Abstract
Abstract. The potential of the shortwave infrared channel of the atmospheric spectrometer SCIAMACHY on Envisat to provide accurate measurements of total atmospheric water vapour columns is explored. It is shown that good quality results can be obtained for cloud free scenes above the continents using the Iterative Maximum Likelihood Method. In addition to the standard cloud filter employed in this method, further cloud screening is obtained by comparing simultaneously retrieved methane columns with values expected from models. A novel method is used to correct for the scattering effects introduced in the spectra by the ice layer on the detector window. The retrieved water vapour total vertical columns for the period 2003–2007 are compared with spatially and temporally collocated values from the European Centre for Mid-Range Weather Forecast (ECMWF) data. The observed differences for individual measurements have standard deviations not higher than 0.3 g/cm2 and an absolute mean value smaller than 0.01 g/cm2 with some regional excursions. The use of recently published spectroscopic data for water vapour led to a significant improvement in the agreement of the retrieved water vapour total columns and the values derived from ECMWF data. This analysis thus supports the superior quality of the new spectroscopic information using atmospheric data.
Highlights
Water vapour is, after nitrogen and oxygen, the most abundant atmospheric constituent
The use of recently published spectroscopic data for water vapour led to a significant improvement in the agreement of the retrieved water vapour total columns and the values derived from European Centre for MidRange Weather Forecast (ECMWF) data
Clouds hide part of the column, and they occur rather frequently in the relatively large ground pixels of these instruments. This paper describes another opportunity for gathering information on the distribution of atmospheric water vapour: exploiting the short-wave infrared measurements by SCIAMACHY around 2.3 μm
Summary
After nitrogen and oxygen, the most abundant atmospheric constituent. Its presence is essential for life, and has a great impact on human society. Because water vapour is the most important greenhouse gas, contributing the major part of the greenhouse effect, it has a huge influence on climatic conditions. In the anthropogenic changes of the greenhouse effect it plays an important role through various feedback mechanisms, the size and influence of which is not well established. In comparison to other greenhouse gases, the distribution of water vapour is much more variable and inhomogeneous. Its highest concentrations are found in the lower troposphere, especially in tropical regions
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