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NOP from Metop-B

Description: Near real-time coarse resolution ozone profile product provides ozone profile reported as partial columns between 41 pressure levels logarithmically spaced between and including surface pressure and 0.1 hPa. For cloudy and partially cloudy scenes, the cloud-top pressure replaces the nearest pressure level.

Type: Near real-time. Based on product requirements, the product files must be available to users in three hours from sensing.

Theoretical basis: Global Ozone Monitoring Experiment-2 (GOME-2) measures the radiance spectrum of sunlight scattered from the atmosphere in the wavelength region 270 - 340 nm. The absorption of ozone decreases as the wavelength increases. Therefore the vertical distribution of ozone in the atmosphere can be derived from the measured spectrum.

Processing: At KNMI, Ozone ProfilE Retrieval Algorithm (OPERA) uses an iterative method in the retrieval process to match a simulated radiance spectrum to the measured earthshine spectrum: non-linear optimal estimation. Initial values for a set of fit parameters (the state vector: ozone profile and possibly other parameters, such as surface albedo) are used for a first simulation by the radiative transfer model (RTM). The state vector is updated after each optimal estimation inversion step. Optimal estimation requires a priori information (value and error covariance) for the state vector elements. Usually the initial state vector comes from an ozone climatology and albedo database which is then also used for a priori. Convergence criteria based on the magnitude of the state update and the deviation between measurement and simulation are applied to decide on a possible next iteration.

Units and spatial resolution: The ozone profile is reported as partial columns, in Dobson Units (DU). GOME-2 has nominal spatial resolution of 80 km x 40 km, but for the shortest UV wavelengths the integration time is 8 times longer. Therefore, NOP spatial resolution is 640 km x 40 km.

Validation: This product is validated by DWD and RMI. The validations are based on detailed comparisons of existing satellite data with ground-based measurements (balloon soundings, lidar and microwave radiometer measurements). Visit O3M SAF ozone profiles validation website for further information.

Dissemination: See NRT access information.

File format: This product is available in two formats: HDF5 and BUFR (only BUFR via GTS). Each file contains one PDU (Product Dissemination Unit), equal to three minutes of satellite data.

Algorithm version information:

Time period GOME-2 / Metop-A GOME-2 / Metop-B
until 30.05.2008 0.98 N.A.
30.05.2008 – 09.12.2008 0.99 N.A.
09.12.2008 – 09.11.2009 1.00 N.A.
09.11.2009 – 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 algorithm changes in 1.12: