83rd Annual

Monday, 10 February 2003
A new reference radiosonde for precise upper air measurements
William H. Bauman III, Yankee Environmental Systems, Inc, Turners Falls, MA; and W. M. Stein and M. C. Beaubien
Performance of a new chilled mirror reference grade radiosonde is described. The technical approach solves a number of known problems with existing upper air humidity and temperature measurements. Most radiosondes use a single thermistor to derive temperature and a polymer-based relative humidity sensor to derive humidity. The new radiosonde employs a forced aspiration chilled mirror hygrometer to determine water vapor content and three thermistors to determine temperature. In addition, pressure is derived using Global Positioning System (GPS) altitude and surface temperature, humidity, and pressure, or directly measured with a pressure sensor. Wind data is obtained using GPS wind finding.

The hygrometer technology was chosen based on long-term experience with industrial and meteorological chilled mirror hygrometers and radiosonde intercomparisons of chilled mirror hygrometers with carbon hygristors. The forced aspiration chilled mirror hygrometer is known to provide better accuracy over polymer-based relative humidity sensors and provides one of the few truly direct physical measurements of dew point. It is recognized as the most precise method of determining the water vapor content of a gas.

Three-thermistor temperature measurement based on the Accurate Temperature Measuring (ATM) radiosonde technique developed at Goddard Space Flight Center employs aluminum, black, and white coated surfaces for radiative error compensation. Three simultaneous equations are solved based on the known emissivity and absorptivity of the different coatings on each thermistor. This provides the most accurate temperature measurements day or night. The thermistors are mounted on a 15-inch boom that extends above the sonde so the thermistors sample undisturbed air during ascent.

Expected uses for the new sensor package include climate reference data, calibration of standard radiosondes, global warming studies, complete highly accurate synoptic soundings, field experiments, and tethersonde measurements.

Supplementary URL: