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Offline total and tropospheric NO2 column

Composite images of the latest overpasses

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

Image gallery

Description

Offline total and tropospheric NO2 column products provide information about vertical column densities of nitrogen dioxide in the atmosphere.

Type

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

Theoretical basis

The retrieval of the products is based on GOME-2 (ir)radiance measurements in the wavelength region of 425-450 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

NO2 columns are given as densitites (molecules/cm2).

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

These products are validated by Belgian Institute for Space Aeronomy (BIRA-IASB). The validation is based on an end-to-end approach, that has been developed to evaluate independently all critical components of the level-1-to-2 retrieval chain, using correlative observations performed by ground-based and satellite instruments. Visit BIRA NO2 validation page for further information.

Online quality monitoring

The product quality is constantly monitored by BIRA-IASB. The online monitoring is based on TBD. Visit BIRA quality assessment page for further information.

Archiving and dissemination

These products are 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 products are 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

  • Improved retrieval algorithms and quality flags
    • NO2: provision of tropospheric NO2 columns for unpolluted and cloudy conditions
    • Cloud algorithm improvements (OCRA & ROCINN)

Documents

GOME-2 pages at DLR: WDC, ATMOS