INDIRECT MEASUREMENT 



27 



RF 

 TRANSMITTER 



BLOCKING 

 OSCILLATOR 



ANEROID 

 CAPSULE 



BAROSWITCH 



Figure 2.2. Block diagram of the radiosonde. 



There is no uniformity of sensors used in the world's radiosondes. 

 Hence, it is difficult to compare measurements from different countries. 

 At one international comparison at Payerne, Switzerland, in 1956, 14 

 nations participated [10]. The results indicated significant differences. 

 Temperature measurements corresponded to within ±1.5 °C for night 

 flights but corresponded only to withm ±3.5 °C for daytnne flights. 

 Pressure measurements agreed well at low altitudes but indicated a dis- 

 persion of ±1.5 mbar above 9,000 m (29,000 ft), and ±2.5 mbar above 

 16,000 m (50,000 ft). Humidity comparisons were poor, indicating that 

 15 percent would be the most optimistic estnnate of the standard devia- 

 tion from the mean for all flights. On the average, it is estimated that 

 the standard American temperature sensor indicated a value approxi- 

 mately 1.5 °C below the mean for all sondes used in the test. The pres- 

 sure determination was below the mean by 0.5 mbar, whereas the humid- 

 ity sensor could not be quantitatively evaluated due to the erratic be- 

 havior of all sensors. 



No attempt was made at these comparison trials to determine the 

 absolute accuracy of any radiosonde. Although the absolute accuracy 

 of the American sonde has not been determined, satistical evaluation of 



