Subvisible-Enhanced Level2 dataset [SEL2]

The Subvisible-Enhanced Level 2 dataset contains information of optically thin clouds retrieved from the analysis of Level 1 data from the CALIPSO lidar CALIOP. This dataset provides, for CALIOP profiles averaged over 5-km distances: altitudes of base and top for cloud layers detected in the profile (up to 20), their midlayer temperature and integrated attenuated total backscatter. The dataset is focused on high optically thin clouds, with optical depths as low as 0.001. The covered period extends from june 2006 to november 2017.

SVC seasonal maps from SEL2, from Martins et al. 2011
Cloud Fraction for cloud layers with optical depths below 0.03 retrieved by season over 2006-2008, data from SEL2

The algorithms used to produce this dataset are presented, along with seasonal statistics derived from it and other results, in Martins et al. 2011: 

E. Martins, V. Noel and H. Chepfer (2011): Properties of cirrus and subvisible cirrus from nighttime Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), related to atmospheric dynamics and water vapor , J. Geophys. Res., 116, D02208, doi:10.1029/2010JD014519. 












Data description

The dataset is distributed as netCDF files, which follow the CALIOP orbit naming scheme: there is one SEL2 file for every CALIOP Level 1 file, which span half-orbits. There are therefore roughly 13-14 SEL2 files per day, as SEL2 data was computed using CALIOP nighttime measurements.


Documents describing the datasets available in the SEL2 files will be made available here (hopefully)





Variables present in SEL2 files:

  • lon, lat: profiles coordinates. Shape: [nprof]

  • time: Time. Unit: TAI, as in CALIOP L1 file. Shape: [nprof]

  •  ztop, zbase: Altitude of layers base and top. Unit: km. nan if no layer. Shape: [nprof, 20]

  • T_lay: temperature of layers. Unit: degrees Celsius. Shape: [nprof, 20]

  • i_atb: integrated attenuated total backscatter. Unit: sr-1. Shape: [nprof, 20]

Please note: 

  • Only layers with temperatures colder than -40°C have been validated. Warmer layers should not be used for scientific studies.

  • This dataset was extensively explored between ±60deg, but higher latitudes were not. The accuracy of the cloud detection algorithm might not be relied on at latitudes higher than 60°, although we expect the data to be sensible.


The dataset is stored on the climserv data center  and can be accessed by FTP at 


Acknowledgments and Contact 

This dataset was created by E. Martins and is maintained by V. Noel  [vincent dot noel at lmd dot polytechnique dot com].   

The dataset was created using computation facilities and dataset hosting provided by ICARE  and ClimServ. Funding for this dataset was provided in part by ANR as part of the project ANR-07-JCJC-0016.

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Dernière mise à jour : ( 04-05-2018 )