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New ERS-2 GOME Level 1 v5.1 dataset available online

20 June 2018

The post-operational full-mission reprocessing campaign of ERS-2 GOME consolidated data has been completed with an improved instrument processor version (Level-0-to-1 GDP Version 5.1). A new GOME Level 1b dataset has been generated for the 16-year mission period. The new data bring relevant quality improvements for the revised calibration approach, compensating aging and instrument degradation, and provide enhanced accessibility.

Data are made available to the user community via direct download from ESA archives. For new users, access to GOME products is provided through ESA Fast Registration. Users already having access to GOME data can retrieve the details for the account via the "My Online data" area (on the My Earthnet pages) using their SSO credentials.

Relative intensity of GOME

Relative intensity of GOME Sun mean reference spectra (one spectrum per year) with respect to spectrum from 3 July 1995. Smooth solid lines denote results of the polynomial fit performed during the degradation correction. Source: Coldewey-Egbers et al., AMTD, 2018, under review.


Level 1 processor updates

Algorithm and data set improvements applied to the GOME processing baseline version 5.1 comprise:

  • A new polarization correction: for the parameterization of the Generalized Distribution Function (GDF), the Ozone climatology is replaced by Ozone column densities retrieved from GOME measurements.
  • Improved usage of dark signal measurements: calibration measurements over the South Atlantic Anomaly (SAA) are discarded during preprocessing.
  • Revised and improved spectral calibration: lamp line positions used for wavelength assignment were selected on the basis of whole-mission stability.
  • Fully calibrated products: calibration algorithms adopted by the former extraction software (gdp01_ex) are now integrated into the Level 0 to 1 processing baseline and are applied for the generation of fully calibrated Earthshine radiance and solar irradiance.
  • Updated degradation correction: the loss in throughput due to degradation of the instrument's optical components has been monitored and corrected for the entire mission.
  • Input Level 0 data: A revised master set of consolidated Level 0 files (80154 orbits) was used as input for the reprocessing campaign. The new master dataset includes ~10% of data repatriated from on-ground receiving stations and concatenated, which were of lower quality or missing in the previous dataset.
  • Cloud parameters: information retrieved with the OCRA and ROCINN algorithms have been integrated into the new Level 1 product.
  • Format and structure: The output product has been entirely revised implementing the NetCDF-4 format. Data structure is similar to EO products used for other satellite data (e.g. SCIAMACHY, Sentinel-5P). Measurements are organized in groups for modes and bands. Geo-location and other associated data are incorporated in such groups and match the measured ground pixels. Forward and backward scans are separated into different groups.


New Level 1 dataset version 5.1

The reprocessed dataset covers the whole operational mission lifetime period, from 28 June 1995 (orbit 979) to 02 July 2011 (orbit 84699), and comprises 75286 Level 1b files for a total data volume of about 3.45 TB. Users of GOME Level 1 products are strongly recommended to migrate to the new reprocessed dataset; which now provide fully calibrated and ready to use Earthshine spectral radiance and solar irradiance spectra (usage of extraction software tool is not required). Please consult the "GOME Product Quality Readme file" before using the data.

All GOME data are accessible through a single account (login credentials remain unchanged). The previous Level 1 dataset version 4 (with extraction tool GDP01_ex v4.03) will remain available for a limited time of 6 months.

An overview of the completeness of the GOME consolidated Level 1 version 5.1 dataset is provided here.


Product format

The GOME Level 1 version 5.1 products have a revised structure with NetCDF-4 format.

A new file name scheme identifies the new GOME products:

ER2_RPRO_GOM_L1B____YYYYMMDDThhmmss_YYYYMMDDThhmmss_02610_02_051000_YYYYMMDDThhmmss.nc

Standard NetCDF or HDF5 library and tools can be used to access the data. VISAN and Panoply offer a convenient interactive tool for data evaluation.


Documentation

More detailed information on the changes implemented for the reprocessing with Level 1 baseline version 5.1 and the validation of measured radiances within GOME dataset version 5 are available in the following documents available on the ESA Sensor Performance, Products and Algorithms portal.

  • Algorithm Theoretical Baseline Document (ATBD), GOME-DLR-L1-ATBD, issue 7A, 2016
  • Product User Manual (PUM), ER-PS-DLR-GO-0016, issue 6D, 2018
  • Products Quality Readme File, ESA-EOPG-MOM-TN-13, issue 1, 2018
  • GOME L1v5 Radiance Validation, issue 1, 2017

An overview of the evolution of the GOME baseline is provided in Coldewey-Egbers, M., Slijkhuis, S., Aberle, B., Loyola, D., and Dehn, A.: The Global Ozone Monitoring Experiment: Review of in-flight performance and new reprocessed 1995–2011 level 1 product, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-118, in review, 2018.