University of Bremen IUP ONPD





Onion Peeling DOAS (ONPD)

Introduction       Retrieval Method       Data Products      References     Acknowledgements     Contact

Top Introduction

The Onion Peeling DOAS (Differential Optical Absorption Spectroscopy) (in short ONPD) algorithm has been developed for the retrieval of stratospheric concentrations of atmospheric constituents from solar occultation measurements of the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on ENVISAT.
Currently, the algorithm is used to derive stratospheric methane, carbon dioxide and water vapour number densities and in a second step also volume mixing ratios (VMRs).
The method is in principle (e.g. by adaptation of fit windows) also applicable to other species.
A previous version of the algorithm (using a slightly different approach) has already been used for the retrieval of water vapour profiles (NoŽl et al., 2010).
The current methane and carbon dioxide V4.5.2 product is described in NoŽl et al. (2016).
A publication of the water vapour results V4.5.2 is under preparation.

Top Retrieval Method

A detailed description of the ONPD retrieval method for methane and carbon dioxide is given in the ATBD.
Further details and first retrieval results for V3.3.6 data can be found in NoŽl et al. (2011) and in NoŽl et al. (2016) for V4.5.2.

Top Data Products

ONPD stratospheric methane profiles are available for the time interval August 2002 to April 2012.
They cover latitudes between about 50įN and 70įN (restricted by the geographical coverage of the SCIAMACHY solar occultation measurements).
Reasonable results are obtained between 17 and 45 km altitude.
Current product version is V4.5.2.
This version is also part of the ESA GHG-CCI data set (methane and carbon dioxide only).
Previous methane and carbon dioxide data sets V4.2.1 and V3.3.6 are also still available, but use of the actual data set is recommended.
The data products are ASCII files; the format is described in the header (lines marked by #).
A more detailed description of the product format is given in the Product User Guide (for the methane and carbon dioxide product, but similar for water vapour).

Access to the data is possible if you agree to the conditions for data use.

Top References

Top Acknowledgements

SCIAMACHY is a national contribution to the ESA ENVISAT project, funded by Germany, The Netherlands, and Belgium. SCIAMACHY data have been provided by ESA.
We thank the European Centre for Medium RangeWeather Forecasts (ECMWF) for providing us with analysed meteorological fields.
We thank Geoffrey Toon of the NASA Jet Propulsion Laboratory for providing the empirical solar line list used in this work.
This work has been funded by DLR Space Agency (Germany), the ESA GHG-cci and by the University of Bremen.

Top Contact

If you are interested in more information on Onion Peeling DOAS, please contact Stefan NoŽl.

Author of this page: Stefan NoŽl