Overview of Cloudnet data

This page describes the flow of data within Cloudnet and the meanings of the various "levels" of data, summarised in the schematic below:

Level 0

The raw data recorded in real-time by the instruments, such as radar echo power, brightness temperatures etc. These data often uncalibrated, in their own unique format and may contain noise and artifacts. They are kept by the particular institute operating the Cloudnet station and are not made available except on request for special studies (such as when very high resolution is required, e.g. 1 s).

Level 1a

Generally used to indicate an instrument (or model) dataset after some processing has been applied (such as temporal averaging to 30 s, conversion to NetCDF, removal of artifacts), but which is not fully ready for release, usually because it has not been calibrated. The presence of this level of data then makes it much easier to apply a new calibration figure to a dataset, as the unaveraged raw data do not need to be analysed again.

Level 1b

Used to indicate a calibrated and quality controlled instrument or model dataset in NetCDF or Nasa AMES format. Instrument datasets at this level are held at the hosting site (at Reading, KNMI and SIRTA), while the model data are held centrally at Reading. These datasets are available to Cloudnet partners. For other users, the model data are available, but the instrument datasets should be accessed by contacting the site directly or via existing channels (such as the British Atmospheric Data Centre for Chilbolton data). In any case, the instrument data provided at Level 1c contains many useful extra fields, so users are advised to access this level instead.

Level 1c

Just a single dataset is available at this level, the "Instrument Synergy/Target Categorization" product, which contains data from radar, lidar, microwave radiometer, rain gauge and model, on a uniform grid and including correction for attenuation, error estimates, quality control flags and a bit field describing the type of target (liquid cloud, ice, drizzle, insects, aerosol etc.) in each pixel. Many retrieval algorithms are able to work just with this dataset. This and all datasets at higher levels will be available to all users from the Reading web/ftp site.

Level 2a

Retrieved meteorological parameters, such as water content and particle size, on the same grid as the original data (e.g. 30 s, 60 m).

Level 2b

Retrieved meteorological parameters averaged on the same height grid as a particular model, and with temporal averaging to correspond approximately to the horizontal grid-box size of the model given the wind speed at each level. These products facilitate direct comparison between models and observations, and include cloud fraction, grid-box mean ice water content and so on.

Level 3

Monthly statistics derived either purely from an observational dataset, or with the statistical analysis tailored to comparison with a specific model. In general it is better to couple statistical analysis to a particular model, because most statistics from the observations will be conditional on factors such as a certain instrument being operational or no rain being measured at the ground. For a fair comparison with the model it is necessary to discount such occasions from the model statistics as well.

Data of level 1c and above are available in Preliminary and Release versions. Access to Preliminary data is restricted to Cloudnet partners. Release data is available for download.