Products » Formaldehyde total column (HCHO)





Algorithm

The operational HCHO 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.
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 DOAS slant column fit of HCHO is performed in the UV wavelength range 328.5-346 nm [De Smedt et al. (2008)]. A HCHO cross-section is included in the fit, as well as the cross-sections of the interfering trace gases: ozone, NO2, BrO and OClO. Two Ring reference spectrums are included as an additive fitting parameter. The detailed DOAS settings used for GOME-2 HCHO slant columns retrieval are given in the [DLR/GOME-2/ATBD].

Reference sector correction

To reduce the impact of fitting artifacts due to unresolved spectral interferences with ozone and BrO, an absolute normalisation is applied on a daily basis using the reference sector method. The mean HCHO slant column in the reference sector (central Pacific Ocean) is fitted by a polynomial which is subtracted to all the SCD of the day and replaced by the HCHO background taken from the tropospheric 3-D Chemistry Transport Model (CTM) IMAGES [Stavrakou et al. (2009)].

AMF and VCD determination

The AMF is calculated with the LIDORT 3.3+ model for the 340 nm, since HCHO is an optically thin absorber in this wavelength region. The AMF depends strongly on the vertical profile shape of HCHO in the troposphere, the surface albedo and the presence of clouds. The monthly output of the IMAGESv2 CTM has been used to specify the vertical profile of HCHO distribution

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 HCHO retrieval is being developed by scientists from BIRA and DLR
• BIRA: Isabelle De Smedt, Michel Van Roozendael
• DLR: Nan Hao, Pieter.Valks, Sunil Emmadi
and is funded by EUMETSAT O3M-SAF and national contributions.


For further information please contact:

Nan Hao, DLR-IMF
E-Mail: Nan.Hao [at] dlr.de

DLR IMF AP Copyright © 2010 | Imprint