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Offline high-resolution ozone profile from Metop-B

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 2 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.

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 onwards 1.12 1.12

Important changes in the latest algorithm version (1.12):