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History of modifications
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Comparison of the ICDR dataset against the reference dataset using the defined KPIs confirms that, for MetOp-A,-B and NOAA-18, the ICDR reference dataset differs from the reference dataset in the same way that the TCDR dataset does. The relevant MHS channel on NOAA-19 (channel 3), has shown erratic behaviour since July 2009, and should not be used (Hans et al, 2017). Detailed results will be provided in the forthcoming ICDR Product Quality Assessment Report (PQAR) [D3], due for delivery at the end of November 2020.
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Validated products
The validated product is the microwave upper tropospheric humidity (UTH), which is based on observations from the microwave (MW) sounder, the Microwave Humidity Sounder (MHS), on board the satellite platforms NOAA [18 and 19] and MetOp [A and B].
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Description of validating datasets
Until July 2019, the validation of the C3S UTH product was conducted against the UTH calculated from the ERA-Interim reanalysis (https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era-interim), as was done for the CM SAF equivalent product, described in detail in the CM SAF Validation Report [D1], and from August 2019 in the same manner against the UTH calculated from the ERA-5 (https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5) reanalysis.
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Description of product validation methodology
The accuracy requirements applicable for this validation are the Key Performance Indicators (KPIs), defined in terms of deviations of the UTH ICDR from the ERA-Interim reanalysis reference data set, by the methods described in [D2].
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Only data within ±60° latitude were considered for the performance assessment because very low water vapour loading in the upper troposphere outside those regions can make the UTH retrieval there unreliable. Upper and lower performance targets on the UTH difference between the TCDR UTH and reference dataset were chosen such that 95% of the UTH differences lie within the target range. 97.5% of the differences are above the lower target, and 2.5% of the differences are above the higher target. For any one satellite, no more than 2.5% of the TCDR data were found to have a UTH value more than 0.47% below the reference UTH, and a maximum of 2.5% of the TCDR UTH data were more than 0.55% higher than the reference UTH. These were taken as the KPI values. The number of values of the ICDR – ERA-Interim equivalent UTH differences falling within and without the performance targets was counted, and the relevant percentages of the total data points determined. Comparison of the ICDR dataset against the reference dataset using the defined KPIs confirms that, up to July 2019, the ICDR reference dataset differed from the reference dataset in the same way that the TCDR dataset does, and since August 2019 the ICDR performance against the reference dataset has remained similar to the performance throughout 2018. Detailed results will be provided in the forthcoming ICDR Product Quality Assessment Report (PQAR) [D3], due for delivery at the end of November 2020.
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Summary of validation results
The main conclusion is that in terms of the defined key performance indicators, up to July 2019, when ERA-Interim stopped being available, the performance of the UTH ICDR product against the reference dataset is comparable with that of the UTH TCDR dataset against the ERA-Interim reanalysis reference. Since August 2019, the ICDR performance against the ERA-5 reanalysis reference dataset has been comparable with its performance over the previous year (2018) against that reference. Hence the key performance of the UTH ICDR is good (except for NOAA-19, whose relevant channel has had known issues since 2009 and should not be used (Hans et al, 2017)). A detailed summary of the validation results will be provided in the forthcoming C3S UTH ICDR Product Quality Assessment Report (PQAR) [D3], due for delivery 30/11/2020
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