ESA FRM4DOAS: Towards the launch of the NDACC MAX-DOAS Central Processing Service

Since it provides vertically-resolved information on atmospheric gases at a horizontal scale approaching the one from nadir backscatter satellite sensors, the ground-based MAX-DOAS technique has been recognized as a valuable source of correlative data for validating space-borne observations of air-quality-related species such as NO2, HCHO, SO2, O3, etc. In this context, the ESA Fiducial Reference Measurements for Ground-Based DOAS Air-Quality Observations (FRM4DOAS) project is aiming at developing a near-real-time (6-24h latency) central processing system for the delivery of harmonized, quality-controlled, and fully traceable data products from MAX-DOAS instruments. The first phase of the project has been dedicated to the development of a prototype version of this processing system for 3 key products (NO2 vertical profiles, total O3 columns, and tropospheric HCHO profiles) and its demonstration at 11 project partners MAX-DOAS stations.In this presentation we will describe the efforts carried out during the last months to develop the first MAX-DOAS central processing service to be operated within the Network for the Detection of Atmospheric Composition Change (NDACC). The main aspects of the service development will be presented, like the FRM4DOAS prototype algorithm optimisation, operationalisation, and validation, and the establishment of MAX-DOAS NDACC instrument and data retrieval certification procedures, user data policy, datasets DOI, etc. This operational service is expected to be launched in Spring 2020 for a limited number (5-10) of NDACC-certified MAX-DOAS instruments. Corresponding data sets will be stored in the NDACC and ESA EVDC data handling facilities.This activity and its future upscaling in terms of stations and data products will ensure that MAX-DOAS observations at a FRM quality level will be made available for the validation of present and future satellite missions like the Copernicus atmospheric Sentinels (5p, 4, 5).