A Procedure to Use Satellite Measurements to Determine Differences Between Radiosonde Types

Radiosondes report the temperature of a sensor that is in equilibrium with both the thermal and radiative environments. This means that, although the radiosonde is used to report atmospheric temperatures, the temperatures that it reports are influenced by both visible and solar radiation. These size of effects is a function of the atmospheric profile, the radiation environment, and the sensor design. Campaigns have been conducted to measure the differences between these effects for specific instruments. These campaigns are useful, but they are not complete because the difference is a function of the atmospheric condition and only a few conditions have been sampled. Numerical models also make adjustments for different types of radiosondes. These usually take the form of location dependent biases which remove some of the effect, but obviously can not completely remove an error that is a function of the atmospheric profile. As a measurement device, satellites have the advantage that one instrument is used to measure all locations. This provides a means of determining and removing the systematic component of the bias. The procedure to be used is the following. Radiosonde observations from two types are compared to find the observation from instrument type A, that most closely matches a given observation from instrument type B. Each radiosonde observation is accompanied by a satellite observation. The satellite measurements are then converted to temperatures using a retrieval operator and subtracted to find the actual difference between the atmospheric profiles for the two observations. This atmospheric difference is then subtracted from the total difference between the two radiosondes to obtain the net difference between the radiosonde types. This is repeated to build a sample of radiosonde differences along with the radiosonde profiles. Then a regression relationship is established to predict the difference as a function of the measured variables. Relationships are being developed for the common radiosondes to adjust all to a standard radiosonde reference in support of the AIRS mission. A preliminary adjustment has been developed for the Viasalla and VIZ radiosondes.