Offline high-resolution ozone profile

Description

Offline high-resolution vertical ozone profile product provides an ozone profile from the GOME-2 nadir scanning mode, the full error covariance matrix, the retrieval noise covariance matrix, the a priori profile, the averaging kernels and the retrieved auxiliary parameters, like surface or cloud albedo. Also included are: geo-location, the specific spectral windows used and retrieval diagnostics, like the number of iterations and spectral fit indicators.

The offline ozone profile product bundles all the PDU-based NRT ozone profile products into one single orbit. The offline product is better for archiving purposes, but does not contain different information than the products produced in NRT.

Type

Based on product requirements, the product files must be available to users in less than two weeks, but in practice the data is available in 2-3 days from sensing.

Resolution

High resolution

Metop-A: 40 x 80 km² (2010 – 16/07/2013) and 40 x 40 km² (16/07/2013 – present).
Metop-B: 40 x 80 km² (12/12/2012 – present).

Theoretical basis

Global Ozone Monitoring Experiment-2 (GOME-2) measures the radiance spectrum of sunlight scattered from the atmosphere in the (UV) wavelength region 260-330 nm. The absorption of ozone decreases with increasing wavelength. This differential absorption makes it possible to derive the vertical distribution of ozone in the atmosphere from the measured UV spectrum.

Processing algorithm

At KNMI, Ozone ProfilE Retrieval Algorithm (OPERA) iteratively finds the vertical ozone profile best matching the GOME-2 reflectance using optimal estimation. The forward model is based on LidortA and uses an externally prescribed instrument response slit function. The a priori ozone climatology is (currently) based on McPeters/Labow/Logan. The surface pressure and the vertical temperature profile come from operational ECMWF forecasts. Special adaptations have been made to handle spikes in the measured radiance spectrum in the South Atlantic Anomaly.

Units and spatial resolution

The vertical ozone profiles are given as partial ozone columns in Dobson Units (DU) in 40 layers from the surface up to 0.001 hPa. The ground pixel size corresponds to the footprint of the Band-1b integration time, which usually means 40 x 80 km² (along-track x cross-track, see also resolution above).

Validation

This product is validated by DWD (Germany) and KMI (Belgium). The validations are based on detailed comparisons of the operational retrieved profiles from GOME-2 satellite data with ground-based measurements (balloon soundings, lidar and microwave radiometer measurements). Visit AC SAF ozone profiles validation website for further information.

Quality monitoring

This GOME-2 product is compared daily with the ozone profiles from the Ozone Mapping and Profiler Suite Limb Profile (OMPS LP) instrument on board the Suomi NPP satellite. Comparison results are presented here.

Archiving and dissemination

This product is archived at the FMI and available via offline data access page.

File format

HDF5.
HDF5 is the product format of choice for scientific users. This product contains all the profile, error and diagnostics information.
Each offline ozone profile product file contains one full orbit of data.

Algorithm version information

Time period	GOME-2 / Metop-A	GOME-2 / Metop-B
until 29.04.2010	1.01	N.A.
29.04.2010 – 13.05.2013	1.10	N.A.
13.05.2013 – 15.07.2013	1.11	N.A.
15.07.2013 – 23.02.2015	1.11	1.11
23.02.2015 - 13.08.2018	1.12	1.12
13.08.2018 - 19.11.2018	1.30	1.30
19.11.2018 onwards	2.00	2.00

Important changes in the latest algorithm version (1.30)

Degradation correction