M. Zara1, K.F. Boersma1,6, I. De Smedt2 , A. Richter3, E. Peters3, J. van Geffen1, S. Beirle4, T. Wagner4, S. Marchenko5, N. Krotkov5 , H.J. Eskes1

OMI STM, September 2017

Quality Assurance for NASA, KNMI, BIRA-IASB and QA4ECV spectral fitting algorithms for NO2 and HCHO Slant Columns

from OMI and GOME-2A

1Koninklijk Nederlands Meteorologisch Instituut, KNMI, the Netherlands 2Institut royal d'Aéronomie Spatiale de Belgique, BIRA-IASB, Belgium 3Institut für Umweltphysik, IUP, Bremen 4Max-Planck-Institut für Chemie, MPI, Mainz 5Goddard Space Flight Center, NASA, USA 6 Wageningen University, WUR, Wageningen

Motivation

Recently, the Global Climate Observation System (GCOS) has identified NO2 and

HCHO as precursors to Essential Climate Variables (ECVs) because of their value in

detecting and attributing changes in ozone and aerosol distributions (GCOS-138, 2010).

Need for reliable and traceable quality information. The EU FP7-project Quality

Assurance for Essential Climate Variables (QA4ECV) (http://www.qa4ecv.eu/) is addressing

this need by providing a fully traceable quality assurance effort on all aspects of the NO2 and

HCHO retrieval algorithms.

Here, our topic is the quality assurance of state-of-science spectral fitting algorithms for

the NO2 and HCHO slant column densities (SCDs) from OMI and GOME-2A from

NASA, KNMI, BIRA-IASB and QA4ECV.

OMI NO2 SCD retrieval algorithms

(1) Bucsela et al., 2006; (2) Van Geffen et al., 2015; (3) QA4ECV Deliverable 4.2, 2016; (4) Marchenko et al., 2015

Reference

New

OMNO2A v1, OMNO2A v2, QA4ECV and NASA NO2 SCDs

SP v3.0 - online

SP v3.1

DOAS SCD uncertainty Statistical SCD uncertainty

Comparable SCDs: their spatial variability as proxy for the SCD uncertainty

We evaluate how good the uncertainty provided by the fitting procedure is.

DOAS: a (non) linear least-square fit between observed and modelled spectra

SCD uncertainty driven by: • Reflectance uncertainty (I, I0) • Wavelength calibration • Accuracy of fitting model to mimic

observations • Stripes

+ Possible systematic effects!

Random!

OMI NO2 Statistical & DOAS SCD uncertainty

OMNO2A v1 OMINO2-QA4ECV

DOAS = random + systematic

Statistical = random

SP v3.0 SP v3.1

OMINO2-NASA

2005-2015: OMI NO2 SCD uncertainty

OMINO2-QA4ECV

The effect of stripiness on the OMI NO2 SCD uncertainty

OMI NO2: 2005-mean solar irradiance

The effect of stripiness on the OMI NO2 SCD uncertainty

OMI NO2: 2005-mean solar irradiance

OMI HCHO: daily radiance spectra vs

50 × 1015 molec. cm−2

2 × 1015 molec. cm−2

Stripiness for HCHO before and after daily radiance as reference spectra:

OMNO2A v1 (01/01/2012)

1. Reduction of NO2 SCD DOAS uncertainty globally.

2. Removal of extreme (red) uncertainties from the swath edges.

QA4ECV (01/01/2012)

Clouds affect the SCD uncertainty brighter scenes.

The SCD uncertainty is mostly driven by the SNR (TOA-reflectance) rather than the signal strength (SCD).

OMINO2-QA4ECV DOAS unc. (01/01/2015)

www.temis.nl

GOME-2A NO2 SCDs from BIRA-IASB and QA4ECV

Similar to OMI

2007-2015: GOME-2A NO2 SCD uncertainty from BIRA-IASB and QA4ECV

September 2009

Conclusions

This research was funded by the FP7 project QA4ECV grant No. 607405