Release of the CM SAF / WV_cci TCWV CDR: a combined near-infrared and microwave imager total column water vapour climate data record

The global total column water vapour (TCWV) data record combines microwave and near-infrared imager based TCWV over the ice-free ocean as well as over land, coastal ocean and sea-ice, respectively. The data record relies on microwave observations from SSM/I, SSMIS, AMSR-E and TMI, partly based on a fundamental climate data record (Fennig et al., 2020; Fennig et al., 2017) and on near-infrared observations from MERIS (3rd reprocessing), MODIS-Terra (collection 6.1) and OLCI (1st reprocessing). Details of the retrieval are described in Andersson et al. (2010) and ATBD HOAPS for the microwave imagers as well as in Lindstrot et al. (2012), Diedrich et al. (2015) and ABTD NIR Level 2 for the near-infrared imagers. The water vapour of the atmosphere is vertically integrated over the full column and given in units of kg/m². The microwave and near-infrared data streams are processed independently and combined afterwards by not changing the individual TCWV values and their uncertainties. The combined data record has a spatial resolution of 0.5°x0.5° and 0.05°x0.05°, with the near-infrared based data being averaged and the microwave-based data being oversampled to match the lower and higher spatial resolution, respectively. The product is available as daily and monthly means and covers the period July 2002 – December 2017. Two example spatial maps of TCWV are shown in Figure 1.

Figure 1: Global maps of daily TCWV in units of kg/m2 from the combined microwave and near-infrared imager data record: 1 July 2007 (left) and 1 July 2015 (right). Grey areas mark regions that are not observed by the satellites.

A comprehensive evaluation was conducted and results are summarized in the Validation Report, which composes, along with the Product User Manual and the Algorithm Theoretical Baseline Document a rich set of documentation for the CM SAF/WV_cci TCWV CDR. A high quality was demonstrated and the CDR exhibits a high stability over ocean and, when looking at clear-sky and until March 2016, also over land. Given its high spatial resolution, in particular over land, and its spatial coverage makes this CDR in particular suitable for process studies on global scale.

The data record can be ordered via the Web User Interface. More information on the data record and accompanying documentation is available from the DOI page: 10.5676/EUM_SAF_CM/COMBI/V001

The combined MW and NIR product was initiated and funded by the ESA Water_Vapour_cci project. The NIR retrieval was developed by Spectral Earth. The MW retrieval was originally developed at the University of Hamburg and the Max-Planck-Institute for Meteorology. Based on retrieval updates by CM SAF MW was processed by EUMETSAT CM SAF. The NIR data was processed and combined with the MW data by Brockmann Consult. NIR data is owned by Brockmann Consult and Spectral Earth.

References:

• Diedrich, H., R. Preusker, R. Lindstrot, and J. Fischer, 2015: Retrieval of daytime total columnar water vapour from MODIS measurements over land surfaces. Atmospheric Measurement Techniques, 8:823-836.
• Fennig, Karsten; Schröder, Marc; Hollmann, Rainer (2017): Fundamental Climate Data Record of Microwave Imager Radiances, Edition 3, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/FCDR_MWI/V003.
• Fennig, K., Schröder, M., Andersson, A., and Hollmann, R.: A Fundamental Climate Data Record of SMMR, SSM/I, and SSMIS brightness temperatures, Earth Syst. Sci. Data, 12, 647–681, https://doi.org/10.5194/essd-12-647-2020, 2020.
• Fischer, J., R. Preusker, M. Schröder, O. Danne: Algorithm Theoretical Baseline Document – Part 1 (ATBD). ESA Water_Vapour_cci, version 2.1, January 2021.
• Graw, K., A. Andersson, M. Schröder, K. Fennig: Algorithm Theoretical Baseline Document - HOAPS version 4.0. EUMETSAT Satellite Application Facility on Climate Monitoring, Issue 2.3, 31 January 2017, DOI: 10.5676/EUM_SAF_CM/HOAPS/V002.
• Lindstrot, R., R. Preusker, H. Diedrich, L. Doppler, R. Bennartz, and J. Fischer, 2012: 1D-Var retrieval of daytime total columnar water vapour from MERIS measurements. Atmospheric Measurement Techniques, 5: 631–646.

MS / Feb2023