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Version Date Description of modification Chapters / Sections 1.0 09.12.2019 First version all 1.0.1 16.12.2019 Minor corrections 1.0.2 18.02.2020 Minor corrections 1.0.3 08.10.2020 Corrections after KM's comments 1.0.4 14.10.2020 Values in the text are now consistent with Table 4 2-3 & clean up Chap 4 1.1 21.01.2021 First version 01.02.2020 Correction of file name version and update of D1

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Deliverable ID Product title Product type (CDR, ICDR) Version number Delivery date 3.3.11 TCWV_MERIS_SSMI_TCDR monthly TCDR 1.0 31/08/2019

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Related documents

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Reference ID Document D1 El Kassar, J., Preusker, R. (2020) C3S Water Vapour Service: Product Quality Assurance Document. Copernicus Climate Change Service, Document ref. C3S_312b_Lot1.2 Document for TCWV_MERIS_SSMI_TCDR, V1.1, 2020 (Deliverable D2.3.5-v1.1_202008 )_PQAD_v1.1.2 TCWV MERIS & SSM/I Total Column Water Vapor Thematic Climate Data Record TCDR: Product Quality Assurance Document (PQAD) Last accessed on 01.09.2023 D2 Validation Report SSM/I and SSMIS products HOAPS version 4.0 Link to the Validation Report HOAPS 4.0

Acronyms

D3 Meirink, J.F., et al, (2023) C3S cross ECV document Service: Key Performance Indicators (KPIs). Copernicus Climate Change Service, Document ref. C3S2_D312a_Lot1.3.7.1_202303_Unified_KPI_Approach_v1.0 Key Performance Indicators (KPIs) Last accessed: 23.08.2023

Acronyms

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Acronym Definition AERONET Aerosol Robotic Network ATBD Algorithm Theoretical Basis Document ARM Atmospheric Radiation Measurement C3S Copernicus Climate Change Service CAWA Cloud Aerosol and Water Vapor algorithm CDR Climate Data Record CDS Climate Data Store CMSAF Satellite Application Facility on Climate Monitoring cRMSD centered Root Mean Square Deviation CUS Copernicus User Support DKRZ Deutsches Klimarechenzentrum (German Climate Computing Center) DMSP Defense Meteorological Satellite Program DWD Deutscher Wetterdienst (Germany's National Meteorological Service) ECMWF European Centre for Medium-Range Weather Forecasts ERA-Interim ECMWF Re-Analysis Interim (1979-2019) ESA European Space Agency ESGF Earth System Grid Federation EUMETSAT European Organization for the Exploitation of Meteorological Satellites FUB Freie Universität Berlin GCOS Global Climate Observing System GridFTP Extension of the File Transfer Protocol (FTP) GNSS Global Navigation Satellite System GPS Global Positioning System GUAN GCOS Upper-Air Network GRUAN GCOS Reference Upper-Air Network HOAPS Hamburg Ocean and Atmosphere Parameters and Fluxes from Satellite http Hypertext Transfer Protocol ICDR Interim Climate Data Record KPI Key Performance Indicator MAD Mean Absolute Deviation MERIS Medium Resolution Imaging Spectrometer OPeNDAP Open-source Project for a Network Data Access Protocol RMSD Root Mean Square Deviation RSS-TMI Remote Sensing System – TRMM Microwave Imager SSM/I, SMMI Special Sensor Microwave/ Imager SQAD System Quality Assurance Document SUOMINET SuomiNet TCWV Total Column Water Vapor (also: Integrated Water Vapor (IWV), Precipitable Water Vapor (PWV)) TRMM Tropical Rainfall Measuring Mission WCRP World Climate Research Programme WEW Institut für Weltraumwissenschaften (Institute of Space Sciences) WMO-OSCAR World Meteorological Organization – Observing Systems Capability Analysis and Review Tool– Observing Systems Capability Analysis and Review Tool

List of tables

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Table 1-1: Overview of benchmarks to compare the validation results, taken from CMSAF Validation Report for HOAPS 4.0 [D2] Table 2-1: Summary of the Level 2 match-up validation Table 2-2: Results of Level 2 global mean intercomparison analysis for SSMI/S (HOAPS 4.0) taken from [D1] Table 2-3:  Results of Level 3 monthly observation intercomparison analysis for different validation metrics between TCWV_GV and GUAN TCWV

List of figures

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Figure 2-1: Each dot in the plots represents a collocation Figure 2-2: Scatterplot of all collocated monthly mean TCWV values for the 960 GUAN stations Figure 2-3: Time-series of the cRMSD, MAD and Bias for the whole time period of the dataset for all 960 GUAN stations

General definitions

In the scope of the Copernicus Climate Change Service (C3S), a Thematic Climate Data Record (TCDR) has a fixed end point, whereas an Interim Climate Data Record (ICDR) is extended continuously. The TCWV_MERIS_SSMI_TCDR L3 product is a TCDR which consists of two satellite-based estimates of the Total Columnar Water Vapor (TCWV) of the atmosphere for the time period 2002-2012. The two estimates are derived by two different instruments over two types of surface. Over land, data from the Medium Resolution Imaging Spectrometer (MERIS) are used. Over water, the Special Sensor Microwave/Imager (SSM/I) is used.

