The TOVS/ATOVS observing system in ERA-40.

The TOVS/ATOVS observing system in ERA-40.
Date Published
ERA-40 Project Report Series
Angeles Hernandez
G.A. Kelly
S. Uppala
Abstract TOVS/ATOVS is a major component of the ERA-40 observing system. From October 1978, when TIROS-N was launched, the TOVS/ATOVS system has been providing global observations of the radiation emitted by the surface and atmosphere of the Earth, covering regions and atmospheric layers where the coverage by conventional observations is sparse. Preparation of observations is an essential activity in any reanalysis, and in ERA-40 a special effort was devoted to preparing the TOVS and ATOVS radiance datasets. On one hand, the assimilation of the TOVS/ATOVS radiance data has a considerable impact on the quality of the analysis, and on the other, the relative uniformity of the datasets makes the task feasible despite of the massive volume of data involved. This report describes the work carried out, as part of the ERA-40 project, to prepare the TOVS and ATOVS datasets for reanalysis. The whole ERA-40 TOVS level-1b archive from October 1978 to December 2002 has been processed to generate an archive of calibrated radiances. The TOVS and ATOVS datasets of calibrated radiances have been checked and monitored in order to obtain information that can help to make the best possible use of the observations in the reanalysis. Quality monitoring of observations in general, and of satellite data in particular, is a key task of the day-to-day operations in NWP centres, as it is in reanalysis environments. However, there are some important differences: the scale of the tasks involved and the amount of available information. Consequently, methods and tasks are different as well; an important part of the preparation of the TOVS and ATOVS datasets for ERA-40 has been the development of methods appropriate for a reanalysis environment.