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Offline total H2O column

Composite offline images

NOTE: Metop-B+C image is for demonstrational purposes only, such multi-satellite product is not processed or disseminated.

Metop-B

Metop-C

Metop-B+C

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Description

Offline total H2O column product provides information about vertical column densities of water vapour in the atmosphere.

Type

Offline. The product is available to users in 15 days from sensing. Typical delay is 2-3 days.

Theoretical basis

The retrieval of the product is based on GOME-2 (ir)radiance measurements in the wavelength region of 614-683.2 nm.

Processing

DLR generates vertical column products with Universal Processor for UV/VIS Atmospheric Spectrometers (UPAS), inside which the GOME Data Processor (GDP) operational algorithm is the baseline algorithm for the trace gas column retrievals from GOME-2.

The latest GDP 4.8/4.9 uses an optimised DOAS (Differential Optical Absorption Spectroscopy) algorithm to determine the trace gas slant column. The DOAS slant column fitting is followed by Air Mass Factor (AMF) conversions to generate vertical columns.

Units and spatial resolution

H2O columns are given as densitites (kg/m2).

GOME-2/Metop-A has 24 forward-scan pixels with a nominal resolution of 40 km × 40 km, and 8 back-scan pixels with a nominal resolution of 120 km × 40 km.

GOME-2/Metop-B and GOME-2/Metop-C have 24 forward-scan pixels with a nominal resolution of 80 km × 40 km, and 8 back-scan pixels with a nominal resolution of 240 km × 40 km.

Both forward- and back-scan pixels are processed and written to the products.

Validation

This product is validated by DLR and FMI.

The validation of GOME-2/Metop-A water vapour total columns is performed by comparison using ground-based observations obtained from University of Wyoming and comparison to SSM/I measurements (open ocean only) and by comparing the GOME-2/Metop-A H2O total column data to similar data retrieved from the SCIAMACHY/ENVISAT and GOME/ERS-2 instruments.

GOME-2/Metop-B water vapour total columns are evaluated using comparisons with GOME-2/Metop-A results, ground-based observations obtained from University of Wyoming and independent SSMIS F16 satellite measurements from the Remote Sensing System (REMSS).

Online quality monitoring

The product quality is constantly monitored by DLR. The online monitoring is based on TBD.

Archiving and dissemination

This product is archived at the DLR and available via offline data access page. Upon request, products can be directly pushed to dedicated FTP servers located at the users' premises.

File format

The product is delivered in HDF5 format, each file containing one satellite orbit (sunlit portion).

Algorithm version information

Time period GOME-2 / Metop-A GOME-2 / Metop-B GOME-2 / Metop-C
04.01.2007 – 15.07.2013 GDP 4.6 N.A. N.A.
15.07.2013 - 15.10.2016 GDP 4.7 GDP 4.7 N.A.
15.10.2016 - 16.01.2019 GDP 4.8 GDP 4.8 N.A.
16.01.2019 onwards GDP 4.8 GDP 4.8 GDP 4.9

Important algorithm changes in GDP 4.8

  • Cloud algorithm improvements (OCRA & ROCINN)

Documents

GOME-2 pages at DLR: WDC, ATMOS