The Chilbolton Observatory, Hampshire, have had a Vaisala CT75K lidar ceilometer deployed since 13th September 1996. This dataset contains measurements of the range of first, second, and third cloud base from the lidar and attenuated backscatter coefficients of aerosols within the atmosphere from 1996 to 2013. Plots of the attenuated backscatter coefficient at different heights are also available.

The instrument has been regularly calibrated using the method described by O'Connor, Ewan J., Anthony J. Illingworth, Robin J. Hogan, 2004: A Technique for Auto-calibration of Cloud Lidar. J. Atmos. Oceanic Technol., 21, 777–786. doi: http://dx.doi.org/10.1175/1520-0426(2004 )021<0777:ATFAOC>2.0.CO;2 .

Prior to April 2014 this technique had been applied manually, but from 2014 this was automated to provide a routine, automated application of O'Connor et al's calibration technique. This also highlighted an instrument calibration drift not previously spotted in earlier data and so a corrected data have been added to the archive for the following periods (denoted by "_cor1" in the filename): 1st July 2003 – 31st December 2003, January 2006 to December 2012 and February and March 2013. Users should see the data quality notes for further details.

For post 2013 data please refer to the "all-years" dataset.