Analysis and validation of 17 years of broadband radiation data from the Geostationary Earth Radiation Budget (GERB) instruments

Christine Aebi 1 , Edward Baudrez 1 , Johan Moreels 1 , Pierre de Buyl 1 , William Moutier 1 , Nicolas Clerbaux 1 , Jacqueline  Russell 2

  • 1 Royal Meteorological Institute Of Belgium, Brussels
  • 2 Imperial College London, London

Abstract

The continuous measurement of the components of the Earth radiation budget is fundamental for climate studies. The Top-Of-the-Atmosphere (TOA) broadband reflected solar and emitted thermal radiances and fluxes are provided by four Geostationary Earth Radiation Budget (GERB) instruments on board the Meteosat Second Generation (MSG) satellites since 2004. The repeat cycle of 15 minutes and the spatial resolution of 9 × 9 km allows to resolve the diurnal cycle of the shortwave and longwave radiation fluxes at the TOA. The respective GERB instrument considered is located at longitude 0°. Additionally, since 2016, there is a GERB instrument located at 41.5° E (Indian Ocean) in order to extend the data availability.

The GERB radiance and flux data sets are validated (i) using products from the Clouds and the Earth's Radiant Energy System (CERES) instruments on the Terra, Aqua and Suomi-NPP satellites, (ii) using an internal product converting narrowband to broadband fluxes from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on MSG and (iii) using ERA5 reanalysis data. The first two GERB instruments (2004 – 2012) have already been validated regarding the ageing of the instruments (Parfitt et al., 2016) and its performance in general in comparison to one of the CERES instruments (Clerbaux et al., 2008).

The current study aims at the extension of the validation of the GERB shortwave and longwave radiances and fluxes over the 17 years of data available so far, with focus on the more recent data sets from both, longitude 0° and 41.5° E. For this validation, the newest available editions and versions of GERB and CERES data are used. Preliminary results show an overestimation of the GERB shortwave radiances and fluxes and a slight underestimation of the GERB longwave radiances and fluxes in comparison to the CERES Single Scanner Footprint (SSF) data sets. The comparison of the GERB radiation data with ERA5 data shows a similar pattern. Additional analyses and validations will be presented in more detail.


Bibliography:

Clerbaux, N., Russell, J.E., Dewitte, S., Bertrand, C., Caprion, D., De Paepe, B., Gonzalez Sotelino, L., Ipe, A., Bantges, R. and Brindley, H.E.: Comparison of GERB instantaneous radiance and flux products with CERES Edition-2 data, Remote Sensing of Environment, 113, 102-114, https://doi.org/10.1016/j.rse.2008.08.016, 2008.

Parfitt, R., Russell, J.E., Bantges, R., Clerbaux, N. and Brindley, H.E.: A study of the time evolution of GERB shortwave calibration by comparison with CERES Edition-3A data, Remote Sensing of Environment, 186, 416-427, https://doi.org/10.1016/j.rse.2016.09.005, 2016.

Introduction

  • Since 2004, top-of-atmosphere (TOA) broadband reflected solar and emitted thermal radiances and fluxes are provided by the Geostationary Earth Radiation Budget (GERB) instruments (Harries et al., 2005) on board of the Meteosat Second Generation (MSG) satellites.
  • The repeat cycle of GERB of 15 minutes allows to resolve the diurnal cycle of the shortwave (SW) and longwave (LW) radiation fluxes at the TOA.
  • Location of the operational GERB instrument: Longitude 0° (2004-now) and an additional GERB instrument at longitude 41.5° (2016-now).
  • GERB products: NANRG (Nonaveraged, nonrectified, geolocated), ARG (Averaged, rectified, geolocated), BARG (Binned, averaged, rectified, geolocated), HR (High-resolution) in different levels (L1.5, L2, L3), with different spatial (44 km and 9 km) and temporal resolutions (e.g. instantaneous, 15 min bins, monthly mean). All data products are also available in near real-time (NRT).
  • Shown are on one hand an overview about the GERB data sets, and on he other hand some preliminary results of a comprehensive analysis and validation of the (so far) 17 years of GERB data. The results of the validation will thereafter be used to better understand and improve the GERB data set itself before releasing a new edition.

Preliminary Results

GERB - CERES FM1 and FM5 SSF Ed. 4A

Daily mean

Time series of the daily mean shortwave (blue) and longwave (red) flux ratios between GERB (GX) and CERES FM1.

Correlation between the daily mean GERB-4 and CERES FM5 SSF shortwave (left) and longwave (right) fluxes. There is a bias of nearly 12 % in the SW flux of GERB-4. Clearly visible are the two levels in GERB-4 radiation data caused by a quartz filter issue at the instrument. A new corrected data set will be available soon.

