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Note: The S5P L2_CLOUD data product has recently been reprocessed with processor version 02.04.01, replacing older data versions. First validation results for this full-mission reprocessing are published in the quarterly validation report #18. Users still making use of previous data versions are requested to refer to the quarterly validation report #17.

Validation Summary

The Sentinel-5p TROPOMI L2_CLOUD data product (Loyola et al., 2018) contains several cloud-related quantities, retrieved with the Optical Cloud Recognition Algorithm (OCRA) and with the Retrieval of Cloud Information using Neural Networks (ROCINN) either with the Cloud-As-Layers approach (CAL) or the Cloud-as-Reflecting Boundaries approach (CRB) (Lutz et al., 2016, Loyola et al., 2010):

  • OCRA radiometric Cloud Fraction (CF);
  • ROCINN_CAL Cloud Top Height (CTH) and Cloud Optical Thickness (COT);
  • ROCINN_CRB Cloud Height (CH) and Cloud Albedo (CA).

The Sentinel-5p MPC performs in routine the following validation checks:

  • ROCINN_CAL CTH and ROCINN_CRB CH are compared to correlative ground-based measurements from the CLOUDNET and ARM networks;
  • ROCINN_CAL CTH and COT are compared to those measured by Suomi-NPP VIIRS;
  • OCRA CF, ROCINN_CAL CTH and ROCINN_CRB CH are compared to Sentinel-5p radiometric cloud fraction and cloud height data retrieved with the FRESCO algorithm;
  • OCRA CF, ROCINN_CAL CTH and ROCINN_CRB CH are compared to the Aura OMI O2-O2 measurements.


Given their different nature, we look at low (cloud top height below 4km) and high clouds separately. The bias of ROCINN_CAL cloud top height vs. CLOUDNET cloud top height is within the 20% mission requirement for low clouds, but not for high clouds. The bias of ROCINN_CRB cloud height vs. CLOUDNET cloud mean height is within the 20% mission requirement for high clouds, but exceeds it slightly for low clouds. For both ROCINN_CAL and ROCINN_CRB, the dispersion requirement of 0.5 km is met for low clouds but not for high clouds. Given the large difference in sensitivity between the TROPOMI near-infrared observations and the ground-based lidar/radar observations, the agreement is fair.


Product ID Stream Product Bias  Dispersion Special features
 CAL CTH (high)  -35%  2 km Low clouds: CLOUDNET CTH<4km; high clouds: CLOUDNET CTH>4km.

 CAL CTH (low)  -15%  0.5 km
 CRB CH (high) -20% 2 km
 CRB CH (low)  -25%  0.5 km


A detailed description of the method and a comprehensive discussion of validation results can be found in the Sentinel-5p Quarterly Validation Report #19: April 2018 - May 2023

  Latest Quarterly Validation Report     Product info     Current Processor Version  
 #19: April 2018 - May 2023  See  




Loyola, D. G. et al., The operational cloud retrieval algorithms from TROPOMI on board Sentinel-5 Precursor, Atmos. Meas. Tech. , 11, 409-427, 2018, doi:10.5194/amt-11-409-2018

Lutz, R. et al., OCRA radiometric cloud fractions for GOME-2 on MetOp-A/B, Atmos. Meas. Tech., 9, 2357-2379,2016, doi:10.5194/amt-9-2357-2016

Loyola, D. al., Global patterns in daytime cloud properties derived from GOME backscatter UV-VIS measurements, Int. J. Remote. Sens., 31, 2010, 4295-4318, doi:10.1080/01431160903246741