The Sentinel-5p TROPOMI OCRA/ROCINN retrieval is a two-step algorithm, with two model variants for the second step (ROCINN_CAL and ROCINN_CRB). OCRA computes the radiometric cloud fraction (RCF), ROCINN_CAL retrieves the cloud top height (CTH) and the cloud optical thickness (COT) and ROCINN_CRB retrieves the cloud height (CH, corresponding to the optical centroid) and the cloud albedo (CA).

The different quantities are validated as follows:

• The ROCINN_CAL cloud top height is compared to ground-based lidar/radar CTH measurements of the CLOUDNET and ARM network.
• Similarly, the ROCINN_CRB cloud height is compared to cloud mean height data, derived from the CLOUDNET vertical classification profile data.
• From the ROCINN_CAL cloud top height and the (parametrized) ROCINN_CAL cloud base height, a cloud mean height is derived, and then compared with the CLOUDNET-derived cloud mean height data.
• Several comparisons with cloud parameters of other satellite products are performed: NPP-VIIRS (CTH, COT), Sentinel-5p FRESCO (RCF, CH), Aura OMI O2-O2 (RCF, CH), MODIS (CTH).

Details on the methodology and results are described in Compernolle et al., AMT 2021.

References

Compernolle, S. et al., Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O₂-O₂, MODIS and Suomi-NPP VIIRS, Atmos. Meas. Tech., 14, 2451–2476, 2021, doi:10.5194/amt-14-2451-2021.