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TCWV_GV product is compared against the validation benchmarks that have been set by CMSAF in the requirements review for HOAPS-4 TCWV (D2). They can be found in Table 1-1 and are divided into three categories: threshold (minimum usefulness), target (significant improvement compared to threshold) and optimal (no improvement necessary). The KPIs have been put together from requirements established in GCOS, WMO OSCAR and other literature.

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table1-1 table1-1

Table 1-1: Overveiw Overview of benchmarks to compare the validation results, taken from CMSAF Validation Report for HOAPS 4.0 [D2]

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2. Validation results

2.1 Level 2 individual, instantaneous match-ups

Figures 2-1 a) to d) show the scatterplots between MERIS TCWV and collocated reference TCWV. Overall we see very good agreement between all datasets with high correlation, low bias and low cRMSD. Anchorfigure1figure1

a)                                                                      b)

c)                                                                     d)

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Figure 2-Figure 1: Each dot in the plots represents a collocation. The color represents the frequency of occurance, blue meaning low and red meaning high frequency.

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Table 2-1: Summary of the Level 2 match-up validation

We can observe very good agreement between ARM, GNSS and GRUAN concerning the bias. The bias in comparison with AERONET, however, is much higher. This discrepancy is most likely due to the dry bias of the AERONET TCWV dataset. This dry bias can amount to between 5 – 9% of TCWV in comparison with other means of TCWV retrieval such as microwave radiometry (ARM), GPS (SUOMI GNSS) or radiosondes (GRUAN) (see Ramírez et al., 2014).

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For SSMI/S L2 dataset the validation results from the validation report of CMSAF HOAPS 4.0 [D2] are summarized in Table 32-2.

The comparison has been performed for two products, i.e. ERA-Interim and RSS-TMI (Remote Sensing System-TRMM Microwave Imager).   According to Table 1-1, the optimal requirements for bias and cRMSD are met by  SSMI/S L2 total column water vapour product toward comparison products. Further details on validation method can be found in the [D2] document.

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table2_2 table2_2 table3 table3

Table 32-2: Results of Level 2 global mean intercomparison analysis for SSMI/S (HOAPS 4.0) taken from [D1].

2.2 Level 3 Monthly observations

In this section we present the validation results for Level 3 monthly observations (as can be found in the TCWV_GV dataset).

Figure 2-2 shows the scatterplot of collocated GUAN monthly radiosonde data and MERIS, SSM/I and SSMIS TCWV grid boxes. Overall there were 33887 valid collocations (collocation criteria can be found in the PQAD [D1]).

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Figure 2-2: Scatterplot of all collocated monthly mean TCWV values for the 960 GUAN stations. The color represents the frequency of occurrence, blue meaning low and red meaning high frequency. Overall there were 33887 valid collocations.

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There still is room for improvement, currently work is being done on the first revision of the TCWV_GV dataset, version 1.1. Nevertheless, the usefulness of the dataset v1.0 has been proven and we meet the requirements set by CMSAF.

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Figure 2-3: Time-series of the cRMSD, MAD and Bias for the whole time period of the dataset for all 960 GUAN stations.

In figure 2-3 the time series of cRMSD, MAD and Bias is shown. The bias only exhibits a small trend of 0.18 kg/m2 per decade. The significance of this trend is low. The p-value against the null-hypothesis (that the bias trend is 0) is quite high at 0.29 (>0.05). Nevertheless, we observe a trend in the cRMSD of -0.8 kg/m2/dec. We have not looked into the possible causes for this trend.

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All results for the validation of the Level 3 monthly observations have been summarized in Table 42-3.

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table2-3 table2-3 table4 table4

Table 42-3:  Results of Level 3 monthly observation intercomparison analysis for different validation metrics between TCWV_GV and GUAN TCWV.

3. Application(s) specific assessments

N/A

4. Compliance with user requirements

The user requirements – as set by the KPIs taken from the CMSAF TCWV Validation Report for HOAPS 4.0 [D2]– were met. In all cases, the threshold requirements (minimum requirements) are achieved. For the instantaneous match-ups, the target requirements are met with a bias (excluding Aeronet, due to this networks dry bias) between -0.13 kg/m² and 0.7kg7 kg/m2 (target:1.4 kg/m², optimal 0.6 kg/m²) and cRMSD between 1.54 kg/m² and 2.56 kg/m² (threshold: 5kg/m², target: 2kg/m²).

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Preusker R., H. Diedrich and J. Fischer, 2015: Retrieval of Total Column Water Vapor from MERIS/OLCI and MODIS above Land- and Ocean Surfaces ATBD

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This document has been produced with funding by the European Union in the context of the Copernicus Climate Change Service (C3S) .The activities leading to these results have been contracted , operated by the European Centre for Medium-Range Weather Forecasts , operator of C3S on behalf of on the European Union ( Delegation agreement Contribution Agreement signed on 11 22/ 11 07/ 2014 2021). All information in this document is provided "as is" and no guarantee or of warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt, the European Commission and the European Centre for Medium-Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.

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