Comparison of Selected In-situ and Remote Sensing Technologies for Atmospheric Humidity Measurement

Present-time operational radiosondes are able to produce atmospheric humidity observations with high resolution and precision, but also remote sensing technologies have shown good progress in producing more detailed humidity profiles with reasonable small uncertainties. In addition, several remote sensing methods can provide accurate integrated precipitable water (IPW) column data for meteorological purposes. As the accuracy of both numerical weather prediction models and global climate models is largely dependent on the quality of the available water vapor pressure data, it was seen relevant to comparatively evaluate the performance of latest in-situ and remote sensing technologies.

In this study humidity measurements of Vaisala Radiosondes RS41 and RS92 were compared against water vapor pressure profiles measured with a high capability water vapor Raman lidar situated at Jet Propulsion Laboratory Table Mountain Facility in California, USA. Test flights were conducted as dual soundings in various humidity conditions. Another performance analysis was made by comparing IPW columns calculated from the radiosonde relative humidity measurements to simultaneous IPW measurements of microwave radiometers and/or GPS receivers of the same site. Comparative soundings were also conducted at Arctic Research Center of Finnish Meteorological Institute in Sodankyla, Finland. In these soundings a Cryogenic Frostpoint Hygrometer (CFH) was used as an in-situ reference instrument.

This comparison of various humidity measurement technologies confirmed the good performance of both operational radiosondes and the Raman lidar instrument. It also gave valuable information about differences between in-situ and remote sensing methods for humidity measurement.