Products » Water Vapour total column (H2O)





Algorithm

The operational H2O total column products are generated using the algorithm GDP (GOME Data Processor) version 4.x integrated into the UPAS (Universal Processor for UV/VIS Atmospheric Spectrometers) processor for generating level 2 trace gas and cloud products.
The total H2O column is retrieved from GOME solar backscattered measurements in the red wavelength region (614-683.2 nm), using the Differential Optical Absorption Spectroscopy (DOAS) method. A description of the algorithm and validation is given in the reference documents listed in the GOME-2 documentation pages.

DOAS slant column fitting

The fitting window 614-683.2 nm was selected for GOME-2 [Wagner et al. (2003)]. An effective H2O cross-section for a single temperature of 290 K is included in the fit, as well as the cross-sections of O2 and of the interfering trace gas O2-O2. A Ring reference spectrum and 3 vegetation spectra are included as an additive fitting parameter. The detailed DOAS settings used for GOME-2 H2O slant columns retrieval are given in the [DLR/GOME-2/ATBD].

AMF and VCD determination

The AMF of H2O is set equal to the AMF of the O2-C band times a correction factor [Wagner et al. (2006)]. The AMF for O2 is calculated from the known O2 VCD and the fitted O2 slant column. The fitted H2O and O2 slant columns are corrected for saturation effects. The correction factor is calculated for a single H2O profile, as function of viewing geometry and surface albedo. The surface albedo in the retrieval is taken from the Koelemeijer database, except over ocean where it is set to 0.02.

Remark

In the region of the Southern Atlantic Anomaly (SAA), the GOME-2 satellite instrument is subject to an increased particle flux which creates spurious signals in individual detectors resulting in a reduced quality of the retrieved GOME-2 trace gas columns, i.e. increased scatter in trace gas columns over South America and the Southern Atlantic.

Scientific Papers



Acknowledgments

GDP 4.x for total H2O retrieval is being developed by scientists from MPI-Chemie in Mainz and DLR
• MPI: Thomas Wagner, Steffen Beirle, Kornelia Mies
• DLR: Sander Slijkhuis, Bernd Aberle, Sunil Emmadi, Diego Loyola
and is funded by EUMETSAT O3M-SAF and national contributions.


For further information please contact:

Sander Slijkhuis, DLR-IMF
E-Mail: Sander.Slijkhuis [at] dlr.de

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