MAJA and the new CAMS aerosols 48r1

The Copernicus Atmospheric Monitoring Service (CAMS) is about to release a new version of its aerosol products on 27 June 2023, referred as 48r1. Their evolution has a direct impact on MAJA, and requires us to adapt the processor. MAJA will not be ready to support 48r1 before the next release scheduled for September 2023. Therefore, users are advised not to use the ‘–cams’ option to process Sentinel-2 products after 27 June until the next release.

The number and type of aerosols described by CAMS has evolved over time, along with the versions of MAJA, starting with five species before 10 July 2019, and then seven species until the next CAMS release scheduled for 27 June 2023. To properly account for the aerosols, MAJA relies on per-aerosol Look-Up Table (LUT) calculated with a radiative transfer model. Each aerosol is described by its optical properties, ie. its refractive index, its size distribution, its growth factor for those whose size varies with the relative humidity of the atmosphere.

The upcoming 48r1 release of the CAMS products includes several changes :

  • Biogenic and anthropogenic Secondary Organic Aerosols (SOA) are two new aerosols previously included in Organic Matter. They are both hydrophilic, which means that their size varies with humidity;
  • The size distributions of Organic Matter and Dust species change with this new version.

Such changes require quite some work on MAJA’s side :

  • Prepare the new Look-up Tables and extend the GIPP to the new aerosols specifications ;
  • Adapt the processor so that MAJA picks the right LUT according to the L1C product date ;
  • Adapt the cams_download tool to collect the adequate AOD and mixing ratios.

Unfortunately, this will not be done in the blink of an eye. We need :

  • to ensure that the quality of the L2A products obtained using the 48r1 aerosols fit MAJA’s specifications, by validating AOD and spectral reflectances with our in-situ ROSAS network ;
  • to assess the differences of the L2A produced with both 47r1 and 48r1 ;
  • to ensure that the next release of MAJA is fully backward-compatible with 47r1 and handles the processing of a time series mixing CAMS versions properly.

We are doing our best to release this new version of MAJA by the end of September. In the meantime, we strongly advise users not to use the CAMS option for Sentinel-2 products acquired from June 27th onward.

Thank you for your patience,

The MAJA team

A first analysis suggest than it’s worth using the 48r1 CAMS auxiliary data rather than deactivating the CAMS option with the current version of MAJA. Therefore, we reconsider our former recommendation to deactivate the use of CAMS. Learn more here :