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Data description

The focus in Cloud_cci is on the following cloud properties: cloud detection (mask/fraction), cloud phase, cloud optical thickness, cloud effective radius, cloud liquid/ice water content and cloud albedo. Table 1 (below) gives more details on these cloud properties. The retrievd cloud properties are summarised in two global dataset families (see below). The datasets cover 1982 through 2014 (Figure 1). Pixel based retrievals (L2 products) are further processed to:

L3U products: Sampled into daily global fields (0.05° resolution, 0.02° for MODIS era over Europe) and

L3C products: Agregated into monthly averages and histograms on a global grid with 0.5° resolution). The monthly averages of LWP and IWP are calculated as in-cloud and all-sky (a.k.a. grid-mean) values.

The available processing levels are summarizes in Table 2 (see below).
 

Table 1 List of generated Cloud_cci properties. CMA/CFC and CPH are derived in a pre-processing step. In the next step, COT, CER and CTP are retrieved simultaneously by fitting a physically consistent cloud/atmosphere/surface model to the satellite observations using optimal estimation (OE). Moreover, LWP and IWP are obtained from COT and CER. In addition, a spectral cloud albedo for two visible channels is derived.

Cloud_cci products Abbrev. Description
Cloud mask/cover CMA, CFC A binary cloud mask per pixel (L2, L3U) and therefrom derived monthly total cloud fractional coverage (L3C, L3S) and separation into 3 vertical classes (high, mid-level, low clouds) following ISCCP classification.
Cloud phase CPH The thermodynamic phase of the retrieved cloud (binary: liquid or ice; in L2, L3U) and the therefrom derived monthly liquid cloud fraction (L3C, L3S).
Cloud optical thickness COT The line integral of the absorption coefficient and the scattering coefficient along the instruments line of sight in cloud pixels.
Cloud effective radius CER The area weighted radius of the cloud drop and crystal particles, respectively.
Cloud top pressure/height/temperature CTP/CTH/CTT The air pressure [hPa] /height [m] /temperature [K] of the uppermost cloud layer that could be identified by the retrieval system.
Cloud liquid and ice water path LWP/IWP The vertical integrated liquid/ice water content of existing cloud layers; derived from CER and COT
Joint cloud property histogram JCH This product is a spatially resolved two-dimensional histogram of combinations of COT and CTP for each spatial grid box.
Spectral cloud albedo CLA The blacksky albedo derived for channel 1 (0.67 µm) and 2 (0.87 µm), respectively (experimental product)

 

In Cloud_cci two global data set families for the GCOS cloud property ECVs including uncertainty estimates are generated:

  • AVHRR-heritage dataset familiy covering all AVHRR, MODIS and (A)ATSR(-2) sensors onboard NOAA, MetOp and ENVISAT satellites. The algorithm developed and applied is CC4CL (Community Cloud Retrieval for Climate). The datasets of this family are named:
    - Cloud_cci AVHRR-PM
    - Cloud_cci AVHRR-AM
    - Cloud_cci MODIS-Aqua
    - Cloud_cci MODIS-Terra
    - Cloud_cci ATSR2-AATSR
     
  • ENVISAT synergistic dataset family based on simulatneous use of MERIS and AATSR measurements taken onborad the ENIVSAT satellite. The algorithm applied is FAME-C (Freie Universität Berlin AATSR MERIS Cloud). The synergistic dataset is named:
    - Cloud_cci MERIS+AATSR


Figure 1 Overview of Cloud_cci datasets and the time periods they cover.

Table 2 Processing levels of Cloud_cci data products. Processing level definitions are based on [R-4] with additional clarifications for Cloud_cci.

Processing level Abbrev. Spatial resolution Description
Level 2 L2 MODIS: 1km
AATSR: 1km
AVHRR: 5 km
Combined MERIS-AATSR: 1km
Retrieved cloud variables at the same resolution and location as the level 1 source [R-4]
Level 3U
(Uncollated)
L3U 0.05° lat/lon Cloud properties of L2 data granules remapped to a global space grid without combining any observations from overlapping orbits. Only sampling is done [R-4]. Common notation for this processing level is also L2b or L2G. Temporal coverage of this product is 1 day.
Level 3C
(Collated)
L3C 0.5° lat/lon Cloud properties combined (averaged) from a single instrument into a global space-time grid [R-4]; sampled for the histograms. Temporal coverage of this product is 1 month.
Level 3S
(Super-Collated)
L3S 0.5° lat/lon Cloud properties combined (averaged) from multiple instruments/platforms into a global space-time grid [R-4]; sampled for histograms. This product only exists for the AVHRR-MODIS-AATSR product family. Temporal coverage of this product is 1 month.