Contributors: Nabiz Rahpoe (DWD)
Issued by: DWD / Nabiz Rahpoe
Date: 22/10/2020
Ref: C3S_D312b_Lot1.3.6.3-v1.1_202102_PUGS_TCWV_SSMIS_TCDR+ICDR_v1.1.1
Official reference number service contract: 2018/C3S_312b_Lot1_DWD/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
Scope of the document
This document is the Product User Guide and Specification (PUGS) for Total Column Water Vapour (product C3S_D312b_Lot1.3.3.14 v1.0 and v1.1) based on SSM/I & SSMIS measurements. It provides a brief guide to the use of the data product, and describes the contents and format of the data files.
The original CM SAF user manual, to which the present document refers, is the “CM SAF Product User Manual SSM/I and SSMIS HOAPS 4.0” [D1]. It can found at the CM SAF web site http://www.cmsaf.eu.
The TCDR data products are provided as a brokered service from the EUMETSAT CMSAF and the ICDRs (which are a continuation of the TCDR) are produced within the framework of C3S project at DWD and are extension of prior delivered TCDRs.
Executive summary
The project C3S_312b_Lot1 includes brokering of total column water vapour gridded monthly mean and 6-hourly daily composite data from the EUMETSAT CM SAF and the production of an ICDR extension.
The CM SAF documentation [D1] covers only the TCDR. The TCDR covers the time period January 1988 to December 2014, while the ICDR covers the time period from January 2015 to December 2020. The updated ICDR has the same characteristics as the TCDR, which has been generated in a CM SAF reprocessing activity.
1. Total Column Water Vapour
1.1 Product description
Instruments used for the creation of the TCWV product are the Special Sensor Microwave Imager (SSM/I) and Special Sensor Microwave Imager Sounder (SSMIS). The available processing levels are the Level 3 monthly means and 6-hourly daily composites of different satellite overflights. The measurements of daily composites are spatially and temporally averaged for different local time overflights within the 6-hour time slot. The dataset is available at a resolution of 0.5° with a spatial coverage of 80°S-80°N, and the time period between January 1988 to December 2020 is covered.
The ICDR (2015-2020) is based on the same production scheme as the brokered TCDR (1988-2014).
The historical background of CM SAF data procedure is described in Section 2 of CM SAF PUM [D1].
Further details of the product definition are described in Section 3 and related to water vapour product brokered by the C3S project is specifically described in Section 3.1.1 of [D1].
1.2 Target requirements
For the TCWV, the target requirements are listed in Table 1.
According to the validation report of HOAPS 4.0 [D2], the requirement for ‘optimal category’ is met for the bias (<0.4 kg/m2) and ‘target category’ is met for the cRMSD (≤1.1 kg/m2) according to the requirements (Table 1) for TCDR. The decadal stability of TCDR HOAPS 4.0 is 0.00±0.008 kg/m2/decade, which fulfills the requirements for ‘optimal category’ (<0.08 kg/m2/dec) as described in Sec. 7 [D2].
The validation and quality assessment of TCDR+ICDR (1988-2020) is described in the PQAD [D3] and PQAR [D4]. The general picture of validation shows an overall good performance of HOAPS 4.0 TCDR (CMSAF) + ICDR (C3S) for the time period from 1988 to 2020. The target requirements (Table 1) set for the inter-comparison of bias, stability, and RMSD have been met at optimal category toward reference sensors, respectively. See PQAD [D3] and PQAR [D4] for further details on methods and results for derivation of the validation metrics.
Table 1: KPIs for the Water Vapour TCWV TCDR as defined by CMSAF (See Table 6-6 in [D2])
Category | Bias [kg/m2] | RMSD [kg/m2] | Stability [kg/m2/decade] |
Threshold | 3 | 5 | 0.4 |
Target | 1.4 | 2 | 0.2 |
Optimal | 1.0 | 1 | 0.08 |
1.3 Data usage information
The data format is CF-1.6-conform netCDF-files that can be read with applications such as Panoply. The filenames have a straight-forward structure containing all necessary information.
Included in the files is the main product, monthly mean of TCWV and 6-hourly composites for daily files. Also provided are the associated standard deviation, number of days with observation, number of valid observations, and satellite bit mask to indicate the satellites used F08-F18 (see Table 2).
The monthly means are stored in yearly files with a size of approx. 8 MB and the daily composites are stored in monthly files with the size of approx. 36 MB.
Table 2: Description of the variables in the files.
Variable name | Units | Explanation |
time | 1 | Days since 1987-01-01 00:00:00 |
lon | degrees_north | Longitude of the regular grid |
lat | degrees_east | Latitude of the regular grid |
wvpa | kg/m2 | Total Column Water Vapour (also called integrated Water Vapour (IWV), Water Vapour Path (WVPA) or Precipitable Water Vapour (PWV)) is the integrated amount of gaseous water in the total column of the atmosphere over an area of 1 m2. |
stdv | kg/m2 | Water vapour path standard deviation |
numo | 1 | Number of observations |
numd | 1 | Number of days with observation |
satm | 1 | Satellite bit mask. |
Details of data quality and limitations of ICDRs corresponds to brokered TCDRs and the original CMSAF documentation can be used (described in Section 3.2 [D1]). Hence information on gridding of the data products and composites of ICDRs are related to TCDRs and are described in Section 3.3 [D2]. The file formats and products contents are described in Section 5 [D1].
2. Data access information
The netCDF file format, the applicable conventions, and the contents of the data files are described in Section 1.3 and in Section 5.1 of the CM SAF PUM [D1] for the TCDR. For the ICDR, the details are the same as for the TCDR.
The data are available directly in the C3S Climate Data Store. Since the TCDR data sets are brokered, please be aware of the copyright and license, by using the original citation (see Section 2.1 in this document).
The ICDR data are produced within the framework of C3S and need no further external licensing. Be aware of the license change from TCDR (1988-2014, brokered from EUMETSAT CMSAF) and current ICDR (2015-2020) product which should contain the C3S license.
The original data set, from which the TCDR is brokered, is available at CMSAF download page https://www.cmsaf.eu. The data ordering process is met via web user interface. The user service includes information and documentation. Registration is a pre-requirement for ordering the data set. The order is confirmed via automatic email notification. The product ordering process, user help desk, feedback and service message are described in detail in Section 6 of the CM SAF PUM [D1].
2.1 EUMETSAT CM SAF products licence for TCDR
All intellectual property rights of the CM SAF products belong to EUMETSAT.
(www.cmsaf.eu) All intellectual property rights of the CM SAF products belong to EUMETSAT. The use of these products is granted to every interested user, free of charge. If you wish to use these products, EUMETSAT's copyright credit must be shown by displaying the words "copyright (year) EUMETSAT" on each of the products used.
When exploiting EUMETSAT/CM SAF data you are kindly requested to acknowledge this contribution accordingly and make reference to the CM SAF, e.g. by stating "The work performed was done (i.a.) by using data from EUMETSAT's Satellite Application Facility on Climate Monitoring (CM SAF)". It is highly recommended to clearly identify the product version used.
Andersson, Axel; Graw, Kathrin; Schröder, Marc; Fennig, Karsten; Liman, Julian; Bakan, Stephan; Hollmann, Rainer; Klepp, Christian (2017): Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data - HOAPS 4.0, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/HOAPS/V002, https://doi.org/10.5676/EUM_SAF_CM/HOAPS/V002.
2.2 Product ordering process on CDS
You need to be registered and logged in to order products in the CDS. A login is provided upon registration, all products in the CDS are delivered free of charge.
