Articles | Volume 10, issue 6
Research article
27 Jun 2017
Research article |  | 27 Jun 2017

Consistency between GRUAN sondes, LBLRTM and IASI

Xavier Calbet, Niobe Peinado-Galan, Pilar Rípodas, Tim Trent, Ruud Dirksen, and Michael Sommer

Abstract. Radiosonde soundings from the GCOS Reference Upper-Air Network (GRUAN) data record are shown to be consistent with Infrared Atmospheric Sounding Instrument (IASI)-measured radiances via LBLRTM (Line-By-Line Radiative Transfer Model) in the part of the spectrum that is mostly affected by water vapour absorption in the upper troposphere (from 700 hPa up). This result is key for climate data records, since GRUAN, IASI and LBLRTM constitute reference measurements or a reference radiative transfer model in each of their fields. This is specially the case for night-time radiosonde measurements. Although the sample size is small (16 cases), daytime GRUAN radiosonde measurements seem to have a small dry bias of 2.5 % in absolute terms of relative humidity, located mainly in the upper troposphere, with respect to LBLRTM and IASI. Full metrological closure is not yet possible and will not be until collocation uncertainties are better characterized and a full uncertainty covariance matrix is clarified for GRUAN.

Short summary
GRUAN temperature and water vapour radiosonde measurements are shown to be consistent with infrared hyperspectral measurements from IASI using LBLRTM as a reference radiative transfer model. Long-term climate data records of temperature and water vapour can be derived from radiosonde measurements and from space-based instruments. In order to have accurate and homogeneously useful data series, it is a critical necessary condition that these data sets be consistent with each other.