  • In the mean, the SW fluxes of GERB-1 and GERB-2 are around 6 % to 7 % higher than the corresponding CERES SSF fluxes.
  • GERB-3 and GERB-4 have anomalies in their timeseries due to an issue with the quartz filter.
  • Nevertheless, the GERB-4 SW flux is around 12 % higher in comparison to the CERES SSF flux.
  • The LW fluxes from all GERB instruments are in the mean 1 % to 3 % lower than CERES SSF fluxes.

Monthly mean

Monthly mean SW (top row) and LW (bottom row) flux data from GERB-4 (left) and SSF CERES FM1 (middle) and the ratio per pixel between the two aforementioned data sets (right) for June 2019. 

GERB - GERB-like:

Hourly mean

Shortwave (SW; top) and longwave (LW; bottom) flux images [in Wm-2] from GERB-4 (left) and GERB-like (right) on May 3, 2019 12 UTC.

Hourly mean shortwave (blue) and longwave (red) flux ratios between GERB-4 and GERB-like (GL).

  • For LW, no significant differences in the mean ratios between day- and nighttime.
  • The variation in the SW during a day is within the uncertainty of the GERB-like product.

GERB - ERA5

SW (top) and LW (bottom) flux images [in Wm-2] from GERB-4 (left) and ERA5 (right) on August 15, 2018 12 UTC.

Bias of the SW (black) and LW (red) fluxes between GERB and ERA5 for the time period 2004 - 2018. Therefore, data have been taken from all the four GERB instruments. GERB-1 and GERB-2 data are not corrected for the ageing.

RMS of the shortwave (black) and longwave (red) fluxes of GERB and ERA5. The comparison of SW and LW fluxes between GERB 1-4 and ERA5  reanalysis data show similar patterns as the comparisons between GERB and CERES SSF and GERB and GERB-like, respectively.

Summary

  • The radiance and flux data from the GERB instruments are validated with various data sources (as some preliminary results are shown here).
  • SW and LW radiances and fluxes from GERB-1 and GERB-2 (between 2004 and 2013) are released and available for science (data can be found here: https://gerb.oma.be).
  • GERB-1 and GERB-2 SW fluxes are within max. 7 % and LW fluxes are within max. 3 %  differences to GERB-like or CERES SSF Ed. 4A data.
  • GERB-3 and GERB-4 data suffer both from an issue with the quartz filter. Additionally, GERB-3 has either some strong ageing issues or problems with the mirror correction. 
  • In the periods with no quartz filter anomaly, GERB-4 has differences in the SW and LW fluxes in comparison to GERB-like and CERES SSF Ed. 4A within 12 % and 3 %, respectively.
  • The comparison of the GERB radiation data with GERB-like and ERA5 confirm the patterns as shown for the comparsion with CERES SSF data.
  • Corrected data for the quartz filter anomaly periods of the GERB-4 instrument will be available soon.

Acknowledgement

The CERES SSF data were obtained from the  NASA Langley Research Center Atmospheric Sciences Data Center.

References

  • Clerbaux, N., Russell, J.E., Dewitte, S., Bertrand, C., Caprion, D., De Paepe, B., Gonzalez Sotelino, L., Ipe, A., Bantges, R. and Brindley, H.E.: Comparison of GERB instantaneous radiance and flux products with CERES Edition-2 data, Rem. Sens. of Env., 2008.
  • Harries, J.E. et al.: The geostationary earth radiation budget project, Bulletin of the American Meteorological Society, 2005.
  • Parfitt, R., Russell, J.E., Bantges, R., Clerbaux, N. and Brindley, H. E.: A study of the time evolution of GERB shortwave calibration by comparison with CERES Edition-3A data, Rem. Sens. of Env., 2016.
  • Russell, J.E. et al.: Quality summary: GERB L2 Edition 1 products, 2017.

GERB Instruments

Overview

Overview of the data availability of the operational GERB instruments at longitude 0°. In 2016, GERB-2 was moved to longitude 41.5° E (Indian Ocean) and is continuing to measure at this location.

Validation Overview

Overview of the possible validation of all four GERB instruments. Currently, the main focus is put on the comparison of the GERB radiances and fluxes with CERES products and with the internal product GERB-like. GERB-1 and GERB-2 radiances and fluxes have already been validated (e.g. Clerbaux et al., 2008 and Parfitt et al., 2016). There is also a quality summary available for GERB-1 and GERB-2 L2 Edition 1 data (Russell et al., 2017) proposing the application of a correction factor to the radiances and fluxes (due to calibration and ageing issues of the two aforementioned instruments).

What is GERB-like (GL)?

GERB-like is a broadband radiance and flux product calculated from data from ten narrowband channels in the shortwave (SW) and the longwave (LW) of the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on MSG satellites.