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table1_1
table1_1
Table 1.1: Different sensors and the lifetime of SSM/I on different platforms on DMSP satellites (F8-F19).

Sensor

Channels

Frequencies



 Platform/Lifetime


SSM/I


7


4


F8,11,13,14,15

1987-2008


SSMIS


24


21



 F-16,17,18,19

2005-onward

2. User Requirements

2.1 Water Vapour THP TCDR v1.0

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table2_1
table2_1
Table 2.1: Water Vapour TPH ICDR target requirements

KPI Title

Percentile

Performance target

Accuracy Tropospheric Humidity Profile ICDR wrt reference dataset

97.5

0-4 km: -0.93%

4-8 km: +0.82%

8-12 km: +2.13%

Accuracy Tropospheric Humidity Profile ICDR wrt reference dataset

2.5

0-4 km: -2.00%

4-8 km: -1.04%

8-12 km: -0.66%

The ICDR used ERA-Interim as reference data set initially but from August 2019 and onward ERA5 is the reference.

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table2_2
table2_2
Table 2.2: Water Vapour UTH TCDR target requirements

KPI #

KPI Title

Performance Target

Frequency

KPI.D10.1

Accuracy Upper Tropospheric Humidity TCDR

Mean absolute error: 5%

At release

KPI.D10.2

Stability Upper Tropospheric Humidity TCDR

1% / dec

At release

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table2_3
table2_3
Table 2.3: Water Vapour UTH ICDR target requirements

KPI Title

Percentile

Performance target

Accuracy Upper Tropospheric Humidity ICDR wrt reference dataset

97.5

0.55% (until 31/12/2018)
1.57% (from 01/01/2019)

Accuracy Upper Tropospheric Humidity ICDR wrt reference dataset

2.5

-0.47% (until 31/12/2018)
0.40% (from 01/01/2019)

2.3.2 Discussion of requirements with respect to GCOS and other requirements

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table2_4
table2_4
Table 2.4: KPIs for the Water Vapour TCWV_GV TCDR as defined by CMSAF.

Category

Bias

cRMSD

Stability (bias trend)

Threshold

3 kg/m2

5 kg/m2

0.4 kg/m2/dec

Target

1.4 kg/m2

2 kg/m2

0.2 kg/m2/dec

Optimal

0.6 kg/m2

1 kg/m2

0.08 kg/m2/dec


GCOS also states that the frequency of TCWV observations should be 4 h, with a spatial resolution of 25 km. While this resolution is barely achievable with a microwave imager such as SSM/I (footprint approx. 50 km with 25km spot spacing), MERIS (and other NIR imagers with similar band configurations) have resolutions of approx. 1 km or higher. Thus, the required resolution is achievable.

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Diedrich, H., Preusker, R., Lindstrot, R., and Fischer, J.: Retrieval of daytime total columnar water vapour from MODIS measurements over land surfaces, Atm. Meas. Tech., 8, 823-836, doi:10.5194/amt-8-823-2015 , 2015.

Soden, B. J., & Bretherton, F. P.: Upper tropospheric relative humidity from the GOES 6.7 μm channel: method and climatology for July 1987. J. Geoph. Res., 98(D9), 1993.

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