontal wind in the lower atmosphere from the troposphere to lower stratosphere. The type of radiosonde used in this system is the Vaisala Radiosonde RS80 (before 2004) and RS92 (after 2004) with an automatic signal processor (DigiCORA MW11 before 2004, III after 2004). The TA1000 or TX1000 type of balloons made by the TOTEX corporation was used to obtain the vertical structure of the atmosphere up to ~30 km. In the observations using the Vaisala Radiosonde RS80 and RS 92 as a transmitter, the horizontal location of the balloons was measured by means of the GPS navigation. Then, the horizontal wind velocity is calculated from time derivative of the horizontal displacement of the balloon.