# Synthetic Sentinel-4 NO2 data processing

This chapter describes the tasks performed for processing a set of synthetic Sentinel-4 NO2 data.

## Product description

The Sentinel-4 mission includes instruments that observe trace gasses over Europe from a geo-stationairy orbit. The intended lauch in in 2023.

- Sentinel-4 Mission Introduction

Artist impression of Sentinel-4 at geo-stationary position observing Europe. Shaded area on the right shows extent of the domain used by CAMS Regional Ensemble, which for a large part overlaps with the Sentinel-4 Geographic Coverage Area (GCA).

The Sentinel-4 instrument will provide at daytime hourly snapshots of trace gasses at a resolution of about 8x8 km. The amount of data values is therefore much higher than for the polar orbiting Sentinel-5p instrument. In the context of the CAMS_61 project, a first evaluation has been made of the resources needed to process the future Sentinel-4 data within simulation models. For this, a synthetic data set of Sentinel-4/NO2 data has been created using simulations from the MONARCH model (BSC), accompanied with realistic error characteristics and averaging kernels produced using machine-learning. An extensive description of how the data was produced and evaulated is available in:

- Final report of WP6130 R&D activities (not available online yet)

Example of synthetic Sentinel-4 NO2 retrievals.

## Downloading

The data set be available through a public server.

The data set consists of hourly files for July 2018:

    S4_v3_r/BSC_S4-syn_NO2_20180701_0000.nc
            BSC_S4-syn_NO2_20180701_0100.nc
            BSC_S4-syn_NO2_20180701_0200.nc
                                     :
            listing.csv

Also a listing file is included for use with the CSO observation operator.

A catalogue of images of the data could be made similar to the S5p NO2 image catalogue.

## Configuration of observation operator

The observation operator described in chapter ‘Observation operator’ requires settings from an rcfile. Template settings are included as:

    oper/tutorial_oper_S4-syn.rc

The tutorial program `tutorial_oper_S5p.F90` should be changed to use these settings rather than the default settings:

    !~ input settings for synthetic S4/NO2
    rcfile = 'tutorial_oper_S4-syn.rc'
    ! base of keywords in rcfile:
    rcbase = 'tutorial.S4-syn.no2'

Without further changes, the tutorial program will create (dummy) simulations of the synthetic Sentinel-4 retrievals.

A catalogue of images of the, by the tutorial, simulated data could be made similar to the simulated S5p NO2 image catalogue.